Mechanistic insights into the structure–mechanical property relationship of polymer insulating materials during aging in environmentally liquid dielectric

This study investigates the microscopic mechanisms governing the structure–mechanical property relationship of cellulose-based insulating paper during aging in natural ester liquid dielectrics. Molecular dynamics simulations are employed to systematically characterize structural evolution in both amorphous and crystalline regions across different aging stages. A notable and counterintuitive phenomenon is observed, wherein the tensile strength of cellulose paper increases by 31.4% during the early aging stage, despite a 46.5% reduction in the degree of polymerization. Detailed analyses of hydrogen bonding, cohesive energy density, free volume fraction, and mechanical parameters indicate that this enhancement originates from molecular-level reorganization, in which natural ester molecules promote the formation of stabilizing intermolecular interactions within amorphous regions, partially compensating for chain scission. With further aging, the progressive degradation of the crystalline structure becomes dominant, resulting in the eventual deterioration of macroscopic mechanical properties. Accelerated thermal aging experiments are conducted to validate the simulation results, demonstrating good agreement between molecular-scale evolution and experimentally measured mechanical performance. These findings provide a mechanistic understanding of the structure–property relationship in cellulose insulation materials and offer theoretical support for the optimization of environmentally friendly oil–paper insulation systems.