Bioresource Technology 101 (2010) 8406–8415

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Bioresource Technology

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Effect of glycidyl methacrylate (GMA) on the thermal, mechanical andmorphological property of biodegradable PLA/PBAT blend and its nanocomposites

Mukesh Kumar a, S. Mohanty a, S.K. Nayak b,*, M. Rahail Parvaiz a

a Laboratory for Advanced Research in Polymeric Materials (LARPM), CIPET Bhubaneswar 751024, Indiab Central Institute of Plastic Engineering & Technology, Guindy, Chennai 600032, India

a r t i c l e i n f o

Article history:Received 25 August 2009Received in revised form 17 May 2010Accepted 26 May 2010Available online 22 June 2010

Keywords:Poly (lactic acid)Glycidyl methacrylateBlend nanocompositeDifferential scanning calorimetryScanning electron microscopy

0960-8524/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.biortech.2010.05.075

* Corresponding author. Tel.: +91 674 2742852; faxE-mail address: drsknayak@gmail.com (S.K. Nayak

a b s t r a c t

Poly(lactic acid) (PLA)/Polybutylene adipate co-terephthalate (PBAT) blend and its nanocomposites wereprepared using melt blending technique. Glycidyl methacrylate (GMA) has been used as a reactive com-patibilizer to improve the interface between PLA and PBAT. Mechanical studies indicated an increase inimpact strength and tensile modulus of PLA matrix with the increase in PBAT loading. PLA/PBAT blendprepared at ratio of 75:25 exhibited optimum impact strength. Further, incorporation of GMA to the tuneof 5 wt.% and nanoclay shows an increase of impact strength. Morphological interpretations through SEMreveals improved interfacial adhesion between the PLA/PBAT blend in presence of GMA and nanoclay.XRD studies indicated an increase in d-spacing in PLA/PBAT/C20A blend nanocomposite thus revealingintercalated morphology. DSC and TGA thermograms also showed improved thermal properties as com-pared with virgin PLA. DMA tests revealed an increase in damping factor, confirming strong influencebetween PLA/PBAT blend in presence of GMA and nanoclay.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction blending with various biodegradable and non-biodegradable poly-

In the recent years increased volume of domestic and industrialwaste accumulated in the landfills and sites has generated consid-erable environmental problems (Avérous, 2004; Huang, 1985;Hwang et al., 2006). Development of biodegradable polymers fromrenewable resource based feed stocks has received considerable re-search interests in the recent years with a primary aim to reducethe consumption of petroleum polymers in various applications.Biodegradable polymers can be degraded upon disposal in bioac-tive environments by organisms such as bacteria, algae, fungi,etc. or by hydrolysis in buffer solutions or sea water. Poly(lacticacid) (PLA), linear aliphatic biodegradable polyester derived frombiomass through bioconversion and polymerization has become apotential candidate for various large-scale industrial applicationsin the areas of packaging, biomedical, pharmaceutical, etc. (Andersand Mikael, 2002; Van de Velde and Kiekens, 2002; Lunt, 1998).The polymer with its inherent biodegradable characteristics is alsocompostable which allows for easier waste management with re-spect to traditional synthetic plastics. The extrusion grade of PLAhas high strength and modulus comparable to that of many petro-leum based plastics. However, inherent brittleness characteristicsof PLA and its low glass transition temperature around 60 �C hasbeen the major limitation for its use in variety of application. Sev-eral modifications such as copolymerization, plasticization and

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: +91 674 2743863.).

mers have been suggested to improve the mechanical properties ofthe virgin matrix. Blends of PLA with other biodegradable polyes-ters to prepare flexible materials with widespread applicationshave been reported widely. PLA/PBAT blends with improvedmechanical properties in particular; good level of toughness hasbeen investigated by various authors (Ray and Bousmina, 2005;Raquez et al., 2008; Shi et al., 2005; Jiang et al., 2006).

However, the latter blends constitute a two phase systemwherein the final properties primarily depends on level of compat-ibility, processing and morphological properties.

In the present investigation Poly(lactic acid) (PLA)/Polybutyleneadipate co-terephthalate (PBAT) blends at various ratios have beenprepared using melt blending technique. Reactive processing agentGMA has been introduced as a plasticizer to improve the inter-phase balance between the constituent polymers. Also organicallymodified nanoclay has been added with an aim of optimizing themechanical properties (Pluta, 2006; Chen et al., 2005; Lee et al.,2007). Various characterization studies such as WAXD, SEM, DSC/TGA and DMA has been studied. The reciprocal effects of plasticiza-tion and toughening have also been considered.

2. Experimental

2.1. Materials

PLA (Grade: 4042D) with a density of 1.24 g/cc and averagemolecular wt of 74,000 g/mol was purchased from M/s Cargil

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Dow (Bair, US-NE) and consists of 92% L-lactide, 8% d-lactide units.PBAT (Grade: Ecoflex FBX 7011) with density of 1.25 g/cc and aver-age mol. wt of 145,000 g/mol and melting point of 110–120 �C wasobtained from M/s BASF, Japan. Commercial available Cloisite 20A(C20A), organically treated montmorillonite (MMT), procured fromM/s Southern clay product, Inc. (Gonzales, Texas) has been used asnanoclay. C20A was organically modified with dimethyl dihydro-genated tallow quaternary ammonium to reduce its hydrophilicityand improve its dispersion within the blend matrix. Glycidyl meth-acrylate (GMA) with mol. wt of 142.16 g/mol was supplied by M/sHi Media Laboratories Pvt. Ltd. Prior to compounding, the nanoclayC20A was dried under vacuum at 80 �C for a 12 h to remove mois-ture and prevent agglomeration during processing. PLA pelletswere dried at 60 �C for 8 h in vacuum to release moisture as recom-mended by the supplier prior to processing while PBAT was used assuch without drying.

