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The effect of types of maleic anhydride-grafted polypropylene

The effect of types of maleic anhydride-grafted polypropylene
The effect of types of maleic anhydride-grafted polypropylene

The e?ect of types of maleic anhydride-grafted polypropylene

(MAPP)on the interfacial adhesion properties of

bio-?our-?lled polypropylene composites

Hee-Soo Kim,Byoung-Ho Lee,Seung-Woo Choi,Sumin Kim,Hyun-Joong Kim

*

Laboratory of Adhesion and Bio-Composites,Program in Environmental Materials Science,Seoul National University,Seoul 151-921,South Korea

Received 12August 2006;received in revised form 8January 2007;accepted 9January 2007

Abstract

The e?ect of processing temperature on the interfacial adhesion,mechanical properties and thermal stability of bio-?our-?lled,poly-propylene (PP)composites was examined as a function of ?ve di?erent maleic anhydride-grafted PP (MAPP)types.To investigate the e?ect on the interfacial adhesion of the composites,the ?ve MAPP types were subjected to characterization tests.The MAPP-treated composites with su?cient molecular weight and maleic anhydride (MA)graft (%)showed improved mechanical and thermal stability.The enhanced interfacial adhesion,and mechanical and thermal stability of the MAPP-treated composites was strongly dependent on the amount of MA graft (%)and the MAPP molecular weight.The morphological properties of the MAPP-treated composites showed strong bonding and a paucity of pulled-out traces from the matrix in the two phases.In addition,the improved interfacial adhesion of the MAPP-treated composites was con?rmed by spectral analysis of the chemical structure using attenuated total re?ectance (FTIR-ATR).The crystallinity of PP,MAPP,MAPP-treated composites and non-treated composites was investigated using wide-angle X-ray scattering (WAXS)and di?erential scanning calorimetry (DSC).ó2007Elsevier Ltd.All rights reserved.

Keywords:A.Thermoplastic resin;E.Extrusion;B.Mechanical properties;E.Thermal analysis

1.Introduction

In recent years,bio-?ller-?lled thermoplastic polymer composites have been widely studied for the application and development of environmentally friendly materials in line with the rising environmental consciousness worldwide [1–3].The composites have several advantages such as envi-ronmental superiority,low cost,low density,lower manu-facturing energy,low CO 2emission,renewability and biodegradability,compared to inorganic-?ller reinforced thermoplastic polymer composites [2–5].Rice husk ?our (RHF)and wood ?our (WF)are considered two bio-?llers.

Especially,RHF is an agricultural waste material generated in rice-producing countries in the Asian,Paci?c and North American regions.The composites have predominant dimensional stability under moisture exposure,termite resistance and high resistance to biological attack com-pared to wood-based materials.Due to these superior properties,composites are being used increasingly in the building industry for sidings,window and door frames,decks,interior paneling,and automotive interior parts such as door panels,trunk liners,and door trims [1,6,7].

The main disadvantage of using composites is the low compatibility between the hydrophilic character of the polar bio-?ller and hydrophobic character of the non-polar matrix polymer [2].Bio-?llers do not disperse easily in ther-moplastic polymers such as polyole?n and biodegradable polymer.Due to strong intermolecular hydrogen bonding between bio-?llers,they tend to agglomerate during the

1359-835X/$-see front matter ó2007Elsevier Ltd.All rights reserved.doi:10.1016/https://www.sodocs.net/doc/4f9503754.html,positesa.2007.01.004

*

Corresponding author.Tel.:+8228804784;fax:+8228732318.E-mail address:hjokim@snu.ac.kr (H.-J.Kim).

https://www.sodocs.net/doc/4f9503754.html,/locate/compositesa

Composites:Part A 38(2007)

