Further evidence of crystallinity-induced biodegradation of synthetic atactic poly(3-hydroxybutyrate) by PHB-depolymerase A from Pseudomonas lemoignei. Blends of atactic poly(3-hydroxybutyrate) with crystalline polyesters

Blends of atactic poly[(R,S)-3-hydroxybutyrate], a-PHB, with poly(epsilon-c aprolactone), PCL, and with poly(L-lactic acid), PLLA, were obtained in the form of compression-molded films. The phase behavior of the blends was dif ferent: a-PHB and PCL were totally immiscible, whereas a-PHB/PLLA blends we re miscible over the whole composition range. Biodegradation experiments we re carried out on the blends and on the plain polymers in a buffered soluti on of PHB-depolymerase A from Pseudomonas lemoignei (Tris-HCl, pH 8, T = 37 degrees C). None of the pure blend components (a-PHB, PCL, PLLA) showed an y weight loss upon enzyme exposure. Conversely, both a-PHB/PCL and a-PHB/PL LA blends biodegraded. Analysis of the biodegradation products and of blend composition changes during biodegradation demonstrated that in both blends only the a-PHB component undergoes enzymatic hydrolysis. The results suppo rt the hypothesis that the crystalline polyester blended with a-PHB promote s a-PHB enzymatic hydrolysis by providing stable binding sites to the enzym e. The dependence of biodegradation rate on blend composition is different in (immiscible) a-PHB/PCL and (miscible) a-PHB/PLLA blends and can be expla ined in terms of different phase behavior and morphology.