Thermal Properties and Crystallization Behavior of Fractionated Blocky and Random Polyhydroxyalkanoate Copolymers from Mixed Microbial Cultures

This study represents the first detailed analysis of the thermal, morphological, and crystallization properties of the blend components within a range of mixed-culture polyhydroxyalkanoates (PHAs), with 3-hydroxyvalerate content in the as-produced materials and in the fractions ranging from low (12 mol %) to high (91 mol %). Both coarse and fine fractionation of the as-produced copolymers confirmed that they were blends of nominally blocky and/or random copolymers of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), with very broad compositional distributions as governed by the PHA accumulation strategy. The crystallization kinetics and thermal properties of the fractions were found to be very significantly different from each other, consistent with the hypothesis that the overall mechanical properties were primarily controlled by the more rapidly crystallizing components. Two materials produced using an alternating feeding strategy demonstrated unique crystallization and thermal properties in their fractions, which are considered to have contributed to distinctly more elastic mechanical properties in these particular samples. (C) 2014 Wiley Periodicals, Inc.