eg

y a

re, U

D. Mechanical testing

leneeffthevedineatn. I

nt natt for cmechatons oer pulpfor lig

linkages present in lignin are phenolic AOH, aliphatic hydroxyl,carbonyl, alkyl aryl ether, biphenyl, diaryl ether, phenylpropane,guaiacyl, syringyl, etc. [1,2]. The details of the chemical functional-ities and inter unit linkages are reported in literature [1,2]. Tracesof carbohydrates also remain with lignin. Lignin nds applicationsin adhesives, asphalts, polyurethanes, and phenolformaldehyde

creased the modulus but decreased the tensile strength andelongation of the blends [9]. However, coupling agents have beenused to improve the mechanical properties of lignin composites[10]. Lignin itself has also been used as a compatibilizer in naturalbre composites [11]. It has been reported that lignin acts as bnucleating agent, re retardant and toughening agent for neat PP.However, very limited studies have been done on lignin blendedwith biodegradable biopolymers such as starch, polyhydroxyalk-anoates and polylactic acid. Lignin acts as a plasticizing agent forstarch [12], nucleating agent for polyhydroxybutyrate (PHB) poly-mers [13] and adhesion promoter in cotton brePLA composites

Corresponding author at: Bioproducts Discovery and Development Center(BDDC), Department of Plant Agriculture, University of Guelph, Ontario, CanadaN1G 2W1. Tel.: +1 519 8244120x56664; fax: +1 519 763 8933.

Composites: Part A 42 (2011) 17101718

Contents lists available at

Composite

evE-mail address: mohanty@uoguelph.ca (A.K. Mohanty).in the United States in the near future, about 225million tons of lig-nin generation is expected from the cellulosic bioethanol industry[1]. Only about 2% of the generated lignin is being used for valueadded applicationswhile the rest is used as burning fuel in the samegenerating industries. Sustainability of these industries greatly de-pends upon the value added applications of this co-product.

Lignin is an amorphous substance that has potential for mate-rial applications. It is a complex polyfunctional macromoleculewhich is composed of a large number of polar functional groups[2]. Important functional groups, chemical units and inter unit

polyvinyl alcohol (PVA) [4]. LigninPP, ligninPET, ligninPVC(polyvinyl chloride) and ligninPS (polystyrene) composites havealso been reported in literature [57]. Lignin is compatible withpolystyrene (PS) [7] and its compatibility increases with increasinglignin content. In case of ligninPVC blends, lignin is more compat-ible to unplasticized PVC than plasticized PVC [7]. Ligninpolyeth-ylene composites compatibilized with ethylene vinyl alcoholcopolymer was studied by Samal et al. [8]. Incorporation of ligninin low density polyethylene (LDPE), linear low density polyethyl-ene (LLDPE), and high density polyethylene (HDPE) slightly in-E. Extrusion

1. Introduction

Lignin, the second most abundaworld, serves as a matrix componenlose in plant cell walls and providesbres. Currently, about 70 millionannually as a co-product in the papmore, in order to fulll the demand1359-835X/$ - see front matter 2011 Elsevier Ltd.doi:10.1016/j.compositesa.2011.07.025ural biopolymer in theellulose and hemicellu-nical strength to bio-f lignin are generatedindustry [1]. Further-

nocellulosic bioethanol

resin formulations [1,3]. Lignin has interesting grafting and cross-linking abilities that makes it an interesting material for its usein polyurethanes and other polymeric systems [3]. However, verylimited studies have been conducted on lignin-based polymercomposites or polymer blends. Ligninpolymer blends and com-posites have been reviewed recently [1]. Lignin forms miscibleblends with polyethylene terephthalate (PET) and polyethyleneoxide (PEO) and immiscible blends with polypropylene (PP) andA. Thermoplastic resinB. Strength compatibilized composites.

2011 Elsevier Ltd. All rights reserved.Enhanced properties of lignin-based biodusing injection moulding process

Saswata Sahoo a, Manjusri Misra a,b, Amar K. MohantaBioproducts Discovery and Development Center (BDDC), Department of Plant Agricultub School of Engineering, University of Guelph, Ontario, Canada N1G 2W1

a r t i c l e i n f o

Article history:Received 2 December 2010Received in revised form 21 July 2011Accepted 21 July 2011Available online 28 July 2011

Keywords:

a b s t r a c t

Composites from polybutymelt mixing process. The(PMDI) compatibilizer onmaterial into PBS was achieIncorporation of 1% PMDIstrength simultaneously. Hnin and PMDI incorporatio

journal homepage: www.elsAll rights reserved.radable polymer composites

,b,niversity of Guelph, Ontario, Canada N1G 2W1

succinate (PBS) and lignin-based natural material were fabricated using aects of lignin material and polymeric methylene diphenyl diisocyanateproperties of composites were investigated. Incorporation of 65% ligninwith an improvement in the tensile and exural properties of composites.50% lignin lled composites enhanced the tensile, exural and impactdeection temperature (HDT) of the virgin plastic also increased with lig-mproved interfacial adhesion was observed from SEM micrographs of the

SciVerse ScienceDirect

s: Part A

ier .com/locate /composi tesa

[14]. It has been reported that tensile strength and elongation at

PBS composites have been studied by many authors [1619]. Nat-

: Parural bres are not compatible with hydrophobic polymers andhence result in inferior material properties. In order to improvethe properties of natural bre composites, surface treatments of -bres have been reported in literature [17,18]. Compatibilizers/cou-pling agents have also been used to improve the performance ofcomposites. Various types of compatibilizers have been testedare silanes, titanates, maleic anhydride grafted polymers and isoc-yantes. Use of polymeric methylene diphenyl diisocyanate (PMDI),one of the isocyanate compatibilizers, has improved the tensilestrength and elongation of natural ller based composites [20,21].

