Effect of mould release agent on epoxy resin surface degradation

Abstract

Epoxy resin is moulded to produce high voltage insulation components. To release the component from the mould, among other techniques, silicon-based release agents are used. The authors demonstrate that release agent is absorbed by resin during casting, and describe the change in reaction to electrical discharge stressing. Partial discharge stressing of epoxy resin contaminated with release agent causes surface crazing and silicon products, not evident prior to stressing, are detectable on the surface. Noncontaminated samples exhibit signs of erosion and chemical change, but show no evidence of cracking nor of silicon products. Chemical, mechanical and radiative stresses applied to contaminated resin failed to produce silicon material on the resin surface. It is proposed that partial discharge stressing of noncontaminated resin causes erosion of the sample surface, producing volatile products and chemical changes: there is no crazing of the surface layer, as the pure resin is homogeneous. Partial discharge stressing of contaminated epoxy resin results in erosion of the organic resinous material, but leaves nonvolatile silicon products on the resin surface. These mask the chemical changes occurring in the resin: the surface crazing is due to a differential stress reaction between the contaminated surface layer and the noncontaminated region below.