Wear resistance of lightly cross-linked ultrahigh-molecular-weight polyethylene crystallized from the melt under uniaxial compression

Ultrahigh-molecular-weight polyethylene (UHMWPE) was crystallized under the molecular orientation in order to improve the wear property against Co-Cr-Mo alloys for artificial joints. Commercial UHMWPE blocks of 30 mm thick were first irradiated under vacuum at room temperature to below 2.0 Mrad with γ-rays. Due to the irradiation, the lightly cross-linking is created. Next, the lightly cross-linked samples were compressed to different extents between two metal plates at 200°C and crystallized by cooling to room temperature over a period of 3 h. It was found that the samples had a very special spatial orientation of the crystalline phase. The thermodynamic and the mechanical properties of the compressed samples were higher than those of the non-compressed sample. Friction and wear tests were carried out using a six-station reciprocating pin-on-flat apparatus. The weight loss of compressed UHMWPE was lower than that of a non-compressed sample and it was suggested that the wear resistance was dependent on the compression ratio. In conclusion, the compressed UHMWPE is low in friction. Therefore, the sample can be available as a component of artificial joints.