Closed-loop recycling of waste ultra-high molecular weight polyethylene via inducing melt fracture coupled with...

Ultra-high molecular weight polyethylene (UHMWPE) is a high-performance engineering thermoplastic characterized by outstanding mechanical strength, chemical stability, resistance to crack propagation, exceptional wear resistance, and extremely high melt viscosity. These attributes, while advantageous for performance, render UHMWPE highly challenging to recycle using conventional approaches. Consequently, there is an urgent demand for innovative recycling strategies that preserve, or potentially enhance, its intrinsic properties. This study introduces a mechanical recycling approach that integrates high- and low-temperature shear fields through the use of double-roll open mills and solid-state shear milling equipment. High-temperature shear stresses induce melt fracture in UHMWPE, generating structural defects, while the three-dimensional shear forces in solid-state shear milling accelerate defect initiation and propagation. This coupled shear-field process mitigates the limitations imposed by UHMWPE's high melt viscosity and highly entangled chain architecture, thus overcoming conventional recycling barriers. Application of this method to waste UHMWPE sheets enabled effective closed-loop recycling. The recycled samples retained up to 93% of the tensile strength of the original sheets. Furthermore, the processed material exhibited irregular morphologies with micrometer-scale particle sizes and reduced thickness. Notably, molded samples derived from this process demonstrated enhanced tensile fracture strain compared with the original sheet waste. Overall, the coupled high-low temperature shear-field strategy presents a facile and promising pathway for the closed-loop recycling of UHMWPE and potentially other difficult-to-process engineering thermoplastics.