2.2. Melt compounding

PLA/PBAT blends at variable ratios (85:15, 80:20 and 75:25)were prepared in a batch mixer of 69 cm3 volumetric capacity(M/s Haake, Germany) at temperature range of 160–200 �C and40 rpm speed for duration of 10 min. The reactive processingagent, GMA and organoclay, C20A were added to the optimizedPLA/PBAT blend at a ratio of 75:25 to prepare plasticized blendand blend nanocomposite respectively. At this step the concentra-tion of GMA as well as C20A was varied from 3 to 5 wt.% to attainstable interfacial morphology. Subsequently, the melt mixer wasbrought to room temperature conditions and was pre-dried at60 �C for 6 h prior to specimen preparation.

2.3. Specimen preparation

Molded sheets of 3 ± 0.1 mm thickness of the virgin matrices,blend and blend nanocomposites were prepared using a compres-sion press (M/s. Delta Malkison 100T, Bombay) at a temperature of200 �C, pressure of 48 kg/cm and cycle time 10 min respectively. Fi-nally, the test specimens were prepared from sheets using counter-cut copy milling machine (M/s. Ceast, Italy) as per ASTM D standard.

3. Testing and characterization

3.1. Mechanical properties

The test specimens of virgin matrices, blends and blend nano-composites were dried in vacuum at 100 �C and kept in sealed des-iccators for 24 h prior to testing. At least three and typically fivereplicate specimens were subjected to mechanical testing and anaverage of these measurements was reported. Corresponding stan-dard deviation of experimental data has also been indicated. Ten-sile specimens of 165 � 13 � 3 mm conforming to ASTM-D-638were strained at a cross head speed of 50 mm per min and gaugelength 50 mm in a Universal testing machine, UTM (LR 100 K,Lloyds Instruments, UK). For Izod Impact test a notch angle of45� with a V notch depth of 2.54 mm was made with a notch cutteron specimens having dimension of 63.5 � 12.7 � 3 mm. Subse-quently the measurements were carried out in an Impacto meter(6545, Ceast Italy) as per ASTM-D-256.

4. Morphological properties

4.1. Scanning electron microscopy (SEM)

Fractured surface morphology was studied for selected PLA/PBAT blend nancomposites by using scanning electron microscopy,

energy dispersion X-ray analysis (SEM HITACHI 3400 N Japan). Thefractured surface was gold coated to avoid electrostatic chargingduring inspection.

4.2. Transmission electron microscopy (TEM)

TEM is performed on a TEM analyzer (Hitachi, H-7500, andJapan) operated at an accelerating voltage of 200 kV. Prior toTEM imaging, thin cross-sections of the nanocomposite must beprepared, cryotomed, and stained. Because the electron densitiesof the hard and soft ABS segments are similar, typically samplesare stained with osmium tetroxide (OsO4) in saturated solutionof uranyl acetate. After at least 24 h the sample, the chamber iskept at �170 �C using a dewar filled with liquid N2 during section-ing. The glass knife was used LEICA ultra-cut UCT-GA-D/E-100ultra-microtome. The sections are then strained with saturatedsolution of uranyl acetate, counter stained with 4% lead citrate.The samples are then ready for examination in the TEM. Afterimage exposure, the film is developed in the dark room using thespecified procedure. The dry negatives were scanned onto a com-puter and saved at their original size at the highest resolution pos-sible and then analyzed.

4.3. Wide angle X-ray diffraction (WAXD)

Wide angle X-ray diffraction (WAXD) analysis was carried outusing X-ray diffractometer (Philips X Pert MPD, Japan) which hadgraphite monochromatic and a Cu Ka radiation source operatedat 40 kV and 30 mA. The basal spacing or (d001) reflection of thesamples was calculated from Bragg’s equation by monitoring thediffraction angle 2h from 1� to 10�.

4.4. Fourier transformation infrared spectroscopy (FTIR)

FTIR spectra of PLA/PBAT blends with 5 wt.% GMA and PLA/PBAT blend nanocomposite (with 5 wt.% C20A) were recordedusing Perkin-Elmer1720X, UK spectrometer. Each spectrum wasobtained by co-adding 64 consecutive scans with a resolution of4 cm–1 within the range of 4000–500 cm�1 with a resolution of1 cm�1.

5. Thermal properties

5.1. Differential scanning calorimeter (DSC)

Samples of 5–10 mg were subjected to non-isothermal crystal-lization process using differential scanning calorimeter (DiamondDSC, M/s. Perkin Elmer, USA). Temperature calibration was per-formed using Indium as a reference (Tm = 156.60 �C and Heatflow = 28.5 J/g). During the analysis, dried nitrogen gas was purgedthrough the calorimeter at a constant flow rate of 20 ml/min. Thesamples were heated from room temperature to 600 �C at the rateof 10 �C/min and then kept at this temperature for 5 min to eraseprevious thermal history in the sample and subsequently cooledto room temperature at the rate of 20 �C/min to obtain the crystal-lization curve as a function of temperature.

5.2. Thermogravimetric analysis (TGA)

The virgin matrices, blend as well as the blend nanocompositeswere subjected to thermogravimetric analysis in using TGA (M/s.Perkin Elmer, USA) equipment. Samples of approximately 5 mgwere heated from 30to 600 �C at a heating rate of 20 �C/min innitrogen atmosphere (50 mm/min). Corresponding initial degrada-

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tion temperature, weight loss and final degradation temperatureand percentage char in the samples were recorded.

