Improvement of space charge suppression of polypropylene for potential application in HVDC cables

High-performance polypropylene (PP) plays an important role in electrical/electronic engineering fields. Especially in high voltage direct current (HVDC) cables it compares well to cross linked polyethylene (XLPE) for its potential application as an eco-friendly material without cross-linking. The space charge injection under high electric stress is main obstacle for the development of HVDC cables. Here we adopted chemical modification on PP with polar functional group to improve the electrical properties, whereby the molecular structure has been designed to obtain excellent insulating material. The space charge suppression, dielectric properties and crystal characteristics of PP with and without grafting with maleic anhydride (MAH) were investigated. Results demonstrated that the MAH was successfully grafted onto PP macromolecular chain. Compared to pure PP, the grafting with 2 wt% MAH can effectively suppress space charge injection and provide better stability in volume resistivity as temperature increases. Besides, their dielectric properties were studied, and the mechanism of space charge suppression was proposed. This provides a useful method to prepare the HVDC cable insulating materials.