mechanical performance of kenaf fibre...
TRANSCRIPT
MECHANICAL PERFORMANCE OF KENAF FIBRE REINFORCED
THERMOPLASTIC COMPOSITE
NUR ASILAH BINTI CHE AZIZ
A thesis submitted in fulfillment of the
requirement for the award of the degree of
Bachelor of Chemical Engineering
Faculty of Chemical Engineering and Natural Resources
University Malaysia Pahang
MAY 2011
ii
ABSTRACT
Natural fibre is one of the potential candidates to be used with the thermoplastic
as a composite. Kenaf fibre was mixed with Polypropylene (PP) in addition of maleic
anhydride (MAPP). Kenaf were separated from the outer layer and bast fibre and were
cut using crusher. The ash content is removed by sieving and washing the fibre. The
fibre is then treated with alkaline treatment using three different concentrations of 5wt%,
10wt% and 15wt% in three different time’s treatments which are 1 hour, 1.5 hour and 2
hour. 10wt% fibre and 1.5 hour of time treatment were chose as an actual value for fibre
loading of the composites which were 10wt%, 20wt%, 30wt%, and 40wt%. MAPP was
added with weight ratio 1:10 of fibre and finally PP was added to complete the sample.
All of the samples were compounded using plastic mixer and palletized using plastic
crusher. Samples were then molded by injection molding. An alternative method has
been used to find a better solution for fibre treatment by using Ultrasonic for 10wt%
fibre and 1.5 hour treatment. Some tests were done to analyze samples such as Fourier
Transform Infrared Spectroscopy (FTIR), Melt Flow Index (MFI), water adsorption,
density (Pcynometer), and tensile strength (Tensile Test). For feasibility study of
alkaline treatment, the results showed that the best value is for 15wt%, 1 hour of alkaline
treatmen. For feasibility study of fibre loading, the best composite selected was sample
with 40wt% of fibre with tensile strength of 49.1547MPa and for comparison by using
Ultrasonic for treatment; it was showed that this alternative method gave a better
composite. From the data and supported theories by various authors, it can be concluded
that alkaline treatment, fibre loading and treatment method have a significant effect on
the composite.
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ABSTRAK
Gentian asli merupakan salah satu elemen yang berpotensi untuk digabungkan
dengan termoplastik. Gentian kenaf dicampurkan bersama Polypropylene (PP) dengan
tambahan Maleic Anhydride (MAPP). Kenaf pada mulanya dipisahkan dari lapisan luar
dan serat dan dipotong menggunakan pemotong. Kandungan abu dipisahkan dengan
mengayak dan membasuh gentian. Gentian kemudiannya dirawat dengan rawatan
beralkali dengan tiga konsentrasi berat serat yang berbeza iaitu 5%, 10% dan 15% dalam
tempoh rawatan yang berbeza iaitu 1 jam, 1.5 jam dan 2 jam. 10% berat serat dan 1.5
jam tempoh rawatan dipilih sebagai satu nilai untuk pemuatan serat berat komposit
untuk 10%, 20%, 3% dan 40%. MAPP telah ditambah dengan nisbah berat 1:10 serat
dan akhirnya PP ditambah bagi menyiapkan sampel. Kesemua sampel digabungkan
menggunakan pencampur plastik dan dipotong menggunakan penghancur plastik.
Sampel kemudiannya dibentuk melalui pembentuk suntikan. Satu kaedah alternatif
digunakan sebagai penambahbaikan rawatan gentian dimana rawatan ultrasonik
digunakan untuk 10% berat gentian serat dengan 1.5 jam rawatan. Beberapa analisis
dijalankan seperti Fourier Transform Infrared Spectroscopy (FTIR), Melt Flow Index
(MFI), penjerapan air, ketumpatan (Pcynometer) dan kekuatan tegangan (Tensile Test).