1473–1482

compounding process with the matrix polymer.The low compatibility and interfacial adhesion of composites lead to low mechanical and thermal properties of the?nal prod-ucts[9–11].Therefore,the study of ways to improve the interfacial adhesion between bio-?llers and matrix poly-mers is very important for the application of composites in industrial materials.In recent years,the various methods that have been studied to improve the interfacial adhesion of composites,by modifying the bio-?ller surface,have included the use of maleic anhydride-grafted polypropylene (MAPP)[2],the addition of silane coupling agents[12], grafting matrix polymer with hydrophilic functional group [9],chemical modi?cation of bio-?ller surface[8,10,11]and plasma treatment of the bio-?ller surface[13].The use of MAPP,which is a very e?ective compatibilizer for bio-?ller and matrix at the interface,has been the most common method to improve interfacial adhesion.The maleic anhy-dride(MA)-grafted,thermoplastic polymer increases the polarity which leads to better adhesion with bio-?llers[2]. The mechanical and thermal properties of MAPP-treated composites are likely to be di?erent from those of MAPP in terms of molecular weight,MA graft(%),and melt?ow index(MFI).Thus,?ve types of commercially used MAPP were investigated in this study.

The objective of this research was to investigate and compare the interfacial adhesion of di?erent MAPP-trea-ted composites.We used?ve types of MAPP that are com-mercially used in industries requiring enhanced adhesion. In particular,we evaluated MAPP characterization to investigate its e?ect on the interfacial adhesion of compos-ites.We compared the mechanical properties,thermal properties,and e?ect of manufacturing temperature of MAPP-treated and non-treated composites as a function of di?erent MAPP types.The crystallinity of PP,MAPP, MAPP-treated and non-treated bio-composites was deter-mined by WAXS and di?erential scanning calorimetry (DSC).We determined that selecting the proper MAPP type is an important step in improving the interfacial inter-action of composites.

2.Experimental

2.1.Materials

Polypropylene(PP)was supplied by Hyosung Co., South Korea.It has an MFI of 1.7g/10min(190°C/ 2160g)and a density of0.91g/cm3.The bio-?llers used as the reinforcing?ller were RHF and WF,obtained from Saron Filler Co.and Dong Yang CMI Co.,South Korea, respectively.The particle size of RHF was860–270l m and that of WF was110l m.Table1shows the chemical constituents of bio-?our.The?ve types of MAPP were obtained from Eastman Chemical Products,Co.(Epolene G-3003and E-43),Crompton Polybond,Co.(Polybond 3150and Polybond3200),and Polyram,Co.(Bondyram 1004),respectively.

https://www.sodocs.net/doc/4f9503754.html,pounding and sample preparation

RHF and WF were oven dried at105°C for24h to adjust the moisture content to1–3%and then stored in sealed polyethylene bags before compounding.PP was blended with the RHF and WF in a laboratory-sized,co-rotating,twin-screw extruder using three general processes: melt blending,extrusion and pelletizing.The extruder bar-rel was divided into eight zones with the temperature in each zone being individually adjustable.The temperature of the mixing zone in the barrel was maintained at 190°C with a screw speed of250rpm.The extruded strand was cooled in a water bath and pelletized using a pelletizer. Extruded pellets were oven dried at80°C for24h and stored in sealed polyethylene bags to avoid unexpected moisture in?ltration.The RHF and WF application level was30wt%,based on the total weight,prior to compound-ing.The?ve types of MAPP,used as the compatibilizing agent,were applied at3wt%based on the total weight of bio-?our and PP.Extruded pellets were injection molded into tensile(ASTM D638),Izod impact(ASTM D256), and three-point bend test bars(ASTM D790)using an injection molding machine(Bau Technology,South Korea) at190°C with an injection pressure of1200psi and a device pressure of1500psi.The tensile specimen had the following dimensions:W=3.18±0.03mm,L=9.53±0.03mm,G=7.62±0.02mm,T=3.00±0.08mm,where W is the width of the narrow section,L the length of the narrow section,G the gage length,and T the thickness of the narrow section.After injection molding,the test bars were conditioned before testing at50±5%RH for at least 40h according to ASTM D618-99.

