Miscibility, melting and crystallization of poly(ε-caprolactone) and poly (vinyl formal) blend

Abstract

Solution cast blends of poly(e-caprolactone) [PCL] and poly(vinyl formal) [PVF] from dichloromethane was investigated for miscibility by Differential Scanning Calorimetry [DSC], Fourier Transform Infrared Spectroscopy [FTIR] and optical microscopy. Melting (T_m) and crystallization (T_c) temperatures were for the PCL fraction while the glass transition temperature (T_g) was for PVF fraction in the blends. Blends with 20 wt% and less PCL showed a depression in T_m and T_c. Depression in T_c indicated that during the non-isothermal crystallization process, the presence of PVF decreased the PCL segments migrating to the crystallite-melt interface thus reducing the nucleation rate, growth rate and the thickness of the lamella resulting in a depressed T_m. Crystallinity (X_c) decreased gradually with decreasing content of PCL in the blend and was due to the dilution of PCL by PVF. A depressed T_g was observed for 10 wt% PCL blend and remained the same for all other blend compositions. These observations suggested that this blend system has very low degree of miscibility. The degree of miscibility increased at low polyester concentration. FTIR spectra of the blends with low polyester concentrations showed changes in the C=O, O-H and C-O-C regions in the blended PVF and PCL spectra. Optical microscopy showed phase separation in the melt and in the PCL spherulites.