available online at: effects of coupling …journal.ippi.ac.ir/manuscripts/ipj-2011-04-7189.pdf ·...

Iranian Polymer Journal20 (4), 2011, 281-294

PLA;wood flour;PLA/WF composites;mechanical properties;interfacial adhesion.

(*) To whom correspondence to be addressed.E-mail: [email protected]

A B S T R A C T

Key Words:

Effects of Coupling Agent and Interfacial Modifierson Mechanical Properties of Poly(lactic acid)

and Wood Flour Biocomposites

Yanling Wang, Rongrong Qi*, Cheng Xiong, and Mark Huang

School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,Shanghai 200240, P.R. China

Received 6 September 2010; accepted 10 January 2011

To reduce our dependency on depleting fossil fuels and their cost, biocompositeswere prepared using polylactic acid (PLA) as a matrix and wood flour (WF) asfiller by a twin-screw extrusion method. Because of poor wettability between

wood flour and PLA matrix, the properties of the PLA/wood flour composite are notright. Thus, the silane coupling agents (as the surface treatment agent of wood flour)and the interfacial modifiers (various copolymers) have been used to improve theirinterfacial adhesion. The effects of wood flour content, types of silane coupling agentsand their content, interfacial modifiers and their concentration on the properties andmorphology of PLA/WF biocomposites were systematically studied in detail, includingmicrostructures, mechanical and rheological properties. The results revealed that theproperties of biocomposites were expected to be improved by dispersing wood flouraggregations into microfibrils and improving the interfacial adhesion between PLA andWF with the addition of epoxy silane or ethylene-methyl acrylate-glycidyl methacrylate(EMAGMA). Especially, the interficial modifier of EMAGMA could improve not only theinterfacial action but also the impact strength of PLA. Further studies indicated that theco-interfacial modifiers of epoxy silane and EMAGMA could effectively enhance theinteraction between PLA matrix and WF and further improve mainly the impact strengthand elongation-at-break of PLA/WF biocomposites.

INTRODUCTION

Advances in synthetic plasticsmade from petroleum have broughtconsiderable benefits to humanlife. However, the widespread useof plastics has also become a significant concern due to theirnegative impact on the environ-ment and the fossil fuels resources.Therefore, there is an immediateneed to develop a non-petroleum-based and sustainable feedstock,and this has predominantly shiftedthe attention of many researchers

towards bio-based plastics [1]because they reduce our dependen-cy on depleting fossil fuels anddecrease CO2 release into theatmosphere. One of the most interesting bio-based polymers ispolylactide (PLA) which is madefrom plants and it is readilybiodegradable [2].

In general, PLA is synthesizedby ring-opening polymerization oflactide and lactic acid monomers,which are obtained from the fermen-

Available online at: http://journal.ippi.ac.ir

tion of sugar feed stocks [3]. The as-synthesized PLAis a kind of favourable biocompatible, biodegraded,thermoplastic, high-strength and high-modulus poly-mer [4] which can substitute conventional polymersin many ways, such as barriers for sanitary productsand diapers, planting, disposable cups and plates and others [5]. However, its high cost, brittleness, low deformation-at-break and narrow processingwindows restrict its widespread applicability.Recently, the combination of PLA with natural materials [6-8] or synthetic polymers [9-11] providesa new way to obtain the tailored properties at lowcost. Numerous studies have been devoted to blending PLA with biocompatible plasticizers [12-14] and other polymers, and different kinds of partial-ly biodegradable [15,16] or totally biodegradablecomposites were obtained [3, 17,18].

Wood flour (WF), usually made by conventionalgrinding [19] is gaining increasing acceptance as akind of filler materials for polymers since it offersmany advantages, including low density, non-signifi-cant damage during processing, biodegradability,high stiffness, noise absorption, availability, andrenewability as well as relatively low cost [20].Furthermore, biocomposites comprised of naturalfibres [21] and bio-based plastics [22,23], specifical-ly wood fibres-thermoplastic composites, have alsodisplayed the cost-effective reinforcement of woodfibres in several thermoplastics. Their uses havereceived considerable attention in industrial fields[19, 24-26] not only as feasible problem solving togrowing environmental threats, but also as a sustainable solution to the uncertainty of the world'spetroleum supply [1, 19, 27-30].

