Space Charge and Conduction Characters of PP/POE Composites and Their Influence on the Aging Lifetime Under DC Voltage

The polypropylene (PP) has a great potential to be used as recyclable cable insulation, but its high hardness and brittleness make it not suitable for the cable manufacture. Polyolefin elastomer (POE) was usually dopped into PP to improve the mechanical property, but the electrical properties of PP/POE composites decrease. This article studied the mechanical and electrical properties of PP/POE composites with different contents. It is found that with the increase of POE content, the elastic modulus and tensile strength of PP/POE composites decrease. The 20%, 30%, and 40% POE composites have similar breakdown strengths, which are about 15% lower than that of PP. The breakdown strengths of 50% and 60% POE composites decrease fast with the increase of POE content. The conductivities of PP/POE composites increase with the increase of POE content at low electric field. At high electric field, the conductivity of 40% POE composites is the lowest among all the composites as it has reduced electrode electric field due to small amount of homocharge. The 20%, 30%, and 40% POE composites accumulate small amount of space charge, and the 50% and 60% POE composites accumulate high amount of heterocharge. It is due to the high amount of ionization in POE. The electrical aging lifetime of PP/POE composites is tested with step-stress method. It is found that the total aging lifetime of PP/POE composites decreases with the increase of POE content in step-stress tests. At low electric field strength, the aging lifetime of the 40% POE composites is longer than the other composites and PP. In total, the 20%, 30%, and 40% POE composites have similar electrical properties. To further improve the space charge accumulation in PP/POE composites, the ionization in POE should be reduced.