2.3.MAPP characterization

2.3.1.Molecular weight of MAPP

Three of the MAPP types,Polybond3150,Polybond 3200and Bondyram1004,were eluted using1,2,4-trichlo-robenzene(TCB)as the eluent solvent at170°C at a?ow rate of1mL/min.Molecular weights were measured by GPC at170°C using a PL-GPC210system(Polymer Lab-oratories)equipped with refractive index(RI)detectors and a PL-gel10l m column(two mixed-B).The weight-average molecular weights(M w)were calculated using a calibration curve from polystyrene standards.M w of G-3003and E-43were obtained from Eastman Chemical Products Co.

Table1

Chemical constituents of bio-?our

Others(%)Holocellulose(%)Lignin(%)Ash(%)

Wood?our a10.962.526.20.4

Rice husk?our b 6.359.920.613.2

a Wood?ours from Ref.[2].

b From Saron Filler Co.

1474H.-S.Kim et al./Composites:Part A38(2007)1473–1482

2.3.2.Melt?ow index(MFI)of MAPP

MFI values of the?ve MAPP types were measured at 190°C with a load of 2.16kg following ASTM D1238 using a melt indexer(Tinius Olsen Co.,USA).

2.3.3.Melting temperature(t m)and glass transition temperature(t g)of MAPP

DSC analysis was carried out using a TA Instrument DSC Q1000(NICEM at Seoul National University)with 5–8mg of each di?erent MAPP type.Each sample was scanned fromà80to200°C at a heating rate of10°C/ min and then cooled at the same rate under a nitrogen atmosphere.Two thermal properties,T m and T g,were determined from the second scan.T m was de?ned to be the maximum of the endothermic melting peak from the heating second scan and T g as the de?ection of the baseline in the cooling second scan.

2.3.4.Thermogravimetric analysis(TGA)of MAPP

TGA measurements were carried out using a thermo-gravimetric analyzer(TA instruments,TGA Q500)on 5-mg samples of the di?erent MAPP types,over a tem-perature range from25to700°C,at a heating rate of 20°C/min.TGA was conducted with the compounds placed in a high quality nitrogen(99.5%nitrogen,0.5% oxygen content)atmosphere at a?ow rate of40ml/min in order to avoid unwanted oxidation.

2.4.Mechanical property tests of composites

The tensile test for the composites was conducted according to ASTM D638-99with a Universal Testing Machine(Zwick Co.)at a crosshead speed of100mm/ min and a temperature of24±2°C.Notched Izod impact strength was measured on an impact tester(Dae Yeong Co.)by ASTM method D256-97at room temperature. The three-point bend tests of the composites were carried out in accordance with ASTM D790.The specimen had a span to depth ratio of16:1.The composites were tested at a crosshead speed of5mm/min.Five measurements were conducted and averaged for the?nal result.

2.5.Morphological test

Scanning electron microscopy(SEM)was used to measure the fracture surfaces of the MAPP-treated and non-treated tensile specimens using a SIRIOM scanning electron microscope(FEI Co.,USA).Prior to the measure-ment,the specimens were coated with gold(purity,99.99%) to eliminate electron charging.

2.6.Thermogravimetric analysis(TGA)of composites

The thermal degradation and stability of the MAPP-treated and non-treated composites according to manu-facturing temperature and time were measured by the isothermal condition of TGA.TGA measurements were carried out using the same TGA Q500analyzer on8–

10mg samples,over a temperature range from25°C to 180,200and220°C,at a heating rate of20°C/min,under a nitrogen?ow of40ml/min.After ramping to the target-ing temperature(180,200and220°C),the composites underwent isothermal testing for20min.TGA was mea-sured with the composites placed in a high quality nitrogen (99.5%nitrogen,0.5%oxygen content)atmosphere to pre-vent unwanted oxidation.

