pla review article

Perspective on Polylactic Acid (PLA) based Sustainable Materials forDurable Applications: Focus on Toughness and Heat ResistanceVidhya Nagarajan,†,‡ Amar K. Mohanty,*,†,‡ and Manjusri Misra†,‡

†School of Engineering, Thornborough Building, University of Guelph, Guelph, N1G2W1 Ontario, Canada‡Bioproducts Discovery and Development Centre, Department of Plant Agriculture, Crop Science Building, University of Guelph,Guelph, N1G2W1 Ontario, Canada

ABSTRACT: Evolution of the bioplastics industry haschanged directions dramatically since the early 1990s. Thelatest generation is moving toward durable bioplastics havinghigh biobased content. The main objective is to replace “fossilcarbon” with “renewable carbon”, a holistic strategy to mitigateclimate change by minimizing the environmental impact of aproduct throughout its life cycle. Durable bioplastics is desiredfor multiuse long-term application in automotive, electronicsand other industries. One necessary requirement for them is tobe both tough and strong, yet the two attributes are oftenmutually exclusive. Does this mean a biobased andbiodegradable polymer as polylactic acid (PLA) with its highstrength but low toughness cannot be adopted for durableapplications? Well, not exactly; this is where the concept of tailoring the properties of PLA to achieve stiffness−toughness balancealong with acceptable heat resistance comes into play. In this perspective, we summarize the recent research progress inaddressing the toughness vs strength and heat resistance conflict inherent in PLA. Blends having super toughness and compositesbased on the toughened PLA blends formulated to obtain desired material properties are covered. Morphology and crystallinitythat individually contribute to toughness and heat resistance have also been elucidated.

KEYWORDS: Super toughened, Heat resistant, Impact strength, HDT, Reactive blending, Compatibilization, Morphology,Crystallinity, Nucleating agent, Copolymers

■ INTRODUCTIONThe past is prologue for durable bioplastics; the quest formaterials with properties similar to those of engineering plasticsbut derived from renewable resources is becoming a reality inthe 21st century. Although several biobased engineering plasticsare already available in the market, the idea here is to takeadvantage of the cost competiveness and unique properties ofpolylactic acid (PLA). The past decade has seen a remarkablesurge of research interest in developing PLA based blends andcomposites for durable applications in automotive, electronicsand semistructural parts. The diversity of the approaches, andthe specialty additives and toughening agents has increased ourknowledge on controlling the performance of PLA for long-term durable product applications. This perspective provides acritical review of the literature in the field of super toughened,heat resistant PLA blends and biocomposites followed byrecommendations for future work.

■ GETTING OUR RESEARCH BEARINGS FOR AN ERAOF DURABLE BIOPLASTICS

PLA is a biodegradable thermoplastic polyester produced bycondensation polymerization of lactic acid, which is derived byfermentation of sugars from carbohydrate sources such as corn,sugarcane or tapioca.1,2 From energy consumption, CO2

emissions and end of life options, PLA is superior to manypetroleum based polymers.1 PLA already serves as analternative to certain petroleum based plastics in commercialapplications. It is available in the market at a price on a par withthat of common plastics like polypropylene. Market demand forPLA has grown dramatically over the past decade, with much ofit being in the packaging industry.2 PLA was initially promotedfor single use packaging applications, given the key benefit ofshort life cycle due to its compostable nature. The applicationareas for PLA are widening with usage in durable structuralparts generating particular high demand. According toEuropean trade association for the bioplastics industry, theglobal production of durable bioplastics is forecasted to increaseby 535% from 2014 to 2019.3

Besides property enhancement with suitable additives, whenthe final formulations are intended for compostable applica-tions, the materials should satisfy the compostability standardsset forth in ASTM D6400 or EN 13432. On the flip side, thereare not many cost-effective and compostable additives that areavailable to raise substantially the performance level of PLA

Received: February 14, 2016Revised: March 29, 2016Published: May 17, 2016

Perspective

pubs.acs.org/journal/ascecg

© 2016 American Chemical Society 2899 DOI: 10.1021/acssuschemeng.6b00321ACS Sustainable Chem. Eng. 2016, 4, 2899−2916

This is an open access article published under an ACS AuthorChoice License, which permitscopying and redistribution of the article or any adaptations for non-commercial purposes.

pubs.acs.org/journal/ascecg

http://dx.doi.org/10.1021/acssuschemeng.6b00321

http://pubs.acs.org/page/policy/authorchoice/index.html

http://pubs.acs.org/page/policy/authorchoice_termsofuse.html

while retaining its compostability. Industries are thereforeseeing a major shift in the marketplace from “compostability” to“renewability”. However, being compostable and being renew-able are not dependent or in conflict with each other, each hasits own advantages. Preference for “renewable carbon” insteadof “fossil carbon” stems from the very realization of our need toreduce nonrenewable resource consumption, and greenhousegas (GHG) emissions. The Kyoto Protocol was the first criticalstep taken toward a truly sustainable future; it mandatesemission cuts for industrialized nations. Ratified by 145 nationsaround the world, the protocol entered into force in February2005.4 At the 10 year mark, United Nation FrameworkConvention on Climate Change (UNFCCC) announced thosecountries who took on the targets of the protocol havecollectively reduced the emissions over 20% as opposed to theaimed target of 5%.5 A successor climate change agreementapproved in Paris COP21 Conference, December 2015, has seta goal to keep the world under 1.5 °C temperature rise.6 AJapanese government directive says by 2020, 20 wt % of allplastics used in Japan must be derived from renewableresource.7 Leadership in Energy and Environmental Design(LEED) certifications, carbon tax and other local regulationsare also driving the demand for durable biopolymers.Current research around the world on PLA modification and

application is focused on producing high performance partiallyrenewable materials that can compete with conventionalplastics. However, much like other synthetic plastics, PLA hasits own inherent weakness that prevents it from being widelyadopted for durable applications, in particular its low toughnessand heat resistance. PLA has a very slow crystallization rate,whereas a high level of crystallinity is desirable in finishedproducts as it dictates most of the mechanical and thermalproperties. The toughness and ductility of PLA have beenimproved with multiple strategies including plasticization,copolymerization, and melt blending with different toughpolymers, rubbers and thermoplastic elastomers. Researchprogress in toughening PLA based on these strategies can befound in several recent review articles.8−14 However, none ofthese articles have articulated the efforts taken toward achievinga PLA based material with improved short-term heat resistance.This perspective summarizes the most recent developments inachieving super toughened and heat resistant PLA blends andcomposites. Exhaustive literature available on these topics areorganized based on the strategies and approaches taken toresolve the material problems. Various factors governing thetoughness and heat resistance of the blends and composites arealso discussed.

■ SUPER TOUGHENED BLENDS: CURRENT TRENDSEEKING TOUGHER PLA

Toughness: Definitions and Mechanisms. Toughness isa complicated property; it is defined in terms of “impactstrength/toughness”, the ability to absorb sudden impactenergy without breaking and “tensile toughness”, the abilityto absorb energy while being pulled apart or stretched.Emphasis is on the ability to absorb energy before fracture. Agood combination of strength and ductility is the key totoughness. PLA is a brittle polymer with low crack initiationenergy (measured by unnotched impact test) and low crackpropagation energy (measured by notched impact test); it failsby crazing. Although it may be relatively easy to improve theductility (elongation at break), it is much more challenging toincrease the impact toughness of PLA. Impact toughness

depends on many extrinsic (notch, temperature, loading mode,specimen geometry, fracture behavior) and intrinsic (phasemorphology, chain structure and entanglements) variables. Theresponsiveness of a particular polymer to be rubber toughenedis also said to depend on entanglement density (νe) andcharacteristic chain ratio (C∞); these two will decide thefracture behavior of crazing and yielding.15 See Wu’s work15 fordetailed understanding of these concepts.Toughening mechanisms including shear yielding, multiple

crazing and a combination of both have been reported fortoughened PLA blends.9 According to toughening theo-ries,15−19 stress concentration due to the presence of sphericalrubbery particles is the first step to complex tougheningprocess. Multiple crazing occurs when the stress required forcraze initiation is less than the yield stress. In this situation,maximum triaxial stress concentrations at the dispersedparticles initiate crazes. Craze termination is the next naturalstep in this mechanism through the formation of small multiplecrazes leading to crack propagation. New surfaces generatedduring the creation of multiple crazes consume more energythan a small number of large crazes. Shear yielding occurs whenthe stress required for craze initiation is greater than yieldstress. Toughening by this mechanism is usually achieved byhydrostatic tension in the dispersed particles acting as shearband initiators. When the yield stress and craze initiation stressare comparable or when there are interactions between theshear bands and crazes formed in the matrix, the combinationof shear yielding and multiple crazing becomes the predom-inant mechanism. Cavitation is another important precursorphenomenon to any toughening mechanism. Two types ofcavitation have been observed in PLA toughened with arubbery phase: (i) internal cavitation, which occurs when theinterfacial bonding is strong between the rubber domains andmatrix; (ii) debonding cavitation, which occurs when there ispoor interfacial bonding strength. To prevent the localization ofstrain, cavities formed either in the rubber particle (internal) orthe matrix (debonding) alters the triaxial stress state and favorsthe formation of shear bands ultimately leading to shearyielding of the matrix. Combination of internal and debondingcavitation is also a possible mechanism.The particle size, shape and distribution of toughening agent

can be tailored to reduce substantially the amount of impactmodifiers or elastomers required for a desired toughness.Multicomponent blends containing reactive copolymers aretherefore being developed to tune the phase morphology ininteresting ways and obtain blends with moderate stiffness andsufficient toughness by employing techniques like in situreactive compatibilization and dynamic vulcanization. Theseprocesses increase interfacial strength by promoting chemicalreactions between blending components establishing strongbridge for transmission of stresses. Resulting PLA blends withdrastic improvement in impact toughness are being referred toas “super toughened” PLA. This term was first known to beused by Wu15 for convenience to denote arbitrarily blendshaving notched impact strength higher than 10 ft/lb or ∼530 J/m (energy lost per unit width, North American standard),which is approximately equal to 53 kJ/m2 (energy lost per unitcross-sectional area, European standard) depending on thedimension of the sample. Research work specifically focused onachieving super toughened PLA blends (impact strengthbeyond 35 kJ/m2) is reviewed in this section. They arecategorized according to the type of reactive tougheningpolymers and techniques used. This is followed by recom-

ACS Sustainable Chemistry & Engineering Perspective

DOI: 10.1021/acssuschemeng.6b00321ACS Sustainable Chem. Eng. 2016, 4, 2899−2916

2900


mendations for future work. Range of impact properties thus farobtained in super toughened PLA blends are summarized inTable 1. Most of the articles in this section were focused onachieving super toughness and have not investigated the effecton crystallinity or heat resistance.Reactive Compatibilization with Functional Mono-

mers. Successful application of a reactive compatibilizationtechnique has provided enormous opportunities to compatibi-lize otherwise immiscible and incompatible blends. Reactivecompatibilization is therefore seen as a powerful technique toenhance effectively the compatibility of PLA with other toughpolymers. Melt blending PLA with other suitable polymers inthe presence of a reactive monomer forms a graft copolymer atthe interphase, decreases the interfacial tension of theimmiscible polymer components and promotes interfacialadhesion. A finer phase morphology developed in the blendsfacilitates stress transfer between the two phases, therebyimproving the properties of the blends. Maleic anhydride,glycidyl methacrylate, isocyanate and epoxy are some of thewidely investigated reactive monomers proving to be successfulin compatibilizing the blends of PLA with other bio- andpetroleum based polymers. In the work of Harada et al.,20 0.5%lysine triisocyanate (LTI) was found to increase the impactstrength of PLA/PBS (90/10) blend from 18 kJ/m2 to 50−70kJ/m2. These improvements were attributed to effectiveinterfacial reactions accomplished between the isocyantefunctionalities of LTI and carboxyl, hydroxyl end groups ofthe blending polymers.Glycidyl methacrylate (GMA) is one of the versatile

functional monomers tailored to meet a variety of applications.A great number of PLA super toughening studies report use ofGMA in one or other forms to facilitate compatibility byreacting with functional end groups of PLA. Effectiveness ofGMA in improving the toughness of PLA is explored mainlythrough these three routes: (i) addition of GMA monomers orcopolymers such as ethylene glycidyl methacrylate (EGMA),ethylene methyl acrylate glycidyl methacrylate (EMAGMA)and ethylene butyl acrylate glycidyl methacrylate (EBAGMA),(ii) addition of tough polymers grafted with GMA to facilitatecompatibility between the blending components (two-stepprocess of grafting followed by reactive compatibilization) and(iii) addition of tough thermoplastic elastomers in combinationwith GMA copolymers in one-step reactive extrusion. Factorsdrastically affecting the toughening behavior of PLA blendscontaining GMA are the reactive extrusion screw rpm andresidence time, which in turn affects important morphologicalaspects such as dispersed phase size and interparticle distance.Increasing the screw rpm from 30 to 200 in low molecular

weight PLA containing 20% EGMA was found to have a drasticeffect on elongation,21 as the value went up from 26% to>200%. However, a super toughened PLA blend with 72 kJ/m2

of impact strength was achieved only after annealing theprocessed samples at 90 °C for 2.5 h. Another parameterappearing to have a significant effect on the resultingtoughening is GMA grafting content. Polyethylene octene(POE), a metallocene catalyzed thermoplastic polyolefinelastomer grafted with different percentages of GMA (1.8 and0.8%), was used to toughen PLA.22,23 To achieve an impactstrength of 55 kJ/m2, 45 wt % of POE-g-GMA (1.8%) had to beblended with PLA,22 whereas in another study,23 20 wt % ofPOE-g-GMA (0.8%) was sufficient to attain super toughness ofover 80 kJ/m2. These super toughened blend systems wereproved to be efficient in absorbing external energy through acombination of crazing and shear yielding mechanisms.Poly(ether-block-amide), PEBA, a commercial class of thermo-plastic copolyester elastomer from Arkema, is seen as anefficient impact modifier for brittle polymers as it is highlyresistant to sudden impact even at very low temperatures (−40°C). In spite of such favorable properties,24 30 wt % PEBA wasrequired to improve the impact strength of PLA to 60 kJ/m2.Zhang et al.25 used EMAGMA as a reactive interfacialcompatibilizer for blends of PLA/PEBA and achieved impactstrength up to 500 J/m, while maintaining tensile strength at 50MPa (Figure 1). Performance improvements in these ternary

Table 1. Impact Strength Results for Super Toughened PLA Blends

technique/additives range of impact strength achieved reference

GMA based copolymers, thermoplastic elastomers and GMA grafted copolymers: notched Charpy: 46.1−72 kJ/m2 21−27EGMA, POE, POE-g-GMA, PEBA, PEE EMAGMA, PEBA-g-GMA notched Izod: 40−80 kJ/m2, 450−650 J/m

compatibilizers and chain extenders for PLA blends with PBS, PBSA, PBAT:LTI, Joncryl, TPP

notched Izod: nonbreak 20, 28, 29notched Charpy: 16−40 kJ/m2

acrylic impact modifiers and acrylic copolymer with GMA: 31−41MBS, ABS-g-GMA, AcrylPEG, ACR with different BA and MMA content, KM-365 and Paralloid BPM 500 from Rohm and Haas, Biomax strong from DuPont

notched Izod: 35−120 kJ/m2 540 J/m

dynamic vulcanization: 42−56EBAGMA, EMAA based ionomers, PUEP, NR, ENR, UPE notched Izod: 480−800 J/m (nonbreak) 38−60 kJ/m2

random aliphatic copolyesters, polyurethanes, and other flexible polymers: 57−66P(CL-co-LA), P(CL-co-VL), TPU, CPU, EVA notched Izod: 40−83 kJ/m2 450−550 J/m

Figure 1. Components, morphology and impact strength ofsupertoughened PLA blends. [Reprinted with permission from ACSApplied Materials and Interfaces, Vol. 6, K. Zhang, V. Nagarajan, M.Misra, A. K. Mohanty. Supertoughened renewable PLA multiphaseblends system: Phase morphology and performance, 12436−12448,Copyright 2014, American Chemical Society.]



