The role of backbone chain rotation in the hydrophobicity recoveryof polymeric materials for outdoor insulation

摘要

A series of experiments was conducted on polymeric insulators tonexamine the role of molecular bond motion in the recovery ofnhydrophobicity. The samples were also analyzed with characterizationntechniques which provided important information concerning surfacentopography, surface hydrophobicity level, and surface chemicalncomposition. Silicone rubber and EPDM (ethylene propylene diene monomer)nsamples, in the form of cylindrical rods with 25 mm diameter and 150 mmnin length, were subjected to dry band arcing in a fog chamber, tonsimulate outdoor service conditions. It is shown that the diffusionnprocess is not the only mechanism responsible for the recovery ofnhydrophobicity in polymeric insulators. Heat treatment after hexanensoaking showed evidence of recovery by molecular bond motion.nHeat-induced changes occurring on the surface of polymeric insulators,nas analyzed by ESCA (electron spectroscopy for chemical analysis) andnCOV (cross-over voltage) measurements, are comparable to those inducednby dry band arcing. The formation of cyclic polymers, as well as theirnconformational changes during the thermal degradation process, helpsnexplain the increase of oxygen level in the hydrophilic state, and thenincrease of carbon level in the hydrophobic state