Untuk rawatan beralkali, nilai yang terbaik ialah 15% berat konsentrasi serat dengan 1
jam masa rawatan manakala untuk pemuatan serat, komposisi yang terbaik adalah 40%
berat gentian dengan kekuatan tegangan sebanyak 49.1547MPa. Melalui aplikasi
ultrasonik, keputusan menunjukkan kaedah ini memberikan hasil yang lebih baik. Dari
data dan menyokong teori oleh pelbagai penulis, kesimpulannya rawatan beralkali,
komposisi serat dan kaedah rawatan adalah sesuatu yang penting kepada komposit.
iv
TABLE OF CONTENT
CHAPTER TITLE PAGE
ACKNOWLEDGEMENT i
ABSTRACT ii
ABSTRAK iii
TABLE OF CONTENTS iv
LIST OF TABLES vii
LIST OF FIGURES ix
LIST OF NOMENCLATURE xi
LIST OF APPENDICES xii
1 INTRODUCTION
1.1 Background of Study 1
1.2 Problem Statement 3
1.3 Objective of Study 4
1.4 Scope of Study 4
2 LITERATURE REVIEW
2.1 Introduction 6
2.2 Natural Fibre 6
2.2.1 Types of Natural Fibre 7
2.2.2 Properties of Natural Fibre 8
2.2.3 Kenaf Fibre 9
2.2.4 Characteristic and Properties of 10
Kenaf Fibre
2.3 Matrix 11
2.3.1 Thermoplastic 11
v
2.4 Kenaf Fibre Reinforced Polypropylene 13
2.5 Factors Controlling Performance of 13
Fibre Reinforced Composites
2.5.1 Fibre Thermal Stability 13
2.5.2 Fibre Hydrophilic Nature 14
2.5.3 Fibre Critical Length 15
2.6 Modification of Composite 16
2.6.1 Fibre Content in Composite 16
2.6.2 Alkali Treatment in Natural Fibre 16
2.6.3 Coupling Agent 17
2.6.4 Ultrasonic 18
2.7 Fabrication Methods 18
2.7.1 Compounding Process 19
2.7.2 Molding Process 19
2.8 Research Done by Other Researcher 19
3 RESEARCH AND METHODOLOGY
3.1 Material Selection 23
3.1.1 Kenaf 23
3.1.2 Polypropylene 24
3.1.3 Sodium Hydroxide (NaOH) 25
3.1.4 Maleic Anhydride Grafted 26
Polypropylene (MAPP)
3.2 Research Design 27
3.2.1 Separating Core and Fibre 28
3.2.2 Kenaf Cutting Process 29
3.2.3 Removing Ash from Fibre 30
3.2.4 Fibre Treatment 32
3.2.5 Drying Process 34
3.2.6 Compounding Process 34
vi
3.2.7 Palletizing Process 36
3.2.8 Moulding Process 37
4 RESULT AND DISCUSSION
4.1 Fibre Treatment 39
4.1.1 Effect of Alkaline Treatment on 39
Fibre Structure
4.1.2 FT-IR Analysis 40
4.2 Fibre Loading Effect 46
4.2.1 Tensile Strength Analysis 47
4.2.2 Flexural Modulus Analysis 49
4.2.3 Elongation at Break Analysis 50
4.2.4 Melt Flow Index (MFI) Analysis 51
4.2.5 Density Analysis 53
4.2.6 Water Absorption Analysis 55
4.3 Ultrasonic Mixing Method 57
4.3.1 Tensile Strength Analysis 58
4.3.2 Flexural Modulus Analysis 59
4.3.3 Elongation at Break Analysis 60
4.3.4 Melt Flow Index (MFI) Analysis 61
4.3.5 Density Analysis 62
4.3.6 Water Absorption Analysis 63
5 CONCLUSION AND
RECOMMENDATION
5.1 Conclusion 64
5.2 Recommendation 65
REFERENCES 66
vii
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Comparison between natural and glass fibre 7
2.2 Properties of natural fibre 8
2.3 Characteristic and properties of kenaf stems, 10
Malaysia
2.4 Research done by orther researcher 20
3.1 Properties of polypropylene (PP) 25
3.2 Properties of sodium hydroxide (NaOH) 26
4.1 Condition for alkaline treatment with different 39
concentration and time treatment
4.2 FT-IR functionsl group 41
4.3 FT-IR adsorbance of lignin and hemicellulose 45
content for treated and untreated kenaf fibre
4.4 Different fibre loading for composite composition 46
4.5 Tensile streangth of different loading fibre 48
composition
4.6 Flexural modulus of different loading fibre 49
composition
4.7 Elongation at break of different loading fibre 50
composition
4.8 Average Melt Flow Index (MFI) of different 52
loading fibre composition
4.9 Density of different loading fibre composite 54
viii
4.10 Tensile strength for different treatment mixing 58
method
4.11 Flexural modulus for different treatment mixing 59
method
4.12 Elongation at break for different treatment mixing 60
method
4.13 Melt Flow Index (MFI) for different treatment 61
mixing method
4.14 Density for different treatment mixing method 62
ix
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Molecular structure of Polypropylene (PP) 12
3.1 Structure of Polypropylene 24
