Influence of Kaolin and LDPE Fillers on Electrical and Mechanical Properties of Ethylene-Propylene Rubbers for Cables

Wind power torsion cables that connect wind power generators and other equipment endure both electric field and torsional stress during operation, putting a great challenge on cable insulation materials. Here, we propose a doping strategy to synergistically enhance the mechanical and electrical properties of ethylene-propylene rubber (EPR) for advanced wind power torsion cables. Two kinds of filling materials kaolin (Al2O3 $\cdot$ 2SiO2 $\cdot$ 2H2O) and low-density polyethylene (LDPE) were doped in an EPR matrix to tune the mechanical and electrical properties, and the contents’ dependence of properties and their corresponding structural origin were investigated thoroughly. The mechanical properties including the elongation at break and tensile strength are significantly enhanced up to 1.7 times and 2.6 times, respectively, higher than that of pristine EPR by kaolin doping within 30%–40% addition, and they are further enhanced up to 1.37 times and 1.53 times, respectively, by LDPE doping for its crystallization characteristic. The electrical resistivity increases with kaolin doping within 30% addition and then decreases beyond that, and it reaches its maximum at $3.3\times 10^{{14}}~ \Omega \cdot $ m, while it remains unchanged with LDPE addition. The electrical breakdown strength at 90 °C slightly decreases with kaolin and LDPE addition. Consequently, the optimal composition is obtained and the comprehensive performance is successfully improved. Microstructure investigation reveals that the enhanced properties should be ascribed to the bonding on kaolin fillers and the increased crystallinity induced by LDPE. This work provides an experimental basis for developing EPR for advanced wind power torsion cables.