Non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear conditions

Abstract

The non-isothermal crystallization of poly(L-lactide) (PLLA) under quiescent and steady shear flow conditions was in situ investigated by using polarizing optical microscopy (POM) with a hot shear stage and wide-angle X-ray diffraction (WAXD). The shear rate and the cooling rate both play a significant role in the final crystalline morphology and crystallinity. Under quiescent conditions, the morphology assumes different sized spherulites, and its crystallinity dramatically reduces with increasing the cooling rate. On the other hand, the shear flow increases the onset crystallization temperature, and enhances the final crystallinity. When the shear rate is above 5 s−1, cylindrite-like crystals are observed, furthermore, their content depends on the cooling rate.