imperial college londonspiral.imperial.ac.uk/.../1/mitchell-j-2015-phd-thesis.pdf · 2019. 11....

Recycled Polymers Reinforced with Paper Plastic

Laminates

By

Jonathan Mitchell

A thesis submitted in fulfilment of the requirements for the degree of

Doctor of Philosophy

Department of Civil and Environmental Engineering

Imperial College London

2014

http://www3.imperial.ac.uk/

2

I, Jonathan Mitchell, confirm that the work presented in this PhD thesis is my own original work.

Signature: J. Mitchell

Date:

Supervisors:

1. Prof. C.R. Cheeseman

Department of Civil and Environmental Engineering


South Kensington

SW7 2AZ

2. Dr. L.J. Vandeperre

Department of Materials


South Kensington

SW7 2AZ

3. Prof. K. Tarverdi

Wolfson Centre for Materials Processing

Brunel University

London

UB8 3PH

4. Prof. E. Kosior

Nextek Ltd

107-111 Fleet Street

London

EC4A 2AB

‘The copyright of this thesis rests with the author and is made available under a Creative Commons Attribution Non-Commercial No Derivatives licence. Researchers are free to copy, distribute or transmit the thesis on the condition that they attribute it, that they do not use it for commercial purposes and that they do not alter, transform or build upon it. For any reuse or redistribution, researchers must make clear to others the licence terms of this work’

Abstract

The aim of this research project was to develop new structural materials from the paper plastic

laminate (PPL) waste stream. PPLs containing both paper fibre and plastic coatings are problematic

for non-thermal recycling options. The current end of life disposal for PPL is primarily landfill. This

work focuses on combining PPL wastes with recycled plastics to produce paper plastic composites

(PPCs) that can be used as raw materials for a variety of applications.

Plastic from a material recycling facility (MRF) consisting of polyolefins, together with polypropylene

(PP) from Waste Electrical and Electronic Equipment (WEEE) wastes have been the main source of

material for the composite matrix. The PPL wastes investigated include paper polyethylene coated

disposable beverage cups and multi-layer Tetra Pak cartons. The majority of disposable cups are made

from PPLs which consist of high quality cellulose fibre with a thin internal polyethylene coating. There

are limited recycling options for PPLs and this has contributed to disposable cups becoming a high

profile, problematic waste. In this work PPL wastes have been shredded to form PPL flakes and these

have been used to reinforce polyolefins to form novel paper plastic composites (PPCs) based on the

waste streams used. The PPL flakes and polyolefins were mixed, extruded, pelletised and injection

moulded at temperatures to prevent degradation of the cellulose fibres. The PPLs were prepared by

removing waste contaminants and granulated to the correct size to prevent bridging during extrusion.

Processing temperatures were kept as low as possible to prevent fibre degradation. Extruded PPC

blends were pelletised and injection moulded to form samples for testing.

The effects of PPLs in PPCs on processing and properties have been investigated. This included

studying the rheology of the extrusion mixes and the strength and stiffness of the PPCs. The effects of

coupling agents such as maleated polyolefins and silane based compatibilisers to enhance adhesion

between the PPL and the plastic have also been investigated. The level of PPL flake addition and the

use of a maleated polyolefin coupling agent to enhance interfacial adhesion have been investigated.

PPCs have been characterised and mechanically tested by a range of techniques including tensile

testing, thermogravimetric analysis (TGA) and rheological experiments. Use of a coupling agent allows

composites containing 40 wt.% of PPL flakes to increase the tensile strength of the recycled PP in this

research by 50% to 30 MPa. The Young's modulus also increases from 1 to 2.5 GPa and the work to

fracture increases by a factor of 5. The work presented here demonstrates that PPLs have potential to

be beneficially reused as reinforcement in novel PPCs.

4

Acknowledgments

I would like to express my deepest gratitude to Prof Chris Cheeseman and Dr Luc Vandeperre. The

guidance, technical assistance and patience have been invaluable. It was a real pleasure to work with

you both and hopefully we will again in the future.

I would also like to thank Edward Kosior and Robert Dvorak of Nextek Ltd, who gave me years of advice

and knowledge that I will carry with me forever. Ed, the opportunity to work with you over the last

few years has been a tremendous honour. The knowledge and experience is vital for someone who is

entering this expanding area of sustainability and recycling. I thoroughly enjoy my work with you and

hopefully will continue to discover and work on ground breaking and leading research projects.

I would also like to thank Karnik Tarverdi, Steve Ferris and Peter Allan from Brunel University. Their

assistance for this research has been very helpful. Further acknowledgements should be given to

London Metropolitan University, Bangor University and Loughborough University for allowing the use

of their facilities for this research.

Lastly I would like to thank my family and friends for their support and encouragement throughout

the PhD. I feel the PhD process is more than the thesis at the end; it is a journey that changes directions

many times but ultimately leads to a breadth of personal knowledge and skills that will be used in all

areas of life.

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Opening Statement

In 100 years the greed of humans will still be causing divisions in wealth, religion and culture. However

one aspect that should unite the world despite other differences is the need to conserve the

environment. Enormous technological changes are needed along with political decisions as science

alone will not change the world we live in.

To a Realm of Possibilities......

6

Publications

Waste Management, Elsevier:

Title: Recycling disposable cups into paper plastic composites

Authors: Jonathan Mitchell, Luc Vandeperre, Rob Dvorak, Ed Kosior, Karnik Tarverdi,

Christopher Cheeseman

Conference Papers and Presentations

1. Wood Plastic Composites 2011

Title: Advanced Recovery and Recycling Technologies for use of Post-Consumer Polymers in WPC

and PPC Products

Author: Jonathan Mitchell of Nextek Ltd and Imperial College London

Location: 8th-10th November 2011, Austria Trend Savoyen hotel, Vienna, Austria

2. Antec 2014

Title: PAPER PLASTIC COMPOSITES FROM RECYCLED DISPOSABLE CUPS Authors: Jonathan Mitchell, Luc Vandeperre, Rob Dvorak, Ed Kosior, Karnik Tarverdi,

Christopher Cheeseman

Location: April 28th-30th 2014, Rio All-suite Hotel and Casino, Las Vegas, Nevada, USA

Posters

Title: Waste to Resources: Cups to Composites

Author: Jonathan Mitchell of Nextek Ltd and Imperial College London

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Notation

ABS = Acrylonitrile Butadiene Styrene

ACE = Alliance for Beverage Cartons and the Environment

Br = Bromine

Cl = chlorine

σ c = Composite strength

σ m = Composite matrix strength

DSC = Differential Scanning Calorimetry

DMA = Dynamic Mechanical Analysis

EC, m, f = Modulus of the composite, matrix and filler

Ef = Modulus of the fibre

EfW = Energy from Waste

FBC =Fluidised bed combustion

FTIR = Fourier Transform Infrared

HDPE = High Density Polyethylene

ΔHm = Latent heat of melting

ΔHmo = Specific heat of melting if the polymer was 100% crystalline

K = Flow consistency index [Pa.sn]

LCA = Life Cycle Assessment

LDPE = Low Density Polyethylene

LLDPE = Linear Low Density Polyethylene

MAH = Maleic Anhydride

MAPP = Maleic Anhydride grafted Polypropylene

MAPE = Maleic Anhydride grafted Polyethylene

MCB = Multilayer Carton Board

MFI = Melt flow Index

MFR = Melt Flow Rate

MRF = Materials Recycling Facility

MSW = Municipal Solid Waste

8

MWD = molecular weight distribution

Mw = Molecular Weight

n = Flow behavior index

PBDDs = polybrominated dibenzo-p-dioxins

PBDFs = dibenzofurans

PDMS = polydimethylsiloxane

PE = Polyethylene

PEI = Polyethylenimine (PEI)

PET = Polyethylene Terephthalate

PHB = Polyhydroxybutyrate

PLA = Polylactic acid

PP = Polypropylene

PPC = Paper Plastic Composite

PPL = Paper Plastic Laminate

PPR = Paper Plastic Residue

PPVTES = Polypropylene Triethoxy(vinyl)silane

PS = Polystyrene

SAP/AN = Saponification Number / Acid Number

SEM = Scanning Electron Microscope

τ = Shear stress [Pa],

TGA = Thermogravimetric Analysis

UTS = ultimate tensile strength

Vf and f = Volume fraction of filler (fibres)

Vf = volume fraction

WEEE = Waste Electrical and Electronic Equipment

WPC = Wood Plastic Composite

�̇� = Shear rate [s-1

]

XRF = X-ray fluorescence

9

Table of Contents

Abstract ....................................................................................................................................... 3

Acknowledgments ....................................................................................................................... 4

Opening Statement ...................................................................................................................... 5

Publications ................................................................................................................................. 6

Notation ...................................................................................................................................... 7

Table of Contents ......................................................................................................................... 9

List of Tables .............................................................................................................................. 13

List of Figures ............................................................................................................................. 15

Chapter 1 ................................................................................................................................... 22

1. Introduction ........................................................................................................................... 22

1.1 Background to the Research ................................................................................................... 22

1.2 Outline of the Thesis ............................................................................................................... 23

Chapter 2 ................................................................................................................................... 25

2. Aims and Objectives ............................................................................................................... 25

2.1 Aims ......................................................................................................................................... 25

2.2 Objectives ................................................................................................................................ 25

2.2.1 Composition of PPCs ........................................................................................................ 25

2.2.2 Processing Conditions ...................................................................................................... 25

2.3 Outcomes of the Objectives .................................................................................................... 26

2.3.1 Microstructure ................................................................................................................. 26

2.3.2 Properties ......................................................................................................................... 26

Chapter 3 ................................................................................................................................... 28

3. Literature Review ................................................................................................................... 28

3.1 Introduction ............................................................................................................................ 28

3.2 Composite Filler Materials ...................................................................................................... 28

3.2.1 Paper Plastic Laminates (PPLs) / Disposable PE Coated Paper Beverage Cups ............... 28

3.2.2 Paper Plastic Laminates (PPLs) / Multilayer Carton Board (MCB) / Tetra Pak Cartons ... 31

3.3 Composite Matrix Materials ................................................................................................... 34

3.3.1 Polypropylene (PP) for use as the Matrix Material .......................................................... 34

3.3.2 High density polyethylene (HDPE) for use as the Matrix Material .................................. 35

3.3.3 Recycled Plastic from Material Recycling Facilities (MRF) ............................................... 35

3.3.4 Polymers from Waste Electrical and Electronic Equipment (WEEE) ................................ 35

10

3.5 Coupling Agents for the Matrix and Filler Interface ............................................................... 37

3.6 Composite Materials: Combining the Matrix, Filler and Coupling Agent ............................... 40

3.6.1 Composite Fracture .......................................................................................................... 41

3.6.2 Wood Plastic Composites (WPCs) .................................................................................... 42

3.6.3 Paper Plastic Composites (PPCs) ...................................................................................... 44

3.7 Modelling of Paper Plastics Composites ................................................................................. 46

3.7.1 Long fibre composites: Elastic Modulus .......................................................................... 46

3.7.2 Voigt Model (Axial Stiffness) ............................................................................................ 46

3.7.3 Reuss Model (Transverse Stiffness) ................................................................................. 47

3.7.4 Halpin and Tsai Model ..................................................................................................... 47

3.7.5 Short Fibre Composites: Shear Lag and Axial / Eshleby Method ..................................... 47

3.7.6 Elastic Modulus for Particulate Composites .................................................................... 48

3.7.7 Strength of Particulate Composites ................................................................................. 49

3.8 Rheology of PPCs ..................................................................................................................... 50

3.9 Conclusions ............................................................................................................................. 50

Chapter 4 ................................................................................................................................... 51

4. Experimental .......................................................................................................................... 51

4.1 Preparation of Raw Materials for Processing ......................................................................... 51

4.1.1 Size Reduction of Raw Materials ...................................................................................... 51

4.1.2 Blending of Raw Materials ............................................................................................... 51

4.1.3 Pre-Blending the Filler and Coupling Agents ................................................................... 51

4.2 Plastics Processing for PPCs .................................................................................................... 52

4.2.1 Compounding by Twin Screw Extrusion........................................................................... 52

4.2.2 Injection Moulding ........................................................................................................... 53

4.3 Characterisation and Testing Techniques ............................................................................... 54

4.3.1 Thermogravimetric Analysis (TGA) / Differential Scanning Calorimetry (DSC) ................ 54

4.3.2 Fourier Transform Infrared (FTIR) Golden Gate ............................................................... 55

4.3.3 X-ray Fluorescence (XRF).................................................................................................. 56

4.3.4 Rheology .......................................................................................................................... 56

4.3.5 Water Absorption ............................................................................................................ 57

4.3.6 Optical Microscopy .......................................................................................................... 57

4.3.7 Scanning Electron Microscope (SEM) .............................................................................. 58

4.3.8 Density ............................................................................................................................. 58

4.3.9 Mechanical Testing of the Plastic Matrix and PPCs ......................................................... 58

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Chapter 5 ................................................................................................................................... 65

5. Materials Characterisation and Initial Trials ............................................................................ 65

5.1 Composite Matrix Materials ................................................................................................... 65

5.1.1 Polypropylene and Polyethylene from Material Recycling Facilities (MRF) .................... 65

5.1.2 Polypropylene from Waste Electrical and Electronic Equipment (WEEE) ....................... 65

5.1.3 High Density Polyethylene (HDPE) ................................................................................... 65

5.2 Characterisation of Matrix Polymers ...................................................................................... 66

5.2.1 Rheological Properties of the Composite Matrix ............................................................. 66

5.2.2 Differential Scanning Calorimetry (DSC)/ Thermogravimetric Analysis (TGA)................. 69

5.2.3 Fourier Transform Infrared (FTIR) Analysis of Composite Matrix .................................... 72

5.2.4 X-ray Fluorescence (XRF) of WEEE PP ............................................................................. 75

5.2.5 Mechanical Testing of Matrix Polymers ........................................................................... 75

5.3 Conclusions of Composite Matrix Plastics .............................................................................. 82

5.4 Composite Filler Materials ...................................................................................................... 83

5.4.1 Paper Plastic Laminates (PPLs) / Polyethylene (PE) Coated Paper Beverage Cups ......... 83

5.4.2 Paper Plastic Laminates (PPLs) / Multilayer Carton Board (MCB) / Tetra Pak Cartons ... 83

5.5 Paper Plastic Laminate Fillers: Material Characterisation ...................................................... 83

5.5.1 Disposable Beverage Cups ............................................................................................... 83

5.5.2 Tetra Pak / Multilayer Carton Board (MCB) ..................................................................... 86

5.5.3 Mechanical Testing of PPLs .............................................................................................. 86

5.6 Conclusions of PPL Characterisation ....................................................................................... 87

5.7 Coupling Agents for the Matrix and Filler Interface ............................................................... 87

5.7.1 Coupling Agents used in this Research ............................................................................ 87

5.8 Melt Flow Rate (MFR) Additives ............................................................................................. 90

5.9 Material Selections and Initial Studies .................................................................................... 91

5.9.1 Selection of Filler Loadings .............................................................................................. 91

5.9.2 Summary and Conclusions of Initial Studies with PPCs ................................................... 91

5.9.3 Further Optimisation Recipes and Processing Steps: Selection of Filler Loadings .......... 96

5.9.4 PPC Mixes for Optimisation Trials .................................................................................... 97

5.9.5 Final Conclusions of the Initial Studies .......................................................................... 100

Chapter 6 ................................................................................................................................. 101

6. Further Optimisation Studies: Results and Discussion ............................................................ 101

6.1 Introduction .......................................................................................................................... 101

6.2 Further Optimization of PPCs using PE Coated Beverage Cups ............................................ 101

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6.2.1 Mechanical Properties of WEEE PP and PE Coated Beverage Cups............................... 101

6.3 Mechanical Properties of WEEE PP and PE Coated Beverage Cups with Optimised Coupling

Agents ......................................................................................................................................... 106

6.3.1 Material Characterisation of Paper Plastic Composites (PPCs): The Volume Fraction of

Fillers ....................................................................................................................................... 131

6.4 Multilayer Carton Board (MCB) / Tetra Pak .......................................................................... 145

6.4.1 Mechanical Properties: Paper Plastic Composites (PPCs): The Volume Fraction of Fillers

................................................................................................................................................ 145

6.5 PPCs with High Density Polyethylene (HDPE) as the Composite Matrix: Optimising Filler and

Coupling Agent ............................................................................................................................ 152

6.5.1 High Density Polyethylene (HDPE) / PE Coated Beverage Cup ...................................... 152

6.6 High Density Polyethylene (HDPE) / Multilayer Carton Board (MCB) / Tetra Pak ................ 162

6.6.1 Mechanical Properties ................................................................................................... 162

6.7 Conclusions ........................................................................................................................... 167

Chapter 7 ................................................................................................................................. 168

7. Final Comparisons: Optimum Blends of PPCs......................................................................... 168

7.1 Thesis Summary .................................................................................................................... 168

7.2 Optimum Blends of PPCs ...................................................................................................... 168

7.2.1 Creep Analysis ................................................................................................................ 169

7.2.2 Fracture Toughness ........................................................................................................ 178

7.2.3 Water Absorption .......................................................................................................... 182

7.2.4 Material Comparisons: CES EduPack ............................................................................. 187

7.3 Final Remarks and Conclusions ............................................................................................. 188

7.3.2 Conclusions of Optimum Blends of PPCs ....................................................................... 191

Chapter 8 ................................................................................................................................. 192

8. Conclusions and Further Work .............................................................................................. 192

8.1 Conclusions ........................................................................................................................... 192

8.2 Recommendations for Further Work .................................................................................... 193

8.2.1 Recyclability ................................................................................................................... 194

8.2.2 Filler Shape ..................................................................................................................... 194

8.2.3 Processing Equipment .................................................................................................... 194

8.2.4 Contaminated PPLs ........................................................................................................ 195

8.2.5 Pallet Manufacture ........................................................................................................ 195

9. References ........................................................................................................................... 196

10. Appendix ........................................................................................................................... 208

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List of Tables

Table 3-1: Shows the disposal options for different disposable cups.

Table 3-2: Emissions for energy use of paper, polystyrene and ceramic beverage cups.

Table 3-3: Mechanical properties of WPCs, PPCs and virgin polymers found in the literature.

Table 4-1: Extrusion settings for PPC on the Thermo Scientific co-rotating twin screw (26mm and

L/D=40) extruder.

Table 4-2: Injection Moulding conditions on the Demag for manufacturing test bars for PPC.

Table 5-1: MFR data for recycled polymer used as the matrix material.

Table 5-2: Material Identification by FTIR analysis of an MRF waste stream.

Table 5-3: Material Identification by FTIR analysis of PP from WEEE sources.

Table 5-4: Shows the density of selected polymers of interest.

Table 5-5: Flexural Strength of recycled matrix plastics vs virgin polymers.

Table 5-6: Material Identification by FTIR analysis of paper cups.

Table 5-7: Tensile results from trimmed pieces of PPLs.

Table 5-8: Key properties of coupling agents supplied by Honeywell.

Table 5-9: Key properties of E-43 supplied by Eastman.

Table 5-10: Key properties of Bondyram.

Table 5-11: Trial 2 a) and b). A variety of PPCs with varying volume fractions of PPL cups, percentages

of coupling agents and different matrix polymers.

Table 6-1: Tensile testing data for PPCs with increasing volume fractions and the effect of the 907P

coupling agent.

Table 6-2: Modulus of toughness for PPC blends with 2 wt.% 907P and increasing volume fractions of

PPL cup.

Table 6-3: Table showing the flow consistency index (y-intercept) values and the flow behaviour index.

Table 6-4: Tensile Testing results of MCB / Tetra Pak based PPCs.

Table 6-5: HDPE tensile data without the extensometer.

14

Table 6-6: Tensile data of HDPE composites between 0-30 wt.% PPL Tetra Pak and 2-3 wt.% coupling

agents.

Table 7-1: PPCs blends that showed the highest mechanical properties.

Table 7-2: Steady state creep rate for WEEE PP and PPC with 2 wt.% Struktol 30 wt.% over a range of

constant stresses at laboratory temperature and 400C.

Table 7-3: Flexural strength and modulus values of PPCs after 4032 hours immersed in water.

15

List of Figures

Figure 3-1: Life cycle of paper based cups. Considered stages are illustrated in grey. Stages not

considered are illustrated in white.

Figure 3-2: Maleic Anhydride grafted to PP (MAPP).

Figure 4-1: PPC pelletised after extrusion.

Figure 4-2: Flexural Testing setup (Zwick/Roell Z2.5, Machine reference A704548).

Figure 4-3: Fracture toughness specimens after machining and a slit made with a razor blade. The

colour of recipe 13 to recipe 8 is clearly shown. Recipe 13 has a higher filler loading.

Figure 5-1: Shows the effects of adding the processing aids. By making the polymer matrix less

viscous the fibrous filler is carried along the screw with less shearing in the extruder.

Figure 5-2: Influence of A-C additive from Honeywell on the melt flow rate of HDPE at 190oC and

230oC.

Figure 5-3: DSC curves between 0-250oC for a variety of recycled PP and PE.

Figure 5-4: TGA/DSC curve for WEEE PP between 0-500oC and being held at processing temperature

to note any significant changes. Ramp from 0-180oC at 20oC/min, Isothermal at 180oC for 3 minutes

then 180oC – 500oC at 20oC/min in Nitrogen.

Figure 5-5: Showing a section of data from TGA experiments (Ramp 20oC to 180 oC, 200 oC and 220oC,

then isothermal for 20 minutes in nitrogen.

Figure 5-6: Fourier Transform Infrared (FTIR) data of the WEEE PP is shown, identifying an atactic PP

structure.

Figure 5-7: Stress Strain curve for recycled WEEE PP, HDPE and MRF polymers used for the matrix

with a comparison to virgin polymers.

Figure 5-8: Tensile testing showing the elongation of WEEE PP. The tensile bar was 195 mm long before

elongating.

Figure 5-9: Showing failure of the WEEE PP after a tensile test.

Figure 5-10: Engineering Stress vs. Strain curve for HDPE used as the matrix material for PPCs.

Figure 5-11: stages in tensile test for HDPE showing deformation through necking.

16

Figure 5-12: Charpy impact energy of potential polyolefins for use as in PPCs compared to virgin

polyolefins (HDPE and PP).

Figure 5-13: Paper cup with thin LDPE coating.

Figure 5-14: TGA curves for PE coated Beverage Cup (Solocup) in N2 atmosphere.

Figure 5-15: TGA/DSC analysis of the Tetra Pak / MCB filler up to 500oC in N2 atmosphere.

Figure 5-16: Stress strain curves comparing the matrix (MRF PP), the addition of a filler (40 wt.% PPL

cup) and the addition of a filler and coupling agent (2 wt.% 907P MAPP).

Figure 5-17: Highlights the effect of different coupling agents on the tensile strength of PPCs. The

addition of coupling agents greatly enhances the tensile strength.

Figure 5-18: 68 wt.% MRF PP / 30 wt.% disposable cup / 2 wt.% 907p MAPP after a tensile test showing

fibre break.

Figure 5-19: 60 wt.% MRF PP / 40 wt.% disposable cup tensile fracture showing a PE coated paper

flake embedded within the matrix.

Figure 5-20: 60 wt.% MRF PP / 40 wt.% disposable cup flexural test showing broken embedded paper

flakes with a hole around part of the flake.

Figure 6-1: Ultimate tensile strength (UTS) and Young’s modulus against increasing volume fractions

of PPL cups in WEEE PP.

Figure 6-2: Comparing the Young’s modulus of PPCs with ROM and Halpin and Tsai models for the

elastic modulus of long fibre composites.

Figure 6-3: PPCs in agreement with a) Modified Shear Lag models and b) Eshleby models at higher

aspect ratios.

Figure 6-4: Comparing the Young’s modulus of PPCs against various models for the elastic modulus of

particulate composites with increasing volume fractions of PPL cups.

Figure 6-5: Variation in mechanical properties for composite containing increasing additions of PPL

flakes with and without 2 wt.% MAPP coupling agent a) tensile strength b) Young’s modulus.

Figure 6-6: Ultimate tensile strength (UTS) and Young’s modulus against increasing weight

percentages of MAPP 907P in 40 wt.% PPL cups in a WEEE PP matrix.



17

Figure 6-8: a) 10 wt.% PPL b) 30 wt.% PPL: PP and paper cup extruded out of the die exhibiting melt

fracture.

Figure 6-9: PPC extrudate with 30 wt.% PPL and 2 wt.% Struktol.

Figure 6-10: Ultimate tensile strength (UTS) and Young’s modulus against PPCs with various coupling

agents at 2 wt.% in 30 wt.% PPL cups in a WEEE PP matrix.

Figure 6-11: Extruded PPCs at 30 wt.% PPL cup with (right bar) and without (left bar) PPVTES coupling

agent.

Figure 6-12: A comparison of the engineering stress vs. engineering strain curves for polypropylene,

and composites containing 30 wt.% disposable cup with and without 4 wt.% coupling agent. The WEEE

PP is only shown to a strain value of 0.2 to show the effect of the PPL and coupling agent more clearly.

Figure 6-13: The modulus of resilience and modulus of toughness for WEEE PP.

Figure 6-14: The modulus of resilience and modulus of toughness for WEEE PP/10 wt.% PPL cup.

Figure 6-15: Notched charpy impact strength of PPCs with increasing volume fractions of PPL cups

between 0-40 wt.%.

Figure 6-16: Notched charpy impact strength of PPCs with increasing volume fractions of PPL cups

between 0-40 wt.% with 2 wt.% 907P.

Figure 6-17: Flexural strength of WEEE PP based PPCs with 2 wt.% 907P and PRIEX 25097 at increasing

volume fractions between 0-40 wt.% PPL cups.

Figure 6-18: Flexural strength of WEEE PP based PPCs at 1-4 wt.% 907P and PRIEX 25097 at 30 wt.%

PPL cups.

Figure 6-19: Flexural modulus of WEEE PP based PPCs with 2 wt.% 907P and PRIEX 25097 at increasing


Figure 6-20: Flexural modulus of WEEE PP based PPCs at 1-4 wt.% 907P and PRIEX 25097 at 30 wt.%

PPL cups.

Figure 6-21: Flexural strength and Flexural modulus of WEEE PP based PPCs at 1-4 wt.% 907P and

PRIEX 25097 at 40 wt.% PPL cups.

Figure 6-22: Flexural strength vs. flexural strain of 30wt.% PPL cups in WEEE PP with 3 wt.% 907P and

3 wt.% Struktol coupling agents.

18

Figure 6-23: shows the well dispersed filler encapsulated by the surrounding matrix in a 3point bend

test.

Figure 6-24: Storage modulus vs. temperature for samples containing between 0 and 40 wt.% PPL

flakes.

Figure 6-25: Loss modulus vs. temperature for samples containing between 0-40 wt.% PPL flakes.

Figure 6-26: Tan Delta vs. temperature for PPCs between 0-40 wt.% PPLs.

Figure 6-27: Shear rate vs. Shear stress for PPCs containing WEEE PP and PPL cups from 10-40 wt.%.

Figure 6-28: Shear rate vs. Viscosity for PPCs containing WEEE PP and PPL cups from 10-40 wt.%.

Figure 6-29: Extruded strands of PPCs in the rheology testing showing the difference between a WEEE

PP composite containing 30 wt.% PPL and 30wt.% PPL with 2 wt.% Struktol.

Figure 6-30: Shear rate vs. Shear stress for PPCs containing WEEE PP and PPL cups from 10-40 wt.%

with 2 wt.% 907P and 2 wt.% Struktol.

Figure 6-31: Log shear stress vs. Log shear rate plot of WEEE PP and increasing volume fraction (Vf) of

PPL paper cups.

Figure 6-32: Thermal degradation behaviour of increasing volume fraction of PPL cups up to 500oC.

Figure 6-33: Percentage weight loss as a function of volume fraction of PPL in WEEE PP up to 250oC

and 400oC.

Figure 6-34: Weight loss over isothermal time periods between 3-20minutes at 180oC.

Figure 6-35: Weight loss from 40 wt.% PPL content in WEEE PP with an isothermal period at 180oC.

The red line indicates the point at which the isothermal period starts.

Figure 6-36: Weight loss from 10 wt.% PPL content in WEEE PP with an isothermal period at 180oC in

a nitrogen atmosphere. The red line indicates the point at which the isothermal period starts.

Figure 6-37: Weight percent loss up to 500oC at 10oC and 20oC a minute heating rates.

Figure 6-38: a) TGA curves showing weight loss against temperature for 6 different MAPP coupling

agents used in this research. b) DSC curves showing heat flow against temperature for 6 different

MAPP coupling agents used in this research.

19

Figure 6-39: Fracture surfaces of composite samples (68 wt.% PP, 30 wt.% PPL) with a) no coupling

agent showing flake pull-out and b) 2 wt.% coupling agent (MAPP) showing fractured PPL flake that

remains attached to the surrounding polymer matrix.

Figure 6-40: PP-fibre composite without PEI (left image) and PP-fibre composite with PEI.

Figure 6-41: Young’s modulus with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

Figure 6-42: Tensile strength with increasing volume fractions of PPL Tetra Pak and 2 wt.% - 3 wt.%

907P.

Figure 6-43: Flexural strength with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

Figure 6-44: Flexural modulus with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

Figure 6-45: Charpy impact energy with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

The addition of the coupling agent did not have any affect at the high strain rate to failure.

Figure 6-46: Shear rate vs. viscosity with increasing volume fractions of PPL Tetra Pak.

Figure 6-47: Tensile strength and Young’s modulus of with increasing volume fractions of PPL cups

blended with HDPE.

Figure 6-48: Tensile strength of HDPE/PPL cups with 2-3 wt.% AC 1687 and PRIEX 1203 between 0-

30wt% PPL cups.

Figure 6-49: A comparison of the engineering stress vs. Engineering strain curves for HDPE, and

composites containing 30 wt.% disposable cup with and without 2 wt.% PRIEX 12031.

Figure 6-50: Tensile failure of a HDPE composite with 30 wt.% PPL cups and 2 wt.% PRIEX 12031.

Figure 6-51: Young’s modulus of HDPE PPL cups between 0-30 wt.% and AC 1687 and PRIEX 12031 at

2-3 wt.%.

Figure 6-52: Impact testing of HDPE with PPL cups and coupling agents.

Figure 6-53: Flexural strength and Flexural modulus for PPCs between 0-30 wt.% PPL cup.

Figure 6-54: Flexural strength and Flexural modulus for PPCs between 0-30 wt.% PPL cup with 2-3

wt.% AC 1687 and PRIEX 12031.

Figure 6-55: Shear rate viscosity curves for HDPE and PPCs with 0-30 wt.% PPL cups.

20

Figure 6-56: TGA showing weight loss over typical processing temperatures for HDPE based PPCs at 0-

30 wt.% PPL cups.

Figure 6-57: Tensile strength with increasing PPL Tetra Pak up to 30 wt.% with 2-3 wt.% PRIEX and AC

coupling agents.

Figure 6-58: Young’s modulus with increasing PPL Tetra Pak up to 30 wt.% with 2-3 wt.% PRIEX and AC

coupling agents.

Figure 6-59: Impact testing of HDPE with PPL Tetra Pak and coupling agents.

Figure 6-60: Flexural Strength of Tetra Pak and HDPE based PPCs with AC 1687 as a coupling agent.

Figure 7-1: a) Engineering Strain vs. Time curve for creep testing at constant stress stressed at 20-60%

of its UTS and at 400C for 30 minutes with 30 minutes recovery time. b) Engineering stress vs. strain

for WEEE PP stressed at 20-60% of its UTS.

Figure 7-2: Engineering Strain vs. Time curve for creep testing at constant stress stressed at 20-60% of

its UTS and at 400C for 30 minutes with 30 minutes recovery time.

Figure 7-3: Average temperature of the sample being tested in the creep test at 40oC.

Figure 7-4: Engineering Strain vs. Time curve for creep testing at constant stress stressed at 20-60%

of its UTS for 30 minutes with 30 minutes recovery time.

Figure 7-5: a) Engineering Strain vs. Time curve for creep testing at constant stress stressed at 20-

60% of its UTS for 30 minutes with 30 minutes recovery time for HDPE/30 wt.% PPL cup / 2 wt.%

PRIEX 12031. b) Engineering Strain vs. Time curve for HDPE/30 wt.% PPL cup /2 wt.% PRIEX 12031 vs

HDPE/30 wt.% PPL cup.

Figure 7-6: This shows relatively short steady state creep data on HDPE/30 wt.% PPL cup / 2 wt.%

PRIEX 12031 subjected to high stress creep testing over 48 hours at 60% UTS.

Figure 7-7: Fracture toughness of WEEE PP based PPCs with different PPLs and coupling agents.

Figure 7-8: Fracture toughness of HDPE based PPCs with different PPLs and coupling agents.

Figure 7-9: Critical strain energy release rate of WEEE PP based PPCs with different PPLs and coupling

agents.

Figure 7-10: Critical strain energy release rate of HDPE based PPCs with different PPLs and coupling

agents.

21

Figure 7-11: Fracture toughness testing of WEEE PP / 30 wt.% PPL / Struktol 3 wt.% showing crack

growth during loading.

Figure 7-12: Percent increase in mass after water absorption of PP based PPCs at 30 wt.% PPL cups

with a variety of coupling agents.

Figure 7-13: Percent increase in mass after water absorption of HDPE based PPCs at 30 wt.% PPL cups


Figure 7-14: Percent increase in mass after water absorption of PP based PPCs between 0-40 wt.% PPL

cups.

Figure 7-15: a) Percent increase in mass after water absorption of PP based PPCs at 40 wt% and 1-4

wt.% of 907P, b) Percent increase in mass after water absorption of PP based PPCs at 30 wt% and 1-4

wt.% of 907P.

Figure 7-16: Engineering stress strain data after water absorption for PP based PPCs at 40 wt% and 4

wt.% of 907P.

Figure 7-17: TGA data showing weight loss against increasing temperature for WEEE PP and HDPE.

Figure 7-18: Modelling PPC tensile strength.

Figure 7-19: Predicting the strength of paper cups in a PP matrix.

Introduction Chapter 1

22

Chapter 1

1. Introduction

1.1 Background to the Research

Paper plastic laminates (PPLs) are widely used in a range of products which include disposable cups

and Tetra Pak cartons. Disposable paper based cups are typical PPLs. They consist of high quality virgin

paperboard with a thin internal polyethylene (PE) coating. They are designed for single-use and have

become an iconic symbol of modern life. It is estimated that around 20 billion disposable cups are

used each year in the USA and this forms 165,000 tonnes of waste per year. This is estimated to

generate 65,000 tonnes of methane (CH4) and 90,000 tonnes of carbon dioxide (CO2). Approximately

2.5 billion paper cups are reported to be used in the UK each year. This represents a significant amount

of material that is a potential resource as PPLs contain useful materials which should be beneficially

reused (Royal Society of Chemistry).

The aim of this research is to combine PPLs with other high volume polymer wastes to develop paper

plastic composites (PPCs) that are commercially viable for use in a range of potential applications.

Initial research by Nextek Ltd showed that PPLs can be added to plastics to create paper plastic

composites (PPCs). However further research was required to optimise the mix of materials,

determine the optimum processing technology and control fibre-matrix interfacial adhesion. A major

technical challenge for PPCs is to determine the volume fraction of PPL that can be used to achieve

the desired properties. Low energy processing is needed to ensure that PPLs do not degrade during

PPC production and the environmental impact of processing needs to be analysed (Yin, 2009). The

objectives relate to understanding how PPL, polymer, coupling agents and low energy processing

could be used to produce PPCs.

PPL waste is available in large volumes globally. The opportunity to turn this waste into products via

the manufacturing process developed in this research is significant. The research has potential to

develop new manufacturing technology that can create value. This project also contributes to the UK

science technology base by improving the understanding of PPCs. If PPLs are manufactured into new

products then the advantages over existing materials would be the reduction in greenhouse gas

emissions arising from the diversion of waste from landfill and the reduction in use of virgin materials

for products. Recycling of PPCs would need to be considered as end of life options are important for

any new product introduced onto the market. This research focuses heavily on materials


23

characterisation and analysis of PPCs and a major focus is on the relationship between the

composition, processing and properties of PPCs containing PPLs.

From the project outset, the key markets considered appropriate for PPCs were pallets. The major

advantages of PPCs are derived from the low cost of the waste material and the use of low

temperature/low energy processing to allow competitive products to be manufactured. Industry

currently uses approximately 50 million new pallets a year, over 90% of which are wood. PPC pallets

would not have to be fumed like wood pallets, they would not splinter and they could be price

competitive given that waste materials are used in production. Other potential products include

decking materials, other construction products and potentially materials for use in the automotive

sector. This research has built on initial work completed by Nextek Ltd, who partly funded the research

through an EPSRC Industrial Case Award.

1.2 Outline of the Thesis

The aims and objectives of this research are set out in Chapter 2 along with a brief description and

illustration of the research methodology followed.

Chapter 3 summarises the literature related to PPCs. This includes a review of the wood plastic

composite (WPC) industry and the materials used for PPCs. The literature review focuses on current

issues, published work and key drivers. The literature highlighted the importance of coupling agents

as these have led to the increase in the WPC industry over the last decade. Improving the bond

between the fibrous polar filler and non-polar matrix is vital for a successful composite.

Chapter 4 includes all the experimental procedures used. The preparation and materials

characterisation techniques are discussed including testing methods for composite characterisation

and mechanical testing.

Chapter 5 characterises the materials involved. A range of different fillers, matrix polymers and

coupling agents are investigated. Initial trials on the materials are discussed along with the PPCs mixes

that are characterised in Chapter 6.

Chapter 6 reports on further optimisation studies. This focuses on the selected materials from chapter

5 that show potential for PPC manufacture. Further optimisation of the mixes is reported including

the optimisation of the fillers and coupling agents.

Chapter 7 reports on fundamental testing to understand the mechanical properties of PPCs. This

chapter compares and examines the optimum mixes and discusses the results.


24

Chapter 8 presents conclusions and suggestions for further work. PPCs manufactured from recycled

materials are reviewed.

Aims and Objectives Chapter 2

25

Chapter 2

2. Aims and Objectives

2.1 Aims

The aim of this research was to develop Paper Plastic Composites (PPCs) using recycled Paper Plastic

Laminates (PPLs) and polymers from different waste streams. The aim was to understand how

different composition and processing variables control the properties of PPCs so that commercially

viable materials could be formed that provide a new reuse application for problematic PPLs such as

paper cups.

2.2 Objectives

The aims of the research were achieved by meeting the following objectives:

Developing detailed understanding of PPCs by focusing on the relationships between:

- Composition

- Processing conditions

A variety of PPC mixes were made and analysed to prove viable reuse applications for PPLs can be

developed.

2.2.1 Composition of PPCs

The objective was to optimise the properties of PPCs prepared using selected PPLs, polymers and

coupling agents. The most promising waste materials from a selection were studied further. Key

analysis included:

- The volume fraction (Vf) of PPL within the matrix polymer.

- The type and volume of coupling agent.

- The type and volume of polymer.

2.2.2 Processing Conditions

The objective was to investigate different processing options that can be used to form PPCs.

- The effect of extrusion and injection moulding conditions on the micro-structure and

properties of PPCs was investigated.


26

2.3 Outcomes of the Objectives

The objectives determine the microstructure and properties which are analysed in subsequent

chapters.

2.3.1 Microstructure

It is important to understand how the microstructural characteristics control PPCs properties.

- The filler/matrix adhesion and the effects of adding coupling agents to the PPC during

processing was investigated.

2.3.2 Properties

This research attempted to produce PPCs with properties appropriate for use in specific applications.

The properties obtained can be compared against similar materials in the literature. Key steps

included:

- To optimise the materials through testing and characterisation and compare properties

with other materials produced by the WPC industry.

The final objective was to determine the suitability of manufacturing PPCs for a commercial use from

the selected materials. The combinations of materials and the effects on the properties of the PPCs

are discussed and recommendations for future work suggested.


27

Novel Paper Plastic Composites (PPCs) from extruded Paper Plastic Laminates (PPLs)

Materials Characterisation and Initial Trials

Screening Waste Materials for PPC Manufacture

Waste Material Selection

o Fibrous waste

Disposable cups

MCB / Tetra Pak

o Polymer

Recycled polymer sources

o Coupling agents

Industry analysis

Characterisation and Analysis

Characterisation techniques

o TGA/DSC

o FTIR

o Rheology

o Optimal Microscopy

o Density

o Water Absorption

Mechanical Analysis

o Tensile, flexural, Impact, Fracture

toughness,

Further Optimisation Studies Final Comparisons: Optimum Blends

Optimisation of PPC Blends

o Volume fraction (Vf) of filler

o Weight percentage (Wt.%) of

coupling agent

Further materials of interest

o Additional coupling agents

Characterisation and Analysis

Characterisation techniques

TGA/DSC

FTIR

Rheology

Optimal Microscopy

Density

Water Absorption

Mechanical Analysis

Tensile, flexural, Impact,

Fracture toughness,

Modelling of PPCs

Optimum Blends : PPC Analysis

o Key recipes analysed further through

creep tests, fracture toughness and

water absorption experiments

o Modelling

o Concluding remarks

o Comments on future work

The recyclability of PPCs

Filler Shape

Processing equipment

Contaminated PPLs

Pallet manufacture

Literature Review Chapter 3

28

Chapter 3

3. Literature Review

3.1 Introduction

Chapter 3 presents an overview of all the aspects related to this research. This includes the individual

materials that make up PPCs, the experimental processes and research that is related to PPCs in terms

of processing, characterisation and mechanical analysis. Related industries such as wood plastic

composites (WPCs) are then discussed along with modelling of PPCs.

