Ameliorated DC Insulation Performance of EPDM through Chemical Grafting with a Voltage Stabilizer

Ethylene-Propylene-Diene Rubber (EPDM) is widely utilized as a high-performance insulation material in high-voltage direct current (HVDC) cable accessories, owing to its exceptional electrical and thermal properties. In this study, we have successfully synthesized and employed 4-vinyl oxyacetophenone (VPE) as a modification agent to develop the chemically grafted EPDM materials (EPDM-g-VPE) just through thermal crosslinking reaction and melt blending approach. Infrared spectroscopy results reveal that during thermal cross-linking process, VPE efficiently grafted onto EPDM molecular-chains through free radical addition reaction. Following VPE grafting, the DC dielectric breakdown strength and electrical conductivity of EPDM are significantly increased and noticeably decreased respectively. Theoretical electronic structure calculations corroborate that VPE's electron-affinity and energy-gap enable it to efficiently absorb thermal electron energy without undergoing collision ionization, thereby enhancing EPDM's breakdown resistance. Simultaneously, VPE molecules exhibit a high affinity for capturing electron charge carriers within EPDM polymer-molecules. Space charge and thermally stimulated current tests demonstrate that the stable and uniformly distributed charge traps can be effectively introduced into EPDM matrix by grafting VPE modification, thereby suppressing transport and injection of charge carriers. Consequently, this approach substantially improves DC electrical insulation performance of EPDM.