Structural design of a new XLPE Insulation material without cross-linking by-products and theoretical study on the reaction mechanism: An alternative to peroxide crosslinking

The cross-linked polyethylene (XLPE) is used in most advanced power cable insulation. The cross-linking byproducts based on typically dicumyl peroxide (DCP) cross-linking process increase the electrical conductivity of the insulation material. In order to remove the hazardous byproducts, an essential time-consuming and energy-consuming procedure is needed. Hence, a new XLPE production process without cross-linking by-products receives considerable attention. Here, the structural design of a new XLPE based insulation materials have been established. The cross-linking of epoxy and reactive functional groups between two polyethylene copolymers in situ through reactive compounding is an alternative to DCP crosslinking without cross-linker and byproducts. Theoretical investigation on the reaction process of covalent bonds forming and reaction mechanism is accomplished by density functional theory. Two reaction mechanisms, synergistic reaction and step-by-step reaction, are proposed. The reaction potential energy information of the twelve reaction channels at B3LYP/6–311 +G(d,p) level are obtained. The calculation results show that the epoxy and reactive functional groups between two poly-ethylene copolymers can react in situ and crosslink through the formation of covalent bond to realize the networking of XLPE. The reaction of maleic anhydride with H₂O (or CH₃OH) is more kinetically and thermodynamically favorable than that of maleimide. The reactivity of carboxylic acid functional group is stronger among three cross-linking reaction systems considered. The reaction Gibbs energy barrier heights of synergistic reaction are lower than that of step-by-step reaction by about 0.6 eV. The theoretical study on the reaction mechanism of epoxy and reactive functional groups between two polyethylene copolymers would be beneficial to avoid the forming of hazardous cross-linking byproducts, which is a promising method to design thermoplastic insulation materials for future power cables.