2901


blends were attributed to their unique morphology of partialencapsulation of PEBA by EMAGMA in PLA matrix. Interfacialcavitation and good adhesion between phases resulted inmassive shear yielding of PLA matrix.Vachon et al.26 used EMAGMA and poly(maleic anhydride-

alt-octadecene) (PMAOD) to compatibilize PLA and thermo-plastic poly(ether ester) elastomer, PEE. A sharp transition inimpact strength values to 650 J/m was noticed in PLA ternaryblends containing 12% of PEE and 12% of EMAGMA, withEMAGMA being more efficient compared to PMAOD.Recently, Zhou et al.27 investigated the effect of adding GMAgrafted PEBA (PEBA-g-GMA) as an impact modifier for PLAand thermoplastic starch acetate (TPSA). This work showed anotched Izod impact strength of ∼60 kJ/m2 could be achievedfor PLA/TPSA/PEBA-g-GMA (70/15/15) blend. A TPSAesterification degree of 0.04% was needed to improve thecompatibility between TPSA and PLA/PEBA-g-GMA. Proper-ties of polymers are influenced to a greater extent by the lengthof the macromolecule. When the macromolecular chain islonger, the molar mass and entanglement degree is higher,which increases the melt temperature and viscosity. Adding achain extender (CE) to PLA increases the molar mass of PLAby connecting the short and long polymer chains via a reactivefunctional end groups present in the CE. When a multifunc-tional epoxy based chain extender, Joncryl was used for in situreactive compatibilization of PLA and poly(butylene succinate-co-adipate), PBSA, the alteration of blend structure from linearto long branched chains enhanced the impact strength of PLA/PBSA (60/40) blend28,29 as shown in Figure 2.

The particle size of the PBSA dispersed phase was reducedby 74% with the addition of 0.6% Joncryl, and further reductionwas noticed with increase in Joncryl content owing to effectivecompatibilization. Dong et al.30 have also reported Joncryl iseffective in increasing the ductility and percentage elongation ofPLA/PBAT blends, to a maximum of 500%. As previousstudies29 have established the presence of induction time forreactivity of Joncryl, the effect of increasing the temperature toincrease the reactivity of Joncryl could be an interesting aspectof future investigations.Acrylic Copolymers and Core−Shell Impact Modifiers.

Acrylic polymers such as poly(methyl methacrylate), PMMA,and poly(butyl acrylate), PBA, have been found to be partiallymiscible with PLA; therefore, they have been used to toughenPLA.31,32 Achieving significant increase in impact strength is

however a challenge in simple binary blends of PLA with suchpolymers.31−33 Researchers have looked into core−shell acryliccopolymers such as methyl methacrylate−butadiene styrene,acrylonitrile−butadiene styrene and methyl methacrylate−butylacrylate copolymers to super toughen PLA.34−40 The rubberycore provides impact resistance whereas the glassy shell impartsrigidity. Outer shell can be designed specifically to becompatible with the PLA matrix. Core−shell composition,particle diameter and its distribution, grafting percentage andcross-linking degree are all important factors to achieve thenecessary toughening and they have all been investigated indetail in PLA matrix. Acrylic impact modifiers (ACRs)containing different ratios of methyl methacrylate, MMA(hard/shell monomer) and butyl acrylate, BA (soft/coremonomer) were used to super toughen PLA.36,37 Impactstrength and elongation at break gradually increased withincrease in the amount of soft monomer in the ACR. In PLA/ACR (90/10) containing BA/MMA in the ratio of 90/10, theunnotched impact strength was significantly increased to 68 kJ/m2 compared to 17 kJ/m2 for neat PLA. Tensile and flexuralproperties were not drastically reduced as the ACR content wasonly 10%.36 As the concentration of MMA hard shell monomerincreased, the impact strength initially increased and thendecreased, signifying the presence of a critical concentration ofMMA. The highest notched Izod impact strength of 77.1 kJ/m2

was achieved when the ACR core−shell ratio was optimized at79.2/20.8 for the 80/20 PLA/ACR blend.37 With increase inBA content, the interactions between ACR and PLA werepostulated to get stronger and the interface between thesephases was indistinct. Internal and debonding cavities in theACR domains induced crazes and shear bands in the PLAmaking the matrix around the ACR particles to deform easily toachieve shear yielding as shown in the schematic,36 Figure 3.

Poly(ether glycol) methyl ether acrylate, abbreviated asAcrylPEG, has been most effective in imparting supertoughness to PLA thus far. Two different approaches wereinvestigated by Kfoury et al.:38 (i) polymerization of AcrylPEGto poly(AcrylPEG) using free radical initiator, Luperox and (ii)direct one step reactive extrusion with PLA, where in situgrafting of AcrylPEG onto PLA backbone was achieved.Substantial improvement of notched Izod impact strength to102 kJ/m2 was achieved for PLA with 20 wt % AcrylPEG, and35 kJ/m2 for PLA with poly(AcrylPEG). Commercial non-

Figure 2. Notched impact strength as a function of PBSA content andJoncryl weight fraction. The schematic depicts the modification of thePLA/PBSA blend interface by Joncryl through the formation ofnonlinear copolymer. [Reprinted from Polymer, Vol. 80, V. Ojijo, S. S.Ray. Supertoughned biodegradable polylactide blends with nonlinearcopolymer interfacial architecture obtained via facile in situ reactivecompatibilization, 1−17, Copyright 2015, with permission fromElsevier, License number: 3794351260132.]

Figure 3. A simple schematic of a possible mechanism by which ACRtoughens PLA. [Adapted from BioResources, Vol. 9, X. Song, Y. Chen,Y. Xu, C. Wang. Study of tough blends of polylactide and acrylicimpact modifier, 1939−1952, 2014.]



2902


biodegradable acrylic impact modifiers available under thetradename Paraloid BPM-50039 and KM-36540 from Rohm andHaas, and Biomax Strong41 from DuPont are also available totoughen PLA. PLA blends with Paraloid BPM-50039 possessedgood flexibility compared to neat PLA, impact strengthhowever did not improve beyond 40 J/m. PLA has beenreported to show brittle to ductile transitions when KM-365and Biomax Strong are added beyond 20 wt %. In some cases,impact modifiers were observed to hinder the crystallization ofPLA and decrease the tensile properties of the blends.Dynamic Vulcanization. Dynamic vulcanization is one of

the most versatile areas of polymer modification. It is a processin which selective vulcanization of elastomer with non-vulcanizing thermoplastic is achieved during shearing in meltmixing, leading to the formation of a two-phase material whereparticulate cross-linked elastomeric phases are dispersed in theplastic matrix.42 Zhang et al.43 introduced a super toughenedPLA ternary blends with moderate tensile strength andmodulus by melt blending PLA with ethylene n-butyl acrylateGMA (EBAGMA) and ethylene methacrylic acid based zincionomer (EMAA-Zn). Unlike other blends, in addition toreactive compatibilization between PLA and EBAGMA,dynamic vulcanization of EBAGMA was also achieved. Ternaryblends containing EMAGMA/ionomer weight ratio ≥ 1, Znmetal ion, higher percentage of MMA functionality andincreased degree of neutrality were found to have enhancedinterfacial compatibility and hence higher impact strength.44−46

Morphological analysis based on SEM images demonstratedthat with the increase in EMAA-Zn content, the occludedsubinclusion phase of EMAA-Zn turned to continuous phasewithin the “salami”-like dispersed domains. This morphologywas not dependent on reactive blending temperature; however,higher reactive extrusion temperatures resulted in anunfavorably higher degree of cross-linking in EBAGMA thatwas resisting internal cavitation.Polyurethane elastomer prepolymer (PUEP) with isocyanate

(−NCO) terminal groups vulcanized to a rubber phase hasbeen shown to toughen PLA.47 The −NCO groups reactedwith hydroxyl, carboxyl end groups of PLA to form urethanelinkages in addition to vulcanization reaction of the PUEP.These reaction products bridged the PLA phase with vulcanizedrubber phase of PUEP. Predominant internal cavitation indynamic vulcanized blends imparted major toughening effect toPLA/PEUP (70/30) blends with impact strength of 55 kJ/m2

and elongation values reaching over 400%. In another recentwork, researchers have developed super tough PLA materialsthrough in situ reactive blending with polyethylene glycol baseddiacrylate (PEGDA) monomers.48 The cross-linking of acrylategroups resulted in phase separated morphology with PEGDA asthe dispersed phase. Sea-island morphology had been thetypical, predominant morphology of thermoplastic vulcanizates(TPVs) but Chen49,50 and Yuan et al.51,52 discovered it ispossible to achieve continuous cross-linked rubber phase inperoxide induced dynamic vulcanization of PLA with naturalrubber (NR) and epoxidized natural rubber (ENR). Impactstrength results and SEM morphology of dynamic vulcanizedPLA/NR (65/35)49 are shown in Figure 4. After cryofractureand etching of PLA phase, formation of continuous honey-comb-like network structure by the NR phase was clearlyvisible. Extensive plastic deformation of the surrounding PLAdeformed the rubber domains due to heterogeneous stressfields and enhanced the toughness. A brittle ductile transitionwas observed at PLA/ENR (60/40) blend ratio with notched

Izod impact strength of 47 kJ/m2, which was 15 times highercompared to 3 kJ/m2 for neat PLA.50 At dicumyl peroxide(DCP) content beyond 0.03 phr, interfacial adhesion betweenphases were enhanced and a higher degree of cross-linking wasachieved in ENR. “Fully biobased and super tough PLA TPV”displaying a quasi-co-continuous morphology with vulcanizedunsaturated polyester elastomer (UPE) is yet anothersuccessful effort to super toughen PLA using dynamicvulcanization.53 Tensile and impact strength of PLA/UPETPVs improved from 3.2 MJ/m3 and 16.6 J/m to 99.3 MJ/m3

and 586 J/m, respectively. Other researchers have alsoexperimented with the dynamic vulcanization technique onPLA blends of biobased polyester elastomers (BPE),54 ethylenecovinyl acetate (EVA)55 and ultrafine fully vulcanized powderrubber (UFPR).56 They have been successful in achievingtremendous improvements in elongation at break (>400%);however, the impact strength is either not reported or very lowin the case of UFPR.

Melt Blending with Random Aliphatic Copolyesters,and Other Toughening Polymers. In a series of studies,Joziasse57 and Odent et al.58−60 synthesized random biode-gradable copolyester: CL with D,L-lactide, (P[CL-co-LA]) andCL with δ-valarectone (VL), (P[CL-co-VL]) to be used asimpact modifiers for PLA. When silica nanoparticles (10%)were added to PLA blends containing these copolyesters,spherically dispersed domains converted to cocontinuousmorphology, increasing the impact strength to 39.7 kJ/m2 vs2.7 kJ/m2 for neat PLA.60 Li et al.61 prepared sliding graftcopolymer (SGC) where PCL side chains are bound topolyrotaxane (PR) cyclodextrin rings and used them totoughen PLA. Methylene diphenyl diisocyanate (MDI) wasused as the reactive compatibilizer. Blends of PLA/SGC/MDIdisplayed super toughening with impact strength values as highas 48.6 kJ/m2. Unfortunately, preparing such copolymers is notcurrently economically viable to be adopted by the industry forwide scale production. Unique combination of toughness,durability and flexibility makes thermoplastic polyurethaneelastomers (TPU) a suitable material to blend with PLA.Addition of 30% TPU to PLA resulted in blends with impactstrength of 315 J/m and elongation at break of 363%.62 Liu etal.63 noticed that toughening PLA by in situ polymerization ofPEG and PMDI to form cross-linked polyurethance (CPU) wassuccessful, where the impact strength of PLA with 30% CPUincreased from 16 to 546 J/m. Liu et al.64 introduced PDLAinto PLLA/TPU blends to form stereocomplex crystals that candramatically improve the melt viscosity and change the sea-

Figure 4. (a) Notched Izod impact strength of neat and dynamicallyvulcanized PLA/NR blends, (b) SEM Images of dynamicallyvulcanized PLA/NR (65/35). [Reprinted with permission from ACSApplied Materials and Interfaces, Vol. 6, Y. Chen, D. Yuan, C. Xu.Dynamically vulcanized biobased polylactide/natural rubber blendmaterial with continuous cross-linked rubber phase, 3811−3816,Copyright 2014, American Chemical Society.]



2903


island morphology of PLLA/TPU to a unique network-likestructure. High levels of crystallinity in these blends wereachieved by injecting the samples into a preheated mold at 130°C and postannealing. This resulted in PLLA/TPU/PDLA(70/15/15) blends with remarkable improvement in impactstrength up to 63.2 kJ/m2. Ethylene-co-vinyl acetate (EVA)with different vinyl contents and ethylene acrylic elastomer(EAE) has also been found to impart super toughness to PLAat 20 wt %.65,66 Formation of shear bands initiated by theinternal cavitation of EVA resulted in shear yielding type offracture behavior in the blend, no crazing or interfacialdebonding occurred. As a consequence of numerous internalcavitations, stress whitening was noticed on a macroscopic scaleas shown in the Figure 5.

■ EVALUATION OF FACTORS AFFECTINGTOUGHNESS: INSIGHTS FOR FUTURE WORK

In any rubber toughened polymers, factors such as rubbercontent, type, particle size, particle size distribution andinterparticle distance are closely interrelated and greatly affectthe resulting toughening effect. The majority of all inves-tigations concerning super toughened PLA have reported theexistence of an optimum loading level of the toughening agent,and beyond this level fracture toughness ceases to improve orin some cases starts to decline. This might be due to severalintrinsic factors related to the microstructure and the efficiencyof rubber to support any kind of toughening mechanism at highrubber contents when there is not much matrix material toundergo plastic deformation. Toughness improvements can beexpected only in a certain rubber content range, in which therubber is dispersed in desired particle sizes and size distributionto cavitate effectively or fibrillate for maintaining a substantialdegree of structural integrity in response to impact. Theexperimental evidence reported for such a limit is 20−30 wt %of rubber content; therefore, modeling and theoretical work canbe developed to predict and explain this limit in future. Therubbery phase added as a toughening agent is generallypreferred to be compatible with PLA to such an extent thatthere is satisfactory dispersion and wetting but not completelymiscible to result in a single homogeneous phase morphology.When the two phases are miscible as in PEG-plasticized PLA,the elongation ratio (percentage) is improved tremendously but

the inability of the second phase to act as stress concentratordoes not favor multiple crazing or shear yielding resulting inblends with only moderate toughness. Similarly, low toughnesswas reported for PLA with in situ formed PU containing non-cross-linked product that acted as a plasticizer.63 In the case ofPLA/EVA blends, toughness improvements were marginalbecause of the formation of homogeneous morphology below20 wt % EVA.65

Toughness improvement is also the highest at an optimumrubber particle size. When the dispersed phase is incompatiblewith the matrix, it would exist as spherical particles to reducesurface tension. If the components in the blend have goodcompatibility, uniform dispersion of the rubbery tougheningagent with relatively small particle size can be expected. With anoverlap in stress fields around the well dispersed particles,plastic deformation can propagate through the entire matrixgiving rise to effective energy dissipation. Reactive compatibi-lization has been found to reduce the particle size of thethermoplastic elastomer or rubbery copolymer consider-ably20,23,29,63 and in some cases their shape evolves fromspherical to distinct cocontinuous morphology.29,61 The shapeand size of the dispersed particles are dependent on thedynamic viscosity, the shear rate of melt blending, and theinterfacial tension. The dispersed particles will have the smallestaverage size when the viscosity ratio of the two phases is closerto unity and when the interfacial tension is lower.17 Highershear rate generated by increasing the screw rotation speed inan extruder can drastically reduce the particle size of the rubber.For example, increasing the screw rpm from 30 to 200significantly decreased the particle size of EGMA in highmolecular weight PLA (PLA-H) compared to low molecularweight PLA (PLA-L).21 Proximity of viscosity ratio to unity inthe case of PLA-H reduced the particle size to 50−100 nmwhereas in PLA-L it was reduced to 100−300 nm.21 However,very small particle size may not be beneficial for achieving supertoughness as small particles may not effectively absorb theenergy of the external force. Other researchers who quantifiedthe particle size of dispersed phase in super toughened PLAalso have established the fact that having optimum particle sizehad resulted in superior toughening effect.20,23,63 On the basisof the theories of Wu,15,16 the entanglement density, νe isrecognized to be one of the main factors governing the

Figure 5. Morphology of the PLA/EVA50 (80/20) blends after impact testing: (a) initial impact bars, (b) optical images, and TEM images of (c)undeformed part, (d−d″) the stress whitening zone at different magnifications. [Reprinted from European Polymer Journal, Vol. 48, P. Ma, D. G.Hristoca-Bogaerds, J. G. P. Goossens, A. B. Spoelstra, Y. Zhang, P. J. Lemstra. Toughening of poly(lactic acid) by ethylene-co-vinyl acetate copolymerwith different vinyl acetate contents, 146−154, Copyright 2012, with permission from Elsevier, License number: 3794310181202.]



2904


deformation mechanism. For brittle polymers in general supertoughening is predicted to occur at an optimum νe of 0.1mmol/cc, as massive crazing and yielding of the matrix occursat this level of νe.

16 Depending on composition, PLA ispredicted to have νe in the range of 0.12−0.14 mmol/cc.57,67

Using Wu’s relationship16 between optimum rubber particlesize, do and νe,

= −d vlog 1.19 14.1o e (1)

the do for PLA can be calculated to be in the range of 0.16−0.31μm. On the basis of theoretical investigations, this range can beexpected to be the guiding value of particle size in future PLAwork aiming at achieving successful super toughening effect.However, if the dispersed rubber phase contains rigidsubinclusions as in the case of core−shell or salami-likemorphology in ternary blends, the inclusion phase can anchorthe load bearing fibrils to the matrix, which can effectivelyreduce premature cavitation. Therefore, in an alternative view,particle size range required to achieve optimum toughness alsodepends on other factors such as strain rate, morphology of thedispersed particles, rubber content and the rubber shearmodulus.Unfortunately, PLA super toughening studies have not

delved into the effect of particle size distribution. Bimodalparticle size distribution was observed when P[CL-co-VA] withhigh molar mass was used to toughen PLA samples prepared bycompression molding.59 Although a super toughening effectwas not achieved, compression molded samples containingP[CL-co-VA] in bimodal particle size distribution attainedhigher impact strength compared to their injection moldedcounterparts. Such improvements in compression moldedsamples were thought to be because of the relatively largersize of the microdomains in them compared to the morphologyof injection molded samples. The authors did not providefurther explanation behind this experimental observation.Smaller particles can toughen the localized shear bands formedin between the large particles.68 This makes the crack tip regionsustain higher fracture load by maintaining a higher criticalstress level. If this critical stress level generates greater triaxialstress ahead of the crack tip, it causes higher degree ofcavitation in the larger particles; consequently, the adjacentmatrix undergoes shear yielding before fracture.68 Optimumsize and biomodal distribution would be necessary to achievesynergistic super toughening. There is great scope forinteresting future work on examining the effects of suchbiomodal particle size distribution. One way to achieve suchdistribution in PLA matrix would be to use small fine rubberparticles in combination with large coarse particles. Synergistictoughening with a combination of 1−2 and 70 μm rubberparticles from recycled tires has been observed in epoxy resin.69

Another factor to consider for efficient rubber toughening isthe average interparticle distance, L. According to tougheningtheories,18 L should be below a value, Lc, in order for therubbery particles to effectively initiate plastic deformation in thesurrounding matrix, despite L being directly related to rubberparticle size and content. In PLA toughened with POE-g-GMA,23 when the rubber content and particle size wereincreased, interparticle distance was reduced. The critical value,Lc for effective toughening of the blend was found to be 0.5μm.23 However, there is no unique agreement betweenresearchers whether Lc is more important than content andsize. If so, the ultimate goal of manipulating the content andsize will be to drive the L below the Lc. On the other hand,

observations reporting very small particle size but no substantialtoughening effect do not follow this theory on L and Lc.Further studies are needed to establish any possible relation-ships.

■ HEAT RESISTANCE: CRITICAL ASPECTCONFERRING DURABILITY

Heat resistance can be defined as the ability of a material tomaintain properties of interest at a desired level at themaximum service temperature for a prolonged period of time.Having a certain level of heat resistance is one of the principalcriteria for material selection. The heat resistance of PLAdepends on its level of crystallinity and crystallization behavior.The crystallization model suggests the chain segments ofsemicrystalline PLA coexist in three different forms: (i)crystalline fraction, (ii) rigid amorphous fraction (RAF) and(iii) mobile amorphous fraction (MAF).70 Crystalline fractionis where the chain segments are all in ordered crystalline state.Random long molecular chains of amorphous fraction coexistwith the crystalline chains.70,71 When a polymer approaches itsglass transition temperature, Tg, molecular chains of thecrystalline region are unlikely to move due to strongintermolecular interactions, but chains of the amorphousphase move freely. Within the amorphous region, there aresome chain segments that are rigid, consequently hindering freemovement of the entire long chain. This fraction is referred toas rigid amorphous fraction (RAF). The remaining longmolecular chains in the amorphous region are known asMAF.70−72 PLA with very low degree of crystallinity has a greatproportion of its chains in the MAF, which has high mobilitynear its Tg and therefore exhibits very low heat resistance, withdistortion temperatures often occurring close to its Tg. Whenthe crystallization of PLA is facilitated with external aids such asnucleating agents, the proportion of the crystalline and rigidamorphous fraction is increased, which impedes chain mobilityand resists heat induced distortions, resulting in enhanced heatresistance.71,72 A schematic of the CF, RAF and MAF is shownin the graphical abstract.Heat resistance is often quantified by the detection of a

softening point under a certain load. The two most commonlyadopted techniques measure: heat deflection or distortiontemperature (HDT) and Vicat softening temperature (VST).HDT is defined as the temperature at which a specimendeflects 250 μm, under a specified load and thickness at aheating rate of 2 °C per min.72 The two common loads usedare 0.46 MPa (66 psi) and 1.8 MPa (264 psi). VST is defined asthe temperature at which the specimen is penetrated to a depthof 1 mm by a flat-ended needle with a 1 mm2 cross-sectionalarea.72 Common loads are 10 and 50N with heating rates ofeither 50 or 120 °C per hour depending on the standardsfollowed.73,74 It is generally understood VST is the temperatureat which a material loses its form-stability and HDT is thetemperature at which material loses its load bearing capacity.However, the difference in assessing the softening point byHDT or VST is mainly a matter of defining the “end point”.74

VST values are usually higher than the HDT values, and thedifference is quite modest in the case of PLA, which showsHDT of ca. 55 °C and VST of 65 °C. Various techniques andmethods have been explored to improve the crystallinity andheat resistance of PLA. This section reviews the state-of-the arttechnologies for improving the heat resistance of PLA by (i)addition of nucleating agents and stereocomplex; (ii) adoptingdifferent processing strategies; (iii) blending with heat resistant



2905


polymers; and (iv) fabrication of biocomposites with naturalfibers and nanoreinforcements. A summary of PLA blends withimproved HDT/VST is presented in Table 2.

Nucleating Agents and Processing Strategies. Nucleat-ing agents can effectively promote crystallization by providingnucleation sites around which the polymer chains cancrystallize. Shorter crystallization half time achieved with theaddition of nucleating agents can help to increase thecrystallinity and shorten the molding cycle time. Nucleatingagents for PLA include, but are not limited to, talc,75,76 N,N′-ethylene bis-stearamide (EBS),77 carbon nanotubes,78 metalsalts of phenylphosphonic acid,79 multiamide and hydrazidecompounds,80−85 barium sulfate,86 titanium dioxide,86 calciumcarbonate (CaCO3),

86 nano-CaCO387 and orotic acid.88

Numerous investigations have been conducted on improvingcrystallization of PLA with the help of nucleating agents.However, only a handful of them corelate the increase incrystallinity due to nucleation to increase in heat resistancemeasured through HDT/VST. Recently, TMC-328, a commer-cial heterogeneous multiamide nucleating agent, has beenfound to enhance greatly the heat resistance of PLA at a verysmall concentration (0.2%).72 Benoylhydrazide (BH) com-pounds, in particular octamethylenedicarboxylic dibenzoylhy-drazide (OMBH) and decamethylenedicarboxylic dibenzoylhy-drazide (DMBH), are known to impart enhancement in thecrystallization of PLA.84,89 The nucleation ability (Tc and ΔHc)of OMBH was found to be higher than that of DMBH, andethylenebis (12-hydroxystearylamide), EBH/talc mixture at 1wt % loading in PLA.84 In addition to using hydrazidenucleating agent, a high molding temperature of 110 °C was

adopted to achieve substantial improvements (results are inTable 2). In spite of the successful enhancement of thecrystallization rate of PLA through the addition of nucleatingagents, obtaining injection molded articles of PLA with highcrystallinity remains difficult with a fast mold cooling rate.Nucleated PLA molded in room temperature molds with fastcooling (>100 °C/min) does not show substantial improve-ment in HDT. Therefore, the effect of performing annealingpostprocessing on the mechanical and thermal properties, andthe fracture behavior of PLA has been studied. The crystallinityof PLA has been found to increase consistently throughannealing in most of the studies and the increase lead to animprovement in its heat resistance and overall mechanicalperformance. Park et al.90 and Nascimento et al.91 performedannealing of PLA under various conditions to obtain micro-structures with different spherulite sizes and densities. The heatresistance of PLA was markedly improved when its crystallinitywas increased by annealing. PLA with 1% EBH molded at roomtemperature and then annealed for 1, 2, 4, 10 and 20 min at 105°C showed increasing HDT with increasing annealing time. Asharp step change in HDT was noticed when the crystallinitywent 25%, indicating a threshold for crystallinity content.77

However, annealing adds a postprocessing step, which may notbe economical or industrially feasible.As an alternative to annealing, researchers84,92,93 have looked

at increasing the mold temperature during the injectionmolding process. This technique can be called as an in-moldannealing process, where the cooling time is increased tofacilitate effective demolding of the samples. Harris and Lee92

increased the injection mold temperature to 110 °C and weresuccessful in obtaining PLA molded articles with highpercentage of crystallinity and high HDT. However, theproblem with this step is molding cycle time of ∼2 min isrequired due to higher cooling time; demolding of theprocessed components would be difficult with short coolingcycle. Li and Huneault93 also observed similar effect of moldtemperature on crystallinity as shown in Figure 6. At mold

Table 2. PLA Blends with Improved Heat Resistance:Summary of Results

PLA blends with improved heatresistance

softening point from HDTand VST reference

nucleating agents, stereocomplexTMC-328 (0.6%) 134.3 °C (VST, 10N) 72OMBH (1%) 124 °C (HDT, 0.45 MPa) 84EBH/talc mixture (1%) 110 °C (HDT, 0.45 MPa) 84PLLA/PDLA (50/50) blend 150 °C (HDT, 0.45 MPa) 103PLLA/hPLLA (95/5) no deformation at 70 °C,

50 g for 5 min105

processing strategiesPLA/1% EBH, 10 minannealing at 105 °C

93 °C (HDT, load notmentioned)

77

PLA with NA annealing at 80°C for 15 min

HDT, 0.45 MPa

PLA/2% EBS 70 °C 92PLA/2% talc 77 °CPLA/talc/PEG (80/10/10) VST, 10N23 °C epoxy mold 123.6 °C 9590 °C steel mold 117.9 °C

blending PLA with heat resistantpolymers and nanofillers

PLA/POM (60/40) and (50/50)

∼72 and 135 °C (HDT,0.45 MPa)

99

PLA/PHBV/PBS (30/60/10) and (10/60/30)

72.2 and 87.5 °C (HDT,0.45 MPa)

100

PLA/organically modifiedMMT (93/7)

112 °C (HDT, 0.98 MPa) 108

PLA/ OMSFM (96/4) and(90/10)

92 and 117 °C (HDT,0.98 MPa)

109

PLA/5% DCPD capsules 78.05 °C (HDT, load notmentioned)

110

Figure 6. Effect of molding temperatures on crystallinity (Xc)developed for PLA with 5% acetyl triethyl citrate (ATC) and 1% talc.[Reprinted from Polymer, Vol. 48, H. Li, M. A. Huneualt. Effect ofnucleation and plasticization on the crystallization of poly(lactic acid),6855−6866, Copyright 2007, with permission from Elsevier, Licensenumber: 3794330203855.]