This research developed from a project based on release liners and the potential to provide PPCs from

this large waste stream of PPLs. Chapter 1 highlighted the huge volumes of PPLs in the market, which

currently only have limited options at the end of their service life, namely disposal. This chapter

reviews the topics around PPCs that are relevant to this research.

3.2 Composite Filler Materials

Composites are materials made of two or more constituents that when combined produce superior

properties compared to the individual components. The filler material can have a number of roles

within a composite material. Furthermore, fillers can be load bearing providing stiffness and strength,

and also provide thermal stability. Fillers are added to improve the properties of the composite

material whether it is structurally, thermally or even electrically. The fillers used in this project are

shredded disposable beverage cups and multilayer carton boards (Mazumdar 2001).

3.2.1 Paper Plastic Laminates (PPLs) / Disposable PE Coated Paper Beverage Cups

The combination of materials used in disposable cups and the way they are bonded together makes

disposable cups difficult to recycle. Furthermore contamination from the waste stream or coffee from

the service of the cups affects the fibre quality. Previous recovery trials have recognized that

disposable cups with contamination levels higher than 10 wt.% will be discarded due to the fibre

quality. Most cups are currently being disposed of via landfill or through combustion in energy from

waste facilities (Read, 2008).

In 2009, Starbucks held a summit on coffee cups to see if they can be recycled. At that time 3 billion

of Starbucks coffee cups were being landfilled. It was concluded that the cups are repulpable and

recyclable and that more recycling opportunities are always needed. Paper mills see paper cups as a

hindrance due to the plastic film adhering to the fibres. The plastic can clog up the equipment and can

be a nuisance to paper mills.


29

A recent LCA study on paper cups was conducted in Finland. The goal of the research was to study the

material choices on an environmental basis (Häkkinen and Vares, 2009).

The LCA stages considered in the study are shown in Figure 3-1:

Figure 3-1: Life cycle of paper based cups. Considered stages are illustrated in grey. Stages not

considered are illustrated in white (Häkkinen and Vares, 2009).

Table 3-1: Shows the disposal options for different disposable cups (Häkkinen and Vares, 2009).

PET Issues, processes and environmental loading to be considered

Landfilling No energy recovery

No degradation

Incineration Feedstock energy recovery

CO2 and other emissions into air

Composting Is not an option

PE coated cardboard

Issues, processes and environmental loading to be considered

Landfilling No energy recovery


30

No degradation of PE

Very slow degradation of cardboard. CH4 and/or CO2 are released in decomposition. Part of the material may be sequestered into landfill. Methane may be collected in order be used for energy generation. In order to calculate, assumptions have to be made. In the calculations, the CO2 bound in the biomass can be taken into account.


CO2 emissions into air. CO2 bound in the biomass can be taken into account.

Composting Is not an option

PLA coated cardboard

Issues, processes and environmental loading to be considered

Land filling No energy recovery

Very slow degradation of PLA

Very slow degradation of cardboard

Within decomposition CH4 and/or CO2 are released. Part of the material may be sequestered into landfill. Methane may be collected in order be used for energy generation. In order to calculate, assumptions have to be made. In the calculations, the CO2 bound in the biomass can be taken into account.


CO2 emissions into air

The negative CO2 (biomass) can be taken into account.

Composting

Degradation of PLA in temperature >60 °C, degradation of cardboard. Part of carbon absorbed in the weight of the vegetable material is released to the atmosphere during composting. For example it may be assumed that of the total 60% decomposed of which 90% as CO2, 10% as CH4, and that the rest 40% sequestered in the compost. In the calculations, the CO2 bound in the biomass can be taken into account.

The study suggested that it is the end of life disposal option that controls the environmental impact

and therefore extra attention should be focused on this part of the products life. This creates an

opportunity for other end of life scenarios to be considered and analysed so that products can be seen

as a useful resource.

The Paper Cup Recovery and Recycling Group have been working with paper mills in the UK to recycle

PE coated beverage cups into tissues. The PE coating has to be removed through pulping. Also the

contamination has to ideally be lower than 10 weight percent but a trial in 2008 consisted of 25 weight

percent contamination. This can lead to a lower fibre quality when recycled which could mean that


31

the cups will be sent to energy from waste plants or even landfill. The contamination rate is clearly

still an issue and a separate step to remove the PE film is needed (Read, 2008). This project focuses

on recycling this material without separating the mix of materials which is another waste disposal

option for the disposable coated paper cup.

Carbon Clear analysed the environmental impact of different types of cups for beverages including

paper, polystyrene (PS) and ceramic cups. The end of life disposal for cups and emissions from energy

use for 2000 servings is shown in Table 3-2. Interestingly the paper cups emit the most emissions from

landfill. This identifies a need to look at other end of life disposal options.

Table 3-2: Emissions for energy use of paper, polystyrene and ceramic beverage cups (www.carbon-clear.com).

Key points to take from Tables 3-1 and 3-2 are that disposable cups are ending up in landfill. High

quality fibres can be reused saving the use of virgin materials. Most paper mills do not want to recycle

paper cups due to the thin polymer coating. There are also regulations about the use of recycled

content in paper cups, leaving other end of life disposal options worth investigating.

The interest in waste materials is increasing, especially in the materials that are still landfilled. Zhao

and Zhao (2012), looked at additional options for paper cups. Disposable cups were used as a carbon

source to form graphene.

3.2.2 Paper Plastic Laminates (PPLs) / Multilayer Carton Board (MCB) / Tetra Pak Cartons

MCB produces significant tonnages of waste material that is often landfilled. MCB is often referred to

as Tetra Pak. Tetra Pak is a brand name for this type of material. There are many other brands

manufacturing similar materials known as Elopak and SIG. These are all members of the Alliance for

Beverage Cartons and the Environment (ACE) UK.

Beverage cartons contain approximately 75% paperboard, 21% LDPE to prevent leakage and

aluminium (4%) as a layer preventing light and oxygen entering.

ACE UK have stated reasons to recycle beverage cartons.

Cartons are 100% recyclable

Cartons have a market value and can be recycled in the UK creating value within the UK


32

Landfill diversion

The use of beverage cartons is still increasing

Recycling of MCB is increasing. Having kerbside collections increases recycling by up to 6 times. In

2012 global recycling of cartons increased by 10% from 528 Kt to 581 Kt which is 23% of the total that

has the potential to be recycled. 39 billion cartons were recycled worldwide in 2012. Some countries

such as Luxemburg, Belgium and Germany have recycling rates of 70% and above for cartons. However

many other countries do not have the infrastructure to match this, including collections and recycling

facilities. Further solutions and disposal options are needed.

(ACE) states that in 2005 used beverage cartons were recycled in about 20 paper mills across Europe.

Many paper mills cannot take too many cartons for recycling. Cartons at paper mills however can be

recycled with waste paper by separating the structure of the carton. This process is a water based

technique known as repulping. The paper fibres are separated from the polymers and aluminium

layers. ACE state that the virgin fibres used in the initial manufacture of beverage cartons are chosen

due to their strength and stiffness at the lowest possible weight. These fibres have the potential to be

utilised in other new paperboard products (www.ace-uk.co.uk).

Tetra Pak also states that the most common way to recycle beverage cartons is through fibre recovery

at paper mills. The mills put cartons into a container where the fibres separate from each other. The

non-paper parts of the structure like the polymer either float or sink and can be sieved out. This is a

short process. The fibres are then used as a valuable raw material for other paper products as stated

above. The aluminium and polyethylene can also be utilised instead of being sent to landfill. In

Germany the polyethylene and the aluminium are both used in cement kilns where they are used as

an alternative fuel.

In Italy Tetra Pak are used for ‘Ecoallene’ which is a new plastic material. This was created by Lecce

Pen. The paper is recovered for the paper industry whereas the aluminium and polyethylene is put

through a cleaning and extruding process to make pellets for other products. Ecoallane is a material

developed by Lecce Pen and uses PE and aluminium. It is currently used to make small toys and home

and office products. These two materials can be also used as catalysts for cement kilns replacing coal

as a fuel (Tetra Pak International, 2010).

Despite all of the above, collections are low. Not all of the local authorities collect cartons and many

members of the public do not know that they can be recycled. Public perception is still and will be an

ongoing issue in years to come.


33

It should be repeated that waste materials should have many end of life disposal options. Many of the

procedures named above require a lot of energy and water like pulping which separates the individual

layers. What if you did not have to separate the individual materials, could the mixture still be used as

a useful product? This is a question that this research attempts to answer and therefore giving a low

cost solution using a lower amount of energy to produce a useable, efficient and in some cases high

value product.

ACE and Sonoco Alcore have especially built their own recycling facility for beverage cartons in the UK.

The facility can recycle up to 40% (25,000 tonnes) of the beverage cartons used in the UK each year.

The plant does stop cartons being recycled in Swedish mills and saves 122 tonnes of transport related

CO2 (www.ace-uk.co.uk).

The fibres used in beverage cartons are long, strong and can be recycled up to six times. The

polyethylene and aluminium are currently stored instead of landfilling and exporting, as the most

suitable solution for them is being assessed and will be known in 2014.

The plant process for beverage cartons is relatively straight forward. The cartons enter a pulper for 20

minutes separating the aluminium and polyethylene from the fibrous slurry. The materials now have

two paths that they take. The pulp enters a high density cleaner where many fines such as grit and

glass are removed. The material then passes through two screens where any leftover polymer and

aluminium are taken out. Then the water content is reduced and the material is stored for subsequent

operations. After pulping the majority of the polymer and aluminium are cleaned dewatered and

baled for storage.

It is known that carton products can be recycled but many companies do not take responsibility for

the end of life disposal of their products. Only a few councils in the UK collect carton waste as many

of them see it as a minor waste stream and economically unacceptable. Many companies do not see

the volume of waste as a threat and therefore do not think it is financially worth setting up a recycling

system.

Companies such as Tetra Pak aim to recycle their products through reuse or recovery of materials

(TetraPak International, 2010). The most widely used method for recycling cartons is to recover the

fibres which can then be utilised to produce paper, tissue paper and liner for corrugated boxes.

A company called Corenso recovers the aluminium through a gasification plant and produces energy.

Corenso recycle the fibres to produce paper and high strength coreboards. The polyethylene is heated

to produce energy for the paper mill.


34

Tetra Pak have patented equipment that separates the PE and aluminium which means a greater

amount of fibre is recovered. Compressed boards are manufactured from the PE and aluminium.

Tetra Pak products have been recycled into low density boards (Murathan et al., 2007). Tetra Pak

samples were shredded and compressed under heat (70oC) and pressure (400 MPa) but this was

unsuccessful. PVA glue was then tried as a compatibilising agent under the same heat and pressure

mentioned above. There were issues with the water absorption tests due to the swelling of the

cardboard.

MCB materials are rarely recycled together. Usually the materials are separated first due to the mix of

materials. There is limited literature in this area, and an opportunity to present a novel recycling

process for carton products still exists.

Sceptics of carton products have researched alternatives for replacement. Renewable resource based

bilayer films, polyhydroxybutyrate films (PHB) and cellulose cardboard were compression moulded in

a recent study. Water absorption, moisture absorption and water vapour permeation were examined.

The PHB was said to form a layer around the cellulose cardboard and improve the resistance to absorb

moisture. This layer also improved the mechanical properties of the cellulose cardboard. The tensile

properties are enhanced by the addition of PHB, with 20% PHB looking the optimal addition. The

research concludes that this material could replace this carton based packaging (Cyras et al., 2009).

3.3 Composite Matrix Materials

The matrix plays many key roles in a composite material. The matrix binds the fillers together and

transfers the load from the matrix to the filler material. The matrix helps distribute the filler which can

prevent crack propagation. The matrix prevents the filler materials from being damaged from the

surrounding environment. The choice of matrix helps with mechanical properties such as impact

strength (Mazumdar, 2001).

3.3.1 Polypropylene (PP) for use as the Matrix Material

Polypropylene (PP), part of the polyolefin family, is widely used due to its low cost, exceptional

chemical resistance, excellent low temperature processing ability and high mechanical properties.

These attributes make PP ideal for use as a matrix material in PPCs.

Due to the nature of PP in terms of stability, weight, properties and abundant use in many applications,

many PP products end up in landfills. PP from household waste can be more challenging in acquiring

a consistent feed stock rather than PP drinks bottles or car bumpers for example. Recycled PP can

often be blended with other materials to enhance the properties. Mineral fillers or elastomers can be


35

added to recycled polymers to improve mechanical properties including ethylene propylene which can

improve toughness but can reduce the strength and stiffness. Therefore calcium carbonate can be

added which is known not only to improve impact energy but also the hardness, strength, stiffness as

well as lowering the cost. Often the recycled material can be found sandwiched between layers of

virgin material to reduce virgin plastic use (Uan-Zo-li 2005; Brydson, 1999).

3.3.2 High density polyethylene (HDPE) for use as the Matrix Material

HDPE is a widely used polymer that has huge potential for use as a recycled polymer. Recycled HDPE

is often used for boxes and pallets due to its strength and toughness properties making it an excellent

candidate for a matrix material. Sanchez-Soto et al., (2008) studied the effect of the properties after

recycling HDPE. If polymers experience multiple recycling processes then they are susceptible to

irreversible thermo-oxidative degradation in the form of chain scission and crosslinking. Additives to

prevent degradation are often added to recycled materials but this increases the cost significantly over

time. Blending HDPE with LDPE from the PPLs should exhibit some adequate properties due to

intertwining and co-crystallisation of the polymer chains. However LLDPE blends do not blend very

well due to the difference in the melt flow rate (MFR). Adding PP to HDPE makes the blend brittle due

to the lack of bonding. Sanchez-Soto et al., (2008) found that 2-4wt.% talc added to the recycled HDPE

would exhibit excellent mechanical properties due to the nucleating effect of the talc. Kostadinova et

al., (1997) showed that having a short residence time can significantly improve the mechanical and

rheological properties even after being recycled five times.

3.3.3 Recycled Plastic from Material Recycling Facilities (MRF)

Different types and colours of plastics are sorted at a plastics sorting station. Reflected near infrared

light is used to identify plastics and then the identified plastic is air blasted to the correct container.

Multistage processing lines are available with chemical composition and transparency being detected

followed by a second stage identifying the colour saving the costs of previous systems used (Tachwali

et al., 2007). All of the materials collected are baled and sent to paper mills or plastic recyclers ready

for reprocessing. The remaining waste that was in the compactor is sent to landfill or EfW plants.

Reground plastics can also be produced from MRFs. Once the materials have been effectively sorted

they can be granulated, washed and dried ready for reprocessing.

3.3.4 Polymers from Waste Electrical and Electronic Equipment (WEEE)

WEEE is currently the fastest growing hazardous waste stream. The WEEE directive defines electrical

and electronic equipment as (Chancerel and Rotter, 2009):


36

‘Equipment which is dependent on electric currents or electromagnetic fields in order to work

properly and equipment for the generation, transfer and measurement of such currents and

fields.’

Electrical products contain harmful heavy metals and chemicals that can pollute the environment and

be detrimental to human health. Current recycling processes are not keeping up to date with the

speed of growth of this waste stream and many processes are too expensive to employ. Electrical

waste has been overlooked for far too long and numerous products are ending up in landfill (Cobbing,

2008).

Cobbing (2008) states that across the European Union (EU) WEEE waste amounts to 8.7 million tonnes

a year with only 2.1 million tonnes collected. The remaining material is known as the ‘hidden flows of

EU waste.’ It has been reported that:

‘no precise data is available on what happens to this waste, whether it is stored, disposed of

otherwise within the EU, or exported, to be either reused, recycled or disposed of in Asian

countries such as India and China as well as Africa.’

Despite the Basel ban (restricting imports and exports of hazardous waste), this hidden flow still exists.

Hidden flow correlates to the waste that is not collected, recycled, or reused and is basically

unaccounted for. In countries like China and India the emphasis seems to be on recovery and not

safety or human health. This means that it is very cheap to recycle and as a result a lot of waste from

the US and EU will end up being exported as the cheapest disposal option.

According to Huisman et al., (2007) cited by Chancerel and Rotter (2009), 8.3-9.1 million tons per year,

17 kg per capita, of WEEE across the EU is generated. WEEE typically contains between 10 and 30 wt.%

of engineering plastics with polypropylene (PP) as the major fraction. A global figure for 2007 for the

amount of E-waste came to 20–25 million tonnes per year, where the majority of waste produced was

in Europe, the United States and Australasia (Robinson, 2009).

If a sufficient recycling procedure is to be put into place then fundamental knowledge on the

characteristics of the WEEE being supplied is essential. Also the recycling process that would need to

be put into place is a huge step which involves collection points, logistic systems, treatment plants and

marketing of the secondary raw materials (Chancerel and Rotter, 2009).


37

Research has shown that PP was the most common polymer used for thermal household appliances

and Acrylonitrile butadiene styrene (ABS) was used for equipment such as vacuum cleaners and other

small household products.

The difficulties with recycling certain WEEE plastics are the additives within the plastic which can be

hazardous. Examples include bromine flame retardants and heavy metals (Chancerel and Rotter,

2009). A large amount of non-ferrous metals like copper and nickel, about 0.1% concentration, can

indicate that additives are in the polymer.

One of the key problems of plastics recycled from WEEE products is the existence of cadmium, and

polybrominated dibenzo-p-dioxins (PBDDs) or dibenzofurans (PBDFs) which can be produced during

the recycling process. This is an issue because if the presence of these materials is above legislation,

this can inhibit the recycling distribution within Europe (Dimitrakakis et al., 2009). Another study

mentions that PBDDs and PBDFs can form during thermal and mechanical stress depending on the

temperatures and residence time during processing. At lower processing temperatures this is not an

issue and should not be a worry unless the polymer reaches temperatures where it starts to degrade

(Bart, 2001).

A more updated report of contaminants in WEEE plastics shows that brominated flame retardants are

the main cause of PBDDs and PBDFs. Shredders have been reported to produce PBDDs and PBDFs due

to temperatures reached (Schlummer et al., 2007). The tests in this study found the same amount of

PBDDs and PBDFs present in previous reports over ten years ago. Alternative flame retardants have

been reviewed yet no improvement was found (Schlummer et al., 2007). Further studies have included

whether WEEE recycling actually is environmentally the right disposal option. Such studies include

comparing a recycling system that included all secondary material processing against incineration and

primary production of reproducing WEEE parts like the steel and precious metals. The results clearly

show the recycling option is environmentally preferred (Hischier et al., 2005).

3.5 Coupling Agents for the Matrix and Filler Interface

The main role of coupling agents are to create a link between the matrix and filler which allows stress

transfer from the matrix to the fibres (Kalia et al., 2011).

Many different coupling agents have been studied within the wood plastic composite industry. These

include organic, inorganic and organic-inorganic coupling agents. This research focuses on maleic

anhydride (MAH) grafted to polyolefins (organic), silanes (organic-inorganic) and a coupling agent

known as Polyethylenimine (PEI), a low molecular weight ethylenimine copolymer.


38

Coupling agents are needed because in the growing field of WPCs, fibres are polar and hydrophilic

while the polymer tends to be non-polar and hydrophobic which causes compatibility concerns. It is

well known that coupling agents enhance the interfacial bond between the filler and the matrix. One

part of the molecule must be reactive with the surface of the fibrous filler and the other part must

interact with the matrix creating a link between the two (Schofield, 2005). A variety of methods for

incorporating coupling agents into composite materials has been researched. The fibre matrix

interface can be either physically or chemically modified to ensure better adhesion (Bledzki and

Gassan, 1999).

A coupling mechanism such as chemical bonding is important for WPCs introducing covalent bonds to

the fibre and matrix. The matrix co-crystallises and entangles with the polymer part of the coupling

agent. Many additives are in fact used with WPCs as well as coupling agents. Some can change the

surface energy of the fibre by making it non-polar like the polymer matrix and reducing the tensions

between the two. Examples of this would be stearic acid, which can be seen as a lubricating agent,

and paraffin wax. With the addition of these two additives the melt flow of the composite can be

severely reduced due to the interaction between the acid groups and hydroxyl groups of the fibres

preventing the polymer chains at the interface having freedom to flow. The stearic acid causes a

reaction with the hydroxyl groups preventing the polymer and fibres reacting which can cause less

interfacial adhesion and therefore a reduction in mechanical properties, (Kuk. and Pal, 2010).

However, small additions of stearic acid have proven to increase strength and 3% stearic acid

significantly helps fibre dispersion. Stearic acid has been used as a dispersing agent which can help the

fibres spread throughout the matrix preventing agglomeration of fibres and promote interfacial

adhesion (Dányádi et al., 2010; Raj and Kokta, 1989; Grossman and Lutz, 2000; Kim and Pal, 2010).

Maleic anhydride (MAH) is well known within the WPC industry for helping to bond fibres and

polymers. Grafting MAH to the backbone of saturated and unsaturated polymers is well documented.

MAH has been grafted onto PE, PP and PS. This is done to enhance adhesion, crosslinking and

compatibility with other polymers and fillers and also to improve heat resistance (Culbertson, 1987).

Adding maleic anhydride based coupling agents secures the interface between the filler and matrix.

The bonding at the interface is key to improving the mechanical properties of the composite. A

disadvantage of MAH may be that the molecular chain of MAH is shorter in length than the polymer

and the fibres which can reduce interfacial adhesion. Therefore MAH is grafted to PP or PE. It has been

reported that if the chains are too long, then migration of the coupling agents to the surface during


39

the short residence time in plastics processing, may hinder the effectiveness of the coupling agent. A

coupling agent with too high a molecular weight can entangle with the matrix polymer but the polar

groups of the coupling agent may struggle finding the alcohol (–OH) groups on the surface. If the Mw

is too low then there is not enough of the PP in the MAPP to interact and entangle with the matrix

material. Also if the Mw is too high then the coupling agent may not reside at the interface. It is

therefore imperative to have a polymer grafted to MAH that has a Mw that is high enough to co-

crystallise and entangle with the matrix and a high percentage bound MAH for attracting the filler

(Keener et al., 2004).

In MAPP coupling agents, chain entanglement is key to a successful bond at the filler matrix interface

because any stresses faced by one chain can be transferred to other chains and therefore spread

across the entangled chains (Neilsen, 1974). Therefore the chain length of polymers needs to be

considered when discussing polymers for use in coupling agents. If the chains are smaller in length it

is possible to slide past one another. Longer chains means a higher percentage of entanglement which

can cause a higher viscosity of the polymer. More entangled chains can provide mechanical strength.

The coupling agent at the interface is therefore important and relies on chain length and covalent

bonding at the filler interface (Thakur, 2013).

The reaction between the coupling agent and any reinforcement/filler leaves an aliphatic PP chain on

the fibre surface that enhances wettability and compatibility at the interface. The saponification (SAP)

number is an indication of the free and combined acids. It is used as an indication to the maleic

anhydride bonding in a coupling agent and levels of free maleic anhydride, by many companies such

as Honeywell (multinational company producing consumer products including specialty materials like

coupling agents). The reacted MAH is what is important in coupling agents because it provides the key

link to the polymer and therefore bonding can take place between the polymer and filler with an

effective bridge between the two.

Honeywell state that the percentages of bound and unbound MAH (which they refer to as the bound

SAP) are very important characteristics. The higher percentage of bound MAH signifies that more

coupling points are available because the MAH has grafted to the PP chain to produce MAH-g-PP,

ready to provide an effective bond between the fibre and the matrix. The percentage of unbound

MAH indicates that more MAH is unreacted and therefore not available for coupling which provides

the vital link for a successful bond. The MAH creates a covalent ester bond with the hydroxyl groups

of the filler. This is due to the carboxylic acid which contains a carboxyl group in the MAH and the

alcohol groups in the filler. This is known as a condensation reaction (Crowe, 2014).


40

Qingxiu et al., (2005), suggest that the bonding mechanism between the maleic anhydride and fibrous

filler is due to covalent bonding whereas Lu et al., (2000) suggest a mixture of bonding at the interface

namely covalent bonding, hydrogen bonding, mechanical interlocking and van der Waals forces.

Maleated polyolefins such as MAPP and MAPE are usually made by grafting MAH onto the polymer

backbone commonly with radical reactions. The MAH further reacts with the hydroxyl groups under

processing temperatures. Klyosov, 2007, says that this further reaction is inconclusive and the

esterification reaction actually produces a crosslinked cellulose-maleic half ester structure. Figure 3-2

shows partial and full esterification reactions.

Figure 3-2: Maleic Anhydride grafted to PP (MAPP) (www.addcomp.nl).

3.6 Composite Materials: Combining the Matrix, Filler and Coupling Agent

Composite materials offer superior properties to the individual components that they consist of.

Composite materials have two or more phases separated by a distinct interface. One phase is

continuous and most often consumes the majority of space within the composite and is termed the

matrix. The second phase usually is termed the reinforcing phase which in most cases is harder,

stronger and stiffer than the matrix. Composites are desirable because products can be made that to

weigh less, at a higher strength with a lower cost. Weight savings in the current climate is very

important due to the emissions and cost saved in transportation.


41

The geometry of the reinforcement has a huge effect on the composites’ mechanical properties.

Generally there are fibre reinforced composites with continuous (long fibres with high aspect ratios)

and discontinuous fibres (short fibres with low aspect ratios). There are also particle reinforced

composites that contain dimensions approximately equal in all directions and typical shapes of the

reinforcement include spherical, cubic and platelet for example. Particulate based composites tend to

show isotropic tendencies (Smith and Yeomans, 2005).

The matrix has a number of key roles in the composite. The matrix isolates the fibres and protect them

from being damaged. A ductile matrix can help slow cracks down that start around broken fibres. The

matrix aims to transfer the load to the more stiff reinforcing fibres through shear stresses at the

interface. A strong interfacial bond is vital for natural fibre composites to work (Wambua et al., 2003).

The properties of the resulting composites can be significantly different to the properties of the

constituent materials used to manufacture the composite (Milton, 2002).

The general behaviour of the composites largely depends on the volume fraction of fibres, mechanical

properties of the constituents, the orientation of the reinforcement within the composite and the

interfacial properties (Shah et al., 2012; Harris, 1999).

3.6.1 Composite Fracture

Composite materials can fracture through failure at the interface of the two constituents or by

cracking of the matrix material. For example during a tensile test experiment the failure can occur

through a crack growing along the interface and this can then lead to fibre pull-out known as

debonding (adhesive failure). The crack can also grow out towards the resin away from the interface

causing matrix failure known as cohesive failure (Gent and Wang, 1993).

In WPC, fibre pull-out shows a weak interface and this can indicate that the fibres are not being held

within the matrix sufficiently by the coupling agent. If however the fibre breaks first it shows that the

interface is sufficiently strong to allow the fibres to take the load upon the material. The filler materials

usually of a fibrous nature are stronger than the matrix and therefore the composites can reach higher

strengths if the composite is well bonded. If the matrix cracks the stress has not been sufficiently

transferred to the fibres. Fibre break is the preferred option due to fibre pull-out indicating a weak

interfacial adhesion with the matrix.


42

3.6.2 Wood Plastic Composites (WPCs)

Wood plastic composites (WPCs) are composite materials made of natural fibres and plastic. WPCs

are typically used to replace existing wood products such as decking. Natural fibre composites are a

good replacement for wooden pallets because wood can splinter and they often need to be fumed.

Other key growth areas include decking and the automotive sector.

Natural fibres can be split into different categories. Many of these fibres have been used in natural

fibre composites. Plant fibres include bast or stem fibres typically jute flax or hemp fibres, leaf or hard

fibres, seed (cotton and coir), fruit, cereal straw fibres, grass fibres and wood fibres (Lopez et al., 2012).

As early as 1916 WPCs were used by Rolls Royce in gear knobs. In the 1970s WPC became very popular

and then interest accelerated in North America in the 1990s. The maintenance costs of wood are

higher than WPCs and the outdoor durability of WPCs is higher. WPCs have taken some of the market

share in some industries from glass fibre composites because natural materials are typically 40%

lighter in weight than glass fibres and they only require 20% of the energy needed for glass fibre

production (Pritchard, 2004).

Key applications for WPCs has been decking in North America. The construction industry and

automotive industries have also been developing WPCs for their products. The automotive industry

has seen huge growth with WPCs being used for dashboards and door panels. Growth rates for WPCs

are typically in the region of over 20% a year (Bismarck, 2006).

Fibrous flakes have been used before in natural fibre composites. Flakes are seen as a problem due to

poor wetting ability, the agglomeration of fibres making processing more difficult and producing

weaker composites. A study using wood flakes in a plastic matrix has been researched as wood flakes

do not need to be further separated and pre-treated saving on cost. One particular study focused on

how flake wetting and flake distribution was affected by the flow properties of the matrix. Wood flakes

at 10wt.%-70wt.% were extruded with HDPE of different melt flows (Balasuriya et al., 2001).

Properties of WPCs vary depending on the types of wood used. A typical value with a 60 wt.% wood

content and 40 wt.% for tensile strength would be 20 MPa according to Stark, 1999. Table 3-3 shows

a summary of typical mechanical properties of WPC and PPCs.


43

Table 3-3: Mechanical properties of WPCs, PPCs and virgin polymers found in the literature.

Polymer Paper / Wood

Plastic Composite Author Mechanical Property

Tensile

Strength Young's Modulus

Flexural Strength

Flexural Modulus

MPa GPa MPa GPa

Virgin HDPE Adhikary (2008) 21.4

Recycled HDPE Adhikary (2008) 23.2

Virgin PP(copolymer)

CES EduPack

2014 17-22.5 1.03-1.23 31.6-37.5 1.02-1.28

Virgin HDPE CES EduPack

2014 22.1-31 1.07-1.09 30.9-43.4 0.997-1.55

PP/wood plastic

composite Stark (1999) 20 4.87

PE/ wood plastic

composite Stark (1999) 14.6 4.14

HDPE/ 30wt.%

MDF / E-43 (1%)

Jayaraman and Bhattacharyya

(2004) 11.1 2.3 21.6 2

PP / 40% radiata

pine / 3 wt.% MAPP

Beg and Pickering (2008)

40 4

HDPE/ 30wt.%

wood flour Adhikary (2008) 15.9 1.37 24.3 1.29

HDPE/ 30wt.%

wood flour/3wt.% Epolene G-3015

Adhikary (2008) 19.3 2.35 24.9 1.81

recycled PP/55wt.%

recycled newsprint/ 2%

MAPP

Ashori and Nourbakhsh

(2009) 12 0.6 14 1.25

recycled HDPE/55wt.%

recycled newsprint/ 2%

MAPP

Ashori and Nourbakhsh

(2009) 13 0.65 15 1.5

Isotactic PP / wood flour /

MAPP (Equistar)

Hosseinaei et.,al (2012)

33.8 4.5

Isotactic PP / wood flour

Hosseinaei et.,al (2012)

23.7 4.4

PP/30wt.%

newsprint/2-3wt.% MAPP

Peltola et al., (2002)

46.3 2.14


44

The composite properties are dependent on the fibre and matrix properties. The tensile strength of a

WPC shown in Table 3-3 by Beg and Pickering (2008) has a PP matrix that has a high tensile strength.

The addition of fillers and coupling agents increase the strength values by approximately 10 MPa.

Pritchard, 2004, noted that the critical strain energy release rate (GIc) of uncompatibilsed WPC does

not differ from the matrix material. Pritchard, 2004, also noted comparing wood to WPCs is hard

because of the moisture in wood can significantly change the properties. It was also noted that

without coupling agents the flexural strength and flexural modulus are not as high as wood like spruce

and oak. It is reported that typical WPC values for flexural strength lie in the region of 15-75 MPa

(Stark, 1999).

Waste plastics can be used as the matrix material in WPCs as noted by Najafi (2013). Najafi (2013)

notes that generally virgin polymers are used for the matrix material in WPCs and that recycled plastics

are gradually being used more. A factor that is noted to be important with recycled plastics for WPCs

is the melting point. A mixture of plastics will have different melt temperatures and processing

temperatures may start to degrade them. Also the immiscibility of the recycled plastics should also be

noted as an important point. The effect of recycled polymers on the mechanical properties is varied.

Mali et al., (2003) comments that recycled PP achieves higher tensile properties than virgin. Other

studies on recycled plastics in WPCs are noted by Najafi (2013) and Mali (2003).

Leu et al., (2011) studied the use of wood flour in WPCs. The results showed that producing WPCs with

a wood flour content above 50% decreases mechanical properties. MAPP added at 3% was optimum

and increased tensile strength by at least 10 MPa. Kuo et al., (2009) found that 3-4.5% MAPP added

to wood flour and a PP matrix showed the optimum results in terms of mechanical properties.

3.6.3 Paper Plastic Composites (PPCs)

The use of waste materials in composites is becoming more frequent. Cost reduction is the major drive

along with the energy savings associated with virgin materials. Using every day waste products for

paper plastic composites are relatively new. The exponential increase of the wood plastic composite

industry over the last decade has led to other fibrous materials being used in a plastic matrix. Fisal and

Salmah (2012), investigated the use of waste white office paper in low-density polyethylene

composites. An earlier study (Fisal and Salmah, 2010) showed the importance of coupling agents with

debonding at the filler matrix interface and filler pull-out in absence of any compatibilisation. The filler

in the 2012 study was ground to a powder and mixed at 180oC with a LDPE matrix and a MAPE coupling

agent, put through a mill and then hot pressed into sheets. At 3% MAPE a very small increase in tensile

strength was observed, but proved a reaction was taking place at the interface of the fibre and filler.


45

As predicted the elongation at break was reduced with increasing filler content. A 350% reduction was

seen with just a 10 wt.% addition of filler into the LDPE matrix. The Young’s modulus was seen to

increase more than the tensile strength values due to the fibres reducing the ductility of the matrix. .

Further studies in this field include recycled high density polyethylene (HDPE) and PP combined with

recycled newspapers for use as composite panels. Results suggest that recycled materials produce

adequate properties for the panel application. Different grades and previous applications can greatly

affect the properties of the reprocessed material (Ashori and Nourbakhsh, 2009).

Limited data is available in the literature for the types of fillers used in this project. Previous research

has used similar materials to PPCs (Peltola et al., 2002). The matrix materials were recycled PE and PP

with a range of paper fillers; newsprint, liner paper with a siliconised coating, liner paper with a PP

coating, liner paper which was the surface layer of corrugated cardboard and wet strong paper. Peltola

et al., (2002) reports that both mechanical fibres and cellulose fibres are known as wood fibres but

the mechanical fibres contain lignin whereas the cellulose fibres have the lignin removed. Both of

which are used in the paper making industry. The lignin is reported to decrease the polarity of the

fibre which improves the adhesion between the fibre and matrix. Polybond 3200 was used at 2-3wt.%.

Compounding took place in a Brabender 350 E batch type laboratory mixer. The filler content was 30

wt.% which was introduced after the coupling agent and plastic were fed into the mixer. The tensile

tests followed the standard SFS-En ISO 527/1a. It was found that the tensile strength only increased

when PP was mixed with the newsprint (containing lignin), wet strong paper and liner (surface layer

of corrugated cardboard). The tensile strength reached 46.30 MPa while the modulus reached 2138

MPa with the newsprint. The impact strength was found to decrease compared to the PP alone with

results around 20 KJ/mm2 across all recipes. When PE was used as a matrix the tensile strength and

modulus values were lower than the PP but a higher impact strength was shown. The matrix materials

in this project include a PP/PE mix which could explain the slightly lower modulus values. The

mechanical properties for siliconised liner did not increase by a noticeable amount which section 10.1

shows. This is due to the material used for the coating on the PPLs. The wetting is very high and further

analysis would be needed.

Malak (2011) focused on a program called ‘Waste for Life’ in areas of poverty that focused on hot

pressing plastic and paper composites. Malcenji et al., (2010) studied the waste materials produced

from extracting cellulose from waste paper in paper mills. De-inked residue and mixed waste plastic

were used to make a composite material. Up to 30,000 tonnes of de-inked residue is available from

paper mills per annum with 3,000 tonnes of mixed plastic waste. The study showed that these wastes


46

could be mixed to produce composites but the mixed plastic waste that comes from paper mills needs

sorting based on its variability.

Lopez et al., (2012) compared three fillers in a PP matrix. These were deinked pulp from newspapers,

mechanical pulp and jute strands. At 40 wt.% deinked pulp the tensile strength increased by 10MPa

when 6% MAPP was added. A virgin PP was used with a high melt flow and a tensile strength of 27.6

MPa.

Winandy and Stark (2004) noted that the newspaper based polymer composites showed comparable

properties to wood flour composites and that recycling the newspaper based composites in terms of

re-extruding and injection moulding does not alter the mechanical properties too much. Lopez et al.,

(2013) noted that newspapers could successfully be used as reinforcement within a starch based

thermoplastic.

3.7 Modelling of Paper Plastics Composites

3.7.1 Long fibre composites: Elastic Modulus

The use of fillers to reinforce composites can be achieved in many different ways. Predicting how

materials may behave helps understand and prove the reinforcing effect. The addition of fillers is most

often required to enhance the properties. Many models have been applied in the wood plastic

composite field. Initially the rule of mixtures was applied to the PPCs in this research in order to predict

the behaviour of the composite materials. This is because the main aim of adding fillers would be to

improve the mechanical properties.

A starting point for predicting properties would be to look at the stiffness of the composite with the

filler (i.e the fibres) all aligned in the same direction. This is known to improve the properties such as

strength and stiffness parallel to the fibres. The axial stiffness can be estimated assuming equal strain

in the direction of the fibre (Voigt model).

3.7.2 Voigt Model (Axial Stiffness)

A basic first step approach considers the filler and matrix to be treated as slabs that are perfectly

bonded and when a force is applied in parallel to the filler, the matrix and filler experience the same

strain. Equation 3-1 predicts the composite stiffness assuming the filler is long enough for the equal

strain assumption to apply (Hull and Clyne, 1996).

EC = (1-f)*Em + f*Ef equation 3-1


47

Where,

EC, m, f = Modulus of the composite, matrix and filler

f = Volume fraction of filler (fibres)

3.7.3 Reuss Model (Transverse Stiffness)

Hull and Clyne (1996) use the slab model to explain the Reuss model. Essentially the force is applied

perpendicular to the fibres. The stress is assumed equal in the filler and matrix (equation 3-2).

EC = [ 𝑓

𝐸𝑓 +

(1−𝑓)

𝐸𝑚 ]-1 equation 3-2

The Reuss model is known to underestimate the Young’s modulus due to the non-uniform distribution

of stress and strain. The Reuss model is however treated as the lower bound in the rule of mixtures

with the Voigt model as the upper bound. Kim et al., (2001) found for high volume fractions of fibres

the plastic flow and mechanical data tended to fit the Voigt model and exist within the ROM at lower

volume fractions.

3.7.4 Halpin and Tsai Model

Halpin and Tsai takes into account the effect of the fibre load bearing with the equal stress

assumption. The equation for transverse stiffness is shown in equation 3-3.

EC = 𝐸𝑚(1+𝜉𝜂𝑓)

(1−𝜂𝑓) equation 3-3

𝜂 = ( 𝐸𝑓

𝐸𝑚 – 1) / (

𝐸𝑓

𝐸𝑚 +𝜉)

ξ = adjustable parameter, assuming a value of 1

3.7.5 Short Fibre Composites: Shear Lag and Axial / Eshleby Method

Previous models assumed long fibres within a matrix to gain a basic understanding of how the

composites may behave. To try and predict more accurately the behaviour of PPCs the shear lag and

Eshelby models were investigated. The shear lag model assumes a cylindrical shape whereas the

Eshelby method assumes an ellipsoidal shape. The ellipsoidal shape could be in the form of a sphere,

cylinder or plate and has greater mathematical complexity and more of an accurate approach

compared to the shear lag approach. The shear lag model (equation 3-4) focuses on interfacial shear

stresses and the transfer of tensile stress form the matrix to the fibre by means of the interface (Hull

and Clyne, 1996; Nairn, 1996).


48

Ec = VfEf(1-(𝐸𝑓− 𝐸′𝑚)tanh (𝑛𝑠)

𝐸𝑓𝑛𝑠 + (1-f)Em equation 3-4

Where,

E’m = 𝐸𝑓 [1−sech(𝑛𝑠)]+𝐸𝑚

2

n2 = 2𝐸𝑚

𝐸𝑓(1+𝜐𝑚)ln (1

𝑓)

3.7.6 Elastic Modulus for Particulate Composites

The elastic modulus of the composite material is determined by the individual modulus of the

materials such as the filler and the matrix and the volume fraction of filler used as well as the filler

aspect ratio. When the filler is spherical in shape the aspect ratio is equal to 1.

Assuming perfect adhesion and dispersion between the filler and the matrix, Einstein’s equation for

Young’s modulus of particulate composites is shown in equation 3-5 and is valid at low filler

concentrations and does not take into account particle size.