PLA and wood flours (WF) are two of the mostpromising biomaterials possessing potentials for thereplacement of petroleum-based commoditiesbecause of low cost and availability. Furthermore,their biodegradability and compatibility can also beassets in applications where there is a demand forrecycled materials [31-33]. However, the poor wettability between hydrophilic wood microfibresand hydrophobic polymeric matrices would lead totheir direct mixture with poor interfacial adhesion andmechanical strength and ductility [29,34]. Thus, it isimportant to find some suitable interface modifiers toimprove the interfacial interaction between filler and

matrix, and further obtain biocomposites with desirable properties [35-37].

In this paper, PLA/WF biocomposites were prepared as a means to reduce the overall materialcost and tailor the material properties through a twin-screw extrusion method. To improve the interfacialinteraction between PLA and WF and processability,some low molecular weight silane coupling agentswere used to treat the surface of wood flours andsome copolymers were used as interfacial modifiers.The properties of biocomposites can be improved by dispersing wood flour aggregations into microfibrilsand improving the interfacial adhesion between PLAand WF with the addition of epoxy silane or ethylene-methyl acrylate-glycidyl methacrylate (EMAGMA),while it is not easy to break the extruded bar. Theeffect of wood flour content, the types of interfacialmodifers and their concentration on the properties ofPLA/WF biocomposites has been studied in detail,including the mechanical, thermal and rheologicalproperties. Moreover, the co-interfacial modifiers ofepoxy silane and EMAGMA have been used in thePLA/WF biocomposites where they could effectivelyenhance the interaction between PLA matrix and WFand further improve mainly the impact strength andelongation-at-break of PLA/WF biocomposites.

EXPERIMENTAL

MaterialsPLA (3051D) was obtained from Natureworks Co.Ltd. (USA), and was polymerized mainly from L-lactic acid. It had a specific gravity of 1.25 g/cm3 anda melt flow index about 25 g/10 min (210°C/2.16Kg). Its glass transition was in the range of 55-65°Cand melting temperature was in the range of 150-165°C. Pine wood flour (nominal 80 mesh, moisturecontent ~10%, specific gravity ~0.25 g/cm3, and theaspect ratio of fibril ~102) was supplied by LinanMingzhu Bamboo & Wood Flour Co. Ltd., China)whose composition was cellulose (42±2%), hemicel-lulose (27±2%), lignin (28±2%) and volatile matter(3±1%). Vinyltrimethoxysilane (vinyl silane), γ-aminopropyl triethoxysilane (amino silane), γ-glyci-doxypropyltrimethoxysilane (epoxy silane) and γ-methacryloxypropyltrimethoxysilane (allyl ester

Effects of Coupling Agent and Interfacial Modifiers ... Wang Y et al.

Iranian Polymer Journal / Volume 20 Number 4 (2011)282

silane) were purchased from National Medicines Co.Ltd., China and used as wood flour surface treatmentagents. LDPE-g-MAH (grafting degree 0.8%) andPOE-g-MAH (grafting degree 1.0%) were preparedby our group. Grafting reactions were carried out inthe molten state with a TSE-35 co-rotating twin-screwextruder (Ruiya Group, Nanjing, China) at 170°C.LDPE (722, Dow Chemical Co., Unite States) or ethylene-octene copolymer (POE) (Exact 4049,Exxon Mobil Co., USA), MAH, initiators, solvents, and co-monomers were simultaneouslyintroduced into the twin-screw extruder after dryblending which was similar to that of the preparationof ABS-g-MAH [38]. Ethylene methyl acrylatecopolymer (EMA, 24MA005, MA content 24%) orethylene-methyl acrylate-glycidyl methacrylate(EMAGMA, AX8900, GMA content 8%) resins wereused as interfacial compatibilizers and supplied by

Arkema Investment Co., Ltd., China.

