PHBV-CNT POLYMER ENGINEERING AND SCIENCE—-2012

Mechanical and Electrical Multifunctional

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)—Multiwall Carbon Nanotube Nanocomposites

Shailesh Vidhate,1Lucia Innocentini-Mei,2Nandika Anne D’Souza1

1Department of Materials Science and Engineering,University of North Texas,Denton,Texas76201

2School of Chemical Engineering,State University of Campinas-UNICAMP,CP6066,50013083-970 Campina,SP Brazil

In this work,nanocomposites of poly(hydroxybutyrate-co-hydroxyvalerate)PHBV and multiwalled carbon nanotubes(MWNT)were prepared by melt blending. Mechanical,thermal,morphological,and electrical properties of the prepared PHBV/MWNT nanocompo-sites were investigated.Differential scanning calorime-try(DSC)and X-ray diffraction(XRD)results showed MWNT effectively enhanced the crystallization and nucleation of PHBV.Dynamic thermo-mechanical and static uniaxial mechanical tensile and compressive properties were increased by the addition of MWNT. MWNT observed in the nanocomposites using trans-mission electron microscopy(TEM)showed dimen-sions similar to separated nanotubes inferring a good dispersion.The presence of nanotubes in close vicinity with each other formed an interconnecting network that led to the formation of electrically conductive nanocomposites.The electrical resistance of the nano-composites was reduced with the addition of MWNT.POLYM.ENG.SCI.,52:1367–1374,2012.ª2012Soci-ety of Plastics Engineers

INTRODUCTION

Recent concern about the harmful effects of petroleum based nonbiodegradable polymers on the environment has raised new challenges for polymer industries.One of the solutions to tackle this problem is to replace the synthetic petroleum-based polymers with equally competitive bio-based biodegradable polymers.Poly(hydroxyalkanoates) (PHA),a family of biopolymers has attracted much atten-tion recently,due to their complete biodegradability,bio-compatibility,and natural origin.Most significantly,their mechanical properties are similar to that of widely used polypropylene.Several applications have been proposed for PHA polymers in thefields of medicine,agriculture,and packaging[1].The most studied and easily produced member of this family is poly(3-hydroxybutyrate)(PHB), an isotactic,high molecular weight polymer whose me-chanical properties compare favorably with polypropylene [2].Produced in the form of intracellular granules by sev-eral microorganisms,PHB serves as a carbon and energy storage material.However,some drawbacks have pre-vented its introduction in the market as a valid alternative to the currently widespread nondegradable oil-based ther-moplastics.Some of these drawbacks are its fragility, thermal degradability at temperatures not far above the melting point,and its high price[3].

To improve the properties of PHB,several kinds of PHA copolymers have been described in the literature incorporating structural units such as3-hydroxyvalerate to obtain poly(hydroxybutyrate-co-valerate)(PHBV)[4]. PHBV is an attractive material for environmental waste management and can be used as a substitute for conven-tional polymers when recovery for recycling or incinera-tion is difficult or not cost effective[5–7].Unfortunately, PHBV presents the following problems to be solved—slow crystallization rate,relatively difficult processing due to low melt viscosity,low elongation at break,and very high crystallinity.Slow crystallization rate of the PHBV during processing causes tackiness for long period of time in thefinal product until it becomes completely crystal-line.Even after cooling,PHBV with higher fractions of hydroxyvalerate(HV)units will be tacky to touch and the PHBV chains still remain in the amorphous state[8]. Many researchers,including us,have proved improvement in the crystallization rate of the polymers by addition of fillers such as nanoclays,talc,carbon nanofibers,carbon nanotubes,etc.[9–13].In all these efforts,solution cast-ing and melt blending techniques were used to prepare polymer composites.In general,all methods showed higher recrystallization temperatures by addition offillers. When comparing the melting temperature to the recrystal-lization temperature,the slow crystallization rate of PHB

Correspondence to:Nandika Anne D’Souza;e-mail:ndsouza@ DOI10.1002/pen.23084

Published online in Wiley Online Library().

V C2012Society of Plastics Engineers

POLYMER ENGINEERING AND SCIENCE—-2012