High elastic modulus polyethylene: Process‐structure‐property relationships

Abstract

Previous studies have shown that gel‐spun‐ultra‐high‐molecular‐weight polyethylene (UHMWPE) produces thin fibril products that exhibit high tensile moduli (35–200 GPa). The elaborate gel‐spinning process involves complex drawing stages with solvent incorporation. In this study, a previously proposed two‐stage, environmentally friendly solventless methodology was optimized. The two‐stage process included cross‐rolling (Stage 1) and orientation (Stage 2) to obtain oriented HDPE thin rods with an impressively high modulus using conventional HDPE. The optimization of the process was successfully achieved by thoroughly investigating the voiding mechanism. In addition, rapid relaxation during orientation supports the cavitation mechanism. Owing to this optimization, a modulus of 75 GPa was readily attained. The significant enhancement in the mechanical properties was a direct result of the optimization of our processing methodology to achieve a high degree of orientation. Notably, the fabricated oriented HDPE thin rods showed moduli comparable to those of the gel‐spun UHMWPE fibers but were at least 40 times thicker. Our comprehensive characterization of the voiding process and stress relaxation during our two‐stage process indicated the formation of a highly taut network structure and craze‐like configuration with controlled delamination. Thus, our proposed hierarchical model was refined to elucidate the process‐structure‐property relationships in greater detail. An optimized two‐stage environmentally friendly solventless process has been developed to create oriented polyethylene thin rods with impressively high modulus (75 GPa). The optimization was achieved by thoroughly investigating the voiding effect during cross‐rolling and crystalline relaxation during orientation. Comparison of the modulus from our process are similar to various commercial, gel‐spun fibers. Our thin rod products are at least 40 times thicker than commercial gel‐spun fibers. The thin rod product has impressively high modulus‐to‐weight and strength‐to‐weight ratios for future study in composite systems.