Study On Synthesis And Application Of Highly Branched High Residual Resin Silicone For Ablation Thermal Protection Coating

The new-generation aircraft has a complex aerodynamic shape and a more demanding heat flow environment.It has higher heat flow,stronger shearing and longer thermal protection time.The traditional epoxy and silicone rubber thermal protection coatings can not meet the requirements of back temperature and ablation surface in the new environment.Problems such as sharp ablation,low residual carbon,and large amount of stripping obstruct the enhancement of thermal protection efficiency.Therefore,it is urgent to develop a new generation of ablative heat-resistant coating materials.As an important part of ablation thermal protection coating(ATPC),the resin matrix directly determines the performance of the coating,which has become the key to the development of a new generation of ATPC.In order to solve this problem,molecular structure design and synthesis of high residual carbon resin-silicone resin grafted copolymer was carried out and thermal protection efficiency of ATPC was elevated.First of all,the molecular structure design and synthesis of silicone modified epoxy resin was conducted.Epoxy resin has poor toughness and epoxy based coating may crack during the storage and application process,however,it has high residual,high ablation efficiency and low back-face temperature.On this basis,highly branched polymethylphenylsiloxane grafted epoxy resin(HBPSE)was synthesized by grafting silicone intermediate onto epoxy resin via the condensation between methoxyl and hydroxyl.The chemical structure of the highly branched copolymer was characterized by FT-IR,~1H-NMR and GPC.The thermal stability of the HBPSE copolymer was characterized by TGA and muffle furnace ablation test.The introduction of silicone not only promoted the thermalstability and toughness of epoxy,but also broadened its pyrolysis temperature range.Besides,the molecular structure design and synthesis of phenolic resin modified silicone rubber was conducted.Silicone rubber has good thermalstability,toughness and low heat conductivity,however,its ablation efficiency is low and will form ash layer after ablation.Under the shear flow impact,ablative retreat of silicone rubber is serious.Hence,phenolic resin was choosed to modified silicone rubber.Highly branched phenolic resin grafted silicone rubber(PGS)was synthesised by grafting allyl ether phenolic resin onto silicone rubber with Si–H groups via hydrosilylation.The chemical structure of the copolymer was characterised by FT-IR,~1H-NMR and GPC,and its co-continious microphase morphology was observed via SEM.The mechanical properties and thermal stability of the material were also characterised.Overcoming the poor compatibility between phenolic resin and silicone rubber,the synthesized resin combined the characteristics of high char layer strength of phenolic resin and good toughness of silicone rubber and possessed higher thermalstability.Furthermore,ATPC based on HBPSE and PGS copolymer was prepared respectively.The thermal properties of ATPCs were assessed through muffle furnace ablation,quartz lamp test and used in actual environment.Compared with traditional epoxy and silicone rubber based ATPC,HBPSE and PGS based ATPC has better ablation morphology and lower back-face temperature.Problems of cracking and pulverization of coatings during ablation were solved.After oxygen-acetylene test,the micromorphology and chemical composition of ATPCs were characterized by SEM,EDS FT-IR and XRD,and the ablation mechanisms of ATPCs was also studyed.