Miscible crystalline/crystalline polymer blends of poly(vinylidene fluoride) and poly(butylene succinate-co-butylene adipate):: Spherulitic morphologies and crystallization kinetics

Spherulitic morphologies and overall crystallization kinetics of miscible poly(vinylidene fluoride) (PVDF)/poly(butylene succinate-co-butylene adipate) (PBSA) blends were studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD). PVDF and PBSA crystallize separately in the blends. For the high-T-m component PVDF, the crystallization mechanism does not change, while both the spherulitic growth rate and the overall crystallization rate of PVDF decrease with increasing crystallization temperature and the PBSA content in the blends. Much more attention has been directed to the spherulitic morphologies and overall crystallization kinetics of the low-T-m component PBSA, which are affected not only by blend composition and crystallization temperature but also strongly by the preexisting crystals of the high-T-m component PVDF in the blends. PBSA spherulites nucleate in the matrix of the PVDF spherulites and continue to grow until impinging on other PBSA spherulites. The overall crystallization rate of PBSA is accelerated in the blends compared with that of neat PBSA, which reduces with increasing crystallization temperature despite blend composition for the PBSA-rich blends. The presence of the preexisting PVDF crystals shows two opposite effects on the overall crystallization of PBSA, i.e., enhanced nucleation ability and slower crystal growth rates.