Sample PreparationSurface Treatment of Wood FlourPine wood flour (WF) was dried first at 80°C for 24 hin a vacuum oven to remove water and low molecularweight organic materials [5,39]. Then, silane (5 wt%silane in 95% ethanol aqueous solution) was addedinto a fixed amount of dried wood flour in a high-speed mixer. The silane content (2 wt%) employed inthis study was a percentage amount relative to WFcontent in the formulation, and thus the higher the WFcontent, the higher was the silane content. After beingmixed for about 10 min, the wood flour was removed and dried at 120°C in a vacuum oven for 2 h to complete the reaction of wood flour with coupling agent, and then cooled to 105°C and held for12 h.

283Iranian Polymer Journal / Volume 20 Number 4 (2011)

Effects of Coupling Agent and Interfacial Modifiers ...Wang Y et al.

Composites PLA(phr)

WF (phr)

Coupling agent (phr)

Compatibilizer(phr)

WU10WU20WU30

100102030

0 0

W30-aW30-bW30-cW30-d

100 30

0.6 (Amino silane)0.6 (Epoxy silane)0.6 (Allyl ester silane)0.6 (Vinyl silane)

0

WP10WP20W30-bWP40

100

10203040

Epoxy silane

0.20.40.60.8

0000

WU30WCO30-BWCO30-CWCO30-DWCO30-E

100 30 0

0LDPE-g-MAH/15EMA/15POE-g-MAH/15EMAGMA/15

WMA10WMA20WMA30WMA40

100

10203040

Epoxy silane

0.20.40.60.8

EMAGMA/15

AX13AX26AX52

100 26 Epoxy silane

0.52EMAGMA/13EMAGMA/26EMAGMA/52

Table 1. Formulations of PLA/WF biocomposites.

Preparation of BiocompositesDifferent interfacial modifiers were used in thePLA/WF system with varied ratio in order to modulate the properties of the obtained bio-composites. Table 1 shows the formulas in terms ofWF and interfacial compatibilizers.

After PLA was dried in a vacuum oven at 80°C for24 h, PLA, dried WF and other agents were added into a high-speed mixer. Then they were mixed for 10 min and extruded through an ZE 25A twin-screwextruder (Berstorff GmbH, Germany) with a screwdiameter of 25 mm and a length-to-diameter ratio of36/1. The corresponding temperature profile alongthe extruder barrel was 20/120/140/160/170/170/175/170°C, the temperature at the die was 165°C, and thescrew speed was 150 rpm. The extruded rods werecut into short cylinders of about 10 mm in length, andthen the blends were dried again in the vacuum ovenat 80°C for 24 h before moulding.

The short cylinders were pressed into thin platesby a hot press at 170°C and 20 MPa for 8 min, andthen cut into bars for tensile and impact strength tests.

Characterization Mechanical TestingTensile tests were performed on an Instron testingmachine (Instron 4465, Instron Corp., USA) accord-ing to ASTM D882 with a crosshead speed of 10 mm/min. The specimen for tensile test was dumbbell-shaped with a dimension of 2×6×80 mmunder 50% humidity and 23°C. All samples were pre-conditioned at 23°C and 50% RH for 16 h. Atleast five replicate specimens were tested for each formulation.

Notched Izod impact testing was performed on auniversal pendulum impact tester (RAY-RAN TestEquipment Ltd., UK) according to ASTM D256 (samples of 4×10×80 mm dimensions and notch

depth of 2 mm). The impact resistance was calculated through dividing the total energy requiredto break the sample by the area of impact specimens.The specimens were pre-conditioned at 23°C and50% RH for 16 h. Both tests were conducted on fivesamples and the average values were recorded.

