Preparation Of High Performance Aerospace Sulfur-containing Sealant And Their Application

The aerospace sulfur-containing sealant is based on a sulfur-containing polymer containing sulfur,oxygen and other elements,combined with certain fillers and other additives.The aviation sulfur-containing sealant can form a cross-linked elastomer through vulcanization reaction,which is used in the aircraft’s overall fuel tank seal,fuselage anti-corrosion seal,flap cover seal,windshield glass seal,etc.It is one of the most used non-metallic materials on the aircraft and the key material to ensure the reliability of the aircraft structure seal.With the rapid growth of flight technology in the new era,the types and functions of aircraft are more abundant,which also makes the structure of aircraft more and more complicated,the flight range is wider,and the life of the aircraft is longer.The sealant materials used are required to have higher performance and more differentiated development.To meet the sealing needs of different parts,to ensure that the aircraft has better safety and long-term stability in various environments and working conditions,so high-performance sulfur-containing aviation sealant is one of the important development directions of aviation materials.In view of the characteristics of different functional sulfur-containing sealants,this article starts from three aspects:functional additives,vulcanization system,rubber matrix,etc.,study of the special effects of basic materials on functional materials,and respectively prepare sulfur-containing sulfur with different functions or functions.The sealant material has passed the assessment of the corresponding application environment to meet the sealing needs of advanced aircraft for different application parts,and provides a solid research foundation for subsequent material applications.It has important theoretical and practical significance.The main research includes the following parts:（1）Sulfur-containing sealants generally use MnO₂ as the vulcanizing agent,and the degree of vulcanization determines the key factor of the performance of the sealant.In order to improve the properties of the sealant after vulcanization,a series of highly active nano-MnO₂ materials were synthesized,including:MnO₂ nanowires and nanorods were synthesized by a simple hydrothermal method.The specific surface area of the MnO₂ nanowires was 156.4 m²/g,which was higher than 67.9 m²/g of MnO₂nanorods;highly ordered macroporous MnO₂ crystals of different sizes were prepared using PS microspheres of different sizes as template agents.When the above-mentioned nano-MnO₂ is applied to polysulfide rubber,they all show higher activity than ordinary MnO₂,and can improve the mechanical properties and storage modulus of the sealant.（2）Using PS microspheres and block copolymers as macroporous and mesoporous templates,an ordered macroporous-mesoporous Ce_0.4Zr_0.6O₂ with a macroporous structure of 309 nm and a mesoporous structure of 7 nm was synthesized by a one-step method.Ordered macropore-mesoporous Ce_0.4Zr_0.6O₂ solid solution is highly ordered,its pore wall is highly crystalline,has a large specific surface area of 67 m²/g,and has a strong ultraviolet absorption capacity.Based on the open macroporous structure and mesoporous structure of macroporous-mesoporous Ce_0.4Zr_0.6O₂ material,it can be evenly dispersed in liquid polysulfide rubber,prepared into an excellent anti-ultraviolet polysulfide sealant.It can also absorb ultraviolet rays and improve the UV resistance of the polymer.After 1000 hours of ultraviolet irradiation,the tensile elongation of the composite sealant decreased by only 16.2%,while the tensile elongation of the blank sample decreased 31.4%,showing excellent anti-ultraviolet effect.（3）Using P123 as the mesoporous template,aluminum isopropoxide as the aluminum source,tetrahydrofuran as the solvent,and nitric acid as the acid regulator,through solvent evaporation-induced self-assembly method,successfully synthesized mesoporous Al₂O₃ with super large diameter without the use of a hole expanding agent.When the calcination temperature is 600℃,the pore structure of mesoporous Al₂O₃ is kept more complete without obvious shrinkage and collapse.It has a mesoporous pore diameter of 18.1 nm and the pore structure is ordered.The mesoporous Al₂O₃material is added to polysulfide rubber as an anti-compression filler to prepare a compression-resistant sealing material.The reinforcement effect of mesoporous alumina is more obvious,and the anti-compression effect is more obvious,which effectively improves the compression resistance of the material.（4）A series of GO-MnO₂nanocomposites with different graphene oxide contents were prepared by ultrasonic physical mixing,and the morphology and structure of the materials were characterized.The effect of different contents of graphene on the performance of polysulfide sealant was studied,and it was found that the presence of a small amount of GO nanosheets（2%）can promote the dispersion of MnO₂ in polysulfide and promote the overall crosslinking degree and mechanical activity of the polysulfide sealant.But high content of GO will cause the catalytic activity of MnO₂polysulfide sealant to decrease.At the same time,the presence of graphene improves the anti-fungus level of the sealant.The anti-fungus level can be increased from 4 to 1.The addition of graphene can make the sealant maintain better mechanical properties after environmental assessment such as damp heat,salt spray,etc.Therefore,graphene can be used as a functional additive for new"three-proof"sealants.（5）As a new generation of sulfur-containing rubber,polythioether rubber has excellent high and low temperature resistance and medium resistance.The synthesis of narrow distribution liquid polythioether rubber is one of the research focuses.Using block copolymers as soft templates to synthesize highly ordered mesoporous TiO₂,which has a high specific surface area（162 m²/g）and a large pore volume（0.24 cm³/g）,and also has strong UV absorption ability.In the"thiol-ene"click reaction,mesoporous TiO₂ is used as a photocatalyst and structure directing agent,using the actual mesoporous structure to regulate the final molecular weight and the final polymerization degree data,the specific polythioether rubber with molecular weight dispersion was further obtained,the sealant prepared with it has higher mechanical properties and compression properties,and shows better high temperature resistance than polysulfide sealant.（6）In order to further improve the high or low temperature resistance of sulfur-containing rubbers,carborane hybrid polythioether rubbers were synthesized,including main chain carbon-containing borane polythioether and side chain carbon-containing borane polythioether;silane hybrid polythioether rubber,including silicone hybrid polythioether and fluorosilicone hybrid polythioether.The synthetic rubber is prepared as a sealant material,and the corresponding high and low temperature resistance assessments are conducted respectively.Among them,the carborane hybridization can improve the retention rate of the mechanical properties of the sealant after heat aging,especially the main chain carbon borane hybrid has excellent heat resistance,which can meet the heat aging of 160℃×7 d.Silane hybridization can reduce the glass transition temperature of the sealant,and can meet the low-temperature sealing requirements at-65℃.Among them,the fluorosiloxane hybrid polythioether has better media resistance.