Shape memory polyimide composite aerogel material for self-deployable thermal protection system and preparation method of shape memory polyimide composite aerogel material

Abstract

The invention discloses a shape memory polyimide composite aerogel material for a self-expandable thermal protection system and a preparation method of the shape memory polyimide composite aerogel material. The preparation method comprises the following steps: (1) preparing polyamide acid-polysiloxane; (2) preparing polyamide acid-polysiloxane composite sol; and (3) preparing the polyimide composite aerogel: carrying out standing defoaming, freezing, freeze drying and thermal imidization on the polyamide acid-polysiloxane composite sol to obtain the polyimide composite aerogel. The preparation method comprises the following steps: mixing a ceramic filler, a fluxing agent and polyamic acid-polysiloxane to obtain polyamic acid-polysiloxane composite sol, and freezing, freeze-drying and thermally imidizing to obtain a shape memory polyimide composite aerogel product with high strength, high storage modulus, high shape recovery rate and high thermal protection performance.

Description

Technical Field

[0001] The invention relates to the technical field of thermal protection materials, and in particular to a shape memory polyimide composite aerogel material for a self-expandable thermal protection system and a preparation method thereof. Background Art

[0002] The deployable thermal protection system is a new thermal protection design concept with the characteristics of high storage ratio, high temperature ablation resistance, high temperature insulation, etc. When the spacecraft enters the planetary surface at high speed, due to its controllable deployable thermal protection structure, it can increase the friction area with the atmosphere, effectively reduce the ballistic coefficient, and achieve effective deceleration and braking, thereby achieving a larger mass load of the spacecraft and high-altitude landing in a complex planetary environment. It has broad application prospects in deep space exploration, manned spaceflight and other technical fields. Compared with traditional mechanical or inflatable deployable structures, shape memory deployable structures have attracted widespread attention due to their advantages such as simple mechanical structure, light weight and strong reliability. However, the current shape memory deployable structures are limited in their application in deployable thermal protection system materials due to their poor mechanical properties, difficult to control response conditions, and insufficient thermal protection performance.

[0003] Therefore, the preparation of self-deployable thermal protection system materials needs to meet the following conditions: (1) shape memory performance, the self-heating response at high temperature triggers shape recovery, and the excellent shape recovery rate enables the thermal protection structure to be deployed; (2) high-temperature thermal protection performance, when the deployed thermal protection structure faces high heat flux impact, it has excellent anti-ablation performance and high-temperature mechanical properties to resist the incoming flow ablation and surface load, and at the same time, the excellent high-temperature thermal insulation performance prevents heat from being transferred backward.

[0004] Polyimide is a special polymer material. Due to the presence of the imide ring (-CO-NR-CO-), it has excellent toughness, heat resistance and high mechanical strength. It also has excellent shape memory properties. In addition, it has low density, high specific surface area, and low thermal conductivity (as low as 0.025W m -1 K -1 ) and other characteristics, have attracted widespread attention from researchers in the field of aerospace thermal insulation. However, the thermal insulation performance of polyimide aerogel can only withstand temperatures below 500°C. When the ambient temperature exceeds its decomposition temperature, carbonization and decomposition will occur, and the structure will collapse severely. The ceramic transformation technology is a new method that can transform polymer composites into high-temperature resistant ceramic materials in situ at high temperatures. It realizes the transformation of materials from organic to inorganic through melt adhesion and eutectic reaction, which can greatly improve the thermal protection performance of organic composite materials.

[0005] In the prior art (CN118563556A, CN119286150A), a ceramifiable composite material was prepared by means such as impregnation and blending. This material is compounded with materials such as rubber, resin, and fiber felt. It has a small aerogel content and has problems of relatively large density and poor heat insulation performance. Moreover, due to problems such as a large matrix rigidity and lack of shape memory performance, it is difficult to carry out the structural design of deployable thermal protection. The prior art cannot simultaneously achieve the self-deployment of the protection structure and high-temperature thermal protection performance. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present invention provides a shape memory polyimide composite aerogel material for a self-deployable thermal protection system and a preparation method thereof. After the composite aerogel of the present invention is heated and deployed, as the heat flux continues to increase and the surface temperature reaches 800 °C or above, the flux on the surface melts, and adheres the residual carbon and silicon dioxide generated by the thermal decomposition of the polyimide-polysiloxane matrix and the ceramic fillers dispersed in the matrix, forming a high-temperature resistant ceramic structure on the surface of the material. This can effectively improve the ablation resistance and mechanical properties of the material. And due to the formation of the ceramic layer and the existence of residual carbon, the infrared emissivity of the material is increased, which can effectively resist the energy transfer of thermal radiation and improve the high-temperature heat insulation performance of the composite aerogel material, having excellent thermal protection ability.