5.3. Dynamic mechanical analysis (DMA)

Specimens of virgin matrices, blends and blend nanocompositesof dimensions 35 � 12 � 3 mm were subjected to dynamicmechanical test using a dynamic mechanical analyzer (M/s. TAinstruments, USA). The measurements were carried out in bendingmode and corresponding viscoelastic properties were determinedas a function of temperature. The temperature range used in thepresent investigation was varied from �80 to 200 �C with a heatingrate of 10 �C/min under nitrogen flow. The samples were scannedat a fixed frequency of 1 Hz with a dynamic strain of 0.1%.

6. Result and discussion

6.1. Mechanical properties

The tensile and impact properties of virgin PLA and PLA/PBATblend at variable ratios are represented in Table 1. It is evident thatthe tensile strength and tensile modulus of virgin PLA decreasedwith the increase in PBAT content from 15 to 25 wt.%. This behav-iour is probably due to the presence of soft elastomeric phase thatreduced the crystallinity in the virgin matrix which is confirmedfrom DSC studies in the later sections (Jiang et al., 2006; Penget al., 2010).

PLA/PBAT blend prepared at a ratio of 75:25 exhibits a decreasein tensile strength of 62.8% and tensile modulus of 55.1% respec-tively as compared with the virgin PLA matrix. It is observed thatPLA has superior strength properties at room temperature butlacks flexibility which is apparent from distinct yielding and stableneck growth through cold drawing during fracture in a tensile test.On the contrary, PBAT shows a moderate strength and highelongation at break of 600%. Addition of flexible PBAT to PLA wassuccessful in increasing the flexibility in the blend (Mohantyet al., 2010). Moreover, the presence of PBAT within PLA reducesits brittleness characteristics which is evident from the increaseof impact strength value from 21.09 J/m in virgin PLA to 50.00 J/m in case of PLA/PBAT blend at 75:25 ratio.

However, tensile strength of PLA dropped gradually in presenceof PBAT and a minimum value of about 29.47 MPa was observed ata blend ratio of 75:25. A similar reduction in tensile modulus from1254 MPa to 808.15 MPa was also observed. This reveals incom-patibility between the constituent polymers in the blend systemwhich results in phase separation and deterioration in tensileproperties. Further, as evident from group contribution theory,the solubility parameters of PLA and PBAT have been found to be10.1 (cal/cm3)1/2 and 22.95 (cal/cm3)1/2 respectively (Siemann,1992; Schott, 1982). This indicates large difference in solubilityparameter of the individual constituents in the blend matrix andless interaction between PLA and BPAT. Hence, in order to enhance

Table 1Tensile and impact properties of virgin PLA, PBAT, PLA/PBAT blend with GMA and blend n

Compositions Tensile strength (MPa) Ten

PLA virgin 48.71 125PBAT virgin 11.03 3PLA/PBAT (85/15) 31.26 90PLA/PBAT (80/20) 32.02 90PLA/PBAT (75/25) 29.47 80PLA/PBAT/GMA (72/25/3) 22.75 131PLA/PBAT/GMA (70/25/5) 30.52 174PLA/PBAT/C20A/GMA (67/25/5/3) 19.36 184PLA/PBAT/C20A/GMA (65/25/5/5) 26.55 210

the interfacial compatibility, Glycidyl methacrylate (GMA) hasbeen used as a reactive compatibilizer because of the presence ofcarboxylic and hydroxylic groups that are hydrolysed in PLA andPBAT under heat and high shear stress during extrusion. PLA/PBATblend prepared at a ratio of 75:25 exhibited optimum impactstrength; hence this composition was retained to fabricate blendsin presence of GMA (Semba et al., 2006).

The tensile and impact properties of GMA compatibilized blendis also depicted in Table 1.

It is observed that with the incorporation of GMA, the tensilemodulus increased from 1254 MPa (PLA matrix) to 1746 MPa (incase of PLA/PBAT blend prepared using 5 wt.% GMA) which indicatesreactivity control at the interface due to the formation of randomterpolymer of ethylene acrylic ester and GMA represented inFig. 1.The impact strength of PLA in the blends also increased tothe tune of 72.45%. This is probably due to formation of ester linkageat the interface with the addition of GMA. The improvement in im-pact strength has been further corroborated using SEM microscopy.

The effect of nanoclay loading on the mechanical properties ofGMA compatibilized PLA/PBAT blend prepared at a ratio of PLA/PBAT/GMA (70:25:5) is represented in Table 1. It is observed thattensile modulus of virgin PLA increased from 1254 MPa to2106 MPa to the tune of 60% with the incorporation of 5 wt.%C20A nanoclay. This behaviour is mainly due to high stiffnessand modulus of nanoclay platelets that reinforce the blend matrix.Furthermore, in case of blend nanocomposite, the addition ofnanoclays also reduced the particle size of PBAT which leads toefficient dispersion of PBAT particles within PLA matrix therebyenhancing the tensile modulus.

