Polyethylene Based Ionomers as High Voltage Insulation Materials

Polyethylene based ionomers are demonstrated to feature a thermo-mechanical and dielectric property portfolio that is comparable to cross-linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct-current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high-pressure/high-temperature free radical copolymerization of ethylene in the presence of small amounts of ion-pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt-processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct-current (DC) electrical conductivity of 1 to 6·10⁻¹⁴ S m⁻¹ at 70 °C and an electric field of 30 kV mm⁻¹. Evidently, the investigated ionomers represent a promising alternative to XLPE-based high voltage insulation, which may permit to ease the production as well as end-of-use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts.