Isothermal crystallization of poly(ε-caprolactone) in blend with poly(styrene-co-acrylonitrile): Influence of phase separation process

The isothermal crystallization process of poly(ε-caprolactone) (PCL) and its blend with styrene-acrylonitrile random copolymer containing 27.5 wt.-% acrylonitrile has been investigated as a function of crystallization and melting temperatures for different melting times in the vicinity of the lowest critical solution temperature (LCST)-type phase diagram using DSC. The obtained results showed that the isothermal crystallization kinetics from the melt of PCL in the blend was greatly affected by the presence of SAN. For a given crystallization temperature, the crystallization half time (t_0.5) in the case of PCL/SAN = 80/20 blend was much longer than the corresponding value for pure PCL. This depression in the crystallization kinetics of PCL in the blend was mainly attributed to the favorable interaction between the two components and the reduction in chain mobility as a result of increasing the T_g by adding the amorphous component (SAN). In addition, the value of t_0.5 was found to be independent of the melting temperature (T_m) and melting time for pure PCL. The isothermal crystallization kinetics for samples that were crystallized after decomposition into different stages of phase separation were also investigated. A major acceleration in the crystallization kinetics was observed isothermally for the samples that had undergone phase separation in the early and middle stages. The isothermal crystallization kinetics was also analyzed based on the Avrami approach. Although the crystallization kinetics was accelerated to a great extent by the liquid-liquid phase separation, no change in the crystallization mechanism could be predicted. Furthermore, the phase separation process of PCL/SAN blend has been studied indirectly by following the variation in t_0.5 at different melting temperatures and melting times above the LCST phase diagram.