Ec = Em(1 + 2.5f) equation 3-5

Where

EC, Em = Composite modulus and matrix modulus

f = volume fraction

Guth (1945) added another term known as the particle interaction term shown in equation 3-6.

Ec = Em(1 + 2.5f + 14.1f2) equation 3-6

Kerner (1956) predicted the modulus of a composite (equation 3-7) constituting of spherical particles in a matrix (Fu, 2008).

Ec

Em = 1+

Vp

(1−Vp) 15(1−νm)

(8−10νm) equation 3-7


49

Another model used to predict the elastic modulus of particulate composites is the modified rule of

mixtures. A particle strengthening factor has been added by Verbeek (2003) and the model lies

between the rule of mixtures models. Equation 3-8 assumes the filler and matrix have perfect

adhesion with the stress transferring via a shearing mechanism.

EC = χpEfVf + Em(1-f) equation 3-8

Where χp = 1 – tanh(Vfmax)/Vfmax

Ef = Modulus of the fibre

3.7.7 Strength of Particulate Composites

The strength under uniaxial tensile loading is an indication of the maximum stress the composite can

cope with. Of course in composites, the filler matrix adhesion is important along with particle loading

and size (Fu, 2008; Danusso and Tieghi, 1986; Levita et al., 1989). Equation 3-9 assumes that the stress

cannot be transferred from the matrix to the filler and that the matrix absorbs the load.

σ c = σ m (1- f ) equation 3-9

σ c = Composite strength

σ m = Composite matrix strength

Assuming no adhesion between the filler and the matrix, with the matrix absorbing the load, is shown

in equation 3-10 (Nicolais and Nicodemo, 1973; Nicolais and Narkis, 1971). This gives a lower bound

strength of the composite, whereas the upper bound is given by the strength of the matrix.

σ c = σ m (1-1.21 f 2/3) equation 3-10

Equation 3-10 can be modified to include some adhesion between the filler and the matrix shown in

equation 3-11 (Lu et al., 1992).

σ c = σ m (1-1.07 f 2/3) equation 3-11

Additional strength analysis and models can be seen in Chapter 7 comparing the mixed blends of PPCs.


50

3.8 Rheology of PPCs

The composites in this research can be described as non-Newtonian where the viscosity changes with

applied stress. Pseudoplastic behaviour is most commonly modelled by the Oswald-de Waele power-

law model shown in equation 3-12.

τ= K 𝛾 ̇ n equation 3-12

Where,

τ = Shear stress [Pa],

K = Flow consistency index [Pa.sn]

�̇� = Shear rate [s-1

]

n = Flow behaviour index

The flow consistency index is obtainable from the y –intercept from the log shear stress vs log shear

rate curve. The slope of the curve determines the flow behaviour index. These values can be attributed

to the behaviour of the composites under melt. The closer the flow behaviour index is to one, the

closer the behaviour is to Newtonian flow.

3.9 Conclusions

Chapter 3 presented an overview of the materials used in PPCs and related industries surrounding

PPCs. Recycling of materials is becoming an industry wide normality and using waste materials that

currently have end of life disposal options as landfill and incineration are of particular interest. The

waste materials chosen in this research are widely available and currently do not all have end of life

disposal options. WPC properties and the PPCs obtained in this research will be compared to the

literature findings.

Experimental Chapter 4

51

Chapter 4

4. Experimental

This chapter describes the experimental procedures used in this research. It includes information on

the processes used to manufacture composites and materials characterisation techniques.

4.1 Preparation of Raw Materials for Processing

The following experiments were required to ensure the filler materials were fit for processing in the

extruder.

4.1.1 Size Reduction of Raw Materials

The filler materials needed to be size reduced so that they could effectively mix with the polymer and

coupling agent in the extruder. Previous research (Nextek Ltd) found 3-4mm was the optimum flake

size for the filler. The fillers were granulated; Figure 10-14, at Loughborough University with a 3mm

mesh. The granulator produced very similar results to the previous trial.

4.1.2 Blending of Raw Materials

All samples were measured out on a weight basis. The correct quantities of materials were put into a

container and hand mixed and shaken to distribute the coupling agents and filler effectively for 3

minutes before extruding. Additional blending took place in the mixing equipment shown in Figure

10-15.

4.1.3 Pre-Blending the Filler and Coupling Agents

PEI and VTES coupling agents were supplied in liquid format. The coupling agents were still measured

on a weight basis. The PEI coupling agents were warmed in the oven at 65oc for 10 minutes to lower

the viscosity of the coupling agent so it could be successfully blended with the filler and polymer. The

PEI coated flakes were put into a vacuum oven for 24 hours at 40oC. The VTES coupling agent was pre-

blended with the PP to ensure the PP was fully coated with the coupling agent. The filler could then

react with the coupling agent, as the polymer did not absorb the liquid agents, and instantly reacted

with the filler materials changing the colour of the flakes before processing proving a reaction took

place. The flakes were shaken in a sealed bag until the liquid fully coated the PPL flakes. The samples

were then ready to be extruded.


52

4.2 Plastics Processing for PPCs

This section describes the extrusion process and the injection moulding of mechanical test bars.

The extrusion process converts materials to compounds ready for final processing. Material is fed

through a hopper and is gravity fed to the extruder barrel. The material reaches a rotating screw which

conveys the polymer melt along the barrel to the die. Twin screw extruders are extruders with screws

that turn side by side at the same speed with the same diamater. The three types of twin screws

available include co-rotating intermeshing, counter-rotating intermeshing and counter-rotating non-

intermeshing. A large variety of twin screw extruders exist. Each design, depending on the intended

use is different. The direction of rotation and the degree of intermeshing of the screw flights all play

important roles when processing. The screws in twin screw extrusion are made up of conveying,

kneading and mixing sections. Arguably the most important section of the screw is the kneading block.

This is comprised of a number of discs at a variety of angles. When the screw turns the discs cause a

powerful shearing process and cut the flowing polymer material at which point most of the melting

takes place. The most common twin screw extruders are intermeshing co-rotating extruders. A major

advantage with these screws is that they are self-cleaning, which leads to the shorter residence time

than single screw extruders. This is especially useful for thermal and shear sensitive materials, because

dead spots, where material builds up and degrades, are reduced (Rauwendaal, 2001).

4.2.1 Compounding by Twin Screw Extrusion

The reactive extrusion process took place in a Thermo Scientific Haake Polylab operating system. The

extruder was a co-rotating twin screw (26 mm and L/D=40) at Brunel University (Figure 10-16). The

extruder consisted of 10 temperature zones shown in Table 4-1. This compounding stage was used to

convert the mixture of materials into one composite material in the form of pellets shown in Figure 4-

1. Table 4-1 summarises the optimised processing conditions. The co-rotating screws are self-cleaning

and have excellent mixing capabilities ensuring the filler is well dispersed. The filler would break down

especially in the kneading block section.


53

Figure 4-1: PPC pelletised after extrusion

Table 4-1: Extrusion settings for PPC on the Thermo Scientific co-rotating twin screw (26mm and

L/D=40) extruder.

Extrusion Settings

Barrel / Cylinder Temperatures (oC)

Zone

1

Zone

2

Zone

3

Zone

4

Zone

5

Zone

6

Zone

7

Zone

8

Zone

9 DIE

160 160 170 170 175 175 175 175 180 180

Residence time (s)

75-85

With the small die head on this extruder the die pressure did seem to increase rapidly and had a cut-

off point which would raise an alarm especially at higher filler contents with a die pressure of 100

MPa. Therefore the PPCs were extruded through a slot die into bars and then granulated to pellets.

The bars are shown in Figure 10-17 which were approximately 30 cm in length and 3-4 cm in diameter.

4.2.2 Injection Moulding

Injection moulded products are manufactured in a variety of industries from automotive to medical

and recreation. Two important parts of the moulding cycle include the injection unit and the clamping

unit. The injection unit conveys, melts and injects the molten polymer into a mould. The clamping unit

ensures the correct shape is formed and suitable pressures are maintained.

The moulding also took place at the Wolfson Centre at Brunel University. This moulding stage was

used to convert the extruded pellets into test bars for analysis. Figure 10-18 shows the injection

moulding machine used at Brunel University. The settings are shown in Table 4-2.


54

Table 4-2: Injection Moulding conditions on the Demag for manufacturing test bars of PPCs.

Moulder Settings

Barrel / Cylinder Temperatures (oC)

Zone 1 Zone 2 Zone 3 Zone 4 Nozzle

175 175 180 175 175

Stroke

Screw after plasticising 27mm

Dosing stop 25mm

Start holding pressure 12mm

Speeds

Plasticising screw speed 50rpm

Injection step 40%

Screw return after plasticising 7rpm

Pressures

Injection pressure 90 Bar

Holding pressure 15 Bar

Times

Injection time 5s

Holding time 17s

Cooling time 13s

Carriage return 2s

Optimisation of the settings was required to mould the test bars successfully. The optimisation process

for moulding involved changing the shot size and pressures before complete bars were observed.

Figure 10-12 shows test bars that were moulded for analysis. After injection moulding, the samples

were left for 24 hours at laboratory temperature before analysis.

4.3 Characterisation and Testing Techniques

This section firstly highlights the experiments that help with material identification and processing

properties by thermogravimetric analysis (TGA), x-ray fluorescence (XRF), Fourier transform infrared

spectroscopy (FTIR) and rheology experiments. The experiments then focus on the mechanical

properties of the composite materials.

4.3.1 Thermogravimetric Analysis (TGA) / Differential Scanning Calorimetry (DSC)

In order to investigate cellulose fibre stability during processing, thermogravimetric analysis


55

(TGA) was used to determine the weight change of composite samples. TGA is a process that focuses

on the change in weight with a change in temperature. DSC measures the heat flow as a function of

temperature. The equipment used was a Scientific PL-STA 1500 S/N 11293 which is a simultaneous

TGA/DSC linked to RSI Orchestrator computer software for analysis.

The TGA/DSC works by having two crucibles, one for a reference and one for a sample, which are

linked to a balance. Samples were prepared by drying in an oven until constant weight was achieved

and then stored in a desiccator. Ramp and isothermal experiments were conducted with samples that

were as close as possible to 20mg for consistency. This meant that one pellet was enough for one

sample. Ramp tests were carried out at 20oC a minute and 10oC a minute from ambient to 500oC,

whereas isothermal tests were held at 180oC for 3 minutes, 10 minutes and 20 minutes to simulate

processing and exaggerate the residence time in the extruder. This temperature was chosen because

the processing window is between 160oC-200oC. The fibres degrade at temperatures higher than

approximately 200oC and the melting point (Tm) of the matrix would be near 160oC. Tests were

completed under a nitrogen and oxygen atmosphere. Holding for 3 minutes to 20 minutes is longer

than the residence time in the extruder so if any changes were to occur then the results would show

this. By raising the temperatures beyond the degradation point the max processing temperatures

were observed and how the materials behaved over a wide temperature range. Three samples were

trialled for each run but further samples were needed if inconsistencies were found. Heat flow and

weight were recorded over the temperature range set above.

4.3.2 Fourier Transform Infrared (FTIR) Golden Gate

To aid in identifying the composition of the material an image preserving Attenuated Total Reflectance

(ATR) accessory known as the Specac Imaging Golden Gate Diamond ATR was used. Advantages of

using this technique are not needing to prepare the sample and still obtaining a 2D chemical infrared

image. Paper, powders and polymer pellets can all be successfully identified. Due to the waste

material possibly having a varied composition the 2D infrared image produced may have been

affected.

An FTIR Spectrometer is based on the Michelson Interferometer. This interferometer has a beam

splitter as well as fixed and moving mirrors. The beam splitter separates the incoming radiation into

two beams which transmit to the fixed and moving mirrors and then is reflected back to the beam

splitter. This causes one beam to be sent back to the source and the other to the detector.

In this study a Nicolet iS10 spectrometer was used with the golden gate accessory named above. The

background spectrum was collected at first to ensure the sample chamber was clear of CO2 (~2300


56

cm-1) and H2O (~1400 cm-1 and 1800 cm-1). The plastic waste obtained from each of the waste streams

were then identified by the spectrum shown and were also compared with the Nicolet library

software.

The Infrared part of the electromagnetic radiation spectrum consists of low energy photons that do

not have enough energy to excite electrons but may cause vibrational excitation. The

frequency/wavelength (cm-1) at which this occurs depends on the strength of the bonds involved and

the mass of the atoms. The intensity of absorptions by molecules depends on a certain attribute which

is that an electric dipole moment of the molecule must change for a particular vibration to absorb

infrared energy (Reusch, 2007). Infrared radiation passes through a sample and the fraction of incident

radiation that is absorbed at a particular energy is measured. The FTIR analysis obtains a molecular

fingerprint of the material being examined (Stuart, 2004). FTIR spectroscopy is widely used due to the

ability in determining composition, tacticity, conformation and crystallinity (Gulmine et al., 2002).

4.3.3 X-ray Fluorescence (XRF)

The WEEE PP was scanned for elements that may be hazardous due to the previous service life of the

PP. The instrument used was the Bruker S4 Explorer WD XRF. Particular elements used in flame

retardants were searched for such as Br and Cl.

4.3.4 Rheology

i) Melt Mass-Flow Rate (MFR)

A standard method (ISO/DIS 1133-1:2009) was followed on a Davenport melt flow tester which

established the MFR by extruding molten material through a die of a certain length and diameter

under a set temperature and load.

Equation (4-1) was used to calculate the MFR:

MFR (T, mnom) =600 ×m

t equation 4-1

Where,

T = Cylinder temperature (190oC)

mnom = Load in Kg (2.16Kg)

600 = grams per 10 minutes (600s)

m = mass of the cut offs from the die (g)

t = time between cut offs (s)


57

Pellets were placed into the MFR equipment and forced in a molten state through the die as described

in the standard.

ii) Capillary Rheometry: Shear Rate vs Shear Viscosity

Capillary Rheometry is similar to the MFR test but can show more rheological properties of a material.

MFR is a quick test that can help rank a material but is limited. In capillary rheometers a sample of

material is extruded through a die of certain dimensions where the shear pressure drop across the die

is recorded at set volumetric flow rates. This is achieved through pressure transducers placed above

the die exit.

Simulating the extrusion and moulding process can help understand how the material will behave

under heat and pressure in the extruder but without the shear caused by the screws.

Polymer and PPC pellets were placed within the barrel of the Gottfert Rheograph Rheometer 6000

which can offer a maximum force of 60 kN and a piston speed of 40 mm/s. Shear stress and shear

viscosity of the PPCs and the polymer matrices were calculated at a temperature of 190oC, just using

one of the 3 bores available with die dimensions of 2 mm internal diameter bore, 30 mm length and

a 180 degrees run in angle. The piston was 12 mm in diameter. The recipes were subjected to 3

minutes of heating time before the test started to ensure the material was compressed with no air

bubbles and that the material was molten. The piston speed varied through the run as shown in the

results.

4.3.5 Water Absorption

All recipes were dried at constant weight to ensure minimal moisture content. Samples were then

immersed in distilled water. The samples were 80 mm in length, 10 mm in width and 4 mm thick. The

sample surfaces were dried with a cloth to remove surface water and weighed at 2 hours, 24 hours,

168 hours, 672 hours, and 4,032 hours. Three samples from each recipe were measured and the

average weight change calculated. Samples were left for 24 hours and then subjected to a 3 point

bend test and tensile test to study the effect of immersing PPCs in water.

4.3.6 Optical Microscopy

i) Stereoscope

The fracture surfaces were studied under a stereoscope before being subjected to the scanning

electron microscope (SEM) to see what fracture surfaces would need further analysis by SEM. The

stereoscope used was a Novex R2-Range with a Motic camera adjoined (Motic Images 2000 Version

1.3).


58

4.3.7 Scanning Electron Microscope (SEM)

JEOL JSM-5610LV scanning electron microscope was used. Fracture surfaces were gold coated using

an EMITECH K550.

4.3.8 Density

The density of the recipes was measured by using the ends of the tensile bars in a water displacement

method (based on method A of ASTM D792 – 13, ‘Density and Specific Gravity (Relative Density) of

Plastics by Displacement). Three samples of each recipe were measured and the results can be seen

in section 10.3.

4.3.9 Mechanical Testing of the Plastic Matrix and PPCs

The mechanical tests outlined in this section will focus on the test equipment used, the procedure,

and the standard followed.

i) Tensile Testing

Tensile tests are important in material analysis because they provide data on the ultimate tensile

strength (UTS), elongation, Young’s modulus and Yield strength. Further details can be obtained from

the stress strain curve but this project is concerned with tensile strength and Young’s modulus.

In accordance with AS 1145.1-2001, samples were conditioned and tested at ~23oC. The equipment

used was a Zwick/Roell Z010. The standard followed was the BS EN ISO 527-2/1A/1 and the BS EN ISO

527-2/1A/5, ‘Plastics – Determination of tensile Properties.’

Tensile bars were moulded on the equipment shown in Figures 10-13 and 10-18. All samples were

measured with a micrometer and a mean value was taken. TestXpert version II was the computer

software used to evaluate the results. The sample dimensions fit the standard requirements named

above. The load cell was 10KN. The data obtained showed standard travel against standard force. The

engineering stress and strain data points were calculated from this data using basic stress strain

equations. The standard deviation, standard error and averages were noted for each recipe. Five

samples were measured and tested for each recipe in each mechanical test. The Young’s modulus was

measured along the linear part of the stress strain curve at 1mm/min for all samples to ensure a fair

comparison according to the standard named above.


59

Extensometer

The extensometer was added to ensure a more accurate assessment of the modulus. The stress strain

data was measured over a smaller region of 20mm of the gauge length where the extensometer was

clipped on.

ii) Flexural Testing

Flexural testing was performed in accordance with the British Standard BS EN ISO 178:2003 ‘Plastics –

Determination of Flexural Properties’ on a Zwick/Roell Z2.5. A 2KN load cell was used with TestXpert

version II software.

Flexural bars were produced by trimming the ends of the tensile bars and using the 80mm gauge

length. The flexural stress and flexural strain were calculated by the equations below. The flexural

strength was calculated using equation 4-2.

𝜎𝑓=3𝐹𝐿

2𝑏ℎ2 equation 4-2

Where,

σf = flexural stress

F = applied Force (N)

L = Span (mm)

b = width of specimen (mm)

h = thickness of specimen (mm)

The flexural strain is given by equation 4-3.

𝜀𝑓 = 6𝑠ℎ

𝐿2 equation 4-3

Where,

εf = Flexural Strain

s = Deflection (mm)

h = thickness of the specimen (mm)

L = span (mm)


60

According to the standard followed the span was determined by,

L = (16 ± 1)h equation 4-4

All of the dimensions of the specimens moulded met the recommended standard dimensions of:

Length, l: 80 mm 2 mm, Width, b: 10.0 mm 0,2 mm, Thickness, h: 4.0 mm 0,2 mm

A preload of 0.1 MPa was used to maintain contact with the sample before it was tested. The test

speed was 2mm/min as stated in the standard. Five samples for each recipe were measured and the

average, standard deviation and standard error were calculated.

Figure 4-2: Flexural Testing setup (Zwick/Roell Z2.5, Machine reference A704548).

iii) Charpy Impact Energy

The Charpy Impact Energy was measured to look at the amount of energy PPCs could absorb before

fracture. The tests were carried out in accordance with ‘Plastics – Determination of Charpy Impact

Properties Part 1: (ISO 179:2010).’

A Zwick/Roell Charpy Impact tester was used. The maximum amount of energy that could be absorbed

was 50J. A minimum of five samples for each recipe were tested. The samples were un-notched and

placed edgewise on the supports. The standard was followed as closely as possible with pre-

conditioning and the correct sample size was used. The Charpy imapct energy was calculated in

kilojoules per square metre using equation 4-5.


61

𝑎𝑐𝑈 = 𝐸𝑐

ℎ𝑏 x 103 equation 4-5

Where,

Ec = energy absorbed (J)

h is the thickness (mm)

b is the width (mm)

iv) Fracture Toughness

The fracture toughness followed as closely as possible the British Standard BS ISO 13586:2000 ‘Plastics

- Determination of fracture toughness (GIC and KIC) —Linear elastic fracture mechanics (LEFM)

approach.’ Samples were machine notched and then a razor blade skimmed the notch to ensure a

sharp notch was created. The samples were tested on the same 3-point bending equipment used in

the flexural tests.

Figure 4-3: Fracture toughness specimens after machining and a slit made with a razor blade. The

colour of recipe 13 to recipe 8 is clearly shown. Recipe 13 has a higher filler loading.

The test speed was at 10 mm/min, the support separation at 40mm and a crack length of 4.5 mm.

The following equation was used to calculate the critical stress intensity factor (KIC):

KIC = 3PLΨ √πa0

2bW2 equation 4-6


62

Where,

P = failure load (N)

B = width (mm)

W = total depth (mm)

a0 = notch depth (mm)

L= span length (mm)

Ψ is give by the following equation (Rooke, 1976)

Ψ = 1.11 – 1.55 (𝑎0

𝑊) +7.71 (

𝑎0

𝑊)2 – 13.5(

𝑎0

𝑊)3 + 14.2(

𝑎0

𝑊)4 equation 4-7

The KIC of a material is related to its critical energy release rate GIC by the following equation:

GIC = 𝐾2𝐼𝐶

𝐸 equation 4-8

v) CREEP Behaviour of PPCs

The samples that exhibited the highest mechanical properties were put through a creep test which is

a fundamental test that all materials should be analysed with. Tests were run for 30 minutes at a

constant stress and then put through a recovery (stress removed) for 30 minutes at 20%, 40% and 60%

of the UTS value at laboratory temperature and 40oC.

This test was a force controlled creep test with 1 cycle with a 1 MPa pre-load, 10mm/min speed pre-

load. The grip to grip separation was 80mm. The speed for creep was 1 MPa/s, a test time of 3600s

was used with hold and recovery at 1800s. Recipe 14 of trial 2 b) was subjected to another test with a

hold time of 172800s and a recovery of 43200s.

At first a heated rubber strap was used for creep testing at elevated temperatures. A thermocouple

was placed the other side of the sample to keep track of the material either side of the tensile bar.

Then to ensure a more uniform heating approach a heated coil was used (Figure 10-29). The strap

would cause elevated temperature fluctuations on one side of the specimen whereas the coil was

more uniform. The temperature controller measured the temperature every 12 seconds which caused

temperature fluctuations but the average temperature was taken over the test run and noted.


63

vi) Dynamic Mechanical Analysis (DMA)

Dynamic mechanical analysis (DMA, TA Instruments Q800) was used to determine the storage

modulus (E') and loss modulus (E'') of different composite samples over a range of temperatures

(Tajvidi et al., 2006; Joseph et al., 2003). Single cantilever beam samples were heated at 3°C per minute

from -50°C to 180°C. The frequency of oscillation was fixed at 1Hz and the strain amplitude was kept

within the linear viscoelastic region at 0.1%.


64

Novel Paper Plastic Composites (PPCs) from extruded Paper Plastic Laminates (PPLs)

Waste / Raw Materials

Pre – Processing

Compounding

Plastics Processing and Testing

PPL beverage cup

WEEE PP/ MRF/ HDPE

PPL Tetra Pak

Size reduction

Blending + Coupling Agents

Injection Moulding

Tensile / Impact bars

Twin Screw Extrusion

Pelletising

Materials Characterisation and Initial Trials Chapter 5

65

Chapter 5

5. Materials Characterisation and Initial Trials

This chapter describes the materials used in this research. It includes information on the raw materials,

composition and material properties as well as the reasons why the materials were selected.

5.1 Composite Matrix Materials

Recycled plastics were targeted as the composite matrix material. Plastics are widely available with

ideal properties for manufacturing natural fibre composites through conventional plastic processing

equipment. Plastics are still disposed of in landfills and further end of life options are always required.

A variety of recycled polyolefins were studied to gain an insight into the recycling industry.

5.1.1 Polypropylene and Polyethylene from Material Recycling Facilities (MRF)

A mix of polypropylene (PP) and polyethylene (PE) polymers were obtained from a material recycling

facility and supplied by Express Polymers Europe Ltd. This mix consisted of materials that had been

hand sorted, granulated, washed and dried. This chapter describes methods used to characterize the

material and an image of the recycled plastic used is shown in the appendix Chapter 10 (Figure 10-1).

Initially PP was trialled from an MRF (Figure 10-1). A second batch of material from the same MRF was

obtained but with a different chemical composition. Companies should aim to quality control material

coming into their facilities. It reinforces the point that recycled material varies from batch to batch.

This has put major companies off using recycled material due to the inconsistency of the incoming

material they are receiving. Section 10.2 discusses this further along with other experiments that were

part of the initial trials (Peeters et al., 2014).

5.1.2 Polypropylene from Waste Electrical and Electronic Equipment (WEEE)

PP was obtained from WEEE. This had been subjected to sink and electrostatic float separation

followed by drying, shredding, granulation and extrusion into pellets. This material was sourced from

BlueSky recycling. Characterisation data is given in chapters 5 and 6 and in the appendix with a

photograph of the supplied plastic in Figure 10-2.

5.1.3 High Density Polyethylene (HDPE)

HDPE was sourced from Regain Polymers Ltd and was a recycled extrusion grade from crates.


66

5.2 Characterisation of Matrix Polymers

5.2.1 Rheological Properties of the Composite Matrix

ii) Melt mass Flow Rate (MFR) Analysis of the Polymer Matrix.

The measure of the MFR value can be vital information to a process engineer because it can determine

the ease of flow of the material in its molten state. A high MFR value translates to a lower amount of

force required to move the material along the screw during processing. A low MFR value describes a

material needing a higher force to progress the material along the screw.

The results shown in Table 5-1 highlight the MFR values of the recycled polymer from the trial at

Bangor University but measured at London Metropolitan University.

Table 5-1: MFR data for recycled polymer used as the matrix material

Recipes MFR (g/10min) (190oC, 2.16kg) Std Error

MRF 4.96 0.55

WEEE 3.21 1.01

MRF New 3.55 1.33

HDPE 0.32 0.29

The melt flow behaviour of the matrix material is important in WPCs. The structure and properties of

the composite are influenced by the melt behaviour and processing method (Balasuriya et al., 2001).

Therefore it was necessary to explore how the melt flow of the matrix could be modified.


67

WEEE PP 2% 5% 10% 20%

0

5

10

15

20

25

30

35

40

MFR_Sassolwax 5603_190oC_2wt.%-20wt.%

Mel

t F

low

Rat

e (M

FR

) (g

/10m

in)

Recipe

MFR_A-C 1089_190oC_2wt.%-20wt.%

Figure 5-1: Shows the effects of adding the processing aids. By making the polymer matrix less viscous

the fibrous filler is carried along the screw with less shearing in the extruder.

At just 2 wt.% the WEEE PP matrix can improve up to 7 g/10min. At 20 wt.% the PP matrix can have a

MFR up to 34 g/10min. Figure 5-1 shows that the melt flow rate of the plastic can be improved. Faster

flow rates help carry the PPL through the extruder reducing the residence time. PPL can start to

degrade at temperatures above 200oC. If the torque in the extruder increases due to the inability of

the material to flow, the shear stress can increase and fibre degradation is likely to occur. Therefore

improving the melt flow behaviour of the matrix can reduce degradation of the filler.

The HDPE grade used was an extrusion grade with relatively low MFR. However further steps have

been taken to look at increasing the MFR if necessary, Figure 5-2.


68

HDPE 2% 5% 10% 20%

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

MFR_A-C_190oC_2wt.%-20wt.%

Mel

t F

low

Rat

e (M

FR

) (g

/10m

in)

Recipe

MFR_A-C_230oC_2wt.%-20wt.%

Figure 5-2: Influence of A-C additive from Honeywell on the melt flow rate of HDPE at 190oC and 230oC.

The MFR can be increased with the A-C additives from Honeywell, but very high additions of the

additive are needed to even reach a MFR of 3 g/10min. This explains the flow of HDPE at processing

temperatures and why it was so hard to push through the extruder. By adding the filler the melt flow

rate was even lower. In fact the HDPE recipes tended to smell due to fibre degradation through shear

in the extruder. This does not show up through TGA analysis but trials have brought this issue up.

However excellent results were still obtained with HDPE PPCs.


69

5.2.2 Differential Scanning Calorimetry (DSC)/ Thermogravimetric Analysis (TGA)

DSC establishes key melt characteristics of the matrix material, namely the melting temperature. H

eatF

low

(m

W)

Temperature (oC)

Heat flow of WEEE PP

Heat flow of MRF_PP_PE

Heat flow of MRF_PP

Figure 5-3: DSC curves between 0-250oC for a variety of recycled PP and PE

Figure 5-3 shows the heat flow against temperature for a variety of recycled polyolefins used in this

research. The WEEE PP used as the matrix in this project shows a major change in the curve around

170oC which is believed to show the polymer melting temperature. A small decrease in the heat flow

is seen close to 130oC which could show a small polyethylene fraction. This curve was purposely

chosen for comparison reasons. Two samples of recycled polyolefins were obtained from an MRF.

They can both be seen in Figure 5-3. The two curves highlight problems that can arise when using

recycled materials. The MRF stated that both batches were PP. The results shown in Figure 5-3 prove

how vital it is to check samples before use. The MRF PP/PE curve shows the major change in the heat

flow at 130oC with a small change in the heat flow at 170oC and the MRF PP curve displays a change

at 170oC. Knowing the plastic matrix is critical when deciding what coupling agent will be added. Many

MRFs still sell their flakes as PP or PE with a percentage of PP or PE within it (Manivannan and Seehra,

1997; Uan-Zo-li, 2005).


70

The MRF PP shows a wide melting area indicating the mixture of different materials, shown in Figure

5-3. The material has come from a number of different sources including crates and lids with varied

polypropylene starting materials which all may have different melting temperatures as indicated by

the large change in the heat flow of the curve in Figure 5-3. Najafi (2013) mentions the range of melt

temperatures that can be seen with recycled plastics. The MRF PP/PE curve shows the majority of the

polymer was PE with the lower melting point close to 130oC. This polymer was confirmed to be mostly

PE after further characterisation with FTIR.

Wt.

% C

han

ge

(%)

Temperature (oC)

Weight Percent change

Heat flow

Hea

tFlo

w (

mW

)

Figure 5-4: TGA/DSC curve for WEEE PP between 0-500oC and being held at processing temperature

to note any significant changes. Ramp from 0-180oC at 20oC/min, Isothermal at 180oC for 3 minutes

then 180oC – 500oC at 20oC/min in Nitrogen.

The WEEE PP used as the matrix in this project shows a decrease in heat flow in the curve around

170oC which is believed to show the polymer melting temperature. A small change is also seen in the

curve close to 130oC which could show a small polyethylene fraction. This curve was purposely chosen

for comparison reasons. The high melting point of this PP can be attributed to the PP copolymer.

Random (atactic) PP can often not show a clear melting point and has low crystallinity with ordered

regions surrounded by amorphous material, exhibiting tough and flexible properties (Maier and

Calafut, 2008). The weight loss of WEEE PP (Figure 5-4) is not substantial over the extrusion processing


71

temperature range of 180-200oC. Between 350-400oC the weight starts to decrease as the polymer

degrades. This is a positive sign for processing as the polymer should not be affected by the processing

temperature in the extruder. The extrusion process would add more heat due to friction caused by

shearing.

i) Crystallinity Analysis

Figure 5-3 shows heat absorbed by the polymer against temperature. The heat capacity can be

calculated from a DSC plot. The energy required to heat the material to a certain temperature is known

as the heat capacity. DSC analysis determines polymer crystallinity and amorphous content.

Knowing the crystallinity in polymers can be useful when characterising and predicting material

properties. One way is to integrate the trough found on the DSC plot in Figure 5-3 and then dividing

by the specific heat of melting (Uan-Zo-li, 2005).

The mechanical properties are hugely affected by the crystallinity. The higher the crystallinity the

higher the stiffness, yield stress and flexural strength but the lower the impact properties (Maier and

Calafut, 2008).

The total heat given off to melt the polymer shown by the red trough (WEEE PP) in Figure 5-3 is

calculated by:

ΔHm = Area of trough

Heating rate x m equation 5-1

Percent crystallinity,

% Crystallinity = [[

ΔHm

ΔHmo]

𝑚] x 100 = 24.5% equation 5-2

Where,

m = mass of sample, ΔHm = Latent heat of melting and ΔHmo = 207.1 (J/g) Specific heat of melting if

the polymer was 100% crystalline.

Equation 5-2 is not the most accurate method to calculate crystallinty but provides an adequate

estimate (Uan-Zo-li, 2005).

In Figure 5-4 the weight change from 160-200oC is important because these are typical processing

temperatures needed for PPC manufacture and any weight change may indicate degradation which

would be unacceptable. Knowing this information can help the processer with upper and lower


72

processing temperatures. The samples were examined at 10oC min-1 until 180oC and then held at 180oC

for 3min-20min to try and simulate the residence time during processing. The samples then continued

from 180-500oC. The same experiment was conducted at 20oC min-1. Very similar results were

observed.

Figure 5-5: Showing a section of data from TGA experiments (Ramp 20oC to 180 oC, 200 oC and 220oC,

then isothermal for 20 minutes in nitrogen.

Figure 5-5 shows that at 220oC the weight percent of WEEE PP drops slightly. This is negligible and can

be something degrading off of the recycled polymer. This is a point worth noting but batches of

recycled polymer may vary slightly from time to time.

5.2.3 Fourier Transform Infrared (FTIR) Analysis of Composite Matrix

FTIR analysis focused on the individual flakes sent from the MRF. This technique is a useful, quick

analysis that can help analyse polymers by identifying the structure which can then be related to the

property performance.

0 5 10 15 20

99.0

99.5

100.0

100.5

Wei

ght

Per

cent

(wt.

%)

Time (Minutes)

Isothermal at 180oC for 20min




73

Table 5-2: Material Identification by FTIR analysis of the coloured flake from the MRF waste stream (Figure 10-1).

Waste stream FTIR Identification

Black MRF PP/PE

Dark Blue MRF PE low density

Green MRF PP/PE

Grey MRF PP/PE

Light blue MRF PP/PE

Orange MRF PP/PE

Purple MRF PP/PE

Red MRF PE low density

White MRF PP/PE

Yellow MRF PP/PE

Table 5-3: Material Identification by FTIR analysis of PP from WEEE sources (Figure 10-2).


WEEE PP PP atactic

Figure 5-6: Fourier Transform Infrared (FTIR) data of the WEEE PP is shown, identifying an atactic PP

structure.

Knowing the tacticity of the polymer is very useful in determining and understanding the properties

of the polymer which in this case is the matrix material. There are three types of stereoisomers seen

for vinyl polymers, namely, isotactic, syndiotactic and atactic. Infrared bands are produced due to the

link between stereoregularity and regular chains.

3000 cm-1 PP

2962 cm-1 Methyl CH3 asymmetric

stretching

2872 cm-1 symmetric stretching

g

1460 cm-1 1375 cm-1

g


74

In the case of PP, tacticity refers to the presence of methyl groups attached to carbon atoms on the

chain backbone. Atactic relates to a random structure where the methyl groups are randomly

distributed on either side of the chain backbone. Atactic PP is amorphous with an irregular structure.

Isotactic PP, methyl groups all reside the same side of the molecule, is stiff and mostly crystalline.

Knowing this information can help understand the properties of the material. For example generally

the more crystalline the PP the higher the softening point, stiffness, tensile strength and hardness.

The WEEE PP was identified to be atactic. Indicating the random nature of the side groups on either

side of the pseudochiral centres, (Brydson, 1999; Uan-Zo-li, 2005).

The absorption bands 970 cm-1 and 1460cm-1 do not depend on the tacticity, while absorbance at 840

cm-1, 1000 cm-1 and 1179cm-1 are usually due to isotactic PP. An absorbance at 870cm-1 usually refers

to syndiotactic PP but cannot be clearly seen above. These differences are due to the helical structures

in the isomers which can help predict the amount of isotactic and syndiotactic PP in a material (Stuart,

2004).

The sharp band around 3000cm-1 is well known to identify PP. This is a stretching vibration and is

usually a very sharp band. Methyl (CH3) shows asymmetric stretching at ~2962cm-1 while symmetric

stretching bands at ~2872cm-1. Bending vibrations are usually shown at ~1460 cm-1 for asymmetric

while a band at 1375cm-1 shows a symmetric bend. All of these peaks are clearly visible in Figure 5-6.

The large band at 2300cm-1 is usually not shown for PP but could be CO2. The band in-between 1500-

1600 cm-1 could be the carbon carbon double bond stretch or H2O.

The branches in polyethylene consist of methyl groups which mean that any differences in the FTIR

analysis for methyl groups may give an indication about the branching. PE produces complex spectra’s

due to crystal field splitting. This is because PE has a small repeat unit and these repeat units pack

closely together which causes interaction between them.

iii) Density of Composite Matrix Materials

Table 5-4 shows the density of selected polymers of interest.

Recipe Average Density (g/cm³)

Standard Error

WEEE PP 0.926 0.0125

MRF 0.896 0.0855

MRF New 0.952 0.0752

HDPE 0.960 0.0241


75

Densities are important when designing materials for applications. The densities were measured by

the experimental methodology shown in Chapter 4.

The density of recycled material can vary depending on the source and composition. Plastic properties

can vary with a change in density. The density can affect the feeding to the extruder for processing or

mechanical strength for example.

5.2.4 X-ray Fluorescence (XRF) of WEEE PP

WEEE PP was further analysed because WEEE polymers can contain hazardous additives such as

bromine flame retardants and heavy metals, as explained in the literature. The major problem with

these additives is that in an incinerator or landfill site they can contaminate the environment. Chapter

3 states that PP is one of the most common WEEE polymers and was therefore characterised further.

The intended commercial application of the PPCs indicates that physical properties are more relevant

but analysis of the PP is important to understand the material being used.

XRF technique is an excellent characterisation technique that gives rapid analysis with minimal sample

preparation. The sample was scanned for hazardous substances, (Taurino et al., 2010). The WEEE PP

pellets were scanned for just the elements of interest that could be found in high concentrations in

WEEE material, such as the flame retardants (Peeters et al., 2014).

Calcium (Ca) had the highest concentration and comes from PP that is filled with calcium carbonate

(CaCO3). This is often added as a filler or pigment. There are a number of advantages to using CaCO3,

typically being higher impact properties as well as heat aging, good colourability and lower mould

shrinkages.

Titanium oxide (TiO2), showing the second highest concentration is from pigment used to make

products white. The bromine (Br) and chlorine (Cl) are from flame retardants used in electrical plastics.

Menad et al., (2013) found that most of the WEEE polymer examined contained flame retardants.

None of the levels are greater than the Restriction of hazardous substances (RoHs) limits.

5.2.5 Mechanical Testing of Matrix Polymers

i) Tensile Testing of Matrix Polymers

Knowing the tensile strength and Young’s modulus is important to manufacturers or engineers

because the tensile strength tells you the ultimate loading the material can withstand whilst the

Young’s modulus is the stiffness of the material. The yield point is also important and should be

considered when choosing a material because after the material reaches the yield point the material


76

no longer obeys Hooke’s law and will not return to its original shape after loading. Brittle materials do

not exhibit a yield point and have an elastic region until fracture.

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

MRF PP

WEEE PP

MRF PE

HDPE

Virgin PP coploymer

Virgin HDPE

Figure 5-7: Stress Strain curve for recycled WEEE PP, HDPE and MRF polymers used for the matrix with

a comparison to virgin polymers.

Figure 5-7 shows the stress strain curve for WEEE PP and mixed polyolefins from an MRF. The WEEE

PP is a tougher material based on the area under the curve in terms of energy absorbed before

fracture, but a similar strength to the MRF PP. This could be due to the mix of polymers in the MRF

batch of recycled polymer. The material arrived as mixed flake whereas the WEEE PP had been pre-

blended. The exact origin of recycled material can be challenging to source. The way the polymer is

produced via catalysts can have an influence on the properties. For example PP produced through

metallocene catalysts can produce a lower molecular weight distribution (MWD) which leads to lower

melt elasticity and elongational viscosity during extrusion. However a lower molecular weight

distribution (MWD) does mean the PP is less shear sensitive than a wider MWD.

The WEEE PP has been stretched 300% from its starting position (Figure 5-8) indicating excellent

elongational properties compared to the other MRF samples. Generally WPC require strength and

toughness especially for pallets or decking. The WEEE PP should therefore be studied further for PPCs


77

with further optimisation trials. The PP samples tested lie in the virgin PP copolymer region. This range

is from CES EduPack 2014. The HDPE range is higher between 22.1 – 31 MPa. In terms of tensile

strength the PP plastics compete with virgin polymers and the HDPE lies just outside the range given

by CES EduPack for a moulding and extrusion grade.

Commercial recycled polymers that are currently on the market do not vary a huge amount to the

properties of WEEE PP. Early signs of WEEE PP signify that it is more than capable of being the matrix

material for PPCs. A commercial product made with recycled PP, with known mechanical data values,

from an MRF based in Ireland was tested to ensure the equipment was producing reliable results. This

was sourced on site and used as a comparison against the PP. Section 10.4 shows the results.