Lignin-based PBS composites are very rarely reported in litera-ture. In the present study, a lignin-based natural material with thetrade name Arboform F 45 has been used as reinforcing ller in aPBS matrix. Arboform F 45 is a melt processable thermoplasticmaterial available in pellet form. It contains modied alkali lignin(obtained from paper pulp industry), natural additives, and 45%ground plant bres like hemp, ax and wood particles [22,23].Arboform F 45 pellets (described as lignin in this manuscript)were used as received in this study. It is believed that lignin ismore compatible with polar polymers due to the presence of polarfunctionality in its chemical structure. Poor compatibility of ligninwith conventional polyolen polymers can be understood from theinferior mechanical properties of lignin lled polyolen compos-ites. The tensile strength of polyethylene drastically decreasedwith 27% lignin incorporation [10]. Similarly, incorporation of lig-nin to polypropylene gradually decreased the tensile strength ofcomposites [6,24]. Incorporation of lignin to PLA also reduced theproperties of the polymer [15]. PBS was selected as the polymermatrix for our study because of its toughness, polar nature, nearlysimilar solubility parameter with lignin, biodegradability, and pos-sible renewability. In this research, the effect of lignin (Arboform

F 45) content and the effect of polymeric dimethylene diphenyldiisocyanate (PMDI) compatibilizer were tested with respect tothe mechanical, thermal and thermo-mechanical properties ofthe generated composite materials.

2. Experimental

2.1. Materials and method

2.1.1. MaterialsLignin Arboform F 45 was received from Tecnaro GMBH, Ger-

many. PBS (Bionolle 1020), a product of Showa Highpolymers Co.Ltd., Japan, was received from Toyo Plastics Co. Ltd., Osaka, Japan.Polymeric methylene diphenyl diisocyanate (PMDI) under thetrade name Rubinate Mwas used in this study. Rubinate M usedwas a product of Huntsman polyurethanes, NJ, USA.break of polylactic acid (PLA) decreased with lignin incorporation.As well, thermal degradation was accelerated when lignin contentreached 20% [15].

PLA and polyhydroxyalkanoates (PHAs) are the most widelyused biopolymers but they are facing challenges due to their infe-rior impact performance. Polybutylene succinate (PBS) is a com-paratively tough polymer and is capable of incorporating a highvolume of biomass. PBS can be made from both fossil and renew-able resources which offer a great future for the composite indus-tries regarding availability of raw material. The growing interestfor PBS manufacturing predicts a future cost reduction which issignicantly lower than the current price. Natural bre reinforcedS. Sahoo et al. / Composites2.1.2. Composites fabricationLignin (Arboform F 45) was not melt processable alone in a

15 cc microextruder (DSM Xplore, Netherland). Hence, it was meltmixed with PBS to develop composites from lignin. Before compos-ite processing, PBS and lignin pellets were dried at 80 C for 3 and4 h respectively using a convection oven. Lignin of varying weightpercentages (30%, 50% and 65%) with calculated quantities of PBSwere melt mixed in a 15 cc microextruder at 160 C barrel temper-ature, 150 rpm screw rotation (co-rotation conguration) andcompounded for 6 min. The hot melt was collected and compositeswere fabricated using a 12 cc microinjection moulder (DSMXplore) at 160 C melt temperature and 30 C mould temperature.Composites with compatibilizer were made by adding 12 wt.%PMDI to 50% lignin lled PBS composites. All the composites weremade at similar processing conditions. All the composite speci-mens acquired a lignin like dark reddish brown colour.

2.2. Characterisation

The effect of lignin (Arboform F 45) content (30%, 50% and 65%)on the PBS matrix was studied and the properties of the resultingcomposites were compared with neat PBS polymer (control). Com-posites with 50% lignin content were selected for PMDI incorpora-tion. Composites were prepared with the incorporation of 1 and2 wt.% PMDI compatibilizer. The properties of the compatibilizedcomposites were compared with the properties of 50% lignin lledcomposites and neat PBS. The types of characterisations carried outare discussed below. All results presented are the average values ofve replications for mechanical properties and three replicationsfor thermal and physical properties.

2.2.1. C, N, S analysisTotal carbon, nitrogen and sulphur content of lignin pellets

were evaluated through elemental analysis at Laboratory Services,University of Guelph.