Also C20A has two di tallow units which induce strong attrac-tion with the hydroxyl group (–OH) of blend consequently decreas-ing the bond mobility as well as increasing the brittlenesscharacteristic and reducing the impact strength. The modulus ofPLA/PBAT nanocomposite (with 5 wt.% of GMA) increases linearlywith the filler volume fraction where as for these nanoparticlesmuch lower filler concentrations increased the modulus sharplyand to a much larger extent. The better dispersion of silicate layersin GMA compatibilized PLA/PBAT blend may also be due to the ten-dency of the silicate layers to remain in the interface which is fur-ther discussed in the later section under TEM and XRD (Haradaet al., 2007). Cloisite 20A clay increases the crystallization rate ofthe blend and finally the modulus of blend nanocomposite in-creased and impact strength decreased from 76.5 J/m (GMA com-patibilized blend) to 46.9 J/m in case of blend nanocompositeapproximately to the tune of 30% (Jiang et al., 2006).

6.2. Morphological analysis

6.2.1. Scanning electron microscopy (SEM)SEM micrographs of the impact fractured surface of the blend

matrix with and without GMA and blend nanocomposite aredisplayed in Fig. 2a–c As observed from Fig. 2a, the white round

anocomposites.

sile modulus (MPa) Impact strength (J/m) Elongation (%)

4 21.09 4.59.06 54.28 521.60.2 25.72 5.13.5 43.35 5.78.15 50.44 6.754.23 63.85 6.66.4 76.56 6.51.40 41.58 2.86.66 46.90 2.4

Fig. 1. Predicted reaction between PLA, PBAT and GMA.

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particles indicates the PBAT phases distributed within the PLA ma-trix. The micrographs of impact fractured surface of the blend ma-trix shows ductile fracture which is evident from presence of moreand longer fibrils pulled out during test. Crazing, cavitations, shearbending, crack bridging and shear yielding have been identified asimportant energy dissipation processes involved in the impactfracture of toughened polymer systems. In present investigation,the blends are prepared in the form of sheets, as a result the cavi-tations caused by debonding can be clearly identified. The largevoids as evident in the micrographs might be formed by the coales-cence of neighboring small cavities (Kim and Michler, 1998a).

Further, virgin PLA, which did not show necking phenomenon inthe tensile test, exhibited a longitudinal fracture surface withoutvisible plastic deformation. The SEM micrographs of PLA/PBATblend at 25 wt.% PBAT loading depicted a toughening mechanism.The micrographs have been taken at different locations of thenecked down regions with variable stress at various magnifications(Kim and Michler, 1998b; Wu et al., 1994; Kim et al., 1996). Deb-onding of the round PBAT particles from the PLA matrix under ten-sile stress was clearly observed in Fig. 2a wherein oval cavities andPBAT particles are visible. These cavities were formed during ten-sion when the stress was higher than the bonding strength at theinterface between the PLA matrix and PBAT inclusions remainundeformed during the course of tensile deformation. This furtherconfirms two phase morphology with incompatibility between theconstituent polymers in the blend. The white lines observed in thefigure were formed by the coalescence of neighboring cavities(Kunz-Douglass et al., 1980; Pearson and Yee, 1991).

Since PBAT has different elastic properties compared with PLAmatrix, its particles act as stress concentrators under tensile stress.The stress concentration gives rise to high triaxial stress in the par-ticles in rubber toughened polymeric materials, there exist twotypes of cavitations either formation of holes within the cores of

rubber particles when there is a strong interfacial bonding be-tween the components and relatively weak strength of rubberphase itself or at interface when the interfacial bonding strengthis lower than PBAT strength (Kambour and Russell, 1971; Wu,1985).

From the SEM micrographs, it is observed that there werepresence of voids and interfacial debonding occurs under triaxialstress perspective of presence of GMA. The voids caused by deb-onding altered the stress state in PLA matrix surrounding thevoids and triaxial tension was locally released and shear yieldingwas allowed (Bucknall et al., 1973). The SEM micrographs of thefractured surface of PLA/PBAT (75/25 wt.%) blend with 3 wt.% and5 wt.% GMA is shown in Fig. 2b and Fig. 2c respectively. In pres-ence of GMA, the blends of PLA and PBAT showed better miscibil-ity and more shear yielding when it was fractured under shockloading (Yee et al., 1993; Wu et al., 1994; Meccereyes et al.,1999).

6.2.2. Transmission electron microscopy (TEM)The dispersion characteristics of organically modified clay

(C20A) within the PLA/PBAT matrix are represented in Fig. 3(a),which reveal intercalated clay galleries as well as stacks of agglom-erated clay galleries were noticed within the PLA/PBAT blendmatrix.

In case of PLA/PBAT/GMA blend nanocomposite, smalleramount of stack platelets appear in broad and obscure regions,since the layer silicates are composed of heavier elements like alu-minium, silicon, magnesium than surrounding matrix, they appeardarker in bright field images. Regions of intercalated clay galleriesalong with exfoliated stacks were also evidenced in the TEM micro-graphs of PLA/PBAT/GMA blend nanocomposite, (Fig. 3(b)) whichfurther confirmed improved interface due to formation of chemicalbonds.

Fig. 2a. SEM micrographs of PLA/PBAT at different magnifications (a) 1.5 kX, (b) 1.0 kX and (c) 0.5 kX.

Fig. 2b. SEM micrographs of PLA/PBAT/3%GMA at different magnifications (a) 1.5 kX, (b) 1.0 kX and (c) 0.5 kX.

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Fig. 2c. SEM micrographs of PLA/PBAT/5%GMA at different magnifications (a) 1.5 kX, (b) 1.0 kX and (c) 0.5 kX.

Fig. 3. TEM micrographs of (a) PLA/PBAT/C20A and (b) PLA/PBAT/GMA/C20A.

