Preparation And Properties Of Silicone Rubber Sealing Materials For Aerospace

Silicone rubber has excellent properties,such as high elasticity and high-low temperature alternation resistance.It is widely used as sealing material in aerospace field.With the development of aerospace engineering,the problem of insufficient sealing of silicone rubber is gradually prominent,so it is of great significance to study the formula and properties of silicone rubber sealing materials.In this paper,methyl vinyl silicone rubber was used as raw rubber.First,the reinforcement formula of silicone rubber were optimized by changing the content of curing agent,reinforcement filler and structure control agent.Then,the silicone rubber was modified with Fe₂O₃,bio-graphene nanoplatelets and carbon nanotubes for heat aging resistance.The silicone rubber was modified with talc,graphite powder and 26 type fluororubber for low permeability.In the reinforcement research of silicone rubber sealing materials,the effects of curing agent DCP,silica and structure control agent on mechanical properties and heat aging resistance of silicone rubber were studied.The results of DCP showed that the tensile strength of the samples at room temperature and after aging for 48h at 250℃increased first and then decreased with the addition of DCP from 0.4phr to 1.6phr.The optimal dosage of DCP was 1.0phr,and the tensile strength of the sample at room temperature and the retention rate of tensile strength after aging reached 7.66MPa and 64%.The results on reinforcement by silica showed that the reinforcing effect of gaseous silica was the best.The optimal filling amount of gaseous silica was 45phr,and the tensile strength of the sample before aging and after aging for 48h at 250℃could reach 7.66MPa and 4.87MPa,respectively.The compressive permanent deformation was 21%.The study of the structure control agent showed that the material of hydroxysilicone oil/hexamethyldisilazane compound had the best comprehensive performance.When the total amount of structure control agent was 9phr and the ratio of hydroxysilicone oil to hexamethyldisilazane was1:1,the tensile strength of the sample at room temperature could reach 7.36MPa.After aging for 48h at 250℃,the retention of tensile strength and elongation at break could reach71%and 21%,respectively.By comprehensive comparison,the best reinforcement formula of silicone rubber were as follows:silicone rubber raw rubber 100phr,gaseous silica 45phr,hydroxy silicone oil 4.5phr,hexamethyldisilazane 4.5phr,DCP 1.0phr.In the heat aging modification of silicone rubber,the effects of Fe₂O₃,biomass-graphene nanoplatelets and carbon nanotubes on the heat aging properties of silicone rubber were compared.The results showed that Fe₂O₃,biomass-graphene nanoplatelets and carbon nanotubes could significantly enhance the heat aging resistance of silicone rubber.Compared with Fe₂O₃and biomass-graphene nanoplatelets,carbon nanotubes had the best heat-resistant reinforcing effect.After aging at 300℃×12h,the tensile strength of carbon nanotubes could reach 5.36MPa,which could be increased by 105%,9%and 17%,respectively,compared with the blank sample,the optimal Fe₂O₃sample and the optimal biomass-graphene nanoplatelets sample.In the study of the low permeability modification of silicone rubber sealing materials,two methods were adopted:talc and graphite powder filling modification and fluori-ne/silicone rubber blending modification.The results of filling modification showed that both modified talc and modified graphite powder could significantly improve the air tightness of silicone rubber,and the comprehensive performance of the sample with modified graphite powder was better than that with modified talc.The optimal filling amount of modified graphite powder was 15 phr,and the gas permeability parameter of the sample was 5.16×10^-15mol·m/（m²·s·Pa）,which was reduced by 26%compared with the blank sample.The study on the modification of fluorine/silicone rubber blends showed that the reduction effect of fluorine/silicone rubber blends on the permeability of vulcanized rubber was significantly better than that of modified talc and modified graphite powder.When the total amount of fixed raw rubber was 100phr and the blend ratio of fluororubber was 30%,the comprehensive properties of the blend adhesive were the best.Compared with the unblended sample,the stress at 200%of the sample could be increased by 38%,the oil volume change resistance and gas permeability parameters could be reduced by12%and 45%,respectively.