Constructing High-content, Highly Ordered Shish-Kebab Crystals during Hot-stretching via Varying Contents of Reserved Shish in Ultra-long Chain Ultra-high Molecular Weight Polyethylene Gel Systems

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is widely utilized in low-dimensional materials due to its ultra-long chain imparted excellent strength and modulus. By employing gel-molding technology with a gradient temperature control, this study successfully produced gel films with varying shish crystal contents of the UHMWPE with a molecular weight of 8.0 million. The structural evolution during film hot-stretching was investigated by in-situ wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), ultra-small-angle X-ray scattering (USAXS), and ex-situ methods of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The ultra-long molecular chains delay stress transfer during stretching but provide more nucleation sites for shish-kebab crystallization to form well-ordered shish-kebab crystals under high strain. The reserved high-content shish facilitates structural evolution, inducing the formation of highly-ordered shish-kebab crystals that eventually transfer into shish crystals in the later stage of stretching. The samples with low shish content, although the structural evolution is facilitated during stretching, predominantly result in newly formed shish-kebab crystals through melt recrystallization. However, some unoriented lamellae persists in unreserved samples stretching progress, leading to less ordered shish-kebab structures. By comparing with previous work of UHMWPE with low molecular weights, we demonstrate that the ultra-long molecular chains also play a key role on enabling the construction of highly-ordered shish-kebab crystals with high shish content during hot-stretching of UHMWPE gel films, providing new insights into processing control and optimization for engineering applications.