ENZYMATIC DEGRADATION OF BINARY BLENDS OF MICROBIAL POLY(3-HYDROXYBUTYRATE) WITH ENZYMATICALLY ACTIVE POLYMERS

The miscibility and biodegradability of binary blends of microbial poly(3-hydroxybutyrate) (PHB) with poly(beta-propiolactone) (PPL), poly(ethylene adipate) (PEA) and microbial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV, HB 24 mol% and HV 76 mol%) have been studied by analysis of differential scanning calorimetry (DSC), scanning electron micrography (SEM) and enzymatic degradation. The glass transition temperature (T(g)) data indicated that the blends of PHB/PPL, PHB/PEA and PHB/PHB-HV were immiscible in the amorphous state. 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 Tl. The films of PPL, PEA and PHB-HV polymers, as well as the films of PHB, were degraded by the PHB depolymerase. The rates of enzymatic degradation of the PHB/PPL, PHB/PEA and PHB/PHB-HV blend films were higher than the rate of each polymer component film. In the SEMs of the surface and cross-section of a PHB/PPL (26:74, w/w) film, large holes, 10-30-mu-m in diameter, were detected not only on the surface but also inside the film. The acceleration of enzymatic degradation of the blend films may be caused by an increase in the surface area of film active to the PHB depolymerase.