The MRF PP data in Figure 5-7 shows the variation that can occur with different batches. The MRF PP

came in two batches. For the sake of this research one batch is called MRF PE. The MRF PE produced

a stress strain curve that was tougher than MRF PP. The two batches of material varied significantly in

properties. This can be worrying for the receiving company and also highlights the need for quality

control checks. In this case understanding how blends of polyolefin work is necessary. Many

researchers have studied this including (Kukaleva et al., 2003). Clemons (2010) actually showed that

the PP/PE blends can be used as the matrix for WPCs with an EPDM compatibiliser.

Some recyclers think it is not economic to separate polyolefins into PP and PE. Strapasson et al., (2005)

noted that it is uneconomic to separate the polyolefin fraction using an alcohol solution after being

separated through floatation in a MRF. Therefore often, globally, the MRF mixes blends of polyolefinic

material creating incompatible blends with weak mechanical properties. Compatibilising agents can

be used such as ethylene-propylene-diene monomer copolymer (EPDM), but this of course adds cost

to the recycled material. The work by Strapasson et al., (2005) showed that the processing (injection

moulding) temperature had a huge influence on properties. A 10oC increase caused the elongation

properties to severely drop. With PP and PE blends the optimum processing temperature is between

170-180oC. The MRF PP sample in Figure 5-7 shows minimal elongation. This could be due to the

processing settings described in the research by Strapasson et al., (2005). The ratio of PP and PE and

processing can significantly affect the properties. An addition of 25% of LDPE in PP can have the same

negative effect on PP as a 10oC increase in processing temperature. Madi (2013) also comments on

the costly separation due to similar densities and the potential of improving the properties if blends

of PP and PE are used. However for WPCs a small amount of polyolefin blending does not impact the

results but ideally with the coupling agents being used, just PP or PE would be better.


78

Figure 5-8: Tensile testing showing the elongation of WEEE PP. The tensile bar was 195 mm long before

elongating.

Figure 5-9: Showing failure of the WEEE PP after a tensile test.


79

Figure 5-9 shows the WEEE PP fracture after axial loading. The fracture shows a plastic failure with a

long elongated neck. The polymer molecules orientate in the direction of the force applied. PP is a

semicrystalline thermoplastic, where any deformation can depend on the morphology of the

crystalline phase. The spherulites in the crystalline phase can affect how the deformation behaves.

Depending on how the molten polymer is cooled depends on how the polymer molecules align

themselves. Rapid cooling can cause a random nature of alignment with a lot of entangled molecules.

Slower cooling causes crystalline lamellae to form. Spherulites form when lamellae grow in all

directions and consist of a semicrystalline structure with lamellae and a random amorphous region.

Spherulites can affect the mechanical properties like the tensile strength depending on the size. The

amorphous regions between lamellae can help with the material’s toughness and elasticity properties.

During fracture cracks propagate along the spherulite boundary. Ductile fracture occurs with smaller

spherulites formed after rapid cooling. Larger spherulites tend to cause brittle fracture. The MRF PP

exhibits little necking behaviour. The material is more brittle. This can be from how the material was

formed for the intended product during its service life (Karian, 2003; Raff and Ahmed, 1970). With

elongations up to 500%, the chain extension is relatively easy and is responding to neatly folded

conformations. Karian (2003) notes that local deformation depends on how chain folded crystals

respond to stress. Hamza et al., (2005) and Gent (1986, 1989, 1996) also commented on the necking

mechanism of unfolding chains in crystalline blocks. It was also noted that the folded chain blocks in

the necking zone are tilted, sheared and broken off lamellae that become incorporated in the

amorphous microfibrils (Peter and Olf, 1966).

Crazing in PP has been debated whether it is a deformation mode in PP. It is rare to see crazing in

semicrystalline polymers above their glass transition point (Tg). The Tg of PP is shown in Chapter 6 to

be around zero degrees Celsius (Brydson 1999).

If crazing is observed the crazes grow perpendicular to the direction of the major stress because the

spherulite boundaries form in all directions. Crazing in PP relies on the structure. The number of tie

molecules is important during the deformation of PP. During deformation the matrix separates by a

process called drawing or necking where fibrils are formed. The stress required for necking is affected

by the density of the tie molecules which are pulled from the lamellar section which are found in

spherulites and are seen as chain folded lamella (Karger-Gocsis, 1999).

Necking originates from a localized point. Usually strain hardening is evident; otherwise the reduced

cross section through necking would cause the polymer to fracture. Strain hardening occurs through

molecular orientation and possibly recrystallization. Failure in ductile polymers occurs through chain

slipping, shear and orientation effects (Nielson and Landel, 1994).


80

ii) High Density Polyethylene (HDPE)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

5

10

15

20

25

UTS = 21.35 MPa

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

HDPE

Yield Stress = 13.4 MPa

Strain at break = 0.74

Figure 5-10: Engineering Stress vs. Strain curve for HDPE used as the matrix material for PPCs

The HDPE shows a high strain to failure with excellent toughness. The reasons for trialling HDPE would

be to trial a tough material for applications such as pallets for example. Also the coating of the cup is

PE. The coating is LDPE but small additions can mix with the matrix without concern as reported by

Kukaleva et al., (2003). Figures 5-11 helps show the toughness properties through necking of the HDPE

matrix.

Figure 5-11: Stages of failure in a tensile test for HDPE showing deformation through necking.


81

iii) Flexural Analysis of Composite Matrix

Flexural testing can be important for a number of reasons. Product designers may be designing a

product that needs to withstand a certain flexural load such as pallets.

The 3-point bending test is often quoted due to the high flexural properties obtained with this method.

This does not always give a true representation of the flexural property of the material. The test

method consists of a single force acting at the top of the test specimen and this generates a large

value for flexural strength. A more accurate result would be a 4-point bend test because it has load

distributed over four points and does not have local stress concentration. In 3-point bending tests the

maximum flaw is placed where the maximum stress will be. In industry it is not likely that the

maximum flaw is opposite the maximum stress.

The ideal flexural strength required for pallets for example is ideally greater than 22 MPa and a

modulus greater than 950 MPa (Naday, 2009).

Table 5-5: Flexural Strength of recycled matrix plastics vs virgin polymers.

Recycled/Virgin Plastic

Flexural Strength (MPa)

WEEE PP 30.6

MRF PP 28.1

MRF PE 26.8

HDPE 24.9

Virgin PP 31.6-37.5

Virgin HDPE 30.9-43.4

WEEE PP has higher flexural strength values than the MRF polymers indicating reasons for continuing

with WEEE PP for use in PPCs. The virgin PP is just slightly higher than the recycled PP. Again the virgin

PP, a copolymer, and the virgin HDPE are from CES EduPack. The strength values are greater than the

22 MPa set by Naday (2009), meaning they could be suitable for pallet manufacture. The flexural

modulus of WEEE PP and HDPE are 1.12 and 0.99 GPa respectively which means they are also higher

than the 950 MPa required for pallets set by Naday (2009).


82

iii) Impact Energy of Composite Matrix

MRF PP WEEE PP MRF PE HDPE Virgin PP Virgin PE

0

10

20

30

40

50

60

Notc

hed

Char

py I

mpac

t E

ner

gy (

KJ/

m2)

Recycled Matrix Plastics and Virgin Polymers

Notched Charpy Impact Energy

Figure 5-12: Charpy impact energy of potential polyolefins for use as in PPCs compared to virgin

polyolefins (HDPE and PP).

The notched samples are very similar and all exhibit a toughness of around 10 KJ/m2, with the MRF PE

samples showing a slightly higher toughness. The fabrication method can affect how the materials

deform. PP that has been injection moulded can be up to three times higher than other manufacturing

methods due to the crack growth moving across the orientation direction from the moulding,

compared to cracks that grow parallel to the orientation direction (Kinloch and Young, 1983). In Figure

5-12 recycled HDPE is higher than the virgin HDPE extracted from CES EduPack. The CES grade is a

moulding and extrusion grade. Other higher molecular weight grades can have notched impact

strengths of up to 80 KJ/m2.

5.3 Conclusions of Composite Matrix Plastics

Section 5.2 characterises a variety of plastics for the matrix of PPCs. Key properties include mechanical

properties and ease of processing. WEEE PP not only needs a new route at the end of its life as more

WEEE products are available, but the mechanical properties are also sufficient in terms of strength,

stiffness and toughness compared to the other plastics tested.


83

The MRF polymers were shown to have an inconsistent source and not as high mechanical properties

compared to the WEEE PP. The HDPE exhibited very tough properties but not as high as PP in terms

of strength. All of the recycled plastics examined did compete and are not far off virgin polymer

properties.

5.4 Composite Filler Materials

5.4.1 Paper Plastic Laminates (PPLs) / Polyethylene (PE) Coated Paper Beverage Cups

Polyethylene (PE) coated beverage cups were supplied by Solo Cup Europe, a leading manufacturer of

high performance single-use foodservice products. Paper cups are disposed of to landfill due to the PE

coating which is difficult for recyclers and paper mills to process. Figure 10-3 shows the PE coated

paper cups.

5.4.2 Paper Plastic Laminates (PPLs) / Multilayer Carton Board (MCB) / Tetra Pak Cartons

Multilayer cartons are widely used in a range of products and the multilayer structure causes recyclers

many problems due to the complex mix of materials. Appropriate recycling facilities are often not

available and many multilayer cartons are landfilled. Recycling of this product is possible but products

need many end of life disposal options. Tetra Pak cartons were collected from local supermarkets.

Figure 10-4 shows the collected samples.

5.5 Paper Plastic Laminate Fillers: Material Characterisation

5.5.1 Disposable Beverage Cups

i) Fourier Transform Infrared (FTIR)

The paper cups supplied by Solocup were subjected to FTIR analysis for quality control purposes.

Samples were placed under the golden gate accessory on the FTIR equipment explained in Chapter

4.

Table 5-6: Material Identification by FTIR analysis of paper cups


Coating on Solocup PE low density

Solocup Paper Cellophane


84

Figure 5-13: Paper cup with a thin LDPE coating

The coating on the paper cups shown in Figure 5-13 was identified as low density polyethylene. This

seals and protects the fibrous paperboard against the contents of the cup. The coating amounts to

only 5 wt.% of the total weight of the cup but its purpose is essential. The coating was shown to be

low density PE, providing protection to the fibrous paperboard which was identified as cellophane

(Table 5-6).

ii) Thermogravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC) of Composite Fillers

TGA/DSC analysis helped show how the fibrous cup would behave in the extruder under the high

temperatures that the fibres would be exposed to.

Knowing the thermal properties of fibrous materials is essential when processing WPCs. It is important

to know the onset of thermal degradation of the filler and composite material, as well as the release

of moisture and volatiles up to processing temperatures. It is understood that it is not just the thermal

properties of the filler that is important but other factors during processing such as residence time

and the shear can be major factors.

Tests were performed in air and nitrogen under constant ramp and isothermal conditions as noted in

Chapter 4.

Low density polyethylene (LDPE) film

100% Bleached virgin paperboard


85

The initial analysis studied the percentage weight change and heat flow (mW) through the filler

materials up to typical processing temperatures. This was to show how the filler responds

independently to the matrix polymer which enabled the filler to clearly define its own properties.

Figure 5-14 shows the data obtained from the experiment.

Figure 5-14: TGA curves for PE coated Beverage Cup (Solocup) in N2 atmosphere.

Any initial loss in mass is presumed to be the weight loss due to moisture. Between 100oC-225oC very

low levels in weight loss were observed, highlighting minimal or no volatiles given off at these

temperatures which is an excellent sign for processing these fillers with plastics to produce PPCs.

Thermal degradation was not shown until 240-260oC where a major loss in mass was observed. It is

reported that temperatures above 200oC can degrade fibrous material and cause composites with

lower densities and lower mechanical properties. Two decomposition steps are shown on TGA curves

for natural fibres. Hemicelluloses and the glycosidic links of cellulose are reported to degrade around

200oc. There is another peak around 360oc for alpha cellulose. Lignin usually degrades between 200-

350oC (Alvarez and Vázquez, 2004). Hemicellulose and lignin are removed in the paper making industry

due to the degradation of the paper produced which is why the DSC curve does not have many

features (Figure 5-15).

0 100 200 300 400 500

0

20

40

60

80

100

Wei

ght

Per

cent

(wt.

%)

Temperature (oC)

PPL Cup Coating

PPL Cups


86

5.5.2 Tetra Pak / Multilayer Carton Board (MCB)

Figure 5-15: TGA/DSC analysis of the Tetra Pak / MCB filler up to 500oC in N2 atmosphere.

The Tetra Pak filler (Figure 5-15) shows the same weight loss as the PPL cups in Figure 5-14 which is

assumed to be moisture loss up to and just over 100oC. This accounts for a couple of weight percent

shown in Figure 5-14 and Figure 5-15. Over the processing range in the extruder the Tetra Pak filler

material does not show weight loss. The coating is again not showing up on the heat flow curve due

to the small amounts of the coating present but it does show LDPE properties in the DSC test when

tested separately.

5.5.3 Mechanical Testing of PPLs

Tensile testing of PPLs was attempted using cardboard as inserts to help grip the material within the

jaws of the tensile testing equipment. The beverage cup and Tetra Pak fillers tended to fracture at

lower values than their true stiffness values. This could be due to several reasons including the

preparation method of trimming the filler material to the required shape by using a polymer tensile

piece as a template. The edges of the cut-out piece could have had many small cuts which may have

caused premature fracture in the bars. However results were obtained that compared with literature

values with the use of an extensometer and the results obtained are displayed in Table 5-7. The

expected values were obtained from CES EduPack and these values were deemed acceptable to use.

The data in the CES software shows Young’s Modulus values between 2-4 GPa for paper fibres.

0 100 200 300 400 500 600

0

20

40

60

80

100

Wei

ght

Per

cent

(%)

Temperature (oC)

Tetra_Change in Weight Percent (%)_10oC/min

-28

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0H

eatFlo

w (m

W)

Tetra_Heat Flow_10oC/min


87

Table 5-7: Tensile results from trimmed pieces of PPLs

Filler Tensile Strength

(MPa) (3.s.f) Standard Error

(3.s.f) Young's Modulus

(GPa) (3.s.f) Standard

Error (3.s.f)

PE coated Beverage cup 28.4 3.20 3.28 0.12

MCB/Tetra Pak 45.7 5.14 4.13 0.0913

5.6 Conclusions of PPL Characterisation

The laminated materials tended to show excellent properties over the processing range without

degrading. CES EduPack values were compared to the mechanical data found in this research for the

filler modulus values.

5.7 Coupling Agents for the Matrix and Filler Interface

5.7.1 Coupling Agents used in this Research

i) Maleic Anhydride (MAH) Grafted Polypropylene (MAPP) / Polyethylene (MAPE)

Honeywell are a leading provider of speciality materials from speciality films to luminescent materials

and additives (http://www.honeywell.com/sites/uk/specialty-materials.htm).

A selection of coupling agents supplied from Honeywell included:

950P: Propylene Maleic Anhydride Copolymer MAPP-AC 950P



575P: Ethylene Maleic Anhydride Copolymer MAPE-AC 575P

Table 5-8: Key properties of coupling agents supplied by Honeywell

Honeywell

Coupling Agent 907P 950P 1325P 575P

Saponification Number (SAP) mgKOH/g 87 50 18 35

Bound SAP 60 33 14 28

unbound SAP 27 17 4 7

Acid Number 44 9 19

Molecular Weight 8000-9000 18000 20000 6700

Drop point (oC) 153 153 153 106

The coupling agents in Table 5-8 exhibit a range of properties when compounded with polymers to

produce PPC. The 907P coupling agent has the highest percentage bound SAP which should obtain

http://www.honeywell.com/sites/uk/specialty-materials.htm


88

high mechanical properties compared to the others listed in Table 5-8. The Mw of 907P is rather low

which may limit properties.

Coupling agent: High Density Polyethylene (HDPE) Grafted to MAH (MAPE - AC 1687)

Recommended by Honeywell for HDPE based natural fibre composites.

Key properties of ACX 1687:

- SAP Number (mg KOH/g): 35

- Bound SAP (70%)

- Mw: 5000

- Viscosity (cps): 1.800

- Hardness (dmm): <0.5

- Drop point (oC): 115

Coupling Agent (MAPP) Epolene (E-43)

Epolene (E-43) is a maleated polypropylene wax (Eastman Chemical). It has a high hardness and

softening point compared to the other similar materials. E-43 is added as a coupling agent to improve

the tensile properties, stiffness and heat deflection temperature of moulded products. It is used

because of high polarity and anhydride functionality.

Table 5-9: Key properties of E-43 supplied by Eastman

EASTMAN

Coupling Agent E-43

Saponification Number (SAP) mgKOH/g 78

Bound SAP 44

unbound SAP 34

Acid Number 45

Molecular Weight (Mn) 7100

Drop point (oC) 157

Eastman have said that by Honeywell’s definitions the percentage bound SAP is 44. Lu et al., (2000)

claims that E-43 acts like more of a dispersing agent due to the low Mw. 907P has similar Mw values

but it has a higher percentage bound SAP number. Typical weight average molecular weight comes to

15800, with a polydispersity index (PDI) of 2.2.


89

Coupling Agent (MAPP) Polybond (PB3200)

PB3200 was supplied by Chemtura. Polybond 3200 is a polypropylene (homopolymer) grafted with

maleic anhydride. PB3200 is used to improve processing and mechanical properties.

Coupling Agent (MAPP) PRIEX 25097

This material is a random polypropylene copolymer that is grafted with a very high content of maleic

anhydride with a very low concentration of free maleic anhydride.

- % Grafted MA: 0.45

- ppm Free MAH: <50

- MFR190,2.16: 330

- Very low viscosity (hyperfluid grade).

PRIEX 25097 has been used as a compatibiliser for polymer blends and a coupling agent for glass fibre,

wood flour, and other natural fibres. The low viscosity enables excellent wetting.

ii) Non Maleic Anhydride based Coupling Agents

Non Maleic Anhydride Coupling Agent Struktol SA 1120

SA 1120 from Struktol was developed to aid difficult feeding systems. It has a dosage recommendation

of 1-3 wt.%. This product has been known to help against moisture and weathering as well as being

able to run and retain properties at high speed processing rates unlike MAH based couplers.

Non Maleic Anhydride Coupling Agent Polyethylenimine (PEI)

PEI Lupasol® PR8515 from BASF is a Low molecular weight ethylenimine copolymer. Clear to slightly

turbid, colourless to pale yellow, viscous liquid. Typical applications of Lupasol include promoting

adhesion of wood laminates, cement, and bricks. It enhances the effectiveness of wood preservatives,

and adheres to metal surfaces.

Non Maleic Anhydride Coupling Agent GENIOSIL GF 56 Triethoxy(vinyl)silane (PPVTES)

GENIOSIL® GF 56 from Wacker Chemie AG is an alkoxyvinylsilane, which is a clear and colourless liquid.

Typical uses of GENIOSIL GF 56 include the production of silane modified polymers that serve as

binders in paints and adhesives.


90

Non Maleic Anhydride Coupling Agent Bondyram

Bondyram 5108 was supplied by ADDCOMP. Bondyram 5108 is a maleic anhydride modified high

density polyethylene (MAPE), ideally used for coupling of PE and other fillers in PE composites.

Table 5-10: Key properties of Bondyram

Property ASTM Test Method Unit

Bondyram®

5108

MFI D-1238, 190° C/2.16kg g/10min 4.5

Density D-792 g/cm3 0.96

Melting point DSC °C 131

Maleic Anhydride level FTIR % >1%

Non Maleic Anhydride Coupling Agent PRIEX 12031

PRIEX 12031 from ADDCOMP is a low viscosity hyperfluid MA grafted PE. PRIEX 12031 has been used

for compatibilisation, coupling agents and to reduce pigment related warpage in polyolefins. The

maleic anhydride is said to introduce polarity to increase compatibility with polar materials.

- % Grafted MA: 0.40

- ppm Free MAH: <50

- MFR190,2.16: 25

5.8 Melt Flow Rate (MFR) Additives

Additive for Increasing the Melt Flow (Honeywell A-C 1089)

A polypropylene homopolymer

- Viscosity @ 190°C (373°F) Brookfield: 40 - 50 cps

- Hardness @ 25°C (77°F): <0.5 dmm

- Softening Point: 146°C (295°F)

- Density: 0.91g/cc

Additive for Increasing the Melt Flow (Honeywell A-C 820A)

A polyethylene homopolymer

- Hardness @ 25°C (77°F): 301-OR <1 dmm

- Viscosity @ 140°C (284°F) Brookfield: 400-OR 50 -150 cps

- Drop Point, Mettler: 401-OR 123 - 133°C (260 - 266°F)

Additive for Increasing the Melt Flow (SASOLWAX 5603)

A paraffin wax powder, Sasolwax 5603.


91

5.9 Material Selections and Initial Studies

Initial experiments conducted investigated a wide variety of recipes with varied filler concentrations

and coupling agents to assess the viability of using these waste materials for PPCs.

5.9.1 Selection of Filler Loadings

The size of the filler material was based on previous work completed by Nextek Ltd. Initial trials found

that 4x4 mm paper flakes were free flowing and still long enough to be an effective filler. It was found

that the filler loading percentage worked well between 30-50 wt.% and that a large pallet with 30

wt.% release liner flakes could be successfully moulded. Paper flakes from disposable cups presented

more of an everyday challenge to a growing waste problem. Trials for the release liner can be seen in

section 10.1.

The recipes shown in Table 10-4 were chosen as it is important to investigate a range of properties if

a final recipe is to be optimal. The aim of the recipes in Table 10-4 was to understand the bonding

mechanisms and the novel composite structure of the different waste streams.

Previous work completed by Nextek was a key driver to the study and understanding of how waste

plastic composites can be bonded for use in commercial products. Therefore a range of coupling

agents were considered as well as different waste streams. Previous work by Nextek demonstrated

that fibrous materials can be successfully moulded and that a PPL waste stream can be seen as a useful

raw material, which can be moulded in low energy processes. This work focuses on a wide range of

waste materials and coupling agents to try and optimise PPCs. A lower amount of filler by weight was

initially introduced with the aim to increase this as the process was optimised but 30 wt.% still equates

to a substantial amount of waste material. A variety of coupling agents, fillers and matrix materials

were trialled to assess what would work in PPCs. Initial trials took place at Bangor University and

London Metropolitan University shown in section 10 in the appendix. Key conclusions from these trials

allowed further optimisation for this research.

5.9.2 Summary and Conclusions of Initial Studies with PPCs

A variety of experiments and subsequent analysis were completed on PPCs. A key conclusion

learnt from the initial study was the loading volume of filler. A 40 wt.% addition of PPL was

sufficient in terms of extruding and moulding. On the equipment in this project, greater than 40

wt.% PPL flake content would be hard to process. An important finding from the initial studies

was the MAPP 907P coupling agent from Honeywell. This consistently performed very well

throughout mechanical testing.


92

Figure 5-16: Stress strain curves comparing the matrix (MRF PP), the addition of a filler (40 wt.% PPL

cup) and the addition of a filler and coupling agent (2 wt.% 907P MAPP).

Figure 5-16 shows the effects of the filler and the coupling agent compared to the matrix alone. The

initial addition of a filler has a slight reinforcing affect but the toughness of the material is dramatically

reduced with the composite becoming less ductile. The addition of a coupling agent shows a huge

increase in tensile strength indicating bonding at the interface resulting in an improved toughness.

The filler has clearly showed that it is sufficient in acting as reinforcing filler when the fibre matrix

interface is modified by adding a coupling agent.

The research has shown that PPC can be successfully manufactured from waste materials and obtain

competitive properties able to compete in a commercial environment. Further optimisation to the

exact percentages of coupling agents and filler volumes is needed but initial research has shown that

PPC could perform in a variety of applications based on the results obtained.

Initial results indicated that the MRF PE/PP regrind and WEEE PP exhibited similar properties when

used with fillers. The PE coated beverage cup waste produced higher mechanical properties across all

of the tests compared to the multilayer carton board and paper mill waste. This must be due to the

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

MRF/40wt.% PPL Cup_2wt.% 907P

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

MRF

MRF_40wt.% PPL Cup


93

complex mix of materials involved in the Tetra Pak / MCB and paper mill waste. The aluminium does

not bond with anything and therefore may be seen as points of weakness. The coupling agents bond

with the fibres along with the PE layer, which is why the disposable cup waste shows higher properties.

This is because each flake of PPL disposable cup waste has a PE layer and paper fibres which can both

react with the coupling agent. Each flake of PPL disposable cup in theory creates a bond because the

PE coating and fibre are laminated meaning that the PE coating can react and entangle with the matrix

while the fibres can form covalent bonds with the MAH with every piece of flake. The MCB recipes still

produced similar results to the disposable cups and further analysis should take place on this waste

stream.

The higher filler content the less ductile the sample but a slight increase in mechanical properties is

shown. This may be due to the PE coating co-crystallising with the matrix polymers. Depending on the

product properties required, 30 wt.% filler should be used for more elongated properties compared

to the 40wt.% filler sample which can offer higher strength and stiffness properties.

The better performing recipes used disposable cups and the coupling agent known as 907P. The best

recipe based on mechanical performance was with the tensile strength at 29MPa compared to 18MPa

without coupling. A flexural strength of 50MPa compared to 36MPa without coupling was observed.

This mix seems to have enough coupling agent to create a sufficient bond with the matrix and exceeds

the requirement for pallet design with flexural strength values greater than 22 MPa.

The MRF material showed an inconsistent feed from the MRF source and the WEEE PP is a fast growing

industry for recycled material. The research also highlighted a few toughness issues for the MRF PP

sample being less ductile compared to the WEEE PP even before any filler was added.

Based on mechanical results the 907P and 950P coupling agent achieved the better properties (Figure

5-17). The higher SAP number in 907P must provide the extra coupling points. 950P has a lower SAP

but a higher Mw for co-crystallisation.

The SEM images show that some samples still show fibre pull-out. This means that further

optimisation should be considered to try and achieve superior PPCs.


94

MRF

30wt.%PPLcup --

30wt.%PPLcup/2wt.%907P

30wt% PPLcup/2wt.% E-43

30wt% PPLcup/2wt.% PB3200

30wt% PPLcup/2wt.% 1325P



0

5

10

15

20

25

3056% increase (coupling)

13% increase

(coupling)

Ultimate Tensile Strength (UTS) (MPa) of PPCs

Ult

imat

e T

ensi

le S

tren

gth

(M

Pa)

Recipe

Figure 5-17: Highlights the effect of different coupling agents on the tensile strength of PPCs. The

addition of coupling agents greatly enhances the tensile strength.


95

Figure 5-18: 68 wt.% MRF PP / 30 wt.% disposable cup / 2 wt.% 907p MAPP after a tensile test showing

fibre break.

Figure 5-19: 60 wt.% MRF PP / 40 wt.% disposable cup tensile fracture showing a PE coated paper

flake embedded within the matrix.


96

Figure 5-20: 60 wt.% MRF PP / 40 wt.% disposable cup flexural test showing broken embedded paper

flakes with a hole around part of the flake

The results show that the materials with a higher percentage of filler show higher mechanical

properties due to the bond successfully taking some of the load. To achieve reinforcing effects,

particular conditions must be met. The filler material usually must have a sufficient fibre length to

diameter ratio. A critical fibre length must also be reached otherwise the fillers would be points of

weakness. The strength of the fibres must be greater than the matrix material and adequate bonding

between the two phases should occur. Failure can often occur when the tensile forces stretch the

matrix more than the filler. This causes shearing at the interface. For fibre pull-out the tensile forces

near the fibre ends exceed the matrix tolerance which causes fibre pull-out, an indication of weak

bonding. The fracture surfaces show that some fibres pull-out and some break indicating further

reinforcement can be made in the PPCs in this research. What is desired in PPCs is the fibre breaking

during failure showing a sufficient bond. This occurs if tensile forces exceed the tolerances of the fibres

(Gunter, 2006).

5.9.3 Further Optimisation Recipes and Processing Steps: Selection of Filler Loadings

Having seen how PPCs behave, further work was continued in the further optimisation section. It was

clear from initial research that if WPCs and PPCs are to be successful a reliable strong bond between

the filler and matrix is required and therefore further research into how coupling agents perform is

necessary. It was also concluded that further work should be carried out on WEEE PP and HDPE due

to the strength and toughness properties and consistent feedstock available. The MRF proved

Hole showing flake not

sufficiently bonded to the matrix


97

inconsistent with the supply due to the real mix of polyolefin flake. The paper cup proved to show very

promising results after the first trial along with the Tetra Pak material.

The recipes shown in Table 10-4 were chosen to compare coupling agents proven in the WPC industry

which should also be sufficient to trial on PPCs. The aim of Table 5-11 is to further develop the research

behind PPCs and try to look at the bonding mechanisms more closely. The key to the optimisation trial

was to optimise the filler content and the amount of coupling agent needed for optimum properties.

5.9.4 PPC Mixes for Optimisation Trials

Through further research and networking new materials were considered for PPC use. New PE based

coupling agents were trialled. Through the WPC 2011 conference a couple of new coupling agents

were investigated which included the PRIEX range and Struktol coupling agents.

Table 5-11: Trial 2 a) and b). A variety of PPCs with varying volume fractions of PPL cups, percentages

of coupling agents and different matrix polymers.

Trial 2: (a)

Recipes Matrix Filler Coupling Agent (CA)

Polymer Wt.% PPL Wt. % CA Wt.%

1 WEEEPP 90 Paper Cup 10




5 WEEEPP 88 Paper Cup 10 907P 2






11 WEEEPP 88 Paper Cup 10 PRIEX 2







98

17 WEEEPP 88.5 Paper Cup 10 PEI 1.5



20 WEEEPP 100

Trial 2: (b)

Recipes Matrix Filler Coupling Agent

Polymer Wt.% PPL Wt.% CA Wt.%

1 WEEE PP 58 Paper Cup 40 907P 2



4 WEEE PP 68 Paper Cup 30 Bondyram 2

5 WEEE PP 67 Paper Cup 30 Bondyram 3

6 WEEE PP 68 Paper Cup 30 Struktol 2

7 WEEE PP 67 Paper Cup 30 Struktol 3

8 WEEE PP 87.5 Paper Cup 10 VTES 2.5



11 HDPE 70 Paper Cup 30

11A HDPE 90 Paper Cup 10

11B HDPE 80 Paper Cup 20

12 HDPE 68 Paper Cup 30 AC 1687 2

13 HDPE 67 Paper Cup 30 AC 1687 3

14 HDPE 68 Paper Cup 30 PRIEX 12031 2

15 HDPE 67 Paper Cup 30 PRIEX 12031 3

16 WEEE PP 80 TETRA 20

16A WEEE PP 90 TETRA 10



18A WEEE PP 88 TETRA 10 907P 2

19 WEEE PP 78 TETRA 20 907P 2




99




25 HDPE 67 TETRA 30 AC 1687 3

25A HDPE 77 TETRA 30 AC 1687 2

26 HDPE 67 TETRA 30 PRIEX 12031 3

26A HDPE 77 TETRA 30 PRIEX 12031 2

26B HDPE 88 TETRA 10 AC 1687 2

26C HDPE 78 TETRA 20 AC 1687 2

26D HDPE 90 TETRA 10

26E HDPE 80 TETRA 20

26F HDPE 70 TETRA 30


28 WEEE PP 90 Paper Cup 10

29 MRF 100

30 MRF 67 Paper Cup 30 AC 1687 3

31 WEEE PP 70 Paper Cup 30

HDPE 100

WEEE PP 100

Recipes 1-19 in trial 2 (a) and recipes 1-10 in trial 2 (b) looked at PPCs with different percentages of

filler (paper cup) and three different types of coupling agents at different percentages to analyse how

they affect the composite properties at different filler weights. Recipes 11-15 in trial 2 (b) focused on

HDPE as a matrix material with coupling agents to suit. Recipes 16-24 investigates further the use of

Tetra Pak as filler with Honeywell 907P as a coupling agent and WEEE PP as a matrix for comparison

reasons. Recipes 25-26F focused on recipes with HDPE as the matrix and Tetra Pak (MCB) as the filler

with the same coupling agents as recipes 11-15 so a direct comparison of the filler can be made. Recipe

27 looked at the possibility of how PPC would reprocess. This particular recipe was

recycled/reprocessed three times. Recipe 28 focused on possibly using different shape fillers with

longer fibres. Recipe 29 and 30 remoulded MRF polymers and investigated a different coupling agent

with the MRF polymer. A discussion of which is in the appendix section 10.2.5.


100

5.9.5 Final Conclusions of the Initial Studies

- Recipe 13.5 which consisted of 40 wt.% paper cup with the MRF PP as the matrix, as well as 2

wt.% 907P coupling agent, showed the highest mechanical properties. This is due to the

fibrous flakes imparting rigidity as well as the coupling agent bonding the interface allowing

stress transfer from the matrix to the fibres.

- Comparing the results to Table 3-3 shows the mechanical results obtained can compete with

WPC properties. The recycled polymers are also comparable to virgin polymers therefore

saving energy through recycling.

- The WEEE PP at 30 wt.% had better properties in terms of just adding the filler and the

addition of coupling agents improved at very similar rates to the MRF PP matrix samples. The

WEEE PP showed a higher toughness which would be better considering pallet design.

- WEEE PP has a consistent improving supply chain without the mix of PE and is in more of a

need for end of life disposal options. The WEEE PP has huge increasing quantities and

problems associated with the industry that a recycling source would be more beneficial than

the MRF PP.

- MRF PP showed an inconsistent feed material and the toughness under the stress strain graph

could be improved. Section 10 in the appendix explains the issues found with MRF PE trial.

- The 907P coupling agent has a relatively low Mw compared to other coupling agents but has

a high percentage bound SAP. Based on the mechanical results this bound SAP number has a

high influence on the filler matrix interface.

The 907P MAPP coupling agent, PPLs and the WEEE PP and HDPE are further optimised in Chapter 6.

New targeted coupling agents were also trialled with an aim to improve PPC properties.

Further Optimisation Studies: Results and Discussion Chapter 6

101

Chapter 6

6. Further Optimisation Studies: Results and Discussion

6.1 Introduction

Chapter 5 demonstrated that PPCs are an important research area. Useful resources that are destined

for landfill can be extruded and moulded into useful new materials.

This chapter describes further optimisation studies of PPCs. The optimum loadings of filler and

coupling agents are determined along with other key mechanical properties. New materials that can

contribute to further optimising PPCs were also studied. The coupling agent that bonds the fibrous

filler and the PP most successfully was Honeywell 907P. Therefore further analysis is shown within this

chapter along with an investigation into further potential coupling agents identified later in the

research.

6.2 Further Optimization of PPCs using PE Coated Beverage Cups

6.2.1 Mechanical Properties of WEEE PP and PE Coated Beverage Cups

A clear opportunity seen from the initial trials in chapter 5 was that paper cups can be used with

polymers to create PPCs. The effects of adding paper cups to WEEE PP, was seen to be most promising

for PPCs from the plastic material examined.


102

i) Tensile Testing of PPCs

Figure 6-1: Ultimate tensile strength (UTS) and Young’s modulus against increasing volume fractions

of PPL cups in WEEE PP.

Different levels of PPLs were added to the PP matrix. Figure 6-1 shows the tensile strength values from

10 wt.% to 40 wt.% PPL filler compared to the WEEE PP matrix alone. The tensile strength at 10 wt.%

PPL addition decreased. This is thought to be due to the paper flakes acting as points of weakness and

therefore stress concentrators at the fibre/matrix interface. At 20-40 wt.% PPL there was a very small

increase in tensile strength indicating that the load is not effectively being transferred to the fibres

proving an insufficient bond between the filler and matrix. As predicted the strain at failure is lower

with higher additions of paper cup flakes. The strain at yield for 40 wt.% PPL was 0.929% and for WEEE

PP 1.35%.

Figure 6-1 also highlights the stiffness values of the PPCs. As expected the Young’s modulus increases

due to the addition of the paper flakes with the more stiff fibres. The stiffness at lower strains

increases relative to the amount of PPL added. The 40 wt.% PPL sample increased by 1.3 GPa

compared to the WEEE PP matrix. Chapter 5 showed that the toughness is dramatically reduced when

the flakes are added to the polymer matrix. The PPL paper flakes cause structural changes to the

0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

Tensile Strength _WEEE PP/PPL cups

Linear Fit

Ten

sile

Str

eng

th (

MP

a)

Volume Fraction (Vf)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

Young's Modulus_ WEEE PP/PPL cups

Linear Fit

Yo

un

g's M

od

ulu

s (GP

a)


103

matrix by hindering the flow of the polymer chains when stress is applied, reducing ductile behaviour.

Increasing the volume fraction of flakes further restricts the polymer chains and reduces the strain at

failure.

ii) Elastic Modulus for Long Fibre Composites

The PPC data agrees with the rule of mixtures (ROM) model shown in Figure 6-2 based on equations

3-1 and 3-2. The Young’s modulus values of the PPCs are very close to the values predicted by the

Voigt model. The filler shown in Figure 10-3 has a flake like shape. The Voigt model assumes a long

fibre as described in section 3.7.2 which is surprising as the PPCs values lie close to the this model. As

previously discussed the fillers do further break down in the extruder and due to granulation, which

may alter the shape and reinforcing abilities within the composite.

0.0 0.1 0.2 0.3 0.4 0.5

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

Modulu

s (G

Pa)


Axial Modulus

Rule of Mixtures 1

Transverse Modulus

Rule of Mixtures 2

Halpin and Tsai

WEEE PP _PPL cups

Linear Fit

Figure 6-2: Comparing the Young’s modulus of PPCs with ROM and Halpin and Tsai models for the

elastic modulus of long fibre composites.

The Halpin and Tsai model (1967) further develops the Reuss model and takes into account the fibre

load bearing properties based on equal stress. The data closely follows the Voigt model data.


104

Therefore particulate models including Eshleby and the shear lag models were studied, shown in

Figure 6-3.

iii) Elastic Modulus for Particulate Composites

Figure 6-3: PPCs in agreement with a) Modified Shear Lag models and b) Eshleby models at higher

aspect ratios.

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

Modulu

s (G

Pa)


Shear Lag_aspect 1

Shear Lag_aspect 3

Shear Lag_aspect 10

WEEE PP_PPL

Linear Fit

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

Modulu

s (G

Pa)


Eshleby_ Aspect Ratio 1



WEEE PP_PPL

Linear Fit


105

It is evident from Figure 6-3 that the aspect ratio has a huge effect on the predicted values. The PPC

data as shown in Figure 6-3 agrees with the Eshleby and modified shear lag models at higher filler

aspect ratios. With an aspect ratio of greater than 3 PPC data agrees with the models.

The Einstein model (equation 3-5) agrees with data at very low volume fractions. However the data in

Figure 6-4 lies closely with the Einstein model up to 40 wt.% with and without coupling agent. Without

the coupling agent the data tends to fall just under the Einstein model and with 2 wt.% 907P the PPC

values lie just above the Einstein line moving towards the spherical particle model and the particle

strengthening factor model.

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2

3.6

4.0

4.4

4.8

5.2

5.6

6.0

PPC 0-40wt.% PPL Cups

PPC 0-40wt.% PPL Cups_2wt.% 907P

Young's

Modulu

s (G

Pa)


Einstein

Modified Einstein (Particle Interaction)

Spherical Particles

Particle Strengthening Factor

Figure 6-4: Comparing the Young’s modulus of PPCs against various models for the elastic modulus of

particulate composites with increasing volume fractions of PPL cups.

Guth (1945) attempted to incorporate the effect of neighbouring particles by adding a particle

interaction factor alongside the linear term shown in equation 3-6. At lower concentrations of filler

the modified Einstein model lies close to the PPC data with coupling agent but at higher additions of

filler the predicted values increase rapidly. Kerner (1956) used a model for spherical particles that lies

very close to the PPC data up to 20 wt.% filler. The particle strengthening factor added by Verbeek

(2003) which was a modified rule of mixtures (ROM) model lies above the PPC data. In summary the


106

best fit line is the simple Einstein model that assumes perfect adhesion between the filler and matrix

and perfect dispersion of filler. The filler is well dispersed in the co-rotating twin screw extruder. The

particle interaction may need more modifying as the incompatibility may be greater than a coupling

agent can modify. Further modification may be needed to improve the results which may fit the

modified Einstein model.

The values used in the models above are from the experiments in this research. These are calculated

values for the matrix and the maximum modulus for the fibre, taken from CES EduPack which is close

to the values obtained in this research.

Adding a coupling agent to PPCs is essential to improve the mechanical properties. The initial trials

showed the improvement in properties of PPCs by adding a coupling agent. Section 6.3 optimises this

further.

6.3 Mechanical Properties of WEEE PP and PE Coated Beverage Cups with Optimised Coupling

Agents

i) Tensile Testing of PPCs: Optimising Filler and Coupling Agent

Honeywell 907P was added as a coupling agent at 2 wt.%. Literature showed that 2 wt.% should be

sufficient for a coupling agent. It was decided that all recipes would be analysed at 2 wt.% coupling

agent. The 907P coupling agent was the most successful in the initial trials. Further optimisation was

therefore needed. Figure 6-5 shows the effect of 907P in PPCs at varying levels of filler and coupling

agent.


107

Figure 6-5: Variation in mechanical properties for composite containing increasing additions of PPL

flakes with and without 2 wt.% MAPP coupling agent a) tensile strength b) Young’s modulus.

