Radiation induced free radical stability and degradation behavior in GUR resin and 1900 resin types UHMWPE over 20 years of aging

Vollständiger Abstract

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Abstract Radiation-induced free radical stability was evaluated using Electron Spin Resonance (ESR) for two medical-grade Ultra High Molecular Weight Polyethylene (UHMWPE) resins, GUR 4150 and 1900H, after 20 years of aging in air and vacuum at 23 °C, 37 °C, and 75 °C. Spectral analysis revealed oxygen-induced radicals in samples aged in air at 23 °C and 37 °C, with higher concentrations at 23 °C, whereas vacuum-aged samples retained primary radiation-induced radicals that decreased progressively with increasing temperature; no radicals were detected in air-aged samples at 75 °C. Overall, radical concentration decreased by about two orders of magnitude over 20 years. At 23 °C, 1900H exhibited lower FRC than GUR 4150 by about two-thirds, indicating improved oxidative stability. After air aging at 23 °C, 1900H also showed reduced carbon-centered polyenyl radicals (R1, 0.6×) and oxygen-induced polyenyl radicals (R2, 0.5×) compared to GUR 4150. X-ray diffraction (XRD) confirmed the crystalline structure of both materials through the characteristic orthorhombic peaks at Bragg angles 2θ = 22° (110) and 24° (200). The average crystallite sizes for GUR 4150 were 21.76, 20.24, and 21.84 nm, while for 1900H they were 17.14, 20.22, and 21.56 nm at 23 °C, 37 °C, and 75 °C, respectively. Fourier Transform Infrared Radiation measurements revealed oxidation index values of 11.3%, 17.7%, and 38.2% for GUR 4150, compared with significantly lower values of 5.2%, 7.4%, and 10.5% for 1900H, indicating enhanced oxidation resistance of 1900H after 20 years of aging.