MorphologyScanning electron microscope (SEM) was used toobserve the microstructure of composites. The extruded rods were cooled in liquid nitrogen for 20 min and then broken to obtain fracture surfaces.The fracture surfaces were vacuum-coated with goldfor SEM observation. The instrument was a Hitachi S-2150 SEM (Hitachi High-Technologies Corp.,Japan) with an accelerated voltage of 15 kV.

Rhological BehavioursDynamic measurements (G' and G") were accom-plished using the cone and plate feature of a Gemini200 HR (Bohlin Instruments, UK). The cone angleand the cone diameter were 0.1 radians and 25 mm,respectively. Preliminary studies were conducted toensure that the dynamic properties were measured inthe linear viscoelastic region. The measurementswere conducted in a frequency range 0.1-100 s-l at anapplied strain of 1%. All samples were dried in anoven at 60°C for 24 h prior to being tested.

RESULTS AND DISCUSSION

Mechanical PropertiesEffect of WF ContentThe high cost and low deformation-at-break limit thewide applications of PLA, and the addition of woodflour can provide the cost reduction and combinationof properties. To obtain high performance PLA/WF

Iranian Polymer Journal / Volume 20 Number 4 (2011)284


Table 2. The effect of WF content on the mechanical properties.

Sample Tensile strength (MPa)

Elongation-at-break (%)

Notched Izod impact strength (KJ/m2)

Pure PLAWU10WU20WU30

54.9±1.137.4±0.834.0±0.827.6±0.7

2.5±0.32.6±0.31.8±0.21.3±0.2

2.3±0.23.0±0.22.6±0.22.4±0.2

composites, the influence of wood flour content onmechanical properties, tensile strength, elongation-at-break (EB) and impact resistance were initially investigated. Table 2 shows the effect of WF contenton the mechanical properties (PLA/WF biocompositeformulations are listed in Table 1). Pure PLA is a kindof brittle and stiff material because its elongation-at-break is as low as 2.5%. Based on the results in Table 2, it is evident that both tensile strength andelongation-at-break values of PLA/WF biocompositesare lower than those of pure PLA which decrease withincreased WF content. This may imply that there is apoor interfacial interaction between reinforcing fibreand polymer matrix because of the poor stress trans-formation across interphase, which can be alsoobserved in the traditional thermoplastic compositeswith the addition of fibres [40]. Unlike tensilestrength, the impact strength increased initially and

then dropped with higher WF content, where the maximum value of WF content was achieved at 10 phr. On the whole the impact strength of all thePLA/WF biocomposites is slightly higher than that ofpure PLA. This is because a small amount of woodflour would increase the free volume in the composites and segmental movements are facilitatedwhen composites are subjected to an impact force[41]. However, excessive wood flour could lead to itsaggregation due to poor interfacial interactionbetween WF and PLA, resulting in lower impactstrength.

Effect of Silane Coupling AgentsIn general, tensile strength is more sensitive to theproperties of matrix and the interfacial interactionbetween the fibres and matrix. The same happens inall the wood composites where there is a weak


Iranian Polymer Journal / Volume 20 Number 4 (2011) 285

(a) (b)

(c)

Figure 1. Mechanical properties of PLA/WF biocomposites as a function of different silane couplingagents: (a) tensile strength, (b) elongation-at-break, and (c) notched Izod impact strength.

interfacial interaction between highly hydrophilicwood flour and weakly hydrophilic plastics [29]. Asexpected, the addition of WF into PLA matrix without any interfacial compatibilizers would alsoreduce the tensile strength and elongation-at-breakvalues of the composites given in Table 2. Moreover,in the extrusion process, it is difficult to add fluffywood flour into PLA matrix, as the extrudate bar iseasily broken, and thus, it prevents a smooth process.To improve interfacial interactions, wood flour is usu-ally treated by some silane coupling agents beforemixing procedure. Herein, different kinds of silane arechosen as surface treatment agent and their effects onthe mechanical properties are studied for PLA/WFbiocomposites (the content of wood flour is fixed at30 phr as given in Table 1). In the process, due to theaddition of coupling agent, wood flour becomesdense, more easily mixed with polylactic acid and theextrudant bar is not easily broken.

