Structural Evolution of High-Entanglement Ultrahigh Molecular Weight Polyethylene Films with Reserved Shish Crystals during the Hot Stretching Process

Shish crystals are a crucial crystal structure in ultrahigh molecular weight polyethylene (UHMWPE), composed of fully extended, nonentangled molecular chains, enabling the exceptional mechanical properties of low-dimensional UHMWPE products. During the molding process, precise control of the processing temperature allowed for the fabrication of high-entanglement UHMWPE films containing shish crystals. Rheological characterization revealed that the introduction of nonentangled shish crystals contributed to a partial reduction in the degree of entanglement in the UHMWPE films. Using in situ small-angle X-ray scattering (SAXS)/ultrasmall-angle X-ray scattering (USAXS)/wide-angle X-ray diffraction (WAXD), combined with ex situ SEM and DSC measurements, the structural evolution in high-entanglement UHMWPE films with reserved shish crystals was investigated during hot stretching. The results indicated that the introduction of shish crystals contributed to the reduction of inclined lamellar stacking caused by high entanglement, thereby facilitating the transformation of inclined lamellae into shish-kebab crystals. Higher-temperature stretching resulted in a partial untangling of molecular chains, promoting molecular chain crystallization and orientation, thereby fostering the formation of additional shish-kebab crystals.