3.2 Cultivated kenaf from Rompin, Pahang 28
3.3 Kenaf fibre (separated from its outer layer) 28
3.4 Plastic mixer 29
3.5 Kenaf fibre (cut) 29
3.6 Sieving kenaf fibre 30
3.7(a) Kenaf before washing 31
3.7(b) Kenaf fibre during washing 31
3.7(c) Kenaf fibre after washing 31
3.8 Preparing sodium hydroxide (NaOH) solution 32
3.9 Immersed fibre for alkaline treatment 32
3.10(a) Treated fibre before rinsed 33
3.10(b) Treated fibre after treatment 33
3.11 Oven for drying fibre 33
3.12 Plastic Mixer 34
3.13(a) Kenaf fibre and PP compounded in plastic mixer 34
3.13(b) Compounded material after using plastic mixer 34
3.14 Plastic crusher 35
3.15 Compounded material after grinded with plastic 35
crusher
3.16 Injection molding 36
3.17 Product molding 37
4.1 Fourier Transform Infra-Red (FT-IR) 40
4.2 FT-IR absorbance result of treated and untreated 41
kenaf fibre
x
4.3 FT-IR absorbance result of kenaf fibre with 5wt% 42
of alkaline treatment
4.4 FT-IR absorbance result of kenaf fibre with 10wt% 43
of alkaline treatment
4.5 FT-IR absorbance result of kenaf fibre with 15wt% 44
of alkaline treatment
4.6 Universal Testing Machine 47
4.7 Tensile Strength of different loading fibre 48
composition
4.8 Flexural modulus of different loading fibre 49
composition
4.9 Elongation at break of different loading fibre 51
composition
4.10 Melt Flow Indexer (MFI) 52
4.11 Melt Flow Index for different loading fibre 53
composition
4.12 Pycnometer 54
4.13 Density value for different loading fibre composition 55
4.14 Soaked composites for water absorption analysis 56
4.15 Water absorption analysis for different fibre loading 56
4.16 Ultrasonic Cleaner 57
4.17 Tensile strength for different treatment mixing method 58
4.18 Flexural modulus of different treatment mixing method 59
4.19 Elongation at break of different treatment mixing 60
method
4.20 Melt Flow index for different treatment mixing method 61
4.21 Density value for different treatment mixing method 62
4.22 Density value for different treatment mixing method 63
xi
LIST OF NOMENCLATURE
% - Percentage
wt% - Weight percentage
vol% - Volume percentage
°C - Degree celsius
T - Extraction temperature
V - Volume
μ - Micro
Gpa - Giga pascal
MPa - Mega pascal
KPa - Kilo pascal
T - temperature
m - Molecular mass
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LIST OF APPENDICES
APPENDIX TITLE
A FT-IR Fibre Analysis
B Tensile Strength
C Density Analysis
CHAPTER 1
INTRODUCTION
1.1 Background of Study
The volume of thermoplastics used in the housing, automotive, packaging and
other low-cost, high-volume applications is enormous. Recent interest in reducing the
environmental impact of materials is leading to the development of newer materials or
composites that can reduce the stress to the environment. In light of potential future
petroleum shortages and pressures for decreasing the dependence on petroleum products,
there is an increasing interest in maximizing the use of renewable materials (Roger M.
Rowell et al., 1999).
Natural fibre reinforced unsaturated polyester have generated much interest in
recent years as a potential environmentally friendly and cost-effective option for making
low cost engineering materials. New environmental regulations have forced the
industries to search for new materials that can substitute for the traditional non-
renewable reinforcing materials such as carbon fibres and glass fibres. Thus the
environmentally friendly natural fibres combined with unsaturated polyester resin are
widely introduced to the industries as they possess many advantages compared to other
thermosetting resins including room temperature cure capability, good mechanical
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properties and transparency. Natural plant fibre reinforced polymeric composite also
have some disadvantages such as the incompatibility between the hydrophilic fibres and
hydrophobic thermoplastic and thermoset matrices requiring appropriate treatments to
enhance the adhesion between fibre and the matrix (Gassan et al., 2000, Dhakal et al.,
2007).