[0007] The technical solution of the present invention is as follows:

[0008] The first object of the present invention is to provide a preparation method of a shape memory polyimide composite aerogel for a self-deployable thermal protection system, including the following steps:

[0009] (1) Prepare polyamic acid-polysiloxane

[0010] The diamine is dissolved in a polar solvent, and then the dianhydride is added for polycondensation reaction to obtain a polyamic acid solution. Then, an amino-terminated polysiloxane is added for block copolymerization reaction to obtain a polyamic acid-polysiloxane solution, and then after precipitation and drying, polyamic acid-polysiloxane powder is obtained;

[0011] (2) Prepare polyamic acid-polysiloxane composite sol

[0012] The polyamic acid-polysiloxane powder is dissolved in deionized water, and then triethylamine, ceramic fillers, and flux are added and mixed to obtain a polyamic acid-polysiloxane composite sol;

[0013] (3) Prepare polyimide composite aerogel

[0014] The polyamic acid-polysiloxane composite sol is subjected to static defoaming, freezing, freeze-drying, and thermal imidization to obtain a polyimide composite aerogel.

[0015] In one embodiment of the present invention, in step (1), the diamine is one or more of 3,5-diaminobenzoic acid, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and p-phenylenediamine; the dianhydride is one or more of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-diphenylethertetracarboxylic dianhydride, pyromellitic dianhydride, and biphenyltetracarboxylic dianhydride; the amino-terminated polysiloxane is bis(aminopropyl)terminated polydimethylsiloxane with a molecular weight of 1000 - 30000.

[0016] In one embodiment of the present invention, in step (1), the polar solvent is one or more of N,N-dimethylacetamide, N-methylpyrrolidone, and dimethylformamide.

[0017] In one embodiment of the present invention, in step (1), the molar ratio of dianhydride to diamine is 1.01 - 1.04:1; the molar ratio of amino-terminated polysiloxane to dianhydride is 0.5 - 1:1.

[0018] In one embodiment of the present invention, in step (1), the amino-terminated polysiloxane is bis(aminopropyl)terminated polydimethylsiloxane, which has amino groups at both ends of its molecular chain and undergoes a polymerization reaction with the anhydride at the end of the polyamic acid molecular chain to form an amide bond, and is converted into an imide bond after imidization.

[0019] In one embodiment of the present invention, in step (1), the conditions for the polycondensation reaction are: reacting at -5 - 25°C for 4 - 24 h; the conditions for the block copolymerization reaction are: reacting at -5 - 25°C for 4 - 24 h.

[0020] In one embodiment of the present invention, in step (1), the mass of the synthesized polyimide-polysiloxane copolymer accounts for 10 - 20% of the total mass of the solution.

[0021] In one embodiment of the present invention, in step (1), the solvents used for precipitation are one or more of water, acetone, and tetrahydrofuran, and the temperature is -5 - 25°C.

[0022] In one embodiment of the present invention, in step (1), drying is carried out by freeze-drying or vacuum drying. The temperature for vacuum drying is 30 - 50°C, and the time is 24 - 48 h.

[0023] In one embodiment of the present invention, in step (2), the ceramic filler is one or more of feldspar, mica, montmorillonite, aluminosilicate, alumina, zirconia, magnesia, silica, silicon carbide; the flux is one or more of ammonium polyphosphate, zinc borate, low melting point glass powder.

