Crystallization Kinetics and Morphology in Miscible Blends of Two Crystalline Polymers

Abstract

Miscibility, crystallization behavior and morphology of blends prepared from two crystalline polymers, poly(butylene succinate) (PBSU), and poly(vinylidene chloride-co-vinyl chloride) [P(VDC-VC)] have been examined by polarized optical microscopy and differential scanning calorimetry. It is found that PBSU is miscible with P(VDC-VC) since each blend showed a single glass transition temperature Tg. Spherulitic morphology and the melting behavior of the blends were strongly dependent upon the crystallization kinetics and some unique phenomena were found out: (i) in contrast to the other results reported so far, growth rate G of low-Tm component (PBSU) was decreased greatly with increasing high-Tm component [P(VDC-VC)] content, (ii) for the PBSU/P(VDC-VC) (40:60) blend crystallized at 90°C (i.e., the growth rate of the two components was appproximately the same) so called interlocked spherulites were formed, where PBSU spherulites grown through the interlamellar regions of P(VDC-VC) spherulites, (iii) for the blends crystallized during fast cooling conditions from the melt (e.g., faster than 10°C min−1), only one melting peak appeared corresponding to PBSU and no noticeable melting peaks of high-Tm component P(VDC-VC) were observed. Hence, it is seen that the crystallization behavior of high-Tm component is heavily affected by the low-Tm component. Therefore, kinetic factors are the most important one in controlling the crystallization behavior and the morphology of the crystalline/crystalline blends.