Synergistic Enhancement of Reserved Shish Crystals and Multistage Hot Stretching Process: Fabrication of High-Strength UHMWPE Films by Melt Extrusion Casting

Ultrahigh-molecular-weight polyethylene (UHMWPE) is widely used in numerous high-tech fields due to its exceptional properties; however, its extremely long molecular chains make it difficult to produce high-performance UHMWPE films using conventional melt processing methods. In this work, by controlling the extrusion temperature, UHMWPE/high-density polyethylene (HDPE) blend films with different reserved shish crystal contents were successfully prepared via melt extrusion casting, and a high-strength film preparation process combining the reservation of shish crystals with a multistage hot stretching process was explored. A combination of various characterization techniques, including wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), ultrasmall-angle X-ray scattering (USAXS), and scanning electron microscopy (SEM), was systematically employed to investigate the effects of different reserved shish crystal contents on the structural evolution and mechanical properties of the films under various stretching temperatures and draw ratios. The results show that the content of reserved shish crystals in the initial samples significantly affects crystal orientation and crystallization perfection, which in turn determines the subsequent crystal structural evolution and mechanical properties of the material. Furthermore, the incorporation of HDPE improves the melt processability of UHMWPE and accelerates the evolution of the crystalline structure. Among the films, those with the highest reserved shish content exhibited the fastest structural evolution and the best mechanical properties, ultimately achieving a tensile strength as high as 2.26 GPa. Through the synergistic effect of reserved shish crystals and multistage hot stretching, this study has established an efficient and green technological route for the fabrication of high-strength UHMWPE films.