Full Paper

Full Paper

Thermo-mechanical characterization ofbioblends from polylactide and poly(butyleneadipate-co-terephthalate) and lignin

Mohamed A. Abdelwahaby, Sarah Taylor, Manjusri Misra,Amar K. Mohanty*

This paper investigates the effect of the incorpora
tion of organosolv lignin and a chainextender on the compatibility between polylactide and poly(butylene adipate-co-tereph-thalate). Bioblends were processed using melt extrusion and injection molding techniques. Areaction was observed during the melt processing as the force increased as the amount of ADRin the formulation increased. This reaction was investigated by Fourier transform infrared spectroscopy. The morphological images showed agood dispersion and an absence of phase separationby the inclusion of the chain extender. Theincorporation of the chain extender enhanced thetensile properties and modulus characterization ofthe bioblends. Dynamic mechanical analysis andrheological characterization revealed that the addi-tion of chain extender increased the storagemodulus of the bioblends. Differential scanningcalorimetry analysis showed a good miscibilitybetween PLA and PBAT in the presence of OL and thechain extender, while thermogravimetric analysisshowed enhancement in the thermal stability byinclusion of the chain extender.
Dr. M. A. Abdelwahaby, S. Taylor, Dr. M. Misra, Dr. A. K. MohantyDepartment of Plant Agriculture, Bioproducts Discovery andDevelopment Centre, University of Guelph, Guelph, Ontario N1G2W1, CanadaS. Taylor, Dr. M. Misra, Dr. A. K. MohantySchool of Engineering, Thornborough Building, University ofGuelph, Guelph, Ontario N1G 2W1, CanadaE-mail: [email protected]

yOn leave from Department of Chemistry, Tanta University, Tanta31527, Egypt

� 2015 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimMacromol. Mater. Eng. 2015, 300, 299–311

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1. Introduction

As the world moves toward the production of sustainable

environmentally friendly plastics (bioplastics), the produc-

tion of biodegradable polymers has become an area of

significant scientific interest.[1] The bioplastic market is

estimated to increase from approximately 1.4 million tons

in 2012 to around 6.2 million tons in 2017.[2] These

bioplastics are being used for a variety of different

applications, including the automotive, agricultural,

pharmaceutical and packaging industries.[3] Biodegrad-

able polymers, such as poly(lactic acid) (PLA) and poly-

(butylene adipate-co-terephthalate) (PBAT), have proven

to be effective in solvingmany of the problems associated

with current commercial plastics, including greenhouse

gas emissions, and end of life issues.[4,5] Research on

novel combinations of biodegradable polymers with

DOI: 10.1002/mame.201400241 299

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M. A. Abdelwahab, S. Taylor, M. Misra. A. K. Mohanty

300

comparatively inexpensive natural fillers, such as com-

monly found plant biomass, agricultural residues, and

industrial co-products, has expanded greatly over the past

few decades.[6–9]

Lignin, being the second most abundant natural

polymeric material on earth and a major by-product of

the paper and cellulosic ethanol industries, has received

particular attention due to its amorphous polyphenolic

properties and large number of chemical functional-

ities.[10,11] Theseproperties give lignin theability to interact

with the polymer blends and give lignin great potential as

a natural filler.[11] Kraft lignin has some disadvantages,

wherein it contains residues of sulfur compounds from

sodium sulfide as it is produced from the pulping and

cooking processes in the paper industry.[11,12] However,

organosolv lignin (OL) uses an organic solvent (e.g.,

methanol, ethanol, acetone, and glycol) as a de-lignifying

agent, therefore produces a higher quality of lignin. The

betterqualityof lignin isdeemedbybeingsulfur free,witha

greater number of carbonyl and phenol hydroxyl groups,

increasing the solubilizing properties, having a lower glass

transition temperature (Tg), making it easier to process, a

lower ash content which is easier to burn, and a lower

molecular weight which increases its reactivity with other

polymers.[13–15] Kubo and Kadla [16] reported a blend of

poly(ethylene oxide) with OL which showed good thermal

and mechanical properties, resulting from the unique

chemical structure of lignin. Teramoto et al.[17] reported a

blend of poly(e-caprolactone) with alkylated OL which

exhibited a miscible blend when the length of the alkyl

chains attached to OL increased.

PLA is a hard, stiff, crystalline polyesterwith good tensile

properties but relatively low impact properties.[18] Many

studieshavebeenexamined for increasing the toughnessof

PLA by thermal treatment (annealing),[19,20] chain orienta-

tion by creating dimensional alignment within the

matrix,[21] adding plasticizers,[22] and incorporating a soft

componentbyblendingwithotherpolymers.[22,23] Polymer

blends have been an attractive method in the industry to

combine the properties of multiple polymers and create a

newmaterial with desirable performance.[24] Furthermore,

polymer blends have the opportunity to improve the

mechanical and the thermal properties of the target

polymers. Several flexible biodegradable polymers have

been used to toughen PLA, including poly(e-caprolactone)

(PCL), [25–27]] poly(butylene succinate) (PBS), [28] poly-

(butylene succinate-co-adipate) (PBSA), [29] and PBAT.[30–

32] This paper examines the use of PBAT blended with PLA

due to its high impact strength and low stiffness, resulting

in a blend with a balance of stiffness and toughness.[30]

