Mechanically robust epoxy with electrical breakdown healing capability for power equipment insulation via dynamic networks

Abstract

Electrical breakdown is a classical failure mod of epoxy when applied as insulating materials in electrical engineering, which greatly threatens the reliability of power equipment. However, as a stiff polymer, the healing of epoxy is usually considered to be inaccessible. In this study, new epoxy networks with electrical breakdown healability were developed for power equipment insulation. The dynamic networks are generated by amine-terminated ring-opened epoxies and bi-functional isocyanates, which endows good reprocessability and healability. Artificial puncture was first made to simulate electrical breakdown features and clarify the influence of failure shape on healability. Electrical damage was carried out afterwards, the thru-hole generated by electrical breakdown is able to be recovered after healing within 10 min. A high healing efficiency of about 90% based on breakdown strength is observed. With temperature and pressure stimulation, the network dissociated reversibly to rejoin the separated surface of the breakdown holes. Meanwhile, the carbon residue generated by electrical discharge is squeezed and isolated by flowed chain segments. Moreover, by replacing bisphenol-A epoxy resin with the hydrogenated epoxy resin of a lower C/H ratio, less carbon residue can be detected after electrical breakdown and improved healability on morphology and insulation properties is discovered.