Hydrolytic degradability of poly(3-hydroxyoctanoate) and of a poly(3-hydroxyoctanoate)/poly(R,S-lactic acid) blend

Films of bacterial poly(3-hydroxyoctanoate) (PHO) (M-n = 85 000) pure or blended with racemic poly[(R,S)-lactic acid] (PLA50) of low molecular weight (M-n = 1100) were prepared by solvent casting techniques and incubated in buffer solutions at 37 degrees C and at different pH. Changes in weight, molecular weight and morphology were recorded during hydrolysis experiments. The PHO hydrolytic degradation process was very slow: after 5 months of degradation, only 0.1% of ester functions were hydrolyzed. In the case of a PHO/PLA50 blend (80/20, w/w), after 1 month, no more PLA50 was present in the film and PHO molecular weight decrease was significantly more important than in the case of pure PHO degradation; the hydrolytic scission of PHO chains was enhanced by the presence of PLA50. Differential scanning calorimetry achieved on PHO/PLA50-blended samples displayed a lack of complete miscibility between both components. In the early stage of ageing, an increase of crystallinity for the different materials was observed in all cases. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.