Aggregated structure modulation endows polypropylene copolymer with enhanced dielectric properties for eco-friendly cable insulation

Impact polypropylene copolymer (IPC) shows significant potential in high-voltage cable insulation owing to its environmentally friendly characteristics. Compared to homopolymerized polypropylene (PPH), IPC has improved mechanical toughness while decreased dielectric properties, which are mainly related to the aggregated structure. This study integrated experiments and simulations to investigate the mechanism of aggregated structure on dielectric properties, and further proposed an effective modulation strategy. The results showed that the introduction of the rubber phase reduced the crystallinity by up to 21 %, while also bringing in more crystal-amorphous interface. Given that electronic transitions tended to occur in the amorphous phase rather than crystal phase due to the bandwidth, and the localized state energy levels made more carriers involved in migration by hopping, especially in amorphous phases and interfaces with more impurities and defects. Therefore, the conductivity of IPC was approximately one order of magnitude higher than that of PPH at 90 °C. Appropriately increased cooling rate effectively shortened or blocked the continuous migration path of the carriers without compromising the integrity of the crystal structure. Under this modulation, the electric field distortion caused by space charge accumulation decreased about 12.2 %, and the breakdown strength was enhanced by 22 %. This research is valuable for both foundational theory and practical industrial applications.