2.7.Attenuated total re?ectance(FTIR-ATR) measurements

The infrared spectra in the FTIR-ATR of G-3003, Bondyram1004,the composites and G-3003-treated com-posites were obtained using a Thermo Nicolet Nexus870 FTIR spectrophotometer(USA).A diamond was used as the ATR crystal.The samples were analyzed over the range of525–4000cmà1with a spectrum resolution of4cmà1. All spectra were averaged over32scans.This analysis of the composites was performed at point-to-point contact with a pressure device.

2.8.Di?erential scanning calorimetry(DSC)analysis of composites

DSC analysis was carried out using a TA Instrument DSC Q1000(NICEM at Seoul National University)with 5–8mg of each composite.Each sample was scanned from à80to200°C at a heating rate of10°C/min and then cooled at the same rate under a nitrogen atmosphere.

The specimens’relative percentage of crystallinity(X c) was calculated according to the following equation:

X c?

D H f100

D H

f

w

where D H f is the heat of fusion of the PP,MAPP and com-

posites,D H0

f

is the heat of fusion for100%crystalline PP (D H100=138J/g)[14]and w is the mass fraction for PP in the composites.

2.9.X-ray analysis

Wide-angle X-ray scattering(WAXS)analysis of PP, MAPP,MAPP(G-3003)-treated and non-treated compos-ites was performed with a Bruker General Area Detector Di?raction System(GADDS;NICEM at Seoul National University)that recorded the intensity of the X-rays dif-fracted by the sample as a function of the Bragg angle using Bruker computer software.Cu K a radiation with wave-length k=1.54A?was used with a nickel?lter.The exposure time was300s with a0.02(°2h)step.Two-dimen-sional scattering patterns were obtained by means of a Hi-Star X-ray detector.The crystallinity index(or percent-age of apparent crystallinity;C.I.%)of the composites was calculated as follows[15]:

H.-S.Kim et al./Composites:Part A38(2007)1473–14821475

CI%?eA:cryst:=A:totalT?100

A.cryst.is the corresponding area of the peak due to crys-tal di?raction of the sample and A.total is the total area; crystal and amorphous of the sample di?ractograms.

3.Results and discussion

3.1.Characterization of MAPP types

MA-maleated PP has been widely used as a compatibi-lizing agent and adhesion promoter for bio-?ller?lled poly-propylene composites.The MA functional group which grafts on the PP backbone acts as the chemical link between the hydrophobic matrix polymer and the hydro-philic surface of bio-?our.Table2shows M w,MA graft (%),MFI,T g and T m of the?ve commercially used,MAPP types investigated in this research.The characterization of MAPP di?ered according to the kind of MAPP processing method.Due to this variation of basic MAPP properties, we expected that the mechanical properties and interfacial adhesion of the composites would be a?ected by MAPP type.

The M w of Bondyram1004and G-3003and the MA graft(%)of G-3003and E-43were the highest,while the M w of E-43and MA graft(%)of Polybond3150were the lowest.According to MAPP types,the di?erence of M w could be seen that M w varied according to MAPP type and processing method.The mechanical properties of MAPP-treated composites were a?ected by the M w and MA graft(%)of MAPP.Low M w MAPP does not su?-ciently di?use and entangle with the PP matrix.Excessively high M w MAPP may not allow the coupling agent to reside at the interface between MAPP and PP matrix.The low MA graft(%)of MAPP did not o?er su?cient interaction and hydrogen bonding between the anhydride group of MAPP and bio-?ller.Excessively high MA graft(%)of MAPP may hold the coupling agent too close to the hydro-philic surface and not allow su?cient interaction with the continuous matrix phase[6,15].These results con?rmed the non-optimum mechanical properties of MAPP-treated composites with excessively low or high M w and MA graft (%).Therefore,the su?cient polymer backbone M w and MA graft(%)of MAPP is more easily di?used into the matrix polymer and provides enough sites for attachment to the polar bio-?our,respectively.The?nal properties and interfacial adhesion of MAPP-treated composites with su?cient M w and MA graft(%)were superior to those of MAPP with low or excessively high M w and MA graft (%)[6,15–18].The MFI of MAPP was a?ected by the M w,polydispersity and MA graft(%)of MAPP.Although they showed similar M w,Polybond3200had the highest MFI while Polybond3150had the lowest,possibly because Polybond3200has lower M w and polydispersity and higher MA graft(%)content.The polydispersity of Poly-bond3150and Polybond3200was5.8and4.3,respec-tively.However,we did not measure the MFI of E-43 due to its very low M w and high MFI.The high MFI value of MAPP slightly increased the production rate of compos-ites in the melt mixing process using twin-screw extruder. T m of E-43was the lowest due to its low M w.T g did not show any signi?cant variation among the?ve MAPP types.