[0024] In one embodiment of the present invention, in step (2), the melting point of the low melting point glass powder is 350 - 900 °C. In one embodiment of the present invention, in step (2), the dosage of triethylamine is 5 - 95% of the molar number of the carboxyl group of polyamic acid; the dosage of the ceramic filler is 15 - 45% of the solid mass in the composite sol; the dosage of the flux is 15 - 45% of the solid mass in the composite sol.

[0025] In one embodiment of the present invention, in step (2), the mass ratio of the ceramic filler to the flux is 0.5 - 1.5:1.

[0026] In one embodiment of the present invention, in step (2), the mixing method is stirring at 25 - 35 °C for 6 - 12 h.

[0027] In one embodiment of the present invention, in step (2), the solid content of the composite sol is 50 - 150 mg / mL.

[0028] In one embodiment of the present invention, in step (3), the freezing temperature is -196 - -30 °C, and the freezing method is isotropic and anisotropic, including unidirectional freezing and bidirectional freezing; the freeze-drying conditions are: at a temperature of -30 - -50 °C and a pressure of 5 - 25 Pa, freeze-drying for 24 - 72 h.

[0029] In one embodiment of the present invention, in step (3), the thermal imidization conditions are: under an inert atmosphere, heat treatment at 220 - 350 °C for 1 - 3 h; the inert atmosphere is one or more of nitrogen and argon.

[0030] The second object of the present invention is to provide a shape memory polyimide composite aerogel for a self-deployable thermal protection system prepared by the above preparation method.

[0031] The third object of the present invention is to provide an application of the above shape memory polyimide composite aerogel, which is used as a thermal protection material in the thermal protection system of deep space exploration spacecrafts and hypersonic aircrafts.

[0032] The beneficial technical effects of the present invention are as follows:

[0033] The polymer matrix material used in the preparation of the composite aerogel in the present invention is a polyamic acid-polysiloxane copolymer. A polyamic acid-polysiloxane copolymer with a specific ratio of soft and hard segments is obtained by block copolymerization of polyamic acid and polysiloxane. The polyimide and polysiloxane in the chain segments are distributed as soft and hard chain segments. The shape memory behavior of the material can be regulated by adjusting the ratio of the soft and hard chain segments, thereby endowing the aerogel with excellent and controllable shape memory ability.

[0034] In the present invention, ceramic fillers, fluxes and polyamic acid-polysiloxane are mixed to obtain a polyamic acid-polysiloxane composite sol. After freezing, freeze-drying and thermal imidization, a shape memory polyimide composite aerogel product with high strength, high storage modulus, high shape recovery rate and high thermal protection performance is obtained. In the composite aerogel, the ceramic fillers and fluxes can form a cross-linked structure by acting on the molecular chains through hydrogen bonds and van der Waals forces, effectively improving the storage modulus of the shape memory aerogel, and enhancing the strength of the polyamic acid skeleton, thereby improving the mechanical properties of the composite aerogel and effectively suppressing shrinkage during freeze-drying and thermal imidization. At the same time, in the composite aerogel, the ceramic fillers and fluxes can be melted and adhered under high-temperature heat flow to generate a high-temperature resistant ceramic structure through eutectic reaction, which can effectively improve the mechanical properties at high temperatures, resist the mechanical action of heat flow impact, and the decomposition temperature of the high-temperature resistant ceramic is extremely high, which can effectively resist the ablation action of heat flow. At the same time, due to the significant increase in surface emissivity, the high-temperature heat insulation performance of the composite aerogel can be effectively improved.

[0035] The composite aerogel thermal protection material prepared in the present invention does not need to be guided by a deployable mechanical structure. Instead, when the ambient temperature reaches the glass transition temperature (305 °C) of the material and above, it realizes automatic shape memory expansion through thermal response. And after expansion, as the heat flow continues to increase and the surface temperature reaches 800 °C and above, the fluxes on the surface melt, and adhere the residual carbon and silica generated by the thermal decomposition of the polyimide-polysiloxane matrix and the ceramic fillers dispersed in the matrix, forming a high-temperature resistant ceramic structure on the surface of the material, which can effectively improve the ablation resistance and mechanical properties of the material. And due to the formation of the ceramic layer and the existence of residual carbon, the infrared emissivity of the material is increased, which can effectively resist the energy transfer of thermal radiation, improve the high-temperature heat insulation performance of the composite aerogel material, and has excellent thermal protection ability. Description of the Drawings

[0036] Figure 1 For the thermal protection performance of the polyimide composite aerogel in Example 2;

[0037] Figure 2 For the high-temperature shape recovery process of the polyimide composite aerogel in Example 2. Detailed Description of the Invention

[0038] The present invention will be specifically described below in conjunction with the accompanying drawings and embodiments.

