Improving the High-Temperature Mechanical Properties and DC Electrical Properties of Polypropylene Insulation Materials through Grafting and Cross-Linking Modification

Abstract Thermoplastic polypropylene (PP) has been widely regarded as a promising alternative to cross-linked polyethylene (XLPE) for cable insulation owing to its excellent recyclability. However, PP exhibits poor mechanical toughness at room temperature, and blending with low-modulus elastomers, although effective for toughening, often compromises the electrical properties and high-temperature mechanical strength of the resulting composites. To overcome this trade-off, acrylic acid (AA)-grafted polyolefin elastomer (APOE) was introduced to improve the interfacial polarity between polyolefin elastomer (POE) and PP and promote the dispersion of POE in the PP matrix. In addition, when using divinylbenzene (DVB) as a crosslinking agent, its two vinyl groups can serve as bridging groups between APOE and PP, forming a micro-crosslinked structure and thereby improving interfacial compatibility. Meanwhile, the polar groups introduced by AA and DVB contributed to the formation of deep charge traps, which suppressed charge transport and improved the electrical properties of PP/POE composites. Compared with PP/POE, the synergistically grafted composite exhibited a one-order-of-magnitude reduction in electrical conductivity at 90 °C, a 21% increase in DC breakdown strength, and a 17.8% improvement in tensile strength. These results demonstrate that the synergistic grafting of AA and DVB enables the simultaneous enhancement of high-temperature electrical properties and mechanical strength, providing an effective strategy for developing high-performance, stable, recyclable, and eco-friendly PP-based insulation materials for high-voltage cables.