Fig.1shows TGA curves of the?ve MAPP types.The thermal stability and decomposition temperature of Poly-bond3200were higher than those of Bondyram1004,Poly-bond3150and G-3003,even though its M w was lower than that of Bondyram1004,Polybond3150and G-3003,possi-bly because the thermal stability of the base PP of Poly-bond3200was the highest.In addition,the thermal stability of E-43was the lowest due to its extremely low M w.Nowadays,the commercial use of MAPP to improve the interfacial adhesion of composites shows variation in thermal stability according to the MAPP type.Therefore, the thermal stability of MAPP is an important consider-ation for enhancement of the interfacial interaction of composites.

Table2

Test results of M w,MA graft(%),MFI,T g and T m of?ve di?erent, commercially used,MAPP types

M w a MA graft

(%)b MFI

(g/10min)

T g

(°C)

T m

(°C)

Polybond315046,0000.520à24165 Polybond320042,000 1.0104à24164

G-300352,000 1.290à24162

E-439100 1.2NDà25154 Bondyram100466,0000.890à23160

a M

w

of G-3003and E-43was obtained from Eastman Chemical Products Co.

b MA graft(%)of the?ve types of MAPP was obtained from Crompton Polybond Co.(Polybond3150and Polybond3200),Eastman Chemical Products Co.(G-3003and E-43)and Polyram Co.(Bondyram1004), respectively.

1476H.-S.Kim et al./Composites:Part A38(2007)1473–1482

3.2.Mechanical properties

The tensile strength of RHF-and WF-?lled PP compos-ites is shown in Fig.2as a function of the?ller loading.The tensile strength of the composites decreased with increasing bio-?our loading,due to the weak interfacial adhesion and low compatibility between the hydrophilic bio-?our and hydrophobic PP[2,8,12,19].This result indicated that the impact and?exural strengths of the composites were slightly decreased with increasing bio-?our loading.The tensile strength of WF-?lled PP composites was higher than that of RHF-?lled PP composites,possibly due to the chemical constituents and particle size of bio-?our. The holocellulose and lignin content of WF is higher than that of RHF(Table1).The bio-?our materials are mainly composed of a complex network of three polymers:cellu-lose,hemicellulose and lignin[12].Lignin not only holds the bio-?our together,but also acts as a sti?ening agent for the cellulose molecules within the bio-?our cell wall. Therefore,the lignin and cellulose content of bio-?our has an in?uence on the strength of bio-?our and the tensile strength of composites.The?ller particle size of WF is smaller than that of RHF,and thereby o?ers a larger spe-ci?c surface area and slightly increased interfacial interac-tion in the matrix polymer,compared to the larger RHF particle size,at the same weight fraction in the composites [3].

