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 α-chitin and chitosan were prepared as completely biodegradable polyester-polysaccharide composites. DSC revealed that the crystallization of PHB in these blends is suppressed when the proportion of the polysaccharide is increased. The same tendency was evident from the FT-IR band intensity of the carbonyl stretching absorption from PHB. Chitosan was found to have a stronger ability to suppress the crystallization of PHB than α-chitin. PHB in the blends was found by 13C NMR spectroscopy to be trapped in the `glassy' environment of the polysaccharide. Upon blending with PHB, the chitosan resonances are significantly broadend as compared to the chitin resonances. Hydrogen bonds are suggested to be formed between the carbonyl groups of PHB and the amide NH groups of chitin and chitosan.