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

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 center dot center dot center dot H-O and C=O center dot center dot center dot H-N). It is very likely that these intermolecular C=O center dot center dot center dot H-N and C=O center dot center dot center dot 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 center dot center dot center dot H-N and C=O center dot center dot center dot H-O hydrogen bondings are formed upon the cleavage of weak C=O center dot center dot center dot H3C hydrogen bondings of PHB. Thus, the formation of the C=O center dot center dot center dot H-N and C=O center dot center dot center dot H-O hydrogen bondings is accompanied by the decrease in the crystallinity of PHB in the blends. (C) 2015 Elsevier Ltd. All rights reserved.