The tensile,impact and?exural strengths of the compos-ites with di?erent MAPP types are shown in Figs.3–5, respectively.The tensile,impact and?exural strengths of the MAPP-treated composites were signi?cantly greater than those of the MAPP non-treated composites due to the enhanced interfacial adhesion of the composites by MAPP.In addition,MAPP underwent esteri?cation reac-tion or hydrogen bonding,at the interface,between the hydroxyl groups of the bio-?our on one side and the car-boxylic groups of the MAPP di?used matrix polymer on the other side[8,9,18].Figs.3–5show that the mechanical

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properties of the composites were a?ected by MAPP type. The tensile,impact and?exural strengths of G-3003-trea-ted composites were the highest,probably because G-3003contained su?cient M w,as opposed to Bondyram 1004which did not,and su?cient MA grafted on PP,com-pared to the insu?cient level of Polybond3150and E-43. The su?cient M w of MAPP allows better di?usion into the matrix polymer which indicates easier entanglement with the matrix polymer[6,15].Furthermore,the su?cient number of MA groups attached onto the PP chains causes strong interfacial interaction,probably due to the forma-tion of chemical bonds between MA groups and hydroxyl groups of bio-?ours[3,17].However,the tensile,impact and?exural strengths of Polybond3150-and E-43-treated composites were the lowest,which was attributed to the low M w(9100)of E-43and too low MA graft(%)of Poly-bond3150.Therefore,we concluded that the improvement in mechanical properties of the composites using MAPP as a compatibilizing agent was strongly dependent on the amount of MA graft(%)and the M w of MAPP.

3.3.Morphological characterization

Figs.6and7show the SEM micrographs of the tensile fracture surfaces of MAPP non-treated and treated(G-3003)composites,respectively.In Fig.6a,examination of the tensile fracture surface of MAPP non-treated compos-ites indicated the presence of pulled-out traces and bigger gaps between the bio-?our and matrix,which is evidence of weak interfacial adhesion at the interface.Such weak interface between RHF and PP can be seen even more clearly in the SEM micrograph of greater magni?cation shown in Fig.6b.Weak interfacial adhesion easily led to complete debonding from the matrix in the tensile fracture surface[18].The SEM micrograph of G-3003-treated composites shown in Fig.7a,along with the

magni?ed Fig.6.SEM micrographs of the tensile fracture surface of MAPP non-treated,RHF-?lled,PP composites:(a)300·and(b)700·

.

Fig.7.SEM micrographs of the tensile fracture surface of MAPP(G-3003)-treated,RHF-?lled,PP composites:(a)300·and(b)700·.

1478H.-S.Kim et al./Composites:Part A38(2007)1473–1482

micrograph of Fig.7b,clearly show the strong bonding and paucity of pulled-out traces from the matrix in the two phases.This result clearly demonstrated that the MAPP treatment of composites provides strong interfacial adhesion and good wetting,as evidenced by the almost complete absence of holes around the matrix and paucity of breaking of bio-?ours during tensile fracture[20].

3.4.FTIR-ATR analysis

Fig.8a and b show the FTIR-ATR spectra of G-3003, Bondyram1004,MAPP(G-3003)-treated and non-treated composites.G-3003and Bondyram1004showed two low absorption peaks at1774and1778cmà1.These peaks were assigned to symmetric C@O stretching of MA functions grafted on PP[21].This result indicated that the MA func-tional groups of MAPP can be reacted with the hydroxyl groups of the bio-?our to produce covalent bonding and esteri?cation reaction[12,22].This result was con?rmed by the stretching vibration of the ester carbonyl groups (C@O)such as at1741cmà1(PP–RHF)and1739cmà1 (PP–WF)which have resulted from esteri?cation reaction between free OH groups of the bio-?our and the MA func-tional groups of MAPP[9,11,22].Thus,the ester bonding of MAPP-treated composites o?ers better wettability and dispersion which can thereby improve the mechanical and thermal properties of the?nal product.