M. Kumar et al. / Bioresource Technology 101 (2010) 8406–8415 8411

6.2.3. Wide angle X-ray diffraction (WAXD)The wide angle X-ray diffractogram of organically modified

nanoclay C20A and PLA/PBAT nanocomposite is shown in Fig. 4.It is evident that (Fig. 3(a), C20A exhibits a diffraction peak corre-sponding to 2h = 3.6� with a d-spacing (d001) of 24.2 nm. TheWAXD pattern of PLA/PBAT blend with 5 wt.% C20A nanoclay(75:25:5) reveals a diffraction peak at 2h = 2.475� correspondingto a d-spacing of 3.58 nm. This indicates that during melt interca-lation PLA/PBAT blend chain segments entered into the clay galler-ies forcing the clay platelets apart which results an increase ind-spacing of C20A nanoclay and shift in the diffraction peak from3.6� to 2.475�. Further incorporation of GMA to the tune of 3 to5 wt.% does not result any appreciable increase in d-spacing ofthe blend nanocomposite. The diffractogram of the GMA compati-bilized blend nanocomposite revealed a 2h peak around 2.42� witha d-spacing of 3.6 nm, this confirming intercalated structure (Chowet al., 2004; Pouton and Akhtar, 1996).

6.2.4. Fourier transformation infrared spectroscopy (FTIR)The FTIR spectra of PLA/PBAT blend (with 5 wt.% GMA) and

blend nanocomposite (with 5 wt.% C20A) is depicted in Fig. 5. Itis evident that the peaks around 1017 cm�1 and 1180 cm�1 repre-sent the carbonyl (C–O) stretching in hydroxyl group andcarboxylic group respectively due to reaction with glycidyl meth-acrylate (GMA). The stretching in carbonyl group (>C@O) in esterlinkage represents a strong peak (sharp peak) around 1712 cm�1

and 1745 cm�1 in FTIR spectra representing aliphatic carbon chainat 727 cm�1 . The bending peak of substituted benzene were lo-cated at 871 cm�1 in both PLA/PBAT blend and blend nanocompos-ites . In the case of the PLA/PBAT blend nanocomposite the sharppeak at 1580 cm�1(in bending mode) representing amine groupof organomodified clay (C20A) which is absent in the case ofPLA/PBAT blend (with 5 wt.% GMA). The spectral band correspond-ing 2920 cm�1 represents the stretching peak in –OH group of car-boxylic acid due to hydrolysis and dehydration during processing

Fig. 4. X-ray differaction pattern of (a) PLA/PBAT/5 wt% Cfig20A/ 5 wt% GMA, (b)PLA/PBAT/5 wt.% C20A/3 wt.% GMA, (c) PLA/PBAT/5 wt.% C20A and (d) C20A.

Fig. 5. FTIR spectra of (a) PLA/PBAT/5 wt.% GMA and (b) PLA/PBAT/5 wt.% GMA/5 wt%C20A.

Fig. 6. DSC thermograms of (a) Virgin PLA, (b) PLA/PBAT, (c) PLA/PBAT/5 wt.%GMA,(d) PLA/PBAT 5 wt.% GMA/5 wt.%C20A and (e) Virgin PBAT.

Table 2Melting and crystallization behaviour of virgin PLA, PBAT PLA/PBAT blend and PLA/PBAT blend nanocomposites.

Compositions Tg

(�C)Tm (�C) Tc

(�C)DHc

(J/m)DHm

(J/m)PBAT PLA

Virgin PLA 66.0 – 151.0 128 9.12 0.7193Virgin PBAT �39.69 119.0 – 66.1 �3.90 12.47PLA/PBAT (75:25) 61.0 117.9 155.3 136.0 �4.01 1.08PLA/PBAT/GMA

(70:25:5)56.0 117.3 150.3 134.5 �3.43 2.27

PLA/PBAT/GMA/C20A(65:25:5:5)

55.9 119.3 150.0 122.7 �5.21 12.39

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of PLA/PBAT blend. Similar stretching peaks corresponding to car-boxylic group were also observed in PLA/PBAT blend and blendnanocomposite (Sarasua et al., 1998).

6.3. Thermal property

6.3.1. Differential scanning calorimetry (DSC)The DSC heating and cooling curves of the virgin matrices, blend

and blend nanocomposite are enumerated in Fig. 6. The secondheating scan of PLA sample processed at 200 �C showed a glasstransition temperature centered at 66 �C, an exothermic crystalli-zation peak at 228 �C and an endothermic melting peak at 151 �Crespectively. Similarly PBAT showed a glass transition centered at�39 �C and a broad endothermic melting peak centered at 119 �C[41]. However in case of PLA/PBAT blend , the melting transitioncorresponding to PLA at 155.3 �C and PBAT at 117.9 �C wasdetected which indicates formation of a two phase system due to

incompatibility between the constituent polymers. Further incor-poration of GMA to the tune of 5 wt.% does not show any apprecia-ble change in melting transition of PBAT in the blend. On the otherhand, the Tm of PLA in the blend decreased from 155.3 �C to150.3 �C which is probably due to formation of a genuine interface.Comparing the DSC therograms of PLA with respect to PLA/PBATblend, it is observed that the crystallization temperature changesfrom 128 �C (for PLA) to 136.8 �C (PLA/PBAT blend). The presenceof 5 wt.% GMA within PLA/PBAT blend decreased the degree ofcrystallinity which results in inward shifting of melting peaks ofthe polymer constituent. This indicates improved compatibility ofPLA/PBAT blend with the addition of 5 wt.% GMA. The cooling ther-mograms of various samples are also displayed in the figure. The Tg

of the blend matrix also decreased from 61 �C to 56 �C in presenceof 5 wt.% GMA which is probably because GMA acts as a reactiveprocessing agent and contributes to an increase in polymer chainmobility. The low enthalpy of crystallization (DHc) and enthalpyof melting (DHm) also indicate low degree of crystallization asshown in Table 2. These results confirm that the interfacial adhe-sion between PLA and PBAT was enhanced by reaction betweenGMA and polymers (Witt et al., 2001).

