Thermal properties and crystallization behavior of poly(3-hydroxybutyric acid) in blends with chitin and chitosan

Films of blends of microbial poly(3-hydroxybutyric acid) (PHB) with alpha-c hitin and chitosan were prepared as completely biodegradable polyester-poly saccharide composites. DSC revealed that the crystallization of PHB in thes e blends is suppressed when the proportion of the polysaccharide is increas ed. The same tendency was evident from the FT-IR band intensity of the carb onyl stretching absorption from PHB. Chitosan was found to have a stronger ability to suppress the crystallization of PHB than alpha-chitin. PHB in th e blends was found by C-13 NMR spectroscopy to be trapped in the 'glassy' e nvironment of the polysaccharide. Upon blending with PHB, the chitosan reso nances are significantly broadend as compared to the chitin resonances. Hyd rogen bonds are suggested to be formed between the carbonyl groups of PHB a nd the amide NH groups of chitin and chitosan.