One of the celebrated constituents of natural fibre reinforced plastic composites
in Malaysia is kenaf fibre. The research in kenaf plastic composite is growing
tremendously along with the plastic industry’s high demand for it for producing
petroleum-based materials. Kenaf long fibre plastic composite could be used for a wide
variety of applications if the properties were found to be comparable to existing
synthesis composites. Since kenaf is always available in long fibre form, the mechanical
properties found could be of use in many industrial applications such as insulators seals.
In addition, kenaf fibre offers the advantages of being biodegradable, of low density,
non-abrasive during processing and environmentally safe (Nishino T., 2003).
The attractive features of kenaf fibres are the low cost, lightweight, renewability,
biodegradability and high specific mechanical properties. Kenaf has a bast fibre which
contains 75% cellulose and 15% lignin and offers the advantages of being biodegradable
and environmentally safe (Kamai R., 1996).
Among natural fibre composites, kenaf fibre reinforced composites have found
potential applications for mobile phone shells consisting 15–20% kenaf fibres (Iji,
2008). Another example in the automobile industry is the Toyota RAUM, which is
equipped with a spare tire cover made of kenaf fibre composites (Maya Jacob John et
al., 2007).
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1.2 Problem Statement
As industry attempts to lessen the dependence on petroleum based fuels and
products there is an increasing need to investigate more environmentally friendly,
sustainable materials to replace the existing glass fibre and carbon fibre reinforced
materials. Therefore, attention has recently shifted to the fabrication and properties of
natural fibre reinforced materials (Mohanty AK et al., 2003).
The worldwide automotive production rate is increasing and is estimated to reach
76 million cars annually by 2020 (WBCSD, 2004). Limited petroleum resources will
increase petroleum-based products’ prices in the near future. It is estimated that a 25%
reduction in car weight would be equivalent to saving 250 million barrels of crude oil
(Lan R. Mair, 2000); therefore it is possible that manufacturers will consider expanding
the use of natural fibre in their new products. Moreover, the recycling concerns being
driven by EU regulations (ELV) are forcing manufacturers to consider the
environmental impacts of their production and possibly shift from petroleum-based to
agro-based materials (Rasshofer W. et al., 2001; Davoodi MM. et al., 2008).
Natural fibre-reinforced (NFR) composites are likely to be environmentally
superior to glass fibre reinforced (GFR) composites in most applications because natural
fibre production results in lower environmental impacts compared to glass fibre. The
production of natural fibre-reinforced transport pallets uses 45% less energy, and results
in lower emission of toxic gases (CO2, methane, SO2, and CO) than production of GFR
transport pallets (Van de Velde K, et al., 2001).
4
However, natural fibres are hydrophilic in nature as they are lignocellulosic,
which contain strongly polarized hydroxyl groups and require chemical modification to
increase the compatibility and adhesion between fibres and matrix (John & Anandjiwala,
2008); which is associated with a low compatibility of hydrophobic polymers like
polypropylene, as well as with a loss of mechanical properties after moisture uptake
(Tajvidi M. et al., 2003; Bledzki KA et al., 1998; Khan AM et al., 1997).
Due to the poor compatibility, surface of fibres must be treated with coupling or
compatibilizing agents to improve the interface between the fibre and the matrix.
However, the use of both matrix resin (maleated polyolefins) and fibre surface treatment
(coupling agents) have received considerable attention due to their effectiveness in
modifying the interface by forming a link between the components (Felix MJ et al.,
1991; Zafeiropoulos EN et al., 2002).
It would be ideal if the chemicals used for the modification of natural fibres
preserve the biodegradable nature of natural fibres. In this study, Sodium Hydroxide
(NaOH) is used for fibre treatment while Maleic Anhydride Polypropylene (MAPP) is
used as a coupling agent to see its effect on interfacial adhesion in kenaf fibre reinforced
polypropylene composites.
1.3 Objectives of the study
The objective of this research is to make an improvement for mechanical
performance of kenaf fibre reinforced thermoplastic.
1.4 Scope of Study
In order to achieve the objective, the scope of research was to make a feasibility
study on fibre treatment for hemicelluloses and lignin removal. Different fibre loading is
used to get the best composition for the composite. Furthermore, affect of using an
alternative method, Ultrasonic, was investigated.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
This chapter describes the physical, chemical and mechanical properties of kenaf
fiber, and some methods to produce composites. Matrix, its types and role of matrix in
composites were also discussed. Major factors controlling the performance of
composites were briefly described. Special emphasis was given on the methods of
modification of fiber-matrix interface as it plays an important role on mechanical
properties of composites.
