Deformation Temperature Dependency of Microstructure\nEvolution in Die-Drawn iPP/UHMWPE Blends

Ultrahigh\nmolecular weight polyethylene (UHMWPE) is one of the\nmost promising polyolefins, but its processability and consequently\napplications are limited by its high melt viscosity. An effective\nmethod to improve the processability is to introduce another polymer\ncomponent. Yet it is challenging to deform the sample if the components\nare not compatible with each other. In this work, we blended the UHMWPE\nwith isotactic polypropylene (iPP) and successfully processed the\niPP/UHMWPE samples via die-drawing at temperatures below, near, and\nabove the melting temperature of UHMWPE. It was found that the melting\nbehavior of the die-drawn samples was determined by the deformation\ntemperature. The molecular chain orientation slightly decreased, while\nthe long periods first increased and then decreased with increasing\ndeformation temperature. Three melting peaks observed in the samples\ndeformed at 130 and 140 °C originated from the melting of cooling-induced\nUHMWPE crystallites, deformation-induced fibrillar UHMWPE crystallites,\nand deformation-induced fibrillar iPP crystallites, respectively.\nThe melting peak of deformation-induced fibrillar UHMWPE crystallites\ncould not be observed in the sample deformed at 150 °C because\nit is unlikely for UHMWPE chains to crystallize at such a high temperature.\nThis sample also has the lowest melting point since the UHMWPE lamellae\nformed during deformation could serve as nucleation sites in the other\ntwo samples.