Development of New Composites of Recycled Polypropylene and

combinations of Organic Fillers and Fibres for the Manufacture

of Fish Farming Cage.

Ferran Martía , Nuria López

a, Vicente Amigo

b, Noemí Ferrando

a

aAIMPLAS (Instituto Tecnológico del Plástico) C/ Gustave Eiffel, 4, 46980 Paterna

(Valencia) fmarti@aimplas.es, nlopez@aimplas.es ,nferrando@aimplas.es. bInstituto de Tecnología de Materiales, Universitat Politècnica de València, Camí de Vera,

46022 València, España vamigo@mcm.upv.es

ABSTRACT

The main objective of the project is to design, produce and optimise innovative aquiculture

structures using a new plastic composite reinforced with a combination of organic filler and

fibres specially developed in the project for applications in permanent contact with water.

The project will also help to solve the problems associated with wooden structures in

permanent contact with water, such as the reduction of mechanical properties (due to the

effects of water) and rotting. In this work, we studied the interaction of post-consumer flax

and cotton fibres and special size rice husk as a material reinforced industrial recycled

injection grade polypropylene. The amount of fillers plus fibres studied in the composite was

fixed at 40% w/w. Some coupling agents based on maleic anhydride were also tested mainly

to improve their impact resistance.

The composite of matrix thermoplastic and fillers leads to a parts with high tensile modulus,

low viscosity and free of warpage, however they have low tensile strength and low impact

resistance. On the other hand, the use of polymer composites using fibres leads to pieces with

suitable strength and impact resistance, whereas the melt viscosity increase a lot and parts

shows a light warpage. Parts injected with a combination of fillers and fibres and

polypropylene as a matrix have intermediate performance, avoiding the problems of warpage

and mould filling due to suitable viscosity. In all compounds prepared, their resistance to

water is suitable for their applications in direct contact with water.

KEYWORDS: compounding, organic fillers, natural fibres, polypropylene, injection

moulding.

INTRODUCTION

Aquaculture is the cultivation of the natural produce of water (fish, shellfish, algae and other

aquatic organisms). Fish farming is the principal form of aquaculture, while other methods

may fall under mariculture. It involves raising fish commercially in tanks or cages, usually for

food. A facility that releases juvenile fish into the wild for recreational fishing or to

supplement a species' natural numbers is generally referred to as a fish hatchery. Fish species

raised by fish farms include salmon, catfish, tilapia, cod, carp, trout and others [1,2].

Increasing demands on wild fisheries by commercial fishing operations have caused

widespread over-fishing. Fish farming offers an alternative solution to the increasing market

demand for fish and fish protein.

The current plastic sea cages are known for their operational stability, optimum flexibility,

durability and ease of use meet performance demands for offshore fish farming.

These cages have mainly circular shape, although, for farming some fish species a square

shape cage is preferred. The cages are available in circumferences ranging between 40m and

120m (and upwards) and can maintain the nets from 8m to 40m and more. The larger units are

designed for deeper nets and very exposed location and enable high and efficient production.

The cage structure is made of polyethylene plastic, durable material that combines the

flexibility and strength. This material has low density to floats perfectly in the water. The

material cannot rust, rot, or corrode and will not be attacked by algae, bacteria or parasites.

Being both flexible and strong the plastic fish cages can overcome the forces of winds,

currents and waves and function safely in the sea.

However, to manufacture these large cage structures virgin polyolefins are used. The use of

recycled material alone to manufacture these structures is not easy due to the limitations of

current post-consumer recycled thermoplastics (market do not offer a constant quality

recycled polypropylene). To overcome these limitations, this work proposes to design and

manufacture a new plastic cage fish using as a raw material a blend of recycled polypropylene

and combinations of organic fibre waste and agricultural waste fillers, in order to improve the

properties of the recycled polypropylene alone.

The use of organic reinforcements, derived from annually renewable resources, as reinforcing

fibers and fillers in both thermoplastic and thermoset matrix composites provides positive

environmental benefits with respect to ultimate disposability and raw material utilization. The

advantages of natural fibers over traditional reinforcing materials such as glass fibers, talc and

mica are: acceptable specific strength properties, low cost, low density, high toughness, good

thermal properties, reduced tool wear, reduced dermal and respiratory irritation. ease of

separation, enhanced energy recovery, and biodegradability [3].

