Effect of Nucleating Agent and Cooling Rate on Dielectric Property of PP/POE Cable Insulation

This article focuses on the effect of cooling rate on crystalline morphology and electrical treeing characteristics of polypropylene/polyolefin elastomer (PP/POE) blended cable insulation and proposes a method of adding sorbitol nucleating agent to induce crystallization, thereby mitigating the effect of the cooling rate. The cooling rates of the insulation inner layer and outer layer during cable extrusion were simulated at 2.5 and 10 °C/min. PP/POE blends with 0, 0.1, 0.2, 0.4, and 0.6 wt% nucleating agent are prepared under each cooling rate. The results show that slow cooling promotes the formation of large-sized spherulites in PP/POE blends, resulting in decreased electrical properties. The addition of an appropriate amount of nucleating agent acts as a heterogeneous nucleating agent, reducing the spherulite size in PP/POE blends. Consequently, it significantly inhibits electrical treeing and partial discharge (PD), reduces conductivity, and improves breakdown strength in PP/POE blends. Furthermore, the addition of the nucleating agent effectively reduces the differences in spherulite size and electrical properties caused by different cooling rates, enhancing the consistency of insulation properties. However, excessive nucleating agent leads to the formation of fragmented spherulites in PP/POE blends, resulting in decreased dielectric properties. The nucleating agent with a content of 0.4 wt% has the best modification effect.