On the use of ball milling to develop PHBV–graphene nanocomposites (I)—Morphology, thermal properties, and thermal stability Jes us Ambrosio-Mart  ın, 1 Giuliana Gorrasi, 2 Amparo Lopez-Rubio, 1 Mar  ıa Jos  e Fabra, 1 Lu  ıs Cabedo Mas, 3 Miguel Angel L  opez-Manchado, 4 Jose Mar  ıa Lagaron 1 1 Novel Materials and Nanotechnology Group, IATA, CSIC, Av. Agust  ın Escardino 7, Paterna 46980 (Valencia), Spain 2 Department of Industrial Engineering University of Salerno, Via Giovanni Paolo II 132, Fisciano 84084 Salerno, Italy 3 ESID, Universitat Jaume I, Avda. Vicent Sos Baynat s/n, Castell on 12071, Spain 4 Institute of Polymer Science and Technology, (CSIC), Juan de la Cierva, 3, Madrid 28006, Spain Correspondence to: G. Gorrasi (E - mail: ggorrasi@unisa.it) and J. Mar  ıa Lagaron (E - mail: lagaron@iata.csic.es) ABSTRACT: In the first part of this work, novel nanocomposites based on poly (3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV) and functionalized graphene nanosheets (FGS) were prepared through ball milling. As revealed by morphological characterization, this blending methodology was able to allow proper nanofiller dispersion and distribution into the matrix. Thermal properties were stud- ied under non-isothermal and isothermal conditions and the addition of FGS into PHBV matrix, although no changes in crystalliza- tion mechanism were observed, it modified the crystallization kinetics leading to increased crystallinity. Thermal stability analysis revealed that FGS affected the mechanism of oxidative thermal degradation and had no effect on thermal degradation by pyrolysis. Furthermore, an analysis of isothermal degradation kinetics showed that FGS speeded up the degradation rate. The Sestak-Berggren model was used as a model to explain the isothermal degradation behavior of the obtained materials in good agreement with the experimental data. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42101. KEYWORDS: biodegradable; biomaterials; biopolymers and renewable polymers; composites; graphene and fullerenes; nanotubes Received 4 December 2014; accepted 11 November 2015 DOI: 10.1002/app.42101 INTRODUCTION The massive use of petroleum-based polymers has resulted in environmental concerns derived not only from waste manage- ment issues, but also from their low degradation rates. As a result, there is a growing interest in the development of renew- able and biodegradable materials to partially replace the oil- based ones. Alternatives such as polyhydroxyalkanoates (PHAs) have sparked great interest due to their biodegradable, biocom- patible and renewable features. PHAs can be produced in differ- ent ways, i.e., chemically or biologically through fermentation from feedstock. This family comprises mainly the homopoly- mer, polyhydroxybutyrate (PHB), which has been extensively studied since it presents mechanical properties similar to those of conventional petroleum-based polymers, relatively good ther- mal properties and high stiffness due to its high crystallinity degree. 1 However, although high crystallinity is useful for some applications, the high stiffness limits its usage in other commer- cial applications. Moreover, another drawback of this polymer is its low thermal stability, making it unstable during melt proc- essing and also limiting its applicability. 2 Several strategies have been developed to overcome these drawbacks, including blending with other polymers, such as poly (vinyl alcohol) (PVA), 3 polypropylene glycol (PPG), 4 and poly-e-caprolactone (PCL) 5 or modification of the homopolymer by incorporation of different monomer types during the fermentation process. Copolymerization with hydroxyvalerate (HV) results in poly(3- hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) which has improved mechanical and thermal properties, since incorpora- tion of HV reduces the crystallinity, thus decreasing stiffness and brittleness, and also reducing the melting point without decreasing the thermal stability of the material, although greater improvements in this parameter are still needed. 1,6 However, reduction in crystallinity is widely known to affect the barrier properties of materials to low molecular weight substances, which is a key property of materials intended to be used in packaging applications. 7,8 Because of that, PHBV copolymers still present several drawbacks including high cost, relative brit- tleness and thermal instability, which had hampered the wide- spread usage of this family of polymers. As a strategy to improve biopolymer performance, many studies have focussed V C 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.42101 42101 (1 of 11)