Properties of biocomposites based on lignocellulosic fillers

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ARTICLE IN PRESS2 L. Avérous, F. Le Digabel / Carbohydrate Polymers xxx (2006) xxx–xxxTable 1Chemical composition (wt%) <strong>of</strong> vegetable fibersFiber Cellulose Hemicellulose Pectin Lignin AshBast fibersFlax a 71 19 2 2 1–2Hemp a 75 18 1 4 1–2Jute a 72 13 >1 13 8Ramie a 76 15 2 1 5Leaf fibersAbaca a 70 22 1 6 1Sisal a 73 13 1 11 7Seed-hair fibersCotton a 93 3 3 – 1Wheat straw a 51 26 – 16 7LCF fillersLCF 0–1 58 8 – 31 3LCF 0–0.1 56 7 – 31 6LCF 0.1–1 59 8 – 31 2a Sources: Young, 2004; Le Digabel, 2004.motivate more and more different industrial sectors (automotive)to replace common fibreglass, for example.Biocomposites are obtained by the combination <strong>of</strong> biodegradablepolymer as the matrix material and biodegradablefillers (e.g., lignocellulosic fillers). Since bothcomponents are biodegradable, the composite as the integralpart is also expected to be biodegradable (Mohantyet al., 2000). For short-term applications, <strong>biocomposites</strong>present strong advantages, and a large number <strong>of</strong> papershas been published on this topic. Except some publications<strong>based</strong> on polysaccharide matrix (e.g., plasticized starch)(Avérous & Boquillon, 2004; Avérous, Fringant, & Moro,2001) most <strong>of</strong> the published studies (Avérous, 2004) are<strong>based</strong> on biopolyesters (biodegradable polyesters) matrices(Mohanty et al., 2000; Netravali & Chabba, 2003). Forinstance, PHA has been combined with lignocellulosicfibres (Bourban et al., 1997; Wollerdorfer & Bader,1998), jute fibres (Mohanty, Khan, & Hinrichsen, 2000a;Wollerdorfer & Bader, 1998), abaca fibres (Shibata, Takachiyo,Ozawa, Yosomiya, & Takeishi, 2002), pineapplefibres (Luo & Netravali, 1999), flax fibres (Van de Velde& Kiekens, 2002), wheat straw fibres (Avella et al., 2000)or lignocellulosic flour (Dufresne, Dupeyre, & Paillet,2003; Fernandes, Pietrini, & Chiellini, 2004). PLA has beenassociated with paper waste fibres, wood flour (Levit,Farrel, Gross, & McCarthy, 1996), kenaf (Nishino, Hirao,Kotera, Nakamae, & Inagaki, 2003), jute (Plackett,Logstrup Andersen, Batsberg Pedersen, & Nielsen, 2003)or flax fibres (Oksman, Skrifvars, & Selin, 2003; Van deVelde & Kiekens, 2002). Some authors have tested flax(Van de Velde & Kiekens, 2002) or sisal (Ruseckaite &Jiménez, 2003) with PCL. Mohanty, Khan, and Hinrichsen(2000b) have reinforced PEA with jute fibres. Aliphaticcopolyesters have been used with cellulosic fibres(Wollerdorfer & Bader, 1998), bamboo fibres (Kitagawa,Watanabe, Mizoguchi, & Hamada, 2002) or flax, oil palm,jute or ramie fibres (Wollerdorfer & Bader, 1998). Aromaticcopolyesters have been associated with wheat straw fillers.Some results on such systems are presented in aprevious publication (Le Digabel, Boquillon, Dole, Monties,& Avérous, 2004). Le Digabel et al. (2004) have showna good compatibility between the fillers and the biodegradablematrix without compatibilizers or special fillerstreatment.This paper is focussed on the processing and on the analysis<strong>of</strong> <strong>biocomposites</strong> <strong>based</strong> on lignocellulosic fillers (LCF)which are by-products <strong>of</strong> an industrial fractionation <strong>of</strong>wheat straw. These fillers are combined with biodegradablearomatic copolyester, polybutylene adipate-co-terephthalate(PBAT). The use <strong>of</strong> low cost bio-fillers is a way to reducethe cost <strong>of</strong> the end product with improved properties. Theaim <strong>of</strong> this paper is more particularly targeted at the thermaland mechanical properties <strong>of</strong> these <strong>biocomposites</strong>. We haveanalysed the influence <strong>of</strong> the filler size and content and, wehave tried to predict by modelling the corresponding evolution<strong>of</strong> the modulus. This paper complements and expands aprevious publication (Le Digabel et al., 2004).2. Experimental2.1. MaterialsThe matrix, a biodegradable and aromatic copolyester(polybutylene adipate-co-terephthalate, PBAT) has beenkindly supplied by Eastman (EASTAR BIO Ultra Copolyester14766). Copolyester chemical structure is drawn inFig. 1. This copolyester is soluble at room temperature indifferent solvents such as THF, CH 2 Cl 2 and CHCl 3 . Theratio between each monomer has been determined by 1 HNMR. Fig. 2 shows the NMR spectrum <strong>of</strong> PBAT, dissolvedin chlor<strong>of</strong>orm. The integration <strong>of</strong> the adequatepeaks (2.33 and 8.1 ppm) gives PBAT composition, 43%<strong>of</strong> butylene terephthalate and 57% <strong>of</strong> butylene adipate.Molecular weight (M w ) and polydispersity index (IP) are48,000 and 2.4, respectively. They have been determinedby size exclusion chromatography (SEC). Melt flow index(MFI) is 13 g/10 mn at 190 °C/2.16 kg. PBAT density is1.27 g/cm 3 at 23 °C.The lignocellulosic materials used as fillers are a byproduct<strong>of</strong> an industrial fractionation process <strong>of</strong> wheatstraw (ARD, Pomacle, France). This product is obtainedFig. 1. Chemical structure <strong>of</strong> the copolyester (PBAT).