From Figure 1, it is observed that the incorporationof silane coupling agents into the formulations cansuitably improve the tensile strength and the elonga-tion-at-break values of composites compared to thoseof PLA/WF biocomposites prepared without any sur-face treatment agent. The slight improvement inimpact strength of composites with silane couplingagent also suggests the positive influence of silane on

PLA/WF biocomposites. There are two aspects on therole of silane coupling agent on mechanical properties of biocomposites. First, the active group ofsilane coupling agent can react with the hydroxylgroup of WF (route II in Scheme I) [42,43], weakenthe polarity of WF and further improve its wettabilitywith PLA matrix. Secondly, the long carbon chain ofsilane coupling agent can twist with matrix PLA. Thecombined effect makes the silane coupling agent toact as a bridge between PLA and WF in the composites, which may improve the interfacial interaction between WF and PLA and then strengthenthe mechanical properties of the composites. Amongsilane coupling agents, epoxy silane is a more effective surface treatment agent for the PLA/WF system. This might be due to the following reactionsbetween epoxy group and PLA [44-47] (Scheme I(route III)) which could further increase the compatibility of the system.

Thus, epoxy silane is chosen as the typical surfacetreatment agent for further investigation. Therefore,the coupling reaction of epoxy silane with fillerpotentially increases the adhesion between polymermatrix and the filler surfaces.

Effect of Copolymer as Interfacial ModifiersAlthough silane coupling agents can to some extent


286 Iranian Polymer Journal / Volume 20 Number 4 (2011)

Scheme I. The reactions among the active group of silane coupling agent, the hydroxyl group of WF, and PLA.

O

Si

OCH3

OCH3

OCH3

3CH3OH

HO CH

CH3

O

OH

HO CH

CH3

O

O CH2 CH

OH

Si O

OH

OH

Wood

(III)

O

Si

OH

OH

O Wood

(II)

O

Si

OH

OH

OH

Wood OH

H2O

+ 3H2OHydrolysis

n

+

Condensation

+

n

Epoxy silane Silanols

Coupling agent

(I)

improve the interfacial interaction between woodflour and matrix, the mechanical properties of thecomposite are still unsatisfactory. It is well knownthat the mechanical behaviour of heterogeneous materials depends on four main parameters:

-modulus of each component;- volume fraction of each component; - morphology and aspect ratio of the filler, length

distribution, and orientation of fibres in compositeand;

- interface properties due to its liability in load transfer. The latter parameter depends mainly on thedegree of interactions between the phases, i.e., fibretreatment for fibre-filled composites [42].

In order to further improve the interfacial interaction between WF and PLA matrix, functional-ized or polar copolymer modifiers were also used as

compatibilizer and toughening agent, such as LDPE-g-MAH, EMA, POE-g-MAH and EMAGMA. Theeffect of various types of copolymer compatibilizerson the mechanical properties of WF/PLA biocompos-ites has been investigated with wood flour fixed at 30 phr (formulations listed in Table 1) and the resultsare given in Figure 2.

From Figure 2, it may be seen that all copolymercompatibilizers can improve the mechanical properties of PLA/WF composites. Among them, theimpact strength of EMAGMA-modified compositesis higher than that of other compatibilizers which isdue to the rich epoxy functional groups reacting withcarboxyl or hydroxyl functional groups of PLA andwood flour (the reaction is similar to (route III inScheme I)). Furthermore, after adding compatibilizer,the bar is not easily broken which indicates that the



(a) (b)

(c)

Figure 2. Mechanical properties of PLA/WF biocomposites as a function of different copolymers ofinterfacial modifiers: (a) tensile strength, (b) elongation-at-break, and (c) notched Izod impact strength.

processability can be improved even though not verysignificantly.