2.2.2. Mechanical testingTensile and exural properties of the composites were mea-

sured by a Universal testing machine, Instron 3382, according tostandards ASTM D 638 and ASTM D 790 respectively. System con-trol and the data analysis were done using Blue Hill software. Thenotched Izod impact strength was measured with a TMI MonitorImpact tester (model No. 4302-01) according to ASTM D 256using a pendulum of 5 ft-lb.

2.2.3. Fourier transform infrared spectroscopy (FTIR)Thermo Scientic Nicolet 6700 FTIR spectrometer in attenu-

ated total reection infrared (ATR-IR) mode with a resolution of4 cm1 and a number of 32 scans per sample was used to obtainthe spectra.

2.2.4. Differential scanning calorimeter (DSC)Heat ow as a function of temperature was studied by a Differ-

ential scanning calorimeter (DSC Q 200, TA Instruments Inc.) usingheatcoolheat mode. Nitrogen was used as purge gas during theexperiment. The data was collected by heating the specimen from50 to 200 C at a constant heating and cooling rate of 10 C perminute. The data was analysed through TA instrumentss Universalanalysis software.

2.2.5. Dynamic mechanical analysis (DMA)The storage modulus, loss modulus and tan delta of the com-

posite specimens as a function of temperature were measuredusing a Dynamic mechanical analyser (TA Instrument Inc. DMA Q800). Experiments were carried out by heating the specimens from50 to 110 C at a constant heating rate of 3 C/min, 20 lm oscil-

t A 42 (2011) 17101718 1711lating amplitude, and 1HZ frequency. Heat deection temperature(HDT) measurements were done at 0.455 MPa load (ASTM D 648).Specimens were heated from room temperature to 110 C using a

heating rate of 2 C /min. A three point bending clamp was used forall the tests.

2.2.6. Thermogravimetric analysis (TGA)Thermogravimetric analysis was carried out by a Thermogravi-

metric analyser (TA Instrument Inc. Q500).The samples werescanned from room temperature to 600 C at a heating rate of20 C/min in a nitrogen atmosphere.

2.2.7. Density measurementThe density of polymer and composites was measured by an

Electronic densimeter MD-300S (Alfa Mirage) that takes measure-ments according to Archimedes principle.

material. Peaks due to a CAH stretching vibration appear at 2920

ites gradually increased with increasing lignin content in thecomposites. The improvement in the properties of composites indi-cates an interaction, possibly polarpolar interaction between lig-nin and the polyester matrix. Improvement of the tensile strengthof the hydroxypropyl lignin and polyethylene blend with the

nset Maximumdegradationtemperature (C)

Weight loss at 400 C(%)

Charred residues at 600 C(%)

402.9 57.1 0.2392.3 67.8 12.0387.9 343.2 63.8 20.4383.7 341.3 57.5 27.3

388.1 344.2h 61.7 22.1357.8 353.1 62.6 21.8

341 380480b 53.4 31.6

1712 S. Sahoo et al. / Composites: Part A 42 (2011) 171017182845 cm1. Characteristic peaks in the spectra appear at1685 cm1, 1590 cm1, 1511 cm1 are due to aromatic C@Cstretching, and peaks at 1040 cm1 and 1260 cm1 appear due toCAOAC stretching from ether groups (broader peak than CAOstretching of polyester). Weak peaks appear at 1220 cm1 and1370 cm1 (not very clearly distinguished due to the overlappingof spectra) also indicate phenolic CAO and phenolic OH in ligninrespectively. A chemical and structural analysis of this materialwas also reported by Haensel et al. [26].

Table 1Thermo gravimetric analysis of composites.

Specimens Degradation onset(C)

Weight loss at degradation o(%)

PBS 306.4 1.030% LigninPBS 260.3 2.450% LigninPBS 237.6 2.665% LigninPBS 236 2.7

50% LigninPBS-1% PMDI 244.5 2.450% LigninPBS-2% PMDI 236.7 2.6

Lignin 179 3.22.2.8. Scanning electron microscopy (SEM)The morphology of tensile fractured surfaces of the composites

was observed through a Hitachi S-570 scanning electron micro-scope (Hitachi High Technologies, Tokyo, Japan) at room tempera-ture. The samples were gold sputtered up to a thickness of 21 nmby means of a Emitech K-550 sputter coater (Ashford Kent, UK).An accelerating voltage of 10 kV was used to collect themicrographs.

3. Results and discussion

3.1. Characterisation of lignin

Lignin pellets were analysed for density, elemental composi-tion, functional groups, and thermal properties. The density of lig-nin was 1.34 g/cm3. The total carbon, nitrogen and sulphur contentin the material were 57.2%, 0.27% and 0.6% respectively. This ligninmaterial showed thermal degradation onset at about 179 C (Ta-ble 1). Lignin degrades at a very broad range of temperatures, be-tween 150 and 800 C. Lignin decomposition occurs by severalcompeting reactions during which various bonds cleave at widerange of temperatures releasing gases like CO, CO2, H2O and CH4[25]. The FTIR spectrum of lignin (Fig. 1) shows a strong and broadpeak at 3342 cm1 which depicts the presence of OH group in theb Broad.h Hump.3.2. Mechanical properties

