Evaluation of Oxidative Degradation of Ultra-High-Molecular-Weight Polyethylene Irradiated by Gamma-Ray

In this study, the oxidative degradation of gamma-irradiated ultra-high-molecular-weight polyethylene (UHMWPE) was evaluated. Tensile yield stress, Young's modulus, and Vickers hardness were measured to characterize oxidative deterioration. Furthermore, we evaluated the existence of residual radicals by the electron spin resonance (ESR) analysis, and discussed the relationship between ESR spectra change and mechanical property indexes. In the tensile test of small UHMWPE specimens, it is often difficult to measure the strain. Therefore, we tried to estimate the Young's modulus simply by using Hertz's theory of elastic contact, and confirmed its usefulness. It is possible to estimate the tensile Young's modulus from the indentation test in this experimental range. This method is applicable to evaluate the relationship between mechanical properties such as Young's modulus and ESR properties over a long term after irradiation.