Morphologies and mechanical properties of HDPE induced by small amount of high-molecular-weight polyolefin and shear stress produced by dynamic packing injection molding

摘要

To better understand the effect of a small amount of high-molecular-weight polyethylene (HMWPE) on the mechanical properties and crystal morphology under the shear stress field, the dynamic packing injection molding (DPIM) was used to prepare the oriented pure polyethylene and its blends with 4% HMWPE. The experiment substantiated that the further improvement of tensile strength along the flow direction (MD) of high-density polyethylene (HDPE)/HMWPE samples was achieved, whereas the tensile strength along the transverse direction (TD) still substantially exceeded that of conventional molding. Tensile strength in both flow and TDs were highly enhanced, with improvements from 23 to 76 MPa in MD and from 23 to 31 MPa in TD, besides the toughness was highly improved. So, the samples of HDPE/HMWPE transformed from high strength and brittleness to high strength and toughness. The obtained samples were characterized via SEM and TEM. For HDPE/HMWPE, the lamellae of the one shish-kebab in the oriented region may be stretched into other shish-kebab structures, and one lamella enjoys two shish or even more. This unique crystal morphology could lead to no yielding and necking phenomena in the stress-strain curves of HDPE/HMWPE samples by DPIM. (C) 2008 Wiley Periodicals, Inc.