The incorporation of lignin within the polymer matrix

(PLA–PBAT) would further increase the bio-content of the

bioplastic-blends and can help in reducing themarket price

of the final product. As of present, there are few reports on

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lignin-based bioplastic-blends. Li et al.[33] reported on PLA-

lignin blendswith various lignin loadings. They found that

with the addition of 20wt% lignin, the maximum strength

and elongation of the blend decreases, while the tensile

modulus remains constant (with little to no thermal

degradation). Sahoo et al.[34] reported the mechanical and

thermal properties of polybutylene succinate (PBS) with

50wt% lignin blends. They found that the addition of 1%

polymeric methylene diphenyl diisocyanate (PMDI), the

mechanical strength increased compared to non-compati-

bilized blend. Li et al.[33] and Ouyang et al.[35] blended PLA

with various lignin loadings. Li et al.[33] found that the

tensile strength andmodulus aswell as elongation at break

decreased by 70%, 33%, and 56%, respectively, with the

incorporation of 40% lignin. However, Ouyang et al.[35]

found that the tensile and impact strength as well as

elongation at break decreased by 37%, 18%, and 55%,

respectively, while the tensile modulus increased by 16%

with the incorporation of 40% lignin. In general, these

studies indicate that the incorporation of lignin to

biodegradable polymers led to a decrease in themechanical

strength of the final product. To enhance the compatibility

and the interfacial adhesion between the polymers, an

epoxy functionalized chain extender Joncryl ADR (ADR)

may be useful for reactive extrusion of (PLA–PBAT)/OL

bioblends. The chain extender (ADR) contains an epoxy

group,whichhas theability to reactwith thecarboxylic and

hydroxyl groups present in the polymer components and

consequently enhances the compatibility between the

polymers.[36,37]

To our knowledge, there are few studies on the blending

of lignin with the biodegradable PLA–PBAT blends.[38,39]

This study aims to report on the effect of 20wt% OL and 1–

2wt% ADR on the various properties, including thermal,

mechanical, rheological, and morphological properties of

the PLA–PBAT bioblends at a fixed ratio of 70/30.

2. Experimental

2.1. Materials

PolylactidePLApolymer6302D (PLA)purchased fromNatureWorks

LLC produced in Minnetonka, Minnesota, USA. PLA has a specific

gravity of 1.24; crystalline melt temperature of 125–135 8C, a glasstransition temperature (Tg) of 55–60 8C, a relative viscosity of 3.0

and melt flow rate of 20 g/10min at 210 8C as reported in the data

sheet. PBATwithgradenameBiocosafe 2003 F, is a product of Xinfu

Pharmaceutical Co., Ltd., China. PBAT has a specific gravity of 1.26,

and melt flow rate of �20g/10min as reported in the data sheet.

PBAT showed a Tg of�35 8C andmelting temperature of 116 8C. OLwas generously provided by Lignol Innovations Ltd., Burnaby,

British Columbia, Canada. The characteristic of OL, as reported in

the data sheet, were as follows: the molecular weight Mw and Mn

around 1551 and 734, respectively, specific gravity of 1.29, and the

glass transition temperature was 98.6 8C. The particle size of OL

015, 300, 299–311

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Thermo-Mechanical of Bioblends . . .

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was controlled using sieve shaker by sieving with different sieved

arranged from largest to the smallest (1mm,425, 300, 212, 150, and

75mm). OL has a particle size less than 75mm. A styrene-acrylic

multifunctionalepoxideoligomeric agent, JoncrylADR-4368(ADR),

was provided by BASF in the flake form and used as chain

extender. As shown in the data sheet, ADR has amolecular weight

of 6800g/mol, an epoxy equivalent weight of 285 g/mol and

glass transition temperature of 54 8C.

2.2. Blend Preparation

Before processing, all of the materials were dried in convection

ovens for 24h to remove excess water, which may have been

adsorbed on the surface. PLA was dried at 50 8C, PBAT was dried at

80 8C, and lignin was dried at 85 8C. Bioblends were prepared

throughmelt mixing and injectionmolding techniques performed

using a DSMXplore 15mLMicro-Compounder and 12mL Injection

Moulding Machine, from DSM Research, the Netherlands. Process-

ing parameters were 160 8C barrel temperature, 100 rpm twin

screw rotation, 2min compounding time, and 30 8C mold temper-

aturewith filling and packing pressures of 6 bars, held for 6 and 8 s,

respectively. Bioblends were prepared by adding 20wt% OL and

1–2wt% ADR to the PLA–PBAT blends with ratio 70–30wt%.

5000

4000

3000

2000

Forc

e (N

)

200150100500Time (Sec)

a)

c)

b)

d)

a) PLA70-PBAT30; b) (PLA70-PBAT30)-20%OL; c) (PLA70-PBAT30) -20%OL/1%ADR; d) (PLA70-PBAT30)-20%OL/2%ADR

Figure 1. The axial forces generated during processing of PLA–PBAT with and without OL and ADR bioblends.

2.3. Characterization of the Blend

Morphology of the impact-fractured surfaces of the bioblends was

observed through a Hitachi S-570 SEM, from Tokyo, Japan at an

accelerating voltage of 20 kV. The samples were sputtered with

gold to 21nm thickness using an Emitech K-550 sputter coater,

from Ashford, Kent, UK.

Atomic forcemicroscope (AFM) experiments were performed at

room temperature using a Veeco Atomic Force Microscope (Bruker

Corporation, Santa Barbara, CA, USA) operating in tapping mode

andpeakforce tappingwithamplitudecontrolat0.996Hz.Thedata

were analyzed using the NanoScope software version 1.40. The tip

is located at the free end of a cantilever that is usually 100–500mm

long. The specimen was cut at room temperature using Ultra-

microtome (Leica Microsystems, Inc.).

Fourier transform infrared spectroscopy (FTIR) spectra of the

bioblendwere obtained using a Thermo Scientific Nicolet TM 6700

FTIR spectrometer in attenuated total reflection infrared (ATR-IR)

mode with a resolution of 4–cm�1 and 64 scans per sample.

Tensile andflexural propertiesweremeasuredusing the Instron

Instrument Model 3382 Universal testing machine according to

ASTM D638 and D790, respectively, using Blue Hill software for

system control and data analysis. Notched Izod Impact strength

wasmeasuredusingaTMIMonitor impact tester (modelno. 43–02)

according to ASTM D256 with a 5 ft-lb pendulum. Flexural tests

were performed at a gauge length of 52mmand a crosshead speed

of 14mm/min. The samples were conditioned for 48h at room

temperature before mechanical measurements. Five samples for

each mechanical test were prepared, and their average value and

standard deviation are reported.

