PHASE-SEPARATION IN A BLEND OF POLY-(HYDROXYBUTYRATE) WITH POLY (HYDROXYBUTYRATE-CO-HYDROXYVALERATE)

Blends containing poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with 18.4% hydroxyvalerate units in various proportions have been studied using differential scanning calorimetry (d.s.c.) and optical and electron microscopy. D.s.c. measurements of melting points and peak areas from crystallized samples show that two-phase crystallization occurs for blend compositions containing 60-70% or more of copolymer, depending on crystallization temperature. The precise composition of the crystal phases obtained is thought to be governed primarily by kinetic factors. Phase separation in the melt was also investigated using d.s.c. by comparing the crystallization behaviour of nucleated and non-nucleated melts subjected to various thermal treatments. A region of liquid-liquid phase separation was identified, indicating partial miscibility between the two blend components. Morphological evidence confirmed the existence of different crystalline phases for the blends of highest copolymer content.