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

Ultrahigh molecular weight polyethylene (UHMWPE) is one of the most promising polyolefins, but its processability and consequently applications are limited by its high melt viscosity. An effective method to improve the processability is to introduce another polymer component. Yet it is challenging to deform the sample if the components are not compatible with each other. In this work, we blended the UHMWPE with isotactic polypropylene (iPP) and successfully processed the iPP/UHMWPE samples via die-drawing at temperatures below, near, and above the melting temperature of UHMWPE. It was found that the melting behavior of the die-drawn samples was determined by the deformation temperature. The molecular chain orientation slightly decreased, while the long periods first increased and then decreased with increasing deformation temperature. Three melting peaks observed in the samples deformed at 130 and 140 °C originated from the melting of cooling-induced UHMWPE crystallites, deformation-induced fibrillar UHMWPE crystallites, and deformation-induced fibrillar iPP crystallites, respectively. The melting peak of deformation-induced fibrillar UHMWPE crystallites could not be observed in the sample deformed at 150 °C because it is unlikely for UHMWPE chains to crystallize at such a high temperature. This sample also has the lowest melting point since the UHMWPE lamellae formed during deformation could serve as nucleation sites in the other two samples.