Differential scanning calorimetery (DSC) studies of the bio-

blendswere performed using a TA Instrument DSC Q200. The tests

were performed by heating the specimen (5–8mg) from �50 to

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205 8C under a heat/cool/heat cycle at a heating and cooling rate of

10 8C/min under a nitrogen flow rate of 50mL/min�1. The first

coolingcycleandsecondheatingcyclewereconsideredforanalysis.

The data were analyzed using TA Instrument’s Universal Analysis

software.

Thermogravimetric analysis (TGA) was performed under a

nitrogen atmosphere using a thermogravimetric analyzer (TGA

Q500, TA Instruments, Inc.). The samples were heated from room

temperature to 610 8C at a heating rate of 10 8C/min�1 and a

nitrogen gas flow rate of 60mL/min�1. The derivatives of TGA

curves (DTG) were obtained using TA analysis software.

DMA was performed using a DMA Q800 from TA Instruments.

A dual cantilever clamp was used at a frequency of 1Hz and

oscillating amplitude of 15mm. The samples were heated from

�70 to 110 8C at a heating rate of 3 8C/min.

The rheological characterizationwas achieved on anAnton Paar

MCR302 rheometer (Anton Paar GmbH, Graz, Austria) with a

parallel plate setup with a plate diameter of 25mm and the

measurements distance of 1mm. The dynamic strain sweep

analyses were determined for all of the samples to determine the

linear viscoelastic limits, which were conducted at a strain of 1%

for oscillation measurements. The frequency sweep was in the

range 0.1–100 rad/s at 160 8C.

3. Results and Discussion

3.1. DSM Processing Curves

The effects of the incorporation of lignin andADR to PLA70-

PBAT30 were studied using the axial force obtained from

themicro compounder curvewith respect to time (Figure1).

This force is used to verify the reaction or the degradation

of the bioblends during mixing.[40] The curves show the

feeding of the PLA70–PBAT30, with andwithout lignin and

ADR. The initial force peak in the curve was due to the

feeding of the polymers. However, the force decreased

at the end of each cycle when the molten sample was

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bH & Co. KGaA, Weinheim 301

Tran

smitt

ance

(%)

2000 1800 1600 1400 1200 1000 800 600Wavenumber (cm-1

)

a)

b)

d)

c)

a) PLA70-PBAT30, b) (PLA70-PBAT30)-20%OL, c) ADR, d) (PLA70-PBAT30)/20%OL/2%ADR

840 cm-1

910 cm-1

1255 cm-11713 cm-1

1750 cm-1

Figure 2. FTIR of the ADR, and PLA–PBAT with and without OL andADR bioblends.

R2

R3

R1 R4

O

R6

O

R5

O

O

O

x y z

R1-R5= H, CH3, higher alkyl groupR6 = alkyl groupx, y and z = 1-20

= CH CH2

O

R``

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collected from the die opening. As com-

pared with the (PLA70/PBAT30)-20%OL

blend, the processing force increased

with the addition of ADR. This is due to

the addition of ADR increasing the

viscosity of the blend, which suggests

crosslinking between OL and the poly-

meric matrix. The bioblend with 2wt%

ADR showed higher forces than the

bioblend with 1wt% ADR which indi-

cated more crosslinking and a stronger

reaction between the polymeric matrix

and ADR. The reaction between ADR and

the bioblend is discussed in the later

sections of this paper.

R` OH + CH CH2

O

R``

R` O CH CH2

R``

OH

R` COOH + CH CH2

O

R``

O CH CH2

R``

OHCR`

O

Reaction of epoxy group of ADR with the terminal group of 1) hydroxyl group of OL2) hydroxyl group of PLA and PBAT3) carboxylic group of PLA

ADR

Figure 3. ADR structure and schematic reaction between the functional group presentin PLA, PBAT, and OL with ADR during reactive extrusion.

3.2. FTIR Analysis

In order to study the effect of OL and ADR

on the interaction between PLA and

PBAT, neat polymer and bioblends were

also included in the FTIR investigations.

Figure2 shows theFTIRspectraof theADR

and PLA70–PBAT30 with and without

lignin and ADR. PLA70–PBAT30 showed

a peak around 1713 and 1750 cm�1

corresponding to the CO bonds for PBAT

and PLA, respectively. The intensity of

the carbonyl group of the PLA–PBAT

decreased after blending with lignin.

A peak was observed at 1595 cm�1

corresponding to the aromatic skeletal

vibration of lignin, which shifted to a

higher wavenumber of 1610 cm�1 in



the ternary blend. This may be attributed to the

formation of a hydrogen and covalent bond between

PLA and PBAT with the functional groups of lignin.[41,42]

Compared with the ADR spectra, it can be seen that the

(PLA70–PBAT30)/20%OL with 2%ADR bioblend showed

no peaks at 840, 910, and 1255 cm�1 corresponding to

the C–O stretching of epoxy group present in the ADR.

Similar results were also observed in the PLA–PBAT

bioblend with glycidyl methacrylate (GMA).[43] This

means that most of the epoxy groups in ADR had been

reacted with the hydroxyl and carboxyl groups present in

the polyester matrix and OL.

Based on these results, the reaction between ADR and

(PLA–PBAT)-OL can be formulated as shown in Figure 3.

Esterification and etherification can occur between poly-

ester hydroxyl and carboxyl functional groups with the

epoxy group present in the ADR, forming covalent bonds.

Moreover, the presence of hydroxyl groups in the structure

of OL may also react with the epoxy group in ADR and

form a covalent bond. The resultant bioblend represents a

015, 300, 299–311



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complex structure due to chain extension, branching and

crosslinking reactions.

3.3. Surface Morphology

The SEM images of the impact surfaces of the neat

polymer and binary bioblends are shown in Figure 4. It

is evident that the incorporation of lignin to the neat

polymer increased the heterogeneity of the blend

resulting in a variety of particle sizes (Figure 4a–d). This

heterogeneity causes greater areas of weakness within

the blend, thereby reducing its toughness and strength.

