BLENDS CONTAINING POLY(HYDROXYBUTYRATE-CO-12-PERCENT-HYDROXYVALERATE) AND THERMOPLASTIC STARCH

Poly(hydroxyalkanoates) form biodegradable composites when blended with starch granules but the mechanical properties are poor. Unlike starch granules, thermoplastic starch is a flexible material that can be reprocessed at elevated temperatures. Mixing thermoplastic starch with poly(hydroxybutyrate-co-12%-hydroxyvalerate) resulted in a true blend in which the starch phase was also deformed. Nevertheless, the blends were still brittle despite the presence of the flexible starch phase. Morphological studies showed that the shapes of the dispersed phases in these blends were irregular and that the sizes were large owing to a large difference in viscosity between the two phases in the melt and inadequate shear during processing. Thermal analysis of the blends and starting polymers showed no indication of any interaction between the two polymers. Even if there is no compatibility between the two phases, improved mechanical properties may be obtained by optimizing the blend morphology during processing.