Intermolecular hydrogen bondings in the poly(3-hydroxybutyrate) and chitin blends: Their effects on the crystallization behavior and crystal structure of poly(3-hydroxybutyrate)

Abstract Crystallization behavior and intermolecular hydrogen-bonding interactions of poly(3-hydroxybutyrate) (PHB)/chitin blends on as-solution cast films were studied as a function of composition and temperature by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and infrared (IR) spectroscopy. The significant changes were observed in the DSC curves, WAXD patterns and IR spectra of the blends with PHB ≤50 wt%. We found that the crystallinity of PHB decreases in the blends, however, its crystal structure is not much affected by blending with chitin. The appearance of a new band at around 1710–1714 cm −1 clearly reveals the formation of intermolecular hydrogen bondings between the C O groups of PHB and the O–H and N–H groups of chitin (C O⋯H–O and C O⋯H–N). It is very likely that these intermolecular C O⋯H–N and C O⋯H–O hydrogen bondings occur in the amorphous phase because of the reduction in the chain mobility in the blends with increasing chitin content, even above the melting temperature of PHB. The C O⋯H–N and C O⋯H–O hydrogen bondings are formed upon the cleavage of weak C O⋯H 3 C hydrogen bondings of PHB. Thus, the formation of the C O⋯H–N and C O⋯H–O hydrogen bondings is accompanied by the decrease in the crystallinity of PHB in the blends.