The main bottlenecks in the broad use of these fibers/fillers in thermoplastics have been the

poor compatibility between the them and the matrix, and the inherent high moisture sorption,

which brings about dimensional changes in the lignocellulosic based fibers.

Some authors covers the complexities involved with the compatibilization of these materials

and the different techniques used to understand the interfacial interaction. The efficiency of a

fiber reinforced composite depends on the fiber-matrix interface and the ability to transfer

stress from the matrix to the fiber. This stress transfer efficiency plays a dominant role in

determining the mechanical properties of the composite and also in the material’s ability to

withstand environmentally severe conditions. In the bibliography, there are many papers to

compatibility organic fillers or fibres with polypropylene.

In the case of fillers, mainly wood, approaches to improve the interaction and thereby the

stress transfer between fillers and polypropylene was based on the use of coupling agents and

compatibilizers of various kinds [4,5]. Coating of wood filler with thermoset resin has also

been proved to enhance the mechanical properties of wood/polypropylene composites [6].

The use of chemical modifiers of wood has drawn attention as adhesion-promoting treatments

for the composites in question. Thermoplasticization of wood with adequate modifiers and

modification rates has been proved to facilitate blending and improve compatibility of the

wood material with plastics [7].

Extensive research has been carried out with different kinds of coupling agents for surface

modification of natural fibers in order to increase the adhesive action with the thermoplastic

matrix. Acha et al. [8] used maleated polypropylene wax as coupling agent to improve the

properties of composites prepared from jute and kenaf reinforced PP. Rana et al. [9] have

studied the interfacial adhesion between jute–PP composites using various surface treatments.

All of the above studies indicated that there was a substantial increase in the surface

properties of the fibers with the addition of the coupling agents.

Fillers are used to increase flexural modulus and temperature resistance without an increase of

melt viscosity, price or warpage problems. However, fillers reduce impact and flexural

resistance of the composite.

On the other hand, fibres, due their high aspect ratio, have a good reinforcement properties

and impact properties reduction is lower in comparison with the fillers. Although fibres

increase the melt viscosity, increase the price of the composite and tends to part deformation

due to their anisotropy.

Tacking into account the advantages and limitation of each one, this work studied to develop

news blends of recycled polypropylene in combination of different types of organic fibres and

fillers. All the fibres/fillers used were a waste from agricultural or industrial sector.

Although in the market there are polymers that contain combinations of inorganic fillers and

fibres (i.e. glass fibres and mica filler), there are not previous works, where compounding of

combinations of organic fillers and natural fibres was prepared and studied.

2. EXPERIMENTAL.

2.1. Materials selection. A recycled block copolymer polypropylene with melt volumetric index 6,1cm

3/10 min

measured at 230ºC and 2,16 Kg was selected as a matrix of all the compounds prepared. The

material was supplied by a local recycler. This material was obtained from post-consumer car

batteries.

As filler, husk rice of particle size between 100 to 450 microns will be used. The material

was supplied by MIFSUD a small company located in Spain. The rice husk was used as it

was supplied. The moisture content of the filler is 10%. Fillers have suitable apparent density

to direct feed to the hopper and side feeder of the compounding extruder. They do not need a

pelletization process. Figure 1.a shows the aspect of the rice husk employed.

FIGURE 1. FILLERS AND FIBRES EMPLOYED : A) HUSK RICE B) COTTON C) FLAX.

Two fibres were selected and studied:

1) Cotton fibre (figure 1.b): This fibre was obtained from a local recycled of jeans

trousers, this is a multicolour waste cotton. The current application of this material

is for acoustic reduction in car applications and other low cost uses. The aspect

ratio is in the range of 150 and 200 and its apparent density is approximately 5

kg/m3. Its moisture content is lower than 3%.

2) Flax fibre (figure 1.c): This fibre was supplied in form of sheets by CELESA

(Spain). This large company is a manufacturer of special papers from natural fibres

(jute, kenaf, flax, etc..). The flax fibre selected is present in their residual flow

during the chemical treatment of the fibre to reduce their content in lignin. The

water content is 8-9%. The aspect radio is lower than cotton fibres (100-150 of

individual fibres) and its apparent density was calculated between 5-7 kg/m3 after

grinding.