3.5.Wide-angle X-ray scattering

The WAXS di?raction curves of PP,MAPP,MAPP(G-3003)-treated and non-treated composites taken by re?ec-tion mode are shown in Figs.9and10,respectively.PP and MAPP showed strong di?raction peaks at2h of 14.1°(110),16.8°(040),18.4°(130)and21.2°(111). These peaks were attributed to the(110),(040),(130) and(111)di?raction planes of the a-form of PP and MAPP crystals with a monoclinic con?guration[23,24]. The hexagonal b-form of PP crystals with additional dif-fraction peaks at2h of16°(300)was not evident,possibly

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due to the injection molding process of PP and MAPP at molten state for a certain time[24].The same result was also seen in the composites and MAPP-treated composites. Pracella et al.[25]reported that no clear evidence of hexag-onal b-modi?cation was detected in Hemp?ber reinforced, PP composites and other PP composites reinforced with modi?ed natural?bers.Table3shows the crystallinity of PP,G-3003,MAPP-treated and non-treated composites using XPS.The crystallinity of G-3003and MAPP-treated composites was slightly higher than that of PP and MAPP non-treated composites,suggesting that the crystallization behavior of MAPP is slightly higher than that of PP due to chain branching of MA and the better dispersion of MAPP in the matrix polymer[25].These results are pre-sented in Table4,which lists T m,D H f and X c for PP,G-3003,MAPP-treated and non-treated composites obtained from the DSC second heating thermograms.T m of PP, G-3003,MAPP-treated and non-treated composites was not signi?cant changed but the X c of G-3003and MAPP-treated composites was slightly higher than that of PP and MAPP non-treated composites.The X c of MAPP and MAPP-treated composites was higher in both DSC and XPS analyzer results.The crystallinity of PP–RHF and PP–WF composites was also seen in Tables3 and4.The crystallinity of PP–WF composites was much higher than that of PP–RHF composites.Wood and ligno-cellulosic materials are complex materials which consist mainly of cellulose,hemicellulose and lignin.Cellulose rep-resents the crystalline structure of wood and lignocellulosic materials while the structures of hemicelluloses and lignin are amorphous[26].In general,the content of proteins, organic acids,pectins,fat,and waxes of lignocellulosic materials is higher than that of wood.Therefore,the higher degree of crystallinity of lignocellulosic materials increases the removal of fat,wax,and amorphous materials by alkali treatment[27].These results indicated that the crystallinity of RHF-PP composites is lower than that of WF-PP com-posites due to the higher content of amorphous materials and silica in RHF.

3.6.Thermal stability:e?ect of processing temperature

The isothermal TGA method was used to measure the degradation temperature and weight loss caused by the actual processing temperature of the composites.The pro-cessing temperature of the composites is generally deter-mined by the T m of the matrix polymer.T m of PP is between160and170°C.The processing temperature of the composites was set about10–30°C higher than the T m of PP to obtain smooth manufacture of the composites. The weight loss of the composites was measured using the TGA isothermal method at a measuring temperature of under180,200and220°C for20min.Figs.11and12show the isothermal TGA curves of the WF-and RHF-?lled PP composites,respectively,under the consistent temperature of180,200and220°C for20min.The ramping period to measure the isothermal condition and isothermal period for20min is shown in Fig.11.In Figs.11and12,the weight loss of composites was slightly increased with increasing isothermal test temperature and time.PP exhib-ited scarcely no weight change at these temperature[28]. The weight loss of composites at isothermal condition is due to the thermal degradation of the main constituents of bio-?our.Hemicellulose and lignin are two of the main constituents of bio-?our which have low thermal stability and degradation temperature compared to the matrix poly-mer[3,14,29].The weight loss of composites at these iso-thermal and actual processing temperatures(180,200and 220°C)are mainly a?ected by the hemicellulose and lignin of bio-?our[28,29].Therefore,achieving the proper pro?le

Table3

Crystallinity(%)of PP,MAPP and composites

Sample Crystallinity(%) PP43.5

MAPP(G-3003)44.8

PP–RHF30wt%32.6

PP–RHF30wt%(G-3003:3%)33.1

PP–WF30wt%38.5

PP–WF30wt%(G-3003:3%)39.1

Table4

Summary of T m,D H f and X c for PP,G-3003MAPP-treated and non-treated composites

