Wide-temperature-range silicone rubber base rubber for aerospace thermal protection, composite material and preparation method of wide-temperature-range silicone rubber base rubber

Abstract

The invention discloses wide-temperature-range silicone rubber-based rubber for aerospace thermal protection, a composite material and a preparation method of the wide-temperature-range silicone rubber-based rubber. According to the invention, three monomers, i.e., methylcyclosiloxane, hexaethylcyclotrisiloxane and phenylene silicon monomer, are subjected to ring opening and condensation copolymerization to obtain polysiloxane macromolecules containing three different chain link structures. A phenylene structure is introduced into a silicon rubber main chain, so that the silicon elastomer main chain is limited to form a volatile cyclic oligomer through a chain back-biting reaction and a chain segment rearrangement exchange reaction, the thermal stability is improved, and the initial decomposition temperature is up to 450.16 DEG C; the regularity of a molecular chain is broken by introducing ethyl, so that the glass-transition temperature is as low as 120.2 DEG C, and no crystallization phenomenon occurs. The base adhesive has excellent cold resistance, radiation resistance, ablation resistance, high temperature resistance and the like, and can be used as the base adhesive to be applied to the aspects of aerospace craft protective coatings, dynamic seal putty adhesives, sealants and the like.

Description

Technical Field

[0001] This invention belongs to the field of silicone rubber thermal protection materials, specifically relating to wide-temperature-range silicone rubber base adhesive, composite materials and their preparation methods for aerospace thermal protection. Background Technology

[0002] Organosilicon materials, as a class of polymeric compounds with silicon-oxygen bonds (Si-O) as their backbone, possess a unique molecular structure that simultaneously contains silicon atoms and organic groups, forming a hybrid structure that is both semi-organic and semi-inorganic. This special chemical composition endows the materials with excellent weather resistance, electrical insulation, and good processability, making them widely applicable in aerospace, electronic packaging, medical devices, and other fields.

[0003] Dimethyl silicone rubber, as a mainstream commercially available silicone rubber, exhibits excellent performance characteristics at low temperatures: its molecular chains have high flexibility, resulting in a low glass transition temperature. However, as the temperature rises, the silicon-oxygen backbone within the material undergoes chain re-biting and segment rearrangement exchange reactions, leading to the formation of volatile cyclic oligomers. This process weakens its high-temperature stability. In contrast, medium- and high-phenyl silicone rubbers, due to the introduction of more rigid phenyl groups into their molecular structure, exhibit better thermal stability in high-temperature environments. However, the steric hindrance effect of phenyl groups simultaneously restricts the mobility of the molecular chains, resulting in insufficient flexibility at low temperatures, making it difficult to meet the requirements of low-temperature applications. While low-phenyl silicone rubber has good low-temperature resistance, its high-temperature resistance and ablation resistance are insufficient due to its limited phenyl content.

[0004] Patent CN 119371663 A proposes a polysiloxane copolymer containing four types of linkages: methyl, ethyl, phenyl, and phenyl ether linkages. It has excellent properties such as low glass transition temperature, high viscosity, and wide temperature range, but the production cost is relatively high. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a wide-temperature-range silicone rubber base adhesive for aerospace thermal protection and its preparation method. The wide-temperature-range silicone rubber base adhesive for aerospace thermal protection of the present invention possesses excellent cold resistance, radiation resistance, ablation resistance, and high-temperature resistance, and can be used as a base adhesive in aerospace vehicle protective coatings, dynamic sealing putties, sealants, and other applications.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection, having a compound with the following structural formula:

[0007] Where Et represents CH3CH2-, x, y, and z represent the number of each structural unit, x is an integer between 100 and 300, y is an integer between 150 and 300, z is an integer between 700 and 2500, and x / (x+y+z) < 0.2.

[0008] In some embodiments, the raw materials for preparing the wide-temperature-range silicone rubber base for aerospace thermal protection, by weight, include: 60-90 parts of methylcyclosiloxane, 0-30 parts of ethylcyclotrisiloxane, 5-15 parts of phenylenesilane monomer, 3-8 parts of end-capping agent, and 0.5-3 parts of catalyst.

[0009] In some embodiments, the raw materials for preparing the wide-temperature-range silicone rubber base for aerospace thermal protection include, by weight parts: preferably 70-85 parts of methylcyclosiloxane, 5-20 parts of ethylcyclosiloxane, 10 parts of phenylenesilane monomer, 6 parts of end-capping agent, and 2 parts of catalyst.