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2.2 Natural Fiber
Natural fiber is class of hair-like materials that are continuous filaments or are in
discrete elongated pieces, similar to pieces of thread. They can be spun into filaments,
thread, or rope. They can be used as a component of composite materials. The use of
natural fibers as reinforcements in polymer composites to replace synthetic fibers like
glass is presently receiving increasing attention because of the advantages, including
cost effectiveness, low density, high specific strength, as well as their availability as
renewable resources.
Since the 1990s, natural fiber composites are emerging as realistic alternatives to
glass-reinforced composites in many applications. Natural fiber composites such as
hemp fiber-epoxy, flax fiber-polypropylene (PP), and china reed fiber-PP are
particularly attractive in automotive applications because of lower cost and lower
density. Glass fibers used for composites have density of 2.6 g/cm3 and cost between
$1.30 and $2.00/kg. In comparison, flax fibers have a density of 1.5 g/cm3 and cost
between $0.22 and $1.10/kg (Foulk JD et al., 2000).
Several different natural fiber–polypropylene composites is determined the
ability to replace glass fiber–reinforced materials. Polypropylene with a very high melt
flow index was used to aid in fiber matrix adhesion and to ensure proper wetting of the
fibers. Samples were made with 40% fiber content of kenaf, coir, sisal, hemp, and jute.
After the samples were fabricated, tensile and impact tests were run to compare the
properties of these composites to those made with glass fiber. The tensile strengths all
compared well with glass, except for the coir, but the only sample with the same flexural
strength was hemp. It was shown with kenaf fibers that increasing fiber weight fraction
increased ultimate strength, tensile modulus, and impact strength. However, the
composites tested showed low impact strengths compared to glass mat composites. This
study demonstrated that natural fiber composites have a potential to replace glass in
many applications that do not require very high load bearing capabilities (P. Wambua et
al., 2003).
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Table 2.1: Comparison between natural and glass fibers
(P. Wambua et al., 2003)
Natural fibers Glass fibers
Density Low Twice that of natural fiber
Cost Low Low, but higher thnoan natural
fiber
Renewability Yes No
Recyclability Yes No
Energy consumption Low High
Distribution Wide Wide
CO2 neutral Yes No
Abrasion to machines No Yes
Health risk when inhaled No Yes
Disposal Biodegradable Not biodegradable
Natural fiber composites are also claimed to offer environmental advantages
such as reduced dependence on non-renewable energy/material sources, lower pollutant
emissions, lower greenhouse gas emissions, enhanced energy recovery, and end of life
biodegradability of components. Since, such superior environmental performance is an
important driver of increased future use of natural fiber composites, a thorough
comprehensive analysis of the relative environmental impacts of natural fiber
composites and conventional composites, covering the entire life cycle, is warranted
(S.V. Joshi et al., 2003).
2.2.1 Types of Natural Fiber
These natural fibers can be split up into two categories, bast and leaf fibers. The
bast fiber composites include kenaf, hemp and flax while sisal maybe considered a leaf
fiber (M. Zampaloni et al., 2007).
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Bast:
The bast fibers exhibit a superior flexural strength and modulus of elasticity (M.
Zampaloni et al., 2007).
Leaf:
The leaf fibers show superior impact properties (M. Zampaloni et al., 2007).
2.2.2 Properties of Natural Fiber
Table 2.2: Properties of Natural Fiber
(P.Wambua et al., 2003; Mohanty A.K et al., 2000; Parikh DV et al., 2009)
Properties Hemp Jute Ramie Coir Sisal Flax Cotton Kenaf
Density g/cm3 1.48 1.46 1.5 1.25 1.33 1.4 1.51 1.4
Tensile
Strength, MPa 550-900
400-
800 500 220
600-
700
800-
1500 400
283-
800
E-Modulus,
GPa 70
10-
30 44 6 38 60-80 12
21-60
Specific (E/d) 47 7-21 29 5 29 26-46 8 -
Elongation at
failure, % 1.6 1.8 2
15-
25 2-3
1.2-
1.6 3-10
1.6
Moisture
absorption, % 8 12 12-17 10 11 7 8-25
-
Natural fiber properties are highly variable and depend on conditions of growth.