Effect of Co-interfacial Modifiers of Epoxy Silane andEMAGMAIn order to further improve the properties of PLA/WFbiocomposites, EMAGMA was also used as a co-modifier with epoxy silane in the present work. Theratios of silane to WF and EMAGMA contents arefixed (WP and WMA series in Table 1) and the resultsare shown in Figure 3. From Figure 3a, we can findthat the tensile strength of PLA/WF composites withor without EMAGMA exhibits the same trend, but thetensile strength of PLA/WF composites withoutEMAGMA is more sensitive towards WF content.Tensile strength is higher compared to that of

PLA/WF composites with EMAGMA which under 28 phr WF content, it reaches that of PLA. This phenomenon could be attributed to the low tensilestrength of EMAGMA (its tensile strength-at-break is4 MPa). However, the addition of EMAGMA leads tosignificant improvements in elongation-at-break andimpact strength because the epoxy functional groupscan improve the distribution and wetting of WF andfurther lead to high impact resistance with strain energy dissipation mechanism (Figures 3b and 3c).

Further studies reveal that the content of EMAG-MA has some effects on the mechanical properties ofPLA/WF biocomposites. AX series in Table 1 showthe formulations of composites under study. Table 3presents the mechanical properties versus EMAGMAcontent for PLA/WF biocomposites. The tensile



(a) (b)

(c)

Figure 3. Mechanical properties of PLA/WF biocomposites as a function of WF content. (PLA 100 phr; WF/silane100/2; EMAGMA zero or 15 phr): (a) tensile strength, (b) elongation-at-break, and (c) impact resistance.

strength of the obtained composite is slightly loweredwith higher EMAGMA content, while the impactstrength and the elongation-at-break values increasewith the increased EMAGMA content due to efficientwettability between the plastics and wood flourbecause of the reaction of epoxy groups in EMAGMAand PLA.

Morphology and MicrostructuresMechanical properties of a composite are closely

related to its morphology, and the wettability betweenstrong hydrophilic WF (containing many hydroxylgroups) and weakly hydrophilic PLA. The clearboundary between wood flour and PLA matrix at theratio of 100/30 (PLA/WF) indicates non-wettabilityof PLA/WF biocomposites prepared without anyinterfacial modifiers (Figure 4a).

In Figure 4a we can also find that wood flour in theform of wood fibre constitutes the disperse phase and PLA as the continuous phase. This result also



Sample Tensile strength (MPa)

Elongation-at-break (%)

Impact strength (KJ/m2)

AX13AX26AX52

31.3±0.627.4±0.621.0±0.5

6.9±0.411.7±0.624.4±0.6

3.4±0.23.8±0.24.1±0.2

Table 3. The effect of EMAGMA content on the mechanical properties.

(L) (R)(a)

Continued

(L) (R)(b)

indicates that there is a poor interaction between thematrix and fibres, which further leads to poormechanical properties of PLA/WF biocomposites.However, the phase boundaries in the PLA/WF biocomposites become blurred when epoxy silane orEMAGMA is used as an interfacial compatibilizer(Figures 4b and 4c) implying that both epoxy silaneand EMAGMA can improve the interface interactionbetween wood flours and PLA matrix which in turncould improve the mechanical properties of PLA/WFbiocomposites.

Moreover, as shown in Figure 4d, wood flour canbe embedded within PLA matrix when both epoxysilane and EMAGMA are used as interfacial modifiers, implying that the combination of epoxysilane with EMAGMA may be more effective forimproving the wettability and interfacial interactionbetween wood flours and PLA matrix.

Rhological PropertiesIn general, the increase in wood flour content in PLAincreases the melt viscosity of PLA/WF composites.The influence of wood flour content on complex viscosity is shown in Figure 5a. One can see that complex viscosity (η*) increases with increased woodflour content and some differences appear at low frequencies. For example, PLA/WF biocompositesexhibit a Newtonian plateau in the low frequencyregion and shear thinning at higher frequencies, whilethe complex viscosity-frequency curve of pure PLA isalmost flat and does not show distinct shear thinningproperty within the entire frequency range. For moreexact comparison and data interpretation, eqn (2) ispresented as follows:

(1)

where, m is a constant index, n is the power-law



1* −= nmγη &

Figure 4. SEM Micrographs of cryofractured PLA/WF biocomposites: (a) WU30, (b) W30-b, (c) WCO30-E, and (d) WMA30.((L): magnification ×1000 and (R): magnification ×3000).