[0010] In some embodiments, the ethylcyclotrisiloxane includes at least one of trimethyltriethylcyclotrisiloxane, hexaethylcyclotrisiloxane, and octaethylcyclotetrasiloxane, wherein the ethylsiloxane unit structure is strictly controlled within y / (x+y+z) < 0.2.

[0011] In some embodiments, the phenylene silicon monomer is at least one of 1,4-(dimethylmethoxysilyl)benzene, 1,4-(dimethylethoxysilyl)benzene and 1,4-(dimethylhydroxysilyl)benzene, wherein the phenylene (silicon) unit structure is strictly controlled within x / (x+y+z) < 0.2.

[0012] In some embodiments, the catalyst comprises at least one of tetramethylammonium hydroxide silanolate, tetraethylammonium hydroxide silanolate, and potassium hydroxide silanolate; the end-capping agent comprises at least one of dimethyl hydroxy silicone oil, diethyl hydroxy silicone oil, and water.

[0013] Taking octamethylcyclotetrasiloxane, hexaethylcyclotrisiloxane, 1,4-(dimethylhydroxysilyl)benzene, dimethylhydroxysilicone oil, and tetramethylammonium hydroxide silanolate as examples, with a polymerization temperature set at 110 °C, the reaction mechanism for preparing a wide-temperature-range silicone rubber base for aerospace thermal protection is as follows:

[0014] In some embodiments, the viscosity range of the wide-temperature-range silicone rubber base for aerospace thermal protection is controlled within 7~20 Pa·s; the wide-temperature-range silicone rubber base for aerospace thermal protection exhibits no crystallization peak within a temperature range of -115 ℃ to 430 ℃. 5% 430 ℃ or higher.

[0015] It should be noted that "no crystallization peak" refers to the absence of crystallization peaks in differential scanning calorimetry (DSC) tests within the stated temperature range. The DSC test conditions are as follows: cooling with liquid nitrogen, the temperature is lowered from room temperature to -140 °C, held for 5 min, then the temperature is increased to 30 °C at a rate of 5 °C / min. The DSC curve is obtained using a DSC 3500 differential scanning calorimeter. 5% ≥430 °C refers to an initial thermal decomposition temperature greater than 430 °C as determined by thermogravimetric analysis (TG). The Tg test conditions are: under a nitrogen atmosphere, the temperature is increased from 30 °C to 800 °C at a heating rate of 10 °C / min, and the thermogravimetric analysis curve is obtained using an SDT Q600 simultaneous thermal analyzer (TA). The initial decomposition temperature Tg is the value of the initial thermal decomposition temperature. 5% The temperature at which a 5% mass loss occurs.

[0016] Secondly, the present invention also provides a method for preparing a wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection, the preparation method comprising the following steps: The methylcyclosiloxane, the ethylcyclosiloxane, the phenylenesilane monomer, the catalyst, and the end-capping agent are mixed to obtain a mixture. The mixture is heated to 80~100 °C and subjected to a first reaction at a pressure of -0.01 to -0.04 MPa for 0.5~1 hours to obtain the primary reaction material. The primary reactant is heated to 110-120 °C to carry out a ring-opening copolymerization reaction for 2-4 hours to obtain the ring-opening copolymerization material. The catalyst is decomposed by heating to 130~170 °C, and then the temperature is raised to 180~200 °C and the low-boiling substances are removed under a pressure of -0.098 MPa. Cooling yields the wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection.

[0017] Thirdly, the present invention also provides a composite material, which is obtained by mixing the wide-temperature-range silicone rubber base for aerospace thermal protection with fumed silica, hollow ceramic microspheres, glass powder, crosslinking agent and organotin catalyst, and curing at room temperature. The crosslinking agent comprises a combination of two or more selected from tetraethyl orthosilicate, triethoxysilane, and methyl orthosilicate; the organotin catalyst comprises at least one or a combination selected from dibutyltin dilaurate and stannous octoate.

[0018] In some embodiments, based on the mass of the wide-temperature-range silicone rubber base for aerospace thermal protection, the amount of fumed silica added is 20%~30%, the amount of hollow ceramic microspheres added is 20%~60%, the amount of glass powder added is 3%~8%, the amount of crosslinking agent added is 5%~8%, and the amount of organotin catalyst added is 0.3%~1%.

