| In recent years,the aerospace industry has developed rapidly,and the requirements for structural efficiency of the next-generation aerospace vehicles and engines have been continuously improved,which poses great challenges to thermal protection materials and structures,therefore,the development of high-temperature insulation material to achieve the protection of key components is particularly important.When the spacecraft is exposed to moderate heat flux for about 2 minutes or at higher temperatures(500-800oC),polymer-based thermal protection materials are often used to increase the performance limits of the corresponding components.Among them,silicone rubber elastomers have excellent properties and are widely used.Their physical and chemical properties are between ordinary polymers and inorganic substances.The chemical bonding force in their molecular network is strong,with low linear ablation rate,high gas production,high residual carbon content and good adhesion performance,in addition to unique high temperature resistance and low temperature resistance,so it has the potential as a thermal protection material.In view of the actual needs in related fields at present,this subject prepared a heat-resistant silicone rubber cured at room temperature with ?,? dihydroxy polydimethylsiloxane as the matrix.The cage silsesquioxane(POSS)with good compatibility with the matrix silicone rubber is selected to improve the rigidity of the matrix silicone rubber molecules from the molecular level,thereby improving its heat resistance,physical and mechanical properties.Explore the changes of thermal properties and mechanical properties of silicone rubber after blending trihydroxyisobutyl silsesquioxane,octahydroxy silsesquioxane,octaamino silsesquioxane,and octavinyl silsequioxane with silicone rubber respectively,among them,the proportion of POSS added is 1 wt%,3 wt%,5 wt%.By comparing and analyzing the effects of four kinds of POSS on the performance of silicone rubber,the interaction mechanism between different POSS and silicone rubber is analyzed and explained,and the reason for the change of silicone rubber performance is explained from the molecular structure level.Experiments show that the performance of octaamino silsesquioxane has the greatest improvement on matrix silicone rubber,its introduction increases the maximum decomposition temperature of matrix silicone rubber from by 18%,and the mass residual rate of 800 oC has increased by 37.1%.The heat resistance of silicone rubber is greatly affected by the curing behavior.Therefore,in order to obtain the best performance of silicone rubber,this topic combined with the literature and selected several curing agents,catalysts and silicone rubber at room temperature,and explore the curing of silicone rubber condition.By analyzing and summarizing the experimental results of the interaction between different curing systems and silicone rubber,the principle of silicone rubber curing is explored.Starting from the curing principle of silicone rubber,two kinds of silicone rubber room temperature curing agents G1 and G2 were prepared synthetically,and the curing molding of silicone rubber was realized without the aid of the catalytic action of organic tin.To summarize and compare the experimental results of the preferred curing system in literature and the two curing agents prepared by ourselves,the curing mechanism of silicone rubber is discussed.It is found that the experimentally synthesized G1 has the best performance,and it acts with silicone rubber at room temperature.The surface drying time is only 6-8h and the maximum decomposition temperature of silicone rubber is increased to 710 oC,and the mass residual rate of 800 oC is increased by 62.3%. |
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