ENZYMATIC DEGRADATION AND MORPHOLOGIES OF BINARY BLENDS OF MICROBIAL POLY(3-HYDROXY BUTYRATE) WITH POLY(EPSILON-CAPROLACTONE), POLY(1,4-BUTYLENE ADIPATE AND POLY(VINYL ACETATE)

The miscibility, morphology and biodegradability of binary blends of poly(3-hydroxy butyrate) (PHB) with poly(epsilon-caprolactone) (PCL), poly(1,4-butylene adipate) (PBA) and poly(vinyl acetate) (PVAc) have been studied by analysis of differential scanning calorimetry, mechanical properties, scanning electron micrography (SEM) and enzymatic degradation. The glass-transition temperature (T(g)) data indicated that the PHB/PCL and PHB/PBA blends were immiscible in the amorphous state, while the PHV/PVAc blend was miscible. On the basis of the mechanical properties and SEM of the immiscible blends, it was suggested that the PHB/PCL blend has a macro-phase separated structure and the PHB/PBA blend has a modulated structure with a micro-phase separation. The enzymatic degradation of the PHB-based blend films was carried out at 37-degrees-C and pH 7.4 in an aqueous solution of an extracellular PHB depolymerase from Alcaligenes faecalis T1. The profiles of enzymatic degradation of PHB-based blends were strongly dependent upon the polymer component blended with PHB. In the case of PHB/PCL blend film, a complicated dependence of PCL weight fraction on the rate of enzymatic degradation was observed. In contrast, the weight loss of PHB/PBA or PHB/PVAc blend film by the PHB depolymerase decreased monotonously with increase in the weight fraction of PBA or PVAc. The enzymatic degradation data have been discussed in connection with the morphologies of PHB-based blend films.