effect of reprocessing cycles on the morphology and properties of poly(propylene)/wood flour...

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Effect of Reprocessing Cycles on theMorphology and Properties of Poly(propylene)/Wood Flour Composites Compatibilized withEBAGMA Terpolymer

Mustapha Kaci,* Amel Hamma, Isabelle Pillin, Yves Grohens

The present study is aimed to investigate the effect of multiple extrusions of iPP/WFcomposites with and without EBAGMA used as compatibilizer. The degradation induced bythe recycling processes was evaluated through changes in molecular structure, morphology,rheology, thermal and mechanical properties. Theresults showed that after six cycles, the presenceof WF imparts stability to the compositematerials. This effect was enhanced for the com-patibilized samples. Further, SEM revealed betterdispersion of the WF in the matrix. In contrast, itwas confirmed that after the first recycling, boththe molecular weight and the properties of PPdrastically decreased due to chain scission result-ing from degradation.

Introduction

The use of wood-based materials, such as wood flour and

wood fibers, as reinforcing fillers for thermoplastics

attracted a number of researchers and manufacturers

during the last decade.[1] Indeed, the addition ofwood flour

as renewable natural filler in polymer composites aims to

produce a unique combination of high performance, great

versatility, lightweight, recyclability, biodegradability and

M. Kaci, A. HammaLaboratoire des Materiaux Organiques, Faculte de la Technologie,Universite Abderrahmane Mira, Bejaia 06000, AlgeriaFax: þ21 33 421 5105; E-mail: [email protected]. Pillin, Y. GrohensLaboratoire d’Ingenierie des Materiaux de Bretagne, Universite deBretagne Sud, Rue de Saint Maude, 56321 Lorient Cedex, France

Macromol. Mater. Eng. 2009, 294, 532–540

� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

processing advantages at favorable cost.[2] Among thermo-

plastic matrices used for composites, special attention was

given topoly(propylene) (PP), due to itsuse in commodityas

well as in engineering applications, when reinforced.[3] PP

possesses outstanding properties such as low density,

sterilizability, good surface hardness, very good abrasion

resistance and excellent electrical properties.[4] Moreover,

composite materials made of cellulosic fibers and PP are

completely combustible, without the production of harm-

ful gases or solid residues.[5] However, themain problem in

the combination of wood flour with polyolefins is the

inherent incompatibility between the hydrophilic wood

flour and the hydrophobic polymers which yield to a poor

resistance to humidity absorption and lack of adhesion and

subsequently in a poor ability to transfer stress from the

matrix to the reinforcing filler.[6,7] A number of investiga-

tions explored the ability of additives to enhance adhesion

and thereby improves properties, such as the tensile and

DOI: 10.1002/mame.200900089

Effect of Reprocessing Cycles on the Morphology and . . .

flexural strengths of these composite materials.[6–10] The

coupling agent is chosen to achieve chemical bonds

between the cellulose and the polymer matrix. The most

commonly used coupling agents are maleated polyole-

fins.[5,11] There have also been some successful coupling

agents such as isocyanates,[12] silanes,[13] and an ethylene/

butyl acrylate/glycidyl methacrylate (EBAGMA) terpoly-

mer.[14] The extrusion, injection and compressionmoldings

are the classical techniques for the processing of PP/wood

flour composites.[15] The literature[16] reported that proces-

sing by extrusion itself represents a kind of energetic shock,

in the course of which the polymer is exposed to elevated

temperatures and mechanical stresses leading to signifi-

cant changes in thepolymer structure, especially adecrease

in molecular weight. Recently, da Costa et al.[17] reported

that PP degradation duringmultiple extrusions at different

temperatures results in an abrupt increase of themelt flow

index (MFI), whereas complex viscosity and elasticity are

reduced. Further knowledge about the properties of

recycled polymeric composite materials is needed in order

to find appropriate and useful applications and increase

recycling rate of these materials. Moreover, repeated

extrusion or injection molding is often used to estimate

their recycling potential.[18] Althougha significant research

workonthereprocessingofPP isavailable in literature,[19–21]

studies on theeffects of reprocessingof theproperties of PP/

wood flour (WF) composites has not been fully per-

formed.[22] The few works on reprocessing of wood

composites based PP concern the use of lignocellulosic

fibers, suchas jute, sisal, kenaf,flax,hemp, rather thanwood

flour.[1] In general, the results arising from those studies

indicate that reprocessing does not show significant effect

on the mechanical properties of PP/vegetable fibers,

whereas the adhesion between fibers and PP is improved

with the reprocessing cycles, and subsequently a reduction

in moisture absorption.[6,22–26]

The objective of this work is to investigate the extent to

which PP/wood flour composite materials are reprocessa-

ble. Changes in chemical structure, as well as in morphol-

ogy, viscosity, thermal and mechanical properties are

evaluated after each reprocessing cycle.

