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

Poly(hydroxyalkanoates) form biodegradable composites when blended wit h starch granules but the mechanical properties are poor. Unlike starc h granules, thermoplastic starch is a flexible material that can be re processed at elevated temperatures. Mixing thermoplastic starch with p oly(hydroxybutyrate-co-12%-hydroxyvalerate) resulted in a true blend i n which the starch phase was also deformed. Nevertheless, the blends w ere still brittle despite the presence of the flexible starch phase. M orphological 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 i nadequate 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 ble nd morphology during processing.