|
The Effects of Raw Material, Irradiation Dose, and Irradiation Source on Crosslinking of UHMWPE
Greer, K. W.
Introduction
Currently manufacturers of highly crosslinked UHMWPE products are using different raw materials, irradiation sources, and irradiation doses. The objective of this study was to determine the effects of irradiation sources and doses on the crosslinking of four different UHMWPE raw materials.
Materials and Methods
Both GUR 1020 and GUR 1050 raw materials having average molecular weights of 3-4 and 5-6 million respectively were evaluated in both the ram extruded bar (REB) or compression molded sheet (CMS) forms. Bars of all four materials were irradiated in a vacuum package using either e-beam or cobalt 60 (i.e. gamma) sources at doses ranging from 3 to 12 MRad followed by quenching of the free radicals above the melt. Tests performed on all groups included tensile, impact, differential scanning calorimetry (to check crystallinity) and swell ratio (from which crosslink density was calculated) while hip simulator wear tests were performed on selected groups.
Results
As expected, increasing the irradiation dose decreased the impact strength, tensile elongation, and swell ratio for all materials and both irradiation sources. Going from the lower molecular weight 1020 (CMS and REB) to the higher molecular weight 1050 (CMS and REB) material, also decreased impact strength, tensile elongation, and swell ratio for both irradiation sources. While e-beam irradiation generally produced higher impact strength and elongation than gamma for a given material and dose, it also produced a higher swell ratio and thus lower crosslink density under the same conditions. As expected, wear decreased with increasing dose for both 1020 and 1050 materials, but when 1020 and 1050 groups having the same crosslink density were compared, the 1020 group had lower wear. This indicates that crosslink density is an indicator of wear rate only within the same raw material and not when comparing different raw materials.
|