Scheme 1. Chemical structure of EBAGMA terpolymer.

Experimental Part

Materials

The PP used in this study is an isotactic homopolymer, provided by

Marun Petrochemical Co (Saudi Arabia) and is commercialized

under the grade name Moplen S30S. The MFI of the polymer is

1.8 g � (10min)�1 and the melting temperature is 175 8C. PP was

selected as the matrix because it is one of the major commodity

polymers which may be processed below the decomposition

temperature of the wood flour which is about 200 8C.



Thewood flourwas extracted fromAleppo Pine tree originating

from the region of Djelfa located in the highland of Algeria. The

average particle diameter of the wood filler is comprised between

45 and 90mm. The chemical composition of the wood was

determined on the basic of absolutely dry substances using

chemical procedures (cellulose: 38.70wt.-%, hemicellulose: 27.63,

lignin: 25.28,mineral filler: 8.39wt.-%). The apparent density of the

Aleppo pine fillers is 0.5664 and its moisture content is 4.04wt.-%.

EBAGMAwasusedasacompatibilizer for thePP/WFcomposites.

It was kindly supplied by Dupont (Belgium) under the trade name

Elvaloy PTW. It contains 66.75wt.-% ethylene, 28wt.-% butyl

acrylate and 5.25wt.-% glycidyl methacrylate. The chemical

structure of the EBAGMA terpolymer is shown in Scheme 1. The

mains properties of EBAGMA terpolymer as provided by the

manufacturer are a melt flow index of 12 g � (10min)�1, as

measured by ASTM method D1238, a melting point of 72 8C, aglass transitiontemperatureof�55 8C,a tensile strengthatbreakof5 MPa and an elongation at break of 950%, according to ASTM

method D 1708. The amount of EBAGMA added to the material

composites was fixed at 10 g on the basis of 100g of the total

mixture of PP and WF composites.

Preparation of PP/WF Composites

The WF was dried in an oven at 70 8C overnight in order to reduce

the humidity content, and processedwith the poly(propylene) in a

co-rotating twin screw extruder (type Collin ZK 25, D¼25mm,

L/D¼56) with the nominal composition of 20wt.-%. The tempera-

tureprofilewassetat170/190/190/190/180 8Candthescrewspeed

maintained at 30 rpm. The processing time was 10min.

Reprocessing

Reprocessing was carried out by successivemixing cycles using an

opened mixer (Brabender, 50 EHT) controlled by a Lab-Station

driven by the Brabender Software Winmix. Blending temperature

was 190 8C, test time 10min. and blade rotation speed 30 rpm.

Samples was then extracted from the blender and molded into

plates of 20�20� 0.2 cm3 from which tensile test samples were

cut.

www.mme-journal.de 533

M. Kaci, A. Hamma, I. Pillin, Y. Grohens

534

Characterization Techniques

Fourier-Transform Infrared (FT-IR) Spectroscopy

The chemical changes due to reprocessingweremonitored by FT-IR

spectroscopy. The IR spectrawere recordedusing a Perkin Elmer FT-

IR spectrometer with 2 cm�1 resolution and 40 scans. All spectra

were recorded in the absorbance mode in the 4 000–600 cm�1

region. The oxidation degree, i.e. carbonyl index was obtained by

calculating the carbonyl absorption at 1 725 cm�1 from the FT-IR

spectra at different extrusion cycles, using the spectrum of the

starting unoxidized materials as reference. All measured absor-

bances were normalized by the film thickness according to

Equation (1):[27]

Macrom

� 2009

Carbonyl index ¼ A1722

d

� �� 100 (1)

Figure 1. FT-IR spectra of PP, PP/WF and PP/WF/EBAGMA recordedin the region 4 000–600 cm�1 before reprocessing.

where A1722 is the measured absorbance at 1 722 cm�1 from the

FT-IR spectrum at certain reprocessing cycle, and d is the film

thickness in mm.