Due the different presentation of both fibres, they were threaded of different form before to

feed to the compounding extruder. Cotton was pelletized to increase its apparent density using

water and small amount of an organic binder. After that the pellet was dried in a oven at 60ºC

during 4 hours. Dry cotton pellets were moisture content less than 1%. The pellets are soft and

break easily.

Flax was grinded in a standard rotor knife grinder. This system produces a separation of the

flax fibres increasing its aspect ratio and reduces its apparent density. After that we follow the

same methodology than in the case of cotton fibres. However, the flax pellets are too strong,

when the moisture is removed from the pellet. Flax fibres has a higher polarity than cotton

fibres. In order to obtain a soft pellets, that could be breaks easily in the extruder, the flax

pellets was not dried after pelletization process. The water from filler and the fibre were

removed from the compound during twin screw extrusion process.

As a coupling agents, three polymer graft maleic-anhydride (MAH) was used. Table 1

summarized the main properties of each coupling agent.

TABLE 1. MAIN CHARACTERISTICS OF THE SELECTED COMPATIBILIZERS.

MFI (g/10 min) Commercial name

Type of

Coupling

MAH

content

Density

g/cm3 190ºC/2.16Kg 230ºC/2.16Kg

INTEGRATE NP

507-30 PP-g-MAH High 0.91 ___ 29

POLYBOND 3200 PP-g-MAH High 0.91 115 ___

ROYALTUF 498 EPDM-g-MAH Medium 0.89 ___ ___

The INTEGRATE NP 507-30 supplied by EQUISTAR (USA) is a PP-g-MAH with a high

content of MAH and an high molecular weight. POLYBONB 3200 provided by POLYONE

(USA) is a graft type coupling agent like INTEGRATE with a high MAH content, but with

low molecular weight. ROYALTUF 498 is a medium content MAH having as a matrix

ethylene propylene diene monomer rubber (EPDM) an elastomeric polymer with good

compatibility with polypropylene resins. The last one was purchased to CROMPTON (USA).

With the objective to improve the resistance to the impact obtained with the systems polymer-

fibre-filler, two impact modifiers were studied. Those are modifiers with low cost used in the

industry as modifiers of impact of polyolefin. Table 2 shows their main properties.

TABLE 2. MAIN CHARACTERISTICS OF THE SELECTED IMPACT MODIFIERS.

Commercial name Co-monomer Type % Co-

monomer

MFI (g/10min)

190ºC/2.16Kg

LOTRIL 29 MA 03 Methyl Acrylate (MA) 29% MA 3

ELVALOY 3427 Butyl acrylate (BA) 27% BA 4

The impact modifiers additives were purchased to ATOFINA (France) and DuPont (USA)

respectively.

Samples preparation.

The natural fibres have been previously pelletized, due to their low apparent density, to ease

the feeding during the compounding process as we described before, Gravimetric feeder

manufactured by Brabender Technology (Germany) and volumetric of K-Tron (Switzerland)

manufacturer feeders were used.

Gravimetric feeders were used to feed all the components compounding extruder. The use of

four different components (polymer, coupling agent and/or impact modifiers, filler and fibre)

with different density, flowability and shape, gravimetric feeders is needed to ensure the

correct percentage of each one.

Nowadays, the compounding of natural fillers/fibres composites in industrial scale is mainly

carried out in co-rotational twin-screw extruders (TSE) [10] that were originally designed to

process petro-based polymers and inorganic fillers and fibres. Due to the inherent flexibility

of the machine design of TSE, where barrel segments, screw elements and dosing points can

be varied, it was possible to adapt this machine to the manufacturing of composites containing

organic fillers/fibres.

Nevertheless degassing capabilities are limited due to the small active surface in the extruder

resulting in quality and/or output problems in the compounding of materials with high

humidity and high shear rates. New approaches were suggested in the project to solve these

limitations. Further flexibility can be achieved by the use of special screw elements, designed

to achieve special flow patterns with TSE, like increase elongational flow and improve

distributive mixing.

Compounding was carried out using a Coperion Werner & Pfleiderer (Germany) co-rotating

twin screw extruder ZSK 25 LAB (diameter=25 mm, L/D=40). The screw speed was fixed at

250 rpm and a temperature profile varies from 190ºC to 170ºC. Special screw configuration

was designed and additional venting point was added to the twin-screw barrel in order to

obtain a good degasification, good blend (mainly distributive blend) without apparent

degradation of the matrix or a significantly reduction of fibre aspect ratio.

