Study on Organic Molecular Damage Mechanism and Environmental Dependence of Silicone Rubber Under the Synergistic Action of Complex Conditions

This study focused on the mechanism of corona discharge and nitric acid damage to silicone rubber organic molecules in order to solve the aging problem of composite external insulation materials in heavy pollution environment. The effects of corona strength, duration and nitric acid corrosion on the physical and chemical properties of silicone rubber were systematically investigated through the independent corona aging test system of composite materials (including 54 sets of pin-plate electrodes), combined with scanning electron microscopy (SEM), static contact Angle analysis, thermal stimulation current (TSC) and Fourier infrared spectroscopy (FTIR). The results show that: (1) During corona discharge, the high energy charged particles preferously destroy C-H bond and Si-C bond through mechanical collision, leading to methyl group loss and hydrophilic group formation; However, nitric acid corrodes Si-O main chain through hydrolysis reaction and forms Al(NO3)3. (2) Hydrophobicity loss showed phased characteristics: After a short time corona (<4h), the hydrophobicity quickly recovered due to the migration of small molecule siloxane; After long exposure (>7h), the inorganic crystal layer obstructs the migration and the recovery rate drops sharply. (3) The variation of trap characteristics shows that the charg-trapping ability increases with aging (TSC peak current increases from 26 pA to 165 pA), and nitric acid corrosion introduces shallow traps to form a double-peak current curve. (4) Under low pressure and high humidity environment, electric field distortion significantly promotes the formation and diffusion of nitric acid, and accelerates the crack propagation on the surface of the material; Under high pressure, charged particle bombardment is the dominant damage mode. The research results reveal the competitive mechanism of molecular chain breaking-oxidation-condensation reaction of silicone rubber under multi-factor coupling, and provide a theoretical basis for the molecular design of weather-resistant composite insulating materials.