Scanning Electron Microscopy (SEM)

Morphologieswere observedwith a Jeol JSM-6031 SEM to examine

the fractured surface of the composite samples. Prior to observa-

tion, the fractured surfaces of the specimenwere coatedwitha thin

gold layer by means of a polaron sputtering apparatus.

Differential Scanning Calorimetry (DSC)

Thermograms were obtained from a Perkin Elmer Pyris 1

differential scanning calorimeter using the Pyris V 3.0 software

for data collection and treatment. Calibration was done with

indium and tin in the temperature range (þ25 8C to þ350 8C).Aluminum panswith holes were used and the sampleweight was

approximately 10mg. All samples were first heated to 200 8C for

2min to get rid of thermal history. The melting temperature

measured at themaximumendothermic peak (Tm) and enthalpy of

fusion were determined at �20 8C �min�1 heating/cooling rates.

Previously, the enthalpy valueswere normalized to the PP amount.

Rheological Measurements

Rheological experiments were performed at 190 8C using a Gemini

200. Parallel plate geometry was used. The diameter of the plates

was 20mm and the gap was 2mm. The viscosity was obtained

using shear rate gradient from 0.001 to 100 s�1. The zero viscosity

was calculated using the Carreau model.

Melt Flow Rate Measurements (MFR)

Assessment of polymer degradation during reprocessing was

accomplished through monitoring its rheological implications.

MFRmeasurementswere carriedoutaccording toASTMD1238/79.

The flow rate measurement of the extrudates was performed at

230 8C and 2.160 kg. Five measurements were performed for every

sample.

ol. Mater. Eng. 2009, 294, 532–540

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Mechanical Measurements

The static tensile tests were carried out in a laboratory where the

temperaturewas 23 8C and the humiditywas 48% according to ISO

527 using an MTS Synergie RT1000 testing apparatus. The loading

speed was 1mm �min�1. The dimensions of the calibrated part

have a width¼4mm and a length¼45mm. Each experimental

point represents an average of five samples.

Results and Discussion

Thebehavior of PPwithwoodflour in absence andpresence

of the EBAGMA compatibilizer was analyzed as a function

of the number of extrusion cycles applied and the impact of

such repetitive cycles on thephysico-mechanical properties

of the composite materials, i.e., thermal, rheological,

mechanical and morphological behavior. Prior to evaluate

such behaviors, FT-IR spectroscopy was used to investigate

the possible changes in the molecular structure of the

composite materials before and after each reprocessing

cycle inorder todetect the formationof carbonylgroupsdue

to oxidative degradation. The results obtained were

compared to the neat PP. Moreover, the thermo-oxidation

rate of the different samples was evaluated through the

carbonyl index evolution as a function of extrusion cycles.

FTIR Spectroscopy

Figure 1 shows the FT-IR spectra of PP/WFwithandwithout

the EBAGMA terpolymer compared to the neat PP recorded

before recycling. TheFT-IR spectra reveal for bothvirginand

compatibilized PP/WF composites, the presence of an

absorption band localized at 1 735 cm�1 which may be

associated with carbonyl stretching of acetyl groups,

aldehyde, carboxyl groups and esters contained in hemi-

celluloses, lignin and extractives.[8] Further, it can be

observed a large increase in the band intensity at

1 735 cm�1 for the compatibilized samples due to the

DOI: 10.1002/mame.200900089


Figure 2. FT-IR spectra of PP, PP/WF and PP/WF/EBAGMA recordedin the region 4 000–600 cm�1 after 5 extrusion cycles.

