Estimation of thermal acceleration factors of ageing epoxy insulation using thermogravimetry and intuitive kinetic model

The long term performance of epoxy resin compounds intended to be applied as electric insulating materials in nuclear equipment has been assessed using an accelerated thermal ageing technique. Conventional bisphenol-A-diglycidyl ether- and cycloaliphatic epoxy resin-based formulations (both crosslinked by anhydrides) have been compared using dynamic and isothermal thermogravimetry. Tests were performed on both virgin samples and on samples exposed to gamma-irradiation. A simple intuitive consecutive thermal decomposition model was suggested and fitted to the isothermal decomposition data. Using the fitted parameters the thermal acceleration factor was established for both kinds of materials. Under practically available thermal conditions radiation ageing had a negligible effect on the decomposition. The bisphenol-A-diglycidyl ether type material proved to be more stable under thermal ageing conditions.