[0019] The present invention provides a wide-temperature-range silicone rubber-based adhesive and composite material for aerospace thermal protection, and their preparation method. Through molecular structure design, a polysiloxane copolymer containing three types of linkages—methyl, ethyl, and phenylene linkages—is obtained. The phenylene linkages in the main chain introduce phenylene groups, which enhance the rigidity of the main chain, limit chain bite-back reactions and chain segment rearrangement exchange reactions, and improve thermal stability. The initial decomposition temperature can be increased from 429.68 °C to 450.16 °C. The ethyl linkages introduce a small amount of ethyl groups, which disrupts the integrity of the molecular chain, lowers the crystallization temperature, and reduces the glass transition temperature to -120.20 °C. Compared with phenylene ethers, phenylene has higher terminal hydroxyl activity and is cheaper, which is beneficial for large-scale industrial production. Attached Figure Description

[0020] Figure 1 The base adhesive prepared in Comparative Example 1 1 H NMR spectrum; Figure 2 The base adhesive prepared in Example 2 1 H NMR spectrum; Figure 3 The infrared spectrum of the No. 2 base adhesive prepared in Example 2; Figure 4 The DSC curves of the base adhesives prepared in Examples 1-4 are shown. Figure 5 The image shows a plasma arc micro-wind tunnel test result of the composite material prepared from the base adhesive obtained in Example 2. Figure 6 The image shows a plasma arc micro-wind tunnel test of the composite material prepared from the base adhesive obtained in Comparative Example 2. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention will be further described below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of aiding understanding of this invention and do not constitute a limitation thereof.

[0022] The number-average molecular weight and viscosity test methods for Examples 1-4 and Comparative Examples 1-2 are as follows: Number-average molecular weight: Gel permeation chromatography (GPC) analysis was performed using an Agilent 1260 gel permeation chromatography (GPC) system (Agilent). The sample was dissolved in tetrahydrofuran (THF), and the analysis was performed using THF as the mobile phase at a column temperature of 35°C to obtain molecular weight and molecular weight distribution data. Viscosity: The viscosity of polysiloxane was measured using a digital viscometer.

[0023] Example 1 This embodiment provides a wide-temperature-range silicone rubber base for aerospace thermal protection. The raw materials for preparing the wide-temperature-range silicone rubber base for aerospace thermal protection include, by weight, 85 g of octamethylcyclotetrasiloxane, 5 g of hexaethylcyclotrisiloxane, 10 g of 1,4-(dimethylhydroxysilyl)benzene, 2 g of tetramethylammonium hydroxide silanolate, and 5 g of dimethylhydroxysilicone oil.

[0024] The preparation method of silicone rubber-based adhesive includes the following steps: The raw materials are added to the reaction vessel all at once; Heat to 80 °C, reduce pressure to -0.04 MPa, and react for 0.5 hours; Continue heating to 110 °C and continue the ring-opening copolymerization reaction for 3 hours; Heat to 160 °C and maintain this temperature for 1 hour to decompose the catalyst; Increase the temperature to 180 °C and reduce the pressure to -0.098 MPa to remove low-boiling-point substances; After cooling to room temperature, base gel No. 1 was obtained, with a viscosity of 13.87 Pa·s and a number-average molecular weight of 94800 g / mol.

[0025] Example 2 The only difference between this embodiment and Example 1 is that 80 g of octamethylcyclotetrasiloxane and 10 g of hexaethylcyclotrisiloxane were used. All other conditions were the same as in Example 1. The viscosity was measured to be 14.57 Pa·s and the number average molecular weight was 106600 g / mol.

[0026] Example 3 The only difference between this embodiment and Example 1 is that 75 g of octamethylcyclotetrasiloxane and 15 g of hexaethylcyclotrisiloxane were used. All other conditions were the same as in Example 1. The viscosity was measured to be 28.10 Pa·s and the number average molecular weight was 124,500 g / mol.

[0027] Example 4 The only difference between this embodiment and Example 1 is that 70 g of octamethylcyclotetrasiloxane and 20 g of hexaethylcyclotrisiloxane were used. All other conditions were the same as in Example 1. The viscosity was measured to be 12.05 Pa·s and the number average molecular weight was 89300 g / mol.

