Injection molding of delamination‐free ultra‐high‐molecular‐weight polyethylene

Abstract

When ultra‐high‐molecular‐weight polyethylene (UHMWPE) in powder form is injection molded, the so‐called delamination layering occurs near the skin of the parts. This layering defect hampers UHMWPE's superior wear resistance property and part surface quality. The delamination layer was caused by a combination of excessive shear stress near the part surface and high degree of molecular entanglement of UHMWPE. A mold insulation method that delays the rapid cooling of UHMWPE to reduce the shear stress and improve the polymer chain “interdiffusion” across the entangled chain bundles was used to eliminate the delamination layer. When the insulation layer thickness and mold temperature were optimized, the delamination layer was eliminated completely while still maintaining a reasonable cooling/cycle time. The delamination‐free parts were found to regain UHMWPE's superior impact resistance and tensile properties. POLYM. ENG. SCI., 59:2313–2322, 2019. © 2019 Society of Plastics Engineers

Thermal, rheological, and mechanical characterization of compression and injection molded ultra‐high molecular weight polyethylene, high density polyethylene, and their blends

“…Injection molded Neat UH and UHMWPE/HDPE blend samples had an obvious delamination defect. The delamination defect manifested during injection molding could be attributed to the excessive shear stress and poor “inter‐diffusion” among entangled UHMWPE chain bundles during the filling and packing stages 16 . The high shear stress at the interface of the frozen skin layer and molten core layer resulted in severe melt fracture, and hence hindered the diffusion and consolidation of the frozen and core layers.…”

“…The delamination thickness decreased with increasing HDPE content. It was found in our previous work 16 that the delamination defect could be eliminated by applying either mold insulation or rapid heat cycle molding (RHCM) technology 31,32 to increase the mold wall temperature.…”

“…A single‐edge razor was mounted in a milling machine to precisely notch the samples on both sides. More details on the sample preparation could be found in the Reference [16]. Two sets of impact tests were carried out.…”

“…Delamination defect usually occurs in the injection molded UHMWPE‐dominant parts. Epoxy coating was used as an insulation to slow down mold cooling and hence yield delamination‐free neat UHMWPE parts 16 . Rapid heat cycle molding (RHCM) 31 is a novel injection molding technology based on dynamic control of the mold temperature that can achieve rapid mold heating and cooling.…”

Fatigue crack propagation behavior of polyether ether ketone under biaxial loading

“…In order to minimize metallic wear, ultra‐high‐molecular‐weight polyethylene (UHMWPE) is used as bushing. [ 3 ] However, the effect of wear particles still cannot be effectively eliminated. [ 4 ] Some studies have shown that polyether ether ketone (PEEK) has much higher wear resistance than UHMWPE.…”