-0.1 0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

30

35

WEEE PP_PPL cups

Linear Fit

Ten

sile

Str

ength

(M

Pa)


WEEE PP_PPL cups_2wt.% 907P

Linear Fit

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

WEEE PP_PPL cups

Linear Fit

Young's

Modulu

s (G

Pa)


WEEE PP_PPL cups_2wt.% 907P

Linear Fit


108

Figure 6-5 shows Honeywell 907P MAPP at 2 wt.% between 10-40 wt.%, shown as a volume fraction.

Just 2 wt.% of 907P increases the tensile strength at all levels as well as the Young’s modulus. Table 6-

1 shows that with the addition of 2 wt.% MAPP, the strain at yield of the 40 wt.% PPL recipe increased

to 1.08%.

Table 6-1: Tensile testing data for PPCs with increasing volume fractions and the effect of the 907P

coupling agent

Materials

Volume Fraction

(Vf)

Ultimate Tensile

Strength (UTS) (MPa)

Young’s Modulus

(GPa) Yield Stress

(MPa) Yield Strain

(%)

WEEE PP 0 20.7 1.05 11.9 1.35

90% PP/10% PPL 0.117 18.8 1.31 12.9 1.11

80% PP/20% PPL 0.230 20.1 1.70 14.3 0.996

70% PP/30% PPL 0.338 20.6 1.86 14.9 0.981

60% PP/40% PPL 0.443 20.7 2.28 15.9 0.929

90% PP/10% PPL/2% 907P 0.119 22.3 1.48 14.5 1.16

80% PP/20% PPL/2% 907P 0.234 24.3 1.73 15.6 1.10

70% PP/30% PPL/2% 907P 0.344 26.7 2.04 18.0 1.07

60% PP/40% PPL/2% 907P 0.451 30.0 2.43 21.5 1.08

At 2 wt.% 907P the increase in tensile strength increases at a steady rate with increasing volume

fractions (Table 6-1). Therefore the amount of coupling agent at the highest strengths which happen

to be at higher volume fractions of fibres, should be considered for further analysis on improving the

mechanical properties.

Figures 6-6 and 6-7 show that the coupling agents have a positive effect on PPCs. Understanding

exactly what is happening requires a discussion on the effect of the filler, matrix and interface.

The PP matrix and the PPCs experience different failure mechanisms. The polypropylene exhibits

cyrstallization effects and orientation. Orientation of the polymer can be seen at the yield stress

through deformation. The orientation of the polymer becomes stronger than the surrounding matrix

which is known as strain hardening (Brydson, 1999).

The filler cannot deform like the polypropylene and therefore affects the failure of the surrounding

matrix. PPC experiences a debonding mechanism due to the inextensible filler. The coupling agents


109

can therefore halt this debonding mechanism. Without a coupling agent the PPL flakes debond at low

strains due to the weak interfacial adhesion between the matrix and filler.

Maleated coupling agents were used to bond maleic anhydride to the hydroxyl groups of

lignocellulosic fibres in the PPL flakes by covalent ester bonds. The grafted PP of the coupling agent

interlocks and co-crystallises with the PP matrix, creating a stronger bond between the PPL flakes and

PP matrix. Similar bonding mechanisms have been described (Kim at al., 2007; de la Orden et al., 2010;

Franco-Marquès et al., 2011; Mutjé et al., 2006; Méndez et al., 2007).



Interfacial adhesion significantly increases with use of coupling agents. The stress required before

crack propagation is considerably increased with a stronger interface, transferring stress to the fibres.

Experiments have shown that 3 wt.% addition of coupling agent is optimal at 40 wt.% PPL cups, using

907P coupling agent. The 40 wt.% PPCs show that the tensile strength and the Young’s modulus both

increase with additions of up to 3 wt.% of the 907P coupling agent (MAPP) and then start to decrease.

At 30 wt.% PPL cups the tensile strength and coupling agents both gradually increase with the addition

of up to 4 wt.% MAPP 907P.

0 1 2 3 4

0

5

10

15

20

25

30

35

40

Tensile Strength WEEE PP_40wt.% PPL cups_0-4wt.% 907P

Polynomial Fit

Ten

sile

Str

ength

(M

Pa)

MAPP (wt.%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Young's Modulus WEEE PP_40wt.% PPL cups_0-4wt.% 907P

Polynomial Fit Young's

Modulu

s (G

Pa)


110



Figures 6-6 and 6-7 underline the importance of the amount of coupling agent used in fibrous

composites. Too much of the coupling agent can have negative effects and too little may limit strength

and toughness. Up to 4 wt.% has been shown to increase the tensile strength whereas 5 wt.% and

above reduces properties due to the self-entanglement of the coupling agents causing slippage (Beg

and Pickering, 2008).

0 1 2 3 4

0

10

20

30

40

Tensile Strength WEEE PP/30wt.% PPL cups_0-4wt.%907P

Polynomial Fit

Ten

sile

Str

ength

(M

Pa)

MAPP (wt.%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Young's Modulus WEEE PP/30wt.% PPL cups_0-4wt.%907P

Polynomial Fit

Young's M

odulu

s (GP

a)


111

Figure 6-8: a) 10 wt.% PPL b) 30 wt.% PPL: PP and paper cup extruded out of the die exhibiting melt

fracture.


112

The effect on the extrudate is clearly seen with the addition of 10 wt.% to 30 wt.% of PPL. The coupling

agents did alter the surface finish and helped the melt flow through the extruder. This is shown in

Figure 6-9 with melt fracture being less severe.

Figure 6-9: PPC extrudate with 30 wt.% PPL and 2 wt.% Struktol.

The coupling agent has controlled the amount of PPL filler that is breaking out of the melt from the

die known as melt fracture or shark skinning. The addition of 2 wt.% coupling agent has significantly

reduced this phenomena.

The coupling agents used in the optimisation study vary and the coupling agents are shown in Chapter

5. Figure 6-10 summarises the tensile strength and Young’s modulus values at 30 wt.% PPL cup filler

with different coupling agents for PP/PPL blends.


113

Figure 6-10: Ultimate tensile strength (UTS) and Young’s modulus against PPCs with various coupling

agents at 2 wt.% in 30 wt.% PPL cups in a WEEE PP matrix.

It is necessary to trial a variety of coupling agents to compare how the interface between the fibrous

filler and polymer matrix is affected. It is important to know which coupling agents are worth further

optimisation. A variety of coupling agents were chosen to see if the interface was influenced in

different ways and to create comparisons for PPCs.

There are many MAPP coupling agents and the initial trials showed key types. Through conferences

and further literature, more coupling agents became apparent. This section discusses the tensile

properties and compares other coupling agents used in this research.

The PRIEX MAPP coupling agent has a high SAP number and Mw with a low concentration of unreacted

MAH, suggesting it is similar to the 907P MAPP coupling agent although the 907P coupling agent has

a lower Mw yet still performs very well. The tensile results shown in Figure 6-10 show that PRIEX 25097

exhibits lower strength but a higher Young’s modulus compared to 907P.

PRIEX 25097 has shown very similar tensile properties to the 907P recipes up to 30 wt.%. ADDCOMP

additives who supplied PRIEX 25097 have reported excellent properties with this coupling agent. The

coupling agent is reported to have very low levels of free MAH meaning that the MAH has mostly been

PPL PRIEX 25097 907P STRUKTOL VTES PEI

0

5

10

15

20

25

30

35

Tensile Strength WEEE PP / 30wt.% PPL / 2 wt.% Coupling agentsTen

sile

Str

ength

(M

Pa)

Recipes

0

1

2

3

4

5

Young's Modulus WEEE PP / 30wt.% PPL / 2 wt.% Coupling agents

Young's M

odulu

s (GP

a)


114

grafted to the polymer. It is ideally suited to random PP co-polymers like the WEEE PP. Both coupling

agents in Figure 6-10 have similar properties and both were further tested to try and optimise the

amount of coupling agent that should be used to obtain the optimum properties. The results indicate

similar properties between the two, with 907P marginally better than the PRIEX 25097 at

concentrations suitable for use in industry.

Polyethylenimine (PEI) and vinyltriethoxysilane (PPTVES) are coupling agents that enhance the bond

and increase the properties of WPC. These coupling agents were trialled to have a comparison against

conventional MAPP based products. They were in liquid form making the comparison to pellets

somewhat misleading. The results were not as high indicating the problem could be the different

preparation methods and therefore the wetting of the fibres.

The effect of fibre loading, coupling agent type and concentration to obtain the best mechanical

strength and also a low water absorption level was investigated. The vinylsilane produced higher

functionalization than MAH. They both had the same molar concentration as the number of molecules

of MAH and VTES were the same with respect to the polymer mass. VTES produced a higher

concentration of functional groups, even though it is bulky and attached to the polymer chains

(Nachtigall et al., 2007). Therefore PPVTES was a favourable coupling agent to trial within PPCs. The

stiffness values of PEI and VTES seem similar to all the other coupling agents, shown in Figure 6-12.

The tensile strength values of PEI and VTES were lower, due to the liquid form they were mixed in

whereas the other coupling agents were in pellet form and were blended in an extruder. As explained

in Chapter 4, the PEI and VTES were premixed with the filler. The tensile strength results reported in

the literature are similar to the results obtained in this research. Clearly some bonding has taken place

but not as much as with other coupling agents. The coupling agents used in the literature were not

the same as the coupling agents (MAPP) used in this research.

Nachtigall et al., (2007) used PPVTES because VTES is less polar than MAH and therefore it can combine

more effectively with the polypropylene matrix. The more functional groups the better, because the

more efficient it will be as a coupling agent. With the addition of coupling agents the tensile strength

was increased to 28 MPa, due mainly to the hydroxyl groups on the surface of the wood fibres that

interact with the coupling agent while the non-polar part of the coupling agents reacts with the matrix.

At higher filler content the MAPP improved the tensile strength while the PP-VTES severely decreases

tensile strength.

Polyethylenimine (PEI) has been considered as a coupling agent (de la Orden et al., 2007). This is a

highly branched polymer with primary, secondary and tertiary amine groups. The study showed that


115

PEI increases the amount of energy required to break the composites. The presence of 1.5 wt.% in

composites with 40 wt.% of cellulose allows a relative increase higher than 78% in the energy required

to break the material in a tensile test.

Figure 6-11: Extruded PPCs at 30 wt.% PPL cup with (right bar) and without (left bar) PPVTES coupling

agent.

Figure 6-11 shows the effect of the VTES coupling agent. A reaction has taken place that alters the

colour of the filler material. The extruded bar on the left is a standard PP/PPL composite without

coupling agent.

The tensile strength properties of the Struktol recipes are clearly very interesting. The particular grade

of Struktol used in this research is becoming well known in the WPC industry. It is protected through

patents and is based on silane chemistry. The results in Figure 6-12 are based on 2 wt.% coupling

agent. Coutinho et al., (1997) showed that 4 wt.% silane addition was optimal compared to 2 wt.%

MAPP. The Struktol product competes with this and shows excellent properties at 2 wt.%. At 3 wt.%

the Struktol properties are significantly better than any other sample analysed, with a tensile strength

of 33 MPa and a Young’s modulus of 2.26 GPa. The silane coupling agent works in a similar manner to

the MAPP based coupling agents. The silane molecule should exhibit bifunctional groups on Si that

can react with the filler and matrix. The molecule consists of hydrolysable alkoxy groups and an

organic-functional group as well as an alkyl bridge joining the Si to the organofunctionality. Amino and

vinyl based silanes are typically used in natural fibre polymer composites (Xje et. al, 2010). This


116

particular material (Struktol SA1120) should be ideally used between 1-3 wt.% and is often used for

helping materials through difficult feeding systems. Figure 6-9 shows further benefits of the Struktol

compatibiliser.

ii) Toughness of PPCs: Optimising Filler and Coupling Agent

The toughness as given by the area under the stress strain curve in Figure 6-12 is significantly different

to the PP due to the less ductile failure caused by the de-bonding of the PPL/PP interface.

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

0

5

10

15

20

25

30

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

WEEE PP

WEEE PP 30wt.% PPL cups

WEEE PP 30wt.% PPL cups_4wt.%_907P

Figure 6-12: A comparison of the engineering stress vs. engineering strain curves for polypropylene,

and composites containing 30 wt.% disposable cup with and without 4 wt.% coupling agent. The WEEE

PP is only shown to a strain value of 0.2 to show the effect of the PPL and coupling agent more clearly.

The stress-strain curves obtained for the different types of composite samples tested in this work are

shown in Figure 6-12. The unreinforced polypropylene exhibits high toughness but requires relatively

low stress to induce permanent strain. The composite containing PPL flake is not significantly stronger,

the modulus is similar and the PPC shows reduced toughness. However, the samples containing PPL

flakes and the optimised addition of coupling agent show increased strength, typically by ~50%, and

significantly increased elastic modulus. The toughness of the modified PPC is considerably increased

compared to the PPL addition without coupling agent. The strain to failure increases with a significant


117

improvement in toughness compared to the unmodified PPC with toughness values approximately 5

times higher.

In Figure 6-12 the Young’s modulus without coupling agent is close to the Young’s modulus with

coupling agent. The strength is significantly improved by the coupling agent, which makes sense as

initially the bond across the interface will be strong enough even without coupling agent but as the

stress increases the lack of coupling agent means detachment occurs sooner.

Strain Energy

Area under the Stress Strain Curve

The toughness of the PPCs can be seen by calculating the area under the stress strain curve. Toughness

can also be measured by the Charpy impact energy. However the strain rates are not comparable. The

Charpy impact energy is measured under a high strain rate and looks at PPCs at one end of the strain

rate scale compared to the tensile tests measuring under relatively low strain rates.

The Energy stored can be as important as any stress or deformation the product/component may be

under. Strain energy (U) can be defined as the stored energy due to deformation. The strain energy

per unit volume is the strain energy density (U0), which is the area under the stress strain curve up to

the point of deformation with V indicating the volume of the component.

U = ∫V U0 dV

Requirements for the toughness vary depending on the product/part in question. Some

materials/products require the toughness up to the yield point, e.g. a spring. Beyond this then the

material no longer behaves elastically and does not obey Hooke’s law.

The area under the stress strain curve up to the yield point is called the modulus of resilience. This

energy is not lost and can be recovered. The material returns to its original shape if relieved of the

stress applied. It is the recoverable elastic energy per unit volume that can be stored in a material. The

area under the stress strain graph up to fracture is known as the modulus of toughness, measuring

the energy per unit volume that can be absorbed without rupture.


118

Figure 6-13: The modulus of resilience and modulus of toughness for WEEE PP.

The stress strain curve in Figure 6-13 has been split into areas to aid in a more accurate determination

of the toughness under the curve.

Area A calculates the modulus of resilience:

Yield Strength = 11.9 MPa

Strain at yield = 0.025243

The area under the curve up to the yield point:

11.9 × 0.025243

2

Therefore area under curve at A = 0.300 kJ/m3 (3.s.f)

Area under B using UTS:

(20.79658 + 11.9) × 0.072207

2

Area under curve at B = 1.18 kJ/m3 (3.s.f)

Area C:

(15.9979 + 20.79658) × 0.40256

2

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0

5

10

15

20

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

WEEE PP_10mm/min

C D E F G

B

A

H


119

Area under curve at C = 7.41 kJ/m3 (3.s.f)

Area D:

(15.98623 + 15.9979) × 0.50002

2

Area under curve at D = 8.00 kJ/m3 (3.s.f)

Area E:

(15.0326 + 15.98623) × 0.999983

2

Area under curve at E = 16.0 kJ/m3 (3.s.f)

Area F:

(15.98775 + 15.9236) × 1.000012

2

Area under curve at F = 16.0 kJ/m3 (3.s.f)

Area G:

(16.70958 + 15.98775) × 0.999988

2

Area under curve at G = 16.3 kJ/m3 (3.s.f)

Area H:

(17.80285 + 16.70958) × 0.93225

2

Area under curve at H = 16.1 kJ/m3 (3.s.f)

Total Area under the Curve:

The modulus of toughness: A + B + C + D + E + F + G + H

Toughness under stress strain curve = 81.3 kJ/m3 (3.s.f)

The toughness of WEEE PP can then be compared to the toughness of the PPCs with the addition of

the PPLs. Figure 6-14 shows the toughness at 10 wt.%.


120

Figure 6-14: The modulus of resilience and modulus of toughness for WEEE PP/10 wt.% PPL cup.

The toughness by adding 10 wt.% PPL equates to 1.11 kJ/m3 (3.s.f). Table 6-2 highlights how the area

under the stress strain curve changes with the volume fraction of PPL and the addition of coupling

agents. As expected, adding the paper fibres dramatically reduces the toughness compared to the

matrix PP. However as seen previously in Chapter 6, the strength of the composite can be increased

significantly. Gradually with more flakes added the toughness reduces to 0.68 kJ/m3 for 40 wt.% PPL.

With the addition of coupling agents the toughness of PPCs under the stress strain curve increased.

This indicates that at the interface the coupling agent is creating a bond that can transfer the load

effectively to the filler and can withstand this loading at the interface. The results suggest that the

907P coupling agent is bonding with the paper and the polymer matrix. This bond strengthens the

interface meaning more energy can be absorbed by the material due to the interfacial bond.

Table 6-2 shows the toughness slightly increased by the addition of a coupling agent. Despite the small

increase, at all levels of filler content the 907P coupling agent increases the toughness due to the

bonding mechanism. This can be further modified to increase the toughness if the final product

required a material with more ductility. Additional toughening resins would then be considered.

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07

0

5

10

15

20

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

90wt.%_WEEEPP/10% PPL_10mm/min

A B C D E F G


121

Table 6-2: Modulus of toughness for PPC blends with 2 wt.% 907P and increasing volume fractions of

PPL cup.

Recipe Modulus of toughness (kJ/m3)

(3.s.f)

WEEE PP 81.3

10% PPL 1.11

20% PPL 1.22

30% PPL 1.05

40% PPL 0.68

10% PPL 907P 1.52

20% PPL 907P 1.43

30% PPL 907P 1.4

40% PPL 907P 1.02

The addition of PPLs make the material stronger but the toughness is reduced significantly as shown

in Figure 6-12.

iii) The Charpy Impact Energy (KJ/m2) of PPCs: Optimising Filler and Coupling Agent

The Charpy v-notch experiment is designed to measure the amount of energy absorbed by a specimen

at a high strain rate (Jang et al., 2008). The observed Charpy impact energy exhibited brittle failure for

all the composite materials. By being a high strain rate test, this indicates how the composites would

behave under sudden impact. It is observed that the properties of the composites in relation to a

sudden impact rely heavily on the matrix material. The paper flake volume and coupling agents do not

have an effect on the Charpy impact energy values. The majority of the composite is made up of the

matrix constituent and the role of the matrix is to protect the reinforcement.


122

Figure 6-15: Notched Charpy impact strength of PPCs with increasing volume fractions of PPL cups

between 0-40 wt.%.

At high strain rates the interfacial strength between the fibre and the polymer does not affect the

properties because of the sudden impact. The high sudden stress is too high for the stress transfer

mechanism. The fibrous flake cannot withstand the load and fracture occurs. By testing at higher strain

rates, an idea of the lower limits of the PPCs in terms of impact properties are shown as well as the

ability to withstand sudden impact at a high loading. The matrix determines the impact strength.

Under high strain rate it is clear that the fillers act as stress concentrators and points of weakness

rather than reinforcing fillers.

0.0 0.1 0.2 0.3 0.4 0.5

0

2

4

6

8

10

WEEE PP/ 0-40wt.% PPL cups

Notc

hed

Ch

arpy I

mpac

t E

ner

gy (

KJ/

m2)



123

Figure 6-16: Notched Charpy impact strength of PPCs with increasing volume fractions of PPL cups

between 0-40 wt.% with 2 wt.% 907P.

The 40 wt.% sample with 2 wt.% coupling agent has shown an increase in impact strength. However

it should be noted that the error bar for this sample is rather big. This was similar for a lot of the

Charpy test samples. The nature of the experiment testing at high strain rates can create errors. The

v-notch could also be cutting through fibres and creating stress concentrations and weakening the

fibre matrix bond. However at 40 wt.% PPL the composite is stronger due to the coupling agents and

amount of filler in the sample. It is not however stronger than the 30 wt% sample with 907P. Care

should be taken when compared against other mechanical properties such as tensile stress as the

specimen experience different test speeds.

Hristov et al., (2004) reports that the impact results are mainly influenced by the matrix behaviour.

With fillers added, the energy required to initiate a crack is lower. The cracks can be started through

different mechanisms. With the composite, debonding or fibre pull-out can occur. The matrix is

hindered by the fibres and cannot absorb the same amount of energy through PP plastic matrix

deformation mechanisms.

0.0 0.1 0.2 0.3 0.4 0.5

0

2

4

6

8

10

12

WEEE PP/ 0-40wt.% PPL Cups/ 2wt.% 907P

Notc

hed

Ch

arpy I

mpac

t E

ner

gy (

KJ/

m2)



124

The other blends/recipes of materials showed very similar results to the above. The recipes that stood

out were only the 10 wt.% filler materials, which is due to the high matrix content.

iv) Flexural testing of PPCs: Optimising Filler and Coupling Agent

0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

30

35

40

45

50

55

WEEE PP / PPL CUPS

Linear Fit

Fle

xura

l S

tren

gth

(M

Pa)


WEEE PP / PPL CUPS / 2 wt.% 907P

Linear Fit

WEEE PP / PPL CUPS / 2 wt.% PRIEX 25097

Linear Fit

Figure 6-17: Flexural strength of WEEE PP based PPCs with 2 wt.% 907P and PRIEX 25097 at increasing



125

0 1 2 3 4

0

5

10

15

20

25

30

35

40

45

50

WEEE PP/30wt.%_PPL/1-4wt.%_907P

Polynomial FitFle

xura

l S

tren

gth

(M

Pa)

MAPP (wt.%)

WEEE PP/30wt.%_PPL/1-4wt.%_PRIEX 25097

Polynomial Fit

Figure 6-18: Flexural strength of WEEE PP based PPCs at 1-4 wt.% 907P and PRIEX 25097 at 30 wt.%

PPL cups.

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

WEEE PP / PPL CUPS

Fle

xura

l M

odulu

s (G

Pa)


WEEE PP / PPL CUPS / 2 wt.% 907P

WEEE PP / PPL CUPS / 2 wt.% PRIEX 25097

Figure 6-19: Flexural modulus of WEEE PP based PPCs with 2 wt.% 907P and PRIEX 25097 at increasing



126

0 1 2 3 4

0.0

0.4

0.8

1.2

1.6

2.0

2.4

WEEE PP/30wt.%_PPL/1-4wt.%_907P

Linear Fit

Fle

xura

l M

odulu

s (G

Pa)

MAPP (wt.%)

WEEE PP/30wt.%_PPL/1-4wt.%_PRIEX 25097

Linear Fit

Figure 6-20: Flexural modulus of WEEE PP based PPCs at 1-4 wt.% 907P and PRIEX 25097 at 30 wt.%

PPL cups.

0 1 2 3 4

0

5

10

15

20

25

30

35

40

45

50

55

Flexural Strength_WEEE PP/40wt.%_PPL/1-4wt.%_907P

Polynomial Fit

Fle

xura

l S

tren

gth

(M

Pa)

MAPP (wt.%)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Flexural Modulus_WEEE PP/40wt.%_PPL/1-4wt.%_907P

Polynomial Fit

Flex

ural M

odulu

s (GP

a)

Figure 6-21: Flexural strength and Flexural modulus of WEEE PP based PPCs at 1-4 wt.% 907P and

PRIEX 25097 at 40 wt.% PPL cups.


127

0.00 0.02 0.04 0.06 0.08 0.10

0

10

20

30

40

50

Fle

xura

l S

tres

s (M

Pa)

Flexural Strain

WEEE PP/30wt.%_PPL/3wt.%_Struktol

WEEE PP/30wt.%_PPL/3wt.%_907P

Figure 6-22: Flexural strength vs. flexural strain of 30 wt.% PPL cups in WEEE PP with 3 wt.% 907P and

3 wt.% Struktol coupling agents.

Figures 6-17 to 6-22 represent the key coupling agents and the results from the flexural testing of PPCs

examining the effect of the volume fraction and weight fraction of coupling agents.

Figures 6-17 to 6-20 show that the 907P coupling agent slightly outperforms the PRIEX 25097, mostly

at higher percentages of MAPP and filler content. Figure 6-22 shows the failure point in the flexural

test. The point of failure is thought to originate from an interface around a paper flake. With the three

point bending test a high stress is focused in one area and the stress at the interfaces is thought to

initiate the crack propagation. With a stronger secure bond between the two phases the amount of

energy required to start the crack propagation is higher.

At 30 wt.% PPL cup the flexural strength has the highest value at 3 wt.% coupling agent (Figure 6-21)

whereas the flexural modulus is still increasing up to 4 wt.% MAPP. In terms of strength properties the

PRIEX coupling agent starts to decline more quickly at 4 wt.% than the 907P grade. At 40 wt.% PPL cup

3 wt.% is also the peak value of MAPP before the strength and modulus start to decrease. Further

additions of MAPP do not make a difference to the properties.


128

Figure 6-22 shows the Struktol and the 3 wt.% 907P recipes. The stronger material is shown to be the

907P recipe. The Struktol recipe is the tougher material with a bigger strain to failure, shown by the

area under the stress strain curve. However this curve is based on one of the tests. Both recipes

average out to be of similar values of 50 MPa. The 907P recipe shows a higher average flexural

modulus by 200 MPa.

Figure 6-23: The well dispersed filler encapsulated by the surrounding matrix in a 3-point bend test.

Similar problems were found to the tensile tests with the VTES and PEI coupling agents. The coating

of the paper cups may also have a factor here and may hinder the coupling.


129

v) Dynamic Mechanical Analysis (DMA)

The variation in storage modulus (E') with temperature for composites containing different additions

of PPL flakes is shown in Figure 6-24. The storage modulus decreases with increasing temperature and

increases with the percentage addition of PPL flakes over the temperature range investigated.

-50 0 50 100 150 200

0

500

1000

1500

2000

2500

WEEE PP

90wt.%_WEEE PP/10 wt.%_PPL




Sto

rage

Modulu

s (M

Pa)

Temperature (oC)

Figure 6-24: Storage modulus vs. temperature for samples containing between 0 and 40 wt.% PPL

flakes.

Loss modulus (E'') data is included in Figure 6-25 and this shows two peaks. E'' also increases for

composite mix designs containing higher percentages of PPL flakes. The first peak occurs between 0

and 10°C and corresponds to the glass transition temperature of the matrix polypropylene. The second

peak, found between 60°C and 75°C, is the α-transition associated with relaxation of the crystalline

phase present in semi-crystalline polypropylene (Tajvidi et al., 2006). With further increases in

temperature the polymer chains become more mobile and the matrix changes from a brittle to a tough

material. Further heating causes a large reduction in viscosity as the melting point of the polymer is

approached, and this causes further reductions in E' and E''.


130

-50 0 50 100 150 200

0

20

40

60

80

100

120L

oss

Modulu

s (M

Pa)

Temperature (oC)

WEEEPP





Figure 6-25: Loss modulus vs. temperature for samples containing between 0-40 wt.% PPL flakes.

The Tan delta in Figure 6-26 helps in obtaining the viscoelastic behaviour of the composites compared

to the polymer. It is a measure of the materials’ dissipation of energy. Up to the glass transition

temperature (indicating close to zero degrees, Figure 6-25) the tan delta values are very similar. The

PP and low fill composites tended to have slightly greater Tan delta values at higher temperatures.

The high fill composites had lower values indicating a more elastic behaviour with less energy

dissipated. Tajvidi et al., (2006) reports that composite materials behave much differently to the PP

alone at higher temperatures, whereas PPCs in this research had more similar tan delta values with

increasing temperature. The addition of coupling agents did not affect the results agreeing with the

results of Tajvidi et al., (2006). It was reported that there has to be free MAPP which could reduce the

glass transition in the composites. This indicates that all the MAPP is used up proving that all the

possible sites are linked and the coupling agent is effectively bonded to the matrix and filler.


131

Figure 6-26: Tan Delta vs. temperature for PPCs between 0-40 wt.% PPLs.

6.3.1 Material Characterisation of Paper Plastic Composites (PPCs): The Volume Fraction of Fillers

i) Rheological Properties: Shear Rate vs. Shear Stress

Sanchez et al., (2011), commented on the pseudoplastic behaviour of composites with increasing

temperature. Also, when composites are exposed to increased temperatures it has been shown that

the viscosity decreases due to the weakening fibre matrix interface strength.

The literature is divided between the effects of coupling agents on the shear viscosity of composites

with fibres. There is much debate arguing that the shear viscosity increases due to the strong bond at

the interface. The strong bond enhances the friction at the interface which then increases the

resistance to shearing (Joseph et al., 2002; Mohanty et al., 2006). Other literature reported that the

coupling agents can cause lubricating effects which actually decrease the shear viscosity (Li and

Wolcott, 2006; Hristov and Vichopoulus, 2007).

In extrusion shear rates at the die may reach up to 1000 s-1 while at the injection moulding nozzle the

shear rates may reach up to 10,000 s-1. Generally the shear viscosity changes the most up to 2000 s-1.

This can be related to their pseudoplastic or shear thinning response. With increasing shear rates the

viscosity is lower. The polymer structure has a significant effect on this behaviour. More crystalline

-50 0 50 100 150 200

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18T

an D

elta

Temperature (oC)

WEEEPP






132

polymers require more heating. There are fewer entanglements in polymer chains with increasing

shear rates and the viscosity lowers. Shear behaviour generates heat and with increasing temperature

the polymers melt and can flow easier.

The filler inhibits the movement of the chains which in turn increase the viscosity by restricting

movement of the polymer in the melt phase. Figure 6-28 shows higher viscosities at lower shear rates

with increasing filler content and Figure 6-27 shows recipes with a higher filler content at low shear

rates have a higher shear stress because more energy needs to be put into the material in order to

make it flow easier. The fillers restrict flow patterns of the polymer.

Figure 6-27: Shear rate vs. Shear stress for PPCs containing WEEE PP and PPL cups from 10-40 wt.%.

0 10000 20000 30000 40000 50000 60000 70000 80000

0

100

200

300

400

Shea

r ra

te (

1/s

)

Shear stress (Pa)

WEEE PP

90wt.%_WEEEPP/10wt.%_PPL





133

Figure 6-28: Shear rate vs. Viscosity for PPCs containing WEEE PP and PPL cups from 10-40 wt.%.

Figure 6-29: Extruded strands of PPCs in the rheology testing showing the difference between a WEEE

PP composite containing 30 wt.% PPL and 30 wt.% PPL with 2 wt.% Struktol.

The coupling agent severely affected the smoothness of the extrudate from the die. Figure 6-29

highlights the difference with the Struktol coupling agent compared to the PPL cup and PP without

coupling agent showing melt fracture. In Figure 6-29 the top strand shows the smooth surface with

fewer signs of melt fracture.

0 50 100 150 200 250

0

5000

10000

15000

Vis

cosi

ty (

Pa

s)

Shear rate (1/s)





WEEE PP


134

Figure 6-30: Shear rate vs. Shear stress for PPCs containing WEEE PP and PPL cups from 10-40 wt.%

with 2 wt.% 907P and 2 wt.% Struktol.

The Struktol recipe is shown to require a higher stress to flow. However the surface quality is

significantly improved with minimal melt fracture. During shear the polymer molecules that were

entangled and randomly orientated become orientated with less entanglement.

For non-Newtonian behaviour a popular model for steady shear viscosity is the Oswald-de Waele

power-law model shown in equation 3-12. Table 6-3 shows the flow consistency index values and the

flow behaviour index. For the flow behaviour index equal to one, a Newtonian behaviour is observed.

The increasing PPCs have decreasing flow behaviour index values indicating non-newtonian and shear

thinning behaviour. The consistency index is increasing with filler content indicating a more viscous

material. This data shows that PPCs are in good agreement with the Oswald-de Waele power-law

model (Boger and Halmos 1981; Jahangiri et al., 2012).

0 50 100 150 200 250 300 350

0

20000

40000

60000

80000

100000

120000

Shea

r S

tres

s (P

a)

Shear Rate (1/s)

30wt.% PPL Cups

30wt.% PPL Cups_2wt.% Struktol

30wt.% PPL Cups_2wt.% 907P


135

Figure 6-31: Log shear stress vs. Log shear rate plot of WEEE PP and increasing volume fraction (Vf) of

PPL paper cups.

Table 6-3: Table showing the flow consistency index (y-intercept) values and the flow behaviour index

(Slope of Log Log plot).

Equation y = a + b*x WEEE PP

Weight No Weighting

Residual Sum of Squares 0.03026

Pearson's r 0.99318

Adj. R-Square 0.98445

Value Standard Error

log shear stress Intercept 3.3944 0.0458

log shear stress Slope 0.59724 0.02651

0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

1

2

3

4

5

6

WEEE PP

Linear Fit

Log S

hea

r S

tres

s (P

a)

Log Shear Rate (1/s)

10wt.% PPL Cups

Linear Fit

40wt.% PPL Cups

Linear Fit


136

Equation y = a + b*x 10 wt.% PPL Cups

Weight No Weighting


Pearson's r 0.99243





Equation y = a + b*x 40 wt.% PPL Cups

Weight No Weighting


Pearson's r 0.99526





ii) Thermogravimetric Analysis (TGA) of PPCs: Optimising Filler and Coupling Agent

TGA analysis was used to investigate how the PPCs behave in the range of temperatures used during

processing. The temperature of the cylinders in the extruder and moulding machine did not exceed

180°C during processing. This is governed by the melting temperature of the PP matrix material. The

processing temperature plays an important role in WPCs and has to be controlled. It is important to

understand how the fibres behave at these high temperatures. TGA experiments help us gather data

on how materials behave under these temperatures. However within the extruder barrel the

temperatures may exceed 180oC through shearing due to the rotating screws. So although it is not a

direct comparison it does help simulate PPC behaviour. Although the matrix melting temperature is

between 160-170oC the processing temperatures are slightly higher to ensure the polymer flows along

the screw and exits the die. TGA experiments can measure the weight loss at processing temperatures.

The matrix, fillers and PPCs were examined at processing temperatures. PPCs were also held for long

periods at these temperatures to see if this affected the weight loss, if the material had a longer

residence time for example.


137

Figure 6-32: Thermal degradation behaviour of increasing volume fraction of PPL cups up to 500oC.

The weight loss data for composites containing up to 40 wt.% PPL flakes when heated between 10 and

500°C at 20°C/min is shown in Figure 6-32. The results show how the increasing amount of filler affects

the weight loss of the PPCs at increasing temperature. The WEEE PP is shown by the solid line and

does not show a weight loss over the processing temperatures of 160-180oC. With the addition of PPLs

the weight percent dropped slightly with increasing temperature. The point of degradation lowers

with increasing filler content. The degradation temperature of the composite is significantly higher

than the processing temperatures used. Isothermal experiments at 180°C for 20 minutes showed no

significant weight loss. The PPL curve in Figure 6-32 shows that PPL loses weight between 50 and

100°C. This can be attributed to water loss. The PP does not change weight over this period.

With the addition of PPL to the polymer matrix, any weight loss up to this temperature is due to PPL

water loss. Figure 6-33 also highlights that PPL is stable up to 250°C before degradation starts to occur.

The PP resin is stable to approximately 400°C. Therefore it is presumed that any weight loss at

temperatures less than 250°C is due to water loss associated with PPL in PP. This is shown in Figure 6-

33 where the weight loss is in proportion with the volume fraction of PPL in PP. The weight loss in the

region between 250°C and 400°C is due to decomposition of the PPC.

0 100 200 300 400 500

0

20

40

60

80

100

Wei

ght

Per

cent

(wt.

%)

Temperature (oC)

10wt.% PPL_20oCp/m_10-500

oC

20wt.% PPL_20oCp/m_10-500

oC

30wt.% PPL_20oCp/m_10-500

oC

40wt.% PPL_20oCp/m_10-500

oC

WEEE PP_20oCp/m_10-500

oC


138

Figure 6-33: Percentage weight loss as a function of volume fraction of PPL in WEEE PP up to 250oC

and 400oC.

Figures 6-34-6-35 shows the weight percent loss over the isothermal periods. At higher levels of filler

the higher the percentage weight loss. The weight loss is due to the thermal degradation of the filler

which has a lower thermal stability than the matrix.

0.0 0.2 0.4 0.6 0.8 1.0

0

20

40

60

80 WEEE PP_PPL up to 250oC

Linear Fit

Wei

ght

Loss

(%

)


WEEE PP_PPL up to 400oC

Linear Fit


139

10 15 20 25 30 35

96.0

96.5

97.0

97.5

98.0

98.5

99.0

99.5

40wt.%_PPL_180oC_3min






Time (Minutes)

Wei

ght

Per

cent

(wt.

%)

0

20

40

60

80

100

120

140

160

180

200

220

240

260

Tem

peratu

re (oC

)

Figure 6-34: Weight loss over isothermal time periods between 3-20 minutes at 180oC.

Figure 6-35: Weight loss from 40 wt.% PPL content in WEEE PP with an isothermal period at 180oC.

The red line indicates the point at which the isothermal period starts.

0 5 10 15 20

96.0

96.5

97.0

97.5

98.0

98.5

99.0

99.5

100.0

100.5

ISOTHERMAL PERIOD

Wei

ght

Per

cent

(wt.

%)

Time (Minutes)

40wt.%_PPL_20oCp/m_Isothermal_180

oC_20min

RAMP PERIOD


oC_10min


oC_3min


140

At 20oC per minute it takes approximately 10 minutes to get to 180 degrees Celsius where the

materials were held for a set time between 3 and 20 minutes to try and emulate how long if at all the

fibrous materials would degrade in the extruder at these temperatures. It should be noted that due

to the higher heating rate the temperature overshoots over the required temperature before settling

down again but this should emphasize and increase the degradation if there is any of the fibrous flakes.

40 wt.% was chosen to illustrate this because there are more fibrous flakes and therefore more chance

of fibre degradation and therefore being the worst case scenario within this research. Approaching

the set temperature the fibrous flakes lose a couple of weight percent at maximum but then hold their

weight at this temperature of 180oC until the temperature starts to rise again and then a dramatic

weight loss is seen over 200oC. This is shown with the blue curves in Figure 6-34 which show the

temperatures. As these curves increase the black curves start to decrease showing the weight

percentage decreasing at a sharp rate.

0 5 10 15 20 25 30 35 40 45 50

96

97

98

99

100

101

102

103

104

105

Wei

ght

Per

cent

(wt.

%)

Time (Minutes)

Ramp 20-500oC_at 20

oC p/m

Ramp period


Ramp period Isothermal period



Figure 6-36: Weight loss from 10 wt.% PPL content in WEEE PP with an isothermal period at 180oC in

a nitrogen atmosphere. The red line indicates the point at which the isothermal period starts.

Across all results for PPCs it has been made clear that at 10 wt.% PPL addition the properties compared

to the PP matrix dramatically reduce and the PPLs are seen as points of weakness and stress

concentrators. Figure 6-36 shows that at 10 wt.% of PPL the weight loss at 10 minutes (isothermal)


141

seems to decrease at a faster rate than the other samples. At this point it should be noted that the

sample size of the TGA/DSC samples was a matter of milligrams and therefore if a pellet had slightly

less filler in for example then it could dramatically change the results. This is why it is important to re-

run samples but this can also explain anomalies in the data.

Figure 6-36 shows that at 10 wt.% PPL the same reasoning applies as the 40 wt.% sample. During the

duration of the isothermal treatment the material maintains its weight and then quickly drops off once

the ramp part of the experiment starts and the temperature increases. Heating up to the processing

temperature seems to release volatiles or moisture and cause weight reduction. Moisture is the

assumed reasoning for the initial weight loss.

Figure 6-37: Weight percent loss up to 500oC at 10oC and 20oC a minute heating rates.

The onset of thermal degradation is similar at different heating rates but measuring the samples at

20oC a minute generally showed a higher onset to thermal degradation, Figure 6-37.

The literature explains the issues with fibrous composites and the compatibility issues between the

polar hydrophilic fibres and the non-polar hydrophobic matrix. The MAH grafts onto the PP backbone

and therefore is capable of covalently bonding with the -OH groups of the cellulose fibres whereas the

PP co-crystallizes and interlocks with the PP matrix (Kim et al., 2007). The use of MAPP coupling agents

have been very popular and are key to forming a successful interfacial bond and therefore better

0 100 200 300 400 500

0

20

40

60

80

100

Wei

ght

Per

cent

(Wt.

%)

Temperature (oC)

10wt.% PPL_20oCp/m_10-500

oC

10wt.% PPL_10oCp/m_10-500

oC


142

composites (Kim et al., 2007). In this research six different commercially available types of MAPP

coupling agents were used to see their effect on paper plastic composites after already proving their

capabilities in the wood plastic composite field. Some of the coupling agents discussed here have been

trialled in chapter 5 but further analysis for comparison reasons is discussed here. The two major

aspects, discussed in section 3.5, are molecular weight and percentage of free maleic anhydride. These

have shown in this research to be vital in determining the overall interfacial adhesion performance.

The work by Kim et al., (2007), also compares MAPP coupling agents with bio-filled PP composites.

