Thermal Aging Mechanism of Epoxy Resin Based on Molecular Structure Change

Epoxy resin insulation material has been widely used in power system because of its excellent insulation performance. However, the influence of long-term thermal stress will lead to degradation and fracture of insulating material surface. Therefore, it is of great significance to analyze the change of thermal aging properties of epoxy resin materials for the safe and reliable operation of power system. In this paper, 11 groups of epoxy resin samples were subjected to thermal aging test at 250°C for 11 days, and the breakdown voltage of epoxy resin was tested during this process. It is found that the breakdown voltage increases first and then decreases. In order to further study the influence mechanism of thermal aging on breakdown voltage of epoxy resin samples, the thermal cracking process of epoxy resin samples was studied based on molecular dynamics simulation of ReaxFF field. Then, density functional theory (DFT) was used to analyze two defects of molecular chain and interchain structure changes caused by thermal aging. The results show that the reduction of crosslinking points leads to the increase of trap density, and the disordered arrangement of molecular structure weakens the stability of the network structure. At the same time, the introduction of a new functional group C=C in the aged epoxy resin leads to the narrowing of the HOMO-LUMO band gap, which is the reason for the decline of physical and chemical properties.