2906


temperatures below 50 °C, low crystallinity level was observed,and crystallinity reached maximum level at 80 °C moldtemperature with a combination of 5% plasticizer and 1% talc.In most of the above reviewed works,72,77,84,89 addition ofnucleating agent in combination with annealing or hightemperature molding was helpful in increasing the mechanicalproperties. Increase in crystallinity increased the tensile andflexural modulus. In some cases, increased number of spherulitestructures with low spherulite size was believed to consumemore energy and thus increase the impact strength of PLAsamples containing nucleating agents.On the contrary, Vadori et al.94 have showed increasing the

mold temperature of PLA decreases the impact toughness andpercentage elongation of high impact PLA. Unique approach ofusing epoxy based PolyJet mold instead of steel mold forconventional injection molding to produce PLA parts with highcrystallinity has been proposed to offer promising results(Table 2).95 Because of low thermal conductivity of epoxybased PolyJet mold, PLA parts containing nucleating agentsproduced from this mold had a significantly higher level ofcrystallinity, thermal and mechanical properties compared toPLA samples molded from steel molds. When PLA is injectedinto 23 °C steel mold, it is cooled below its Tg in 15 s due tohigh thermal conductivity of the steel mold, whereas, in PolyJetmold, PLA material stays above Tg for around 66 s, allowing thematerial to crystallize. As a result, VST of PLA molded in 23 °CPolyJet mold increased to 118−124 °C compared to VST of60−65 °C for PLA samples obtained from 23 °C steel mold.Use of such PolyJet molds show promise in achieving higherlevels of crystallinity for PLA at room temperature moldingconditions.Blending with Heat Resistant Polymers, Stereo-

complexation, and Use of Nanofillers. Blending PLAwith heat resistant engineering polymers such as polycarbon-ate,96 poly(acrylonitrile−butadiene−styrene),97 nylon,98 poly-oxymethylene99 can improve the HDT of PLA when there isgood compatibility between the blending polymers. Biodegrad-able ternary blends of PLA, PHBV and PBS with balancedstiffness and toughness attained HDT of ∼72 °C with 30 wt %PLA in the blend.100 Polyoxymethylene, POM, has a high HDTof 160 °C and it crystallizes fast with 70−80% crystallinitycontent.99 Nonetheless, having POM as a dispersed phase inPLA did not help in improving the HDT; to achieve desiredimprovements in HDT, POM should be the major phase in theblend as significant improvements were observed with phaseinversion, beyond 40%.99 Two different monomers, D-lactideand L-lactide, exist due to chirality of PLA. Homopolymers of D-and L-lactide (PDLA and PLLA) have faster crystallization andhigher melting points compared to common PLA, which has asmall percentage of D-lactide with atactic stereoregularity in amajority of L-lactide. A stereocomplex of two polymers withsame structure but different configuration has a meltingtemperature between 190 and 230 °C. Stereocomplex (SC)PLA can work as a nucleating agent promoting the formation ofordered structures. Various mixtures of PLLA and PDLA havebeen investigated101−104 and 50−50 blend with stereocomplexcrystalline structure improved the HDT to 150 °C. Never-theless, the high cost of PDLA is a bottleneck to stereo-complexation due to difficulty in production of D-lactide andhence PDLA. In a recent publication, Yin et al.105 used highmelting point PLLA homocrystallites (hPLLA) as a nucleatingagent to improve the thermomechanical properties of PLA.About a 20 °C difference in melting point between PLA

(4032D, Ingeo NatureWorks) and hPLLA helped to keephPLLA crystallites unmelted at the processing temperature of170 °C. Presence of 5% hPLLA accelerated PLLA crystal-lization at a remarkable rate compared to PLA containing thesame amount of talc and SC PDLA. PLLAs, with and withouttalc and PDLA, were noticed to deform in less than 2 min whenplaced in an oven at 70 °C for 5 min under a constant load of50 g, whereas PLLA with hPLLA crystallites showed no visibledeformation for 5 min, HDT/VST needs to be measured forany practical comparisons. This work, however, has contributedto new ways of tailoring the crystallization of PLLA withoutinvolving any post processing techniques and more importantlywithout compromising the biodegradable nature of thepolymer.Incorporation of nanoparticles into PLA is a relatively new

strategy that researchers are exploring to improve the heatresistance of PLA. Although addition of 2 wt % talc to PLAresulted in 3 °C HDT improvement,106 addition of 8 wt %montmorillonite (MMT) to PLA increased its HDT by 28°C.107 Layered silicate nanocomposites offer desired improve-ment in HDT only when the silicate layers of the clay areintercalated, stacked and well distributed in PLA matrix.108,109

Organomodified montmorillonite (OMMT) containing tri-methyl octadecyl ammonium cation at 7 wt % increased theHDT of PLA to ∼112 °C,109 10 wt % of organically modifiedsynthetic fluorine mica (OMSFM) increased the HDT of PLAto ∼117 °C,108 under a deflection load of 0.98 MPa.Dicyclopentadiene (DCPD) filled urea formaldehyde micro-capsules added to arrest the crack propagation and promoteself-healing in PLA was observed to act as a nucleating agent.110

Formation of stable cocontinuous morphologies of heatresistant polymer with the aid of well intercalated nanoparticleis a recently explored promising strategy to increase thecrystallinity. PLA phase interpenetrated with a continuousframework of nylon (30 wt %) and 3 phr OMMT showedresistance to temperature up to ∼160 °C (Figure 7); however,the HDT at 0.25 mm was the same as that of neat PLA.98

Figure 7. (a) Sample deflection recorded during creep tests for thesample PLA (squares), PA11 (diamonds), PLA70 (circles) andPLA70-C3 (triangles). The pictures show the samples PLA70 (b)and PLA70-C3 (c) at the end of the test, which is after thetemperature had reached ≈160 °C. [Reprinted from MacromolecularMaterials and Engineering, Vol. 299, A. Nuzzo, S. Coiai, S. C.Carroccio, N. Dintcheva, C. Gambarotti, G. Flippone. Heat resistantfully biobased nanocomposite blends based on poly(lactic acid), 31−40, Copyright 2013, with permission from Elsevier, License number:3794371367676.]



2907


■ PLA BLENDS WITH CONCURRENTIMPROVEMENTS IN TOUGHNESS AND HEATRESISTANCE

Having higher crystallinity in a semicrystalline polymersometimes negatively affects the impact strength, hence theinverse relationship between HDT and impact strength.Crystallites in the polymer can act as stress concentrators,thereby causing the stress acting on a small volume of thematerial to grow much higher than the average stress applied tothe entire sample.11 As a result, material breaks at a stress valuetypically less than the expected critical value.11 Shear yieldingand multiple crazing are also observed to decrease due to thepresence of crystallites. Unfortunately, little attention has beenpaid to achieving PLA blends with balanced toughness and heatresistance because it is still a challenge to control simulta-neously phase structure and matrix crystallization of blends.Perhaps the most useful work toward the search for such PLAblends are confined to using nonbiodegradable engineeringpolymers such as polycarbonate (PC) having high impactstrength and heat resistance. Several commercial PLA/PCblends111−114 have been developed, which are seen asenvironmentally benign materials containing over 50%biodegradable and renewably sourced polymer, PLA. Additionof over 40% PC to PLA has shown some promise in increasingthe impact strength of PLA; however, increasing the heatresistance of this blend has remained a challenge without theuse of compatibilizers. Hashima et al.96 developed a four-component super toughened blend containing PLA/PC/EGMA/SEBS (40/40/15/5) where SEBS toughened PLA inthe presence of EGMA and a further improvement intoughness and heat resistance was achieved through theincorporation of PC in the blend. Wang et al.115 investigatedthe effect of compatibilizers, epoxy (EP) resin and poly-(butylene succinate-co-lactate), PBSL for PLA/PC binaryblends. Combination of PBSL (10%) and EP (10%) in thepresence of catalyst, tetrabutyl ammonium bromide (TBAB,1%) in 50/50 blend of PLA/PC resulted in significant andconcurrent improvement in impact strength and heatresistance, the values are listed in Table 3. Chain extenderssuch as Joncryl and tetraglycidyl-4,4′-diaminodiphenylmethane(TGDDM) in combination with small percentage of acrylicimpact modifiers (BPM-520) have been used to improve theinterfacial interactions in PLA/PC blends.116,117 AlthoughPLA/PC blends showed phase separated morphology andthere were no sign of PLA−PC chain entanglements, interfacialconnection was established between the chain extender andblending polymers that increased the impact strength and heatresistance upon annealing.

■ PLA BIOCOMPOSITES: THE QUEST CONTINUESFOR HIGH PERFORMANCE

A biocomposite is a multiphase system, where plant-derivedfiber or mineral/synthetic filler is dispersed in the biopolymermatrix; either the matrix or the reinforcement phase isbiobased.118,119 Toughened PLA biocomposites have a fargreater potential for minimizing the limitations of PLA, hencemajor research efforts are being taken to develop andcommercialize them. Numerous research works have beenconducted in the field of PLA composites; however, most of theworks report only marginal improvements in impact strengthand HDT.120−125 The scope of this section has been limited toreviewing the research progress in injection molded PLA

biocomposites that used tough PLA blends as the matrix forincorporation of fibers and fillers. The increase in fracturetoughness observed for PLA biocomposite is not as high as inthe case of neat PLA. For instance, improving the toughness ofneat PLA by 20-fold might increase the fracture toughness ofthe composite by 3−6-fold only. Such poor translation ofmatrix toughness into the composite is due to the presence offiber, which is a constraint that suppresses elastic deformationof the matrix at the crack front. However, having a toughenedPLA blend as a starting material to incorporate fibers can be agood way to achieve a balanced performance. Furthermore, costof developing such blends can be offset to a certain extent byadding less expensive lignocellulosic fibers.PLA blended with tough biopolymers such as PBAT and

PCL have been explored as a matrix system to incorporatenatural fibers.126−128 In most cases, surface treatment hasproved to be effective in promoting interfacial interactionsbetween the relatively hydrophobic matrix and hydrophilicfiller. Having 30 wt % PBAT in PLA−PBAT/alkali treated sawdust (70/30) composites improved the unnotched Izod impactstrength by 50%.126 The surface of Kenaf treated with 2% silanecoupling agent was observed to become hydrophobic with theability to bind active groups of the polymer.127 Chemicalinteractions formed between hydroxyl, silanyl and alkoxygroups increased the impact strength of the PLA−PBATbiocomposites by 22%.127 By treating ramie fiber with silanecoupling agent (KH550) for in situ polymerized PLLA−PCLmatrix, tensile and impact strength increased from 12.14 MPa,30.0 J/m to 23.45 MPa, and 88.9 J/m, respectively.128

Incorporation of Cordenka fiber at 25 wt % has been shownto triple the impact strength of PLA without any toughcomponent being present; however, more research is neededtoward the effect of this fiber on HDT.129 Although addition of5 wt % lignin resulted in toughness improvement in PLLA130

from 8.2 to 12.5 kJ/m2, addition of 5 wt % of lignin-g-rubber-g-PDLA to PLLA exhibited a 7-fold enhancement in toughness(from stress−strain curves) compared with neat PLLA. This

Table 3. PLA Blends with Concurrent Improvement inImpact Strength and Heat Resistance

PLA blend formulations

notched Izodimpactstrength

HDT atspecified loadand deflection reference

PLA/PC/EGMA/SEBS (40/40/15/5)

0.45 MPa, 0.36mm

96

40 °C mold temperature 65.9 kJ/m2 88.6 °C80 °C mold temperature 63.3 kJ/m2 94.5 °C

PLA/PC/PBSL/EP/TBAB 0.45 MPa, 0.25mm

115

(50/50/5/0/0) 36.6 kJ/m2 94.8 °C(50/50/10/0/0) 65.1 kJ/m2 76.8 °C(50/50/10/10/0) 25.4 kJ/m2 82.5 °C(50/50/10/10/0.1) 34.0 kJ/m2 94.2 °C

PLA/PC with Joncryl orTGDDM (70/30/0.3phr)

1.82 MPa, 0.32mm

116

room temperaturemolding followed byannealing at 120 °C for6h

∼30 kJ/m2

(Joncryl)∼86 °C(Joncryl)

∼13 kJ/m2

(TGDDM)∼81 °C(TGDDM)

PLA/PC/BPM/Joncryl (85/10/5/0.3phr)

0.45 MPa, 0.32mm

sample molded at roomtemperature sampleannealed at 120 °C for6h

∼10 kJ/m2 ∼57 °C 117∼40 kJ/m2 ∼135 °C



2908


improvement is significant considering the copolymer containsonly 3.8 wt % of rubber.131 In the case of PLA/pine wood floorcomposites, notched Charpy impact strength was found toincrease gradually with increase in addition of wood floor andfurther increment in impact strength was achieved bytoughening the PLA matrix with styrene−butadiene−styrene(SBS) block copolymer.132 Use of reactive impact modifiers canform ductile interface between PLA and fiber, thus increasingthe resultant properties. With this hypothesis, ethylene acrylatecopolymer (Biomax) was used as an impact modifier (IM) forPLA/kenaf fiber (KF) composites.133 Impact strength andelongation at break increased, but only at a high loading level of40 wt % coupled with substantial reduction in tensile strengthand modulus. Liu et al.134 compared the toughening effect ofthree different reactive elastomers: polyoxyethylene graftedwith maleic anhydride (POE-g-MAH), ethylene−propylene−diene rubber grafted with maleic anhydride (EPDM-g-MAH)and ethylene−acrylate−glycidyl methacrylate copolymer(EAGMA) on PLA/basalt fiber composites. EAGMA at 20wt % imparted the most toughening effect by recording a valueof 33.7 KJ/m2 for unnotched charpy impact strength.134 Othermineral fillers such as barium sulfate135 and calciumsulfate136,137 have also been reported to increase the toughnessof the PLA composites. PLA based nanocomposites preparedby incorporation of nanofillers such as cellulose nanofibers andnanowhikers,138 nanocalcium carbonate,139−141 nano- andmesoporous silica,142−145 halloysite nanotubes,146,147 nano-clay147−150 and titanium oxide nanoparticles151 exhibitedgood improvement in toughness, mechanical and barrierproperties. However, none of these studies have reported theheat resistance of the developed materials. Although thehybridization of PLA with impact modifier and nanoparticlecan offer a toughened composite material, challenges exist inachieving good level of dispersion and distribution of thenanoparticles, its compatibility with the matrix and ease ofprocessing.On the flip side, a considerable number of research

investigations have shown the heat resistance of injectionmolded PLA biocomposites to increase with fiber/fillerincorporation in spite of affecting impact strength negatively.Crushed Kenaf fiber152 has been reported to significantlyincrease the HDT of injection molded PLA composites whenadded beyond 10 wt %, as shown in Figure 8.

Stiffness and HDT of the PLA were improved with theaddition of newspaper fibers/talc hybrid with drastic reductionto impact strength.153,154 HDT of the PP−PLA compositescould be increased to 120 °C with 30% Oat hull but in a majorphase of PP, with a drastic reduction in impact strength.155

Incorporating 30 wt % agricultural residues like soy stalk, cornstalk, wheat straw and their hybrids in PLA matrix did notprovide a desired increase in HDT. Only the modulus of thecomposites increased while impact strength remained essen-tially the same as virgin or neat PLA.156 In such cases, additionof fibers alone would not be sufficient to increase the HDT, acombinatorial approach of adding fibers, and use of high moldtemperature could be beneficial.By taking super toughened PLA blend developed based on

PEBA and EMAGMA25 as the matrix material, suchcombination of approaches have proved to be successful inachieving concurrent improvement in impact strength andHDT of PLA biocomposites.157 Although the impact strengthreduced as expected with addition of 10 wt % miscanthus, itwas still considerably higher than the neat PLA matrix,exhibiting 120 J/m (Figure 9). A high mold temperature of

110 °C was required to improve the HDT to 85 °C. A highlevel of crystallinity developed in the composites facilitatedeasier demolding of the samples and the total cycle time waslimited to 1 min including cooling, making it an industriallyfeasible technique.157

Promise of further significant improvement in properties andpossibilities of cost reduction with use of specialty additives andprocessing strategies continues to excite areas of compositematerial research.