In case of the blend nanocomposite presence of nanoclay sepa-rates the melting peak of PLA into two individual peaks. The peaksat higher temperature of 153.1 �C corresponds to the shoulder ofneat PLA where as that at 150 �C suggests the presence of a newcrystalline structure induced by PBAT as well as clay and GMA. This

Fig. 7a. TGA of (a) Virgin PBAT (b) PLA (c) PLA/PBAT (d) PLA/PBAT 5 wt.% GMA (e) PLA/PBAT 5 wt.% GMA/5 wt.% C20A.

M. Kumar et al. / Bioresource Technology 101 (2010) 8406–8415 8413

bimodal melting peak also shows that the less perfect crystals hadsufficient time to melt and reorganize into crystals with higherstructural perfection and remelt at higher temperature. Thus addi-tion of nanoclay results in heterogeneous nucleation effect. Fur-ther, in case of the blend nanocomposites the crystallizationtemperature attained a minimum value of 122.7 �C which is pri-marily due to segmental immobilization of PLA chains due to theaddition of 5 wt.% of C20A where in the nanoclay act as a nucleat-ing agent.

Fig. 7b. DTG of (a) Virgin PBAT (b) PLA (c) PLA/PBAT (d) PLA/PBAT 5 wt.% GMA (e)PLA/PBAT 5 wt.% GMA/5 wt.% C20A.

6.3.2. Thermogravimetric analysis (TGA)The TGA thermograms of virgin PLA, PBAT, PLA/PBAT blend and

the blend nanocomposite are represented in Figs. 7a and 7b. It isevident that the thermal degradation of virgin PLA and PBATstarted at 293.96 �C and 314.53 �C, respectively, and the final deg-radation temperature was noticed at 462.62 �C and 530 �C asshown in Table 3. In both the virgin polymers a single step decom-position process was observed. As evident from the derivative ther-mo gram (DTG), it is clear that PLA/PBAT blend exhibits two stepdegradation with a first maximum decomposition peak of PLA at395 �C and second maximum decomposition peak of PBAT at435 �C. The final decomposition temperature (Tf) in the blend ma-trix was observed around 472.9 �C with a weight of loss about95.73%. The percentage char in the blend was about 2.63% at600 �C which is approximetely10 �C higher than virgin PLA matrix(462.62 �C, wt loss about 97.8% and percentage char of 1.183).

Similarly PLA/PBAT blend in presence of GMA also exhibited atwo step decomposition process. Both the peaks come closer toeach other compared with PLA/PBAT blend indicating improved

Table 3Degradation temperature and % char of PLA, PBAT, PLA/PBAT blends andnanocomposite.

Samples Ti

(�C)T0.1

(�C)T0.5

(�C)Tf

(�C)%Char

PolymerdegradationDY (%)

PLA virgin 293.96 252.57 390.04 462.62 1.183 97.88PBAT virgin 341.53 412.07 442.56 556.13 4.318 93.86PLA/PBAT

(75:25)304.97 361.05 397.49 472.9 2.633 95.73

PLA/PBAT/GMA(70:25:5)

211.16 355.65 397.63 481.48 2.593 94.408

PLA/PBAT/GMA/C20A(65:25:5:5)

194.57 363.76 401.08 465.61 4.803 91.166

8414 M. Kumar et al. / Bioresource Technology 101 (2010) 8406–8415

compatibility between PLA and PBAT. This was probably due todehydration from hydroxyl group of PLA and carboxylic group ofPBAT units and thermal cleavage of ester linkage by hydrolysisand scission of C–O and C–C bonds.

The final decomposition of PLA/PBAT/GMA blend (70:25:5) is481.8 �C which is about 10 �C higher than PLA/PBAT blend. Theweight loss at this temperature was about 94.40% with a char res-idue of carbonaceous products to the tune of 2.59% was left. How-ever, with the incorporation of nanoclay (C20A) within GMAcompatibilized blend, single step degradation was noticed with afinal decomposition peak at 465 �C and a charred residue of4.80% was obtained. Comparing the weight loss in blend nanocom-posite and the blend matrix in presence of GMA, it is observed thatthe weight loss at final decomposition temperature is higher forthe sample (PLA/PBAT/GMA) than that of blend nancomposites.Further the peak corresponding to PBAT matrix exhibits broaden-ing in the transition region. This indicates improved compatibilitybetween PLA and PBAT blend in presence of C20A nanoclay andGMA. Moreover, the blend nancomposites samples displayed high-er char residue as compared with PLA as well as the blend matrixwhich reveals improved flame retardancy in presence of C20Ananoclay (CNR-INFM PolyLab, 2010).

