Miscibility and crystallization behavior of poly(butylene succinate) and poly(vinylidene fluoride) blends

Miscibility and crystallization behavior of biodegradable poly(butylene succinate) (PBSU) and poly(vinylidene fluoride) (PVDF) blends, where two components are crystallizable have been investigated by differential scanning calorimerty and optical microscopy. From cloud point observation of the blends they are found to have lower critical solution temperature behavior. Spherulites of PVDF grew linearly with crystallization time and the growth rate decreased with increase in PBSU content. The interaction parameter chi(12), obtained from melting point depression of PVDF gave the value of -0.139. However, the crystallization and melting behavior of low-T-m component PBSU were quite different from that of high-T-m component PVDF: (i) the magnitude of the melting point depression of PBSU was changed strongly with cooling rate, (ii) for a given T-c, the melting point of PBSU increased with increase in PVDF content, in contrast to the decrease of the melting point in usual amorphous/crystalline blends, (iii) the spherulitic growth rate G of PBSU decreased very slightly with increase in PVDF content at a given T-c and the morphology of the PBSU were strongly dependent upon the crystallization condition. Microscopic observations and Avrami analysis of the crystallization of PBSU in the blends lead to the conclusion that all these unique crystallization behaviors of PBSU presented in this article are ascribed to the presence of PVDF crystals at the temperature where the crystallization of PBSU occurs.