■ CONCLUSIONS: QUO VADIS PLA RESEARCH?Biobased content is an important driver in development ofdurable biopolymer blends and composites. Many majorindustries and business operations are moving towardsustainable sourcing and use of renewable materials. Principles

Figure 8. Distortion temperature under load (DTUL) of PLA/crushedKenaf fiber. [Reprinted from Journal of Applied Polymer Science, Vol.100, S. Serizawa, K. Inoue, M. Iji. Kenaf fiber reinforced poly(lacticacid) used for electronic products, 618−624, Copyright 2006, withpermission from John Wiley and Sons, License number:3794390263152.]

Figure 9. Impact strength and HDT of PLA biocomposites with andwithout nucleating agent (NA) molded at different mold temperaturesand injection cycle times. PLA blend/MS (90/10) at (A) 30 °C, 30 s;(B) 110 °C, 60 s. PLA blend/MS/NA (89/10/1) at (C) 30 °C, 30 s;(D) 60 °C, 60 s; (E) 90 °C, 60 s; (F) 110 °C, 60 s; (G) 120 °C, 60 s.[Reprinted with permission from ACS Applied Materials andInterfaces, Vol. 7, V. Nagarajan, K. Zhang, M. Misra, A. K. Mohanty.Overcoming the Fundamental Challenges in Improving the ImpactStrength and Crystallinity of PLA Biocomposites: Influence ofNucleating Agent and Mold Temperature, 11203−11214, Copyright2015, American Chemical Society.]



2909


of green chemistry, sustainability and engineering are beingintegrated in the R&D to achieve a good balance of productperformance and environmental friendliness. Extensive researcheffort has been devoted to developing PLA blends andbiocomposites with desirable morphology and crystallinity fordurable applications. However, achieving feasible and econom-ical manufacturing processes for mass production of suchmaterials has been quite a challenge. Enhancing matrixcrystallization has been reported to be an effective strategytoward creating heat resistant PLA blends. Both thermalannealing and nucleating agent induced matrix crystallizationcould significantly enhance heat resistance of the blends, whilemaintaining or further increasing the toughening efficiency.However, increasing matrix crystallinity alone cannot guaranteetoughness improvement in most cases because suitablemorphology must be obtained for PLA matrix to undergoplastic deformation. Specifically, optimum elastomer content,particle size and interparticle distance are identified to be themost important deciding factors for toughening PLA. Reactivecompatibilization along with dynamic vulcanization techniqueshave been shown to tailor successfully the morphology of the

blends. Recent explorations have revealed that a uniquenetwork-like or cocontinuous morphology unevenly distributedin the matrix to exhibits much better super tougheningcompared to the common sea-island morphology containingwell dispersed spherical elastomer particles in a polymer matrix.The network-like distribution of the elastomer particles canfacilitate the percolation of the stress field as the plasticdeformation of the matrix around them at lower content.Adding inorganic nanoparticles with strong self-networkingcapability in polymer melts has been shown to assist in thetransition of morphology from immiscible sea-island structureto the network-like, cocontinuous structure.Approach of adding nucleating agents and natural fiber in

combination with a high molding temperature to a supertoughened PLA blend has resulted in composites withconcurrent improvements in both the impact strength andHDT. Epoxy based mold with low thermal conductivity hasdemonstrated significant advantages over conventional steelmolds. Future work is needed to shed light on the effect ofapplying an intense shear flow field through oscillation shearinjection molding (OSIM) to trigger dramatic enhancement of

Table 4. Commercial Toughened and/or Heat Resistant PLA Formulations for Durable End Use Applications

company grade impact strengthHDT at 0.45 MPa

(°C)

tensilestrength(MPa) comment reference

RTP Co. RTP 2099 X Series 694−854 J/m(notched Izod)

96−124 48−52 PLA−PC blends 111

43−187 J/m(notched Izod)

91−160 38−114 PLA with glass fibers or talc

PolyOneCorporation

reSound FR 620 J/m (notchedIzod)

112 PLA−engineering plastic blend 112, 158

Kingfa Sci & TechCo., Ltd.

Ecopond AFR-97 55 kJ/m2 (notchedIzod)

84 (1.82 MPa) 52 PLA−PC and PLA−ABS blends, >40%biobased

113

UGM ABS Ltd. ECO PELLET LA Series 12−27 kJ/m2

(notched Charpy)78−92 48−58 PLA−PC and PLA−ABS blends 114

InterfacialSolutions

deTerra XP698 880 J/m (notchedCharpy)

38 PLA blend, compostable, >85%biobased

159

Teknor ApexCompany Inc.

Terraloy 3D-40040 Series 267 J/m (unnotchedIzod)

75 PLA blend, extrusion filament for use in3D printers

160

Corbion Carbion Purac(development grades)

5−23 kJ/m2 (notchedCharpy)

85−120 30−45 PLLA/PDLA blends with and withouttalc

161

Sukano Polymers Sukano Bioloy 003, 004NC001

60−70 kJ/m2

(unnotchedCharpy)

50−90 35−50 PLA blend, compostable (EN13432),35−97% biobased

162

Toray IndustriesInc.

ECODEAR V751X53,V751X52

21−24 kJ/m2

(notched Charpy)81 49−52 PLA blend 163

Unitika Ltd. Terramac TE 7000, 7307,7300, 8210, 8300

2.0−4.0 kJ/m2

(notched Charpy)110−140 50−70 compostable (ISO 14855) 164

NatureWorksLLC

Ingeo 3100HP, 3260HP 16−32 J/m (notchedIzod)

149−151 63−65 PLA with nucleating agent, moldtemperature of 120 °C

165

Supla Co., Ltd. SUPLA 135 150 PLA blend (90% PLA) 166SK Chemicals Ecoplan-Dura 40 J/m (notched

Izod)100 42 compostable, 80−100% biobased 167

FKuR Plastics Bio-Flex F 6513 3 kJ/m2 (notchedCharpy)

68−130 32 PLA blend, HDT of up to 130 °C byappropriate processing

168

NaturePlast PLI 013, PLE 013, hightemperature

89 kJ/m2 (unnotchedCharpy)

123−133 injection and extrusion grades 169

Barlog Plastics KEBACOMP FE 120204 5 kJ/m2 (notchedIzod)

100 compostable (ISO 13432) 170

EcolBiotechCo.,Ltd.

EcolGreen EGP Series 382−477 J/m(unnotched Izod)

62−72 31.7−45.5 nanocomposite with 12 differentadditives, compostable

171

GEHR Plastics ECOGEHR PLA-L 59.8 kJ/m2 (notchedIzod)

58.4 (VST) 49.5 PLA blend with lignin and fatty acid,compostable, >80% biobased

172

WinGramIndustrial CoLtd.

Ecoplant HRS heat resistance upto 120 °C

compostable (ISO 14855) 173

Teijin Ltd. Biofront grade J20, J201,L201

highly heatresistant

stereocomplex PLA melting point of 210°C

174



2910


crystallization kinetics of PLA. Durable blends of PLA/PC have

shown promising properties with simultaneous improvements

in impact and heat resistance in the presence of compatibilizer

and chain extenders. Thermally stable fillers like biochar from

different fiber sources can be added to such highly toughened

engineering plastic based blends. Properties of these

composites can be tailored to have enhanced performance

with affordable cost to performance ratios for industrial

applications. Much research is needed in the direction of

developing such high performance PLA composites. Future

technological development may focus on the emergence and

exploitation of such renewable carbon based fillers for PLA

materials to serve the need of the era for lightweight, carbon

neutral durable materials.Many PLA formulations with improved toughness and/or

HDT are available in the market for durable applications, as

summarized in Table 4. Most of the impact modifiers used are

high molecular weight polymeric materials with a flexible

component such as acrylic rubber, and hence the problem of

migration is not a concern. However, these impact modifiers

are typically nonbiodegradable. Minimal use of even 5% may

prevent the products from being certified compostable due to

the stringent requirements of the American and European

compostability standards. ASTM D6400-12 describes that

organic constituents present at concentrations of less than 1%

do not need to demonstrate biodegradability. However, the

sum of such unproven constituents should not exceed 5%.175

Finally, one might ask when and where durable PLA materials

may find application. Before answering, we should consider the

evolution of bioplastics industry, which has had multiple shifts

in direction. The first phase was focused on biodegradable and/

or compostable characteristics, primarily intended for single use

packaging applications. The second phase offered compostable

and renewable resource based alternative for nondegradable

petroleum based commodity plastics. The current trend is the

development of durable bioplastics. Commercialization argu-

ably marks the success of research and development efforts, but

the timeline should not be compared to that of mature

technologies. Although PLA based materials are aimed for high

volume applications in interior automotive parts and other

structural and semistructural applications, they will initially find

application in consumer goods such as cell phone casings,

personal and home care products.

■ AUTHOR INFORMATION

Corresponding Author*A. K. Mohanty. E-mail address: [email protected]. Tel.:+1-519-824-4120 ext. 56664. Fax: +1-519-763-8933

Notes

The authors declare no competing financial interest.

Biographies

Ms. Vidhya Nagarajan is currently a Ph.D. candidate in BiologicalEngineering, Bioproducts Discovery & Development Centre (BDDC)at the University of Guelph, ON, Canada. Vidhya graduated with aMaster’s degree from University of Guelph in 2012. She is a recipientof highly qualified personnel (HQP) scholarship from OntarioMinistry of Agriculture, Food and Rural Affairs (OMAFRA). She isalso a HQP of the AUTO21 Network of Centers of Excellenceprogram, a national research initiative supported by the Governmentof Canada. She holds a Bachelor’s degree in Polymer Technology fromCrescent Engineering College, Anna University, India. The primaryfocus of her research is processing and characterization of biopolymerblends and composites for sustainable industrial applications. She haspublished 6 peer reviewed journal articles, 1 patent application (filed)and coauthored 2 book chapters.

Dr. Amar Mohanty, Professor and Premier's Research Chair inBiomaterials and Transportation, is the Director of the BioproductsDiscovery & Development Centre (BDDC) at the University ofGuelph, ON, Canada. Dr. Mohanty's research interests include naturalfiber composites, biobased and biodegradable polymers, biorefinery,biocarbon reinforcement, reactive extrusion and utilization of biofueland biomass coproducts. He has more than 600 publications to hiscredit, including 274 peer-reviewed journal articles (including acceptedmanuscripts), four edited books, 20 book chapters, and 40 patentsawarded/applied. He has received distinguished awards for his work,including the “Andrew Chase Forest Product Award” from theAmerican Institute of Chemical Engineers and most recently the“Lifetime Achievement Award”, from the BioEnvironmental PolymerSociety (BEPS) in the year 2015. Dr. Mohanty holds the Alexandervon Humboldt Fellowship at the Technical University, Berlin. HisResearchGate score is 44.43, higher than 97.5% of the 7 millionResearchGate members. His research impact resulted in 16 962citations with h-index of 62 (Google Scholar, as of April 2016).



2911

mailto:[email protected]


Dr. Manjusri Misra is a Professor in the School of Engineering andholds a joint appointment in the Department of Plant Agriculture atthe University of Guelph, ON, Canada. Dr. Misra’s current research isprimarily focused on novel biobased polymers, and compositematerials from agricultural and forestry resources for the sustainablebioeconomy; and application of nanotechnology in materials uses. Shehas coauthored more than 450 publications, including 250+ peer-reviewed journal papers, 24 book chapters, and 15 granted patents. Shewas an editor of the CRC Press volume, “Natural Fibers, Biopolymersand Biocomposites,” Taylor & Francis Group, Boca Raton, FL (2005);American Scientific Publishers volume “Packaging Nanotechnology”,Valencia, California (2009), and “Polymer Nanocomposites”, Springer(2014). She was the chief editor of “Biocomposites: Design andMechanical Performance” Woodhead Publishing (2015). She was the2009 President of the BioEnvironmental Polymer Society (BEPS). Sheis one of the Associate Editors of the journal “Advanced ScienceLetters”. Dr. Misra received the prestigious “Jim Hammer MemorialAward” from the BioEnvironmental Polymer Society in 2012.

■ ACKNOWLEDGMENTS

We gratefully acknowledge the financial support from (1) theOntario Ministry of Agriculture, Food, and Rural Affairs(OMAFRA)- University of Guelph Bioeconomy-IndustrialUses Theme (Project # 200425); (2) the Ontario Ministry ofEconomic Development and Innovation (MEDI), OntarioResearch Fund, Research Excellence Round 4 program (ORF-RE04) (Project # 050231 and 050289); and (3) the NaturalSciences and Engineering Research Council (NSERC) CanadaDiscovery Grants (Project # 400322) and Networks of Centresof Excellence (NCE) AUTO21 Program (Project # 460372).

■ REFERENCES(1) Drumright, R. E.; Gruber, P. R.; Henton, D. E. Polylactic acidtechnology. Adv. Mater. 2000, 12 (23), 1841−1846.(2) Auras, R.; Harte, B.; Selke, S. An overview of polylactides aspackaging materials. Macromol. Biosci. 2004, 4 (9), 835−864.(3) Bioplastics facts and figures. http://docs.european-bioplastics.org/2016/publications/EUBP_facts_and_figures.pdf (accessed Janu-ary 2016).(4) Kyoto Protocol. http://unfccc.int/kyoto_protocol/items/2830.php (accessed December 30, 2016).(5) As Kyoto Protocol turns 10, UN says ‘first critical step’ musttrigger new 2015 emissions-curbing deal. http://www.un.org/apps/news/story.asp?NewsID=50099#.Vw-FMtL2Y3E (accessed December30, 2015).(6) United Nations conference on climate change. http://www.cop21.gouv.fr/en/ (accessed December 30, 2015).(7) Kuzuhara, Y. Biomass Nippon StrategyWhy “Biomass Nippon”now? Biomass Bioenergy 2005, 29 (5), 331−335.

