Hydrogen-bonding interaction and crystalline morphology in the binary blends of poly(ε-caprolactone) and polyphenol catechin

The specific intermolecular hydrogen-bonding interaction between the ester carbonyl groups of poly(epsilon-caprolactone) (PCL) and the phenolic hydroxyl groups of catechin has been studied by Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). According to quantitative curve-fitting analysis of the FT-IR spectra of PCL/catechin blends, it was found that the fraction of hydrogen-bonded carbonyl groups of PCL increased with catechin content, while that of hydrogen-bonded hydroxyl groups of catechin decreased. The calculated crystallinity of PCL in the binary blends, based on the curve-fitting results, suggested that the crystallization of PCL was restrained in the blends with catechin. Only single glass transition temperature, T-g was observed over the whole range of blend compositions, which was between those of the pure components. The melting point T-m depressed and T-g increased, indicating also the existence of strong intermolecular association. The blend composition dependence of T-g could be predicted very well by the Kwei equation with a positive 'q' value of 124. With the aid of small angle X-ray scattering measurement, the segregation of catechin was investigated. It was found that the extent of extra-lamellar segregation increased with catechin content. It was suggested that the crystal growth rate played the dominant role in the formation morphology. With decreasing crystal growth rate of PCL component in the blends, enough time has been given to cetechin molecules to diffuse into extra-lamellar region.