6.3.3. Dynamic mechanical analysis (DMA)The variation of tand as a function of temperature is illustrated

in Fig. 8. The damping peak of virgin PLA, PBAT, PLA/PBAT blendand its blend nanocomposite showed a decreased magnitude oftand in comparison to virgin PLA. This behaviour is mainly due torubbery phase of PBAT which is well dispersed in PLA matrix andacts as a stress concentrator. Virgin PLA and PBAT represented aglass transition peak around 67 �C and �20 �C respectively. In caseof the blend, the Tg of PBAT decreased from �20 �C to �29.9 �Cwithout significant change in the Tg of PLA matrix phase. This con-firms poor interfacial balance between PLA and PBAT and forma-tion of two phase morphology. Further incorporation of 5 wt.%GMA within PLA/PBAT blend there was an additional shift in Tg

of both PLA and PBAT to 64.15 �C and �28.26 �C as compared withthe blend matrix (67.78 �C and �29.9 �C). This indicates improved

Fig. 8. Damping factor of (a) Virgin PLA (b) Virgin PBAT (c) PLA/PBAT (d) PLA/PBAT5 wt.% GMA (e) PLA/PBAT 5 wt.% GMA/5 wt.% C20A.

interfacial adhesion between PLA and PBAT. In case of the blendnanocomposite, presence of nanoclay C20A, reduces the Tg of PLAand PBAT to 60.06 �C and �25.28 �C. This shows compatibility ofC20A within PLA/PBAT blend which is primarily attributed to de-crease in domain size of polymer matrix due to intercalation of ma-trix chains within the clay galleries. The magnitude of tand in theblend decreased with the incorporation of nanoclay, at the glasstransition was also lower as compared with virgin PLA. This maybe attributed to increase the crystallinity of the blend nanocom-posite (Ray and Okamoto, 2003; Ray et al., 2003).

7. Conclusion

PLA /PBAT blend and its nanocomposite were prepared usingmelt blending technique using batch mixer. The effect of GMAand nanoclay (C20A) on mechanical, thermal and morphologicalbehaviour of blend and blend nanocomposite has been investi-gated. Based on experimental finding following observation werederived:

1. Mechanical studies indicated that incorporation of 3–5 wt.%GMA increases the impact strength of PLA/PBAT blend to thetune of 26.5% and 51.7% while retaining the tensile strength.Incorporation of nanoclay additionally increased tensile modu-lus from 1841.40 MPa to 2106.66 MPa.

2. Morphological investigations through TEM revealed presence ofintercalated as well as exfoliated clay layers in the blend matrixin presence of GMA. SEM studies also confirmed efficient dis-persion of PBAT within PLA matrix with the incorporation ofGMA.

3. The diffractogram of GMA compatibilized blend nanocompositerevealed a 2h peak around 2.420� with a d-spacing of 36 nm,these confirming intercalated structure.

4. DSC thermograms indicated two phase system with the pres-ence of two melting peaks. Addition of GMA was found toenhance the interfacial adhesion between the individual poly-mers with the shift of melting peaks closer to each other.

5. TGA thermograms confirmed two step degradation behavioursin the blend. However incorporation of nanoclay resulted in sin-gle step degradation with a higher thermal stability in the blendnanocomposite.

6. DMA results also confirmed existence of two Tgs of constituentpolymers which revealed biphase morphology. Hence biode-gradable blends of PLA/PBAT and its nanocomposite can be pre-pared with improved properties at optimum blend ratio andclay concentration.

Acknowledgements

The authors would like to gratefully acknowledge the sponsor-ship from Dept. of Science and Technology (DST-SERC) and Dept. ofBiotechnology (DBT), Govt. of India.

References

Anders, S., Mikael, S., 2002. Properties of lactic acid based polymers and theircorrelation with composition. Prog. Polym. Sci. 27, 1123–1163.

Avérous, Luc., 2004. Biodegradable multiphase systems based on plasticized starch:a review. J. Macromol. Sci. Part C: Polym. Rev. C44, 231–274.

Bucknall, C.B., Clayton, D., Keast, W.E., 1973. Rubber-toughening of plastics. J. Mater.Sci. 8, 514–524.

Chen, G., Choi, J., Yoon, 2005. The role of functional group on the exfoliation of clayin poly(L-lactide). J. Macromol. Rap. Comm. 26, 183–201.

Chow, W., MohdIshak, Z.A., Ishiaku, U.S., KargerKocsis, J., Apostolov, A.A., 2004. Theeffect of organoclay on the mechanical properties and morphology of injection-molded polyamide 6/polypropylene nanocomposites. J. Appl. Polym. Sci. 91,175–182.

M. Kumar et al. / Bioresource Technology 101 (2010) 8406–8415 8415

CNR-INFM PolyLab, 2010. Via Risorgimento 35, I-56126 Pisa, Italy.Harada, M., Ohya, T., Iida, K., 2007. Increased impact strength of biodegradable

poly(lactic acid)/poly(butylene succinate) blend composites by usingisocyanate as a reactive processing agent. J. Appl. Polym. Sci. 106, 1813–1820.

Huang, S.J., 1985. Encycl. Polym. Sci. Eng., Biodegradable Polymers, vol. 7. WileyInterscience, New York.

Hwang, K.J., Park, J.W., Kim, Il., Ha, C.S., Kim, G.H., 2006. Effect of a compatibilizer onthe microstructure and properties of partially biodegradable LDPE/aliphaticpolyester/organoclay nanocomposites. Macromol. Res. 14 (2), 179–186.

Jiang, L., Wolcott, M.P., Zhang, 2006. Study of biodegradable polylactide/poly(butylene adipate-co-terephthalate) blends. Biomacromol. 7 (1), 199–207.

Kambour, R.P., Russell, R.R., 1971. Electron microscopy of crazes in polystyrene andrubber modified polystyrene: use of iodine–sulphur eutectic as a crazereinforcing impregnant. Polym. 12, 237-246.

