Influence of electric field on moisture-absorbing characteristics at the FRP/RPUF interface: Experimental study and molecular dynamics simulation

Abstract The interface between fiber-reinforced polymer (FRP) and rigid polyurethane foam (RPUF) is a crucial component of composite cross-arm, not only operating within high electric field environments but also vulnerable to water-induced deterioration. In this paper, the moisture-absorbing characteristics and aging mechanism at the FRP/RPUF interface under the influence of an electric field were investigated through accelerated aging experiments, molecular dynamics (MD) simulations, reactive force filed (ReaxFF) simulations and Density Functional Theory (DFT) analysis. The results indicated that the moisture-absorbing characteristics of the FRP/RPUF system could be divided into two stages: Stage I, dominated by free diffusion, and Stage II, dominated by physical absorption. In Stage I, the electric field inhibited the diffusion behavior of water molecules by affecting the mean square displacement (MSD) of water molecules and the free volume of the FRP/RPUF system. During Stage II, the intrusion of water deepened the aging degree of the system, resulting in the emergence of a large number of free volumes and noticeable channels for water transport at the interface. The electric field enhanced the chemical reaction activity of epoxy resin and polyurethane by influencing their frontier molecular orbital energy, thereby promoting the occurrence of hydrolysis reactions. This intensified the physical moisture absorption process, ultimately promoting the Stage II process.