Improvement Of The Tracking And Erosion Resistance Of Addition-cure Liquid Silicone Rubber Through The Interfacial Enhancement And Catalytic Effect

Due to the worsening environmental pollution and increasing voltage level,in the long service,the tracking and erosion failure of silicone rubber?SR?happens more frequently than ever before.Once tracking occurs,the insulation property of SR is deteriorated,in some severe case,giving rise to a fire risk,which will threaten the security of the power system.At present,incorporating large amount of inorganic fillers,such as aluminum hydroxide?>50wt%?,is a common practice to improve the tracking and erosion resistance of SR.In this case,the mechanical properties and processability of SR are seriously damaged.Moreover,the hydrophobicity of SR is also lost.Therefore,simultaneously improving the tracking resistance and mechanical properties of SR is one of the key problems to be solved in the field of high-voltage insulation.In this work,amino-containing MQ silicone resin?A-MQ?and urethane-containing silane were successfully synthesized to improve the tracking and erosion resistance of addition-cure liquid silicone rubber?ALSR?.The mechanism of A-MQ and US on the tracking and erosion resistance of ALSR was explored,respectively.On this basis,the organic modified zirconium phosphate?M-ZrP?was prepared and used with US to prepare a kind of ALSR with excellent mechanical properties,tracking resistance and flame retardancy.The main contents and results are as follows.?1?Amino-containing MQ silicone resin?A-MQ?was prepared by the hydrolytic polycondensation of hexamethyldisiloxane?MM?,divinyltetramethyldisiloxane(M^viM^vi),N-??-aminoethyl?-?-aminopropyl-triethoxysilane?AEAPTES?and tetraethoxysilane?TEOS?.The structure of A-MQ was characterized by Fourier transform infrared spectroscopy?FTIR?,¹H nuclear magnetic resonance spectrometry?¹H-NMR?and gel permeation chromatography?GPC?.It was found that A-MQ could effectively improve the tracking and erosion resistance of ALSR.When the A-MQ content was 4phr,ALSR/A-MQ passed the 6h inclined plane?IP?test at 4.5kV and the erosion rate decreased from 6.7%to 2.2%,compared to ALSR.Meanwhile,A-MQ improved the mechanical properties of ALSR.Furthermore,the possible suppression mechanism of A-MQ on the tracking and erosion resistance of ALSR was revealed.At the elevated temperature and plasma bombardment produced by arc discharge,A-MQ promoted the breakage of the methyl side groups of silicone chains to generate methane,which suppressed the generation of graphitized carbon,thus A-MQ improved the anti-tracking property of ALSR.?2?Urethane-containing silane?US?was synthesized by using?3-isocyanatopropyl?triethoxysilane,isopropyl alcohol and allyl alcohol via the nucleophilic addition and trans-etherification.The effect of US on the interfacial interactions between nano silica?SiO₂?and ALSR,the vulcanization property,mechanical properties,thermal stability,tracking and erosion resistance of ALSR was studied.It was found that US could improve the dispersion of SiO₂ in ALSR and enhance the interfacial interactions between SiO₂ and ALSR.US significantly improved the tracking and erosion resistance of ALSR/SiO₂.When the US content was 2.5phr,ALSR/SiO₂/US reached 1A4.5 level in the IP test,and the erosion rate decreased from 3.44%to 0.25%,compared to ALSR/SiO₂.Meanwhile,US improved the mechanical properties and thermal stability of ALSR/SiO₂,and had little influence on the vulcanization property of ALSR/SiO₂.?3?The effect of the interfacial interactions between SiO₂ and ALSR on the tracking and erosion resistance of ALSR/SiO₂/US was investigated by thermogravimetry?TG?,thermogravimetry-Fourier transform infrared spectrometry?TG-FTIR?,scanning electron microscopy?SEM?and X-ray diffraction?XRD?.It was found that when 2.5phr US was added,the interfacial interactions between SiO₂ and ALSR had little influence on the anti-tracking property of ALSR/SiO₂/US.When the SiO₂ content increased from 0phr to40phr,all ALSR/SiO₂/US passed the 6h IP test at 4.5kV.However,the interfacial interactions between SiO₂ and ALSR had an important influence on the erosion resistance of ALSR/SiO₂/US?With the addition of SiO₂ increasing,the erosion resistance of ALSR/SiO₂/US was improved.When the SiO₂ content was 40phr,the erosion rate of ALSR/SiO₂/US decreased from 1.57%to 0.25%,compared to ALSR/US.The possible suppression mechanism of the interfacial interactions between SiO₂ and ALSR on the tracking and erosion resistance of ALSR/SiO₂/US was revealed.With the effect of US,large amount of silicone chains were constrained on the SiO₂ surface to form the interphase.During dry-band arc discharge,the restricted chains at the interphase were much easier to form the cross-linked structures than the highly mobile chains,catalyzed by Pt/US.Finally,an intact and compact ceramic layer was formed around the SiO₂ surface,which effectively protected the underlying materials from further arc ablation.?4?The effect of Karstedt?s catalyst?Pt complex?on the tracking and erosion resistance of ALSR/US was investigated.It was found that the content of Pt complex had an important influence on the tracking and erosion resistance of ALSR/US.When the Pt complex content was between 8-60ppm,ALSR/US reached 1A4.5 level in the IP test.Furthermore,the synergistic mechanism of US and Pt complex on the tracking and erosion resistance of ALSR was revealed.US could coordinate with Pt complex and inhibit the oxidation of Pt complex under the heat generated by the dry-band arc discharge,thus Pt complex had the high catalytic activity to promote the cleavage of the methyl side groups of silicone rubber.Large amount of methane was released from silicone rubber,leading to the reduction of the generation of graphitized carbon.Therefore,the tracking of ALSR was suppressed.At the same time,the breakage of the methyl side groups would lead to the crosslinking of the silicone chains,which promoted the formation of the compact ceramic layer to protect the matrix from further degradation.?5?Organic modified zirconium phosphate?M-ZrP?was prepared by the intercalation of tetrabutyl ammonium hydroxide?TBA?in?-zirconium phosphate??-ZrP?.The interactions between US and M-ZrP were characterized by FTIR,XRD,TEM and TG.On this basis,the effect of US and M-ZrP on the mechanical properties,flame retardancy,tracking and erosion resistance of ALSR was investigated.It was found that US and M-ZrP had the synergistic effect to improve the tracking and erosion resistance of ALSR.When the contents of US and M-ZrP were only 1.0phr and 0.1phr respectively,ALSR/US/M-ZrP reached 1A4.5 level in the IP test,and the erosion rate decreased from 3.44%to 0.11%,compared to ALSR.Meanwhile,the addition of US and M-ZrP could endow ALSR with good flame retardancy.Furthermore,the possible synergistic mechanism of US and M-ZrP was revealed.US was absorbed on the surface of ZrP nanosheets through hydrogen bond,thus M-ZrP nanosheets were uniformly dispersed in ALSR to form numerous nano-confinement domains.During dry-band arc discharge,M-ZrP could block the external oxygen to protect the catalytic activity of Pt complex in the nano-confinement domains and delay the oxidative degradation of silicone chains.The restricted silicone chains could quickly crosslink under the synergistic action of the Pt complex and US to form the dense ceramic layer on the surface of ALSR,which protected the matrix from further destruction by the arc.