3.2.1. Tensile propertiesTensile properties of composites are shown in Table 2. It is ob-

served that the tensile strength of the composites rst decreasedwith 30% lignin incorporation and then increased gradually byincreasing lignin content to 65% (Table 2). Tensile strength of com-posites also decreased with increasing ller (agro bre) content inbiodegradable polymers like PLA and PBS [27,28]. This outcomewas attributed to the weak interfacial adhesion between thehydrophilic ller and the hydrophobic polymer matrix. However,improvement in the tensile properties of composites at higher lig-nin content (65%) was observed in this investigation. At 65% lignincontent, the tensile strength increased by a factor of 10 over the50% lignin lled composites, and the strength was about 13% high-er than the neat polymer. The increase in the tensile strength athigher lignin content indicates the reinforcing effect of lignin inPBS polymer that may be attributed to the similarity in the solubil-ity parameter of lignin and PBS, crosslinking ability and adhesivenature of lignin. A highly viscous appearance of the composite meltwas observed during the processing of 65% lignin lled compos-ites; however, the composite melt at 30% and 50% lignin contentwas comparatively less viscous. This result may be attributed tothe crosslinking ability of lignin that increased with increasing lig-nin content in the composites. The tensile modulus of the compos-

Fig. 1. FTIR spectra of lignin, PMDI and composites.

addition of vinyl acetate, a polar component in non polar polyolenmatrix, also supports this interaction concept [29]. Authors haveinterpreted that the interaction was due to the presence of polarcarbonyl group [29]. Therefore, a hydrogen bond formation couldbe possible between the carbonyl group of the polyester matrixand the hydroxyl group of lignin.

Based upon the processing suitability and properties combina-tion, 50% ller based composites were selected for incorporation

failure of composites can be observed from the gure. Strain atbreak of materials decreased with ller incorporation and slightlyimproved by PMDI addition. Reduction of elongation at break withthe ller incorporation and slight improvement by PMDI additioncan also be observed from Table 2. It is reported that PBS is a quiteductile polymer and the percentage elongation reduces signi-cantly even with 10% bioller incorporation [17]. Similar trendsin properties by the addition of PMDI to sugar beet pulp basedpolylactide composites have also been reported [21].

The rule of mixtures as presented in Eq. (1) was used to predictthe modulus of composites. The rule is generally applied to randomoriented short bre composites [27].

Ec VmEm kVf Ef 1Ec, Em, Ef are the elastic modulus of the composite, polymer matrixand ller (lignin) respectively. A modulus of lignin of 6.27 GPa [22]was considered for calculating the modulus of composites. Vm andVf are the volume fraction of polymer matrix and ller respectively.

Table 2Tensile, exural, HDT and impact properties of composites.

Specimen label Tensilestrength (MPa)

Tensilemodulus (GPa)

Elongationbreak (%)

PBS 35 1.5 0.6 0.01 122 2130% LigninPBS 26 1.8 1.1 0.03 4.6 0.350% LigninPBS 29 3.4 2.3 0.35 2.0 0.865% LigninPBS 39 1.1 3.3 0.04 1.5 0.1

50% LigninPBS-1% PMDI 37 6.1 2.0 0.03 3.1 1.350% LigninPBS-2% PMDI 42 4.7 1.9 0.19 4.3 0.7

S. Sahoo et al. / Composites: Parof PMDI compatibilizer. Incorporation of 1% and 2% PMDI increasedthe tensile strength by 27 and 44% over the uncompatibilised com-posites, and was about 7.5% and 22% higher than the neat polymerrespectively (Table 2). From these results it was concluded thatPMDI improved the interfacial adhesion in the composites[20,21]. Addition of PMDI expects the formation of a urethane(AHNACOOA) linkage due to the reaction between the ANCOgroup of PMDI and the AOH group of lignin [30]. Furthermore,the urethane linkage leads to possible secondary intermolecularbonding (i.e. the hydrogen bonding between NAH group of ure-thane linkage and carbonyl group of polyester [30]) which couldbe the cause of improved interfacial adhesion of PMDI compatibi-lized composites. The schematics of the possible interactions areshown in Fig. 2.

The modulus of the composites decreased slightly with 1% PMDIaddition (Table 2) and was reduced further by increasing PMDIconcentration from 1% to 2%. Lowering of the modulus may beattributed to possible plasticisation of the composite materialsdue to the PMDI addition. It is reported that the moisture presentin the bioller reacts with PMDI producing amine or urea com-pounds. These compounds plasticize the composites [21] resultingin a lowering of modulus and an increase in the elongation. Thestressstrain curves of the composites are shown in Fig. 3. Brittle

-O-(CH2)4-O-C-(CH2)2-C-

OH

O

Lignin

O

n

(a)a

O

O-C

OHLignin

OCN

CH2-n

+

N-C=O

CH2-n

H

O-Lignin

(b)Lignin

Polyester Polyurethane linkage

PMDI

Fig. 2. Schematics of reaction between lignin, PBS and PMDI. (a) Interactionbetween lignin and PBS through hydrogen bonding, (b) polyurethane linkageformation.at Flexuralstrength (MPa)

