Chemical Trap Orbital Analysis of Styrene-Grafted Polypropylene for HVDC Cable Insulation

Polypropylene (PP) is regarded as a rather potential insulation material alternative for the next generation HVDC cable system. Grafting styrene is proved to be an effective method to further enhance the DC insulation properties especially under high temperature. The trap introduced by grafting modification is believed to be the key issue on such enhancement. In this paper, the quantum chemistry analysis based on DFT method is adopted to computationally investigate the chemical trap originating from grafting modification. The results indicate that grafting styrene introduces new trap orbitals within the HOMO–LUMO gap of PP, and the grafted aromatic ring, especially the delocalized Pi bond is responsible for it. Besides, the delocalized Pi bond can also lead to the local high negative electrostatic potential area on the PP chain, thus affecting the microscopic charge transportation in PP. This work is expected to provide a reference for investigating the mechanisms of charge transportation and macroscopic electrical properties enhancement of PP-based insulation for HVDC cables.