Degradation and recovery of polydimethylsiloxane (PDMS) based composites used as high voltage insulators

[摘要] ENGLISH ABSTRACT: Polydimethylsiloxane (PDMS) compounds are utilized in outdoor high voltage insulationdue to their low weight, vandalism resistance, better anti-contamination performanceand their superior hydrophobic nature. Under severe environmental conditions and overprolonged service time, however, the hydrophobic surface can gradually becomehydrophilic and then recover with adequate resting period.In this study, room temperature vulcanized (RTV) PDMS samples were prepared withdifferent formulations and then exposed to corona discharge to evaluate its effect. Theinfluence of different additives, such as different types and amount of fillers andadditionally added low molar mass silicone oils, on the hydrophobicity recovery of thematerial was investigated. The effects of two types of corona treatment were alsoevaluated.Hydrophobicity recovery of corona and UV-C aged PDMS samples was evaluated bymeans of static contact angle measurements.Positron annihilation spectroscopy (PAS) gave important information on the microstructural change after corona treatment of RTV PDMS as well as naturally aged hightemperature vulcanized (HTV) PDMS samples. The different formulations of the RTVPDMS samples and the effect of the additives were studied with this technique. Theformation of a thin, highly crosslinked inorganic silica-like (SiOx) layer was confirmedeven at the early stage of degradation. It was also possible to estimate the thickness ofthe silica-like layer formed during corona exposure that is responsible for the loss andrecovery of hydrophobicity.The surface hardness and hydrophilicity change of PDMS samples due to coronatreatment were studied simultaneously with force distance measurements by atomicforce microscopy (AFM). The adhesive force calculated from the pull-off force-distancecurves showed that the adhesive force between the probe and the sample decreasedwith increasing corona treatment time, indicating hydrophobicity recovery. In addition tothis, the increase in hardness after corona exposure provides indirect evidence of theformation of a silica-like layer. In all cases the hydrophilicity and the surface hardness ofthe PDMS samples increased directly after corona treatment and recovered with time.Two types of FTIR spectroscopy were used to analyse the surface of the polymer.

[发布机构] Stellenbosch University