Flexuralmodulus (GPa)

Impactstrength (J/M)

HDT (C)

28 0.4 0.6 0.01 40 8.4 78 1.940 0.5 1.1 0.01 29 1.0 83 3.046 0.3 2.2 0.03 15 0.9 86 3.152 1.1 3.8 0.15 11 0.9 85 0.6

68 1.8 2.3 0.07 29 2.3 90 1.966 0.7 2.1 0.03 24 3.7 94 1.6

i (at full strain)

i (within 6 % strain)

Fig. 3. Stressstrain curve of the composites. (i) Neat PBS specimen, (ii) 30% ligninPBS composite, (iii) 50% ligninPBS composite, (iv) 65% ligninPBS composite, (v)50% ligninPBS composite with 1% PMDI, (vi) 50% ligninPBS composite with 2%PMDI.

t A 42 (2011) 17101718 1713A factor k (contribution of bre length and orientation) was used tot the data. The volume fraction of the bre and matrix was calcu-lated using the density of PBS (1.26 g/cm3) and lignin (1.34 g/cm3).Correlation between theoretical modulus and experimental modu-lus of composites is shown in Table 2. An increase in the moduluswith increasing lignin content can be observed from the Fig. 4.The theoretical modulus calculated from the rule of mixture washigher than the experimental modulus of composites. With a ttingparameter k = 0.67, the theoretical modulus exactly matches theexperimental modulus of 50% lignin lled composites. However,modulus values obtained from 30% and 65% lignin lled compositesshowed slightly lower and higher values than the respective calcu-lated modulus. Considering the random orientation of wheat strawbres, a bre efciency factor of k = 0.9 was reported by authors[27]. However, in our research, lignin pellets (having 45% nely

: Parground biobre, lignin particles and other additives [22,23]) wereused as ller instead of biobre alone, hence, a k value of 0.67 isquite reasonable. The lower modulus values for 30% lignin lledcomposites and the higher modulus values for 65% lignin lledcomposites as compared to the theoretical modulus values maybe attributed to the ligninpolymer interaction which is not takeninto account in the equation.

Fig. 4. Correlation analysis of experimental tensile modulus and rule of mixture(ROM).

Table 3Thermal properties of composites from DSC.

Types of specimen Tg (C) Tm (C)

PBS 31.1 113.230% LigninPBS 26.4 112.050% LigninPBS 20.5 112.065% LigninPBS 12.1 110.450% LigninPBS-1% PMDI 15.8 111.650% LigninPBS-2% PMDI 21.1 110.9

1714 S. Sahoo et al. / Composites3.2.2. Flexural propertiesIt can be observed from Table 2 that the exural strength and

exural modulus of composites increased gradually with increas-ing lignin content. Flexural strength and modulus increased by41 to 84% and 81 to 503% respectively with increasing lignin con-tent from 30 to 65 wt.%. It is believed that, the polar biollers aremore compatible with the polar polymers that improves the misci-bility of the two phases and promotes a good interfacial morphol-ogy. However, the difference in the trend of the tensile and exuralproperties was not clearly understood. The possible cause may bethe behaviour of the material towards the stretching and bendingforces. The addition of 1% PMDI improved exural strength by48% compared to the uncompatibilised material and by 143% com-pared to the neat polymer (Table 2). Greater stress transfer fromthe matrix to the ller through a compatibilizer modied interfaceis believed to be the cause of this signicant improvement. Theexural modulus of composites with 1% compatibilizer remainedalmost the same as that of uncompatibilised materials (Table 2).Increasing PMDI content to 2% slightly decreased the exuralstrength and modulus of the composites. This result may be attrib-uted to the resultant effect of various competing reactions such asplasticisation, urethane linkage formation, and secondary hydro-gen bonding.

3.2.3. Impact strengthImpact strength measures the ability of the material to resist

fracture under high rate stress applied at a high speed. Fibres playa key role towards the impact resistance or toughness of a material.In this research, impact strength of composites decreased drasti-cally with ller incorporation (Table 2). A similar trend wasobserved in the unnotched Izod impact strength of ligninPP com-posites [24]. It is reported that the incorporation of lignin, a brittlematerial, decreases the impact strength of composites. Incorpora-tion of agrobres also decreases impact strength of composites[27,28]. Incorporation of 1% PMDI compatibilizer to lignin compos-ites improved the impact strength by 92% as compared to theuncompatibilized counterpart. This improvement may be attrib-uted to the possible plasticisation as discussed earlier. On increas-ing the PMDI content from 1% to 2%, the impact strength ofcomposites decreased by a small extent. Decrease of impactstrength with increasing PMDI concentration was also reportedby the authors [20]. They observed a detrimental effect at 1% PMDIwhile using bamboo pulp in composites however, the same wasobserved at 2% for lignin lled composites in our study.

