Melt compounding of poly (3-hydroxybutyrate-co-3- hydroxyvalerate)/nanoﬁbrillated cellulose nanocomposites Yottha Srithep a, b , Thomas Ellingham b , Jun Peng b , Ronald Sabo c , Craig Clemons c , Lih-Sheng Turng b, * , Srikanth Pilla b a Faculty of Engineering, Mahasarakham University, Khamriang, Kantarawichai, Mahasarakham Province, 44150, Thailand b Polymer Engineering Center, Department of Mechanical Engineering, University of WisconsineMadison, Madison, WI 53706, USA c USDA Forest Service, Forest Products Laboratory, Madison, WI 53726, USA article info Article history: Received 15 December 2012 Received in revised form 25 April 2013 Accepted 2 May 2013 Available online 13 May 2013 Keywords: Nanoﬁbrillated cellulose (NFC) Poly(3-hydroxybutyrate-co-3- hydroxyvalerate) (PHBV) nanocomposites Mechanical and thermal properties Carbon dioxide solubility and foaming Thermal stability and degradation abstract Using natural cellulosic ﬁbers as ﬁllers for biodegradable polymers can result in fully biodegradable composites. In this study, biodegradable nanocomposites were prepared using nanoﬁbrillated cellulose (NFC) as the reinforcement and poly (3-hydroxybutyrate-co-3-hydroxyvalerate, PHBV) as the polymer matrix. PHBV powder was dispersed in water, mixed with an aqueous suspension of NFC ﬁber, and freeze-dried. The resulting PHBV/15 wt% NFC was then used as a master batch in a subsequent melt compounding process to produce nanocomposites of various formulations. Its properties such as its mechanical properties, crystallization behavior, solubility of carbon dioxide (CO 2 ), foaming behavior, and thermal stability and degradation of PHBV due to NFC were evaluated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the dispersion of NFC ﬁbers. Adding NFC increased the tensile modulus of the PHBV/NFC nanocomposites nearly twofold. Differential scanning calorimetry (DSC) analysis showed that the NFC served as a nucleating agent, promoting the early onset of crystallization. However, high NFC content also led to greater thermal degradation of the PHBV matrix. Dynamic mechanical analysis (DMA) showed an increase of the storage modulus in the glassy state with increasing NFC content, but a more signiﬁcant increase in modulus was detected above the glass transition temperature. The solubility of CO 2 in the PHBV/NFC nanocomposites decreased and the desorption diffusivity increased as more NFC was added. Finally, the foaming behavior of PHBV/NFC nanocomposites was studied and the addition of NFC was found to inhibit foaming. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The development of commercially viable biodegradable plastics is an important effort in preserving and revitalizing our global environment and economy. Polyhydroxyalkanoates (PHAs) have attracted much attention over the last two decades mainly due to increasing environmental concerns and the realization that our petroleum resources are ﬁnite [1,2]. PHAs have received a great deal of research interest because their mechanical performance is similar to petroleum-based polymers such as polypropylene (PP) [3]. PHAs, which also include poly(3-hydroxybutyrate) (PHB) and copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/HV), are a family of polyesters that are synthesized and intracellularly accumulated as a carbon and energy storage material in various microorganisms [4]. Generally, PHB/HV (or PHBV) is less crystalline and more ﬂexible than the highly crystalline and relatively brittle and hydrophobic PHB [5]. Reinforcing ﬁbers of various sizes and formsde.g., natural plant ﬁbers (cellulose ﬁbers), glass ﬁbers, carbon ﬁbers, carbon nanotubes, etc. dhave been effectively used in polymer composites as rein- forcing agents [3]. Nanoﬁllers, however, are found to be preferable in many applications due to their high surface area-to-volume ratios, lower concentrations needed to achieve reinforcing effects, and the ability to potentially improve toughness along with strength and stiffness. Nanoﬁbrillated cellulose (NFC), a biologically derived nanoﬁber reinforcement suitable for polymeric materials, is an interconnected web with ﬁbrils having a diameter in the range of 10e50 nm [6]. Although NFC has numerous advantages, which include low density, renewability, high speciﬁc properties, biode- gradability, gas barrier properties, and derivation from abundant natural resources, the processing temperatures for these materials are restricted to about 200  C due to degradation beyond this * Corresponding author. Tel.: þ1 608 262 0586; fax: þ1 608 265 2316. E-mail addresses: turng@engr.wisc.edu, turng@wid.wisc.edu (L.-S. Turng). Contents lists available at SciVerse ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab 0141-3910/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymdegradstab.2013.05.006 Polymer Degradation and Stability 98 (2013) 1439e1449