To investigate the thermal decomposition characteristics of high-temperature vulcanized silicone rubber (HTV) and liquid silicone rubber (LSR) under different aging conditions, scanning electron microscopy (SEM) and thermogravimetric analysis (TG) were employed to characterize the surface microstructure and chemical properties of silicone rubber samples that had been in service for 15 years. The influence of aging degree on the thermal stability of silicone rubber was initially investigated. ReaxFF-based reactive molecular dynamics simulations were conducted to analyze the decomposition pathways of silicone rubber under high-temperature conditions, as well as the dynamic evolution of decomposition products. In addition, key parameters—including glass transition temperature, mean square displacement, cohesive energy density, and free volume fraction—were calculated before and after decomposition using the Materials Studio platform. The results indicate that LSR exhibits higher thermal stability than HTV, while the thermal stability of both materials decreases after thermal decomposition. Furthermore, the variation in thermal stability was discussed based on these parameters from the perspectives of molecular mobility and intermolecular interactions. This research can provide a reference for the safety operation assessment, aging status determination, and high-temperature service reliability design of silicone rubber insulating materials.

Silicone rubber is an important external insulating material for composite bushings, composite insulators, and other power equipment. During long-term service, it is inevitably exposed to coupled environmental and electrical stresses, such as elevated temperature, moisture ingress, strong electric fields, and partial discharge, which may lead to hydrophobicity loss, surface chalking, crack propagation, and particle shedding. To reveal the microscopic degradation mechanism of silicone rubber under complex operating conditions, a molecular model of methyl vinyl silicone rubber was constructed using Materials Studio. A stable silicone rubber molecular structure was obtained through crosslinking, geometry optimization, and ensemble relaxation. Subsequently, a reactive molecular dynamics simulation system under coupled temperature–humidity–electric field conditions was established using LAMMPS and the ReaxFF reactive force field. Different temperature gradients, electric field intensities, and aging–recovery stages were designed to investigate the degradation behavior of silicone rubber. The evolution of the maximum carbon content, maximum silicon content, carbon-containing decomposition products, and typical small-molecule products, including H₂, H₂O, CH₄, C₂H₂, C₂H₄, and C₂H₆, was statistically analyzed. In addition, atomic trajectory tracking was performed to clarify the processes of methyl group detachment, Si-O bond cleavage, water molecule participation, and molecular chain reconstruction. The results show that high temperature mainly promotes methyl group detachment from side chains and fracture of the siloxane main chain, while a strong electric field accelerates the decomposition process and induces the transformation of long siloxane chains into shorter chains. Water molecules can react with broken siloxane chains to form hydroxyl-containing structures, making the structural degradation partially irreversible. The degradation process of silicone rubber under coupled temperature–humidity–electric field stress can be summarized as side-chain detachment, main-chain scission, water-assisted reactions, free-radical recombination, and local molecular aggregation. This study provides a molecular-level theoretical basis for aging mechanism analysis, condition assessment, and lifetime prediction of composite external insulating materials.