[0028] Comparative Example 1 The only difference between this comparative example and Example 1 is that 90 g of octamethylcyclotetrasiloxane, 10 g of hexaethylcyclotrisiloxane, and 0 g of tetramethyltetraphenylcyclotetrasiloxane were used, and the viscosity was measured to be 13.48 Pa·s, with a number-average molecular weight of 115700 g / mol.

[0029] Comparative Example 2 The only difference between this comparative example and Example 1 is that 80 g of octamethylcyclotetrasiloxane, 10 g of hexaethylcyclotrisiloxane, and 10 g of tetramethyltetraphenylcyclotetrasiloxane were used, and the viscosity was measured to be 78.57 Pa·s, with a number-average molecular weight of 158,600 g / mol.

[0030] The following tests were performed on the base adhesives of Examples 1-4 and Comparative Examples 1-2: 1 H NMR, 13 C10 NMR spectroscopy: The sample was dissolved in CDCl3 without TMS internal standard, and the results were obtained by nuclear magnetic resonance spectroscopy (Bruker Avance III 500 MHz). 1 H NMR, 13 C NMR spectrum; FT-IR testing: Using a Nicolet 6700 infrared spectrometer, the sample was measured at 450-4000 cm⁻¹. -1 FT-IR spectrum at wavelength; DSC test: The temperature was cooled with liquid nitrogen from room temperature to -140 °C and held for 5 min. Then, the temperature was increased to 30 °C at a rate of 5 °C / min. The DSC curve was obtained using a DSC 3500 differential scanning calorimeter. The glass transition temperature (Tg) was used as the reference value. g The temperature at which the heat capacity changes to half is determined. The crystallization status can be determined from the DSC curve. If a crystallization peak appears on the DSC curve, it indicates that the sample crystallizes at this temperature. TG test: Under a nitrogen atmosphere, the temperature was increased from 30 °C to 800 °C at a heating rate of 10 °C / min. The thermogravimetric analysis curves were obtained using an SDT Q600 synchronous thermal analyzer (TA). The initial decomposition temperature was determined by the temperature at which the mass loss was 5%, and the residue rate represents the percentage of mass remaining when the temperature reaches 800 °C. Mechanical property testing: According to GB / T528-2009 standard, the CMT 4104 microcomputer-controlled electronic universal testing machine (MTS) was used for testing. 80 g of base glue was mixed with 20 g of fumed silica, 5.5 g of tetraethyl orthosilicate and 0.5 g of dibutyltin dilaurate using an open mill. The mixture was cured at room temperature for 7 days to obtain the mechanical property test sample. Plasma arc micro-wind tunnel test: The test was conducted according to GJB 7050 standard. 80 g of base adhesive was mixed with 20 g of fumed silica using a two-roll mill. Then, 30 g of hollow ceramic microspheres, 5 g of glass powder, 5.5 g of 1:1 compound tetraethyl orthosilicate and triethoxysilane, and 0.5 g of 1:1 compound stannous octoate and dibutyltin dilaurate were added and stirred evenly. The mixture was then formed using a spray coating process and cured at room temperature for 7 days to obtain the wind tunnel test sample. The performance test results are shown in the table below:

[0031] Table 1 Performance Tests of Silicone Rubber Base

[0032] As can be seen from Table 1, no phenylene was introduced in Comparative Example 1. Compared with Example 2, Comparative Example 1 has a lower glass transition temperature. Since a small amount of ethyl cannot eliminate the effect of methyl crystallization, crystallization occurs at -95 °C. Furthermore, its initial decomposition temperature and residual rate are both lower than those of Example 2.

[0033] In Comparative Example 2, a phenyl group was introduced into the side chain. Compared with Example 2, the glass transition temperature and tensile strength of Comparative Example 2 were similar to those of Example 2 and there was no crystallization. However, its initial decomposition temperature and residual rate were lower than those of Example 2.

[0034] Comparing Examples 1-4, it can be seen that increasing the ethyl content improves the flexibility of the phenylene silicone rubber segments and increases the tensile strength. However, with increasing ethyl content, the glass transition temperature and tensile strength show a decreasing trend.

[0035] Compared to the high viscosity of 78.57 Pa·s in Comparative Example 2, the viscosity of Examples 1-4 was controlled within the ideal range of 7~20 Pa·s. The high viscosity of Comparative Example 2 easily increases process resistance and hinders the smooth addition of fillers; while Examples 1-4, with their suitable viscosity characteristics, successfully balanced processing performance: on the one hand, they avoided the problem of poor filler wettability caused by low viscosity, and on the other hand, they overcame the mixing obstacles caused by high viscosity, thereby significantly promoting the uniform dispersion of reinforcing and ablation-resistant fillers.