Figure 3. Carbonyl index evolution as function of number ofextrusion cycles for PP, PP/WF and PP/WF/EBAGMA.

carbonyl groups contained in both butyl acrylate (BA) and

glycidyl methacrylate groups (GMA) of the EBAGMA

terpolymer. Moreover, a large absorption band is observed

at 3 350 cm�1 in PP/WF composite samples, which is

attributed to hydroxyl groups contained in the cellulosic

filler. The addition of EBAGMA to the composites sig-

nificantly decreases the absorption band intensity of the

hydroxyl groups. These structural changes in the compa-

tibilized composite samples suggest that the esterification

reactionbetweenhydroxyl groupsof thewoodfiller and the

functional groups of the EBAGMA terpolymer, i.e. GMAand

BA groups have occurred.[8,9] The absorption band localized

at around 1600–1 630 cm�1 is probably associated with

absorbedwater in crystalline cellulose.[6] Absorption bands

typical of PP are also observed at frequencies within

1 460 cm�1 for the�CH2 bond, and 1370 for the�CH3 bond.

Theregionof thespectrawithin1 400and600 cm�1belongs

to the composite fingerprint region. In addition, it can be

also observed in the FT-IR spectrum of the neat PP recorded

before recycling, the appearance of an absorption band of a

weak intensity localized at lmax¼ 1 722 cm�1 attributed to

carbonyl groups resulting from thermooxidation of the

polymer and which probably occurred in the initial

processing step, rather than to the presence of antioxidant

additives. This assumptionwas basedon soxhlet extraction

test performed on PP samples before recycling confirming

definitely the persistence of carbonyl groups on the chain

backbone of PP after the extraction procedure with xylene.

In this connection, the literature[28,29] reported that

aldehyde (1 725 cm�1), ketonic (1 715 cm�1), carboxylic

(1 710 cm�1) and ester groups (1 745 cm�1) are the most

frequent groupswhich are generated by oxidative degrada-

tion of polyolefins during processing. Moreover, these

groups are generated by the b-chain scission of the alkoxy

radicals.[30] This processing step performed on PP is

necessary for comparative purposes and corresponds to

‘‘0 reprocessing cycle’’. It is intended to provide the same

extrusion conditions as those used for blending both virgin

and compatibilized compositematerials. Figure 2 shows as

an example the FT-IR spectra of both virgin and EBAGMA

compatibilized PP/WF composites recorded after five

extrusion cycles and the results are compared to the neat

PP. InFT-IRspectrumofPP, it canbeobservedthepresenceof

a carbonyl absorption band at 1 722 cm�1 of higher

intensity indicating pronounced increase in carbonyl

concentration and subsequently enhanced oxidation.[28]

In addition, it is alsonoticed the appearance of a shoulder in

the region 1680–1 640 cm�1 which reflects the emergence

of unsaturated a,b-ketones and vinyl groups, respectively.

These results are in agreement with those reported by

Hinsken et al.[30] who reported that degradation reactions

lead to products containing double bonds and carbonyl

groups during repeated processing cycles of PP. In contrast,

the FT-IR spectra analysis of both virgin and compatibilized



composite samples indicates no significant changes in the

chemical structure during the repeated extrusion cycles

when compared to the initial one. This is well described in

Figure 3, which presents the curves of carbonyl index

evolutionasa functionof reprocessing cycles forbothvirgin

and compatibilized PP/WF composites in comparison with

neat PP. It can be seen in Figure 3 that the formation rate of

carbonyl groups ismuch lower for the compositematerials

than thematrix and it is characterized by the appearance of

a quasi-plateau starting from thefirst reprocessing cycle up

to the 6th one. At this stage, the formation of carbonyl

groups is found to be very moderate compared to neat PP,

which on the contrary, exhibits faster thermo-oxidation

rate. The chemical structure stability observed in the

composite materials could be explained as a result of

different phenomena occurring during repeated recycling.

Oneof themis related to thepresenceof lignocellulosic filler

in the polymer matrix, which imparts stability to the

composite materials by the presence of lignin acting as

natural antioxidants. As a matter of fact, some authors[31]



536

reported the lignin ability to scavenge the radicals

responsible for the oxidation and its radical species.

Figure 5. SEM micrograph of fractured surface of PP/WF/EBAGMAcomposites before recycling. 450�.

Scanning Electron Microscopy (SEM)

As reported in the literature,[14] themorphology of polymer

composites is a very important characteristic because it

determines the physico-mechanical properties. In this

study, the state of the matrix/filler interface with and

without the EBAGMA compatibilizer was investigated by

SEM before reprocessing and after six extrusion cycles.

