Preparation And Properties Of Addition-Cure RTV-2 Liquid Foamed Silicone Rubber

Silicone rubber foam is one kind of porous polymeric materials prepared with foaming silicone rubbers.Flame retardant silicone rubber foams can be prepared with high temperature or room temperature silicone rubbers.Usually high temperature type foams are related to some environmental issue and show poor compression set properties more than room temperature type silicone foams.So the later foams have been more widely used for recent application of sealing and cushioning function for battery pack in new energy vehicles.The flame retardant type silicone foams is mainly prepared by two component addition cure liquid silicone rubbers by room temperature vulcanization?RTV?which can easily processed by free foaming and molding foaming etc.While meeting UL-94 V0 in flame testing the silicone foams will be shrinking and cracking while flame happened,ceramic type silicone rubber skeleton will be transformed from organic silicone foams to show high efficient flame retardant properties which is advantageous for those strict fire insulation application requirement.Usually the formulation of addition cure RTV-2 liquid silicone foam is composed with ethylene silicone oil,foaming aids?alcohol,hydroxy silicone oil?,hydrogen-containing silicone oil,platinum catalyst and inhibitor etc.While two components mixing ethylene silicone oil will be cross-linked with hydrogen-containing silicone oil and the foaming aid is setting to be dehydrogenated and condensed with the hydrogen-containing silicone oil to form silicone rubber foams.The effects of foaming aids?alcohols,hydroxy,silicone oils?,hydrogen-containing silicone oils,platinum catalysts,and inhibitors have been studied with the effect on the foaming properties of RTV-2 liquid foamed silicone rubber and silicone rubber foams.The results show that the gel time of silicone mixture and the foaming density is much related to the hydrogen activity in hydrogen-containing silicone oils.Higher hydrogen activity is resulted in shorter gel time and lower foaming density.Hydroxy silicone oil is more suitable as a foaming aid than organic alcohols.Because the activity of organic alcohols is higher than the hydroxy silicone oil,the foaming reaction is much faster than the crosslinking reaction.The released H₂ quickly overflows and the resulting foam cells in larger size dimension.The activity of the hydroxy silicone oil is slightly lower,so that the foaming reaction and the crosslinking reaction are well matched,and the obtained cells are fine and uniform.When the amount of the hydrogen-containing silicone oil is fixed,increasing the amount of the hydroxy silicone oil can improve the compression set property of the silicone rubber foam.The change in the amount of catalyst and inhibitor has little effect on the performance of the silicone rubber foam and has some influence on the operation time.The base rubber is prepared by treating the silica on-line by a kneading process.The effects of fumed silicon N20,T40 and precipitated silica W995 and W996 on the properties of RTV-2 liquid silicone rubber foaming and silicone rubber foam have been studied.The results showed that the rubber gel prepared by different silicas after silazane treatment the gel time is accelerating,to varying degrees.The fumed silicon viscosifying effect is significantly higher than that of precipitated silica,and the foaming density of the silicone rubber foam is increased.The type of silica has little effect on the compression set properties of silicone rubber foam.The effect of silica on the thermal weight loss behavior of silicone rubber foam is complicated,and the residual weight rate of the material is improved.As increasing the amount of W996,the tensile strength,density and hardness of the silicone rubber foam increase,the compressive property changes little,the elongation at break increases first and then decreases,and the thermal stability in the interval of 410⁵50?increases first and then decreases.RTV-2 liquid foamed silicone rubber was prepared by using 10 parts of base rubber prepared by W996 and adding different amounts of compound mica type ceramifying flame retardant powder.The effect of ceramifying fame retardant powder on the properties of rubber compound and rubber foam and silicone rubber foam was studied.The results show that the amount of ceramifying flame retardant porcelain powder increases,the viscosity of the rubber compound change sharply,and the gel time first becomes longer,followed by little change.The hardness,density,tensile strength,and elongation at break of the silicone rubber foam are reduced,and the compression set property does not change much.The structural integrity of the silicone rubber foam after fire increased,the linear shrinkage of the material is gradually reduced,and the surface cracks are less.The minimum density of the smoke density test DC4and VOF4 is 11.7,22.7,and the bending strength is up to 2.1 MPa.Considering the overall performance of foams for application,it is considered suitable when the amount of ceramifying flame retardant powder is 30 phr.