Ouyang et al.[35] examined the effect of cellulolytic

enzyme lignin (CEL) on the morphology of neat PLA.

They found that the CEL uniformly dispersed and

embedded in the PLA matrix, which suggested good

miscibility and strong interfacial adhesion between PLA

and CEL. PBAT-20%OL (Figure 4d) shows a slightly greater

variety of particle sizes with some larger OL particles,

which may be lignin agglomerates.

Binary blends of PLA70–PBAT30 exhibited an irregular-

layer break structure (Figure 5a). The high-resolution

imageofFigure5bshowsanelongatedPBATfiber separated

from PLA phase. These results agree with previous studies

of PLA–PBAT blends,[31,44,45] which reported black cavities

and non-uniformly distributed PBAT phases suggesting

Figure 4. Scanning electron microscope images (1000�) comparing20%OL. (b) neat PBAT. (c) and PBAT-20%OL (d).



that PBAT and PLA are not miscible. With the addition of

OL (Figure 5c), distinct phases are still visible with

distinguishable lignin particles. Figure 5d, the high

resolution SEM image, shows how the addition of lignin

helped to bridge the PBAT phase with PLA, with some

black cavities from the lignin particles. Ouyang et al.[35]

reported that CEL dispersed well in a PLA matrix with

good adhesion between the filler and the PLA matrix.

Lin et al.[31] reported that the incorporation of tetrabutyl

titanate decreased the interface between the PLA–PBAT

blends. However, the incorporation of 2wt% compatibil-

izer to the bioblend (Figure 5e) shows a smoother break

than the other bioblends, with no evidence of pull-out

or separated particles. The closer image of Figure 2f

also shows less distinct phase separation and the

interface between the polymers is difficult to differ-

entiate within the (PLA70–PBAT30)/20%OL with addition

2%ADR blend.

AFM analysis was also performed to further characterize

the dispersion effects of lignin and the chain extender on

the PLA–PBAT bioblends. Figure 6 shows the peak force

tappingmode of PLA70–PBAT30 and (PLA70–PBAT30)/20%

OL with and without ADR at different magnifications. The

PLA70–PBAT30 image has an array of laterally lamellar

structures of PBAT stretched in the PLA matrix (Figure 6a).

Ravati andFavis[46] reported thephasemodeofAFMinPBS–

neat PLA (a) PLA-

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PLAl–PCL ternaryblend. They found three

different morphologies wherein the PLA

droplets self-assemble at the border of

PCL/PBS phases. Teramoto et al.[17]

reported the phase images of a blend of

PCLwith OLwhich also exhibited a phase

separation. However, blends of modified

lignin (using butyric and valeric anhy-

drides) with PCL exhibited a miscible

blend and an absence of phase separa-

tion.[17] In our study, two different colors

appear in the AFM images (Figure 6b)

corresponding to the phase separation

between PLA and PBAT. PBAT domains

arecharacterizedbyadarkarea,while the

PLA domains are characterized by a

bright area. The peak force tappingmode

AFM has the ability to calculate

the elastic modulus of each phase.[47]

Theelasticmoduluscurves showthatPLA

has a modulus of approximately 4.3 GPa

and PBAThasmodulus of less than 1GPa,

as shown in Figure 6b. The values of

the moduli are much different than the

values determined by tensile testing

because AFMwas calibrated for a harder

PLA than that which was used in our

bioblends, which led to a large error and

eim 303

Figure 5. Scanning electron microscope images (1000�) with different resolutioncomparing (a, b) (PLA70–PBAT30) bioblends. (c, d) (PLA70–PBAT30)/20%OL. (e, f)(PLA70–PBAT30)/20%OL/2%ADR bioblends.

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304

lower elastic moduli. Imre et al.[47] reported the same

modulus error with PLA-b-polyurethane block copolymer.

The inclusion of lignin in the PLA–PBAT matrix showed

heterogeneity where it was difficult to distinguish the

lignin particles (Figure 6c–d). The elastic modulus of the

interface betweenPLA and PBATwas between5and10GPa

(Figure 6e). The incorporation of 2wt% ADR shows a good

dispersionandanabsenceofphaseseparationbetweenPLA

and PBAT where it is difficult to observe the PLA phase

(Figure 6f–g). The elastic modulus of the bioblend has a

continuous modulus between 0.5 and 2.5 GPa as shown in

Figure 3h. Therefore, we can conclude that the incorpo-

Macromol. Mater. Eng. 2015, 300, 299–311

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rationofADRenhances the compatibility

between the PLA–PBAT and OL.

3.4. Mechanical Properties

The mechanical characterizations of

the bioblends are shown in Table 1.

Neat PLA has high tensile and flexural

properties with low elongation at break

and impact strength, while PBAT has

high elongation at break and impact

strength with low flexural and tensile

properties. Evidently, the flexural and

tensile strengths of the binary blends

decreased with the addition of OL

(Table 1). However, the tensile and

flexural moduli of PLA-20%OL increased.

Binary blends of PBAT-20%OL showed

more consistent properties (within a

standard deviation). These results may

indicate that the presence of lignin

caused particles to agglomerate at the

interface with the neat polymer, which

decreased the tensile properties. Ternary

blends displayed a decrease in the

mechanical properties with the incorpo-

ration of 20wt% OL (Table 1). These

results agree with previous studies of

PLA-lignin blends, which showed a

reduction in the tensile strength with

the increase of lignin loading.[33,35] The

authors of earlier studies explained

that the decrease in the mechanical

properties was due to the existence of

lignin particles which prevented the

formation of a long range continuous

phase of PLA.[33] However, the incorpo-

rationofADRshowedanenhancement in

the tensile and flexural properties. For

example, the tensile strength of (PLA70–

PBAT30)/20%OL increased from 37.9 to

42MPawith incorporation of 2wt%ADR.

