Melt shear-induced crystallization of miscible poly(vinylidene fluoride)/poly(1,4-butylene succinate) (PVDF/PBSU) blends was investigated through a series of structural and morphological characterizations. By varying the shear rate and blend composition, we obtained two key findings regarding the γ-phase generation. First, the γ-phase fraction within the samples showed non-monotonic behavior, initially increasing and then decreasing with increasing shear rate ( \(\dot{\gamma}\) ), indicating the existence of an optimal \(\dot{\gamma}\) value for maximizing γ-phase formation. Second, adding PBSU significantly enhanced shear-induced γ-phase crystallization, not only elevating the γ-phase fraction at the optimal \(\dot{\gamma}\) but also considerably broadening the effective \(\dot{\gamma}\) range to achieve a high γ-phase content. In contrast, PBSU did not promote γ-phase formation in untreated blends. These results highlight the synergy between the shear flow and PBSU addition in facilitating the polar γ-phase in PVDF. Finally, we constructed shear phase diagrams to depict the γ-phase crystallization within the parameter space of the shear rate/chain orientation and blend composition. It is speculated that melt shear primarily facilitates γ-phase nucleation through chain orientation, whereas PBSU enhances γ-phase growth after nucleation by promoting chain diffusion and/or hydrogen bonding interactions with PVDF. This study contributes to a deeper understanding of γ-phase crystallization under shear flow and provides a reference for regulating the polar phase of PVDF through direct melt processing.
