Surface composition and biodegradability of poly(3-hydroxybutyric acid)/poly(vinyl alcohol) blend films

Biodegradability in a typical environmental medium of blend films composed of bacterial poly(3-hydroxybutyric acid) (PHB) and chemically synthesized p oly (vinyl alcohol) (PVA) was investigated by BOD test. The degradation pro file of the blend films was found to depend on their blend compositions. Th e blend films with PHB-rich composition showed higher degradation rate and higher final degraded ratio than the pure PHB film. The pure PHB and PHB-ri ch blend films began to collapse after about 3-4 days. The PVA-rich blend f ilms degraded to greater extents than the pure PVA him, but these films did not collapse even after 30 days. The improved degradability of both PHB an d PVA found for the blend films may be at least partly due to the decreases in crystallinity of the minor components in the blends. Surface compositio n of the blend film is expected to affect the biodegradability, especially at the initial stage of degradation. According to the results from ATR-FTIR and contact-angle measurements, the surfaces on the air-side of the cast b lend films were found to have PVA-rich composition. (C) 1998 Elsevier Scien ce Limited. All rights reserved.