Extruded strands were cooled immediately by passing though a water cooling bath. The

cooled strands were cut in cylinder shape pellets using a pelletizer and drier in an air forced

oven at 80ºC during four hours prior injection moulding.

The specimens for mechanical characterization was injected in a standard ISO test bars mould

using an Arburg injection moulding machine (Germany), model Allrounder 420C 1000/350.

This machine has a barrel screw diameter: 35 mm, full hydraulic and clamp force 100Tn. The

barrel temperature employed in all the test was 180ºC in the hopper until 205ºC in the die, the

mold temperature was 70ºC in its both faces, the mould was heated using hot water. The

injection speed was fixed in 50 mm/s, the holding pressure and time was 27 and 5 s.

respectively. In all cases the maximum pressure during the injection step was selected as an

answer parameter.

Samples Characterization.

To determinate the rheological behaviour of the compounded pellets a melt flow index

equipment model MP-E by Göttfert (Germany) was used. This equipment is a dead-weight

extrusion plastometer consisting of a thermostatically controlled melting chamber. During the

polymer is heating at a one temperature fixed of 230ºC and after extruding it through a

standard die at a constant weight of 2,16 Kg. The tests were performed under EN-ISO 1133

standard conditions. As a result of this test the melt flow index (g/10min) or melt volume

index (cm3/10min) is calculated. The flow rate is an inverse measure of the melt viscosity.

This test is the most commonly test used to thermoplastics rheological characterization

The impact strength and flexural properties are two of the most important mechanical

properties for proposed application. It has been measured both properties according to next

standards: EN-ISO 179 (Unnotched Charpy Impact) and EN-ISO 178 (flexural modulus). For

the un-notched Charpy Impact Test, a CEAST equipment (Italy), model 6545/000 was used.

The flexural properties were determined using a Universal Test Dynamometer of ZWICK

(Germany) model 1465.

The dynamic-mechanical tests are the most sensitive techniques available to characterize and

to interpret the mechanical behaviour of a material. A sinusoidal strength is employed over a

sample of material. The rigidity of the material is determined from the amplitude of the

answer and the properties of absorption are measured with the angle of the difference in the

signal of answer. By modifying the temperature and/or the frequency of the strength applied,

we can obtain a big group of data which permit to full characterization of the composite. The

properties of a material deformed under diary efforts of flexion are expressed by a module of

storage, the module of loss and the factor of absorption defined attending to the theory of the

viscoelasticity.

For the tests a DYNAMIC MECHANICAL ANALYZER model 2980 of TA Instruments

(USA) was used. The tests conditions employed were: temperature range: 35 to160ºC at

heating rate 3ºC/min, test bar dimensions: 54x10x4 mm, the type of clamp was dual cantilever

and the frequency of the test was fixed in 1Hz

RESULTS AND DISCUSSION.

Initially, we prepare single blends of the different filler/ fibres selected using in all the cases

the recycled block polypropylene as a matrix. All the blends contain approximately 30% w/w

of organic reinforcement. Table 3 shows the mechanical and the rheological properties of

different composites of PPB containing equal percentages of each fibre/filler selected.

TABLE 3. MECHANICAL AND RHEOLOGICAL PROPERTIES OF SINGLE PPB BLENDS.

Unotched Charpy Impact

(kJ/m2) Type of filler or

fibre 23ºC -5ºC

Flexural

Modulus

(MPa) 23ºC

MVI

(cm3/10min)

230ºC/2,16 Kg

Unfilled No break No break 1494 ± 25 6,1

32% Husk Rice 10,1 ± 1,7 8,1 ± 1,5 2.165 ± 87 5,4

27% Cotton fibre 31,2 ± 1,9 27,5 ± 1,2 2.134 ± 56 3,5

30 % Flax fibre 21,5 ± 2,1 12,7 ± 0,9 2.091 ± 57 4,8

The filler increase mainly the flexural modulus without lost of compound fluidity. However,

husk rice acts as pure filler and in consequence, as an initial residual stresses formation and leads to compounds with very low impact properties. This behaviour was find in previous

studies [11,12]. For this reason, we decided to limit between 10 and 15% the content of filler

to incorporate to the composite, we must taking into account that the cage structures suffer

moderate impacts due to waves, boats and materials that the sea can drag.