Figure 4 shows the SEM micrograph of the fracture

surface forPP/WFsamplesbefore reprocessing.Asexpected,

the addition of 20wt.-% ofwood flour particles to PPmatrix

results in phase separationmorphology. It can be observed

thatno interaction isdevelopedbetweenthewoodparticles

and the polymer. As a result, wood flour aggregates of

various sizes are formed at the PP surface. Moreover, some

defects are also visible on the fracture surface of the

composite materials such as the presence of a number of

voids in the matrix suggesting weak interfacial shear

strength between the filler and thematrix.[14] The addition

of EBAGMA compatibilizer to PP/WF composites results in

the modification of the morphology at the interface

between the wood flour and the PP matrix.

Figure 5 shows the SEM micrograph taken from the

fracture surface of the compatibilized samples with 10 pph

of EBAGMA. From Figure 5, it can be observed better

polymer/filler adhesion than in the noncompatibilized

composites resulting in a reduction of the interfacial

tension between the polymer matrix and the wood filler.

Figure 6 and 7 show the SEMmicrographs of the fracture

surface for both PP/WF and PP/WF/EBAGMA composites

after six extrusion cycles, respectively. In both figures, the

woodflour is found to be distributed evenly throughout the

PPmatrix. For both PP/WF and PP/WF/EBAGMA composite

materials, the major component surrounding the filler

Figure 4. SEM micrograph of fractured surface of PP/WF compo-sites before recycling. 450�.



seems to be the continuous phase. According to

the literature,[25] this behavior is attributed to either the

occurrence of partial degradation of PP matrix, or the

increase in extent of the reaction between the functional

groups of the EBAGMA compatibilizer and the hydroxyl

groups of the cellulose. In this latter case, a better interfacial

adhesion could be obtained as a result of reprocessing.

Rheological Measurements

Figure 8 shows the curves describing the variation of the

Newtonian limit viscosity (h0) with extrusion cycles for

bothvirginandEBAGMAcompatibilizedPP/WFcomposites

compared to theneatPP. InFigure8, it is observedavery fast

decrease in viscosity for neat PP during the first cycle

passing from 13050 to 2 143 Pa � s. Above the second cycle,

theh0valuesareveryclose tozero.At this stage, thepolymer

is effectively highly degraded and becomes very fluid. The

results suggest that the PP material should not be recycled

more thanone time.According to the literature,[17,29–31] this

Figure 6. SEM micrograph of fractured surface of PP/WF compo-sites after 6 extrusion cycles. 450�.

DOI: 10.1002/mame.200900089


Figure 7. SEM micrograph of fractured surface of PP/WF/EBAGMAcomposites after 6 extrusion cycles. 450�.

Figure 9. Melt flow rate as a function of number of extrusioncycles for PP, PP/WF and PP/WF/EBAGMA.

Figure 8. Viscosity as a function of number of extrusion cycles forPP, PP/WF and PP/WF/EBAGMA.

behavior is due to degradation by chain scission giving rise

to a significant decrease in molecular weight and subse-

quently to lower viscosity. The combination of high

temperature, shear and the presence of oxygen and

chromophoric species such as hydroperoxides, carbonyl

groups and catalyst residues in the polymer matrix, could

be the main factors promoting degradation. On the other

hand, when the wood flour is added to the PP matrix, the

evolution of h0 with reprocessing cycles is considerably

reduced as compared with the neat PP. For instance, the

extent of viscosity decrease of PP/WF composites before

reprocessing and after the third cycle is approximately

�68% passing from 15150 to 4 917 Pa � s, respectively.

Above the third cycle, there is the formation of a quasi-

plateauwhere the variation of h0 is found almost negligible

until the sixth cycle. A similar trend is also observed for the

compatibilized PP/WF composites with a decrease in

viscosity of approximately �56% up to the third cycle



passing initially from 39600 to 17 480 Pa � s, respectively.Furthermore, higher viscosity values are observed for the

PP/WF/EBAGMA composites due not only to the viscous

nature of the compatibilizer itself, but also to strong

interfacial bonding occurring between the wood filler and

the PP matrix.[13] These results clearly indicate the role of

wood filler in slowing down the viscosity decrease of the

composite materials during reprocessing and, conse-

quently, reduction in a decrease in the molecular weight

induced by the chain scission mechanism. This behavior is

strongly enhanced in presence of EBAGMA compatibilizer.