(8) Krishnan, S.; Pandey, P.; Mohanty, S.; Nayak, S. K. Tougheningof Polylactic Acid: An Overview of Research Progress. Polym.-Plast.Technol. Eng. 2015, DOI: 10.1080/03602559.2015.1098698.(9) Odent, J.; Raquez, J.; Dubois, P. Highly Toughened Polylactide-Based Materials through Melt-Blending Techniques. In BiodegradablePolyesters; Fakirov, S., Ed.; Wiley-VCH Verlag GmbH & Co. KGaA:Berlin, 2015.(10) Zeng, J.; Li, K.; Du, A. Compatibilization strategies in poly(lacticacid)-based blends. RSC Adv. 2015, 5 (41), 32546−32565.(11) Kfoury, G.; Raquez, J.; Hassouna, F.; Odent, J.; Toniazzo, V.;Ruch, D.; Dubois, P. Recent advances in high performancepoly(lactide): From “green” plasticization to super-tough materialsvia (reactive) compounding. Front. Chem. 2013, 1 (32), 1−46.(12) Liu, H.; Zhang, J. Research progress in toughening modificationof poly(lactic acid). J. Polym. Sci., Part B: Polym. Phys. 2011, 49 (15),1051−1083.(13) Anderson, K. S.; Schreck, K. M.; Hillmyer, M. A. Tougheningpolylactide. Polym. Rev. 2008, 48 (1), 85−108.(14) Rasal, R. M.; Janorkar, A. V.; Hirt, D. E. Poly(lactic acid)modifications. Prog. Polym. Sci. 2010, 35 (3), 338−356.(15) Wu, S. Chain structure, phase morphology, and toughnessrelationships in polymers and blends. Polym. Eng. Sci. 1990, 30 (13),753−761.(16) Wu, S. Control of intrinsic brittleness and toughness ofpolymers and blends by chemical structure: a review. Polym. Int. 1992,29 (3), 229−247.(17) Wu, S. Formation of dispersed phase in incompatible polymerblends: Interfacial and rheological effects. Polym. Eng. Sci. 1987, 27 (5),335−343.(18) Wu, S. Phase structure and adhesion in polymer blends: acriterion for rubber toughening. Polymer 1985, 26 (12), 1855−1863.(19) Perkins, W. G. Polymer toughness and impact resistance. Polym.Eng. Sci. 1999, 39 (12), 2445.(20) Harada, M.; Ohya, T.; Iida, K.; Hayashi, H.; Hirano, K.; Fukuda,H. Increased impact strength of biodegradable poly(lactic acid)/poly(butylene succinate) blend composites by using isocyanate as areactive processing agent. J. Appl. Polym. Sci. 2007, 106 (3), 1813−1820.(21) Oyama, H. T. Super-tough poly(lactic acid) materials: Reactiveblending with ethylene copolymer. Polymer 2009, 50 (3), 747−751.(22) Su, Z.; Li, Q.; Liu, Y.; Hu, G.; Wu, C. Compatibility and phasestructure of binary blends of poly(lactic acid) and glycidylmethacrylate grafted poly(ethylene octane). Eur. Polym. J. 2009, 45(8), 2428−2433.(23) Feng, Y.; Hu, Y.; Yin, J.; Zhao, G.; Jiang, W. High impactpoly(lactic acid)/poly(ethylene octene) blends prepared by reactiveblending. Polym. Eng. Sci. 2013, 53 (2), 389−396.(24) Han, L.; Han, C.; Dong, L. Morphology and properties of thebiosourced poly(lactic acid)/poly(ethylene oxide-b-amide-12) blends.Polym. Compos. 2013, 34 (1), 122−130.(25) Zhang, K.; Nagarajan, V.; Misra, M.; Mohanty, A. K.Supertoughened Renewable PLA Reactive Multiphase Blends System:Phase Morphology and Performance. ACS Appl. Mater. Interfaces 2014,6 (15), 12436−12448.(26) Vachon, A.; Pepin, K.; Beland, O.; Monfette, W. G.; Rochette,A.; Vuillaume, P. Y. Thermal, Mechanical and MorphologicalProperties of Binary and Ternary PLA Blends Containing a Poly(etherester) Elastomer. J. Biobased Mater. Bioenergy 2015, 9 (2), 205−217.(27) Zhou, L.; Zhao, G.; Feng, Y.; Yin, J.; Jiang, W. Tougheningpolylactide with polyether-block-amide and thermoplastic starchacetate: Influence of starch esterification degree. Carbohydr. Polym.2015, 127 (2015), 79−85.(28) Ojijo, V.; Ray, S. S.; Sadiku, R. Toughening of biodegradablepolylactide/poly(butylene succinate-co-adipate) blends via in situreactive compatibilization. ACS Appl. Mater. Interfaces 2013, 5 (10),4266−4276.(29) Ojijo, V.; Ray, S. S. Super toughened biodegradable polylactideblends with non-linear copolymer interfacial architecture obtained viafacile in-situ reactive compatibilization. Polymer 2015, 80, 1−17.



2912

http://docs.european-bioplastics.org/2016/publications/EUBP_facts_and_figures.pdf

http://docs.european-bioplastics.org/2016/publications/EUBP_facts_and_figures.pdf

http://unfccc.int/kyoto_protocol/items/2830.php

http://unfccc.int/kyoto_protocol/items/2830.php

http://www.un.org/apps/news/story.asp?NewsID=50099#.Vw-FMtL2Y3E

http://www.un.org/apps/news/story.asp?NewsID=50099#.Vw-FMtL2Y3E

http://www.cop21.gouv.fr/en/

http://www.cop21.gouv.fr/en/

http://dx.doi.org/10.1080/03602559.2015.1098698


(30) Dong, W.; Zou, B.; Yan, Y.; Ma, P.; Chen, M. Effect of Chain-Extenders on the Properties and Hydrolytic Degradation Behavior ofthe Poly(lactide)/Poly(butylene adipate-co-terephthalate) Blends. Int.J. Mol. Sci. 2013, 14 (10), 20189−20203.(31) Meng, B.; Deng, J.; Liu, Q.; Wu, Z.; Yang, W. Transparent andductile poly(lactic acid)/poly(butyl acrylate) (PBA) blends: structureand properties. Eur. Polym. J. 2012, 48 (1), 127−135.(32) Zhang, G.; Zhang, J.; Wang, S.; Shen, D. Miscibility and phasestructure of binary blends of polylactide and poly(methyl meth-acrylate). J. Polym. Sci., Part B: Polym. Phys. 2003, 41 (1), 23−30.(33) Ye, S.; Ting Lin, T.; Weei Tjiu, W.; Kwan Wong, P.; He, C.Rubber toughening of poly(lactic acid): Effect of stereocomplexformation at the rubber-matrix interface. J. Appl. Polym. Sci. 2013, 128(4), 2541−2547.(34) Zhang, H.; Liu, N.; Ran, X.; Han, C.; Han, L.; Zhuang, Y.; Dong,L. Toughening of polylactide by melt blending with methylmethacrylate−butadiene−styrene copolymer. J. Appl. Polym. Sci.2012, 125 (S2), E550−E561.(35) Sun, S.; Zhang, M.; Zhang, H.; Zhang, X. Polylactide tougheningwith epoxy-functionalized grafted acrylonitrile−butadiene−styreneparticles. J. Appl. Polym. Sci. 2011, 122 (5), 2992−2999.(36) Song, X.; Chen, Y.; Xu, Y.; Wang, C. Study on Tough Blends ofPolylactide and Acrylic Impact Modifier. BioResources 2014, 9 (2),1939−1952.(37) Li, W.; Zhang, Y.; Wu, D.; Li, Z.; Zhang, H.; Dong, L.; Sun, S.;Deng, Y.; Zhang, H. The Effect of Core−Shell Ratio of Acrylic ImpactModifier on Toughening PLA. Adv. Polym. Technol. 2015, DOI:10.1002/adv.21632.(38) Kfoury, G.; Raquez, J.; Hassouna, F.; Leclere, P.; Toniazzo, V.;Ruch, D.; Dubois, P. Toughening of poly(lactide) using polyethyleneglycol methyl ether acrylate: Reactive versus physical blending. Polym.Eng. Sci. 2015, 55 (6), 1408−1419.(39) Ge, X.; George, S.; Law, S.; Sain, M. Mechanical properties andmorphology of polylactide composites with acrylic impact modifier. J.Macromol. Sci., Part B: Phys. 2011, 50 (11), 2070−2083.(40) Liang, H.; Hao, Y.; Bian, J.; Zhang, H.; Dong, L.; Zhang, H.Assessment of miscibility, crystallization behaviors, and tougheningmechanism of polylactide/acrylate copolymer blends. Polym. Eng. Sci.2015, 55 (2), 386−396.(41) Taib, R.; Ghaleb, Z.; Mohd Ishak, Z. Thermal, mechanical, andmorphological properties of polylactic acid toughened with an impactmodifier. J. Appl. Polym. Sci. 2012, 123 (5), 2715−2725.(42) Liu, H.; Chen, F.; Liu, B.; Estep, G.; Zhang, J. Super toughenedpoly(lactic acid) ternary blends by simultaneous dynamic vulcanizationand interfacial compatibilization. Macromolecules 2010, 43 (14), 6058−6066.(43) Liu, H.; Song, W.; Chen, F.; Guo, L.; Zhang, J. Interaction ofmicrostructure and interfacial adhesion on impact performance ofpolylactide (PLA) ternary blends. Macromolecules 2011, 44 (6), 1513−1522.(44) Liu, H.; Guo, L.; Guo, X.; Zhang, J. Effects of reactive blendingtemperature on impact toughness of poly(lactic acid) ternary blends.Polymer 2012, 53 (2), 272−276.(45) Liu, H.; Guo, X.; Song, W.; Zhang, J. Effects of metal ion typeon ionomer-assisted reactive toughening of poly(lactic acid). Ind. Eng.Chem. Res. 2013, 52 (13), 4787−4793.(46) Song, W.; Liu, H.; Chen, F.; Zhang, J. Effects of ionomercharacteristics on reactions and properties of poly(lactic acid) ternaryblends prepared by reactive blending. Polymer 2012, 53 (12), 2476−2484.(47) Lu, X.; Wei, X.; Huang, J.; Yang, L.; Zhang, G.; He, G.; Wang,M.; Qu, J. Supertoughened Poly(lactic acid)/Polyurethane BlendMaterial by in Situ Reactive Interfacial Compatibilization via DynamicVulcanization. Ind. Eng. Chem. Res. 2014, 53 (44), 17386−17393.(48) Fang, H.; Jiang, F.; Wu, Q.; Ding, Y.; Wang, Z. SupertoughPolylactide Materials Prepared through In Situ Reactive Blending withPEG-Based Diacrylate Monomer. ACS Appl. Mater. Interfaces 2014, 6(16), 13552−13563.

(49) Chen, Y.; Yuan, D.; Xu, C. Dynamically vulcanized biobasedpolylactide/natural rubber blend material with continuous cross-linkedrubber phase. ACS Appl. Mater. Interfaces 2014, 6 (6), 3811−3816.(50) Wang, Y.; Chen, K.; Xu, C.; Chen, Y. Supertoughened BiobasedPoly(lactic acid)−Epoxidized Natural Rubber Thermoplastic Vulcan-izates: Fabrication, Co-continuous Phase Structure, Interfacial in SituCompatibilization, and Toughening Mechanism. J. Phys. Chem. B2015, 119 (36), 12138−12146.(51) Yuan, D.; Xu, C.; Chen, Z.; Chen, Y. Crosslinked bicontinuousbiobased polylactide/natural rubber materials: Super toughness,“net-like”-structure of NR phase and excellent interfacial adhesion. Polym.Test. 2014, 38, 73−80.(52) Yuan, D.; Chen, Z.; Xu, C.; Chen, K.; Chen, Y. Fully BiobasedShape Memory Material Based on Novel Cocontinuous Structure inPoly(Lactic Acid)/Natural Rubber TPVs Fabricated via Peroxide-Induced Dynamic Vulcanization and in Situ Interfacial Compatibiliza-tion. ACS Sustainable Chem. Eng. 2015, 3 (11), 2856−2865.(53) Liu, G.; He, Y.; Zeng, J.; Li, Q.; Wang, Y. Fully biobased andsupertough polylactide-based thermoplastic vulcanizates fabricated byperoxide-induced dynamic vulcanization and interfacial compatibiliza-tion. Biomacromolecules 2014, 15 (11), 4260−4271.(54) Kang, H.; Hu, X.; Li, M.; Zhang, L.; Wu, Y.; Ning, N.; Tian, M.Novel biobased thermoplastic elastomer consisting of syntheticpolyester elastomer and polylactide by in situ dynamical crosslinkingmethod. RSC Adv. 2015, 5 (30), 23498−23507.(55) Ma, P.; Xu, P.; Liu, W.; Zhai, Y.; Dong, W.; Zhang, Y.; Chen, M.Bio-based poly(lactide)/ethylene-co-vinyl acetate thermoplastic vul-canizates by dynamic crosslinking: structure vs. property. RSC Adv.2015, 5 (21), 15962−15968.(56) Zhao, Q.; Ding, Y.; Yang, B.; Ning, N.; Fu, Q. Highly efficienttoughening effect of ultrafine full-vulcanized powdered rubber onpoly(lactic acid) (PLA). Polym. Test. 2013, 32 (2), 299−305.(57) Joziasse, C.; Topp, M.; Veenstra, H.; Grijpma, D.; Pennings, A.Supertough poly(lactide) s. Polym. Bull. 1994, 33 (5), 599−605.(58) Odent, J.; Leclere, P.; Raquez, J.; Dubois, P. Toughening ofpolylactide by tailoring phase-morphology with P [CL-co-LA] randomcopolyesters as biodegradable impact modifiers. Eur. Polym. J. 2013, 49(4), 914−922.(59) Odent, J.; Raquez, J.; Duquesne, E.; Dubois, P. Randomaliphatic copolyesters as new biodegradable impact modifiers forpolylactide materials. Eur. Polym. J. 2012, 48 (2), 331−340.(60) Odent, J.; Habibi, Y.; Raquez, J.; Dubois, P. Ultra-toughpolylactide-based materials synergistically designed in the presence ofrubbery ε-caprolactone-based copolyester and silica nanoparticles.Compos. Sci. Technol. 2013, 84, 86−91.(61) Li, X.; Kang, H.; Shen, J.; Zhang, L.; Nishi, T.; Ito, K.; Zhao, C.;Coates, P. Highly toughened polylactide with novel sliding graftcopolymer by in situ reactive compatibilization, crosslinking and chainextension. Polymer 2014, 55 (16), 4313−4323.(62) Li, Y.; Shimizu, H. Toughening of polylactide by melt blendingwith a biodegradable poly(ether) urethane elastomer. Macromol. Biosci.2007, 7 (7), 921−928.(63) Liu, G.; He, Y.; Zeng, J.; Xu, Y.; Wang, Y. In situ formedcrosslinked polyurethane toughened polylactide. Polym. Chem. 2014, 5(7), 2530−2539.(64) Liu, Z.; Luo, Y.; Bai, H.; Zhang, Q.; Fu, Q. Remarkablyenhanced impact toughness and heat resistance of poly(L-lactide)/thermoplastic polyurethane blends by constructing stereocomplexcrystallites in the matrix. ACS Sustainable Chem. Eng. 2016, 4 (1),111−120.(65) Ma, P.; Hristova-Bogaerds, D.; Goossens, J.; Spoelstra, A.;Zhang, Y.; Lemstra, P. Toughening of poly(lactic acid) by ethylene-co-vinyl acetate copolymer with different vinyl acetate contents. Eur.Polym. J. 2012, 48 (1), 146−154.(66) Likittanaprasong, N.; Seadan, M.; Suttiruengwong, S. Impactproperty enhancement of poly(lactic acid) with different flexiblecopolymers. IOP Conf. Ser.: Mater. Sci. Eng. 2015, 87, 012069.



