Shear-induced crystallization of polypropylenes:effect of molecular weight

摘要

The crystallization kinetics of threepolypropylenes with different molecular weights was studiedduring shear under isothermal condition with a fibre pull-outdevice. Nucleation and growth under shear were observedand compared to static conditions. The crystalline growth ratewas measured both in static condition and under shear. Instatic condition , the morphologies are α-phase spherulitesand are formed from nuclei which are randomly distributed.Under shear α-phase morphologies are still observed butthe nucleation density and the growth rate depend on theshear-rate. The nucleation density is strongly enhanced byshear and acts as the main factor on the overall kinetics. Thegrowth rate increases with the shear-rate , but the basicgrowth mechanisms seem to be unmodified. β phaseappears after shear during the relaxation of the orientation.