The elastic module of flexion is maintained constant between the composites with filler and/or

fibres, while the properties of impact fall drastically, especially at low temperatures when

fillers are used. When the comparison is between fibres, the cotton offers composites with

better impact properties at room temperature and mainly at low temperature. However, the

presence of cotton reduces significantly the flow of the compound, from 6,1 until 3,5 cm3/10

min. whereas the reduction with the incorporation of the flax is lower, from 6,1 until 4,8. This

behaviour could be explained taking into account the difference of aspect ratio of the fibres

(high aspect ratio better compound properties), the low polarity of cotton fibres and the soft

pellets obtained with cotton fibres, this contribute to better dispersion in the twin screw

extruder and avoid the formation of agglomerates. The agglomerates act as a interfacial stress

concentration and reduce the impact properties of the compound.

Polypropylene, fibre (cotton and flax) and husk rice compounds. Two polypropylene cotton and husk rice blends were extruded in the twin screw extruder. The

first one contains 30% w/w of cotton and 10% w/w husk rice, whereas the second one

contains 25% w/w of Cotton and 15% w/w rice husk. The sum of filler and fibre in both

compounds was approximately 40% w/w

There are not problems during compounding of both samples, the melt temperature was

204ºC, the melt pressure in the strand die varies between 24 to 27 bar and the torque vas

constant at 44% of the maximum extruder torque. Table 4 shows the viscosity of the ternary

blends prepared.

TABLE 4. MVI OF THE COMPOUNDS PREPARED BASED ON COTTON FIBRE.

Simple description MVI at 230ºC/2.16Kg

(cm3/10min)

32% Husk Rice 5,4

27% Cotton 3,5

30% Cotton / 10% Husk Rice 2,7

25% Cotton / 15% Husk Rice 3,3

As it can be observed, the fibre of cotton increase the viscosity of the composite, while the

ground rice husk does not introduce an important modification regarding to the fluency of the

compound containing only cotton fibres.

In order to determinate its mechanical properties the compounds were injected in an ISO

standard mould using the described injection molding machine. During the injection

significant increase of injection pressure was observed, these results are in accordance with

the values of MVI. Table 5 summarized the results obtained on the tests of un-notched Charpy

impact and the flexural module.

TABLE 5. MECHANICAL BEHAVIOUR OF SAMPLES CONTAINING COTTON FIBRE AND RICE HUSK.

Sample description Unotched Charpy Impact

(kJ/m2)

Flexural

Modulus (MPa)

(percentages in weight) 23ºC -5ºC 23ºC

32% Husk Rice 10,1 ± 1,7 8,1 ± 1,5 2.165 ± 87

27% Cotton 31,2 ± 1.9 27,5 ± 1,2 2.134 ± 56

25%Cotton/15% Husk Rice 16,7 ± 1,7 14,3 ± 1,0 2.073 ± 34

30%Cotton/10% Husk Rice 14,6 ±1,1 11,4 ± 1,1 2.179 ± 69

The introduction of husk rice filler maintain the flexural modulus, however a significantly

reduction of impact properties were determinate. The combination of filler and fibre leads to

compounds with intermediate properties.

In the case of flax due its low impact resistance, only one compound containing 30% w/w of

flax and 10% w/w husk rice was prepared. The compounds was done without any problem

obtain similar values of melt temperature and pressure and torque. During injection process,

similar increases of injection pressure were measured. Table 6 shows a comparison of the

results obtained with three components compounds of both fibres and the husk rice.

TABLE 6. MECHANICAL BEHAVIOUR OF SAMPLES CONTAINING BOTH TYPES OF FIBRES AND RICE HUSK

Sample description Unotched Charpy

Impact 23ºC (kJ/m2)

Flexural

Modulus (MPa)

30% Flax 21,5 ± 2,1 2.091 ± 57

30% Flax / 10% Husk Rice 6,6 ± 0,8 3.109 ± 78

30%Cotton/10% Husk Rice 14,6 ±1,1 2.179 ± 69

The incorporation of the filler to the compound containing flax fibres reduces drastically the

impact properties and increase lightly the flexural modulus. Maybe, the tendency of the flax

fibres to form agglomerates are higher in presence of fillers, the fibres could be involve the

fillers and create a large agglomerates that leads to a low impact properties. Additionally,

large particles tend to increase the flexural modulus, as occur in this case.