2913

http://dx.doi.org/10.1002/adv.21632


(67) Schindler, A.; Harper, D. Polylactide. II. Viscosity−molecularweight relationships and unperturbed chain dimensions. J. Polym. Sci.,Polym. Chem. Ed. 1979, 17 (8), 2593−2599.(68) Chen, T. K.; Jan, Y. H. Fracture mechanism of toughened epoxyresin with bimodal rubber-particle size distribution. J. Mater. Sci. 1992,27, 111−121.(69) Bagheri, R.; Williams, M.; Pearson, R. Use of surface modifiedrecycled rubber particles for toughening of epoxy polymers. Polym.Eng. Sci. 1997, 37 (2), 245−251.(70) Ma, Q.; Georgiev, G.; Cebe, P. Constraints in semicrystallinepolymers: Using quasi-isothermal analysis to investigate the mecha-nisms of formation and loss of the rigid amorphous fraction. Polymer2011, 52 (20), 4562−4570.(71) Arnoult, M.; Dargent, E.; Mano, J. Mobile amorphous phasefragility in semi-crystalline polymers: Comparison of PET and PLLA.Polymer 2007, 48 (4), 1012−1019.(72) Wang, L.; Wang, Y.; Huang, Z.; Weng, Y. Heat resistance,crystallization behavior, and mechanical properties of polylactide/nucleating agent composites. Mater. Eng. 2015, 66, 7−15.(73) Biron, M. Thermoplastics and thermoplastic composites; Elsevier:Amsterdam, 2012.(74) Brydson, J. A. Plastic Materials, 7 ed.; Butterworth-Heinemann:Oxford, 2000.(75) Yu, F.; Liu, T.; Zhao, X.; Yu, X.; Lu, A.; Wang, J. Effects of talcon the mechanical and thermal properties of polylactide. J. Appl. Polym.Sci. 2012, 125 (S2), E99−E109.(76) Tsuji, H.; Takai, H.; Fukuda, N.; Takikawa, H. Non-IsothermalCrystallization Behavior of Poly(L-lactic acid) in the Presence ofVarious Additives. Macromol. Mater. Eng. 2006, 291 (4), 325−335.(77) Tang, Z.; Zhang, C.; Liu, X.; Zhu, J. The crystallization behaviorand mechanical properties of polylactic acid in the presence of a crystalnucleating agent. J. Appl. Polym. Sci. 2012, 125 (2), 1108−1115.(78) Barrau, S.; Vanmansart, C.; Moreau, M.; Addad, A.; Stoclet, G.;Lefebvre, J.; Seguela, R. Crystallization behavior of carbon nanotube−polylactide nanocomposites. Macromolecules 2011, 44 (16), 6496−6502.(79) Han, Q.; Wang, Y.; Shao, C.; Zheng, G.; Li, Q.; Shen, C.Nonisothermal crystallization kinetics of biodegradable poly(lacticacid)/zinc phenylphosphonate composites. J. Compos. Mater. 2014, 48(22), 2737−2746.(80) Bai, H.; Zhang, W.; Deng, H.; Zhang, Q.; Fu, Q. Control ofcrystal morphology in poly(L-lactide) by adding nucleating agent.Macromolecules 2011, 44 (6), 1233−1237.(81) Song, P.; Wei, Z.; Liang, J.; Chen, G.; Zhang, W. Crystallizationbehavior and nucleation analysis of poly(l-lactic acid) with amultiamide nucleating agent. Polym. Eng. Sci. 2012, 52 (5), 1058−1068.(82) Gui, Z.; Lu, C.; Cheng, S. Comparison of the effects ofcommercial nucleation agents on the crystallization and meltingbehaviour of polylactide. Polym. Test. 2013, 32 (1), 15−21.(83) Xu, T.; Wang, Y.; Han, Q.; He, D.; Li, Q.; Shen, C.Nonisothermal crystallization kinetics of poly(lactic acid) nucleatedwith a multiamide nucleating agent. J. Macromol. Sci., Part B: Phys.2014, 53 (10), 1680−1694.(84) Kawamoto, N.; Sakai, A.; Horikoshi, T.; Urushihara, T.; Tobita,E. Physical and mechanical properties of poly(l-lactic acid) nucleatedby dibenzoylhydrazide compound. J. Appl. Polym. Sci. 2007, 103 (1),244−250.(85) Xu, T.; Zhang, A.; Zhao, Y.; Han, Z.; Xue, L. Crystallizationkinetics and morphology of biodegradable poly(lactic acid) with ahydrazide nucleating agent. Polym. Test. 2015, 45, 101−106.(86) Liao, R.; Yang, B.; Yu, W.; Zhou, C. Isothermal coldcrystallization kinetics of polylactide/nucleating agents. J. Appl.Polym. Sci. 2007, 104 (1), 310−317.(87) Liang, J.; Zhou, L.; Tang, C.; Tsui, C. Crystalline properties ofpoly(L-lactic acid) composites filled with nanometer calciumcarbonate. Composites, Part B 2013, 45 (1), 1646−1650.

(88) Qiu, Z.; Li, Z. Effect of orotic acid on the crystallization kineticsand morphology of biodegradable poly(L-lactide) as an efficientnucleating agent. Ind. Eng. Chem. Res. 2011, 50 (21), 12299−12303.(89) Kawamoto, N.; Sakai, A.; Horikoshi, T.; Urushihara, T.; Tobita,E. Nucleating agent for poly(L-lactic acid)An optimization ofchemical structure of hydrazide compound for advanced nucleationability. J. Appl. Polym. Sci. 2007, 103 (1), 198−203.(90) Park, S. D.; Todo, M.; Arakawa, K.; Koganemaru, M. Effect ofcrystallinity and loading-rate on mode I fracture behavior of poly(lacticacid). Polymer 2006, 47 (4), 1357−1363.(91) Nascimento, L.; Gamez-Perez, J.; Santana, O.; Velasco, J. I.;Maspoch, M. L.; Franco-Urquiza, E. Effect of the recycling andannealing on the mechanical and fracture properties of poly(lacticacid). J. Polym. Environ. 2010, 18 (4), 654−660.(92) Harris, A. M.; Lee, E. C. Improving mechanical performance ofinjection molded PLA by controlling crystallinity. J. Appl. Polym. Sci.2008, 107 (4), 2246−2255.(93) Li, H.; Huneault, M. A. Effect of nucleation and plasticization onthe crystallization of poly(lactic acid). Polymer 2007, 48 (23), 6855−6866.(94) Vadori, R.; Mohanty, A. K.; Misra, M. The Effect of MoldTemperature on the Performance of Injection Molded Poly(lacticacid)-Based Bioplastic. Macromol. Mater. Eng. 2013, 298 (9), 981−990.(95) Tabi, T.; Kovacs, N.; Sajo, I.; Czigany, T.; Hajba, S.; Kovacs, J.Comparison of thermal, mechanical and thermomechanical propertiesof poly(lactic acid) injection-molded into epoxy-based RapidPrototyped (PolyJet) and conventional steel mold. J. Therm. Anal.Calorim. 2016, 123 (1), 349−361.(96) Hashima, K.; Nishitsuji, S.; Inoue, T. Structure-properties ofsuper-tough PLA alloy with excellent heat resistance. Polymer 2010, 51(17), 3934−3939.(97) Vadori, R. Bio-Acrylonitrile Butadiene Styrene (ABS): Creatinga New Green Polymer through Melt Blending. MASc, University ofGuelph, Guelph, ON, 2012.(98) Nuzzo, A.; Coiai, S.; Carroccio, S. C.; Dintcheva, N. T.;Gambarotti, C.; Filippone, G. Heat-Resistant Fully Bio-BasedNanocomposite Blends Based on Poly(lactic acid). Macromol. Mater.Eng. 2014, 299 (1), 31−40.(99) Guo, X.; Zhang, J.; Huang, J. Poly(lactic acid)/polyoxy-methylene blends: Morphology, crystallization, rheology, and thermalmechanical properties. Polymer 2015, 69, 103−109.(100) Zhang, K.; Mohanty, A. K.; Misra, M. Fully biodegradable andbiorenewable ternary blends from polylactide, poly(3-hydroxybutyrate-co-hydroxyvalerate) and poly(butylene succinate) with balancedproperties. ACS Appl. Mater. Interfaces 2012, 4 (6), 3091−3101.(101) Anderson, K. S.; Hillmyer, M. A. Melt preparation andnucleation efficiency of polylactide stereocomplex crystallites. Polymer2006, 47 (6), 2030−2035.(102) Rahman, N.; Kawai, T.; Matsuba, G.; Nishida, K.; Kanaya, T.;Watanabe, H.; Okamoto, H.; Kato, M.; Usuki, A.; Matsuda, M.;Nakajima, K.; Honma, N. Effect of polylactide stereocomplex on thecrystallization behavior of poly(L-lactic acid). Macromolecules 2009, 42(13), 4739−4745.(103) Laske, S.; Ziegler, W.; Kainer, M.; Wuerfel, J.; Holzer, C.Enhancing the temperature stability of PLA by compoundingstrategies. Polym. Eng. Sci. 2015, 55 (12), 2849−2858.(104) Bai, H.; Bai, D.; Xiu, H.; Liu, H.; Zhang, Q.; Wang, K.; Deng,H.; Chen, F.; Fu, Q.; Chiu, F. Towards high-performance poly(l-lactide)/elastomer blends with tunable interfacial adhesion and matrixcrystallization via constructing stereocomplex crystallites at theinterface. RSC Adv. 2014, 4 (90), 49374−49385.(105) Yin, H.; Wei, X.; Bao, R.; Dong, Q.; Liu, Z.; Yang, W.; Xie, B.;Yang, M. Enhancing Thermomechanical Properties and HeatDistortion Resistance of Poly(L-lactide) with High Crystallinityunder High Cooling Rate. ACS Sustainable Chem. Eng. 2015, 3 (4),654−661.(106) Yu, F.; Liu, T.; Zhao, X.; Yu, X.; Lu, A.; Wang, J. Effects of talcon the mechanical and thermal properties of polylactide. J. Appl. Polym.Sci. 2012, 125 (S2), E99−E109.



2914


(107) Ray, S. S.; Yamada, K.; Okamoto, M.; Ueda, K. Biodegradablepolylactide/montmorillonite nanocomposites. J. Nanosci. Nanotechnol.2003, 3 (6), 503−510.(108) Ray, S. S.; Yamada, K.; Okamoto, M.; Ogami, A.; Ueda, K.New polylactide/layered silicate nanocomposites. 3. High-performancebiodegradable materials. Chem. Mater. 2003, 15 (7), 1456−1465.(109) Ray, S. S.; Yamada, K.; Okamoto, M.; Ueda, K. Newpolylactide-layered silicate nanocomposites. 2. Concurrent improve-ments of material properties, biodegradability and melt rheology.Polymer 2003, 44 (3), 857−866.(110) Wertz, J. T.; Mauldin, T. C.; Boday, D. J. Polylactic Acid withImproved Heat Deflection Temperatures and Self-Healing Propertiesfor Durable Goods Applications. ACS Appl. Mater. Interfaces 2014, 6(21), 18511−18516.(111) Product Datasheets for Engineered Bioplastic Compounds -RTP Company. http://web.rtpcompany.com/info/data/bioplastics/index.htm (accessed February, 2016).(112) reSound biopolymer Compounds. http://www.polyone.com/files/resources//reSound_Product_Bulletin.PDF (accessed February,2016).(113) Ecopond AFR97 PLA-PC Alloy. http://omnexus.specialchem.com/product/t-kingfa-ecopond-afr-97-pla-pc-alloy (accessed February,2016).(114) Physical properties of Eco Pellet. http://www.umgabs.co.jp/en/products/edt/16.pdf (accessed February, 2016).(115) Wang, Y.; Chiao, S.; Hung, T.; Yang, S. Improvement intoughness and heat resistance of poly(lactic acid)/polycarbonate blendthrough twin-screw blending: Influence of compatibilizer type. J. Appl.Polym. Sci. 2012, 125 (S2), E402−E412.(116) Lin, L.; Deng, C.; Wang, Y. Improving the impact property andheat-resistance of PLA/PC blends through coupling molecular chainsat the interface. Polym. Adv. Technol. 2015, 26 (10), 1247−1258.(117) Lin, L.; Deng, C.; Lin, G.; Wang, Y. Super toughened and highheat-resistant PLA-based blends by enhancing interfacial bonding andPLA phase crystallization. Ind. Eng. Chem. Res. 2015, 54 (21), 5643−5655.(118) Mohanty, A.; Misra, M.; Hinrichsen, G. Biofibres, biodegrad-able polymers and biocomposites: an overview. Macromol. Mater. Eng.2000, 276 (1), 1−24.(119) Mohanty, A.; Misra, M.; Drzal, L. Sustainable bio-compositesfrom renewable resources: opportunities and challenges in the greenmaterials world. J. Polym. Environ. 2002, 10 (1−2), 19−26.(120) Baltazar-y-Jimenez, A.; Sain, M. Effect of bismaleimide reactiveextrusion on the crystallinity and mechanical performance ofpoly(lactic acid) green composites. J. Appl. Polym. Sci. 2012, 124(4), 3013−3023.(121) Petinakis, E.; Yu, L.; Edward, G.; Dean, K.; Liu, H.; Scully, A.D. Effect of matrix−particle interfacial adhesion on the mechanicalproperties of poly(lactic acid)/wood-flour micro-composites. J. Polym.Environ. 2009, 17 (2), 83−94.(122) Xia, X.; Liu, W.; Zhou, L.; Liu, H.; He, S.; Zhu, C. Study on flaxfiber toughened poly(lactic acid) composites. J. Appl. Polym. Sci. 2015,132, 42573.(123) Bledzki, A. K.; Jaszkiewicz, A.; Scherzer, D. Mechanicalproperties of PLA composites with man-made cellulose and abacafibres. Composites, Part A 2009, 40 (4), 404−412.(124) Bledzki, A.; Franciszczak, P.; Meljon, A. High performancehybrid PP and PLA biocomposites reinforced with short man-madecellulose fibres and softwood flour. Composites, Part A 2015, 74, 132−139.(125) Ho, M.; Lau, K.; Wang, H.; Hui, D. Improvement on theproperties of polylactic acid (PLA) using bamboo charcoal particles.Composites, Part B 2015, 81, 14−25.(126) Nomai, J.; Jarapanyacheep, R.; Jarukumjorn, K. Mechanical,Thermal, and Morphological Properties of Sawdust/Poly(lactic acid)Composites: Effects of Alkali Treatment and Poly(butylene adipate-co-terephthalate) Content. Macromol. Symp. 2015, 354 (1), 244−250.(127) Sis, A. L. M.; Ibrahim, N. A.; Yunus, W. Md Zin Wan Effect of(3-aminopropyl) trimethoxysilane on mechanical properties of PLA/

