Structure and properties of UHMWPE products strengthened and toughened by pulse vibration molding at low temperature

Abstract Low efficiency in the fabrication of ultra-high molecular weight polyethylene (UHMWPE) with excellent mechanical properties has limited its wide application, owing to its ultra-high melt viscosity. Present processing methods including compression molding (CM) and high velocity compaction (HVC) can't be used for manufacturing UHMWPE products possessing outstanding mechanical strength, toughness and wear resistance simultaneously. A novel molding process of pulse vibration molding (PVM) first utilizes application of pulsed vibration pressure to UHMWPE powders pre-heated close to melting temperature. This method effectively promotes consolidation at particle interfaces at low molding temperatures, while melt flow in a specific direction during the PVM process accelerates a further fusion at particle interfaces, thus obtaining UHMWPE products with orientation induced by melt flow during the PVM process (i.e. OPVM). The crystallinity and lamellae thickness of PVM-UHMWPE molded at 170 °C for 30 min (PVM-170-30) were significantly greater than those of CM-UHMWPE prepared at 210 °C for 60 min (CM-210-60), consequently yield strength, Young's modulus, and wear resistance of PVM-170-30 were much higher. Inside OPVM-UHMWPE molded at 170 °C for 30 min (OPVM-170-30), orientation of molecular chains along the flow direction generated by melt flow resulted in high crystallinity and formation of numerous shish-kebab structures at particle interfaces. Compared with those of CM-210-60, yield strength, Young's modulus, elongation at break and work-to-failure of OPVM-170-30 increased from 21.5 ± 0.4 MPa, 292 ± 3 MPa, 505 ± 20% and 114 ± 3 kJ/m2 to 23.0 ± 0.2 MPa, 334 ± 8 MPa, 571 ± 17% and 132 ± 6 kJ/m2, and its wear rates and wear index decreased from 3.8 ± 0.3% and 184 ± 15 to 2.8 ± 0.2% and 142 ± 6, respectively. The outstanding performance of OPVM-170-30 was originated from high crystallinity and formation of self-reinforcing shish-kebab superstructures at particle interfaces. The present results suggested OPVM-170-30 has high potential in applications requiring high wear resistance, mechanical strength, and fracture toughness, such as artificial joint.