It is therefore very difficult to get the same mechanical properties after repeat testing.
For this research, kenaf fiber is used instead of other natural fiber. This is
because kenaf requires less than 6months for attaining a size suitable for practical
application. Due to the fast growth and good fiber quality, since the 1960s, there has
9
been increasing interest in kenaf, primarily for its potential use as a commercial fiber
crop for the manufacture of newsprint and other pulp and paper products, leading to
collaborations between R&D, economist, and market research (H.P.S. Abdul Khalil et
al., 2010).
2.2.3 Kenaf Fiber
Kenaf (Hibiscus cannabinus L.) is a traditional, third world crop after wood and
bamboo that is poised to be introduced as a new annually renewable source of industrial
purpose in the so-called developed economies. Kenaf is a warm-season annual fiber crop
growing in temperate and tropical areas. It is related to cotton, okra, and hibiscus due to
systematics. It is a fibrous plant, consisting of an inner core fiber (75–60%), which
produces low quality pulp, and an outer bast fiber (25–40%), which produces high
quality pulp, in the stem. The plant grows to a height of 2.7–3.6mand is harvested for its
stalks, from which the fiber is extracted (H.P.S. Abdul Khalil et al., 2010).
Mankind has skillfully made use of kenaf from ancient times, traditionally as a
rope, canvas and sacking. There are numerous advantages of using natural
lignocellulosic fibers as reinforcements of the matrix. Especially, kenaf is well known as
a cellulosic source with economical and ecological advantages. Kenaf exhibits low
density, non-abrasiveness during processing, high specific mechanical properties, and
biodegradability.
Recently, kenaf is used as a raw material to be alternative to wood in pulp and
paper industries for avoiding destruction of forests (Pande H et al., 1998), and also used
as non-woven mats in the automotive industries (Magurno A. et al., 1999).
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Kenaf is an herbaceous annual plant that is grown commercially in the United
States in a variety of weather conditions, and it has been previously used for rope and
canvas. Kenaf has been deemed extremely environmentally friendly for two main
reasons; (a) kenaf accumulates carbon dioxide at a significantly high rate and (b) kenaf
absorbs nitrogen and phosphorous from the soil (Michell A., 1986).
2.2.4 Characteristic and Properties of Kenaf Fiber
Kenaf has a bast fiber which contains 75% cellulose and 15% lignin and offers
the advantages of being biodegradable and environmentally safe (Kamani R., 1996).
Malaysian kenaf is composed of two distinct fibers, bast and core, with a makeup of
about 35% and 65%, respectively. Each fiber has its own usage; thus, separation of the
fibers produces higher monetary returns over whole-stalk kenaf. Major factors involved
in separation of kenaf into its two fractions include: size and amount of each portion;
type and number of separation machinery; processing rate through separation
machinery; moisture content of whole-stalk kenaf; humidity of ambient air (H.P.S.
Abdul Khalil et al., 2010).
Table 2.3: Characteristic and properties of kenaf stems, Malaysia
(H.P.S Abdul Khalil et al., 2010)
Characteristics/properties Bast Core Stem
Dimension (cm)
Height (range)
Diameter
Perimeter
1.52 (0.095)
5.73 (0.131)
145-250
1.74 (0.212)
6.60 (0.101)
Proportion (%)
Cross-section area
Weight proportion
21.96 (2.03)
32.2
78.04 (2.51)
68.5
Density (g/cm3) - 0.21 (0.038) 0.29 (0.044)
Acidity (pH) 7.13 5.21 5.87
11
2.3 Matrix
The first and the most important problem is the fiber-matrix adhesion. The role
of the matrix in a fiber reinforced composite is to transfer the load to the stiff fibers
through shear stresses at the interface. This process requires a good bond between the
polymeric matrix and the fibers. Poor adhesion at the interface means that the full
capabilities of the composite cannot be exploited and leaves it vulnerable to
environmental attacks that may weaken it, thus reducing its life span. Insufficient
adhesion between hydrophobic polymers and hydrophilic fibers result in poor
mechanical properties of the natural fiber reinforced polymer composites (P. Wambua et
al., 2003).
2.3.1 Thermoplastic
While, natural fibers traditionally have been used to fill and reinforce thermosets,
natural fiber reinforced thermoplastics, especially polypropylene composites, have
attracted greater attention due to their added advantage of recyclability (Mohanty AK et
al., 2002).