Moreover, the tensile modulus of the same bioblend

increased from 1910 to 2480MPa by the incorporation of

the sameamount of theADR. These results indicate that the

ADRenhanced the compatibility between thepolymers. Al-

Itry et al.[37] reported the enhancement of the tensile

modulus of PLA80/PBAT20 by the incorporation of 0.5wt%

of ADR. The author explained that the enhancement in the

mechanical properties was due to the formation of ester

linkages between the epoxy functional groups of ADR and

the functional groups (–OH and –COOH) present in the PLA

and PBAT polymers. In our study, by FTIR analysis, we

confirmed the possibility of a reaction occurring between

im www.MaterialsViews.com

Figure 6. AFM phase images of (a) surface DMT elastic modulus and (b) the scan size of elasticmodulus of PLA70–PBAT30. (c) and (d) surfaceDMT elastic modulus of (PLA70–PBAT30)/20%OL at low and highmagnification, respectively. (e) the scan size of elastic modulus of (PLA70–PBAT30)/20%OL. (f) and (g) surface DMT elastic modulus of (PLA70–PBAT30)/20%OL/2%ADR at low and high magnification, respectively.h) the scan size of elastic modulus of (PLA70–PBAT30)/20%OL/2%ADR.


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the functional groups of the polyesters, hydroxyl groups

of the lignin and epoxy groups of the ADR, which can

enhance the interfacial adhesion between the polymers,

thusenhance themechanicalproperties.As theSEMimages

show the addition of ADR increases the dispersion of

lignin within the polymers, thus it can be speculated that

Table 1. Mechanical properties of PLA, PBAT, and PLA–PBAT bioblend

Code Tensile

strength

(MPa)

Flexural

strength

(MPa)

PLA 58.3� 0.8 109� 2.8

PLA/20%OL 40.4� 2.2 90.4� 2.6

PBAT 20.2� 1.9 4.8� 0.1

PBAT/20%OL 16.5� 1.1 4.02� 0.3

PLA70kPBAT30 45� 1.5 64.6� 1.6

(PLA70–PBAT30)/20%OL 37.9� 0.9 62� 1.6

(PLA70–PBAT30)/20%OL/1%ADR 40� 1.1 61.7� 0.5

(PLA70–PBAT30)/20%OL/2%ADR 41� 2 64.7� 2

a)NB mean non-break samples.



ADR acts as a compatibilizer between PLA and PBAT in the

presence of 20wt% OL.

The notched impact strength and percent elongation at

break of the neat polymers and bioblends are shown in

Table 1. PLA is a hard polymer with an elongation at break

of 4.6%, while PBAT is a particularly tough polymer, with

s.

Tensile

modulus

(MPa)

Flexural

modulus

(MPa)

Elongation at

break (%)

Notched

Izod impact

(J/m)

2950� 27 3476� 130 4.6� 1 25� 6.3

3010� 76 3666� 301 8.3� 2 17� 2.8

59.1� 5.5 188� 82 698� 121 NBa)

63.1� 4.2 133.2� 17 527� 5 NB

2450� 48 2257� 38 32� 19 43� 8

1910� 38 2209� 74 20� 1.6 36� 0.9

2480� 68 2144� 19 16.8� 0.2 37� 1.8

2350� 75 2102� 67 18� 4.6 37� 4

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Hea

t flo

w (W

/g)

160140120100806040200-20-40Temperature (oC)

PBAT

PBAT-20%OL

PLA

PLA-20%OL

PLA70-PBAT30-20%OL/1%ADR

PLA70-PBAT30

PLA70-PBAT30-20%OL

PLA70-PBAT30-20%OL/2%ADR

-34.6

-22.15

Figure 7. DSC analysis of the neat polymers and bioblends: 2ndheating cycle.

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306

an elongation at break of 698%. The addition of 2wt% OL

showed enhancement of the elongation at break of 79%

compared to neat PLA, while the bioblend with PBAT

showed a slightly decreased elongation at break (by 24%)

compared to neat PBAT. PBAT’s high impact strength is

caused by the chains re-organization through stress

induced crystallization.[30] The addition of lignin restricts

the ability of the polymer chains to slide, and reduces the

chain entanglement and slippage, thereby reducing the

impact strength and elongation at break.[30] These results

confirm that the incorporation of OL is more compatible

with PLA than PBAT. In contrast, the inclusion of 20wt%

OL to PBAT shows non-break samples similar to neat

PBAT, while PLA/20% OL shows the deterioration of

impact strength (by 30%) compared to neat PLA. In

general, the stress transferred from the neat polymer to

Table 2. DSC of the 2nd heating of PLA, PBAT and PLA–PBAT bioblen

Code Tg PLA (8C)

PLA 59.02

PLA/20%OL 56.98

PBAT –

PBAT/20%OL –

PLA70kPBAT30 58.77

(PLA70–PBAT30)/20%OL 56.72

(PLA70–PBAT30)/20%OL/1%ADR 57.09

(PLA70–PBAT30)/20%OL/2%ADR 57.20

a)Tg, Tm are glass transition and melting temperature, respectively.



the filler under the specific mechanism. This mechanism

is affected by two factors; the first factor is the

compatibility between the matrix (PLA or PBAT) and

the lignin filler (polarity effect); the second factor is the

presence of some lignin agglomeration, leading to a

decrease in the impact strength. The incorporation of OL

to the PLA70–BAT30 bioblend decreases the percent

elongation and impact strength; however, the incorpo-

ration of 1wt% ADR to the (PLA70kPBAT30)/20%OL

bioblend slightly enhances the impact strength of the

bioblends. Petinakis et al.[48] observed that the enhance-

ment of the interfacial adhesion between the filler and

the matrix does not result in the enhancement of impact

strength. In general, increasing the amount of ADR from 1

to 2wt% has no significant change in the mechanical

properties, which suggests that the addition of 1wt% ADR

is enough to enhance the mechanical properties. The

elongation at break of (PLA70–PBAT30)/20%OL showed

deterioration around 37% compared to the binary blend.

Due to lignin’s inherent brittleness, it has been reported

that its incorporation into polymers consistently reduces

the elongation at break.[49–51] Moreover, the incorpora-

tion of ADR showed a decrease in the elongation at break

of the bioblend. This may be due to the increase in the

density of the crosslinked chains resulting from the

reaction between epoxy groups of ADR and the functional

groups of the polymers.

