MULTIPLE MELTING IN BLENDS OF ISOTACTIC AND ATACTIC POLY(BETA-HYDROXYBUTYRATE)

The phenomenon of multiple melting endotherms is investigated for the blend system isotactic/atactic poly(beta-hydroxybutyrate) (PHB) for so lvent-cast and melt-crystallized samples. It is shown that a melt/recr ystallization process is operative for both methods of blend preparati on. The overall melt behaviour is rationalized in terms of annealing o f as-formed crystals and recrystallization of this material. Variation s in d.s.c. scan profile with blend composition are ascribed to change s in the magnitude of the recrystallization exotherm. The crystallinit y of the isotactic phase is shown to be invariant with composition. It is demonstrated that the solvent-cast blends are not fully miscible p rior to the first melt.