[0039] Experimental materials:

[0040] 3,5-diaminobenzoic acid, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, p-phenylenediamine, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-diphenylethertetracarboxylic dianhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride and other diamines and dianhydrides were all provided by Sinopharm Chemical Reagent Co., Ltd.; amino-terminated polydimethylsiloxane with a molecular weight of 1000-30000 was provided by Shanghai Merck Chemical Technology Co., Ltd.; ceramic fillers were provided by Suzhou Great Pharmaceutical Technology Co., Ltd.; fluxes were provided by Sinopharm Chemical Reagent Co., Ltd.; solvents such as N,N-dimethylacetamide, N-methylpyrrolidone, dimethylformamide, acetone, and tetrahydrofuran were provided by Shanghai Titan Scientific Co., Ltd.; water was prepared by a MILLI-Q type ultrapure water instrument.

[0041] Testing methods:

[0042] Density: By the weighing method, the density of the composite aerogel is the ratio of the measured mass to the volume. ρ = m / V, where ρ is the density, m is the mass, and V is the volume.

[0043] Shape recovery rate: The shape recovery rate is calculated by measuring the shape recovery angle. R r =(θ f -θ0) / θ f , where R r is the shape recovery rate, θ f is the shape fixation angle, and θ0 is the angle after shape recovery.

[0044] Thermal insulation performance: Measured by a TPS2500s type thermal constant analyzer.

[0045] Mechanical properties: After being treated at 1000 °C for 30 min, the compression performance was measured by an MTS E44.304 type microcomputer-controlled electronic universal testing machine.

[0046] Example 1

[0047] A preparation method of a shape memory polyimide composite aerogel for a self-expandable thermal protection system includes the following steps:

[0048] (1) Preparation of polyamic acid-polysiloxane

[0049] Under nitrogen protection, in a three-necked round-bottom flask, 4,4-diaminodiphenyl ether (4.0048 g) and N,N-dimethylacetamide (80 mL) were added. After mechanical stirring until 4,4-diaminodiphenyl ether was completely dissolved, then pyromellitic dianhydride (5.9727 g) was added. The reaction was carried out at 0 °C for 6 h to obtain a polyamic acid solution. Then, a diamino-terminated polydimethylsiloxane with a molecular weight of 10,000 (10 g) was added, and the reaction was carried out at room temperature for 6 h to obtain a polyamic acid-polysiloxane copolymer solution. The polyamic acid-polysiloxane copolymer solution was precipitated into deionized water at 0 °C and freeze-dried to obtain a polyamic acid-polysiloxane copolymer powder.

[0050] (2) Preparation of polyamic acid-polysiloxane composite sol

[0051] The polyamic acid-polysiloxane copolymer powder (1 g) obtained in step (1) and triethylamine (0.24 g) were dissolved in deionized water (28.5 g). After stirring at 25 °C for 12 h and complete dissolution, mica (0.25 g), ammonium polyphosphate (0.125 g), and zinc borate (0.125 g) were added, and stirred for 2 h to obtain a polyamic acid-polysiloxane composite sol with a total solid content of 5% and a mass ratio of ceramic filler to flux of 1:1, denoted as PAASiC-5 1-1 .

[0052] (3) Preparation of polyimide composite aerogel

[0053] The polyamic acid-polysiloxane composite sol prepared in step (2) was allowed to stand to remove bubbles, placed at -196 °C for 1 h, and then placed in a freeze dryer for drying for 48 h. After the ice crystals sublimated, an isotropic porous polyamic acid aerogel was obtained. The polyamic acid aerogel was placed in a nitrogen atmosphere at 300 °C for thermal imidization for 2 h to obtain a polyimide composite aerogel with a specific structure, denoted as PISiC-5 1-1 .