This section looks at the thermal properties of the composites and relates to other sections in terms

of mechanical and rheological properties to help understand not only how these coupling agents

perform but also move forward and become closer to a decision on which coupling agents are

sufficient for PPCs. To finish the section non-MAPP coupling agents are discussed.

As explained previously, the initial trials helped determine which coupling agents to use in the

optimising trial. Further coupling agents were also trialled through excellent reports on their

properties. Therefore further analysis on these coupling agents at different weight percentages was

necessary. The coupling agents were analysed in the TGA/DSC on their own to see how temperature

affects their weight loss and to determine how the PP behaves in the coupling agent.

The TGA/DSC curves of the six MAPP coupling agents are shown in Figure 6-38. The findings for E-43

are in agreement with Kim et al., (2007) showing that the thermal stability of E-43 proved to be the

lowest out of the selected MAPP products shown. Kim et al., (2007) state that this is due to the low

molecular weight of the Mw. Figure 6-38 also shows 907P coupling agent to have a slightly lower

thermal stability. This also has a low Mw (Table 5-8). The difference however is shown through the

mechanical property tests. Even though the 907P MAPP coupling agent has a low Mw and therefore

arguably does not entangle with the PP matrix, it does however have a high SAP number meaning that

there are plenty of sites for bonding with the fibrous filler.

The DSC curves show melting points around 160-170oC for the MAPP. The melting points are

attributed to the PP grafted to the MAH. The Polybond 3200 shows the highest melting point close to

the processing temperatures used in this research meaning that the viscosity may not be as low as the

others at processing temperatures.


143

Figure 6-38: a) TGA curves showing weight loss against temperature for 6 different MAPP coupling

agents used in this research. b) DSC curves showing heat flow against temperature for 6 different

MAPP coupling agents used in this research

0 100 200 300 400 500

0

20

40

60

80

100

Wei

ght

Per

cent

(wt.

%)

Temperature (oC)

907P_Ramp_20-500oC_20

oC p/m

Polybond 3200_Ramp_20-500oC_20

oC p/m

E-43_Ramp_20-500oC_20

oC p/m

Priex 25097_Ramp_20-500oC_20

oC p/m

950P_Ramp_20-500oC_20

oC p/m

1325P_Ramp_20-500oC_20

oC p/m

50 100 150 200

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

Hea

t F

low

(m

W)

Temperature (oC)

907P_Ramp_20-500oC_20

oC p/m

950P_Ramp_20-500oC_20

oC p/m

Polybond 3200_Ramp_20-500oC_20

oC p/m

E-43_Ramp_20-500oC_20

oC p/m

Priex 25097_Ramp_20-500oC_20

oC p/m

1325P_Ramp_20-500oC_20

oC p/m


144

Scanning Electron Microscopy (SEM) of PPCs:

At higher loadings the coupling agents may not necessarily increase the strength of the composite if

the PPL flakes become the locus of failure as shown in Figure 6-39b. It appears that close to the

optimum level of coupling agent the failure mode switches from fibre pull out to fibre failure. The

maxima in the curves in Figure 6-6 can be attributed to the modified PP improving adhesion to the

point where the fibres become sufficiently load bearing and reach their specific failure strength.

Further additions may increase interfacial adhesion however the failure of the composite will be

limited by the nature and strength of the PPL fibres. The strength of the composite is a function of the

strain to failure at low addition rates and reaches a plateau associated with paper fibre failure.

a

b

Figure 6-39: Fracture surfaces of composite samples (68 wt.% PP, 30 wt.% PPL) with a) no coupling

agent showing flake pull-out and b) 2 wt.% coupling agent (MAPP) showing fractured PPL flake that

remains attached to the surrounding polymer matrix.

100 µm

100 µm


145

Similar adhesion problems were found in the study by (de la Orden et al., 2007).

Figure 6-40: PP-fibre composite without PEI (left image) and PP-fibre composite with PEI (de la Orden

et al., 2007).

With the addition of PEI, the gaps have become smaller and the fibres appear to be broken explaining

the adhesion properties with the addition of PEI.

6.4 Multilayer Carton Board (MCB) / Tetra Pak

Tetra Pak material does not have to be thrown to landfill or separated into individual components as

described in Chapter 3. Due to the growing interest in this type of waste and the volumes of material

available in the waste stream along with the promising results shown in the initial trials, further trials

and optimisation with PPCs is required. Chapter 5 showed that MCB / Tetra Pak composites were

worth investigating further. The following section exhibits the data.

6.4.1 Mechanical Properties: Paper Plastic Composites (PPCs): The Volume Fraction of Fillers

i) Tensile Properties

Initial Trials Summary

In the initial trials it was shown that with Tetra Pak (MCB) added to the MRF flake polymer the increase

in tensile strength with the 907P coupling agent from Honeywell was 34.2%. This with further

optimisation is still worth investigating. The tensile strength showed a higher increase with paper

plastic laminate cups compared to carton board with the addition of a coupling agent. However the

percentage increase with Young’s modulus was higher with the carton board at 30 wt.%. The carton

board is thought to produce lower strength values due to the fibres involved being weaker than the

paperboard fibres. The carton board also has a layer of aluminium which is thought to add weak

boundaries around the polymer and fibres. The results achieved by using carton board are still

reproducible leaving an excellent basis for future optimisation and improvement.


146

The results in Table 6-4 and Figures 6-41 to 6-42 show the effect of Tetra Pak on PPCs through tensile

testing.

Table 6-4: Tensile Testing results of MCB / Tetra Pak based PPCs.

Recipes

Volume Fraction

(Vf) (3.s.f)

Tensile Strength

(MPa) (3.s.f)

Young's Modulus

(GPa) (3.s.f)

Yield Stress (MPa) (3.s.f)

Yield Strain (3.s.f)

Elongation at Break (%)(3.s.f)

WEEE PP 0 20.7 1.05 11.9 0.0135 493

90wt.% WEEEPP/10wt.% TETRA 0.117 21.3 1.36 13.8 0.0116 8.77




88wt.% WEEEPP/10wt.% TETRA/2wt.% 907P 0.119 25.1 1.41 15.0 0.0121 9.90




87wt.% WEEEPP/10wt.% TETRA/3wt.% 907P

0.120

25.6

1.50

15.4

0.0118

9.91




By adding the carton board to the PP matrix, the tensile strength increases at very small levels. The

stiffness however does increase significantly as the volume fraction of filler increases. With 40 wt.%

carton board the Young’s modulus sees an increase of nearly 1 GPa (100% increase) compared to the

PP matrix. The filler does inhibit the polymer molecules from flowing and aligning when stressed

reducing the ductility.

With the addition of 2 wt.% coupling agent the tensile strength does improve, indicating that bonding

at the fibre-matrix interface has more than likely taken place. The paper fibres are relatively

inextensible causing the PPC to break at lower strains shown in Table 6-4. The elongation at break is


147

fairly similar with all the PPCs (Table 6-4). The composites contain many inclusions and weak interfaces

with a higher volume fraction of filler, decreasing the elongation at break as less polymer chains are

free to orientate under the stress.

With the addition of coupling agents (Table 6-4) 2 wt.% 907P proves to be most efficient as 3 wt.%

values do not make a huge difference. Commercially there would be little point in using more coupling

agent due to financial cost savings. The yield stress values improve with the addition of coupling agents

due to the bonding at the interface. The maleic anhydride covalently bonds with the -OH groups of

the cellulose carton board fibres whilst the polymer interacts with the matrix chain.

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

0-40 wt.% PPC

Polynomial Fit

Young's

Modulu

s (G

Pa)


0-40wt.% PPC_2wt.% 907P

Polynomial Fit

Figure 6-41: Young’s modulus with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

Tetra Pak show slightly better tensile properties over the 10-40 wt.% range with 2 wt.% 907P

compared to PPL cups. The UTS at 40 wt.% is smaller than PPL cups. The 2 wt.% 907P is shown to be

optimum with tensile strength values, as 3 wt.% causes a decline in tensile strength (Figure 6-42).


148

0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

30

35

0-40 wt.% PPC

Polynomial Fit

Ten

sile

Str

ength

(M

Pa)


0-40wt.% PPC_2wt.% 907P

Polynomial Fit

0-40wt.% PPC_3wt.% 907P

Polynomial Fit

Figure 6-42: Tensile strength with increasing volume fractions of PPL Tetra Pak and 2 wt.% - 3 wt.%

907P.

The Young’s modulus at higher weight percentages is not as high as PPL cup recipes. The coupling

agent does not seem to have an effect like with PPL cups. This could be the aluminium being a

weakness, or could it be the lower quality carton board. The carton board is also thicker which could

be seen as thicker areas of weakness with a higher chance of cracks to appear at the interfaces.

ii) Flexural Testing of PPCs Based on MCB Fillers: Optimising Filler and Coupling Agent

The flexural results are very similar to the PPL cups in strength and stiffness with and without coupling

agents. The stresses and strains across the flexural samples are different and therefore analysing the

flexural data is necessary to examine the strength and stiffness in different failure modes.


149

0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

30

35

40

45

50

55

0-40 wt.% PPC

Polynomial Fit

Fle

xura

l S

tren

gth

(M

Pa)


0-40wt.% PPC_2wt.% 907P

Polynomial Fit

Figure 6-43: Flexural strength with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0-40 wt.% PPC

Polynomial Fit

Fle

xura

l M

odulu

s (G

Pa)


0-40wt.% PPC_2wt.% 907P

Polynomial Fit

Figure 6-44: Flexural modulus with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P


150

The addition of the coupling agent does not have a huge effect on the modulus values at 40 wt.% filler.

The flexural strength values increase at a similar fashion with increasing filler and coupling agent to

the PPL cups assuming the same mechanisms for coupling apply (Figure 6-43).

iii) Charpy Impact Energy Testing of PPCs Based on MCB Fillers: Optimising Filler and Coupling Agent

The toughness values are quite a bit higher than the PPL cup values. The type of failure is different in

a Charpy impact test and is sudden. The role of the filler can make the material weaker with weaker

interfaces and making the material less ductile. The strength of the Tetra Pak material is stronger than

the PPL which may give reasons to higher failure. The aluminium layer in this case may help against

sudden impact. Also the thicker flakes may impart more impact resistance to sudden failure. The PPL

flakes were actually expected to make the impact properties worse, however very little difference can

be seen. The PP reacts in a similar brittle way unlike the HDPE seen in section 6.6, which exhibits very

tough impact properties.

0.0 0.1 0.2 0.3 0.4 0.5

0

2

4

6

8

10

12

14

16

18

0-40 wt.% PPC

Char

py I

mpac

t E

ner

gy (

KJ/

m2)


0-40wt.% PPC_2wt.% 907P

Figure 6-45: Charpy impact energy with increasing volume fractions of PPL Tetra Pak and 2 wt.% 907P.

The addition of the coupling agent did not have any affect at the high strain rate to failure.


151

iv) Shear Rate vs. Viscosity Testing of PPCs Based on MCB Fillers: Optimising the MCB Filler

Figure 6-46: Shear rate vs. viscosity with increasing volume fractions of PPL Tetra Pak.

The increase in filler shows the effect on viscosity clearly in Figure 6-46. With increasing filler the

viscosity increases. With increasing shear rate the viscosity lowers. At low shear rates the thicker flakes

can be seen to have a high viscosity.

0 20 40 60 80 100 120 140 160 180 200

500

1000

1500

2000

2500

3000

3500

Vis

cosi

ty (

Pa

s)

Shear rate (1/s)

60wt.%_WEEEPP/40wt.%_TETRA




WEEE PP


152

6.5 PPCs with High Density Polyethylene (HDPE) as the Composite Matrix: Optimising Filler and

Coupling Agent

6.5.1 High Density Polyethylene (HDPE) / PE Coated Beverage Cup

i) Mechanical Properties: Tensile Testing: Optimising Filler and Coupling Agent

Figure 6-47: Tensile strength and Young’s modulus of with increasing volume fractions of PPL cups

blended with HDPE.

The HDPE produces some very promising results that compete with the PP/PPL mixes. The PP shows

a higher Young’s modulus at higher volume fractions. At 3 wt.% coupling agent the tensile strength

does not differ to 2 wt.% indicating 2 wt.% PRIEX 12031 is optimal as shown in Figure 6-48. The bonding

between the MAPE at the interface is also an esterification reaction described in section 3.5. The MAH

groups covalently bond with the hydroxyl groups of the PPL cup fibres which forms the ester link.

Mohanty (2006) comments on the non-polar PE of the grafted MAPE that combines with the polymer

matrix. The PE lowers the surface energy which enhances the wettability and dispersion of the filler in

the matrix. Advantages of HDPE composites would be that a lower amount of coupling agent is

required rather than 3 wt.% in the PP/PPL mixes. The AC 1687 according to Honeywell has a high

bound SAP of 70% with a relatively low Mw of 5000 which is very similar to the 907P coupling agent.

Both of these exhibit good bonding characteristics.

0.0 0.1 0.2 0.3 0.4

0

10

20

30

HDPE/PPL_Tensile Strength

Linear Fit

HDPE/PPL_Youngs Modulus

Linear Fit


Ten

sile

Str

ength

(M

Pa)

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Young's M

odulu

s (GP

a)


153

A study by Li and Matuana (2003), focusing on HDPE wood-flour composites showed that with the

addition of the filler (wood-flour) the tensile properties decreased. Even some with coupling agents

did in fact decrease. However the paper cups slightly increased the tensile strength. This is interesting

in that with PP and paper cups shown in Figure 6-1, a smaller increase was observed. The increase

with HDPE is small but nonetheless there is an increase. The work by Li and Matuana (2003) did

however show a rise in the Young’s modulus with increasing filler content agreeing with the results

found in this research approaching 1.8 GPa. However this value was reached with 40 wt.% paper cups

in this research compared to 70 wt.% wood flour.

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

0

5

10

15

20

25

30

35

HDPE/PPL Cups

Linear FitTen

sile

Str

eng

th (

MP

a)


HDPE/PPL Cups_AC 1687_2/3wt.%

HDPE/PPL Cups_PRIEX 12031_2/3wt.%

AC 1687 3wt.%

PRIEX 12031 2wt.%

Figure 6-48: Tensile strength of HDPE/PPL cups with 2-3 wt.% AC 1687 and PRIEX 1203 between 0-30

wt.% PPL cups.


154

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

5

10

15

20

25

30

35E

ngin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

HDPE

UTS = 32.01 MPa

UTS = 23.44 MPa

UTS = 21.35 MPa

70 wt.%_HDPE/30wt.%_PPL

70 wt.%_HDPE/30wt.%_PPL_2wt.%_PRIEX 12031

Figure 6-49: A comparison of the engineering stress vs. Engineering strain curves for HDPE, and

composites containing 30 wt.% disposable cup with and without 2 wt.% PRIEX 12031.

Li and Matuana (2003) stated that the addition of coupling agents improved the yield strengths of the

HDPE wood flour composites. The increase was only compared to the composites without coupling

agents. In the paper by Li and Matuana (2003) mechanical properties were still below the HDPE used

as the matrix except one HDPE composite with MAPE as a coupling agent. Figure 6-49 shows that with

the addition of paper cups at 30 wt.% the strength increases. The yield strength also increases (Table

6-5). With the addition of a coupling agent the toughness is still the same but the interfacial adhesion

has changed and more stress can be loaded on to the fibres because of the bond between the matrix

and filler showing a higher strength. Toughness would have to be considered further to try and

increase the strain to failure with a high percentage of filler. Comparing Figure 6-49 to 6-12 shows that

the PPC, based on PP as the matrix, had an increase in the toughening with the addition of the coupling

agent.


155

Table 6-5: HDPE tensile data without the extensometer

Recipe Yield Stress Strain at Yield Strain at Break

HDPE 13.40 0.02 0.74

70wt.%HDPE/30wt.%PPL 15.30 0.02 0.09

70wt.%HDPE/30wt.%PPL/2wt.%PRIEX 12031 20.70 0.03 0.08

The nature of this interfacial adhesion can again be put down to the reactive functional groups of the

coupling agent and the hydroxyl groups of the fibrous filler with the PE on the coupling agent backbone

reacting and intertwining with the HDPE matrix within the extruder (Li and Mutuana, 2003). Li and

Mutuana, (2003), reported that the esterification reactions occur with the surface of the filler and the

coupling agents with support for this with FTIR and XPS data. The reasoning behind this is thought to

be due to the exposed PE chains on the surface of the filler diffuse into the HDPE matrix and then

entangle with the molecules of HDPE in the melt phase.

Figure 6-50: Tensile failure of a HDPE composite with 30 wt.% PPL cups and 2 wt.% PRIEX 12031.

The HDPE bonds well with the PPL cups. Kukaleva et al., (2003) show an addition of up to 15% of LDPE

can go into HDPE and show good stiffness and toughness properties.

Comparing coupling agents, the AC 1687 does not perform as well as the PRIEX grade in stiffness but

is better than the PRIEX grade in strength shown in Figures 6-48 and 6-51.


156

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

HDPE/PPL Cups

Linear Fit

Yo

un

g's

Mo

du

lus

(GP

a)


AC 1687 3wt.%

PRIEX 12031 2wt.%

HDPE/PPL Cups_AC 1687_2/3wt.%

HDPE/PPL Cups_PRIEX 12031_2/3wt.%

Figure 6-51: Young’s modulus of HDPE PPL cups between 0-30 wt.% and AC 1687 and PRIEX 12031 at

2-3 wt.%.

The Bondyram coupling agent was also trialled but did not show the same level of increase in

mechanical properties as the other coupling agents analysed.

ii) Charpy Impact Energy: Optimising Filler and Coupling Agent

The toughness values of the HDPE are far superior to the PP. The HDPE material is a highly crystalline

orientated polymer with a higher Mw than the PP and the impact properties are very impressive.


157

Figure 6-52: Impact testing of HDPE with PPL cups and coupling agents.

With the increasing volume fraction of PPL cups the lower the impact strength. The addition of

coupling agents did not have a significant effect on the PPC. The 30 wt.% PPL cups with 2 wt.% PRIEX

12031 however did show an increase in the energy absorbed. Even at the high strain rate the bonding

in this composite was strong enough to absorb some of the energy at impact.

iii) Flexural: Optimising Filler and Coupling Agent

The flexural results (Figure 6-53) do not show as high values compared to the PP/PPL data shown in

Figures 6-17 and 6-22. The reason for this is the flexural properties of the matrix because the increase

in properties due to the filler and coupling agents is very similar.

The addition of coupling agents shown in Figure 6-54 show that 2 wt.% is sufficient to increase the

mechanical properties whereas 3 wt.% does not increase the properties further. This is necessary to

know due to the cost savings on a larger scale as well as the optimal performance, as too much of a

coupling agent can have detrimental effects on the mechanical properties.

HDPE

90HDPE/10PPL

80HDPE/20PPL

70HDPE/30PPL

68HDPE/30PPL/2AC1687

67HDPE/30PPL/3AC1687

68HDPE/30PPL/2PRIEX12031

67HDPE/30PPL/3PRIEX12031

0

10

20

30

40

50

HDPE/ 0-30wt.% PPL/ 2-3wt.% AC and Priex coupling agents

Notc

hed

Char

py I

mpac

t E

ner

gy (

KJ/

m2)

Recipes


158

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

0

5

10

15

20

25

30

35

40

HDPE_PPL Cups 0-30wt.%_Flexural Strength

Polynomial Fit

Fle

xu

ral

Str

eng

th (

MP

a)


0.0

0.5

1.0

1.5

2.0

2.5

HDPE_PPL Cups 0-30wt.%_Flexural Modulus

Polynomial Fit

Flex

ural M

od

ulu

s (GP

a)

Figure 6-53: Flexural strength and Flexural modulus for PPCs between 0-30 wt.% PPL cup.

HDPE

HDPE/PPL Cups

2wt.%AC1687

2wt.%PRIEX12031

3wt.%AC1687

3wt.%PRIEX12031

0

5

10

15

20

25

30

35

40

45

Fle

xu

ral

Str

eng

th (

MP

a)


0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Flexural strength 30wt.% PPL Cups

Young's Modulus 30wt.% PPL Cups

Flex

ural M

od

ulu

s (GP

a)

Figure 6-54: Flexural strength and Flexural modulus for PPCs between 0-30 wt.% PPL cup with 2-3

wt.% AC 1687 and PRIEX 12031.


159

Without coupling the flexural strength and modulus values significantly increase. The modulus

increases by 100% and doubles to 2GPa. The strength increases by 10MPa. With the addition of a

coupling agent the strength values increase by another 5-10MPa. The modulus values increase by

approximately 200MPa. When the PPCs are stressed axially minimal increase in tensile strength is

observed with increasing volume fraction. However with flexural tests, the stresses experienced are

different and an increase in strength is observed. The coupling agents however do have a positive

effect and bond the matrix and filler as described in section 3.5. Adhikary et al., (2008) used recycled

HDPE with wood flour. The HDPE has a similar MFR. This research uses MAPE based coupling agents

ideal for use with HDPE and fibrous fillers. Adhikary et al., (2008) uses MAPP. Therefore a direct

comparison between the two can be difficult to comment on. The research by Adhikary et al., (2008)

showed flexural strength values that increased by 10 MPa with the use of a coupling agent, similar to

the PPL cups. However the increase could have been higher if a different coupling agent was used.

Some bonding has taken place even without a coupling agent suggesting the flakes are not just points

of weakness. Interestingly the wood flour can be seen to directly act as a point of weakness embedded

in the matrix with the tensile and flexural properties decreasing with increasing filler content. However

in PPCs in this research the mechanical properties increased with increasing filler content as shown in

Figure 6-53. It could be the PE content on the flakes and it could be the flakes themselves like the size

or the paperboard fibres could be that much better than wood flour. The higher the volume fraction

the more the PE coating is present and the higher the strength. Adhikary et al., (2008) noted that

recycled HDPE showed higher mechanical results than virgin HDPE indicating some further benefits to

use recycled polymers. The PPCs in this research exhibited ductile behaviour at low concentrations of

filler but the filler certainly decreased the elongation at break and increased the brittleness. Adhikary

et al., (2008) notes that this can be caused by the stress concentrations at the fibre ends along with

poor interfacial adhesion. Failure was seen at the interface in a brittle sudden manner with increasing

filler content. Adhikary et al., (2008) also comments on the wood content (cellulose, hemicellulose

and lignin). The aligned fibrils of crystalline cellulose with strong hydrogen bonds creates the high

stiffness properties. Lignin is reportedly removed from the paperboard and paper industry but is

known to bind the cellulose fibrils and therefore impart the stiffness. Adhikary et al., (2008) also

discusses the effect of water molecules on WPC. The wood has hydroxyl groups that can uptake water

with hydrogen bonding. The coupling agents help prevent uptake because the hydroxyl groups bond

with the MAH. The PPCs in this research in Chapter 7 show very little water absorption. This has huge

benefits to why PPC can be used as drying times can be significantly reduced saving energy. One side

of the PPL flakes are not coated but water absorption through protection of the surrounding matrix

also prevents uptake. This is a huge advantage because this protective PE layer can be seen a problem


160

for the recycling industry but for PPCs the thin PE layer could be advantageous. This is discussed

further in Chapter 7.

iv) Rheological: Optimising the Filler Content

Melt Flow Rate (MFR, g/10min) / Shear Rate vs. Viscosity

An estimation of the melt flow rate can be obtained through the shear rate vs. shear stress data. It is

worth noting the MFR behaviour even though the shear rate vs. shear stress analysis can tell you more.

The MFR is often a value referred to in data sheets and is often a quick reference guide for polymer

processing (Macdermott, 1997).

Figure 6-55: Shear rate viscosity curves for HDPE and PPCs with 0-30 wt.% PPL cups.

The increasing filler (PPL cup) content increases the viscosity of the melt as predicted. A huge increase

is seen with 30 wt.% fibres added to the HDPE matrix. The HDPE matrix does not have a high melt flow

and so increasing the filler content would increase the viscosity more preventing the molecules room

to flow. The addition of other additives (Figure 5-2) could be an option if further processing of these

composites was needed.

0 50 100 150 200 250 300

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

Vis

cosi

ty (

Pa

s)

Shear rate (1/s)

70wt.%_HDPE/30wt.%_PPL



HDPE


161

Kukaleva et al., (2003) show the blends of HDPE and LDPE do not alter the viscosity of the blend

indicating that the LDPE coating may not affect the viscosity in PPCs. It was also noted that during

extrusion the low viscosity minor component like LDPE may coat the die wall and provide lubrication.

In PPCs with HDPE the paper cups did not show a significant difference in viscosity at lower volume

fractions.

v) Thermogravimetric Analysis (TGA): Optimising the Filler

Figure 6-56 shows the higher the percentage of paper cup, the higher the weight loss with increasing

temperature. However any initial losses can be attributed to moisture loss. The rate of weight loss is

important. Approximately 1 wt.% weight loss up to 200oC is more than sufficient for extruding and

moulding. Severe weight loss starts to occur at approximately 275oC for the filler and 260oC for the

HDPE.

Figure 6-56: TGA showing weight loss over typical processing temperatures for HDPE based PPCs at 0-

30 wt.% PPL cups.

Araujo et al., (2008) researched HDPE composites with the curaua fibre. 3 wt.% was decided as the

point of initial weight loss. The HDPE used in the study by Araujo et al., (2008) was pure HDPE where

3 wt.% did not occur until over 400oC, whereas the recycled HDPE in this research showed significant

weight loss after 260oC. This is due to the recycled content and the material being put through multiple

0 100 200 300

97

98

99

100

101

102

103

Wei

ght

Per

cent

(wt.

%)

Temperature (oC)

90wt.% HDPE / 10wt.% PPL Cup_20oCp/m



HDPE_20oCp/m


162

heating cycles. The addition of coupling agents can actually make the composite less stable. The

coupling gents in this research do not make a difference to the thermal stability. Araujo et al., (2008)

found that one explanation for this could be the large interfacial interaction between the acid groups

of the maleic anhydride and the hydrophilic groups on the fibre surface. The large interaction also

encourages the degradation between the phases. Another explanation could be the peroxide used to

graft the maleic anhydride to the PE still being present.

6.6 High Density Polyethylene (HDPE) / Multilayer Carton Board (MCB) / Tetra Pak

6.6.1 Mechanical Properties

i) Tensile: Tensile Testing: Optimising Filler and Coupling Agent

Figure 6-57 shows that the tensile results are not as high as the PPL cups with HDPE in strength and

stiffness with coupling agents.

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

0

5

10

15

20

25

30

HDPE/TETRA_0-30wt.%

Linear Fit

Ten

sile

Str

eng

th (

MP

a)


HDPE/TETRA_0-30wt.%_2wt.% AC1687

AC 1687 2wt.%

AC 1687 3wt.% PRIEX 12031 3wt.%

PRIEX 12031 2wt.%

Figure 6-57: Tensile strength with increasing PPL Tetra Pak up to 30 wt.% with 2-3 wt.% PRIEX and AC

coupling agents.


163

Very similar results can be seen with PP and HDPE PPCs. The AC 1687 coupling agent provides more

stiffness to the composite but less strength whereas the PRIEX 12031 provides more strength and less

stiffness. This could be attributed to the structure of the polymer used to graft to the maleic anhydride.

Table 6-6: Tensile data of HDPE composites between 0-30 wt.% PPL Tetra Pak and 2-3 wt.% coupling

agents

Recipes

Volume Fraction

(Vf)

Tensile Strength

(MPa) Standard

Error

Young's Modulus

(GPa) Standard

Error

HDPE 0.000 21.4 0.102 0.777 0.0158

90wt.% HDPE/10wt.% TETRA 0.117 21.9 0.036 0.938 0.0181

80wt.% HDPE/20wt.% TETRA 0.230 23.1 0.105 1.13 0.015

70wt.% HDPE/30wt.% TETRA 0.338 24.6 0.162 1.55 0.0352

88wt.% HDPE/10wt.% TETRA/2wt.% AC1687 0.119 22.5 0.132 0.939 0.0152




68wt.% HDPE/30wt.% TETRA/2wt.% PRIEX12031 0.344 27.5 0.179 1.49 0.0183

67wt.% HDPE/30wt.% TETRA/3wt.% PRIEX12031 0.347 28.2 0.305 1.47 0.022


164

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

HDPE/TETRA_0-30wt.%

Polynomial Fit

Yo

un

g's

Mo

du

lus

(GP

a)


PRIEX 12031 2wt.%

PRIEX 12031 3wt.%

AC 1687 3wt.%

AC 1687 2wt.%

HDPE/TETRA_0-30wt.%_2wt.% AC1687

Figure 6-58: Young’s modulus with increasing PPL Tetra Pak up to 30 wt.% with 2-3 wt.% PRIEX and AC

coupling agents.

Table 6-6 and Figures 6-57 and 6-58 show that PPCs with Tetra Pak and a HDPE matrix are just as

strong as the PPCs with paper cups and HDPE. The level of coupling agent at high filler loadings does

not have a huge influence on the stiffness whereas a linear increase is shown with the strength data

in Table 6-6.


165

ii) Charpy Impact Energy (KJ/m2): The Effect of the Filler Content

0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

30

35

40

45

50

30wt.% PPC_2wt.% Priex12031

Char

py I

mpac

t E

ner

gy (

KJ/

m2)


0-30 wt.% PPC

0-30wt.% PPC_2wt.% AC1687

Figure 6-59: Impact testing of HDPE with PPL Tetra Pak and coupling agents.

The Charpy impact energy for the Tetra Pak based composites exhibit better toughness properties

than the paper beverage cups. This is due to the HDPE matrix having a higher toughness than the

WEEE PP.


166

iv) Flexural Testing of PPCs: Effect of Filler and Coupling Agent

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

0

5

10

15

20

25

30

35

40

HDPE/TETRA_0-30wt.%

Fle

xu

ral

Str

eng

th (

MP

a)


HDPE/TETRA_0-30wt.%_2wt.% AC 1687

Figure 6-60: Flexural Strength of Tetra Pak and HDPE based PPCs with AC 1687 as a coupling agent

The HDPE mixed with Tetra Pak results exhibit similar properties to the paper beverage cup and HDPE

composites. The increase is not as sharp up to 30 wt.% but the 30 wt.% values show higher values.

The aluminium could be seen to be points of weaknesses to a certain extent up to 20 wt.% and then

negligible at higher volume fractions. The addition of the coupling agent does not affect the results.

Without the coupling agent high flexural strengths are still achieved. Further trials with an increase in

the percentage of the coupling agent is required.

v) Density of PPCs with HDPE Matrix

All density measurements are shown in Table 10-1 in the appendix. The filler increases the density but

the volume of the filler and coupling agent does not make a difference.


167

6.7 Conclusions

- Optimisation of PPCs has shown that 3 wt.% coupling agent shows the highest mechanical

properties for paper cup based PPCs, whilst 2 wt.% of coupling agent for HDPE based PPCs

exhibits the highest mechanical properties.

- The two key PPC blends were recipe 7 (67wt.% WEEE PP / 30wt.% PPL Cup / 3wt.% Struktol)

and recipe 14 (68wt.% HDPE / 30wt.% PPL Cup / 2wt.% PRIEX 12031) from trial 2b).

- The 907P coupling agent from Honeywell also improved the properties of the PPC blends with

paper cups and Tetra Pak fillers.

- PPCs are in good agreement with models for stiffness at higher aspect ratios.

- The data shows that PPCs are in good agreement with the Oswald-de Waele power-law model.

- No significant weight loss is shown over the processing temperatures even at prolonged

residences times.

- Comparing the PPCs in this research to the WPC industry shows that PPCs can compete with

this industry. Some fillers used have a higher starting modulus than paper fibres but Table 3-

3 shows the typical properties across a range of WPC samples. The data in this research is

comparable in terms of stability during processing and mechanical properties.

Final Comparisons: Optimum Blends of PPCs Chapter 7

168

Chapter 7

7. Final Comparisons: Optimum Blends of PPCs

7.1 Thesis Summary

The work reported in Chapters 5 and 6 has addressed the objectives outlined in Chapter 2. This

research has shown that PPCs can be extruded and moulded with relatively high volume fractions of

PPLs. This produces excellent reinforcing properties in PPCs producing mechanical properties similar

to data for WPCs. The fillers used were either paper cups or Tetra Pak in flake form, which show a

reinforcing effect when combined with coupling agents to improve the matrix filler interface. This

research demonstrates that a variety of recycled plastic and PPL waste streams can be used to produce

PPCs.

Chapter 5 reported on materials characterisation and initial trials. Chapter 6 reported on additional

experiments to develop the optimum recipes for PPCs. This chapter includes further analysis of the

best performing PPCs in terms of mechanical properties.

7.2 Optimum Blends of PPCs

The blends of materials that produced the optimum combination of mechanical properties are shown

in Table 7-1.

Table 7-1: PPCs blends that showed the highest mechanical properties

Matrix Filler Coupling agent Trial Key Figures

WEEE PP PPL Cups Struktol 2b) recipes 6 and 7 6-10

HDPE PPL Cups PRIEX 12031 2b) recipe 14 6-48, 6-49

Other High Performing PPCs

WEEE PP PPL Cups 907P 2 b) recipe 2 6-6

WEEE PP PPL Cups 907P 2 a) recipes 7, 9, 10 6-7 6-12,6-21

WEEE PP MCB 907P 2 a) recipe 21 6-42

The PPCs in Table 7-1 exhibit excellent mechanical properties and outperformed other trial PPCs. The

Struktol based PPCs exhibited excellent tensile and flexural strengths. Recipe 14 with an HDPE matrix

exhibited excellent properties. Recipe 2 from Trial 2 b) (58 wt.% WEEE PP / 40 wt.% PPL Cups / 3 wt.%

907P) had excellent tensile properties. However in terms of the production of a commercial product,

this particular PPC requires further optimisation. The high filler content at 40 wt.% is likely to cause

processing problems during extrusion involving bridging effects during feeding and die pressure


169

issues. From Trial 2a) the recipes 7, 9 and 10 in Table 7-1 have 30 wt.% blends and these were

significantly easier to extrude than the 40 wt.% samples. Recipe 7 was ideal in terms of processing

because it uses less coupling agent and would therefore be lower cost. Increasing the amount of

coupling agents above 2 wt.% did not improve the mechanical properties, as shown in Chapter 6.

The PE based coupling agents produced variable mechanical properties. AC 1687 should be used if

high stiffness is required but for high strengths PRIEX 12031 should be used. The same affect is seen

with the MCB/Tetra Pak filler. This affect can be attributed to the polymer that is used to graft to the

MAH and copolymerize and interlock with the HDPE and this affects the overall performance of the

PPC.

While many current WPCs use virgin wood fibres the PPCs developed in this research use waste

materials. This chapter reports additional experiments to further characterise the PPCs developed.

7.2.1 Creep Analysis

There is limited data available relating the effects of coupling agents, filler percentage and mechanical

properties to creep behaviour despite the fact that long and short term creep properties are critically

important in many applications (Lee et al., 2004).

Creep is the time dependant change in strain under constant stress. WPC materials are often used for

decking and other products that carry loads during service life and PPCs have potential to be used in

similar types of applications. A major concern for any new material is the long term stability under

constant applied stress (Raghavan and Meshii 1997; Zhu et al., 2013). In this research short term creep

testing has been completed.

i) WEEE Polypropylene (PP) / Paper Plastic Laminates (PPLs)

The creep behaviour of PP was initially analysed to understand how the base PP material behaves.

Under tensile stress the polymer matrix is stressed axially. The amount of stress applied and the

temperature greatly affect the orientation of the polymer molecules (Raghavan and Meshii 1997).


170


of its UTS and at 400C for 30 minutes with 30 minutes recovery time. b) Engineering stress vs. strain

for WEEE PP stressed at 20-60% of its UTS.

0 500 1000 1500 2000 2500 3000 3500 4000

0

1

2

3

4

5

6

7

Engin

eeri

ng S

trai

n (

%)

Time (s)

WEEE PP_20% UTS

30minutes hold time

30mins recovery

WEEE PP_40% UTS

30minutes hold time

30mins recovery

WEEE PP_60% UTS

30minutes hold time

30mins recovery

WEEE PP_40% UTS_40oC

30minutes hold time

30mins recovery

0 1 2 3 4 5

0

3

6

9

12

15

Engin

eeri

ng S

tres

s (M

Pa)

Strain (mm)

WEEE PP_20% UTS

30minutes hold time

30mins recovery

WEEE PP_40% UTS

30minutes hold time

30mins recovery

WEEE PP_60% UTS

30minutes hold time

30mins recovery


171

The Steady State Creep Rate

Creep in polymer composites is highly dependent on the viscoelasticity of the polymer. Figure 7-1

shows how temperature affects the amount of creep and the creep rate. The higher the creep-rate

the more stress the material is under and the more deformation occurs. The recovery of the strain

after deformation shows the extent that creep has occurred.

Key material properties that control creep include molecular orientation, crystallinity and the

experimental conditions such as the stress, temperature and humidity. Creep within polymers is due

to the mixture of elastic deformation and viscoelastic deformation.

Steady State Creep Rate

�̇� = ∆𝜺

∆𝒕

= 𝜺𝟏𝟕𝟎𝟎− 𝜺𝟓𝟎𝟎

𝒕𝟏𝟕𝟎𝟎−𝒕𝟓𝟎𝟎

Table 7-2 shows the steady state creep rate of WEEE PP and the PPC with Struktol as its coupling agent

at 2 wt.%. The higher the constant stress (as a percentage of the UTS) the higher the creep rate.

Table 7-2: Steady state creep rate for WEEE PP and PPC with 2 wt.% Struktol and 30 wt.% PPL, over a

range of constant stresses at laboratory temperature and 400C.

% UTS Steady State Creep Rate (s-1)

WEEE PP 20% 6.67x10-5

40% 2.08 x10-4

60% 6.67 x10-4

40oC 20% 1.16 x10-3

40% 2.46 x10-3

% UTS Steady State Creep Rate (s-1)

Struktol 20% 5.00 x10-5

40% 1.50 x10-4

60% 4.50 x10-4

40oC 40% 5.43 x10-4

At elevated temperatures the creep rate is increased with increasing constant stress rate. The creep

rate is lower in the composite due to the addition of the fibres. The composite can withstand higher

stresses due to stress being preferentially transferred to the fibres. The WEEE PP can deform more


172

easily because it is a weaker material and changes in molecular orientation of PP chains are not being

prevented by the fibrous filler.

The average yield strength for the Struktol recipes and WEEE PP at laboratory temperature were

approximately 20 MPa and 12 MPa respectively. The 60% creep tests were run at stresses very close

to the yield points shown in Figures 7-1 and 7-2 because of the strain in the steady strain region was

still increasing. The composite and polymer chains are deforming and do not reach steady state

because the stresses are too high, which is also the case at elevated temperatures. The 20% UTS and

40% UTS experiments reach a more defined steady state region.

The steady state creep rate occurs in stage two of the strain vs. time creep curve as shown in Figure

7-6. During this stage the creep rate is small as the strain increases very slowly with time. The creep

rate depends highly on the stress applied and the temperature. Table 7-2 shows that creep rate

changes with stress and temperature and that at higher temperature the creep rate increases.

-500 0 500 1000 1500 2000 2500 3000 3500 4000

0

1

2

3

4

5

6

Engin

eeri

ng S

trai

n (

%)

Time (s)

Struktol 3%_20% UTS

30minutes hold time

30mins recovery

Struktol 3%_40% UTS

30minutes hold time

30mins recovery

Struktol 3%_60% UTS

30minutes hold time

30mins recovery

Struktol 3% _40OC_40% UTS

30minutes hold time

30mins recovery


its UTS and at 400C for 30 minutes with 30 minutes recovery time.

The steady state creep rate increases as the constant stress applied to the PPCs increases due to the

higher stresses on the interface of the composite and realigning of the polymer chains.


173

The PPC blends were tested at 40oC as shown in Figures 7-1 to 7-2. The temperature controller

collected data every 12 seconds to maintain the correct test temperature. The average temperature

of the sample was measured as in Chapter 4 and this averaged 40oC (Figure 7-3).

0 50 100 150 200 250 300

0

10

20

30

40

50

60

70

Tem

per

atu

re (

oC

)

Time (s)

Temperature_Controller

Temperature_Sample

Figure 7-3: Average temperature of the sample being tested in the creep test at 40oC.


174

ii) High Density Polyethylene (HDPE) / Paper Plastic Laminate (PPL)

-500 0 500 1000 1500 2000 2500 3000 3500 4000

0

1

2

3

4

5

6

Engin

eeri

ng S

trai

n (

%)

Time (s)

HDPE_60% UTS

30minutes hold time

30mins recovery

HDPE_40% UTS

30minutes hold time

30mins recovery

HDPE_20% UTS

30minutes hold time

30mins recovery


its UTS for 30 minutes with 30 minutes recovery time

The creep behaviour for HDPE in Figure 7-4 is similar to the deformation in the WEEE PP in Figure 7-1.

Data for recipe 14 shown in Figure 7-5 a) exhibits similar behaviour as in Figure 7-2. Approaching the

yield stress the deformation of the material is high and it takes longer to reach the steady state period

of creep.

Figure 7-5 b) shows the effect of PRIEX 12031 addition. The stress at 40% is higher in this composite

because the strength of the PPC is higher than the composite without coupling agent. The composites

show a similar recovery and creep behaviour over the duration of the test.


