MORPHOLOGIES AND ENZYMATIC DEGRADABILITY OF MELT-CRYSTALLIZED POLY(3-HYDROXYBUTYRIC ACID CO-6-HYDROXYBUTYRIC ACID)

The films of poly[(R)-3-hydroxybutyric acid-co-10mol% 6-hydroxyhexanoi c acid] (P[(R)-3HB-co-6HH]) were prepared by melt-crystallized method at various crystallization temperatures. The morphologies and properti es of melt-crystallized films were characterized by means of x-ray dif fraction, differential scanning calorimetry, optical microscopy, and s canning electron microscopy. All of the melt-crystallized films showed the banded spherulite morphology. The enzymatic degradation of melt-c rystallized films was carried out at 37 degrees C in an aqueous soluti on (pH 7.4) of PHB depolymerase from Alcaligenes faecalis. The rate of enzymatic erosion was strongly dependent on the crystallinity of film s, and the highest rate was as large as 2.15 mg.h(-1).cm(-2). After en zymatic degradation, the banded morphology of P[(R)-3HB-co-6HH] spheru lites was visible, suggesting that PHB depolymerase predominantly hydr olyzes polymer chains on the edges of crystalline lamellar stacks.