Study of thermal melting behavior of microbial polyhydroxyalkanoate using two-dimensional Fourier transform infrared correlation spectroscopy

The molecular level premelting process of purified biosynthesized polyester poly(hydroxybutyrate-co-hydroxyvalerate) or P(HB-co-HV) (20.4% HV) was investigated by two-dimensional Fourier transform infrared (2D FT-IR) correlation spectroscopy. Intensity variations and band shifts in the characteristic spectral regions for C=O groups (1710-1770 cm(-1)), C-H groups (2910-3010 cm(-1)), and C-O-C groups (1220-1310 cm(-1)) were selected for a detailed study of the thermally induced phase transition of the copolymer. The 2D correlation approach successfully demonstrated that a fully amorphous liquid-like structure was formed following the disappearance of the crystals in the sample, by going through an intermediate state related to the lost conformation of the highly ordered and helical polyester main chain.