3.5. Thermal Properties

DSC scans were performed to measure the glass transition

temperature (Tg) and melting temperature (Tm) of the

bioblends. This helped in determining themiscibility of the

blends. The second heating cycle is shown in Figure 7.

Table2summarizes the thermalpropertiesof thebioblends.

The DSC scans showed that the PLA blends did not exhibit a

melting temperature, only a glass transition (Tg at 59 8C).However, neat PBAT showed a Tg of�35 8C and Tm of 116 8Cbecause it is a random copolymer and is difficult to

ds.a)

Tg PBAT (8C) Tm PBAT (8C)

–

– –

�34.6 117.1

�22.15 112.19

Not detected Not detected




015, 300, 299–311


3500

3000

2500

2000

1500

1000

500

0

Sto

rage

Mod

ulus

(MP

a)

100806040200-20-40Temperature (oC)

ab

c

efg

d

a: PLA; b: PLA-20%OL; c: PBAT; d:PBAT-20%OL; e: PLA70-PBAT30; f: (PLA70-PBAT30)-20%OL;g: (PLA70-PBAT30)-20%OL/1%ADR

Figure 8. Storage modulus analysis of the neat polymer andbioblends.

2.5

2.0

1.5

1.0Tan

Del

ta

-18

a

b

c

ef

g

d

70


www.mme-journal.de

crystallize.[30,32] The Tg of PLA in the PLA70–PBAT30 blends

stayed at approximately 58.8 8C with minimal change

indicating that there is no interaction between the two

polymers. Jiang et al.[30] found that the PLA–PBAT blend is

an immiscible two phase system from DSC and DMA

analysis. In contrast, with the addition of OL to the PLA70–

PBAT30 blends, the Tg of PLA slightly decreased to a lower

temperature of 56.7 8C. These results agree with previous

studies of PLA-lignin blends.[52] The authors explained that

the decrease in the Tgwas due to the formation of hydrogen

bonding between the hydroxyl phenolic groups of lignin

with the carbonyl groups of PLA. However, the Tg of PBAT

blends in the PLA70–PBAT30 were not detected in the

absence or presence of lignin. Thus, the incorporation of

lignin into immiscible polyester blends may enhance the

compatibility between the polyester polymers.[52] The

addition of ADR to the bioblends slightly increased the Tgof the PLAblends. As previously explained theADR acts as a

chain extender and decreases the polymer chain mobility

while increasing the molecular weight by branching or

crosslinking. Zhang et al.[53] found that the Tg of the PLA

phase and the PBAT phase increased in the presence of the

terpolymer of ethylene, acrylic ester and GMA (T-GMA)

which indicate a hampered activity of polymer chains. The

author concludes that there is an enhancement in the

interfacial adhesion between PLA and PBAT by inclusion of

T-GMA. Thus, it can be speculated that the interfacial

adhesion between the polyesters andOL is enhancedby the

addition of ADR.
0.5
0.0

100806040200-20-40Temperature (oC)

a: PLA; b: PLA-20%OL; c: PBAT; d:PBAT-20%OL; e: PLA70-PBAT30; f: (PLA70-PBAT30)-20%OL;g: (PLA70-PBAT30)-20%OL/1%ADR

Figure 9. Tan d analysis of the neat polymer and bioblends.

3.6. Dynamic Mechanical Properties

The viscoelastic behavior of the neat polymer and the

blends was examined using dynamic mechanical analysis

(DMA). DMA is an effective way to evaluate the adhesion

between the matrix and the filler.[42] The storage modulus

andTandof theneatpolymerandbioblendswith ligninasa

function of temperature are represented in Figures 8 and 9.

Neat PLA has a high storage modulus value around

2800MPa compared to flexible PBAT which has a value

of approximately 1300MPa at�45 8C. The storagemodulus

of neat PLA starts to decrease at approximately 60 8C,which

corresponds to the Tg of the polymer as confirmed by DSC

(Tg¼ 59 8C). While the storagemodulus of neat PBAT starts

to decrease at approximately�30 8Cwhich also close to the

Tg of the polymer (Tg from DSC¼�35 8C). This is due to

softening of the polymer with increasing temperature. The

PLA70–PBAT30 bioblend displayed the same trends as neat

PLA and PBAT, as opposed to the incorporation of lignin

to neat polymers or their binary blends, which resulted in

an increase in the storage modulus at low temperatures

and a decrease at high temperatures. Sahoo et al.[54]

observed similar results wherein the incorporation of

lignin increased the storage modulus of the materials. The



storage modulus of the bioblends increased with the

addition of 1wt% ADR. The storage modulus increased

from 2600MPa for (PLA70–PBAT)/20%OL to 3500MPa

by incorporation of 1wt% ADR. Sis et al.[8] observed

that the incorporation of 10wt% kenaf fiber by 2wt%

of (3-aminopropyl) trimethoxysilane also increased the

storage modulus of the PLA–PBAT blends. The authors

explained that the improvement in the storage modulus

was due to an enhancement of the interfacial adhesion

betweenPLA–PBATandkenaffiber.Another study reported

that the addition of 3wt%maleic anhydride grafted PLA to

PLA/cassava root flour, increasing the storagemodulus due

to the enhancement of the compatibility and interfacial

interaction between the filler andneat PLA.[55] In our study,

the increase in the storagemodulus can be attributed to the

2015, 300, 299–311


Figure 10. Parameter of interaction, A, with temperatures forselected bioblends.

www.mme-journal.de


308

enhancement of the interfacial adhesion between the

polyester matrix and lignin. This result agrees with the

mechanical and thermal analysis results.