[0054] Example 2

[0055] Referring to Example 1, the difference from Example 1 was that the addition amounts of the ceramic filler and the flux were adjusted to make the solid content of the composite sol 10%, that is, mica (1.08 g), ammonium polyphosphate (0.54 g), and zinc borate (0.54 g) were added. The obtained polyamic acid composite sol was denoted as PAASiC-10 1-1 , and the polyimide composite aerogel was denoted as PISiC-10 1-1 .

[0056] Example 3

[0057] Referring to Example 1, different from Example 1, the addition amounts of the ceramic filler and the flux were adjusted so that the solid content of the composite sol was 15%, that is, mica (2.166 g), ammonium polyphosphate (1.083 g), and zinc borate (1.083 g) were added, and the obtained polyamic acid composite sol was denoted as PAASiC-15 1-1 , and the polyimide composite aerogel was denoted as PISiC-15 1-1 .

[0058] Comparative Example 1

[0059] Referring to Example 1, different from Example 1, when polymerizing, bis(3-aminopropyl) terminated polydimethylsiloxane was not added, so that the matrix of the composite sol was pure polyamic acid, and the obtained polyamic acid composite sol was denoted as PAAC-5 1-1 , and the polyimide composite aerogel was denoted as PIC-5 1-1 .

[0060] Comparative Example 2

[0061] Referring to Example 1, different from Example 1, when preparing the composite sol, the ceramic filler and the flux were not added, so that the sol was a polyamic acid-polysiloxane block copolymer sol, and the obtained polyamic acid sol was denoted as PAASi-5, and the polyimide aerogel was denoted as PISi-5.

[0062] Comparative Example 3

[0063] Referring to Example 1, different from Example 1, when preparing the composite sol, while keeping the solid content unchanged, the ratio of the ceramic filler to the flux filler was changed to 1:4, that is, mica (0.1 g), ammonium polyphosphate (0.2 g), and zinc borate (0.2 g) were added, so that the sol was a polyamic acid-polysiloxane block copolymer sol, and the obtained polyamic acid sol was denoted as PAASiC-5 1-4 , and the polyimide aerogel was denoted as PISiC-5 1-4 .

[0064] Comparative Example 4

[0065] Referring to Example 1, different from Example 1, when preparing the composite sol, while keeping the solid content unchanged, the ratio of the ceramic filler to the flux filler was changed to 4:1, that is, mica (0.4 g), ammonium polyphosphate (0.05 g), and zinc borate (0.05 g) were added, so that the sol was a polyamic acid-polysiloxane block copolymer sol, and the obtained polyamic acid sol was denoted as PAASiC-5 4-1 , and the polyimide aerogel was denoted as PISiC-5 4-1 .

[0066] The performance of the aerogels prepared in the examples and comparative examples was tested, and the results are shown in Table 1.

[0067] Table 1

[0068]

[0069] As can be seen from the figure or Table 1, the solid content is correlated with the density of the composite aerogel, and the greater the solid content, the greater the density. The block copolymerization of polysiloxane and polyimide endows the copolymer with excellent shape memory performance. However, with the increase in the content of ceramic filler and flux, the shape recovery rate of the composite aerogel gradually decreases. PIC-5 1-1 Since polysiloxane did not participate in the block copolymerization of polyimide, its shape recovery rate was only 72%, showing a weak shape memory ability. With the increase in the content of ceramic filler and flux, the thermal conductivity of the composite aerogel gradually increases. However, due to PISi-5 1-1 without adding filler, the shrinkage rate of the composite aerogel is relatively large, resulting in relatively poor heat insulation performance. The ceramic filler can effectively increase the high-temperature mechanical properties of the composite aerogel due to the formation of a ceramic structure at high temperatures. With the increase in the content of ceramic filler and flux, the high-temperature mechanical properties of the composite aerogel gradually increase. PISi-5, due to the lack of composite of ceramic filler and flux, completely decomposes at 1000 °C and does not have mechanical properties. From PISiC-5 1-4 and PISiC-5 4-1 's high-temperature mechanical properties, it can be seen that there is a synergistic effect between the ceramic filler and the flux. A reasonable proportion design has an important impact on the thermal protection performance of the composite aerogel. Too much or too little relative content of the ceramic filler or the flux will seriously affect the occurrence of the ceramization transformation, thereby deteriorating the high-temperature mechanical properties of the composite aerogel.

