Assessment of heat and storage conditions on γ-ray and electron beam irradiated UHMWPE by electron spin resonance

Electron spin resonance (ESR) spectroscopic study was undertaken to explore the nature of any remaining radicals in ultra-high molecular weight polyethylene (UHMWPE) after irradiation with γ-rays and electron beams to a dose of 25 KGy in air or N2 environment. The decay of radicals was studied by observing the ESR intensity change as a function of time. The following post-irradiation conditions were employed: (1) storage in air or N2 at 25°C, and (2) heat treatment in air or N2 at 80, 100, and 120°C for time intervals up to 8 h. The study suggests that radicals remaining trapped in the matrix of UHMWPE could be dramatically scavenged by heat treatment, independently of the atmosphere during irradiation and the heating process. The melting temperature and mechanical properties of irradiated UHMWPE under the experimental conditions employed were shown not to alter significantly by heat treatment, except in the presence of air.