BIODEGRADABLE POLYMER BLENDS OF POLY(3-HYDROXYBUTYRATE) AND POLY(DL-LACTIDE)-CO-POLY(ETHYLENE GLYCOL)

The melting and crystallization behavior and phase morphology of poly( 3-hydroxybutyrate) (PHB) and poly(DL-lactide)-co-poly(ethylene glycol) (PELA) blends were studied by DSC, SEM, and polarizing optical micros copy. The melting temperatures of PHB in the blends showed a slight sh ift, and the melting enthalpy of the blends decreased linearly with th e increase of PELA content. The glass transition temperatures of PHB/P ELA (60/40), (40/60), and (20/80) blends were found at about 30 degree s C, close to that of the pure PELA component, during DSC heating runs for the original samples and samples after cooling from the melt at a rate of 20 degrees C/min. After a DSC cooling run at a rate of 100 de grees C/min, the blends showed glass transitions in the range of 10-30 degrees C. Uniform distribution of two phases in the blends was obser ved by SEM. The crystallization of PHB in the blends from both the mel t and the glassy state was affected by the PELA component. When crysta llized from the melt during the DSC nonisothermal crystallization run at a rate of 20 degrees C/min, the temperatures of crystallization dec reased with the increase of PELA content. Compared with pure PHB, the cold crystallization peaks of PHB in the blends shifted to higher temp eratures. Well-defined spherulites of PHB were found in both pure PHB and the blends with PHB content of 80 or 60%. The growth of spherulite s of PHB in the blends was affected significantly by 60% PELA content. (C) 1997 John Wiley & Sons, Inc.