Material propertiesThe 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 Tc 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 Tm of the copolymer from 175.4 °C to a minimum of 168.5 °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 ULTRATALC®609, were tested to increase the Tc and reduce the time for crystallization necessary for injection molding. HPN-68L decreased the Tdecomp of the homopolymer and all copolymers by almost 50 °C. However, the use of ULTRATALC®609 as a nucleating agent slightly enhanced the Tdecomp and had negligible effect on the Tms of all polymers. Also, PHB and PHB-co-HV with 5% (w/w) talc exhibited higher Tc than polymers without ULTRATALC®609. A careful comparison of Tc, Tm and Tdecomp, for PHB-co-HV with 20 mol% of HV indicated that this copolymer is the best option for injection molding, with both a high Tdecomp and more rapid crystallization.