Thermoplastic composites are composites that use a thermoplastic polymer as a
matrix. A thermoplastic polymer is a long chain polymer that can be either amorphous in
structure or semi-crystalline. These polymers are long chain, medium to high molecular
weight materials.
Advantages of thermoplastic matrices:
• Unlimited shelf life
• Short processing time
• Resistance to chemical attack
• Recyclability
• Superior impact
12
Disadvantages of thermoplastic matrices:
• Easy to melt
• High viscosity
Polypropylene (PP)
Figure 2.1: Molecular structure of Polypropylene (PP)
Polypropylene's (PP) intrinsic properties of high stiffness, good tensile strength
and inertness toward acids, alkalis and solvents has secured its position in a wide range
of consumer and industrial products. Polypropylene are also flexible and can have very
high elongation before breaking. The other advantages are:
• Homopolymer
• Good process ability
• Good stiffness
• Good impact resistance
• Copolymer
• High flow index
• Chemically coupled
Although polypropylene gives a lot of advantages, there are several difficulties for this
thermoplastic such as:
• Degraded by UV
• Flammable, but retarded grades available
• Low temperature
13
The advantages of using polypropylene (PP) as matrix are their low cost and
relatively low processing temperature which is essential because of low thermal stability
of natural fibers. Amongst eco-compatible polymer composites, special attention has
been given to PP composites, due to their added advantage of recyclability.
2.4 Kenaf Fiber Reinforced Polypropylene
The research done in this study has proven the ability to successfully fabricate
kenaf–polypropylene natural fiber composites. The optimal fabrication method for the
compression molding process has proven to be the layered sifting of a microfine
polypropylene powder and chopped kenaf fibers. Also shown through this work was that
kenaf–PP composites have a higher Modulus/Cost and a higher specific modulus than
sisal, coir, hemp, flax and E-glass (M. Zampaloni et al., 2007)
2.5 Factors Controlling Performance of Fiber Reinforced Composites
2.5.1 Fiber Thermal Stability
High temperatures must also be avoided due to the possibility of fiber
degradation (M. Zampaloni et al., 2007). The main limitation to the use of
lignocellulosic fibers is the lower processing temperature permissible due to the
possibility of fiber degradation and/or the possibility of volatile emissions that could
affect composite properties. The processing temperatures are thus limited to about
200°C, although it is possible to use higher temperatures for short periods. This
processing factor limits the type of thermoplastics that can be used with lignocellulosic-
fibers; to commodity thermoplastics such as polyethylene (PE), polypropylene (PP),
polyvinyl chloride (PVC) and polystyrene (PS) (Roger M. Rowell et al., 1999).
14
Shinji Ochi et al., 2008, proved that kenaf fibers revealed tensile strength of
kenaf fibers decreased when kept at 180°C for 60 min, therefore the fabrication method
for composite in this research is ensured to be below the temperature. For compounding,
mixing temperature is 190°C (outer temperature) because the rotating blade inside
plastic mixer will be lower than that while for moulding the temperature is 180°C.
2.5.2 Fiber Hydrophilic Nature
In fiber reinforced polymer (FRP), not only polymer matrix that absorb moisture
but also the fiber especially the natural fiber. This particularly due to the hydrophilic
nature of the natural fiber that is more sensitive towards water absorption than synthetic
fiber which causing instability in the properties of the composites (Espert A., 2003).
The inherently polar and hydrophilic nature of lignocellulosic fibers and the
nonpolar characteristics of most thermoplastics result in compounding difficulties
leading to nonuniform dispersion of fibers within the matrix, which impairs the
properties of the resultant composite. This is a major disadvantage of natural fiber-
reinforced composites (Maya Jacob John et al., 2007).
Alkaline treatment was applied in order to solve the problem of fiber–matrix
adhesion when manufacturing biocomposites. Natural fibers are mainly composed of
cellulose, whose elementary unit, anhydro d-glucose, contains three hydroxyl (–OH)
groups. These hydroxyl groups form intramolecular and intermolecular bonds, causing
all vegetable fibers to be hydrophilic. The alkaline solution regenerated the lost cellulose
and dissolved unwanted microscopic pits or cracks on the fibers resulting in better fiber
matrix adhesion (Feng D et al., 2001; Mutje P et al., 2006; Keener TJ et al., 2004).