| Silicone rubber shows great advantages over other materials in high voltage insulation,because of its superior electrical insulating property,weather and aging resistance,and capability to maintain and recover surface hydrophobicity.However,due to the increasing voltage level and worsening surrounding environment,silicone rubber is more likely to be subjected to tracking and erosion which deteriorate performance or even cause insulation failure of the materials.Nowadays,a lot of research work has been conducted to improve the tracking and erosion resistance by incorporating a large amount of inorganic filler.But high loading amount of inorganic fillers may deteriorate the properties of silicone rubber,such as mechanical properties,processability and hydrophobicity.Thus,how to effectively enhance the tracking and erosion resistance of silicone rubber,without sacrificing other properties,becomes one of the urgent problems to be solved.In this work,polymethylvinylsiloxanes(PDMS)with different vinyl contents were blended to prepare locally concentrated crosslinking network which performed excellent mechanical properties.The effect and mechanism of locally concentrated network on mechanical properties were discussed.Then,platinum(Pt)complex and nitrogen-containing silane(NS)were used cooperatively to improve the tracking and erosion resistance of mentioned silicone rubber.The suppression mechanism of Pt complex and NS on thermal degradation and tracking and erosion of silicone rubber was investigated.Lastly,hydrogen MQ silicon resin with urea group(UHMQ)was synthesized via hydrolytic condensation.UHMQ was cooperated with Pt complex to enhance the tracking and erosion resistance of silicone rubber.Accordingly,high performance silicone rubber with superior tracking and erosion resistance and excellent mechanical properties was prepared.The main contents and results are as follows.(1)Locally concentrated silicone rubber with excellent mechanical properties was prepared via blending PDMSs with different vinyl contents.The effects of sort and dosage of PDMS on the mechanical properties of silicone rubber were systematically investigated.The curing characteristic,crosslinking densities,chain mobility and viscoelasticity of such crosslinking network were further investigated.The effect and mechanism of network on mechanical properties were investigated via Mooney-Rivlin curves,tear force-displacement curves and scanning electron microscopy(SEM).The results showed that silicone rubber performed optimal mechanical properties,especially a high tear strength up to 40 kN/m,on such condition:(a)PDMS containing 3 mol% vinyl content and PDMS containing 0.05 mol%vinyl content were blended with a mass ratio of 7/93 ~ 10/90,(b)40 phr fumed silica wasused as the the reinforcing filler,(c)8 phr hydroxyl-containing silicone oil,0.5 phr hydrogen containing silicone oil and 2 phr DBPMH were added.With this formulation,silicone rubber constructed a network structure with locally concentrated crosslinking and predominantly loose crosslinking.Besides,the synergistic effect of different silicone chains in this network was investigated,which contributed to excellent mechanical properties.A large amount of long elastic chains in loose area endowed well ductility of silicone rubber,at the meantime highly concentrated area facilitated stress dispersion and obstructed the crack propagation,thus contributing to high tear strength and tensile strength.(2)The effects of platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane(hereinafter using abbreviation “Pt complex”)and γ-aminopropyltriethoxysilane(AS)orγ-ureidopropyltrimethoxysilane(US)on tracking and erosion resistance of silicone rubber were systematically investigated.Besides,the effect of Pt complex and NS on thermal stability of silicone rubber was also studied through thermogravimetry(TG).Adding either Pt complex or NS hardly improved tracking and erosion resistance of silicone rubber.However,when 0.33 phr of Pt complex,along with NS,were added cooperatively,the tracking resistance of silicone rubber was improved from 2.5 kV to 4.5 kV level in the IP test and the eroded mass was significantly reduced.The effect of NS content on tracking and erosion resistance was investigated.It revealed that silicone rubber containing 1.4~2.1 phr of AS or1.4 phr of US could pass the IP test at 4.5 kV.Though Pt complex or NS alone hardly affected the thermal stability of silicone rubber under air atmosphere,the cooperative addition of Pt complex and NS significantly improved the thermal stability.Under nitrogen atmosphere,Pt complex alone could enhance thermal stability of silicone rubber.Pt complex and NS together improved the thermal stability more obviously.Especially,the residue of silicone rubber at900 oC was increased from 30 wt% to 68 wt%.Further investigation revealed that the NS content had great influence on the thermal stability of silicone rubber.Silicone rubber containing 1.4 phr NS performed optimal thermal stability.Besides,Pt complex and NS also efficiently improved the thermal stability and tracking and erosion resistance of filler-free silicone rubber.The addition of NS and Pt complex had positive effects on mechanical properties of silicone rubber.(3)The suppression effect and mechanism of Pt complex and NS on thermal degradation and tracking and erosion of silicone rubber were investigated by thermogravimetry-Fourier transform infrared spectrometry(TG-FTIR),Fourier transform infrared spectrometry(FTIR),laser Raman spectroscopy(LRS)and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX).It was revealed that only adding Pt complex and NS togetherwould effectively catalyze radical crosslinking,meanwhile suppressing oxidation and depolymerization of silicone chains.Moreover,a dense residue was formed for silicone rubber containing Pt complex and NS,in comparison with loose structure for neat silicone rubber at high temperature.This supported that a tightly crosslinking network was formed at high temperature,which protected inner materials from arc ablation and thermal degradation.Furthermore,carbon deposit during pyrolysis was suppressed by adding Pt complex and NS together,which served as the mechanism of tracking suppression.(4)UHMQ was synthesized via hydrolytic condensation of tetraethoxysilane,γ-ureidopropyltrimethoxysilane,hexamethyldisiloxane and tetramethyldisiloxane.The structure of UHMQ was characterized by gel permeation chromatography(GPC),FTIR and1 H nuclear magnetic resonance spectrometry(1H-NMR).The effects of UHMQ on the tracking and erosion resistance,thermal stability,mechanical properties,hydrophobicity and recovery of hydrophobicity were investigated.It was revealed that silicone rubber containing6 phr of UHMQ and 0.33 phr Pt complex could pass the tracking and erosion inclined test at4.5 kV,along with a reduction of 75% in eroded mass.The addition of Pt complex and UHMQ significantly reduced the average current and discharge frequency during IP test.Moreover,the addition of both Pt complex and NS significantly improved the thermal stability.Besides,the incorporation of Pt complex and NS wouldn’t deteriorate the mechanical properties,hydrophobicity and recovery of hydrophobicity.FTIR,TG and TG-FTIR results indicated that there existed cooperation interaction between Pt complex and UHMQ,which improved the thermal stability of UHMQ and facilitated the synergistic effect of Pt complex and UHMQ on enhancing the tracking and erosion resistance of silicone rubber. |
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