Confined Growth of Poly(butylene succinate) in Its Miscible Blends with Poly(vinylidene fluoride): Morphology and Growth Kinetics

The morphology and confined crystallization behavior of poly(butylene succinate) (PBS) in miscible poly(vinylidene fluoride) (PVDF)/PBS blends has been studied using differential scanning calorimetry (DSC) and optical and atomic force microscopy (OM and AFM). It was found that PBS crystal lamellae nucleated and grew confined inside the matrix of PVDF spherulites. Crystallized PBS domains grow with an ellipsoidal outline within PVDF spherulites formed at a relatively high PVDF crystallization temperature (Tc,PVDF), while circular domains, engulfing several PVDF spherulites, are seen when growing in the PVDF spherulites created at lower Tc,PVDF. The growth kinetics of PBS confined in the PVDF matrix was investigated under various conditions. The growth rate of PBS (GPBS) increases with decreasing crystallization temperature and increasing PBS content under a given PVDF crystallization temperature (Tc,VDF). For Tc,PVDF above 145 °C, GPBS decreases with Tc,PVDF for both 50:50 and 30:70 PVDF/PBS blends. However, for Tc,PVDF below 145 °C, 50:50 and 30:70 PVDF/PBS blends exhibit the opposite GPBS trend; that is, GPBS for the 50:50 blend decreases with decreasing Tc,PVDF, while for the 30:70 PVDF/PBS blend GPBS increases with decreasing Tc,PVDF. It is shown that this behavior cannot be associated with the effect of crossing the boundary of smaller PVDF spherulites formed at a lower temperature. Rather, the behavior appears to be related to the interleaving growth of PBS lamellae among PVDF lamellae or between bundles of PVDF lamellae (fibrils), as in situ AFM observation shows. It is found that the interconnectedness of the molten pockets within the PVDF spherulites, which depends on the PVDF crystallization temperature, is an important factor determining the growth kinetics of PBS confined within the PVDF scaffold.