175

-500 0 500 1000 1500 2000 2500 3000 3500 4000

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

Engin

eeri

ng S

trai

n (

%)

Time (s)

HDPE/30% PPL_2% PRIEX12031_20% UTS

30minutes hold time

30mins recovery


30minutes hold time

30mins recovery


30minutes hold time

30mins recovery

-500 0 500 1000 1500 2000 2500 3000 3500 4000

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Engin

eeri

ng S

trai

n (

%)

Time (s)


30minutes hold time

30mins recovery

HDPE/30% PPL_40% UTS

30minutes hold time

30mins recovery


of its UTS for 30 minutes with 30 minutes recovery time for HDPE/30 wt.% PPL cup / 2 wt.% PRIEX

12031. b) Engineering Strain vs. Time curve for HDPE/30 wt.% PPL cup /2 wt.% PRIEX 12031 vs

HDPE/30 wt.% PPL cup.


176

Creep can alter the dimensions of a material which can lead to product failure. Primary creep is almost

instantaneous and may only last a few seconds. The steady state region of creep can last for years.

Figure 7-6 shows relatively short steady state creep data.

The optimum recipes developed in this research were subjected to high stress creep testing over 48

hours at 60% UTS. The yield stress of recipe 14 was 20.7 MPa. The experiment was run at 60% of the

UTS value of 32 MPa which was 19.2 MPa.

-5000 0 5000 10000 15000 20000 25000 30000 35000

0

10

20

30

40

50

60

70

En

gin

eeri

ng

Str

ain

(%

)

Time (s)

HDPE 30wt.% PPL_ 2wt% PRIEX 12031

Pri

mar

y C

reep

Steady State Creep

Ter

tiar

y C

reep

Figure 7-6: This shows relatively short steady state creep data on HDPE/30 wt.% PPL cup / 2 wt.%

PRIEX 12031 subjected to high stress creep testing over 48 hours at 60% UTS.

The short term creep test used a 48 hour hold and a 12 hour recovery time. After 6.08 hours recipe

14 failed at the constant applied stress of 19.2 MPa.

After the steady state period the tertiary period occurs rapidly. The failure can be very sudden as

shown in Figure 7-6. Engineers often use a 25% strain as the design limit for products so that tertiary

creep does not occur.


177

Steady State Creep Rate

𝜀̇ = ∆𝜀

∆𝑡

equation 7-1

= 𝜀30000− 𝜀1000

𝑡30000−𝑡1000

= 11.7−5.96

29000

= 0.00019793103 s-1

Strain at the start of steady state creep: 5.96%

Strain at end of steady state: 11.7%

Total strain range: 5.74%

Using a 25% safety margin

Useable product life range: 5.74 x 100

125 = 4.592

End of the useable product life range: 5.96 + 4.592 = 10.552%

At 10.6% the test time = 2.19x104 s

= 365 minutes

End of product life = 6.083 hours

Ideally a material should be designed to experience stress well below the yield point. Beyond the yield

point the polymer no longer behaves elastically and starts to deform. The PPC blend in Figure 7-6

experienced a stress very close to the yield point. In practice the product being made should not

experience such stresses although the mechanical property limits of the material need to be clearly

defined.


178

7.2.2 Fracture Toughness

Figure 7-7: Fracture toughness of WEEE PP based PPCs with different PPLs and coupling agents.

Figure 7-7 shows the fracture toughness of PPC recipes using WEEE PP with PPL cups and Tetra Pak.

The fracture toughness data supports the previous observations reported in Chapter 6 that the PPL

cups outperform the Tetra Pak. The coupling agents significantly enhance the toughness. Crack growth

is inhibited due to the bonding between the filler and matrix phases. The critical strain energy release

rate expressed in Figure 7-9 and 7-10 help explain the fracture toughness results. The higher the load

applied to break the material the more energy is released. The critical strain energy is at the point of

crack propagation. The 3 wt.% Struktol PPC requires a higher amount of energy to initiate crack

propagation due to the stronger interfacial bond.

KIC and GIC values of MDF have been reported as 1.81 MPa √m. and 970 J/m2 respectively (Niemz et

al., 1997). The values for the PPCs developed in this research were significantly higher than these

values. MDF is widely used and as a result there are likely to be many applications for the PPCs

developed from this research. The fracture toughness of WPCs using short hemp fibres with a PLA

matrix have been reported (Pickering et al., 2011). A variety of loading rates, fibre contents, fibre

treatment and the matrix crystallinity were investigated. It was shown that the interfacial shear

strength increased with alkali treatment. Treating the fibres removed any non-cellulosic based

WEEE PP30wt.%PPL

2wt.%_907P

3wt.%_PRIEX25097

3wt.%_STRUKTOL

TETRA/2wt.%907P

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

WEEE PP_30wt.%_PPL Cups/TETRA with coupling agents

Fra

cture

Toughnes

s (M

Pa.

m1/2)

Recipes


179

material which improved the bonding. During paperboard manufacture lignin is removed and further

treatment may remove contaminants that may exist in waste packaging.

From Figure 7-8 it is clear that the 2 wt.% PRIEX recipe has the highest fracture toughness of the HDPE

based composites. The Struktol based PPC has the highest toughness of the PPCs examined with WEEE

PP. The HDPE / Tetra Pak / 2 wt.% PRIEX 12031 blend exhibited a very high critical strain energy release

rate that. This is partly due to the HDPE matrix having a higher fracture toughness than WEEE PP. The

fillers showed more of an effect in terms of fracture toughness when added to the PP matrix than the

HDPE which already had a high toughness.

Figure 7-8: Fracture toughness of HDPE based PPCs with different PPLs and coupling agents.

HDPE30wt.%PPL

2wt.%PRIEX12031

TETRA/2wt.%PRIEX12031

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00


Fra

cture

Toughnes

s (M

Pa.

m1/2)

Recipes

HDPE_30wt.%_PPL Cups/TETRA with coupling agents


180

Figure 7-9: Critical strain energy release rate of WEEE PP based PPCs with different PPLs and coupling

agents.

Figure 7-10: Critical strain energy release rate of HDPE based PPCs with different PPLs and coupling

agents.

WEEE PP30wt.%PPL

2wt.%_907P

3wt.%_PRIEX25097

3wt.%_STRUKTOL

TETRA/2wt.%907P

0

500

1000

1500

2000

2500

3000


Cri

tica

l S

trai

n E

ner

gy R

elea

se R

ate

(J/m

2)

Recipes

HDPE30wt.%PPL

2wt.%PRIEX12031

TETRA/2wt.%PRIEX12031

0

500

1000

1500

2000

2500

3000

3500


Cri

tica

l S

trai

n E

ner

gy R

elea

se R

ate

(J/m

2)

Recipes

HDPE_30wt.%_PPL Cups/TETRA with coupling agents


181

Figure 7-11 shows the fracture toughness testing of recipe 7 from trial 2 b) (3 wt.% Struktol). The crack

can be seen to extend. Once the critical strain energy release rate is reached crack propagation occurs.

The energy release rate is the reduction in elastic energy associated with a crack increasing per unit

area of crack. Five samples of each recipe were tested and consistent results were obtained.

Figure 7-11: Fracture toughness testing of WEEE PP / 30 wt.% PPL / 3 wt.% Struktol showing crack

growth during loading.

Crack growth


182

7.2.3 Water Absorption

The water absorption and moisture uptake of WPCs and PPCs is an important issue because of the

hydrophilic nature of the fibrous fillers used.

Figure 7-12: Percent increase in mass after water absorption of PP based PPCs at 30 wt.% PPL cups


Figure 7-12 presents the increase in mass of samples due to water absorption and shows that silane

based coupling agents give improved water uptake compared to MAPP and PEI based coupling agents.

Figure 7-13 shows that the coupling agents make a difference to the amount of water absorbed. This

is because of fewer sites available for moisture uptake because bonding has taken place at the filler

matrix interface where water molecules may have previously entered via the –OH groups on the filler

surface. Figure 7-12 provides additional evidence to support the use of PPCs based on the Struktol

coupling agent.

2wt.% 907P4wt.% 907P

2wt.% PRIEX 25097

2.5wt.% VTES

1.5wt.% PEI

2wt.% STRUKTOL

3wt.% STRUKTOL

0.0

0.5

1.0

1.5

2.0

2.5

3.0

wt.% Increase After 24 Hours_30wt.%_PPL

Per

cent

Incr

ease

in M

ass

(%)

Recipes





183

Figure 7-13: Percent increase in mass after water absorption of HDPE based PPCs at 30 wt.% PPL cups


Table 7-3 shows the flexural strength and modulus of samples after moulding and after water

adsorption. The data indicates that even after 6 months of immersion in water the properties do not

change significantly. No more than a 20% reduction across strength and stiffness. This is a significant

advantage over many WPCs. The reason minimal absorption has taken place is due to the hydrophobic

matrix that encapsulates the fillers during extrusion and protects them. The PE coating on the filler is

also designed to prevent fluid uptake. Retaining this coating on the filler may not only help keep the

flakes together but may also prevent the fibres absorbing moisture.

HDPE

30wt.%PPL Cups

2wt.%Bondy

2wt.%AC1687

2wt.% PRIEX

0.0

0.5

1.0

1.5

2.0

2.5

3.0 wt.% Increase After 24 Hours_30wt.%_PPL

Per

cent

Incr

ease

in M

ass

(%)

Recipes





184

Table 7-3: Flexural strength and modulus values of PPCs after 4032 hours immersed in water

Figure 7-14 shows that the increase in water uptake is a function of the filler content. The higher the

filler content the higher the water uptake. Without bonding at the filler matrix interface there would

be a higher chance of water molecules entering the material if the fillers were at the surface of the

matrix. Figure 7-15 a) and b) indicate whether the amount of coupling agent has an effect at 30 wt.%

and 40 wt.% PPL cup content. The results suggest that the coupling agents slightly reduce the water

uptake and the amount of coupling agent does not make a significant difference. The 4 wt.% addition

of MAPP seems to have absorbed the least amount of water based on the percentage increase in

mass. It has previously been demonstrated that 5 wt.% MAPP helped reduced water uptake by up to

75% for hard wood fibre PP composites (Bledzki and Faruk, 2004).

Percentage Change

After moulding

After water absorption

Strength Modulus

Recipes Flexural Strength

(MPa)

Flexural Modulus

(GPa)

Flexural Strength

(MPa)

Flexural Modulus

(GPa) % change % change

PP 30.57 1.12 30.92 1.13 -1.17 -0.87

90wt.%WEEE/10wt.%PPL

37.64 1.42 36.65 1.38 2.61 2.61


34.34 1.85 36.98 1.85 -7.69 -0.49


36.25 1.93 37.64 1.85 -3.83 4.60

60wt.%PP_40wt.%PPL

37.75 2.48 37.66 2.01 0.24 18.91

60wt.%PP_40wt.%PPL_2wt.% 907P

49.97 2.60 43.05 2.13 13.85 18.06


50.00 2.60 45.72 2.27 8.57 12.79


49.31 2.60 46.25 2.18 6.22 16.21


39.56 2.13 36.50 1.76 7.73 17.51


42.97 2.18 42.95 2.06 0.03 5.51


44.16 2.18 43.13 2.13 2.32 2.34


44.46 2.26 45.12 2.11 -1.48 6.52


185

Figure 7-14: Percent increase in mass after water absorption of PP based PPCs between 0-40 wt.% PPL

cups.

-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

wt.% Increase After 2 Hours P

erce

nt

Incr

ease

in M

ass

(%)


wt.% Increase After 24 Hours




0 1 2 3 4

0

1

2

3

4

5 wt.% Increase After 2 Hours_40wt.%_PPL

Per

cent

Incr

ease

in M

ass

(%)

MAPP (wt.%)






186

Figure 7-15: a) Percent increase in mass after water absorption of PP based PPCs at 40 wt% and 1-4

wt.% of 907P, b) Percent increase in mass after water absorption of PP based PPCs at 30 wt% and 1-4

wt.% of 907P.

The tensile properties of a high performing recipe from Table 7-1 and the best performing composite

in Figure 7-15 is shown in Figure 7-16 after water absorption. A slight decrease can be seen in the

strength of the composite. The stiffness properties are unaffected. The small amount of water uptake

causes the filler material to weaken which can act as points of weakness during the tensile test and

this limits the amount of energy that can be absorbed.

0 1 2 3 4

0

1

2

3

4

5


Per

cent

Incr

ease

in M

ass

(%)

MAPP (wt.%)






187

Figure 7-16: Engineering stress strain data after water absorption for PP based PPCs at 40 wt% and 4

wt.% of 907P.

7.2.4 Material Comparisons: CES EduPack

The highest mechanically performing recipes in this research were obtained using recipe 7 (67 wt.%

WEEE PP / 30 wt.% PPL Cup / 3 wt.% Struktol) and recipe 14 (68 wt.% HDPE / 30wt.% PPL Cup / 2 wt.%

PRIEX 12031) from trial 2b). The properties of these PPCs were compared to materials that have similar

mechanical properties such as high impact ABS and impact modified polybutylene terephthalate (PBT)

using data obtained from the CES EduPack. The tensile and fracture toughness properties were

considered. Sobczak et al., (2012) noted that the density of short carbon fibre and short glass fibre

composites ranges from 1700 to 2800 kg/m3 whereas WPCs range between 1300-1600 Kg/m3 while

PPCs are in the region of 1000 – 1010 Kg/m3. Lowering the density compared to competitive markets

such as WPCs is attractive for companies producing commercial products for light weighting their

goods.

0.00 0.01 0.02 0.03 0.04 0.05 0.06

0

5

10

15

20

25

30E

ngin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

WEEE PP_40wt.%_4wt.%907P_4032 Hours

WEEE PP_40wt.%_4wt.%907P


188

7.3 Final Remarks and Conclusions

The polymer matrices used in this research can both be used to form PPCs. In terms of processing the

WEEE PP had improved flow properties with a higher MFR. The HDPE had higher toughness. If the

temperatures are too high during processing the HDPE grade used would start to degrade as shown

in Figure 7-17.

Figure 7-17: TGA data showing weight loss against increasing temperature for WEEE PP and HDPE.

The processing temperatures for PPCs do not reach 250oC but moulding temperatures have been

known to reach 240oC. As long as low shear technology is used the degradation of the filler can be

prevented. An additive may be degrading here. Further tests should be considered as HDPE should be

stable here and be similar to the PP curve.

The fillers used in this research show bonding capabilities and even without coupling agents some

bonding occurs. This is because the PE coating reacts with the polymer matrix preventing fillers

becoming points of weakness as can be seen in Figure 7-18. The Tetra Pak filler shows more bonding

without coupling agents than the PPL from paper cups.

0 100 200 300 400 500

0

20

40

60

80

100

WEEE PP_20oC p/m_20-500

oC

Wei

ght

Per

cent

(%)

Temperature (oC)

Onset of degradation

HDPE_20oC p/m_20-500

oC


189

0.0 0.1 0.2 0.3 0.4 0.5

0

5

10

15

20

25

30

WEEE PP_Paper cups 10wt.%_40wt.%

Polynomial Fit

Ten

sile

Str

ength

(M

Pa)


WEEE PP_Tetra 10wt.%_40wt.%

Polynomial Fit

HDPE_Paper cups 10wt.%_30wt.%

Polynomial Fit

HDPE_Tetra 10wt.%_30wt.%

Polynomial Fit

Model Assuming No Adhesion

Polynomial Fit

Model Assuming Adhesion

Polynomial Fit

Figure 7-18: Modelling PPC tensile strength.

The strength of the composite depends on the reinforcing fillers with the weakest point determining

the strength. Fillers can cause points of stress concentration and also a reinforcing effect prohibiting

crack growth. Figure 7-18 assumes no adhesion between the filler and matrix. The PPCs in Figure 7-

18 do not have coupling agents. Further research with coupling agents shows that paper cups react to

the coupling agent at the interface. The model shows decreasing strength with increases in the volume

fraction of filler because if no adhesion is assumed then the filler would be points of stress. However

this data highlights the reinforcing capabilities of PPLs without coupling agents and that the PPLs do

not act as points of weakness at increasing volume fractions. At low volume fractions the PPL and

WEEE PP matrix agree with the no adhesion model in equation 3-9. Equation 3-10 assumes no

adhesion and produces the lower bound properties of the composite. However the upper bound

assumes the strength of the matrix as the maximum strength because the matrix absorbs the loading

in this model. The behaviour of the PPCs does not agree with this therefore indicating that PPLs take

some of the load from the matrix and are an effective reinforcement.

Equation 3-11 assumes some adhesion. The data for the PPCs does not lie close to this model, and

therefore significant adhesion can be assumed even without coupling agents. This indicates some of

the stress applied to the composite is transferred to the PPLs.


190

The models in Figure 7-18 do not fit PPC data. Applying composite theory to PPCs can help predict the

properties PPCs may have. Since the failure strain of the filler is lower than the matrix, the behaviour

can be assumed to obey Hooke’s law until failure of the filler. This occurs at a stress given by the

composite elastic modulus multiplied by the failure strain of the filler.

Ec x ԑF’ equation 7-2

Where,

EC = Elastic modulus of the composite

Vf x Ef + (1-Vf)Em

ԑF’ = failure strain of the filler

σ𝑓

𝐸𝑓

0.0 0.2 0.4 0.6 0.8 1.0

0

5

10

15

20

25

30

Str

eng

th (

MP

a)


failure =matrix w/o filler

failure=point where filler fails in matrix

Strength Prediction

Figure 7-19: Predicting the strength of paper cups in a PP matrix


191

The black line moving from left to right in Figure 7-19 shows the point where the filler fails in the

matrix. It is given by the elastic modulus of the composite multiplied by the failure strain of the filler.

Depending on the volume fraction of fillers the matrix can still survive if the filler fails or debonds from

the matrix interface. In this case failure occurs when the matrix fails. The fillers leave holes in the

matrix once failed. Therefore it is not the matrix strength but the strength is governed by:

σ m x (1-Vf) equation 7-3

In Figure 7-19 this is the line going from left to right. This indicates there are two modes of failure.

Either the composite fails when the filler starts failing or the filler fails and the matrix still continues

to absorb load. However both of the criteria above (equations 7-1 and 7-2) need to be met for failure

to occur. The highest values from equations 7-2 and 7-3 gives the strength of the PPC.

Where the lines cross in Figure 7-19, the failure mechanism changes. The matrix survives with the

filler failing at low volume fractions changing to the matrix failing as soon as the filler fails. For

reinforcement the composite strength must show values higher than the matrix strength. This is

known as the critical volume fraction. In Figure 7-18 the PPCs show reinforcement, indicating the

critical volume fractions are reached even at low volume fractions except for the PP / paper cups at

10 wt.% (Hull and Clyne, 1996).

7.3.2 Conclusions of Optimum Blends of PPCs

The optimum blends of PPCs in terms of mechanical properties in this research were recipe 7

(67 wt.% WEEE PP / 30 wt.% PPL Cup / 3 wt.% Struktol) and recipe 14 (68 wt.% HDPE / 30 wt.%

PPL Cup / 2 wt.% PRIEX 12031) from trial 2b).

The Creep behaviour of PPCs is affected by temperature. When PPCs are stressed over a

period of time close to their yield point, the creep rate increases and deformation of the PPC

is higher.

The fracture toughness of the PPCs behaves in a similar manner to the other mechanical tests.

The PRIEX 12031 and the Struktol produced high results. The HDPE matrix was tougher than

the PP matrix and the 40 wt.% PPL Tetra Pak recipe with 2 wt.% PRIEX 12031 could absorb a

large amount of energy before fracture.

The water absorption of PPCs is very low. The PE coating on PPLs is suspected to add to the

prevention of water uptake. Silane based coupling agents work better than MAPP and PEI.

PPCs compete with some high engineered based materials.

Conclusions and Further Work Chapter 8

192

Chapter 8

8. Conclusions and Further Work

8.1 Conclusions

The aim of this research project was to develop new paper plastic composites (PPCs) using paper

plastic laminates (PPLs) and polymers from different waste streams. This requires a detailed

understanding of composition, processing, microstructure and properties.

Disposable PPLs can be processed into flakes and extruded to form PPCs with enhanced

mechanical properties.

Up to 40 wt.% PPL flakes have been incorporated into a PP matrix with increasing mechanical

properties, indicating many potential applications. Commercial realisation can be along the

lines of pallets, decking and automotive trim.

PPC properties compete with high performance materials after comparisons have been made

to current literature. The PPC properties obtained in this work compete with those found in

Table 3-3.

The optimum PPC blends in this research consist of

o 67 wt.% WEEE PP / 30 wt.% PPL Cup / 3 wt.% Struktol

o 68 wt.% HDPE / 30 wt.% PPL Cup / 2 wt.% PRIEX 12031

o Tensile strengths over 30 MPa, flexural strengths over 50 MPa and Young’s modulus

values over 2.2 GPa were obtained.

The use of a coupling agent is essential to obtain improved properties. Struktol coupling

agents improved the mechanical properties and had a significant effect on the surface of the

PPCs during processing which reduced melt fracture.

907P MAPP from Honeywell was the highest performing MAPP based coupling agent. 3 wt.%

addition of 907P MAPP was found to be optimum.

Fracture surfaces indicate that coupling agents added at critical levels results in fracture of

PPL flake rather than pull out. The work to fracture increases by a factor of 5. Some flake pull-

out is still evident at high volume fractions.

Water absorption behaviour of PPCs is very low compared to other WPCs in the literature

removing the necessity to dry the composites.

Instead of separating the PPL for fibres in paper production which requires a lot of energy and

water, this research shows a viable alternative solution. This research emphasises the


193

advantages of keeping the PPLs together. A small amount of LDPE from the PE coating is

advantageous rather than a hindrance.

PPCs are lightweight and show high mechanical properties. PPLs are used all over the world

every day and have shown excellent reinforcing properties. Using virgin wood fibres should

not be an option as useful resources from the waste stream are available.

The use of PPL flakes derived from disposable cups for reinforcing plastics is a resource

efficient alternative that may have significant environmental benefits compared to current

disposal options.

The work presented in this thesis does not suggest that the correct end of life treatment for PPLs

should be PPCs, but offers an alternative to other methods shown in Chapter 3. Enormous volumes of

PPLs are currently being overlooked globally yet they hold high quality fibres with retainable

properties. By creating another end of life option for PPLs is not only competitive which drives business

innovation; it also offers to other industry sectors globally, a material that has many green credentials.

The advantages include saving CO2 and CH4 emissions that currently enter the environment and a new

lighter composite with high mechanical properties. Companies should take responsibility for what

they sell and promote the recycling of PPLs that are ending up in landfills. With correct collection

systems in place the consumer could then see the benefit of recycling their PPLs. Once consumers see

an end goal for their waste they would be more likely to recycle. The materials used in this research

are everyday products that are overlooked and thought of as waste. It is about time that we focused

on the products that are all around us and stop disposing of these high quality materials. The research

here proves that recycled materials have useful properties and should be seen as resources.

Compatibilisation adds a cost but the majority of the composite utilises recycled material.

8.2 Recommendations for Further Work

The potential of PPCs is shown in this research. However extensive further work is possible to

investigate a number of avenues for PPCs. Section 10.5 shows key areas that should be investigated

further:

The recyclability of PPCs

Filler Shape

Processing equipment

Contaminated PPLs

Pallet manufacture


194

8.2.1 Recyclability

A full scale trial needs to be done on commercial products such as pallets. The pallets should be used

pallets that have experienced loads and have been in service. They then need to be ground up and

remoulded numerous times to assess the mechanical properties, stability and life cycle of this

composite material.

The end of life disposal of PPCs is important because this whole research is based on recycling of waste

materials. The results in section 10.5 were designed to try and simulate recycling of PPCs. The recipes

went through three cycles of grinding, and moulding back into test bars for analysis. The results show

that further optimisation is needed. The recycling conditions of real life scenarios are important to

test. This includes mixing with other waste and applying stress to the product before mechanically

recycling the material. Further trials should try and simulate the stresses and degradation experienced

in a typical service life of PPCs depending on the product application. The effect on the rheology of

the composites and thermal stability should also be researched in more detail including the effect of

the filler and coupling agent.

8.2.2 Filler Shape

The next step would be to increase the surface area of the filler by grinding the flake further. The

effects on the reinforcement of the filler can be determined by the mechanical properties. Further

trials will be made on micro sizing the filler content. A potential trial is being planned for micro sizing

the fillers. This is necessary because a failure point identified in this research for PPCs is the

agglomeration failure. Feeding issues at high volume fractions may also be improved. The important

thing is not to add too many processing steps which are why the flakes were trialled. Further questions

would be how the micro-sizing affects the failure mechanism, the PE coating, the water absorption

and wetting of the filler through coupling agents.

Early trials were completed on the filler size by Nextek Ltd. Section 10.5 shows the effect of increasing

the paper cup size to 10mm x 3mm which were blended in a PP matrix at 10 wt.%. However the shape

of the filler should be investigated further with the effects of the filler and coupling agent content.

The breakdown in the extruder of the larger filler size should also be analysed further to understand

the compounding behaviour.

8.2.3 Processing Equipment

The extruders used in this research are laboratory based at universities. The twin screw extruders used

have been very capable of producing PPCs. However a larger trial should be completed on extruders

especially designed for this type of fibrous material. The low shear capabilities of the extruder from


195

MAS shown in Figure 10-28 are worth investigating further. A higher volume fraction of filler may then

be able to be added to the polymer matrix.

8.2.4 Contaminated PPLs

Further work must be completed on contaminated disposable beverage cups. Contaminant removal

is important and should be analysed further. The MCB materials in this research were used samples

but did not go into the waste stream. A large trial with cups entering a public waste stream is

needed.

A small trial took place using contaminated PPL beverage cups, with 2 Kg collected from one

department at Imperial College London in one week. Other contaminants such as foil and food waste

were also collected. Once these had been removed the paper cups were cleaned and shredded. The

results indicate that no significant differences in properties are clearly evident. However a larger

collection across London for example or the whole University would be the next trial in the scale up

process. Due to the nature of use of PPLs the properties are not hugely affected during their service

life as they are designed to be single use products.

8.2.5 Pallet Manufacture

Wood pallets in the US account for 90-95% of all pallets in use. PPCs have potential to be used in this

industry. Literature shows 3-point bending tests using recycled materials for pallets. The wood

particles, rice straw, rice husk and paper sludge showed flexural properties of less than 20 MPa. The

PPCs in this research showed flexural properties of up to 50MPa. Initial trials of pallet manufacture

completed by Nextek will be repeated with the optimised PPCs in this research (Kim et al., 2009; Soury

et al., 2009).

References Chapter 9

196

9. References

ADHIKARY, B. PAN, S. STAIGER, M.P. 2008, Dimensional stability and mechanical behaviour of wood- plastic composites based on recycled and virgin high-density polyethylene (HDPE), Composites Part B: Engineering, Volume 39, Issue 5, July 2008, Pages 807-815 AHMADI, B. & AL-KHAJA, W. 2001. Utilization of paper waste sludge in the building construction industry. Resources, Conservation and Recycling, 32, 105-113

ALLEN, A. 2001. Containment landfills: the myth of sustainability. Engineering Geology, 60, 3-19. ALVAREZ, V. A. & VÁZQUEZ, A. 2004. Thermal degradation of cellulose derivatives/starch blends and sisal fibre biocomposites. Polymer Degradation and Stability, 84, 13-21.

ARAUJOA, J.R. WALDMANB, W.R. PAOLI, M.A. 2008, Thermal properties of high density polyethylene

composites with natural fibres: Coupling agent effect, Polymer Degradation and Stability 93

(2008) 1770–1775.

ASHORI, A. & NOURBAKHSH, A. 2009. Characteristics of wood-fiber plastic composites made of

recycled materials. Waste Management, 29, 1291-1295.

ARANBERRI-ASKARGORTA, I. & LAMPKE, T. & BISMARCK, A, 2003. Wetting behaviour of flax fibers as reinforcement for polypropylene. Journal of Colloid and Interface Science, 263 (2)588-589 ARDANUY, M. & ANTUNES, & IGNACIO VELASCO, J., 2012. Vegetable fibres from agricultural residues as thermo-mechanical reinforcement in recycled polypropylene-based green foams. Waste Management, 32 (2) 256-263. BALASURIYA, P. W., YE, L. & MAI, Y. W. 2001. Mechanical properties of wood flake-polyethylene composites. Part I: effects of processing methods and matrix melt flow behaviour. Composites Part A: Applied Science and Manufacturing, 32, 619-629. BART, J. C. J. 2001. Polymer/additive analysis by flash pyrolysis techniques. Journal of Analytical and Applied Pyrolysis, 58-59, 3-28. BEG, M. D. H. & PICKERING, K. L. 2008. Mechanical performance of Kraft fibre reinforced polypropylene composites: Influence of fibre length, fibre beating and hygrothermal ageing. Composites Part A: Applied Science and Manufacturing, 39, 1748-1755. BENGTSSON, M. & OKSMAN, K. 2006. Silane crosslinked wood plastic composites: Processing and properties. Composites Science and Technology, 66, 2177-2186. BERTIN, S. & ROBIN, J.-J. 2002. Study and characterization of virgin and recycled LDPE/PP blends. European Polymer Journal, 38, 2255-2264. BEYLOT, A. VILLENEUVE, 2013, Environmental impacts of residual Municipal Solid Waste incineration: A comparison of 110 French incinerators using a life cycle approach, Waste Management, 33, 2781–2788


197

BLEDZKI, A. K. & GASSAN, J. 1999. Composites reinforced with cellulose based fibres. Progress in Polymer Science, 24, 221-274. BOUAFIF, H., KOUBAA, A., PERRÉ, P. & CLOUTIER, A. 2009. Effects of fiber characteristics on the physical and mechanical properties of wood plastic composites. Composites Part A: Applied Science and Manufacturing, 40, 1975-1981. BROUGHTON, W.R. & LODEIRO, M.J. & PILKINGTON, G.D, 2010. Influence of coupling agents on material behaviour of glass flake reinforced polypropylene. Composites Part A: Applied Science and manufacturing, 41 (4), 506-514. BULLIONS, T.A., HOFFMAN, D., GILLESPIE, R.A., PRICE-O’BRIEN, J., LOOS, A.C., 2006. Contributions of feather fibers and various cellulose fibers to the mechanical properties of polypropylene matrix composites. Composites Science and Technology, 66 (1) 102-114. CASTELLANO, M., GANDINI, A., FABBRI, P. & BELGACEM, M. N. 2004. Modification of cellulose fibres with organosilanes: Under what conditions does coupling occur? Journal of Colloid and Interface Science, 273, 505-511. CHANCEREL, P. & ROTTER, S. 2009. Recycling-oriented characterization of small waste electrical and electronic equipment. Waste Management, 29, 2336-2352.

CLEOMANS, C. 2010, Elastomer modified polypropylene-polyethylene blends as matrices for wood

flour-plastic composites, volume 41, Issue 11, Pages 1559-1569.

COUTINHO, F.M.B. COSTA, T.H.S. CARVALHO, D.L. 1997. Polypropylene-wood fibre composites: Effect of treatment and mixing conditions on mechanical properties, J. Appl. Polym. Sci., 67: 1227-1235. CULBERTSON, B. M. 1987. Maleic anhydride uses in resins and polymers. Catalysis Today, 1, 609-629.

CYRAS, V. P., SOLEDAD, C. M. & ANALÍA, V. 2009. Biocomposites based on renewable resource:

Acetylated and non acetylated cellulose cardboard coated with polyhydroxybutyrate. Polymer, 50,

6274-6280.

DÁNYÁDI, L., MÓCZÓ, J. & PUKÁNSZKY, B. 2010. Effect of various surface modifications of wood flour on the properties of PP/wood composites. Composites Part A: Applied Science and Manufacturing, 41, 199-206. DE LA ORDEN, M. U., GONZÁLEZ SÁNCHEZ, C., GONZÁLEZ QUESADA, M. & MARTÍNEZ URREAGA, J. 2007. Novel polypropylene-cellulose composites using polyethylenimine as coupling agent. Composites Part A: Applied Science and Manufacturing, 38, 2005-2012. DIMITRAKAKIS, E., JANZ, A., BILITEWSKI, B. & GIDARAKOS, E. 2009. Small WEEE: Determining recyclables and hazardous substances in plastics. Journal of Hazardous Materials, 161, 913-919.

EDWARDS, H.G.M. FARWELL, D.W. WEBSTER, D. 1997, FT Raman microscopy of untreated natural

plant fibres, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, Volume 53, Issue

13, Pages 2383–2392

http://www.sciencedirect.com/science/journal/13861425


198

FRANCO-MARQUÈS, E., MÉNDEZ, J. A., PÈLACH, M. A., VILASECA, F., BAYER, J. & MUTJÉ, P. 2011. Influence of coupling agents in the preparation of polypropylene composites reinforced with recycled fibers. Chemical Engineering Journal, 166, 1170-1178. FU, S.Y. FENG, X.Q, LAUKE, B, MAI, Y.W. 2008, Effects of particle size, particle/matrix interface adhesion and particle loading on mechanical properties of particulate–polymer composites, Composites: Part B 39, 933–961. GENT, A. N. & WANG, C. 1993. What happens after a fibre breaks- pull-out or resin cracking? JOURNAL OF MATERIALS SCIENCE, 28, 2494-2500. GEORGE, J., JANARDHAN, R., ANAND, J. S., BHAGAWAN, S. S. & THOMAS, S. 1996. Melt rheological behaviour of short pineapple fibre reinforced low density polyethylene composites. Polymer, 37, 5421-5431. GLASSER, W. G., TAIB, R. 1999. Fiber-Reinforced Cellulosic Thermoplastic Composites. Journal of Applied Polymer Science 73: 1329-1340. GRUBBSTRÖM, G., HOLMGREN, A. & OKSMAN, K. 2010. Silane-crosslinking of recycled low-density polyethylene/wood composites. Composites Part A: Applied Science and Manufacturing, 41, 678-683. GULMINE, J. V., JANISSEK, P. R., HEISE, H. M. & AKCELRUD, L. 2002. Polyethylene characterization by FTIR. Polymer Testing, 21, 557-563.

GUTH E. 1945, Theory of filler reinforcement. Journal of Applied Physics, 1945;16:205.

HÄKKINEN, T. & VARES, S. Environmental impacts of disposable cups with special focus on the effect of material choices and end of life. Journal of Cleaner Production, In Press, Corrected Proof.

HAMZA, A.A. SOKKAR, T.Z.N, EL-FARAHATY, K.A. EL-MORSY, M.A.M. DESSOUKY, 2005, Detecting and

avoiding the necking deformation along polypropylene fibre axis using the fringe pattern analysis of

multiple-beam microinterferometry, Optics & Laser Technology, Volume 37, Issue 7, October

2005, Pages 532-540.

HARPER, D. & WOLCOTT, M. 2004. Interaction between coupling agent and lubricants in wood-

polypropylene composites. Composites Part A: Applied Science and Manufacturing, 35, 385-394.

HISCHIER, R. WAGER, P. GAUGLHOFER, J. 2005, Does WEEE recycling make sense from an

environmental perspective?: The environmental impacts of the Swiss take-back and recycling

systems for waste electrical and electronic equipment (WEEE), Environmental Impact Assessment

Review, Volume 25, Issue 5, July 2005, Pages 525-539.

HRISTOV, V.N. LACH, R. GRELLMANN, W. 2004, Impact behaviour o modified polypropylene/wood

fiber composites, Polymer Testing, Volume 23, Issue 5, August 2004, Pages 581-589.

ICHAZO, M. N., ALBANO, C., GONZÁLEZ, J., PERERA, R. & CANDAL, M. V. Polypropylene/wood flour composites: treatments and properties. Composite Structures, 54, 207-214.


199

JAYARAMAN, K. & BHATTACHARYYA, D. 2004. Mechanical performance of woodfibre-waste plastic composite materials. Resources, Conservation and Recycling, 41, 307-319. JOSEPH, P.V., MATHEW, G., JOSEPH, K.,GROENINCKX, G., THOMAS, S., 2003. Dynamic mechanical properties of short sisal fibre reinforced polypropylene composites. Composites Part A: Applied Science and Manufacturing, 34 (3), 275-290. KEENER, T. J., STUART, R. K. & BROWN, T. K. 2004. Maleated coupling agents for natural fibre composites. Composites Part A: Applied Science and Manufacturing, 35, 357-362. KERNER, EH. The elastic and thermoelastic properties of composite media. Proc Phys Soc B 1956;69:808–13. KIM, H.-S., LEE, B.-H., CHOI, S.-W., KIM, S. & KIM, H.-J. 2007. The effect of types of maleic anhydride-grafted polypropylene (MAPP) on the interfacial adhesion properties of bio-flour-filled polypropylene composites. Composites Part A: Applied Science and Manufacturing, 38, 1473-1482.

KIM, H.S. HONG, S.I. KIM, S.J. 2001, On the rule of mixtures for predicting the mechanical properties

of composites with homogeneously distributed soft and hard particles, Journal of Materials

Processing Technology, Volume 112, Issue 1, Pages 109-113.

KIM, S., KIM, H.-J. & PARK, J. C. 2009. Application of recycled paper sludge and biomass materials in manufacture of green composite pallet. Resources, Conservation and Recycling, 53, 674-679.

KOSIOR, E. DVORAK, R, ‘Recycling Options for Avery Dennison Roll-stock Materials,’ Nextek Ltd,

October 2008.

KOSTADINOVA LOULTCHEVA, M. PROIETTO, M. JILOVB, N. LA MANTIS, F.P. 1997, Recycling of high

density polyethylene containers, Polymer Degradation and Stability, 57, 77-81. KUK., K. J. & PAL, K. 2010. Recent Advances in the Processing of Wood-plastic Composites. Engineering Materials 32, 176.

KUKALEVA, N. SIMON, G.P. KOSIOR, E. 2003, Modification of Recycled High-Density Polyethylene by

Low-Density and Linear-Low-Density Polyethylenes, POLYMER ENGINEERING AND SCIENCE,

JANUARY, Vol. 43, No. 1

KWON, H. J. & JAR, P. Y. B. 2005. Fracture toughness of polymers in shear mode. Polymer, 46, 12480-12492. LEE, S.Y. YANG, H.S. KIM, H.J. JEONG, C.S. LIM, B.S. LEE, J.N. Creep behaviour and manufacturing parameters of wood flour filled polypropylene composites, Composite Structures, Volume 65, Issues 3–4, September 2004, Pages 459-469

LEU, S.Y. YANG, H.T. LO, S.F. YANG, T.H. 2012, Optimized material composition to improve the

physical and mechanical properties of extruded wood–plastic composites (WPCs), Volume 29, Pages

120-217.


200

LI, R. 2000. Environmental degradation of wood-HDPE composite. Polymer Degradation and Stability, 70, 135-145. LI, Q. MATUANA, L.M. 2003, Surface of cellulosic materials modified with functionalized polyethylene coupling agents, Volume 88, Issue 2, pages 278-286

LOPEZ, J.P. MUTJE, P. CARVALHO, A.A.S. GIRONES, J. Newspaper fiber-reinforced thermoplastic

starch biocomposites obtained by melt processing: Evaluation of the mechanical, thermal and water

sorption properties, Industrial Crops and Products, 44, 2013, 300-305.

LOPEZ, J.P. BOUFI, S. MANSOURI, N.E. MUTJE, P. VILASECA, F. PP composites based on mechanical

pulp, deinked newspaper and jute strands: A comparative study.

LU, J. Z. WU, Q. MCNABB, H. S. Jr. 2000. Chemical Coupling in Wood Fiber and Polymer Composites:A Review of Coupling Agents and Treatments, Wood Fiber and Science, , Vol. 32, No. 1, Pages 88-104.

MADI N.K. 2013, Thermal and mechanical properties of injection moulded recycled high density

polyethylene blends with virgin isotactic polypropylene, Materials and Design, Volume 46, Pages

435-441.

MALAK, N.E. A Processing Method for Plastic-Paper Composites, to be Used as a Poverty Reducing Solution to Specific Ecological Problem, 2011, School of Mechanical Engineering, Western Australia

MALI,J. SARSAMA, P. LINBERG, L.S. PELTONEN, J. VILKKI, M. KOTO, T. TIISALA, S. Wood fiber-plastic

composites, technical research centre of Finland, 2003.

MALCENJI, K. GOODSHIP, V. CHRISTMAS, P. SMITH, G.F. PEARCE, B. (2010) A mixed plastic waste and

de-inked residue composite from recycled paper waste products. Progress in Rubber Plastics and

Recycling Technology, Vol.26 (No.2). pp. 93-106. ISSN 1477-7606

MANIVANNAN, A. SEEHRA, M.S. IDENTIFICATION AND QUANTIFICATION OF POLYMERS IN WASTE PLASTICS USING DIFFERENTIAL SCANNING CALORIMETRY, Physics Department, West Virginia University

MAROTZKE, C. & QIAO, L. 1997. Interfacial crack propagation arising in single-fiber pull-out tests.

Composites Science and Technology, 57, 887-897.

MARTINHO, G., PIRES, A., SARAIVA, L., RIBEIRO, R., 2012. Composition of plastics from waste electrical and electronic equipment (WEEE) by direct sampling. Waste Management, 32 (6), 1213-1217. MCKAY, G. 2002. Dioxin characterisation, formation and minimisation during municipal solid waste (MSW) incineration: review. Chemical Engineering Journal, 86, 343-368.

