The effect of nucleating agents on physical properties of poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV) produced by Burkholderia cepacia ATCC 17759

In the absence of nucleating agents, polyhydroxyalkanoates (PHAs) generally exhibit slow crystallization rates which make them less favorable for injection molding purposes. The copolymer, PHB-co-HV (poly-3-hydroxybutyrate-co-3-hydroxyvalerate), exhibited increased T-c as compared to the homopolymer PHB (poly-3-hydroxybutyrate). Increasing the mol fraction of HV monomer in the PHB-co-HV initially led to a decrease in the T-m of the copolymer from 175.4 degrees C to a minimum of 168.5 degrees C, at 20 mol% of HV and, subsequently, increased in PHB-co-HV copolymers with higher fractions of HV, indicating a typical isodimorphic relationship. Two nucleating agents, heptane dicarboxylic derivative HPN-68L and ULTRATAL (R) 609, were tested to increase the T-c and reduce the time for crystallization necessary for injection molding. HPN-68L decreased the T-decomp of the homopolymer and all copolymers by almost 50 degrees C. However, the use of ULTRATALC (R) 609 as a nucleating agent slightly enhanced the T-decomp and had negligible effect on the T(m)s of all polymers. Also, PHB and PHB-co-HV with 5% (w/w) talc exhibited higher T-c than polymers without ULTRATALC (R) 609. A careful comparison of T-c, T-m and T-decomp, for PHB-co-HV with 20 mol% of HV indicated that this copolymer is the best option for injection molding, with both a high T-decomp and more rapid crystallization. (C) 2012 Elsevier Ltd. All rights reserved.