Electron beam radiation effects on UHMWPE: an EPR study

Abstract

Electron paramagnetic resonance (EPR) technique has been employed to detect and characterise a series of different radical species generated in ultra-high molecular weight polyethylene (UHMWPE) via electron beam irradiation. Three different radical species have been found and assigned on the basis of their EPR spectra and of the related computer simulations. A secondary alkyl species, the prevalent one, is present immediately after irradiation, an allyl species appears only 24 h after irradiation when the alkyl species disappears.The third species, clearly visible at high microwave power only, has been observed for the first time and assigned to a tertiary alkyl carbon radical, whose formation is strictly connected with a Y-shape crosslink and a migration of the unpaired electron on a carbon atom localised in an adjacent position.

HYSCORE and Davies ENDOR study of irradiated ultra high molecular weight polyethylene

“…During this time, a large number of the formed radicals are known to recombine . The recombination process is stopped upon freezing at 77 K. Both CW and ESE detected EPR spectra observed after irradiation (Figs (A) and (B)) are characterized by a six‐line powder pattern typical of an alkyl radical and are extensively described elsewhere . A thorough understanding of the spectra, reported in Figs (A) and (B), is challenging.…”

“…The overall spectral intensity is about 30% of the intensity of the spectrum reported in Fig. (A), and the spectral features are typical of an allyl radical species . This time‐dependent study clearly indicates that the secondary alkyl radicals are unstable and that allyl radicals are also present in the irradiated sample.…”

Radiation-induced oxidation of ultra-high molecular weight polyethylene (UHMWPE) powder by gamma rays and electron beams: A clear dependence of dose rate

“…Upon irradiation, cleavage of C-H and C-C bonds (Joshi et al, 2013;Oral and Muratoglu, 2007;Slouf et al, 2008;Zénkiewicz et al, 2003) will result in the formation of free radicals (Medel et al, 2005;Shah and Fuzail, 2007;Zhao et al, 2010), chain scission (Reinitz et al, 2014), and cross-linking and the release of hydrogen gas (Brunella and Paganini, 2011). Furthermore, in the presence of oxygen, oxidation is a significant effect (Archodoulaki et al, 2011;Jahan and Durant, 2005;Kamweru et al, 2012;Medel et al, 2005;Mehmood et al, 2013;Oral et al, 2006).…”

Effect of Irradiation Treatment on Compressive Properties of Ultra-High-Molecular-Weight Polyethylene

“…Several studies have been conducted on the ESR of free radicals formed in UHMWPE by irradiation 3,16,17) . However, because the generation of radicals depends on the irradiation conditions and changes in a complicated manner over time, the identi cation of radical species and the determination of radical concentrations are dif cult.…”

“…It is well known that the molecular structure of UHMWPE changes with exposure to gamma irradiation, and consequently, its mechanical properties change 2) . Furthermore, multiple free radical species 3) are generated in UHMWPE over time because of gamma irradiation, and the crosslinking points and oxide ratios produced by the generation of free radical species are expected to undergo complex changes according to the irradiation conditions.…”