[0070] The embodiments provided above are not intended to limit the scope covered by the present invention, nor are the described steps intended to limit their execution order. Obvious improvements made by those skilled in the art in combination with the existing common general knowledge also fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a shape memory polyimide composite aerogel for a self-deployable thermal protection system, characterized in that: The preparation method comprises the following steps: (1) Preparation of polyamic acid-polysiloxane The diamine is dissolved in a polar solvent, and then a dibasic acid anhydride is added to carry out a polycondensation reaction to obtain a polyamic acid solution, and then an amino-terminated polysiloxane is added to carry out a block copolymerization reaction to obtain a polyamic acid-polysiloxane solution, which is then precipitated and dried to obtain a polyamic acid-polysiloxane powder; (2) Preparation of polyamic acid-polysiloxane composite sol The polyamic acid-polysiloxane powder is dissolved in deionized water, and then triethylamine, ceramic filler and flux are added and mixed to obtain a polyamic acid-polysiloxane composite sol; (3) Preparation of polyimide composite aerogel The polyamic acid-polysiloxane composite sol is subjected to standing degassing, freezing, freeze drying and thermal imidization to obtain a polyimide composite aerogel.

2. The preparation method according to claim 1, characterized in that: In step (1), the diamine is one or more of 3,5-diaminobenzoic acid, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 4,4-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and p-phenylenediamine; the dibasic acid anhydride is one or more of 4,4'-(hexafluoroisopropylene)diphthalic anhydride, 3,3',4,4'-dibenzophenone tetracarboxylic anhydride, 2,3,3',4'-diphenyl ether tetracarboxylic anhydride, pyromellitic anhydride, and biphenyltetracarboxylic anhydride; and the amino-terminated polysiloxane is bisaminopropyl-terminated polydimethylsiloxane having a molecular weight of 1000 to 30000.

3. The preparation method according to claim 1, characterized in that: In step (1), the polar solvent is one or more of N,N-dimethylacetamide, N-methylpyrrolidone, and dimethylformamide.

4. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of the dibasic acid anhydride to the diamine is 1.01-1.04:1; and the molar ratio of the amino-terminated polysiloxane to the polyamic acid terminal anhydride is 0.5-1:

1.

5. The preparation method according to claim 1, characterized in that: In step (1), the conditions for the polycondensation reaction are: -5 to 25°C for 4 to 24 hours; the conditions for the block copolymerization reaction are: -5 to 25°C for 4 to 24 hours.

6. The preparation method according to claim 1, characterized in that: In step (2), the ceramic filler is one or more of feldspar, mica, montmorillonite, aluminosilicate, alumina, zirconia, magnesium oxide, silicon dioxide, and silicon carbide; and the flux is one or more of ammonium polyphosphate, zinc borate, and glass powder with a melting point of 350 to 900°C.

7. The preparation method according to claim 1, characterized in that: In step (2), the amount of triethylamine is 5 to 95% of the molar number of carboxyl groups of the polyamic acid; the amount of ceramic filler is 15 to 45% of the solid mass in the composite sol; the amount of flux is 15 to 45% of the solid mass in the composite sol; and the mass ratio of ceramic filler to flux is 0.5 to 1.5:

1.

8. The preparation method according to claim 1, characterized in that: In step (3), the freezing temperature is -196 to -30°C, and the freezing methods are one-way freezing and two-way freezing; the freeze-drying conditions are: temperature of -30 to -50°C, pressure of 5 to 25 Pa, and freeze-drying for 24 to 72 hours.

9. The preparation method according to claim 1, characterized in that: In step (3), the thermal imidization conditions are: heat treatment at 220-350° C. for 1-3 h under an inert atmosphere; the inert atmosphere is one or more of nitrogen and argon.

10. A shape memory polyimide composite aerogel material for a self-deployable thermal protection system obtained by the preparation method according to any one of claims 1 to 9.

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