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

The article focuses on the effect of adding low-density polyethylene (LDPE) on the shear-induced crystallization behavior of polypropylene (PP) compared to high-density polyethylene (HDPE) addition. Using a transparent parallel-plate shear device and capillary extrusion, the study found that LDPE significantly accelerates shear-induced crystallization of PP, resulting in higher crystallization temperatures and enhanced molecular orientation, whereas HDPE does not produce this effect. This acceleration is attributed to the exponential increase of the Weissenberg number during cooling, which causes excess deformation in the PP matrix due to stress buildup in LDPE droplets, promoting flow-induced crystallization. The findings were supported by polarized optical microscopy and two-dimensional wide-angle X-ray diffraction analyses, and the enhanced crystallization behavior was also observed in strands extruded via capillary rheometry.