Preparation And Study On Properties Of Silicone Rubber Low Density Composites Modified With Silicone Resin

The rapid development of aerospace technology has stimulated the research boom of thermal insulation composite materials.Silicone rubber has received extensive attention due to its excellent properties such as heat resistance,weather resistance,aging resistance,radiation resistance and other properties,and it has became a research hotspot in the field of thermal insulation composite materials.It was of great significance to develop a heat-insulating and heat-resistant composite material with high temperature resistance,low density,low thermal conductivity,and good mechanical properties by using silicone rubber as a matrix.In this paper,room-temperature curing liquid silicone rubber?RTV-LSR?was used as the matrix,which was reinforced and modified by MQ silicone resin,Then,the density and thermal conductivity of the composite were reduced by adding hollow glass microspheres?HGM?,finally,Finally,the chopped carbon fiber?CF?and high-silica glass fiber?GF?were introduced to further improve the mechanical properties and heat resistance of the composite,and a heat-insulating composite material with low density,high temperature resistance,low thermal conductivity,and good mechanical properties based on silicone rubber were prepared.First,the RTV-LSR was modified with MQ silicone resin,and the effect of MQ silicone content on the performance of RTV-LSR composite was studied.The results showed that with the increase of MQ silicone resin content,the overall viscosity of the composite material showed a decreasing trend.The surface drying time was prolonged and the solidification rate became slower.The tensile strength of the composite material increased first and then decreased,it reached a maximum of 2.96MPa when the MQ silicone content was 60wt%.The initial decomposition temperature T_5%and residual weight of the composites gradually increased.After considering various performance considerations,the optimum content of MQ silicone resin was determined to be 60wt%.Secondly,MQ silicone resin/RTV-LSR composites were filled with HGM with different gradient contents and the effect of HGM content on the properties of the composites was studied.The results showed that the surface free energy of HGM after being treated with the coupling agent KH550 was effectively reduced,the hydrophobicity was increased,and the compatibility with the MQ silicone/RTV-LSR substrate was improved.The addition of HGM can effectively reduce the density of composites,with the increase of HGM content,the density of composites gradually decreased,the tensile strength of composites increased first and then decreased,and when the content was 30wt%,the maximum value reached 4.29MPa.DMA analysis showed that the storage modulus of composites gradually decreased with the increase of temperature.With the increase of HGM content,the glass transition temperature Tg of the composites increased continuously,and the loss factor tan?reached a maximum of 0.27 when the HGM content was 30 wt%.With the increase of HGM content,the T_5%and residual ratio of composites gradually increased,showed that the addition of HGM has a positive effect on improving the thermal stability of composites.The thermal conductivity of composites decreased continuously with the increase of HGM content,When the content of HGM reached 30wt%?38.6vol%?,the thermal conductivity of composites was reduced to a minimum of 0.15W·m^-1·K^-1.The above showed that the HGM/MQ silicone/RTV-LSR composite has the best overall performance when the HGM filling amount was 30 wt%.Finally,the mechanical properties and heat resistance of the composites were further improved by the introduction of chopped CF and chopped GF,and the effects of different chopped fibers on the properties of HGM/MQ silicone/RTV-LSR low-density composites were investigated.The results showed that after chopped GF and chopped CF were treated with concentrated nitric acid and KH550,the mechanical properties of composites were improved.The addition of chopped GF and CF could enhance the mechanical properties of HGM/MQ silicone/RTV-LSR composites.When the content of chopped GF and CF was 5wt%,the tensile strength of the composite reached a maximum of 5.27MPa and 4.72MPa,respectively.With the content of chopped GF and CF increase,the thermal conductivity of HGM/MQ silicone/RTV-LSR composites just increasd slightly.The addition of chopped GF and CF increasd the T_5%T_max,and residual weight of the composites.It indicated that the chopped GF and CF has a certain effect on improving the thermal stability of the composites.