3.3. FTIR analysis

FTIR spectra of neat PBS, lignin, and 50% ligninPBS compositeswith and without PMDI are shown in Fig. 1. Characteristic carbonyl(C@O) stretching at 17351750 cm1, CAO stretching at 11451155 cm1, and CAH stretching at 28502950 cm1 are presentin the spectra of PBS and all its composites. Broad peaks for hydro-gen bonded AOH groups at 34003100 cm1 appear in the spectraof lignin and all the composites. Characteristic peaks of lignin havebeen discussed in the characterisation of lignin. It can be observedthat all the characteristic peaks of PBS and lignin appear in thecomposites. The peak at 1370 cm1 in lignin spectra (due to pheno-lic OH group) shifted to 1388 cm1 in the spectra of compositeswhich is possibly caused due to the interaction between OH groupsof lignin and C@O groups of PBS matrix. No characteristic peak forNCO (isocyanate) group at 2270 cm1 appears in the spectra ofcompatibilized composites which indicates a complete reactionof isocyanate in the composite system. As shown in Fig. 2, NAHand C@O bond formation are expected during the reaction. AsC@O is already present in the matrix and NAH stretching appearsat 33503180 cm1 (overlapping with hydrogen bonded OHstretching), disappearance of peak at 2270 cm1 and increasedintensity of the peak at 33503180 cm1 can be considered as aconrmation of urethane formation in the composites.

3.4. Dynamic mechanical analysis (DMA and HDT analysis)

DHm (J/g) Tc (C) DHc (J/g) v (%)

64.8 78.4 62.2 30.957.3 71.6 43.7 39.049.1 64.3 31.6 46.831.6 63.9 21.6 42.925.7 77.2 25.5 24.726.3 76.9 27.03 25.6

t A 42 (2011) 17101718Dynamic mechanical analysis (DMA) is widely used for theinvestigation of the viscoelastic behaviour and structure of com-posite materials. Damping measurement (Tand) gives informationabout the glass transition temperature (Tg) and the storage modu-lus gives information about the stiffness. The storage modulus ac-counts for the elastic component of the complex modulus ofmaterial. Storage modulus, loss modulus and tan delta of compos-ites as a function of temperature are shown in Fig. 5. Storage mod-ulus of the polymer and composites decreased with increasingtemperature (Fig. 5a). The reduction of storage modulus with tem-perature can be attributed to the softening of the polymer due tothe increase in the chain mobility of the polymer matrix at hightemperatures. As compared to neat PBS, storage modulus of the

: ParS. Sahoo et al. / Compositescomposites at room temperature (25 C) increased by 96495% at3065 wt.% lignin loading. Similar results were observed in agroour lled biodegradable composites [31]. The storage modulusof composites remained almost constant at 1% PMDI addition.However, the storage modulus decreased on increasing the PMDIcontent to 2%. This observation may be attributed to various com-petitive reactions caused by the addition of PMDI.

The loss modulus accounts for the contribution of the viscouscomponent in the complex modulus of the material. At room tem-perature, the loss modulus of composites increased with increasingller content (Fig. 5b). However, very little difference in the lossmodulus was observed near the glass transition temperature. Theglass transition temperature (Tg) obtained from the loss moduluspeak (Fig. 5b) increased with increasing lignin content. Two peaksare observed in the thermogram of 65% lignin lled composites

Fig. 5. Dynamic mechanical analysis. (a) Storage modulus, (b) loss modulus, (c) tandelta of composites. (i) neat PBS specimen, (ii) 30% ligninPBS composite, (iii) 50%ligninPBS composite, (iv) 65% ligninPBS composite, (v) 50% ligninPBS compositewith 1% PMDI, (vi) 50% ligninPBS composite with 2% PMDI.where the rst peak corresponds to the Tg of the polymeric phaseand the second possibly represents the ller (because of very highcontent of ller). Addition of compatibilizer to 50% lignin lled PBScomposites decreased the glass transition temperature slightly.

The damping behaviour of the material is measured by themagnitude of tan d since it is the ratio of loss modulus to stor-age modulus or energy dissipated to energy stored during adynamic loading cycle [16]. Tand decreased with ller incorpora-tion (Fig. 5c). The result indicates that addition of ller de-creased the molecular mobility of the composite materials andthe mechanical loss occurred to overcome the inter-friction be-tween molecular chains was also reduced. Similar observationwas reported for biobre reinforced PBS [16] and PLA [27] com-posites. Good interaction between PBS matrix and lignin can beunderstood from the increased tan d peak temperature (often re-ferred as glass transition temperature, Tg) and broadening ofTand thermograms due to lignin incorporation. Two effects aretaken into account as the cause of increase in the Tg of the com-posites. The rst one may be the creation of an amorphous com-ponent in the composite structure where both the polymer andthe ller coexisted in a closely associated state reducing free vol-ume in the composites and hence increased Tg. Another cause ofincrease in Tg may be the possibility of secondary bonds thatacted as quasi-crosslinks and restricted the Brownian motion oflong chain molecules [29]. The Tg of composites rst increasedat 1% and then decreased by about 6C at 2% PMDI addition. Thismay be attributed to be effects such as improved interaction andplasticisation due to PMDI addition. Improved interaction be-tween polymer and ller improves the Tg and plasticisation low-ers the Tg of a material.

