Solid-state extrusion of nascent disentangled ultra-high molecular weight polyethylene

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) stands out as the preferred material across a wide spectrum of demanding applications, thanks to its remarkable mechanical, chemical and physical attributes. Nevertheless, processing UHMWPE can be an arduous and time-consuming endeavor. Traditional melt-processing techniques, commonly employed for polymers, prove impractical due to the exceedingly high viscosity of the melt that follows from the highly entangled macromolecular chains. Several methods are known to lower the entanglement density of UHMWPE, such as crystallization from a semidilute solution or direct polymerization, resulting in a less interconnected polymer structure. Unfortunately, even with low-entangled UHMWPE, melt processing remains unviable because of the rapid re-entanglement of polymer chains upon melting. However, these low-entangled UHMWPE materials can still be effectively processed in the solid state, a technique employed in the production of high-performance UHMWPE fibers and tapes, currently the only two feasible geometries. This research reports the development of a solid-state extrusion method for nascent low-entangled powder, centering on manipulating the surface energy of the interior wall materials within the extruder and die. Ordinary steel dies proved ineffective for solid-state extrusion, as they generated excessive friction between the die and UHMWPE, resulting in a rapidly escalating extrusion pressure. However, utilizing dies constructed from temperature-resistant polymers allowed for extrusion at a consistent pressure without the need for lubricating agents. We demonstrate the practicality of the developed solid-state extrusion method by fabricating UHMWPE monofilaments and tubes, showcasing its potential in expanding the range of producible UHMWPE geometries. Additionally, a first evaluation of the influence of processing conditions and the entanglement density of the reactor powder used on extrudability, and the properties of the resulting components is presented.Highlights A process for the solid-state extrusion of UHMWPE is developed. UHMWPE processing with higher design flexibility than current industrial standards. UHMWPE processing with higher throughput than current industrial standards. Contrary to previous techniques no lubricating agent or co-extrudate is used.