The effect of temperature on the structural evolution of ultra-high molecular weight polyethylene films with pre-reserved shish crystals during the stretching process

Abstract

The influence of temperature on the structural evolution and macroscopic properties of ultrahigh-molecular weight polyethylene (UHMWPE) films with pre-reserved shish crystals during stretching was investigated by in-situ small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements as well as ex-situ differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) measurements. The UHMWPE films with pre-reserved shish crystals were obtained by compression molding at 135 °C and further stretched at different temperatures of 100, 110, 120 and 130 °C. At all stretching temperatures, the pre-reserved shish can promote the structural evolution of UHMWPE films to form shish-kebab or shish crystals. At 100, 110, and 120 °C, the two-point pattern can be observed for 2D-WAXD, the lamellar crystals fragment to form shish-kebab crystals by epitaxial crystallization on pre-reserved shish crystals. At 130 °C, the two-point pattern signal becomes weak at 2D-WAXD, the lamellar crystals are mainly melted and then recrystallized on the pre-reserved shish crystals to form large-period kebab crystals. Moreover, the temperature of 130 °C favors the growth of kebab crystals with larger lateral size, resulting in a difficult transformation to shish crystals. In addition, at 110 and 120 °C, the crystallinity and orientation of UHMWPE films increase significantly after stretching, resulting in improved mechanical properties.