Heat deection temperature (HDT) is a measure of the dimen-sional stability of the material under a particular load and temper-ature. It is considered as an essential property requirement for awide range of material applications. HDT values of neat PBS andall composites are shown in Table 2. HDT of composites increasedwith increasing lignin content up to 50 wt.% and remained almostunaltered with further increasing the lignin content to 65%.Improvement in the HDT values was also observed in compositesfor biobre reinforcement [32,33]. It may be attributed to the high-er crystallinity of the bio-composites [32] compared to the neatpolymers. Incorporation of compatibilizer further enhanced theHDT of composites which is believed to have occurred due to im-proved interfacial adhesion [32].

3.5. Thermal analysis

3.5.1. Differential scanning calorimetryThe effect of lignin on the crystallisation and melting behaviour

of composites was studied in non-isothermal DSC experiments (3).The degree of crystallinity was calculated using Eq. (2), given be-low [27,34]

v% DHmf DH0m

100 2

where v = degree of crystallinity (%), DHm = enthalpy of fusion ofmaterial studied, DH0m = enthalpy of fusion of 100% crystalline PBSi.e. 210 J/g [35], f = weight fraction of polymer in composite.

Glass transition temperature (Tg) increased by 519 C withincreasing lignin content in the composites (Table 3) which indi-cates good interaction between the polymer matrix and lignin. Lig-nin acts as a nucleating agent for PHB composites and facilitatescrystallisation [13]. In our current study, the degree of crystallinity

t A 42 (2011) 17101718 1715increased with ller incorporation up to 50% and slightly decreasedat 65% ller content (Table 3). It is believed that the amount of lig-nin content (amorphous in nature) might have played some role in

the nucleation activity of the polymer. The decrease in crystallinityat 65% lignin lled composites may have been due to very high l-ler content compared to the polymer matrix. Lignin had no effecton the melting behaviour of the polymer. The addition of PMDIcompatibilizer decreased the crystallinity of composites however;the effect is not consistent for varying PMDI content. Similarly,the glass transition temperature showed varying trends with theincreased PMDI content. Although, the effect of PMDI on the ther-mal properties of natural ller based composites is not very clear[21], polymer-ller interaction and plasticisation due to the PMDIaddition could be considered as the possible causes for the ob-served results in this study.

3.5.2. Thermogravimetric analysisThermal degradation onset, weight loss (%), major decomposi-

tion temperature and charred residue left after 600 C for lignin,neat polymer and all composites are shown in Table 1. Degradationonsets of lignin and PBS polymer are 179 and 306.4 C respectively.Degradation onset and maximum decomposition temperature ofcomposites decreased on increasing lignin content in the compos-ites. Composites with 50 and 65 wt.% lignin content showed veryclose degradation onset temperatures. The addition of PMDI in lig-ninPBS composites increased the degradation onset of compositesby 7 C. Weight loss around 100 C can be attributed to the loss ofmoisture from the materials and degradation at the onset temper-

1716 S. Sahoo et al. / Composites: Part A 42 (2011) 17101718Fig. 6. SEM micrograph of composites. (a and c) 50% LigninPBS composite (lower magni(lower magnication and higher magnication respectively), (e) 50% ligninPBS with 1%cation and higher magnication respectively), (b and d) 65% LigninPBS compositePMDI (lower magnication).

at 400 C compared to neat polymer and composites. The charred

[10] Alexy P, Kokov B, Crkonov G, Gregorov A, Marti P. Modication of lignin

reinforced poly (lactic acid) (PLA) composites. J Mater Sci 2008;43:52229.

: Parresidue left after 600 C was highest (31.6%) for lignin due to thepresence of high ratio of highly condensed aromatic structures.Charred residue increased with the increase in lignin content inthe composites. The addition of PMDI compatibilizer slightly in-creased the percentage of charred residues in the composites,which may be attributed to the presence of aromatic componentsof PMDI. Char yield is directly related to the ame retardant poten-tial of the material [17]. Hence, the ame retardant ability of ligninis reected from this result which is again synergized by PMDIaddition.

3.6. Density of composites

Density of lignin, 1.34 g/cm3, was obtained from the compositesby using the rule of mixtures. The density of the neat polymer andthe composites were measured by a densimeter. The compositesand neat polymer showed densities of nearly 1.3 g/cm3 and1.26 g/cm3 respectively.

3.7. Surface morphology

The SEM photographs of the composites are shown in Fig. 6.Phase separation between polymer and ller can be clearly ob-served from a polymer rich part in 50 wt.% lignin lled PBS com-posites (Fig. 6a).This might have been caused due to loweramounts of crosslinking components in the ller present in thecomposites. However, more homogeneous distribution of polymerand lignin ller can be observed in the micrograph of the 65% lig-nin lled composite (Fig. 6b). Tensile strength data for these com-posites (50 and 65% lignin lled) also supports this observation.Micrographs at higher magnication (Fig. 6c and d) clearly depictthe exact fracture surface morphology of these two composites.More pulled out bres and holes in 50% lignin lled compositesindicate poor interfacial adhesion. The possible cause for the morebres pull-out in 50% lignin lled composites may be the phaseseparation owing to lower lignin content compared to 65% ligninlled composites. More interaction in 65% lignin lled compositespossibly occurred due to higher lignin content. Pulled out brewith adhered resin matrix and a more compatibilized phase indi-cate a stronger interface in the composites having 1% PMDI(Fig. 6e). The improved interface is well reected in the mechanicalproperties of the compatibilized composites.

