Enhancement of Viscosifying Structure and DC Electrical Properties in Polypropylene via Maleimide Reaction

Compared to cross-linked polyethylene, the use of thermoplastic polypropylene in cable insulation can effectively reduce carbon emissions, making it a more environmentally friendly choice. Among various polypropylene materials, impact copolymer polypropylene (IPC) offers a unique combination of flexibility and heat resistance, making it the preferred material for developing polypropylene insulated power cables. However, for large cross-section high voltage cables, the long straight-chain structure of IPC results in low zero-shear viscosity, which makes it difficult to meet the roundness requirement after insulation extrusion. To regulate the viscosity characteristics and DC performance of IPC, we synthesized modified IPC with a high branching structure through maleimide functionalization of maleic anhydride grafted polypropylene, thereby increasing the complexity of the IPC chain structure. Due to enhanced interchain forces and branching, the ethylene propylene rubber (EPR) phase disperses more uniformly. Additionally, the crystallization and melting temperatures slightly increase, while the material’s viscosity at a shear rate of 0.05 rad/s rises substantially by 238%. The DC performance results indicate that the functionalized modified PP with maleimide exhibits superior high-temperature space charge properties and a higher DC breakdown strength. Enhanced the ethylene propylene rubber phase dispersibility, and the introduction of polar groups (carbonyl and amino) has significantly improved the viscosity characteristics, stress-strain characteristics, space charge behavior, resistivity, and electrical strength, resulting in a 33.2% increase in DC breakdown strength. This work provides a novel technological route to synergistically improve the viscosity properties and DC electrical performance of IPC, which is essential for the development of long-length, HVDC polypropylene power cable insulation materials.