MENAD, N. GUIGNOT, S. VAN HOUWELINGEN, J.A. 2013, New characterisation method of electrical

and electronic equipment wastes (WEEE), Volume 33, 3, Pages 706-713


201

MENDEZ, J.A., VILASECA, F., PELACH, M.A., LOPEZ, J.P., BARBERA, L., TURON, X., GIRONES, J., MUTJE, P., 2007. Evaluation of the reinforcing effect of ground wood pulp in the preparation of polypropylene-based composites coupled with maleic anhydride grafted polypropylene, Journal of Applied Polymer Science, 105 (6) 3588–3596. MESSIRY, M. E. Theoretical analysis of natural fiber volume fraction of reinforced composites. Alexandria Engineering Journal. MILTON, G. W. 2002. The Theory of Composites, University Press, Cambridge. MIGNEAULT, S., KOUBAA, A., ERCHIQUI, F., CHAALA, A., ENGLUND, K., KRAUSE, C. & WOLCOTT, M. 2008. Effect of Fiber Length on Processing and Properties of Extruded Wood-Fiber/HDPE Composites. Journal of Applied Polymer Science, 110, 1085–1092. MIGNEAULT, S., KOUBAA, A., ERCHIQUI, F., CHAALA, A., ENGLUND, K. & WOLCOTT, M. P. 2009. Effects of processing method and fiber size on the structure and properties of wood-plastic composites. Composites Part A: Applied Science and Manufacturing, 40, 80-85.

MOHANTY, S. VERMA, S.K. NAYAK, S.K. 2006, Dynamic mechanical and thermal properties of MAPE

treated jute/HDPE composites, Volume 2006, Issues 3-4, pages 538-547

MORRIS, J. 1996. Recycling versus incineration: an energy conservation analysis. Journal of Hazardous Materials, 47, 277-293. MURATHAN, A., MURATHAN, A. S., GÜRÜ, M. & BALBASI, M. 2007. Manufacturing low density boards from waste cardboards containing aluminium. Materials & Design, 28, 2215-2217. MUTJE, P., VALLEJOS, M.E., GIRONES, J., VILASECA, F., LOPEZ, A., LOPEZ, J.P., MENDEZ, J.A.,2006. Effect of maleated polypropylene as coupling agent for polypropylene composites reinforced with hemp strands, Journal of Applied Polymer Science, 102 (1), 833-840. NACHTIGALL, S. M. B., CERVEIRA, G. S. & ROSA, S. M. L. 2007. New polymeric-coupling agent for polypropylene/wood-flour composites. Polymer Testing, 26, 619-628. NADAY. P, 2009, Test Report, MBM. NAIM, J.A.1997, On the Use of Shear-Lag Methods for Analysis of Stress Transfer in Unidirectional Composites, Mechanics of Materials, Volume 26, Issue 2, Pages 63-80 Niemz, P., Diener, M. and Pöhler, E. (1997). “Untersuchungen zur Ermittlung der Bruchzähigkeit an MDF-Platten,” Holz als Roh- und Werkstoff, 55 (5), 327-330. NYGÅRD, P., TANEM, B. S., KARLSEN, T., BRACHET, P. & LEINSVANG, B. 2008. Extrusion-based wood fibre-PP composites: Wood powder and pelletized wood fibres - a comparative study. Composites Science and Technology, 68, 3418-3424.

PEETERS, R.J. VANEGAS, P. TANGE, L. VAN HOUWELLINGEN, J. DUFLOU, J.R. 2014, Closed loop

recycling of plastics containing Flame Retardants


202

PELTOLA, P. JARVELA, P. VIKMAN, J. KUKKO, L. ULFSTEDT, O. 2002, Different kind of papers in

therecycled paper: Plastic composites, Sustainable natural and polymeric composites - sciences

and technology, Riso international symposium on materials science No23, Roskilde,

DANEMARK, pp. 289-298.

PHILLIPS, M. G. 1992. Simple geometrical models for Young's modulus of fibrous and particulate composites. Composites Science and Technology, 43, 95-100. PRITCHARD, G. 2004, Two technologies merge: wood plastic composites. Plastics, Additives and Compounding, 6 (4), 18-21. QIN, C., SOYKEABKAEW, N., XIUYUAN, N. & PEIJS, T. 2008. The effect of fibre volume fraction and mercerization on the properties of all-cellulose composites. Carbohydrate Polymers, 71, 458-467. QINGIXIU L, MATUANA LM, Effectiveness of maleated and acrylic-acid functionalised polyolefin coupling agents for HDPE/wood-flour composites. Submitted for application.

RAFF, R.A.V. AHMAD, A.S. 1970, Dependence of Properties on Spherulite Size in Crystalline Polymers,

Northwest Science, Volume 44, 3, 184-205.

RAGHAVAN, J. & MESHII M. 1997. Creep Rupture of Polymer Composites. Composite Science and Technology 57:375-388. RAJ, R., G. & KOKTA, B., V. 1989. Compounding of Cellulose Fibers with Polypropylene: Effect of Fiber Treatment on Dispersion in the Polymer Matrix. Journal of Applied Polymer Science, 38, 1987-1996. RAJENDRAN, S.,SCELSI, L., HODZIC, A., SOUTIS, C., AL-MADEED, M.A., 2012. Environmental impact assessment of composites containing recycled plastics. Resources, Conservation and Recycling, 60, 131-139. ROBINSON, B. H. 2009. E-waste: An assessment of global production and environmental impacts. Science of The Total Environment, 408, 183-191. ROZMAN, H. D., TAN, K. W., KUMAR, R. N., ABUBAKAR, A., MOHD. ISHAK, Z. A. & ISMAIL, H. 2000. The effect of lignin as a compatibilizer on the physical properties of coconut fiber-polypropylene composites. European Polymer Journal, 36, 1483-1494. RUSSELL D., O’NEILL, J. BOUSTEAD I., Is HDPE Recycling the Best Deal for the Environment? Life Cycle Inventory Analysis of HDPE Bottle Packaging Systems Utilising Various Disposal Options Including Mechanical Recycling, Dow Europe S.A.

SANCHEZ, G.C. VALERO, F.C. MENDOZA, O.A. MECO, G.A. HURTADO, R.E. 2011, Composites Part A:

Applied Science and Manufacturing, Volume 42, 9, Pages 1075 – 1083.

SANCHEZ-SOTO, W. ROSSA, A. SANCHEZ, A.J. GAMEZ-PEREZ, J. 2008, Blends of HDPE wastes: Study of the properties, Waste Management, 28, 2565-2573. SCHLUMMER, M., GRUBER, L., MÄURER, A., WOLZ, G. & VAN ELDIK, R. 2007. Characterisation of polymer fractions from waste electrical and electronic equipment (WEEE) and implications for waste management. Chemosphere, 67, 1866-1876.


203

SCHOFIELD, J. 2005. New coupling agents enhance mechanical properties in filled polymers. Plastics, Additives and Compounding, 7, 38-42. SHAH, D. U., SCHUBEL, P. J., LICENCE, P. & CLIFFORD, M. J. 2012. Determining the minimum, critical and maximum fibre content for twisted yarn reinforced plant fibre composites. Composites Science and Technology, 72, 1909-1917. SHOKRIEH, M. M. & OMIDI, M. J. 2009. Tension behavior of unidirectional glass/epoxy composites under different strain rates. Composite Structures, 88, 595-601. SMITH, P. A. & YEOMANS, J. A. Benefits of Fiber and Particulate Reinforcement Materials Science and Engineering 2, 3. SOURY, E., BEHRAVESH, E.H., ROUHANI ESFAHANI, E., ZOLFAGHARI, A., 2009. Design, optimization and manufacturing of wood–plastic composite pallet. Materials & Design, 30 (10), 4183- 4191. STARK, N. M. & ROWLANDS, R. E. 2003. Effects of wood fibre characteristics on mechanical properties of wood/polypropylene composites. . Wood and Fiber Science, 35, 167-174.

STARK, N. M. & MATUANA, L. M. 2007. Characterization of weathered wood-plastic composite surfaces using FTIR spectroscopy, contact angle, and XPS. Polymer Degradation and Stability, 92, 1883-1890.

STARK , N.M,Forest Products Journal,49,6 (1999) 39-46

STRAPASSON, R. AMICO, S.C. PEREIRA, M.F.R. SYDENSTRICKER, T.H.D. 2005, Tensile and impact

behaviour of polypropylene/low density polyethylene blend, Polymer Testing, Volume 24, Issue 4,

Pages 468-473.

TACHWALI, Y., AL-ASSAF, Y. & AL-ALI, A. R. 2007. Automatic multistage classification system for plastic bottles recycling. Resources, Conservation and Recycling, 52, 266-285. TAJVIDI, M., FALK, R.H., HARMANSON, J.C., 2006. Effect of natural fibers on thermal and mechanical properties of natural fiber polypropylene composites studied by dynamic mechanical analysis. Journal of Applied Polymer Science, 101 (6), 4341-4349.

TAMMY, J. UAN-ZO-LI, 2005, Morphology, Crystallization and Melting Behaviour of Propylene-

Ethylene Statistical Copolymers, Blacksburg, Virginia, Institute and State University.

TARANTILI, P. A., MITSAKAKI, A. N. & PETOUSSI, M. A. 2010. Processing and properties of engineering plastics recycled from waste electrical and electronic equipment (WEEE). Polymer Degradation and Stability, 95, 405-410.

THUMM, A., DICKSON, A.R., 2013. The influence of fibre length and damage on the mechanical performance of polypropylene/wood pulp composites. Composites Part A: Applied Science and Manufacturing, 46, 45-52. VAN DER HARST, E., POTTING, J., 2013. A critical comparison of ten disposable cup LCAs. Environmental Impact Assessment Review, 43, 86-96.

http://www.sciencedirect.com/science/journal/01429418


204

VAN HATTUM, F.W.J. BERNARDO, C. A, 1999, A model to predict The Strength of Short Fiber

Composites, Polymer Composites, 20, 4, pp. 524.

VERBEEK. C.J.R. The influence of interfacial adhesion, particle size and size distribution on the predicted mechanical properties of particulate thermoplastic composites. Mater Lett 2003;57:1919–24. VIGNON, M.R., DUPEYRE, D., GARCIA-JALDON, C., 1996. Morphological characterization of steamexploded hemp fibers and their utilization in polypropylene-based composites. Bioresource Technology, 58 (2) 203-215. WAMBUA, P., IVENS, J. & VERPOEST, I. 2003. Natural fibres: can they replace glass in fibre reinforced plastics? Composites Science and Technology, 63, 1259-1264. WIDMER, R., OSWALD-KRAPF, H., SINHA-KHETRIWAL, D., SCHNELLMANN, M., BONI, H. 2005. Global perspectives on e-waste. Environmental Impact Assessment Review, 25, 436-458.

WINANDY, J.E. STARK, C.M. CLEMONS, CONSIDERATIONS IN RECYCLING OF WOOD-PLASTIC

COMPOSITES, 5th Global Wood and Natural Fibre Composites Symposium April 27-28, 2004 in Kassel

/ Germany

XJE, Y. HILL, C. XIAO, Z. MILITZ, H. MAI, C. 2010, Silane coupling agents used for natural fiber/polymer composites: A review, Composites: Part A, 41, 806–819 XU, X., JAYARAMAN, K., MORIN, C. & PECQUEUX, N. 2008. Life cycle assessment of wood-fibre-reinforced polypropylene composites. Journal of Materials Processing Technology, 198, 168-177. YAN, R., LIANG, D. T. & TSEN, L. 2005. Case studies--Problem solving in fluidized bed waste fuel incineration. Energy Conversion and Management, 46, 1165-1178. YEH, S.-K., AGARWAL, S. & GUPTA, R. K. 2009. Wood-plastic composites formulated with virgin and recycled ABS. Composites Science and Technology, 69, 2225-2230. YEH, S.-K. & GUPTA, R. K. 2008. Improved wood-plastic composites through better processing. Composites Part A: Applied Science and Manufacturing, 39, 1694-1699.

YIN, Y. 2009, Comparison of Carbon Footprint of the Pallets Manufactured From Virgin Plastics and

Waste Composite Materials,’ MSc, Imperial College London, Page 2.

ZHU, Y. LIU, P.Y. JIANG, Z.H. 2013, The Creep Behaviour of Wood-Polymer Composites, Advanced

Materials Research, 815, 632

Standards

Plastics — Determination of the melt volume-flow rate (MVR) and melt mass-flow rate (MFR) of thermoplastics materials - Part 1: Standard method (ISO/DIS 1133-1:2009) Plastics — Determination of Charpy impact properties Part 1: Non-instrumented impact test (BS EN ISO 179-1:2010)


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Plastics — Determination of flexural properties (BS EN ISO 178:2003) Plastics — Determination of fracture toughness (GIC and KIC) — Linear elastic fracture mechanics (LEFM) approach (BS ISO 13586:2000) Plastics — Determination of tensile properties — Part 1: General principles (BS EN ISO 527-1:1996 BS 2782-3: Method 321: 1994 ISO 527-1: 1993) Books

Rauwendaal.C. 2001, Polymer Extrusion, Hanser Verlag, Page 12

Klyosov. A, Klesov. A, 2007, Wood Plastic Composites, Wiley-Interscience , Pages 646-647 Gunter. E. 2006, Designing with Plastics, Munich: Hanser Publishers,

Harper. A. C, 2006, Handbook of Plastic Processes, John Wiley & Sons, Pages 1-36

Stuart. B, 2004, Infrared Spectroscopy: Fundamentals and Applications, John Wiley & Sons, Pages

124-126.

Brydson. J, 1999, Plastics Materials, Butterworth-Heinemann, Pages 251-267

Maier, C. Calafut, T, 2008, Polypropylene: The Definitive User's Guide and Databook, Taylor &

Francis, Pages 13-20

Karian, H. Handbook of Polypropylene and Polypropylene Composites, CRC Press,2003, Page 394

Hull, D. And Clyne, T.W. An Introduction to Composite Materials, 2nd Edition, Cambridge University

Press, 1996.

Macdermott, 1997, Selecting Thermoplastics for Engineering Applications, 2nd Edition, CRC PRESS,

Pages 64-65

Kinloch and Young, 1983, fracture behaviour of polymers, Elsevier science publishers

Karger-Gocsis, 1999, Polypropylene, published kluwer cademic publishers

Nielson and Landel, 1994, mechanical properties of polymers composites, 2nd edition, published

marcel dekker

Thakur, V. K 2013, Green Composites from Natural Resources, CRC Press, 25 Nov 2013 - Technology

& Engineering

Crowe, J. and Bradshaw, T. Chemistry for the Biosciences: The essential concepts, Oxford University

Press, 2014, Science

Mazumdar, S. Composites Manufacturing: Materials, Product, and Process Engineering, CRC Press,

2001, Technology & Engineering.

http://www.google.co.uk/search?tbo=p&tbm=bks&q=subject:%22Technology+%26+Engineering%22&source=gbs_ge_summary_r&cad=0

http://www.google.co.uk/search?tbo=p&tbm=bks&q=subject:%22Technology+%26+Engineering%22&source=gbs_ge_summary_r&cad=0


206

Kalia, S. Kaith, B.S, Kaur, I. Cellulose Fibers: Bio-and Nano-Polymer Composites: Green Chemistry and

Technology, Springer Science & Business Media, 11 April 2011, Technolgy and Engineering

Nielsen LE (1974) Mechanical properties of polymers and composites. M. Dekker Inc, New York

Websites

(www.ace-uk.co.uk) Alliance for Beverage Cartons and the Environment, Viewed March 2010

http://www.addcomp.nl/ Polymer additive solutions, Viewed November 2011.

(www.solocupeurope.co.uk), Viewed 4th September 2010

(http://www.honeywell.com/sites/uk/specialty-materials.htm), Viewed 10th February 2010

(http://www.eastman.com/Pages/Home.aspx), Viewed 17th March 2010

Epolene Polymers, (http://www.epolene.com/index_files/Epolene%20Emulsifier.pdf ), Viewed 12th

January 2010

(http://www.chemtura.com), Viewed 6th August 2010

Imaging Golden Gate™ Diamond ATR Accessory, (http://www.chem.agilent.com/Library/datasheets/Public/si-1079.pdf), Viewed 09th June 2009

Introduction to FT-IR Spectroscopy (http://www.newport.com/store/genContent.aspx/Introduction-

to-FT-IR-Spectroscopy/405840/1033), Viewed 3rd February 2011

William Reusch, 2007, Infrared Spectroscopy,

[http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm#ir1],

viewed 11th November 2010

Capillary Rheometer - FAQ's

(http://www.malvern.com/LabEng/products/bohlin/rh2000/capillary_rheometers_faq.htm), Viewed

8th March 2011

Cobbing M., 2008, Toxic Tech: Not in Our Backyard. Uncovering the Hidden Flows of e-waste. Report

from Greenpeace International, Amsterdam

[http://www.greenpeace.org/raw/content/belgium/fr/press/reports/toxic-tech.pdf]

Denkstatt 2009, Major new study on environmental footprint of plastics previewed ahead of

COP15[http://www.plasticseurope.org/learning-centre/press-room-1351/press-releases-2009/11-

december-2009---major-new-study-on-environmental-footprint-of-plastics-previewed-ahead-of-

cop15.aspx], Viewed 7th July 2010

Read. B. 2008, Paper Cups, Recycling Now In Progress

[http://www.maxabel.co.uk/pdf/press_releases.pdf] viewed October 3rd 2010

Recycling and recovery A hands-on approach

[http://www.tetrapak.com/environment/recycling_and_recovery/pages/recycling.aspx] viewed 18th

December 2009

http://www.ace-uk.co.uk/

http://www.addcomp.nl/

http://www.solocupeurope.co.uk/

http://www.honeywell.com/sites/uk/specialty-materials.htm

http://www.eastman.com/Pages/Home.aspx

http://www.epolene.com/index_files/Epolene%20Emulsifier.pdf

http://www.chemtura.com/corporatev2/v/index.jsp?vgnextoid=6a6238f220d6d210VgnVCM1000000753810aRCRD&vgnextchannel=6a6238f220d6d210VgnVCM1000000753810aRCRD&vgnextfmt=default

http://www.chem.agilent.com/Library/datasheets/Public/si-1079.pdf

http://www.newport.com/store/genContent.aspx/Introduction-to-FT-IR-Spectroscopy/405840/1033

http://www.newport.com/store/genContent.aspx/Introduction-to-FT-IR-Spectroscopy/405840/1033

http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm#ir1

http://www.malvern.com/LabEng/products/bohlin/rh2000/capillary_rheometers_faq.htm

http://www.sciencedirect.com/science?_ob=RedirectURL&_method=externObjLink&_locator=url&_cdi=5836&_issn=00489697&_originPage=article&_zone=art_page&_plusSign=%2B&_targetURL=http%253A%252F%252Fwww.greenpeace.org%252Fraw%252Fcontent%252Fbelgium%252Ffr%252Fpress%252Freports%252Ftoxic-tech.pdf

http://www.plasticseurope.org/learning-centre/press-room-1351/press-releases-2009/11-december-2009---major-new-study-on-environmental-footprint-of-plastics-previewed-ahead-of-cop15.aspx



http://www.maxabel.co.uk/pdf/press_releases.pdf

http://www.tetrapak.com/environment/recycling_and_recovery/pages/recycling.aspx


207

KIM, J. Stress Intensity,

(http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kim/intensity.html), Viewed

12th February 2011

Royal School of Chemistry – ‘Disposable cups and the environment’ (Royal Society of Chemistry). http://www.rsc.org/Education/Teachers/Resources/Inspirational/resources/6.2.2.pdf

http://www.carbon-clear.com/files/cup_assessment.pdf Viewed August 2013

http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kim/intensity.html

https://exchange.imperial.ac.uk/owa/redir.aspx?C=qY-CR99pUEmhWG1TQXHyhGn6gOGcC9EIpXL0P9LmgbzOJPbBe6dXnLue55hhTveXVd17uCT4mV0.&URL=http%3a%2f%2fwww.rsc.org%2fEducation%2fTeachers%2fResources%2fInspirational%2fresources%2f6.2.2.pdf

http://www.carbon-clear.com/files/cup_assessment.pdf

Appendix Chapter 10

208

10. Appendix This section shows key materials and equipment used to make PPCs. Additional testing and trials are

also shown for further information.

Figure 10-1: MRF plastic matrix used in trial 1.

Figure 10-2: WEEE PP plastic matrix used in trial 1 and trial 2.

5mm

3mm

Appendix Chapter 10

209

Figure 10-3: Paper plastic laminate (PPL) flakes derived from shredding disposable cups.

The initial trials of this research used the fibrous material shown in the top picture in Figure 10-3. The

further optimisation trials used the paper cups shown in the bottom of Figure 10-3. The only difference

really is the inks that have been added and the forming of the lips of the cups. The initial trials were

Appendix Chapter 10

210

more of a proof of concept approach while the further optimisation trials focused on optimising the

use of this material with more thorough trials.

Figure 10-4: Multilayer carton board consisting of cardboard, PE film and aluminium film from a

leading commercial retailer.

Figure 10-5: Release liner for labels.

Appendix Chapter 10

211

Figure 10-6: PPR from Smurfit Kappa waste stream.

Figure 10-7: PPR mix from the paper mills that Severnside collect from (St Regis Paper).

Film

Cardboard

Appendix Chapter 10

212

Figure 10-8: PPR from Aylesford Newsprint consisting of mainly polyolefin film.

Figure 10-9: Calculating the percentage of film and fibrous material in PPR.

Appendix Chapter 10

213

Figure 10-10: Severnside waste stream heat pressed into plaques to aid granulating and multilayer

carton board granulated to 3mm.

Appendix Chapter 10

214

Figure 10-11: Mixing the matrix, filler and coupling agent. The coupling agent is mixed within this at

small percentages.

Figure 10-12: Injection moulded test bars to analyse the properties of PPC.

Polymer (matrix)

PE coated

Beverage cup

(filler)

Appendix Chapter 10

215

Figure 10-13: Negri Bossi injection Moulding Machine at London Metropolitan University.

Appendix Chapter 10

216

Figure 10-14: Granulator with 3mm mesh at Loughborough University.

Appendix Chapter 10

217

Figure 10-15: Mixing PPCs at Imperial College London.

Figure 10-16: Thermo Scientific Haake Polylab operating system. The extruder was a co-rotating twin

screw (26mm and L/D=40) extruder at Brunel University.

Appendix Chapter 10

218

Figure 10-17: Extruded test bars/rods ready to be granulated for injection moulding.

Figure 10-18: Demag injection moulding machine for manufacturing test bars of PPCs at Brunel

University.

Appendix Chapter 10

219

10.1 Previous Work by Nextek and Pre-Trial 1 Analysis _Release Liner

Initial processing at the beginning of the research targeted the difference in properties of recycled PP

against PPC produced by Nextek.

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gin

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tre

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m2)

Engineering Strain

Virgin PE

Recipe 5

Recipe 1

Figure 10-19: Initial work comparing polymers to PPC produced by Nextek Ltd. Recipe 1 consisted of

40% paper, 40% PP, 17.5% LLDPE and 2.5% MAPP. Recipe 5 consisted of an agglomerate of 87.5% (60%

PP and 40%) with 10% LLDPE and 2.5% MAPP.

The toughness of the polymer compared to the brittle composite is clearly shown in Figure 10-19. This

initial study kick started the project to enhance the interfacial bond to try and improve the toughness

of the composite. Various studies included comparing the size of the flake and the percentage of the

coupling agents all with the release liner as the filler (Figure 10-5).

Appendix Chapter 10

220

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14

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ng

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eri

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ess (

N/m

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Engineering Strain

4X4 4wt% E-43

8x8 1wt% E-43

8x8 4wt% E-43

Figure 10-20: Initial work focusing on release liner flake size with different percentages of coupling

agent (E-43).

Three coupling agents were compared in the flake size study including E-43, Polybond 3200 and 950P

from Honeywell. The results were very similar in Figure 10-20. The flake size did not make a difference

and more than likely the flakes break down during processing to a similar size no matter what the

feeding size. The amount of coupling agent did not make a difference to the properties indicating that

the major problem is the polydimethylsiloxane (PDMS) coating on the release liner.

‘Paper dust’ or grounded paper (paper particles) were also trialled to see if flakes were a suitable

method to follow or grinding the paper even more produced better mechanical properties. The results

showed that there was a decrease in the tensile strength compared to the matrix material alone. The

results were better than the paper flakes showing an increase in the ductility.

Appendix Chapter 10

221

0.0 0.1 0.2 0.3 0.4 0.5

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Engineering Strain

rPP/release liner dust

Figure 10-21: Paper dust vs Paper flakes for the filler content

Figure 10-21 above shows that the dust improves the ductility compared to the flakes. On the other

hand, the improvement is not by a great deal and the strength did not increase by a significant amount

mainly due to the release liner coating and the surface area of the filler increasing compared to the

flake. From this data it would be worth investigating the effect of paper flake size with the Solo Cup

and Tetra Pak fillers ranging from dust to large flakes.

The PPC with release liner as a filler also went through a recycling stage and were reground and

recycled once. The results were very similar to the properties already received, indicating that the PPC

can survive recycling at least once.

The results above show that the coupling agents do not have an enhancing effect on the composites.

The addition of paper dust without coupling agents also shows that the filler acts like more of points

of weakness rather than reinforcement.

Conclusions from this study were that minimal reinforcement is achieved with release liner

composites and the main problem lies with the release liner coating PDMS. The coating does not bond

with the coupling agents. The coupling agents may entangle and co-crystallise with the matrix but the

PDMS coating causes a site of weakness rather than creating a covalent bond with MAH.

Appendix Chapter 10

222

The work above covers many aspects of PPC including size of paper flakes, coupling agent percentage

and paper particles. This work cannot be compared to the trial at Bangor University. Firstly a different

extruder was used (Figure 10-22). Although both machines are co-rotating twin screws, the screw

geometry would be different and the residence time. The extruder in Figure 10-22 also did not have a

vent zone to remove volatiles. The injection moulding equipment was also different. A simple ram

extruder was used to mould test bars with different dimensions at Imperial College. This means that

the materials did not go through another mixing stage with the injection moulding screw. Also if the

test bars are a variety of sizes then the gauge length would be different, which means the results

would not be comparable as this is the region over which the tensile tests focus on. This is confirmed

in the British Standard used in this research.

Figure 10-22: Twin screw Prism extruder in the Chemical Engineering Department at Imperial College

London.

10.2 Initial Trial Difficulties

10.2.1 Acrylonitrile Butadiene Styrene (ABS) from WEEE

During extrusion ABS was a problem due to the high processing temperatures required causing fibres

to start degrading. ABS also needs drying and any moisture uptake would be a problem for processing

which adds another step to the process. The filler material also absorbs some moisture adding extra

concern.

Appendix Chapter 10

223

This is an area that will be considered in the future but PP and PE are suitable matrix materials because

they are hydrophobic. It would be interesting to compare different matrix materials such as ABS to

compare the properties obtained against the olefins and look at how the fibres/flakes behave at the

higher processing temperatures required for ABS.

10.2.2 End of Life Vehicle (ELV) PP

A source of PP from end of life vehicles was obtained but could not be trialled as a matrix polymer

because of the contaminated wood content. This is however an area of interest as many plastics from

ELV end up in landfill.

10.2.3 Carpet

Waste carpet was obtained and extruded by itself with a little MRF material. Little material was

collected due to the availability of this material. Excellent flow properties were achieved and a source

for a matrix material is possible if enough PP carpet material can be sourced. Another step added with

this material was that it had to be heat pressed to plaques and then granulated to pellets for extrusion

because carpet fibres would bridge the feed throat of the extruder. Also a lot of nylon was found in

the carpet which can cause moisture issues and processing settings are a lot higher for nylon.

10.2.4 Smurfit Kappa Paper Plastic Residue (PPR)

PPR from Smurfit Kappa shown in Figure 10-6 was trialled with Jazz PP from Preston Plastics. The

results obtained only show a small increase in tensile strength similar to the release liner data shown

above. The reason for this is that the PPR waste is not a laminate; it is an independent mix of fibre and

film after contaminants have been removed. The mix within the polymer matrix is random. Coupling

agents have worked well in with the PE coated beverage cup because the MAH could bond with the

fibres and the PP to the matrix on each individual flake. Flakes in PPR are all fibre or all plastic and so

the same bond cannot be created at each flake causing more points of weakness. Bonds are still

created by the coupling agents attaching themselves to the fibres and the PP of the coupling agent to

the matrix causing a link from the fibre to the matrix. It is assumed that having a PE coating significantly

helps with interfacial bonding which translates to enhanced mechanical properties.

10.2.5 Material Recycling Facility (MRF) Polyethylene (PE)

The MRF PP showed some positive results in trial 1. A second batch was ordered for further trials. The

majority of the flake that was received was in fact PE. Therefore a PE coupling agent was trialled with

the material showing some bonding. The inconsistent batches were manageable but with PPCs it is

essential to know the matrix material as the coupling agent needs to bond to create desirable

Appendix Chapter 10

224

mechanical properties. Therefore it was decided to move forward with the WEEE PP analysis and look

for a possible PE based matrix separately.

10.3 Density Results

Table 10-1: Density of PPCs and the Matrix

Recipe Average Density

(g/cm³)

Recipe 10 1.031957762

Recipe 26A 1.070514074

Recipe 18 1.064632607

Recipe 26E 1.043531094

Recipe 26F 1.043531094

Recipe 23 1.038761743

Recipe 12 1.089531559

Recipe 25 1.076603356

Recipe 8 1.091018883

Recipe 18A 1.085959383

Recipe 16A 1.097107515

Recipe 24 1.04494727

Recipe 11B 1.034806753

Recipe 26B 1.012725657

Recipe 16 1.001452203

Recipe 17 1.02776116

Recipe 22 1.035122517

Recipe 11A 1.010484854

Recipe 6 1.038788592

Recipe 4 1.046134194

Recipe 26D 1.007725119

Recipe 13 1.076115728

Recipe 25A 1.068897379

Recipe 7 1.043828666

Recipe 9 1.035108426

Recipe 11 1.11902127

Recipe 21 1.080220653

Recipe 5 1.061828799

Recipe 30 1.059163469

Recipe 19 1.099803229

Recipe 26C 1.028582498

Recipe 15 1.070865196

Recipe 28 1.096784927

Recipe 20 1.036672077

Recipe 26 1.100004199

Appendix Chapter 10

225

Recipe 14 1.074425896

Recipe WEEE PP RUN2 0.938061446

Recipe WEEE PP RUN3 0.938040437

Recipe 31 RUN1 1.039257238

Recipe 31 RUN2 1.040603383

Recipe 31 RUN3 1.03281507

Recipe 27 RUN1 1.050129383

Recipe 27 RUN2 1.047645547

Recipe 27 RUN3 1.055797204

30PPL3%907P 1.026030531

30PPL 1.060719376

30PPL3%PRIEX 1.08163197

30PPL1%PRIEX 1.071139223

Recipe 2 1.055722272

10PPL2%PRIEX 1.011078306

20PPL2%PRIEX 1.049577291

20PPL1.5%PEI 1.042301014

30PPL2%PRIEX 1.07550283

30PPL1.5%PEI 1.06271705

10PPL2%907P 1.014725379

10PPL1.5%PEI 1.022671775

30PPL4%PRIEX 1.070942184

20PPL2%907P 1.035496514

20PPL 1.052375318

Recipe 1 1.067567011

30PPL1%907P 1.07025998

10PPL 1.00938957

30PPL4%907P 1.072003634

RECIPE 3 1.064391567

40PPL 1.102163058

30PPL2%907P 1.06819399

Appendix Chapter 10

226

10.4 Calibrating Tensile Equipment

Table 10-2: Tensile properties of commercial PP and PE ensuring the equipment was producing

reliable results.

Commercial PP

Summary

Sample without

extensometer:

Sample

Tensile

Strength

(Mpa)

Young's

Modulus (Gpa)

Stress at

Yield (Mpa)

Strain at

yield

Stress at

break (Mpa)

Strain at

break

3 20.09 0.51 11.20 0.02 9.03 0.53

4 19.57 0.48 11.30 0.03 12.97 1.21

5 19.11 0.46 11.50 0.03 12.50 0.69

Mean 19.59 0.48 11.33 0.03 11.50 0.81

Standard Deviation 0.49 0.02 0.15 0.00 2.15 0.36

Standard Error 0.28 0.01 0.09 0.00 1.24 0.21

Sample with

extensometer:

Sample

Tensile

Strength

(Mpa)

Young's

Modulus (Gpa)

Stress at

Yield (Mpa)

Strain at

yield

Stress at

break (Mpa)

1 20.07 1.06 11.00 0.02 11.57

2 20.01 1.11 12.30 0.01 6.00

Mean 20.04 1.08 11.65 0.01 8.78

Standard Deviation 0.04 0.04 0.92 0.00 3.93

Standard Error 0.03 0.03 0.65 0.00 2.78

Appendix Chapter 10

227

PP Tensile Strength

Summary

Sample

Tensile

Strength

(Mpa)

1 20.07

2 20.01

3 20.09

4 19.57

5 19.11

Mean 19.77

Standard Deviation 0.43

Standard Error 0.19

Commercial PE Summary

Sample without extensometer:

Sample

Tensile Strength (Mpa)

Young's Modulus (Gpa)

Stress at Yield (Mpa)

Strain at yield

Stress at break (Mpa)

Strain at break

2 20.60 0.38 10.40 0.03 15.82 1.21

3 20.40 0.36 10.30 0.03 16.31 1.21

4 20.60 0.38 10.60 0.03 16.77 1.21

Mean 20.53 0.38 10.43 0.03 16.30 1.21

Standard Deviation 0.12 0.01 0.15 0.00 0.48 0.00

Standard Error 0.07 0.01 0.09 0.00 0.27 0.00

Sample with extensometer:

Sample


Young's Modulus (Gpa)

Stress at Yield (Mpa)

Strain at yield

Stress at break (Mpa)

1 20.50 0.82 10.50 0.01 14.64

5 20.70 0.80 11.00 0.02 13.16

Mean 20.60 0.81 10.75 0.02 13.90

Standard Deviation 0.14 0.02 0.35 0.00 1.05

Appendix Chapter 10

228

Standard Error 0.10 0.01 0.25 0.00 0.74

PE Tensile Strength Summary

Sample


1 20.50

2 20.60

3 20.40

4 20.60

5 20.70

Mean 20.56

Standard Deviation 0.11

Standard Error 0.05

Figure 10-23: Stress Strain curves of commercial recycled PE and PP.

0 . 0 0 . 2 0 . 4 0 . 6 0. 8 1. 0 1. 2 1 . 4

0

5

1 0

1 5

2 0

En

gin

ee

rin

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a)

E n g in e e r in g S tr a in

C om m er cia l PE

C om m er cia l PP

Appendix Chapter 10

229

Figure 10-24: WEEE PP FTIR analysis.

10.5 Initial Studies Generating Future Work in PPCs

10.5.1 Recyclability

A small trial took place in order to gain an insight into how PPCs could be recycled. The mechanical properties retain their values up to three cycles of moulding and granulating.

Table 10-3: Tensile strength and flexural modulus data after recycling three times.

Tensile

Recycled PP/PPC Blends

WEEE PP 70wt.% WEEE PP / 30wt.%

PPL Cup 68wt.% WEEE PP / 30wt.%

PPL Cup / 2wt.% 907P

Tensile Strength

(MPa)

Young's Modulus

(GPa)

Tensile Strength

(MPa)

Young's Modulus

(GPa)

Tensile Strength

(MPa)

Young's Modulus

(GPa)

1st Recycle 20.7 1.05 20.6 1.86 26.7 2.04

2nd Recycle 20.8 1.09 20.8 1.90 27.0 2.01

3rd Recycle 20.3 1.04 19.8 1.79 26.2 2.08

Flexural

Recycled PP/PPC Blends

WEEE PP 70wt.% WEEE PP / 30wt.%

PPL Cup 68wt.% WEEE PP / 30wt.%

PPL Cup / 2wt.% 907P

Flexural Strength

(MPa)

Flexural Modulus

(GPa)

Flexural Strength

(MPa)

Flexural Modulus

(GPa)

Flexural Strength

(MPa)

Flexural Modulus

(GPa)

1st Recycle 30.6 1.12 36.2 1.93 43.0 2.18

2nd Recycle 30.8 1.21 36.2 2.01 43.1 2.24

3rd Recycle 30.6 1.20 36.9 1.95 41.8 2.20

Appendix Chapter 10

230

Table 10-4: Recipes for Initial Trial.

Recipes Plastic Filler Coupling agent

30wt% 40wt% 2wt% 2.5wt%

Recipe 1 MRF Severnside

Recipe 2 MRF Severnside HoneyWell 907P MAPP

Recipe 3 MRF TetraPak

Recipe 4 MRF TetraPak HoneyWell 907P MAPP

Recipe 5 MRF Solocup

Recipe 6 MRF Solocup HoneyWell 907P MAPP

Recipe 7 WEEE PP Solocup

Recipe 8 WEEE PP TetraPak

Recipe 9 WEEE PP Severnside

Recipe 10 WEEE ABS Severnside

Recipe 11 WEEE ABS TetraPak

Recipe 12 WEEE ABS Solocup

Recipe 13 MRF Solocup

Recipe 13.5 MRF Solocup HoneyWell 907P MAPP

Recipe 14 MRF Solocup E-43

Recipe 15 MRF Solocup Chemtura PB3200

Recipe 16 MRF Solocup HoneyWell 1325P



Recipe 19 MRF PP CARPET

Recipe 20 MRF PP CARPET HoneyWell 907P MAPP

Recipe 21 MRF Solocup HoneyWell 907P MAPP

Recipe 22 WEEE PP Solocup HoneyWell 907P MAPP

Appendix Chapter 10

231

Figure 10-25: Tensile strength values after recycling 3 times with the matrix, filler and matrix at 30

wt.% PPL cups and 2 wt.% 907P.

Figure 10-26: Shear stress vs. shear rate of PPCs before and after recycling 3 times.

Figure 10-26 shows that initial signs of rheology of recycled PPCs. The results indicate that the more

PPCs are recycled then the higher the viscosity. At low shear rates a higher stress is required for PPCs

0 100 200 300 400 500 600

-20000

0

20000

40000

60000

80000

100000

120000

140000

160000

Shea

r S

tres

s (P

a)

Shear Rate (1/s)

30wt.% PPL Cups _Reprocess

30wt.% PPL Cups

Appendix Chapter 10

232

to flow. This could be due to the degradation of the components of PPCs. Further analysis of

microstructure of the recycled PPCs is needed.

10.5.2 Filler shape

The initial results are shown in Figure 10-27.

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

0

10

20

En

gin

eeri

ng

Str

ess

(MP

a)

Engineering Strain

90wt.% WEEE PP / 10wt.% PPL Cup

90wt.% WEEE PP / 10wt.% PPL Cup Long Fibre

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

0

5

10

15

20

25

30

35

40

Fle

xu

ral

Str

ess

(MP

a)

Flexural Strain

90wt.% WEEE PP / 10wt.% PPL Cup

90wt.% WEEE PP / 10wt.% PPL Cup Long Fibre

Appendix Chapter 10

233

Figure 10-27: a) Tensile Stress Strain data comparing longer flakes of paper cups against 10 wt.% PPL

3x3mm flakes b) Flexural Stress Strain data comparing longer flakes of paper cups against 10 wt.% PPL

3x3mm flakes and c) Tensile Stress Strain data with longer flakes of paper cups after 4032 hours of

water absorption testing.

The longer fibre analysis showed that the mechanical properties are higher than the flakes. The water

absorption shows a lack of stiffness and strength.

Paper cups were shredded in a paper shredder. A small volume was used initially because the larger

filler size caused feeding issues such as bridging, during compounding.

The results from Figure 10-27 show that the longer fibres show higher mechanical properties and also

higher water absorption. This may be due to the size of the filler content allowing more sites for water

molecules to be absorbed. The tensile properties of the PPC after being immersed in water for over

4000 hours shows a reduction of stiffness properties and strength. Further analysis of how increasing

volume fractions should be investigated. It is evident at the 10 wt.% filler content level the water

absorption affects the PPCs more than the flakes analysed in Chapter 7.

0.00 0.02 0.04 0.06 0.08 0.10

0

5

10

15

20

Engin

eeri

ng S

tres

s (M

Pa)

Engineering Strain

90wt.% WEEE PP / 10wt.% PPL Cups

90wt.% WEEE PP / 10wt.% PPL Cups _ Long fibre_4032 hours

Appendix Chapter 10

234

10.6 Equipment for PPC Processing and Testing

Figure 10-28: MAS extruder developed for compounding of fibrous composites

Appendix Chapter 10

235

Figure 10-29: Creep setup showing the rubber strap and coil used for creep testing at elevated

temperatures.

Appendix Chapter 10

236

10.7 PPC Poster at Imperial College London

Figure 10-30: Winning poster highlighting aspects of this research.

imperial college londonspiral.imperial.ac.uk/.../1/mitchell-j-2015-phd-thesis.pdf · 2019. 11....

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