4. Conclusions

Lignin acted as reinforcing ller in PBS matrix that synergisti-cally improved tensile, exural, some thermal and thermo-mechanical properties of composites. Incorporation of a highweight fraction (65%) of lignin was achieved. Impact strength andthermal degradation onset of the composites gradually decreasedwith increasing lignin content. The addition of PMDI compatibiliz-er to 50 wt.% lignin lled composites improved all mechanicalature may correspond to the scission of weak ether bonds [36]present in lignin inter units (b-O-4 linkage). Maximum decomposi-tion temperature of lignin was much lower than the neat polymer.Unlike the polymer, additional peaks appeared in the derivativecurves of lignin. Second major decomposition peaks between340345 C appeared in composites having higher lignin content(50 and 65 wt.%). As discussed before, lignin decomposition occursby several competing reactions that release many gaseous compo-nents. A lowest percentage of weight loss was observed for lignin

S. Sahoo et al. / Compositesstrength of the composites at 1 wt% incorporation. Increasing PMDIcontent to 2 wt% further improved tensile strength of compositeswhile the exural and impact strength reduced very negligibly.[15] Li J, He Y, Inoue Y. Thermal and mechanical properties of biodegradable blendsof poly (L-lactic acid) and lignin. Polym Int 2003;52:94955.

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[19] Dash BN, Nakamura M, Sahoo S, Kotaki M, Nakai A, Hamada H. Mechanicalproperties of hemp reinforced poly (butylene succinate) biocomposites. JBiobased Mater Bioeng 2008;2:27381.

[20] Jiang L, Chen F, Qian J, Huang J, Wolcott M, Liu L, et al. Reinforcing andtoughening effects of bamboo pulp bre on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) bre composites. Ind Eng Chem Res 2010;49:5727.polyethylene blends with high lignin content using ethylenevinyl acetatecopolymer as modier. J Appl Polym Sci 2004;94:185560.

[11] Acha BA, Marcovich NE, Reboredo MM. Lignin in jute fabricpolypropylenecomposites. J Appl Polym Sci 2009;113:14807.

[12] Baumberger S, Lapierre C, Monties B. Utilization of pine kraft lignin in starchcomposites: impact of structural heterogeneity. J Agric Food Chem1998;46:223440.

[13] Weihua K, He Y, Asakawa N, Inoue Y. Effect of lignin particles as a nucleatingagent on crystallization of poly (3-hydroxybutyrate). J Appl Polym Sci2004;94:246674.

[14] Graupner N. Application of lignin as natural adhesion promoter in cotton bre-The effect of PMDI was not very consistent for tensile and exuralmoduli of composites however, both the moduli showed a slightreduction with increasing PMDI content from 1 to 2%. A higheramount of char content obtained from lignin indicates that it canact as a ame retardant in the composites. Degree of crystallinityof composites increased by the incorporation of lignin up to50 wt.% and slightly decreased with increasing lignin content to65%. Incorporation of PMDI to the composite blends resulted inan improvement of HDT but decreased the degree of crystallinitydrastically compared to the composite with no PMDI. A strong -brematrix interface was observed from the fractured surface mor-phology of PMDI compatibilized composites.

Acknowledgements

Authors are thankful to 2009 Ontario Ministry of Agriculture,Food and Rural Affairs (OMAFRA)/U of G project Renewable, recy-clable lightweight hybrid green composites from lignin, switch-grass, miscanthus and bioplastics and Ontario BioCarInitiative, Ontario Ministry of Research and Innovation for thenancial support to this research work.

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1718 S. Sahoo et al. / Composites: Part A 42 (2011) 17101718

Enhanced properties of lignin-based biodegradable polymer composites using injection moulding process1 Introduction2 Experimental2.1 Materials and method2.1.1 Materials2.1.2 Composites fabrication

2.2 Characterisation2.2.1 C, N, S analysis2.2.2 Mechanical testing2.2.3 Fourier transform infrared spectroscopy (FTIR)2.2.4 Differential scanning calorimeter (DSC)2.2.5 Dynamic mechanical analysis (DMA)2.2.6 Thermogravimetric analysis (TGA)2.2.7 Density measurement2.2.8 Scanning electron microscopy (SEM)

3 Results and discussion3.1 Characterisation of lignin3.2 Mechanical properties3.2.1 Tensile properties3.2.2 Flexural properties3.2.3 Impact strength

3.3 FTIR analysis3.4 Dynamic mechanical analysis (DMA and HDT analysis)3.5 Thermal analysis3.5.1 Differential scanning calorimetry3.5.2 Thermogravimetric analysis

3.6 Density of composites3.7 Surface morphology

4 ConclusionsAcknowledgementsReferences