Melt Flow Rate (MFR)

Themelt flowrate is awidelyused empirical index toassess

polymer rheology and it is strongly influenced by themolar

mass of the molten polymer.[29] Figure 9 shows the

variation of the MFR for the PP/WF composites with and

without the compatibilizer as a function of the number of

extrusion cycles and the results are comparedwith theneat

PP. As expected, the MFR is significantly higher for the PP,

while for the composite samples, a slight increase in the

MFR values is observed in the two first cycles, but a quasi-

plateau is observedduring the successive cycles. The results

clearly indicate that PP undergoes chain scission with

increasing number cycles resulting in reduced melt

viscosity, lower molecular weight and a tendency towards

further degradation.[13]

Tensile Measurements

Figure 10 shows the variation of the tensile modulus as a

function of the number of reprocessing cycles for both PP/

WF and PP/WF/EBAGMA composites compared with

neat PP. Initially, the tensile modulus for neat PP is around



Figure 11. Stress at break as a function of number of extrusioncycles for PP, PP/WF and PP/WF/EBAGMA.

Figure 12. Strain at break as a function of number of extrusioncycles for PP, PP/WF and PP/WF/EBAGMA.

Figure 10. Tensile modulus evolution as a function of number ofextrusion cycles for PP, PP/WF and PP/WF/EBAGMA.

538

1 270 MPa and this value is found to increase by

approximately 15% in the compatibilized PP/WF composite

materials. The increase in tensile modulus for the

compatibilized samples could be ascribed to the beneficial

effect of EBAGMA terpolymer grafting to the PP chains,

which leads to an increase of the interfacial modulus. The

interfacial modulus corresponds to the polymer modulus in

thefiller-matrix interphase.[32] It isalsoobserved inFigure10

that the tensile modulus for the composite materials seems

to be not significantly affected by the repeating extrusion

cycles. Indeed, a very little change on tensile modulus is

noticed during recycling. In contrast, the effect of reproces-

sing onPP tensilemodulus is drastic causing a largedecrease

in this characteristic by approximately 40% between the

second and the third cycles. This is due probably to the drop

in molecular weight induced by reprocessing.[23,25]

Figure 11 shows the evolution of stress at break as a

function of reprocessing cycles for both PP/WF and PP/WF/

EBAGMA composite samples in comparison with neat PP.

FromFigure 11, it can be observed that the stress at break of

neat PP is about 34 MPa. The addition of 20wt.-% of wood

flour to the polymer results in a sharp drop in the initial

value of stress at break to about 20 MPa due to the lack of

interfacial adhesion between the components of the

composite structure.[33] When the EBAGMA compatibilizer

is added to PP/WF composites, the stress at break is slightly

increased from20 to24MPa. This improvement is generally

attributed to better adhesion and the filler reinforcement

effect. In contrast, the reprocessing induces a significant

drop in the stress at break of neat PP to almost 9 MPa after

the third cycle. For both the uncompatibilized composite

samples and those compatibilized with EBAGMA, a very

slight decrease in the stress at break (about 5%) is observed

with the recycling process. These results are in agreement

with those reported in literature,[26,30] indicating that the

recycling process which can induce the molecular weight

decrease in the polymer matrix does not seem to



significantly affect the mechanical properties of the

composites. The stable values of stress at break obtained

in presence of wood flour, which also means that the

molecular weight of the PP matrix of the composites is

almost not affected by reprocessing cycles could be related

to the efficiency of lignin as processing stabilizer in PP/WF

composites. According to the literature,[31,34,35] the radical

scavenging capacity of lignin is well established in PP.

Figure 12 shows the variation of strain at break as a

function of reprocessing cycles for PP/WF and PP/WF/

EBAGMA composites compared with the neat PP. It is

observed in Figure 12, a slight increase in the strain at break

ofPP/WFcompositesdue to increasedadhesionwhich leads

to reduced deformability.[36] Improved adhesion hinders

the formation of large voids, thus preventing catastrophic

failure. Moreover, the location of the compatibilizer at the

interface between the two phases enhances the stress

DOI: 10.1002/mame.200900089


transfer and reduces particle size because of the emulsify-

ing effect.[37] Figure 12 also shows that the strain at breakof

the compatibilized composites appears to be less affected

by recycling taking into account the experimental errors.

