Electrical-Tree Resistant Characteristics of SEBS and Nano-SiO₂ Modified Polypropylene Composites

Abstract

Polypropylene (PP) composite materials with both high mechanical toughness and electrical insulation performance are prepared by incorporating styrene-ethylene/butylene-styrene (SEBS) block copolymer as a toughening agent and nanoscale silica (SiO2) as a inorganic modifier to enhance electrical-tree and breakdown resistances.The elastic modulus of SiO2/SEBS/PP composite is slightly lower than that of pure PP material, while the thermal elongation rate remains superior to cross-linked polyethylene (XLPE), which is competent in mechanical performances for main insulation materials in high-voltage cables. The addition of SEBS facilitates electrical-tree growth in PP matrix and thus leads to a reduction in dielectric breakdown strength of PP material. In contrast, the incorporation of nano-SiO2 can effectively improve the electrical-tree resistance and dielectric breakdown strength of PP material, making the SiO2/SEBS/PP composite a promising candidate for high-voltage cable insulation. The tests and analyses of thermal stimulated depolarization current reveal that the SEBS toughing additive introduces the shallow charge traps in PP matrix, leading to a considerable decrease in electrical-tree resistance and insulation strength of PP material. Meanwhile, the SiO2 nanofiller can introduce deeper charge traps into PP matrix than the structural-defect intrinsic charge traps, resulting in a significant amelioration in the electrical-tree resistant and insulation performances for SEBS/PP composite.