Preparation And Properties Of High-strength Flame-retardant RTV Silicone Rubber With Low-density

Room temperature vulcanized(RTV)silicone rubber has excellent electrical insulation,resistance to ozone aging,weather and radiation,etc.,and was widely applied in the electric power industry.In order to be used safely in the field of high-voltage insulation,silicone rubber is required to have not only excellent mechanical properties,but also lower density and good flame-retardancy.In this work,high-strength flame-retardant RTV silicone rubber with low-density was prepared by using hollow glass microspheres(HGM)as weight-reducing filler,melamine-cyanurate(MCA)and polytetrafluoroethylene(PTFE)as flame retardant,and fumed silica and methyl MQ resin as reinforcing filler.The main contents and results are listed as follows:(1)The effect of fumed silica,nano-calcium carbonate and methyl MQ resin on the mechanical properties,density and viscosity of RTV silicone rubber with?,?-dihydroxy polysiloxane as basic polymer was investigated.It was found that the compound of fumed silica and methyl MQ resin could effectively improve the mechanical properties of RTV silicone rubber without significantly increasing the density and viscosity.When the fumed silica content is 20phr and the methyl MQ resin content is 10phr,the tensile strength and elongation at break of RTV silicone rubber reach 3.23MPa and 318%,respectively,and the density is only 1.12 g.cm^-3,viscosity is 310 Pa.s.(2)HGM was used as weight-reducing filler to add into the RTV silicone rubber reinforced with fumed silica and methyl MQ resin.The effect of HGM particle size and content on the mechanical properties and density of RTV silicone rubber was investigated.The RTV silicone rubber was characterized by scanning electron microscopy(SEM)and thermogravimetry(TG).The results showed that HGM compound with suitable particle size could effectively reduce the density of RTV silicone rubber without significantly damaging the mechanical properties.When using 10 phr HGM with average particle size of 85?m and5 phr HGM with average particle size of 60?m,the tensile strength and elongation at break of silicone rubber are 3.13 MPa and 210%,respectively,and the density reduced to 0.92g.cm^-3.TG results showed that when HGM content increased,the 5%weight loss temperature(T_5%)of RTV silicone rubber also increased,but the maximum weight loss rate temperature(T_max)decreased.(3)The effect of phosphorus nitrogen flame retardant and PTFE on the flame retardancy,mechanical properties,electrical properties and density of RTV silicone rubber with HGM as the weight-reducing filler was investigated.The RTV silicone rubber was characterized by TG,thermogravimetric-infrared(TG-FTIR),cone calorimetry and SEM,and the flame-retardant mechanism of RTV silicone rubber was explored.It was found that PTFE and MCA had good synergistic flame-retardant effect on RTV silicone rubber.When MCA content is 30phr and PTFE content is 1phr,the limiting oxygen index(LOI)value of RTV silicone rubber is 27%,the vertical combustion rating reaches UL94 V-0,the density is 0.99g·cm^-3.,the volume resistivity is 4.6×10¹⁴?·cm,the dielectric strength is 14 k V·mm^-1,the tensile strength and elongation at break are 2.74MPa and 180%,respectively.TG-FTIR results showed that during the combustion process,MCA decomposed to produce non-flammable gases such as NH₃ and CO₂ to dilute the concentration of oxygen and combustible gas.SEM results showed that PTFE promoted the formation of dense residue and led to flame retardant effect in condensed phase.