Influence of tacticity and molecular weight of poly(vinyl alcohol) on crystallization and biodegradation of poly(3-hydroxybutyric acid)/poly(vinyl alcohol) blend films

The crystallinity and the profile of biodegradation by environmental microo rganisms in river water were investigated for bacterial poly(3-hydroxybutyr ic acid) [PHB] blend films with stereoregular poly(vinyl alcohol)s [PVA] an d low-molecular weight atactic PVAs. According to the DSC thermal analysis, the crystallization of PHB was found to be not suppressed by blending with highly isotactic PVA. This result is consistent with previous results obta ined by using Fourier-transformed infrared spectroscopy, that is, PVA sampl e with higher syndiotacticity brings about higher suppression of crystalliz ation of PHB. In the PHB/PVA blend system, the formation of small PHB cryst als was found by wide angle X-ray scattering, even in the samples for which the melting endotherm of PHB was not detected by DSC. The biodegradation p rofile of these blend films depends strongly on the water solubility of the PVA component. The PHB blends with low-molecular weight atactic PVA, which shows higher water solubility than atactic PVA with higher molecular weigh t and stereoregular PVA, exhibited faster degradation compared to the PHB b lends with high-molecular weight atactic PVA system. The biodegradability o f the PHB blends with stereoregular PVA became extremely low, when the PVA composition in the blends became high. (C) 1999 Elsevier Science Ltd. All r ights reserved.