To know the variation of the mechanical properties with the temperature of compounds

containing a blend of fillers and fibres, a DTMA analysis was realized and the storage

modulus calculated. The storage modulus in viscoelastic solids measures the stored energy,

representing the elastic portion. This technique is used for observing the viscoelastic nature of

polymers and it is very sensible to small changes in the material structure. Figure 2 shows the

variation of the storage modulus of selected compounds containing cotton and flax fibre.

0

50

100

150

200

250

300

350

30 50 70 90 110 130 150 170Temperature (ºC)

Sto

rage

Mod

ulus

(M

Pa)

30% COTTON-10% RICE27% COTTONPPB

0

50

100

150

200

250

300

350

400

450

500

30 50 70 90 110 130 150 170Temperature (ºC)

Sto

rage

Mod

ulus

(M

Pa)

30% FLAX-10%GRH-M E

30% FLAXPPB

FIGURE 2. STORAGE MODULUS VARIATION FOR DIFFERENT FILLER-FIBRE BLENDS: A) COTTON, B) FLAX.

As it was expected, the variation of storage modulus with the temperature of both fibres is

very similar. However the increase of storage modulus when the rice husk is added to the flax

compound is higher than in the case of cotton. They confirm the presence of large

agglomerates and/or stress concentrators that reduce the elastic portion of the polymer. This

analysis corroborates the results obtained previously.

In all cases, with the systems filler-fibre we obtain a significant reduction of the impact

properties which incorporate only fibres. To introduce appropriate compatibilizers or even

some modifier of impact in the systems fibre-filler is need in order to improve its impact

properties.

Coupling agents for polypropylene/husk rice/fibre compounds.

An important number of technical articles [8-11] propose for organic filler-polyolefin

composites percentages of compatibilizer of 15% w/w calculated over the amount of

fibre/filler, this means a 6% w/w of coupling agent in the full blend. The justifications they

provide for explain the behaviour of the coupling agents over the properties of the composite

are very different due to the diversity of the systems studied in the literature. Nevertheless, all

of them have in common the fact that the interphase properties are the ones which govern the

effectiveness of the compatibilizer. To improve the compatibilisation of the block

polypropylene with mixtures of fibres and husk of rice, three coupling agents was selected as

summarized table 1.

30% Cotton/10% Husk Rice 27% Cotton

Polypropylene

30% Flax/10% Husk Rice 30% Flax

Polypropylene

During the injection molding has not found significant differences when the injection pressure

was determinate. The variations found are due to intrinsic errors for each process, compound

and injection, caused by the feeding adjustment. The maximum pressure was found when

sample with ROYALTUF was injected.

Table 7 summarized the results obtained in the tests of impact and flexion over the ternary

compounds containing coupling agents. All the compounds have the follow composition: 54%

w/w of recycled block polypropylene, 10% w/w husk rice, 25 % w/w fibre (cotton or flax)

and 6% w/w of coupling agent (INTEGRATE, POLYBOND or ROYALTUF).

TABLE 7. CHARACTERIZATION OF THE DIFFERENT TERNARY BLENDS WITH COMPATIBILIZER.

Coupling agent Un-notched Charpy

Impact (kJ/m2)

Flexural Modulus

(6% w/w) 23ºC -5ºC (Mpa) 23ºC

Cotton fibre

Without coupling agent 16,7 ± 1,7 14,3 ± 1,0 2.073 ± 34

INTEGRATE 507-30 17,3 ± 1,3 15,2 ± 1,6 2.859 ± 104

POLYBOND 3200 17,0 ± 2,4 15,5± 1,4 2.629 ± 78

ROYALTUF 498 13,4± 0,6 11,3 ± 1,1 2.506 ± 73

Flax fibre

Without coupling agent 6,6 ± 0,8 5,6 ± 0,7 3.109 ± 95

INTEGRATE 507-30 16,4 ± 1,3 11,0 ± 1,1 2.446 ± 72

The effect of the coupling agents over the two types of fibres is very different. In the case of

cotton, the compatibilizer leads to an increase of the elastic module of the material, due to the

big interaction between the polymer and the system filler-fibre and light increase of impact

properties. However, the effect over the flax fibre compounds is different, a decrease of

flexural modulus and significantly increases of impact resistance was found.

One of the reasons of this behaviour could be that the compatibilizer can destroy the

agglomerates formed during compounding in the case of the flax fibre, this contribute

significantly to improve impact properties. In the case of the cotton, the presence of a high

melt flow index graft polymer incorporates another component non compatible with the high

viscosity block copolymer matrix.

