Changes in the Molecular Structure of UHMW Polyethylene under the Influence of Thermal and Radiation Modification, as Well as Time

Abstract

The paper presents the results of an examination of UHMW polyethylene type GUR1050 using the EPR, FTIR and SEM methods. The relationship between the number of radicals in the polymer and the absorbed dose of ionizing radiation has been shown. The radicals, being highly active macroparticles, disappear in time, so that after about a year their amount is reduced by approximately one order of magnitude. The disappearance of the radicals over time results in a change in EPR spectra, an increase in the degree of oxidation, and cross-linking. The most probable mechanisms are the formation of alkyl and allyl radicals and their gradual transitions, which lead to the absorption of atmospheric oxygen, and the recombination of radicals, which leads to the formation of cross linkages. Thermal treatment of the samples is an effective method of eliminating the radicals. Tribological tests and their analysis by means of SEM observation showed that the irradiated samples proved to have higher resistance to abrasion than the material that was not exposed to radiation.