Investigation On The Tracking And Erosion Resistance Of Silicone Rubber Containing Karstedt Catalyst And Phenylaminosilane

Silicone rubber is widely used in high and ultra-high voltage power transmission equipment and outdoor insulation because of its excellent flashover resistance,superior electrical insulation,wide temperature adaptability and weather resistance,etc.However,with increasing voltage level of power transmission and the serious air pollution,silicone rubber is prone to tracking and erosion during long-term use,which would eventually lead to dielectric breakdown and even fire.Tracking and erosion of silicone rubber is mainly due to degradation of silicone chains and formation of conductive free carbon.Nowadays,it's a common way to improve the tracking and erosion resistance of silicone rubber by incorporation of inorganic fillers such as Al?OH?₃,Al₂O₃,BN,etc.However,due to their low efficiency,a large number of fillers are required to achieve satisfactory tracking and erosion resistance.This would damage the processing performance and mechanical properties of silicone rubber.In this paper,N-[3-?trimethoxysilyl?propyl]aniline?NTSPA?and Karstedt catalyst?Pt?were incorporated into silicone rubber to study the effect of Pt/NTSPA on the tracking and erosion resistance,thermal stability,plasma radiation resistance and flame retardancy of the silicone rubber.The influences of polymethylvinylsiloxane with higher vinyl content of 2.93mol%?HPMVS?and polyhydromethylsiloxane?PHMS?on the tracking resistance and thermal stability of the silicone rubber system were studied.Based on the analysis of thermal degradation behaviors of silicone rubbers and the characterization of the eroded residues,the anti-tracking mechanism of HPMVS and PHMS was discussed.The main research contents and results are as follow.?1?The effect of NTSPA and Karstedt catalyst on the tracking and erosion resistance,thermal stability,plasma radiation resistance and flame retardancy of silicone rubber was investigated.It was found that silicone rubber with 7 ppm Pt and 2.5 phr NTSPA exhibited the best overall performance.The IPT at 4.5 kV for the silicone rubber sample could last for 6 h without tracking occurring,but the sample exhibited severe erosion.Besides,for silicone rubber with Pt/NTSPA,the residue after thermal treatment at 800?increased remarkably from 46.9 wt%to 66.0 wt%,the LOI increased from 27.5%to 28.3%and the vertical burning level reached UL-94 V-1,compared with silicone rubber without Pt/NTSPA.ATR-FTIR results show that Pt/NTSPA significantly improved the plasma radiation resistance of silicone rubber.?2?HPMVS was incorporated into the silicone rubber containing Pt/NTSPA to modulate the crosslinking density of silicone rubber.Effect of crosslinking density on the thermal stability and tracking resistance of silicone rubber in the presence of Pt/NTSPA was studied.Silicone rubber without HPMVS formed a conductive path within 85 minutes.With addition of 18 phr HPMVS,the tracking and erosion resistance of silicone rubber passed grade 1A 4.5and the average eroded mass reduced remarkably to 0.68 wt%.TGA results indicate that addition of 18 phr HPMVS increased the T₁₀?the temperature of 10 wt%weight loss?of silicone rubber from 434.3?to 461.2?and the residue at 900?from 44.9 wt%to 63.5wt%under air atmosphere.TG-FTIR results show that HPMVS suppressed the rearrangements of silicone chains into cyclic oligomers at elevated temperature,and facilitated the free radical crosslinking reactions induced by Pt/NTSPA.The results of Raman spectroscopy,²⁹Si-NMR and SEM show that HPMVS promoted the formation of a compact SiOC ceramic barrier to protect inner material from further degradation during dry band arcing.Moreover,conductive graphitic carbon in the residue decreased remarkably,thereby inhibiting the formation of a conductive path.Consequently,tracking and erosion resistance of silicone rubber was enhanced significantly.?3?PHMS was added to the silicone rubber containing Pt/NTSPA to study the effect of PHMS content on the crosslinking density,mechanical properties,thermal stability and tracking and erosion resistance of silicone rubber.With the increase of PHMS content,crosslinking density,tensile strength and tear strength of silicone rubber first increased and then remained stable,while thermal stability and tracking and erosion resistance of silicone rubber increased gradually.When the content of PHMS reached 3.6 phr,T₂₀?the temperature of 20 wt%weight loss?of the silicone rubber increased from 484.2?to 494.3?under air atmosphere and the residue at 800?increased from 46.0 wt%to 63.0 wt%,compared with silicone rubber without PHMS.And the tracking and erosion resistance of the silicone rubber reached grade 1A 4.5 with average eroded mass of only 0.36 wt%.TG-FTIR analysis of silicone rubber and FT-IR analysis of the residues after thermal treatment indicate that PHMS promoted a crosslinked network with Si-CH₂-Si as a crosslinking bridge in the presence of Pt/NTSPA at elevated temperature.Therefore,most of the carbon in the condensed phase participated in the formation of a SiOC ceramic barrier,avoiding the accumulation of conductive free carbon,and ultimately improving the tracking resistance of silicone rubber.