Flow-induced epitaxial growth of high density polyethylene in its blends with low crystallizable polypropylene copolymer

Abstract

In this work, we investigated the epitaxial crystallization and its determinant factor in the blends of high density polyethylene (HDPE) and a low crystallizable propylene-ethylene random copolymer (PPR) during injection molding. For PPR dominated blend (blended with 30 wt.% HDPE), epitaxial growth of HDPE on the PPR crystals can be achieved, as demonstrated by two-dimensional wide-angle X-ray diffraction and small-angle X-ray scattering measurements, though the crystallization of PPR was far behind that of HDPE component under quiescent conditions. In-situ shear infrared experiments indicated that PPR crystallized in advance mainly due to larger crystallization window and flow-induced crystallization acceleration. As for the blend with 70 wt.% HDPE, however, one could not observe epitaxy. Shear-induced crystallization of HDPE hindered its epitaxial growth. Once the formation of shish-kebab of HDPE was activated, the epitaxial growth would be suppressed to a large extent.