Summary: Ultra high molecular weight polyethylene (UHMWPE)/zirconia composite has been prepared by in situ polymerization of ethylene using a Ti-based Ziegler-Natta catalyst supported on the surface of zirconia. Comparison of mechanical and tribological properties has been carried out between the in situ polymerized and mechanically blended composites. Microscopic observations of filled composites revealed that the polymerized composite had more uniform dispersion of zirconia and enhanced interfacial properties than the mechanically blended composite. The polymerized composite showed in a tensile test a remarkable increase in elastic modulus and yield strength, in a tensile test, but a loss in elongational properties was insignificant. In a ring-on-block type wear test, the polymerized composite displayed superior wear resistance to the blended composite as well as to neat UHMWPE. At 43 wt.-% of zirconia content, the polymerized composite showed about one fourth of the 1wear rate of neat UHMWPE. Observations of wear surfaces revealed that the abrasive wear, which are observed in unfilled UHMWPE, are greatly suppressed in filled composites. In polymerized composite, moreover, micro-cracks were also significantly reduced in comparison to the blended composite, which eventually led to an additional decrease in the wear rate.
SEM image of powdery polymerized composite (zirconia content: 15%) obtained from the in situ polymerization.