The effects on polyetheretherketone and polyethersulfone of electron and γ irradiation

In this study, the effects of ionizing radiation on the aromatic polymers polyethersulfone (PES) and polyetheretherketone (PEEK) were investigated. UV light, γ rays and a high-energy electron beam were used as radiation sources. A range of techniques has been utilized to investigate changes in PES and PEEK as a result of exposure to these sources. Electron spin resonance (ESR) measurements showed the creation of radicals in PES by UV or γ radiation. These radicals decayed, but some were still present 24 h after irradiation at room temperature. In PEEK, radicals were formed as a result of UV at room temperature and by UV or γ irradiation at 77 K. After irradiation at room temperature, these radicals decayed totally within 24 h. UV-visible absorption measurements of PES samples showed a dose related change at the absorption edge; no such change was observed for PEEK. Phosphorescence after γ irradiation increased in intensity for PES at low temperature but decreased at higher temperatures. For PEEK, no such changes were observed after irradiation. The differential scanning calorimeter (DSC) measurements showed changes in the crystallization, glass transition and melt-point temperatures of both PES and PEEK after electron irradiation. Electrical changes induced by irradiation were investigated using thermally stimulated discharge current (TSDC) and low frequency dielectric responses, derived from transient current (TC) measurements. Dielectric changes were observed for PES exposed to either γ rays or an electron beam. For PEEK only minor changes in the TSDC spectrum were observed after exposure to γ radiation. More significant changes were observed after exposure to the electron beam. Correlations were found between the production of radicals and the changes in the structural and electrical properties of the materials. Since significant changes were observed in the dielectric spectra of PEEK and PES at low frequencies, dielectric spectroscopy may provide a measure of aging in both insulation systems