Kim, G.M., Michler, G.H., 1998a. Micromechanical deformation processes intoughened and particle filled semicrystalline polymers: part 2. Modelrepresentation for micromechanical deformation processes. Polym. 39 (23),5699–5703.

Kim, G.M., Michler, G.H., 1998b. Micromechanical deformation processes intoughened and particle-filled semicrystalline polymers: part 1.Characterization of deformation processes in dependence on phasemorphology. Polym. 39 (23), 5689–5697.

Kim, G.M., Michler, G.H., Gahleitner, M., Fiebig, J., 1996. Relationship betweenmorphology and micromechanical toughening mechanisms in modifiedpolypropylenes. J. Appl. Polym. Sci. 60, 1391–1403.

Kunz-Douglass, S., Beaumont, P.W.R., Ashby, M.F.A., 1980. Model for the toughnessof epoxy-rubber particulate composites. J. Mater. Sci. 15, 1109–1116.

Lee, S., Lee, Y., Lee, J., 2007. Effect of ultrasound on the properties of biodegradablepolymer blends of poly(lactic acid) with poly(butylene adipate-co-terephthalate). Macromol. Res. 15, 44–50.

Lunt, J., 1998. Large-scale production, properties and commercial applications ofpolylactic acid polymers. Polym. Degrad. Stab. 59, 145–152.

Mohanty A.K., Parulekar, Y., Chhidambarakuemar, M., Kositruangchai, N., Harte, B.R.,2010. Biodegardable polymeric nanocomposites particularly for packaging. USPatent no 20100076009.

Meccereyes, R., Jerome, P., Dubois, P., 1999. Novel macromolecular architecturesbased on aliphatic polyesters: relevance of the ‘‘Coordination-Insertion’’ ring-opening polymerization. Adv. Polym. Sci. 147, 1–59.

Pearson, R.A., Yee, A.F., 1991. Influence of particle size and particle size distributionon toughening mechanisms in rubber-modified epoxies. J. Mater. Sci 26, 3828–3844.

Peng, Z.H., Lice, W., We, Q., Ren, J., 2010. Preparation, mechenical and thermalproperties of biodegradable polyesters/poly (lactic acid) blends. J.Nanomaterilas, 2010–2019.

Pluta, M., 2006. Melt compounding of polylactide/organoclay: structure andproperties of nanocomposites. J. Polym. Sci.: Part B, Polym. Phy. 44, 3392–3405.

Pouton, C.W., Akhtar, S., 1996. Biosynthetic polyhydroxyalkanoates and theirpotential in drug delivery. Adv. Drug. Deliv. Rev. 18, 133–162.

Raquez, M., Nabar, Y., Narayan, R., Dubois, P., 2008. Novel high-performance talc/poly[(butylene adipate)-co-terephthalate] hybrid materials. Macromolec. Mat.Eng. 293, 447–470.

Ray, S.S., Bousmina, M., 2005. Biodegradable polymers and their layered silicatenanocomposites: in greening the 21st century materials world. Prog. Mat. Sci.50, 962–1079.

Ray, S.S., Okamoto, M., 2003. Polymer/layered silicate nanocomposites: a reviewfrom preparation to processing. Prog. Polym. Sci. 28, 1539–1641.

Ray, S.S., Okamoto, K., Okamoto, M., 2003. Structure�property relationship inbiodegradable poly(butylene succinate)/layered silicate nanocomposites.Macromol. 36, 2355–2367.

Sarasua, J.R., Prud’homme, R.E., Wisniewski, M., Borgne, A.L., Spassky, N., 1998.Crystallization and melting behavior of polylactides. Macromol. 31, 3895–3905.

Schott, H., 1982. Solubility parameter, specific molar cohesion, and the solubility ofethylene oxide in polymers. Biomaterials 3, 195–209.

Semba, T., Kitagawa, K., Ishiaku, U.S., 2006. The effect of crosslinking on themechanical properties of polylactic acid/polycaprolactone blends. J. Appl.Polym. Sci. 101, 1816–1825.

Shi, X.Q., Ito, H., Kikutan, T., 2005. Characterization on mixed-crystal structure andproperties of poly(butylene adipate-co-terephthalate) biodegradable fibers.Polym. 46, 11442–11450.

Siemann, U., 1992. The solubility parameter of poly (lactic acid). Eur. Polym. J. 28(3), 293–297.

Van de Velde, K., Kiekens, P., 2002. Biopolymers: overview of several properties andconsequences on their applications. Polym. Test. 21, 433–442.

Witt, U., Einig, T., Yamamoto, M., 2001. Biodegradation of aliphatic–aromaticcopolyesters: evaluation of the final biodegradability and ecotoxicologicalimpact of degradation intermediates. Chemosph. 44, 289–294.

Wu, S., 1985. Dielectric and mechanical–dynamical studies on poly(cyclohexylmethacrylate). Polym. 26, 1849–1854.

Wu, J.S., Yee, A.F., Mai, Y.W., 1994. Fracture toughness and fracture mechanisms ofpolybutylene-terephthalate/polycarbonate/impact-modifier blends. J. Mater.Sci 29, 4510–4522.

Wu, J.S., Yee, A.F., Mai, Y.W., 1994. Fracture toughness and fracture mechanisms ofpolybutylene-terephthalate/polycarbonate/impact-modifier blends. J. Mater.Sci. 29, 4510–4522.

Yee, A.F., Li, D., Li, X.J., 1993. The importance of constraint relief caused by rubbercavitation in the toughening of epoxy. J. Mater. Sci. 28, 6392–6398.