ARTICLE IN PRESSL. Avérous, F. Le Digabel / Carbohydrate Polymers xxx (2006) xxx–xxx 3C 6 H 4(8,1 ppm)OCH 2 CH 2COCH 2 CH 2OCH 2COCH 2(2,33 ppm)CHCl 3Integral1.00001.01051.33611.35023.785610.09.59.08.58.07.57.06.56.04.54.03.53.02.52.01.51.00.55.5 5.0(ppm)Fig. 2. 1 H NMR spectrum <strong>of</strong> PBAT.from a multi-step process. 250 kg <strong>of</strong> chopped wheat straw(10–15 cm) are introduced into a 1 m 3 reactor under highshearing to promote fibre fragmentation. Wheat straw ishydrolysed in acid medium (H 2 SO 4 , 0.1 N) under pressure(3.5 bars) at 130 °C, during maintenance <strong>of</strong> 90 mn (Roller,1990). The soluble fraction (mostly hemicellulose sugars) isfiltered and refined for further applications. The insolublefraction, the by-product called lignocellulosic filler (LCF)is neutralised, washed and dried with a turbo-dryer (AlphaVomm, Italy). The process yield from the wheat straw tothe LCF is 33%. The dried LCF filler is sieved with a1 mm grid to eliminate the biggest fillers (20 wt%). Thisproduct is named LCF 0–1 . According to Fig. 3, this lastfraction is sieved with a 0.1 mm grille and then two fractionsare obtained, LCF 0.1–1 and LCF 0–0.1 .2.2. Biocomposites processingIn a previous publication, we have shown that the fillermatrixinteractions are sufficient to avoid filler treatmentand/or addition <strong>of</strong> compatibilizers, which are costly. Priorto blending, fillers and thermoplastic granules are dried inan air-circulating oven at 80 °C, for up to 4 and 1 h, respectively.PBAT and varying amounts <strong>of</strong> LCF are directlyadded in the feeding zone <strong>of</strong> a single screw extruder(SCAMIA S 2032, France) equipped with a specificdesigned torpedo-like element to promote high shearingand mixing. The screw diameter (D) and the L/D ratioare 30 mm and 26/1, respectively. Typically, for technicalreasons due to the quality <strong>of</strong> the filler dispersion, the maximumLCF content is 30–40 wt%. Extrusion temperature is135 °C. Three millimetre diameter strands are pelletizedafter air-cooling. These granules are extruded once againat the same condition to improve the filler dispersion intothe matrix.Standard dumbbell test pieces (NFT 51-034-1981) aremoulded with an injection moulding machine (DK codimNGH 50/100) in a temperature range between 115 and130 °C, with an injection pressure and speed <strong>of</strong> 500 barsand 50 mm/s. Holding pressure and times are 500 barsand 12 s (PBAT) or 14 s (<strong>biocomposites</strong>), respectively.Mould temperature is 30 °C. The total cooling time is22 s (neat PBAT) and 24 s. The injection-moulded specimensare approximately 10 mm wide and 4 mm thick inthe central part (French standard NFT 51-0.34 1981).2.3. CharacterisationsPBAT molecular weights and polydispersity index havebeen determined by SEC with PS standards for the calibration.Analyses are performed in THF on two PL-gel 5 lmmixed-C, a 5 lm 100 Å and a 5 lm Guard columns in aShimadzu LC-10AD liquid chromatograph equipped witha Shimadzu RID-10A refractive index detector and a ShimadzuSPP-M10A diode array UV detector.NMR equipment is a NMR 300 MHz (Bruker 300Ultrashield, USA). Samples have been dissolved in deuteratedchlor<strong>of</strong>orm.
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Properties of biocomposites based on lignocellulosic fillers

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