The effect of lignin on the Tan d of the bioblends is shown

in Figure 9. Two Tan dwere observed for PBAT (broad peak)

and PLA (sharp peak) at�18 and 70 8C, respectively. Both Tgof PLA70–PBAT30blends stayed at approximately the same

value as the neat polymers, indicating that there is no

interaction between the PLA and PBAT polymers. However,

with the incorporation of lignin, the Tg of both polymers

was changed significantly. The addition of 20wt% OL

increased the Tg of PBAT from�18 to�3 8C, while the Tg of

PLA decreased from 70 to 65.5 8C. A similar trend was also

detected in the lignin filled PBS composites.[51] The authors

indicated that the change in the Tan d indicated an

interaction between the filler and thematrix. However, the

Tg of PBAT was not observed in the bioblend after the

addition of lignin, similar to the DSC results. Moreover,

the ADR-compatibilized bioblends had lower Tg values for

PLA than that of the neat polymer. Thus, the Tg of PLA in the

bioblend shifted toward the Tg of PBAT after the addition of

lignin andADR.Another study reported that the addition of

5wt%GMAenhanced the interfacial adhesionbetweenPLA

and PBAT.[43] To study the effect of the addition of ADR to

the blend, we have calculated the adhesion parameter, A,

from the following equation.[56]

A ¼ 1

1þ wv

� �� Tandb

Tandm

� �� 1 ð1Þ

101

102

103

104

105

106

Sto

rage

mod

ulus

(Pa)

i)

iii)ii)

iv)

Where Tan db and Tan dm are the Tan d of bioblend and

polymermatrix, respectively, andfv is the volume fraction

of lignin. The interaction between the matrix and the filler

at the interface will affect the mobility of the polymer

chain. Thus, a strong interaction between the matrix and

the filler would decrease the Tan d value and the A value.

The variation of the A factor as a function of temperature

is represented in Figure 10. The incorporation of ADR

decreased the A values at lower and higher temperatures.

However, by increasing the amount of ADR to 2wt%

slightly smaller A values were shown at higher temper-

atures. These results suggest that there is miscibility

between lignin and the neat polymers by the addition of

ADR,which lead tobetter compatibilitybetweenthematrix

and the filler.

10-1

100

0.1 1 10 100Angular Frequency (ω)

v)

i) PLA; ii) PLA70-PBAT30, iii) (PLA70-PBAT30)/20%OL; iv) (PLA70-PBAT30)/20%OL/2%ADR; v) PBAT

Figure 11. Storage modulus versus sweep frequency of the neatpolymer and bioblends.

3.7. Rheological Characterization

Figure 11 shows the plots of the logarithm of the storage

modulus versus the logarithm of the sweep frequency for

neat PLA, PBAT, and the bioblends. Neat PLA and PBAT

showed viscoelastic behavior. Figure 11 shows the effect of

the inclusion of lignin and ADR on the dynamic storage

modulusofPLA70–PBAT30at lowerandhigher frequencies.



At lower frequencies, the inclusion of 30wt% PBAT

decreased the storage modulus of neat PLA which was

established by Gu’s group when they characterized the

rheological properties of PLA–PBAT blends.[57] Li et al.[45]

explained that by increasing theamount of PBAT from20 to

50wt%, the storage modulus decreased at low frequencies.

The inclusion of OL showed no change in the storage

modulusofPLA70–PBAT30at lowerandhigher frequencies.

However, the incorporation of ADR increased the storage

modulus at lower and higher frequencies. These results

agree with the thermal and mechanical characterization.

Zhang et al.[53] showed an enhancement in the storage

modulus at lower and higher frequencies by the addition

of the reactive agent GMA. Another study reported that

the addition of ADR increased the storage modulus of

015, 300, 299–311


100

80

60

40

20

Wei

ght (

%)

ii)

i)

v)

iv)

iii)

a)

i) Neat PLAii) Neat PBATiii) PLA70-PBAT30 iv) (PLA70-PBAT30)/20%OLv) (PLA70-PBAT30)/ 20%OL/2%ADR


www.mme-journal.de

PLA–PBAT blends.[37] The author explained the enhance-

mentwasdue to the addition of long chain branches,which

improved the melt stability of the bioblend. Moreover, the

reaction between the functional groups present in the

polyester and OL with the epoxy groups of ADR increased

the interfacial adhesion, which led to an enhancement in

the storage modulus.

The logarithm of the dynamic complex viscosity versus

the logarithm of the sweep frequency for neat polymer and

PLA–PBAT blends are shown in Figure 12. Neat PLA showed

a Newtonian behavior at lower frequencies (0.1–4 rad/s). A

similar behavior was observed in previous work.[57] More-

over, neat PBAT showed stronger shear-thinning tendency

at lower frequencies (0.1–7 rad/s). Accordingly, the incor-

poration of PBAT to neat PLA decreased the complex

viscosity of the bioblend at lower frequencies. Li et al.[45]

observed that a higher percentage of PBAT (>20wt%) was

associated with bigger PBAT particle size, such that the

blend became immiscible; thereby showing the decrease in

viscosity with increasing PBAT. The incorporation of lignin

decreased the complex viscosity of the neat polymer. This

indicated an interaction between the polymer matrix and

lignin, enhancing the dispersion of lignin in thematrix. The

addition of lignin to the PLA–PBAT blend decreases the

complex viscosity at higher frequencies. However, at low

frequencies, the inclusionof lignin resulted inan increase in

the complex viscosity. This behavior agrees with previous

studies of other fillers, which indicated the miscibility

between the polymer and the filler.[58,59] Moreover, the

inclusion of lignin in the PLA–PBAT bioblends altered their

behavior at lower frequencies from Newtonian to non-

Newtonian blends, similar to the behavior observed for the

storage modulus. The incorporation of ADR increased the

complex viscosity at lower and higher frequencies. This

102

103

104

105

Com

plex

Vis

cosi

ty ( η

*)

0.1 1 10 100Angular Frequency (ω)

i)

v)

iv)

iii)ii)

i) PLA; ii) PLA70-PBAT30, iii) (PLA70-PBAT30)/20%OL; iv) (PLA70-PBAT30)/20%OL/2%ADR; v) PBAT

Figure 12. Complex viscosity versus sweep frequency of the neatpolymers and bioblends.



indicated a chemical reaction between the polymer matrix

and lignin with ADR during reactive extrusion that

enhanced the dispersion of OL in the matrix and increased

the viscosity.[37] The ADR also enhanced the interfacial

adhesionbetween thepolymer and thefiller, increasing the

elastic and viscous properties of the blends.