(L) (R)(c)

(L) (R)(d)

Figure 5. Plots of (a) complex dynamic viscosity (η*), ofPLA/WF composites as a function of frequency: (A) purePLA, (B) WMA20, (C) WMA30, and (D) WMA40 and (b)storage modulus (G') and loss modulus (G").

exponent, and γ is the frequency. From Table 4, wecan find that the values of n drops with increasedwood flour content, meaning that wood flourenhances the shear thinning behaviour due to solidfillers requiring higher shear rate to achieve the critical shear flow [48]. The constant index mconsiderably increases with increased wood flourcontent, indicating that the addition of wood flourcauses a tremendous increase of melt viscosity.

The storage modulus (G') and loss modulus (G")of the wood flour-filled composites increase greatlywith higher wood flour content (Figure 5b). FromFigure 5b, one can also deduce that PLA exhibits

Table 4. Power-law model parameters at 180°C.

liquid type viscoelastic behaviour (G">G') in thewhole region. While composites WMA20 andWMA30 have intersecting point; exhibiting liquidtype viscoelastic behaviour (G">G') in large fre-quency region, and solid type viscoelastic behaviour(G"<G') in small frequency region. Furthermore, G'is higher than G" with the entire frequency region forcomposite WMA40. These can be attributed toimproved interactions between wood flour andmatrix at high filler loadings and low frequencies,similar to some sorts of network systems.

CONCLUSION

PLA/WF biocomposites were prepared using polylactic acid (PLA) as a matrix and wood flour(WF) as filler by a twin-screw extrusion method. Theeffects of different factors on the properties ofPLA/WF biocomposites were investigated in detail.The important results are summarized as follows:

- PLA/WF biocomposites, prepared without anyinterfacial modifiers, result in poor mechanical properties due to their non-wettability property.

- Silane or EMAGMA can enhance the wettability and interfacial interactions between woodflour and matrix. Moreover, the co-modifiers ofepoxy silane and EMAGMA are more effective inPLA/WF biocomposites and notably improve theimpact strength and elongation-at-break of PLA/WF biocomposites.

- The increase in WF content leads to a substantialincrease in η* value which is favourable for PLAextrusion or blow moulding processes.

ACKNOWLEDGMENTS

This work was financially supported by Shanghai



(a)

(b)

Sample Ratios of PLA/WF/epoxy silane/EMAGMA

m (Pa.sn)

n

PLAWMA20WMA30WMA40

100/0/0/0100/20/0.4/15100/30/0.6/15100/40/0.8/15

142.4476.7

1059.22068.6

0.970.490.300.27

.

Leading Academic Discipline Project (No. B202).The authors thank Mr. Yongan Gu for enthusiasticdiscussion.

SYMBOLS

η* : Complex dynamic viscosityG' : Storage modulusG" : Loss modulusm : Constant indexn : power-law exponentγ : frequency

ABBREVIATIONS

PLA : Polylactic acidWF : Pine wood flour Vinyl silane : VinyltrimethoxysilaneAmino silane : γ-Aminopropyl triethoxysilaneEpoxy silane : γ-GlycidoxypropyltrimethoxysilaneAllyl ester silane : γ-Methacryloxypropyltrimethoxy-

silaneLDPE-g-MAH : Maleic anhydride grafting low

density polyethylene copolymerPOE-g-MAH : Maleic anhydride grafting poly-

(ethylene 1-octene) EMA : Ethylene methyl acrylate

copolymerEMAGMA : Ethylene-methyl acrylate-glycidyl

methacrylat

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