From this analysis, the two compatibilizers of polypropylene-graft-maleic anhydride

INTEGRATE 507-30 and POLIBOND 3200 show a very similar compatibilization effect and

this is better than EPDM-g-MAH compatibilizer. The choice of one or the other will depend

on the combination between the resistance to the impact and the module of flexion provided.

The improvement of the properties, especially the ones of impact for the compatibilizers is

very low. Maybe, this is due to the presence of fillers and fibres with different and complex

morphologies which does not allow the creation of homogeneous and stable interphases.

To determine the influence of each compatibilizer in the elastic properties in a broad range of

temperatures, figure 3 shows the results of the DTMA analysis over the samples with cotton

fibres. Storage modulus studies corroborate the results obtained in table 6.

0

50

100

150

200

250

300

350

400

30 50 70 90 110 130 150 170Temperature (ºC)

Sto

rage

Mod

ulus

(M

Pa)

PPBNON COM PATIBILIZEDINTEGRATE NP 507-30POLYBOND 3200ROYALTUF 498

FIGURE 3. STORAGE MODULUS VARIATION FOR DIFFERENT FILLER-COTTON BLENDS CONTAINING COUPLING

AGENTS.

Impact modifiers for polypropylene/husk rice/cotton compounds.

With the objective to increase the impact properties of the filler-fibre compounds, two

different low cost impact modifiers were used. They were described in table 2.

For the test a fixed percentage of 6% w/w of impact modifier was selected, according

previous works. As a base compound was selected the recycled polypropylene plus 25% w/w

cotton plus 15% w/w Husk Rice plus 6% w/w INTEGRATE 507-30 (coupling agent). Table

8 shows a comparison of the results obtained din the different compounds contain impact

modifiers.

TABLE 8. MECHANICAL PROPERTIES OF 25% W/W COTTON FIBRE -15% W/W HUSK RICE WITH DIFFERENT TYPES OF ADDITIVES

Un-notched Charpy Impact

(kJ/m2)

Coupling

Agent

Impact

Modifier 23ºC -5ºC

Flexural Modulus

(MPa) 23ºC

NO NO 16,7 ± 1,7 14,3 ± 1,0 2.073 ± 34

YES NO 17,3 ± 1,3 15,2 ± 1,6 2.859 ± 104

YES ELVALOY 3427 24,3 ± 0,6 20,2 ± 1,1 2.138 ± 38

YES LOTRIL 29 MA 03 21,4 ± 1,9 14,7 ± 2,3 1.889 ± 23

During the injection of the compounds a reduction of injection pressure was found in

comparison with non impact modifier compounds. This means a positive interaction between

the new additive in the complex blend. The use of both impact modifiers supposes an increase

of the resistance to the impact without a significantly decrease of flexural characteristics.

This presupposes that the resistance to the impact in the composites modified with MA or BA,

it is a combination between an increase of the energy of initiation of the fracture and an

excellent capacity of movement of the interphase which leads to a plastic deformation along

the matrix.

Long et al [13] obtained the same conclusions and they observed important differences when

the elastomer was be able to form a microstructure “core-shell” on the filler. Figure 4 shows

the behaviour of both structures face to an impact.

FIGURE 4. MORPHOLOGIC MODEL OF “CORE-SHELL” MICROSTRUCTURE IN THE BEHAVIOUR OF FRACTURE OF THE

COMPOSITES PP/ELASTOMER/FILLER.

When the elastomer and the rigid filler are separated in the matrix of polypropylene, the

particles of filler tend to produce a wide group of micro-chaps when there is an impact.

Although the elastomer can stop the propagation of many of them, a small part propagates

which gives rise to the complete fracture of the part. While the filler is absorbed in the

elastomer, the micro fissures caused by an impact remain in the interphase, creating a zone of

fluency around the particle of elastomer which contained in the filler. This mechanism

improves the effectiveness of the elastomer. This could be the model that explains the effect

of both impact modifiers over the filler/fibre blends.

CONCLUSIONS

The main conclusions were summarized in the follow lines:

- The use of pellets fibres and gravimetric feeder contribute to obtain an accurate

composition when different types of fillers and fibres were added.

