Shear-induced crystallization of polypropylene/low-density polyethylene blend

Shear-induced crystallization behavior was studied using a phase-separated blend comprising a polypropylene continuous phase and a low-density polyethylene (LDPE) dispersion, which is known to show strain hardening in transient elongation viscosity. In this study, crystallization behavior was mainly evaluated by the light intensity transmitted through a transparent parallel-plate geometry. It was found that shear-induced crystallization was greatly accelerated by the addition of LDPE, resulting in a high crystallization temperature and a highly oriented structure. When the sample was cooled slowly, however, shear-induced crystallization was not accelerated by LDPE. Furthermore, extrusion was performed using a capillary rheometer. The molecular orientation in the strands collected after cooling in the air was found to be enhanced by the LDPE addition, suggesting that flow-induced crystallization was accelerated even at capillary extrusion.