Generation of LMW components in silicone rubbers

Silicone rubber materials (SiR) used for high voltage outdoor insulators are able to recover hydrophobicity after loss. This self-healing process is mainly based on the diffusion of low molecular weight molecules (LMWs). The amount of diffusible LMWs determines the lifetime of the self-healing-process. Former results indicated that lost LMWs are replaced by new LMWs generated from the silicone bulk. For two different SiR the impoverishment and the generation of LMWs are shown by the following experiments: Storing SiR samples continuously in solvent, the absolute amount of LMWs is determined. The influence of the solvent pollution on the value is announced. Sample sets are stored for 4 days at different temperatures (about 20, 80, and 140/spl deg/C). Afterwards the amount of LMWs is determined. To confirm generation of LMWs, several cycles of this experiment are carried out. Only for samples stored at 140/spl deg/C was the LMW amount significantly higher. Gas chromatography combined with mass spectroscopy (GC-MS) investigations are carried out to analyse SiR extracts as well as solvent pollutions. Chemical reactions generating LMWs are presented.