[0036] There is a non-linear dependence between number-average molecular weight and the elongation at break and tensile strength of the material; a higher value is not necessarily better. Data from Examples 1-4 show that when the number-average molecular weight is between 89,000 and 125,000 g / mol, the material can achieve a good balance between tensile strength and elongation at break.

[0037] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection, characterized in that, Compounds with the following structural formula: ， Where Et represents CH3CH2-, x, y, and z represent the number of each structural unit, x is an integer between 100 and 300, y is an integer between 150 and 300, z is an integer between 700 and 2500, and x / (x+y+z) < 0.

2.

2. The wide-temperature-range silicone rubber base for aerospace thermal protection according to claim 1, characterized in that, The raw materials for preparing the wide-temperature-range silicone rubber base for aerospace thermal protection, by weight, include: 60-90 parts of methylcyclosiloxane, 0-30 parts of ethylcyclotrisiloxane, 5-15 parts of phenylenesilane monomer, 3-8 parts of end-capping agent, and 0.5-3 parts of catalyst.

3. The wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection according to claim 2, characterized in that, The methylcyclosiloxane includes at least one of hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and tetramethyltetravinylcyclosiloxane.

4. The wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection according to claim 2, characterized in that, The ethylcyclotrisiloxane includes at least one of trimethyltriethylcyclotrisiloxane, hexaethylcyclotrisiloxane, and octaethylcyclotetrasiloxane, and y / (x+y+z) < 0.

2.

5. The wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection according to claim 2, characterized in that, The phenylenesilane monomer is at least one of 1,4-(dimethylmethoxysilyl)benzene, 1,4-(dimethylethoxysilyl)benzene and 1,4-(dimethylhydroxysilyl)benzene.

6. The wide-temperature-range silicone rubber base for aerospace thermal protection according to claim 2, characterized in that, The catalyst comprises at least one of tetramethylammonium hydroxide silanolate, tetraethylammonium hydroxide silanolate, and potassium hydroxide silanolate; the end-capping agent comprises at least one of dimethyl hydroxy silicone oil, diethyl hydroxy silicone oil, and water.

7. The wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection according to claim 2, characterized in that, The viscosity range of the silicone rubber base is controlled between 7 and 20 Pa·s; the silicone rubber base exhibits no crystallization peak within a temperature range of -115 ℃ to 430 ℃. 5% 430 ℃ or higher.

8. A method for preparing a wide-temperature-range silicone rubber-based adhesive for aerospace thermal protection according to any one of claims 2-7, characterized in that, The preparation method includes the following steps: The methylcyclosiloxane, the ethylcyclosiloxane, the phenylenesilane monomer, the catalyst, and the end-capping agent are mixed to obtain a mixture. The mixture is heated to 80~100 °C and subjected to a first reaction at a pressure of -0.01 to -0.04 MPa for 0.5~1 hours to obtain the first reaction material. The primary reactant is heated to 110-120 °C to carry out a ring-opening copolymerization reaction for 2-4 hours to obtain the ring-opening copolymerization material. The ring-opening copolymer material is heated to 130~170 °C to decompose the catalyst, and then heated to 180~200 °C. After removing low-boiling substances under a pressure of -0.098 MPa, the material is cooled to obtain the wide-temperature-range silicone rubber base for aerospace thermal protection.

9. A composite material, characterized in that, The product is obtained by mixing and refining a wide-temperature-range silicone rubber base for aerospace thermal protection according to any one of claims 1-7 with fumed silica, hollow ceramic microspheres, glass powder, crosslinking agent and organotin catalyst, and then curing at room temperature. The crosslinking agent comprises a combination of two or more selected from tetraethyl orthosilicate, triethoxysilane, and methyl orthosilicate; the organotin catalyst comprises at least one or a combination selected from dibutyltin dilaurate and stannous octoate.

10. A composite material according to claim 9, characterized in that, Based on the mass of the wide-temperature-range silicone rubber base for aerospace thermal protection, the amount of fumed silica added is 20%~30%, the amount of hollow ceramic microspheres added is 20%~60%, the amount of glass powder added is 3%~8%, the amount of crosslinking agent added is 5%~8%, and the amount of organotin catalyst added is 0.3%~1%.

Images