Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating.

A series of poly(l-lactide)/poly(d-lactide) blended chips (LD), as-spun LD fibers (LD) and hot-drawn LD fibers (LD) were prepared for investigating the homocrystallization and stereocomplex crystallization behaviors of LD and LD fibers during heating. Modulated differential scanning calorimetry (MDSC), hot stage polarized microscopy (HSPM), and real-time wide-angle X-ray diffraction (WAXD) were used for studying the crystallization and melting behaviors, fiber morphology, and crystalline structure evolution of the LD and LD fibers' homocrystals and stereocomplex crystals during heating. The molecular chain orientations of the LD and LD fibers were obtained through spinning and improved through the hot drawing processes. When the molecular chain was oriented on the fiber axis, the homocrystals and stereocomplex crystals of the fibers began to form in turn as the heating temperature exceeded the glass transition temperature of the fiber. The side-by-side packing of the molecular chains was promoted by mixing the molecular chains with the extrusion screw during the spinning process, facilitating stereocomplex crystallization. When the LD fiber was heated above the glass transition temperature of the fiber, movement of the fiber molecular chain-including molecular chain orientation and relaxation, as well as crystallization, melting, and recrystallization of homocrystals and stereocomplex crystals-were investigated through HSPM. MDSC and real-time WAXD were used to observe the molecular chains of the melted poly(l-lactide) and poly(d-lactide) homocrystals of the fibers rearranging and transiting to form stereocomplex crystals during heating.