Confined Crystallization and Hydrolytic Degradation Behavior of Dual-Crystalline Core–Sheath Fibers Comprising Immiscible Polymers

This study investigated the thermal and crystallization behaviors of electrospun coaxial fibers comprising immiscible poly(butylene succinate) (PBS) and poly(L-lactide) (PLLA) in the core and sheath, respectively. The PBS and PLLA in the as-electrospun fibers were crystalline and noncrystalline, respectively. Thermal treatment resulted in noticeable crystal development for both PBS and PLLA. The confinement of PBS and PLLA chains in the fibers hindered the development of crystalline lamellae, which resulted in the melting points of PBS or PLLA in the fibers being lower than those in bulk PBS or PLLA. Because of the immiscibility of PBS and PLLA, the PBS and PLLA crystallizations were barely affected by each other. During solvent evaporation in electrospinning, rapid relaxation of PBS chains occurred, which caused PBS crystals to be randomly oriented. By contrast, PLLA chains remained stretched and aligned parallel to the fiber axis. Subsequent crystal development resulted in the unidirectional orientation of PLLA crystals. When PLLA and PBS were prepared with a core–sheath structure, their hydrolysis was considerably enhanced. This finding was attributed to the presence of vulnerable PBS-PLLA interfaces. Thermal treatment increased the crystallinity of PBS and PLLA, resulting in a reduction in their hydrolytic degradation.