Sample T m(°C)D H f(J/g)Crystallinity(%) PP165.581.458.9

MAPP(G-3003)162.283.960.8

PP–RHF30wt%166.050.852.6

PP–RHF30wt%(G3003:3%)165.855.157.0

PP–WF30wt%166.352.854.7

PP–WF30wt%(G3003:3%)165.259.161.2

1480H.-S.Kim et al./Composites:Part A38(2007)1473–1482

of temperature and time settings in the twin-screw extru-sion process for the production of composites is important in order to prevent the degradation of mechanical proper-ties of composites.

Fig.13presents the isothermal TGA curves of WF-?lled PP composites with di?erent MAPP types at 200°C for 20min.The weight loss of MAPP non-treated composites was slightly higher than that of MAPP-treated composites.The improved thermal stability of MAPP-treated compos-ites was a result of the strong interfacial adhesion between the WF and PP that arose from the addition of the MA functional group of MAPP [14].As shown in Fig.13,the weight loss and thermal stability of the composites were slightly a?ected by the MAPP types.The weight loss of Bondyram 1004-and Polybond 3200-treated composites was slightly lower than that of G-3003-and E-43-treated composites,due to the higher thermal stability of the for-mer two MAPP types that is evident in Fig.1.

4.Conclusions

The M w of Bondyram 1004and G-3003and the MA graft (%)of G-3003and E-43were the highest,while the M w of E-43and MA graft (%)of Polybond 3150were the lowest.Low M w MAPP does not su?ciently entangle with the PP matrix and excessively high M w MAPP may not allow the coupling agent to reside at the interface between MAPP and PP matrix.In addition,the low MA graft (%)of MAPP did not o?er su?cient interaction between MAPP and bio-?our.Excessively high MA graft (%)of MAPP may hold the coupling agent too close to the hydrophilic surface and not allow su?cient interaction with the matrix.These results con?rmed the non-optimum mechanical properties of MAPP-treated composites with excessively low or high M w and MA graft (%).MAPP with lower M w and polydispersity and higher MA graft (%)con-tent showed higher MFI.The T g and T m did not show sig-ni?cant change according to MAPP type.The thermal stability of high M w MAPP was superior to that of low M w MAPP.The tensile,impact and ?exural strengths of MAPP-treated composites were signi?cantly increased compared to those of MAPP non-treated composites.This result was con?rmed by the presence of pulled-out traces on the SEM micrographs of the tensile fracture surface between the bio-?our and matrix and by the FTIR-ATR spectral results for the stretching vibration of the ester car-bonyl groups (C @O)such as at 1741cm à1(PP–RHF)and 1739cm à1(PP–WF).

The tensile,impact and ?exural strengths of G-3003-treated composites were the highest and those of Polybond 3150-and E-43-treated composites were the lowest.The satisfactory G-3003results were due to the su?cient level of M w and MA grafted on PP for G-3003.The ?nal prop-erties and interfacial adhesion of MAPP-treated compos-ites with su?cient M w and MA graft (%)were superior to those of MAPP with low or excessively high M w and MA graft (%).The crystallinity of MAPP and MAPP-trea-ted bio-?our-?lled PP composites was slightly higher than that of PP and MAPP non-treated composites.With increasing isothermal test temperature and time,the weight loss of composites was slightly increased.This result con-?rmed the importance of setting the proper temperature and time pro?les for producing composites in the twin-screw extrusion in order to avoid the degradation of mechanical properties in the ?nal products.The weight loss of MAPP non-treated composites was slightly higher than that of MAPP-treated composites.Furthermore,the weight loss of high M w MAPP-treated composites was slightly lower than that of low M w MAPP-treated com-posites.

Acknowledgement

This work was supported by the Brain Korea 21project and by the Cleaner Production Technology Development project.

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