Steady-shear-induced isothermal crystallization of poly(L-lactide) (PLLA)

摘要

The isothermal crystallization of poly(L-lactide) (PLLA) under steady-shear flow was investigated in situ using an optical polarizing microscope with a hot shear stage. The steady-shear-induced crystalline morphology of PLLA, to a great degree, depends on the crystallization temperature. There is a critical temperature, 120 degrees C, below which shear-induced row nuclei enhance nucleation ability, leading to the improvement of crystallinity, and above which cylindrite structure is generated. Their numbers increase and size reduces with temperature owing to the better movement and relaxation behavior of chains in the presence of shear flow. The results of 2D wide-angle x-ray diffraction (WAXD), showing the oriented structure at high T-c, and differential scanning calorimetry (DSC), detecting the rising of T-m with increasing T-c, well confirm the effect of T-c on the crystallization of PLLA under shear flow.