For PP/WF composites, it is observed a regular increase in

strain at break during the two first extrusion cycles before

declining.However, after the thirdcycle, there isavery little

change in the stress atbreakvalueup to the6th cycle. This is

aclear indicationthat theductility isenhancedduring these

two cycles providing better adhesion between the matrix

and the filler.

Differential Scanning Calorimetry (DSC)

Table 1 shows the DSC data of PP and composite samples

before and after three and six extrusion cycles. The data

reported in Table 1 clearly indicates that the PP samples

undergo substantial degradation. The initial melting

temperature of PP is almost 165 8C and this value decreases

gradually to 159 and 153 8C after the 3rd and the 6th cycles,

respectively. Inaddition, it isnotedadrop in theenthalpyof

fusionwith recycling. These resultswhich are in agreement

with previous ones, are attributed to PP chain scission.[17]

On the other hand, there is no noticeable change in the

melting temperature of the composite materials with

reprocessing cycles with and without the compatibilizer.

Themelting temperature value remains almost constant at

approximately 163 8C, which is slightly lower than that of

the neat PP. This is generally interpreted as a result of some

interactionsbetweenthecomposite components, i.e. PPand

EBAGMA compatibilizer on one hand, and on the other

hand, there are also some interactions between the wood

flourand thepolymermatrixor the compatibilizer.[38] Thus,

the compatibility between thewood filler and the polymer

Table 1. Melting temperatures (Tm) and enthalpies of fusion (DHf)of neat PP, PP/WF and PP/WF/EBAGMA composites before repro-cessing and after 3 and 6 cycles.

Sample No. of Cycles Tm DHm

-C J � g�1

PP 0 164.7 94.2

PP 3 159.5 95.1

PP 6 152.6 83.9

PP/WF 0 163.6 97.5

PP/WF 3 163.0 85.13

PP/WF 6 162.4 90.75

PP/WF/EBAGMA 0 162.7 98.45

PP/WF/EBAGMA 3 163.3 98.03

PP/WF/EBAGMA 6 163.1 99.82



matrix is improved, however being much higher for

the compatibilized samples. Further, it is noted that both

theenthalpyof fusionandthemelting temperature seemto

be not affected by repeated recycling.

Conclusion

The experimental results demonstrate that the repeated

recycling of PP/WF composites with and without compa-

tibilizer generatemuchmore stablematerials than theneat

PP. Moreover, the compatibilization effect of EBAGMA in

PP/WF composites induces higher stability with respect to

virgin composites.

After six extrusion cycles, the morphology of the

composite materials analyzed by SEM indicates that the

wood particles are uniformly dispersed and embedded in

the polymer matrix, either for virgin or for compatibilized

samples.

The FT-IR analysis shows that the molecular structure of

the composite materials is not considerably affected with

increasing the number of recycling as indicated by the

carbonyl index evolution which is found to be almost

negligible compared with that of the polymer matrix. This

result clearly reveals the stabilizing effect of lignin

contained in thewood filler for poly(propylene) composites

acting as free radical scavengers.

The obtained rheological properties of both PP/WF and

PP/WF/EBAGMA composites showalmost constancy in the

viscosity especially after the second cyclewhereas theMFR

values remain unchanged with respect to the neat PP.

In addition, it is found that the reprocessing cycles donot

inducevery significant changes in tensileproperties of both

virgin and EBAGMA compatibilized PP/WF composites

compared to neat PP. In conclusion, all results clearly

indicate that both virgin and EBAGMA compatibilized PP/

WFcompositesmay represent goodpotential for utilization

aftermultiple recycling. This is possible due to the capacity

of lignin to act as a radical scavenger in PP/WF composites

subjected to repeat processing cycles.

Acknowledgements: The authors are grateful to EGIDE throughthe TASSILI program for its financial support in this collaborativeproject.

Received: March 3, 2009; Accepted: May 5, 2009; DOI: 10.1002/mame.200900089

Keywords: composites; EBAGMA compatibilizer; poly(propyl-ene); reprocessing; wood flour

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DOI: 10.1002/mame.200900089

effect of reprocessing cycles on the morphology and properties of poly(propylene)/wood flour...

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