Structural evolution of ultra-high molecular weight polyethylene gel film stretching at different temperatures with reservation of shish crystals

Abstract

Shish crystal is the key structure to achieve low-dimensional ultra-high molecular weight polyethylene (UHMWPE) products with high performance. UHMWPE gel film containing shish crystals was prepared by precise temperature control in the gel molding, and its structural evolution in the stretching flow field at different temperatures was investigated by in-situ wide angle X-ray diffraction (WAXD)/small angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). It was found that shish crystals accelerated the structural evolution in both room and high temperature stretching, promoting more highly oriented crystals along the stretching direction. In room temperature stretching, the lamellae were deflected vertically to the stretching direction and gradually accumulated leading to a stabilization of the crystallinity index and the degree of orientation of the crystals along the stretching direction. However, in high temperature stretching, this intermediate orientation was broken and the transition to shish-kebab crystals continued, leading to a sharp increase in the crystallinity index and the degree of orientation of the crystals along the stretching direction.