3.8. Thermogravimetric Analysis

The effect of OL and ADR on the thermal degradation of the

PLA–PBAT polymer matrix was investigated using TGA.

Figure 13 shows the TGAandderivative TGA (DTG) traces of

the bioblends related to the percentage of weight loss

during heating. The decomposition temperatures at 5% (Td)

and the maximum rate of weight loss (Tmax) are shown in

Table 3. Neat PLA polymer degrades from 250 to 320 8C,whereas neat PBAT polymer degrades from 330 to 410 8C.Thus, PBAT is more thermally stable than PLA due to the

presence of aromatic rings in the structure of PBAT.

However, PLA–PBAT curves displayed two degradation

600500400300200100Temperature (oC)

5

4

3

2

1

0

Der

iv. w

eigh

t (%

/o C)

600500400300200100Temperature (oC)

PLA

PBAT

PLA70-PBAT30

(PLA70-PBAT30)/20%OL

PLA70-PBAT30)/20%OL/2%ADR b)

Figure 13. (a) TGA and (b) DTG of the neat polymers andbioblends.

2015, 300, 299–311


Table 3. TGA of PLA, PBAT and PLA–PBAT bioblends.a)

Code Td(8C)

Tmaximum

(8C)

PLA 274 320

PBAT 354 392

PLA70/PBAT30 262 295, 386

(PLA70–PBAT30)/20%OL 266 289, 380

(PLA70–PBAT30)/20%OL/2%ADR 284 343, 382

a)Td, Tmaximum are the decomposition temperatures at 5% and the

maximum rate of weight loss, respectively.

www.mme-journal.de


310

steps. The first and the second decomposition stages are

linked to the degradation of PLA and PBAT, respectively.

Incorporation of OL slightly enhanced the thermal stability

of the bioblends. The Td of (PLA70–PBAT30)/20%OL

increased from 260 to 266 8C by the inclusion of OL. This

is due to the highly condensed aromatic structures present

in OL with complex degradation behavior constituting

several processes. Moreover, the unpaired electrons which

are present in the hydroxyl groups of lignin come into

resonance and increase the stability of the aromatic

rings, hence the increase of the thermal stability of

the bioblend.[60] Interestingly, the incorporation of ADR

enhanced the thermal stability of the bioblend. The Tdincreased 18 8C by the inclusion of 2wt% ADR to the

bioblends. A recent study showed that the inclusion of

ADR to poly(3-hydroxybutyrate) improved the thermal

stabilityof theblendsby increasing theactivationenergyof

the thermal decomposition. The author explained that the

enhancement in the thermal stability was due to the

increase in the molecular weight and chain rigidity.[36] A

recent study showed that the degradation temperature

shifted to a higher temperature with the inclusion of ADR

on PLA/Polyamide 6 blends.[61] The author attributed this

effect to thereactionbetweentheepoxygroupsofADRwith

the hydroxyl or carboxyl group present in the polyester,

which led to the deterioration in the number of active sites

present in the polymer chain ends. This led to a decrease in

the depolymerization by back-biting and consequently

enhanced the thermal properties of the blend.

Derivative TGA (DTGA) curves represent an important

thermal property: the maximum rate of weight loss (Tmax).

Tmax curves for neat PLA and neat PBAT and bioblends are

shown in Figure 13b and their Tmax values are reported in

Table 3. DTGA curves displayed a single peak for the neat

polymers, and two peaks for the PLA–PBAT bioblends. The

Tmax increased by inclusion of ADR, which indicated the

enhancement of the thermal stability of the bioblends.

These results agree with the mechanical and thermal

properties.



4. Conclusion

The preparation of the bioplastic blends (PLA–PBAT) with

20 wt% OL were successfully prepared by using reactive

extrusion. The effects of OL as a filler and Joncryl ADR 4368

as a chain extender and compatibilizer on different

properties were examined. The incorporation of ADR

helped to bridge OL with the two incompatible PLA–PBAT

phases which was confirmed by the SEM and AFM images.

FTIR measurements showed the presence of hydrogen

and covalent bonding, providing strong intermolecular

interactions between the PLA–PBAT bioblends with lignin

by the addition of ADR. The incorporation of ADR enhanced

the tensile properties and modulus characterization of

the bioblends; however, the crosslinking effect of ADR

decreased the impact strength and elongation at break of

the bioblends. DSC results showed that the Tg of the PBAT

blends were not visible, indicating a good interaction

between the PLA–PBAT matrix and OL in the presence of

ADR.DMAshowedanenhancement in thestoragemodulus

of (PLA–PBAT)/OL bioblends by incorporation of ADR.

Moreover, the Tan d of PLA and PBAT shifted toward each

other indicating an enhanced miscibility between PLA and

PBAT by the addition of ADR. Moreover, the rheological

properties showed that the addition of ADR affected the

storage modulus and complex viscosity of the bioblend.

TGA showed enhanced thermal stability by the addition

of the chain extender. All of these results indicated that

the incorporation of ADR helped to bridge and enhance

the compatibility between the PLA–PBAT phases in the

presence of OL, resulting in a stronger, greener bioplastic-

blend.

Acknowledgements: The financial support from the NaturalSciences and Engineering Research Council (NSERC), CanadaNSERC Lignoworks project to carry out this research is gratefullyacknowledged. Authors also acknowledge Lignol Innovations (BC,Canada) for providing the organosolv lignin samples for thisresearch.This article was modified on March 05, 2015, to correct a minorerror in Table 1 and to update the affiliations.

Received: July 11, 2014; Revised: September 7, 2014; Publishedonline: January 15, 2015; DOI: 10.1002/mame.201400241

Keywords: biopolymers; blending; compatibility; reactive extru-sion; renewable resources

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