UV-induced ageing of epoxy resins: surface conductivity evolution related to chemical modification - application to ageing evaluation of insulating materials

In order to improve our understanding of the phenomena implicated in the degradation of insulating properties, we studied the effects of UV irradiation on two epoxy systems. We present results obtained by the follow up of surface chemical composition by FTIR and surface conductivity by Surface Potential Decay measurements (SPD). From those results we have been able to determine the structural difference between the two systems that is responsible for different electrical behaviours after UV irradiation. The decrease of insulating properties is found to be related to an increasing surface hydrophilicity due to the appearance of carboxylic acids. We show how hydrophilicity calculations are possible from chemical considerations and how it influences the surface conductivity. We show finally the way to predict the evolution of polymer surface conductivity during ageing from the analysis of their initial chemical structure and the knowledge of the main degradation mechanism involved.