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 poly (vinyl alcohol) (PVA) was investigated by BOD test. The degradation profile of the blend films was found to depend on their blend compositions. The 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-rich blend films began to collapse after about 3-4 days. The PVA-rich blend films 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 and 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 composition 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 blend films were found to have PVA-rich composition. (C) 1998 Elsevier Science Limited. All rights reserved.