Structural Evolution of Ultra-High Molecular Weight Polyethylene Low-Entangled Films with Reserved Shish Crystals During Hot Stretching

Shish crystals are crucial to achieving high performance low-dimensional ultra-high molecular weight polyethylene (UHMWPE) products. Typically, high stretch and shear flow fields are necessary for the formation of shish crystals. In this study, UHMWPE gel films with reserved shish crystals were prepared by gel molding, the structural evolution and properties of UHMWPE films stretched at temperatures of 100, 110, 120 and 130 °C were investigated by in situ small-angle X-ray scattering (SAXS)/ultra-small-angle X-ray scattering (USAXS)/wide-angle X-ray diffraction (WAXD) measurements as well as scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) measurements. Our findings showed that the reserved shish crystals can facilitate the formation and structural evolution of shish-kebab crystals during the hot stretching. Additionally, the reserved shish crystals promote the structural evolution of UHMWPE films to a greater extent when stretched at 120 and 130 °C, compared to 100 and 110 °C, resulting in higher crystallinity, orientation, thermal properties, breaking strength and Young’s modulus. Compared to UHMWPE high-entangled films with reserved shish crystals prepared by compression molding, UHMWPE low-entangled films with reserved shish crystals prepared by gel molding are more effective in inducing the formation and evolution of shish-kebab crystals during the hot stretching, resulting in increased breaking strength and Young’s modulus.