PBAT blend reinforced kenaf fiber. Iran. Polym. J. 2013, 22 (2), 101−108.(128) Xu, H.; Wang, L.; Teng, C.; Yu, M. Biodegradable composites:Ramie fibre reinforced PLLA-PCL composite prepared by in situpolymerization process. Polym. Bull. 2008, 61 (5), 663−670.(129) Ganster, J.; Fink, H.; Pinnow, M. High-tenacity man-madecellulose fibre reinforced thermoplastics−injection moulding com-pounds with polypropylene and alternative matrices. Composites, PartA 2006, 37 (10), 1796−1804.(130) Mu, C.; Xue, L.; Zhu, J.; Jiang, M.; Zhou, Z. Mechanical andThermal Properties of Toughened Poly(L-lactic) Acid and LigninBlends. BioResources 2014, 9 (3), 5557−5566.(131) Sun, Y.; Yang, L.; Lu, X.; He, C. Biodegradable and renewablepoly(lactide)−lignin composites: synthesis, interface and tougheningmechanism. J. Mater. Chem. A 2015, 3 (7), 3699−3709.(132) Qiang, T.; Yu, D.; Gao, H.; Wang, Y. Polylactide-based woodplastic composites toughened with SBS. Polym.-Plast. Technol. Eng.2012, 51 (2), 193−198.(133) Taib, R. M.; Hassan, H.; Mohd Ishak, Z. Mechanical andmorphological properties of polylactic acid/kenaf bast fiber compositestoughened with an impact modifier. Polym.-Plast. Technol. Eng. 2014,53 (2), 199−206.(134) Liu, T.; Yu, F.; Yu, X.; Zhao, X.; Lu, A.; Wang, J. Basalt fiberreinforced and elastomer toughened polylactide composites: Mechan-ical properties, rheology, crystallization, and morphology. J. Appl.Polym. Sci. 2012, 125 (2), 1292−1301.(135) Yang, J.; Wang, C.; Shao, K.; Ding, G.; Tao, Y.; Zhu, J.Morphologies, mechanical properties and thermal stability of poly-(lactic acid) toughened by precipitated barium sulfate. Russ. J. Phys.Chem. A 2015, 89 (11), 2092−2096.(136) Murariu, M.; Ferreira, A.; Duquesne, E.; Bonnaud, L.; Dubois,P. Polylactide (PLA) and Highly Filled PLA-Calcium SulfateComposites with Improved Impact Properties. Macromol. Symp.2008, 272, 1−12.(137) Murariu, M.; Ferreira, A. D. S.; Pluta, M.; Bonnaud, L.;Alexandre, M.; Dubois, P. Polylactide (PLA)−CaSO4 compositestoughened with low molecular weight and polymeric ester-likeplasticizers and related performances. Eur. Polym. J. 2008, 44 (11),3842−3852.(138) Herrera, N.; Mathew, A. P.; Oksman, K. Plasticized polylacticacid/cellulose nanocomposites prepared using melt-extrusion andliquid feeding: mechanical, thermal and optical properties. Compos. Sci.Technol. 2015, 106, 149−155.(139) Chow, W.; Leu, Y.; Mohd Ishak, Z. Effects of SEBS-g-MAH onthe properties of injection moulded poly(lactic acid)/nano-calciumcarbonate composites. eXPRESS Polym. Lett. 2012, 6 (6), 503−510.(140) Chow, W. S.; Leu, Y. Y.; Ishak, Z. A. M. Mechanical, Thermaland Morphological Properties of Injection Molded Poly(lactic acid)/Calcium Carbonate Nanocomposites. Period. Polytech., Mech. Eng.2016, 60 (1), 15−20.(141) Jiang, L.; Liu, B.; Zhang, J. Properties of poly(lactic acid)/poly(butylene adipate-co-terephthalate)/nanoparticle ternary compo-sites. Ind. Eng. Chem. Res. 2009, 48 (16), 7594−7602.(142) Xiong, Z.; Dai, X.; Na, H.; Tang, Z.; Zhang, R.; Zhu, J. Atoughened PLA/Nanosilica composite obtained in the presence ofepoxidized soybean oil. J. Appl. Polym. Sci. 2015, 132, 41220.(143) Odent, J.; Raquez, J.; Thomassin, J.; Gloaguen, J.; Lauro, F.;Jerome, C.; Lefebvre, J.; Dubois, P. Mechanistic insights on nanosilicaself-networking inducing ultra-toughness of rubber-modified polylac-tide-based materials. Nanocomposites 2015, 1 (3), 113−125.(144) Wu, J.; Kuo, M.; Chen, C. Physical properties andcrystallization behavior of poly(lactide)/poly(methyl methacrylate)/silica composites. J. Appl. Polym. Sci. 2015, 132, 42378.(145) Liang, J.; Li, F. Mechanical properties of poly(l-lactic acid)composites filled with mesoporous silica. Polym. Compos. 2015, DOI:10.1002/pc.23674.(146) Yeniova Erpek, C. E.; Ozkoc, G.; Yilmazer, U. Effects ofhalloysite nanotubes on the performance of plasticized poly(lactic



2915

http://web.rtpcompany.com/info/data/bioplastics/index.htm

http://web.rtpcompany.com/info/data/bioplastics/index.htm

http://www.polyone.com/files/resources//reSound_Product_Bulletin.PDF

http://www.polyone.com/files/resources//reSound_Product_Bulletin.PDF

http://omnexus.specialchem.com/product/t-kingfa-ecopond-afr-97-pla-pc-alloy

http://omnexus.specialchem.com/product/t-kingfa-ecopond-afr-97-pla-pc-alloy

http://www.umgabs.co.jp/en/products/edt/16.pdf

http://www.umgabs.co.jp/en/products/edt/16.pdf

http://dx.doi.org/10.1002/pc.23674


acid)-based composites. Polym. Compos. 2015, DOI: 10.1002/pc.23511.(147) Murariu, M.; Dechief, A.; Ramy-Ratiarison, R.; Paint, Y.;Raquez, J.; Dubois, P. Recent advances in production of poly(lacticacid) (PLA) nanocomposites: a versatile method to tune crystallizationproperties of PLA. Nanocomposites 2015, 1 (2), 71−82.(148) Ojijo, V.; Ray, S. S.; Sadiku, R. Effect of nanoclay loading onthe thermal and mechanical properties of biodegradable polylactide/poly[(butylene succinate)-co-adipate] blend composites. ACS Appl.Mater. Interfaces 2012, 4 (5), 2395−2405.(149) Salehiyan, R.; Yussuf, A.; Hanani, N. F.; Hassan, A.; Akbari, A.Polylactic acid/polycaprolactone nanocomposite Influence of mont-morillonite and impact modifier on mechanical, thermal, andmorphological properties. J. Elastomers Plast. 2015, 47 (1), 69−87.(150) Jandas, P.; Mohanty, S.; Nayak, S. Morphology and thermalproperties of renewable resource-based polymer blend nanocompo-sites influenced by a reactive compatibilizer. ACS Sustainable Chem.Eng. 2014, 2 (3), 377−386.(151) Ostafinska, A.; Fortelny, I.; Nevoralova, M.; Hodan, J.;Kredatusova, J.; Slouf, M. Synergistic effects in mechanical propertiesof PLA/PCL blends with optimized composition, processing, andmorphology. RSC Adv. 2015, 5 (120), 98971−98982.(152) Serizawa, S.; Inoue, K.; Iji, M. Kenaf-fiber-reinforcedpoly(lactic acid) used for electronic products. J. Appl. Polym. Sci.2006, 100 (1), 618−624.(153) Huda, M. S.; Drzal, L. T.; Misra, M.; Mohanty, A. K.; Williams,K.; Mielewski, D. F. A study on biocomposites from recyclednewspaper fiber and poly(lactic acid). Ind. Eng. Chem. Res. 2005, 44(15), 5593−5601.(154) Huda, M.; Drzal, L.; Mohanty, A.; Misra, M. The effect ofsilane treated-and untreated-talc on the mechanical and physico-mechanical properties of poly(lactic acid)/newspaper fibers/talchybrid composites. Composites, Part B 2007, 38 (3), 367−379.(155) Reddy, J. P.; Misra, M.; Mohanty, A. Injection MouldedBiocomposites from Oat Hull and Polypropylene/Polylactide Blend:Fabrication and Performance Evaluation. Adv. Mech. Eng. 2013, 5,761840.(156) Nyambo, C.; Mohanty, A. K.; Misra, M. Polylactide-basedrenewable green composites from agricultural residues and theirhybrids. Biomacromolecules 2010, 11 (6), 1654−1660.(157) Nagarajan, V.; Zhang, K.; Misra, M.; Mohanty, A. K.Overcoming the Fundamental Challenges in Improving the ImpactStrength and Crystallinity of PLA Biocomposites: Influence ofNucleating Agent and Mold Temperature. ACS Appl. Mater. Interfaces2015, 7 (21), 11203−11214.(158) reSound FR Development. http://www.innovationtakesroot.com/~/media/itr2012/2012/presentations/durables/05_non_halogen-flame-retarded-resound_avakian_pdf (accessed February,2016).( 159 ) deTe r r a® B ioba s ed Po l yme r s . h t t p : / /www .innovationtakesroot.com/~/media/ITR2012/2012/presentations/emerging-markets/03_deTerra-Biobased-Polymers_Cernohous_pdf(accessed February, 2016).(160) Terraloy® 3D-40040 Series. http://omnexus.specialchem.com/product/t-teknor-apex-terraloy-3d-40040-series (accessed Febru-ary, 2016).(161) High heat PLA: Unlocking Bioplastic potential for durableapplications. http://www.corbion.com/media/77166/corbion-purac-pla-high-heat-themesheet.pdf (accessed Feb, 2016).(162) Bioloy. http://www.jimshin.com/productshow.asp?b_classid=121&yid=339 (accessed February, 2016).(163) ECODEAR® PLA Resin. http://www.toray.jp/plastics/en/ecodear/grade.html (accessed February, 2016).(164) Unitika Terramac product list and grades. http://www.unitika.co.jp/terramac/e/products/resin/list.html (accessed February, 2016).(165) NatureWorks Technical Resources. http://www.natureworksllc.com/Technical-Resources (accessed February, 2016).

(166) SUPLA 135. http://www.supla-bioplastics.com/en/pro2_detail.php?id=243&class_list=21&class_name=43 (accessed February,2016).(167) Ecoplan-Dura Datasheet. http://www.materialdatacenter.com/ms/en/Ecoplan/SK+Chemicals/Ecoplan+DURA/d2ef4d76/6784 (ac-cessed February, 2016).(168) Bio-Flex® F 6513 Technical datasheet. http://www.fkur.com/fileadmin/user_upload/Produkte/bioflex/F6513/TD_BIO-FLEX_F_6513_en.pdf (accessed February, 2016).(169) NaturePlast materials and additives portfolio. http://www.natureplast.eu/images/pdf/en/Portfolio_Natureplast_eng.pdf (ac-cessed February, 2016).(170) KEBACOMP® FE 120204 Material datasheet. http://www.m a t e r i a l d a t a c e n t e r . c o m / m s / e n / K e b a c o m p /BARLOG+plastics+GmbH/KEBACOMP%C2%AE+FE+120204/ffa76a32/6569 (accessed February, 2016).(171) Ecolgreen Biopolymer. http://www.ecolgreen.com/eng/include/content.php?pageID=ID12052844672 (accessed February,2016).(172) ECOGEHR® PLA-L Technical datasheet. http://omnexus.specialchem.com/product/gehr-plastics-ecogehr-plal-polylactic-acid(accessed February, 2016).(173) WinGram PLA Series. http://www.wingram.hk/index.php/products/pla-series (accessed February, 2016).(174) Highly heat resistant Bioplastic. http://www.teijin.com/rd/technology/bioplastic/ (accessed February, 2016).(175) ASTM Standard D6400-12. Standard specification for labelingof plastics designed to be aerobically composted in municipal orindustrial facilities; ASTM International: West Conshohocken, PA,2012; http://www.astm.org/cgi-bin/resolver.cgi?D6400.



2916



http://www.innovationtakesroot.com/~/media/itr2012/2012/presentations/durables/05_non_halogen-flame-retarded-resound_avakian_pdf



http://www.innovationtakesroot.com/~/media/ITR2012/2012/presentations/emerging-markets/03_deTerra-Biobased-Polymers_Cernohous_pdf



http://omnexus.specialchem.com/product/t-teknor-apex-terraloy-3d-40040-series

http://omnexus.specialchem.com/product/t-teknor-apex-terraloy-3d-40040-series

http://www.corbion.com/media/77166/corbion-purac-pla-high-heat-themesheet.pdf

http://www.corbion.com/media/77166/corbion-purac-pla-high-heat-themesheet.pdf

http://www.jimshin.com/productshow.asp?b_classid=121&yid=339

http://www.jimshin.com/productshow.asp?b_classid=121&yid=339

http://www.toray.jp/plastics/en/ecodear/grade.html

http://www.toray.jp/plastics/en/ecodear/grade.html

http://www.unitika.co.jp/terramac/e/products/resin/list.html

http://www.unitika.co.jp/terramac/e/products/resin/list.html

http://www.natureworksllc.com/Technical-Resources

http://www.natureworksllc.com/Technical-Resources

http://www.supla-bioplastics.com/en/pro2_detail.php?id=243&class_list=21&class_name=43

http://www.supla-bioplastics.com/en/pro2_detail.php?id=243&class_list=21&class_name=43

http://www.materialdatacenter.com/ms/en/Ecoplan/SK+Chemicals/Ecoplan+DURA/d2ef4d76/6784

http://www.materialdatacenter.com/ms/en/Ecoplan/SK+Chemicals/Ecoplan+DURA/d2ef4d76/6784

http://www.fkur.com/fileadmin/user_upload/Produkte/bioflex/F6513/TD_BIO-FLEX_F_6513_en.pdf



http://www.natureplast.eu/images/pdf/en/Portfolio_Natureplast_eng.pdf

http://www.natureplast.eu/images/pdf/en/Portfolio_Natureplast_eng.pdf

http://www.materialdatacenter.com/ms/en/Kebacomp/BARLOG+plastics+GmbH/KEBACOMP%C2%AE+FE+120204/ffa76a32/6569




http://www.ecolgreen.com/eng/include/content.php?pageID=ID12052844672

http://www.ecolgreen.com/eng/include/content.php?pageID=ID12052844672

http://omnexus.specialchem.com/product/gehr-plastics-ecogehr-plal-polylactic-acid

http://omnexus.specialchem.com/product/gehr-plastics-ecogehr-plal-polylactic-acid

http://www.wingram.hk/index.php/products/pla-series

http://www.wingram.hk/index.php/products/pla-series

http://www.teijin.com/rd/technology/bioplastic/

http://www.teijin.com/rd/technology/bioplastic/

http://www.astm.org/cgi-bin/resolver.cgi?D6400


pla review article

Documents