Physical and chemical structure change of filled epoxy due to water absorption

Epoxy composites are widely used for electrical insulation systems. However, the electrical and mechanical properties of them could significantly vary with water absorption. To study the mechanisms of degradation due to water absorption, we observed physical and chemical structure change of filled epoxy and evaluated dielectric properties by accelerated aging. As a result, it was confirmed that the regions of different crosslinked densities were formed in the matrix during accelerated aging. Furthermore, it was suggested that physical structure change, e.g., interfacial debonding between filler and matrix affects dielectric loss but not DC conduction loss. Chemical structure change seems not to affect essentially electrical properties