- The fillers lead to reduce the impact resistance of the composite. However they

increase the flexural modulus and reduce the warpage and control the increase of

viscosity.

- Fibres increase the flexural modulus, with a lower lost of impact properties. A

significant increase of viscosity is observed mainly in the high aspect ratio fibres.

- Flax fibres due its tendency to form agglomerates due its high polarity and this fibre

have lower reinforcement properties than cotton fibres.

- The addition of PP-g-MAH to the blends cotton-husk rice-polypropylene contributes

to increase its flexural modulus without any increase of impact. Whereas in the case of

flax fibre a reduction of flexural modulus and significantly increase of impact

properties was observed, maybe due to a partial destruction of the agglomerates.

- Impact modifiers increase the impact properties and reduces the flexural modulus of

the composites studied.

ACKNOWLEDGEMENTS.

This work was supported by the project "Development of Innovative Plastic Structures for

Aquiculture using a new composite with crop waste as reinforcing Filler” financed by the

Sixth Framework Programme of the European Union’s chief instrument. . Horizontal

Research Activities Involving SMEs. Integrating and Strengthening the European Research

Area. EC CONTRACT COOP-CT-2003-508682.

Special thanks to CELESA and MIFSUD by the material supplied and their support during

the fibre/filler treatment.

REFERENCES.

1. D. Whitmarsh, P. Wattage Public attitudes towards the environmental impact of salmon aquaculture

in Scotland, European Environment, 16, 2006, 108-121.

2. N.J. Scott, E.C.M. Parsons A survey of public opinion in south-west Scotland on cetacean

conservation issues, Aquatic Conservation: Marine and Freshwater Ecosystems, 15, 2005, 299-312.

3. R Karnani, M. Krishnan, R. Narayan, Biofiber-reinforced polypropylene composites, Polymer

Engineering & Sci., 37, 1997, 476-483.

4.M. Takatani, H. Itoh, S. Ohsugi, T. Kitayama, M. Saegusa, S. Kawai, T. Okamoto, Effect of

lignocellulosic material on the properties of thermoplastic polymer/wood composites, Holzforschung,

54, 2000, 197-200.

5. R. Mahlberg, L. Paajanen, A. Nurmi, A. Kivistö, K. Koskela, R. M. Rowell, Effect of chemical

modification of wood on the mechanical and adhesion properties of wood fiber/polypropylene fiber

and polypropylene/veneer composites, Holz als Roh - und Werkstoff , 59,2001,319-326.

6. M. M. Sain, B. V. Kokta, Polyolefin-wood filler composite. I. Performance of m-phenylene

bismaleimide-modified wood fiber in polypropylene composite, J. Applied Polymer Sci., 54,

1994, 1545-1559.

7. D. N.-S. Hon, W. Y. Chao, Composites from benzylated wood and polystyrenes: Their

processability and viscoelastic properties, J. Applied Polymer Sci., 50, 1993, 7-11.

8. B.A. Acha, M. Reboredo, N.E. Marcovich, Effect of coupling agents on the thermal and mechanical

properties of polypropylene-jute fabric composites, Polymer International, 55, 2006, 1104-1113.

9. A.K. Rana, A. Mandal, B.C. Mitra, R. Jacobson, R. Rowell, A.N. Banerjee, Short jute fiber-

reinforced polypropylene composites: Effect of compatibilizer, J. Applied Polymer Sci., 69, 1998,

329-338.

10. J. Z. Lu, Q. Wu, I. I. Negulescu, Wood-fiber/high-density-polyethylene composites: Compounding

process J. Applied Polymer Sci., 93, 2004, 2570-2578.

11. F. Martí-Ferrer, F. Vilaplana, A. Ribes-Greus, A. Benedito-Borrás, C. Sanz-Box, Flour rice husk

as filler in block copolymer polypropylene: Effect of different coupling agents, J. Applied Polymer

Sci., 99, 2006, 1823-1831.

12. Z. A. Mohd. Ishak, B. N. Yow, B. L. Ng, H. P. S. A. Khalil, H. D. Rozman. Hygrothermal aging

and tensile behavior of injection-molded rice husk-filled polypropylene composites, J. Applied

Polymer Sci., 81, 2001, 742-753.

13. Y. Long, R. A. Shanks, PP/elastomer/filler hybrids. II. Morphologies and fracture, J. Applied

Polymer Sci., 61, 1996, 1877-1885.