Polyimide aerogel foam composite material and its preparation method

Abstract

This application relates to the field of new materials, and in particular to a polyimide aerogel foam composite material and its preparation method. The preparation method involves mixing polyimide precursor powder and silica aerogel precursor solution under high-speed shearing to form a paste, followed by one-step foaming and solvent replacement in a high-temperature supercritical environment to obtain the composite material. This method locks the nanoporous three-dimensional network structure of the aerogel within the polyimide pores, protecting structural stability and solving the problems of powder shedding and poor strength in traditional aerogel composite materials. Furthermore, the foaming of the paste is more uniform and the foam structure is finer than direct foaming of the powder. This application efficiently integrates the advantages of polyimide foam and silica aerogel, resulting in a lightweight, heat-insulating, and high-temperature-resistant composite material with broad development prospects.

Description

Technical Field

[0001] This application relates to the field of new materials technology, and in particular to a polyimide aerogel foam composite material and its preparation method. Background Technology

[0002] Polyimide foam is a material that introduces a microporous structure into a polymer matrix. Thanks to the excellent properties of polyimide resin itself, this foam material has the characteristics of high temperature resistance, solvent corrosion resistance, sound absorption and noise reduction, and low temperature resistance. Therefore, it is widely used in cutting-edge fields such as aerospace, national defense and military, and deep-sea exploration.

[0003] Aerogels are nanoscale porous solid materials whose unique nanoporous three-dimensional network structure makes them excellent thermal insulation materials. They possess extremely low density, superior thermal insulation performance, and excellent high-temperature resistance. In particular, silica aerogels, due to their better balance between performance and cost, are widely used in various high-end industries. However, every material has its inherent drawbacks. Polyimide foam, whose main component is a polymer material, experiences a significant performance degradation at temperatures above 400°C, limiting its effectiveness. Aerogels themselves are in dry powder form and cannot be molded and used alone; they must rely on carriers such as fibers, felts, resins, or coatings to form a stable material morphology. However, the introduction of carriers often disrupts the three-dimensional structure of aerogels, leading to problems such as powder shedding and detachment during use.

[0004] To address this, researchers have attempted to encapsulate aerogel within the cellular structure of polymer foams to fully utilize their thermal insulation properties. For example, patent publication CN109666286A adds silica aerogel to polyurethane to create polyurethane insulation cotton; publication CN111320842A adds silica aerogel to epoxy resin before foaming. However, the temperature resistance of matrices such as polyurethane and epoxy resin is inherently low, making the selection of polyimide foam, which offers superior performance, as the matrix of significant importance.

[0005] Currently, the process of introducing aerogel into polyimide foam still has significant shortcomings. The patent published in CN112358649B, which involves impregnating polyimide foam pores with aerogel wet gel followed by drying, offers some improvement over simple physical composites, but the resulting composite material still has a minimum density of 25 kg / m³. 3 This process is insufficient to meet the demands of applications requiring higher lightweighting. Furthermore, it suffers from long processing times and high energy consumption, and even after supercritical drying, aerogel particles still detach during use. More importantly, the composite material has a thermal conductivity of only 0.033 W / (m·K), indicating limited improvement in its thermal insulation performance. Summary of the Invention

[0006] Therefore, the purpose of this application is to overcome the shortcomings of the prior art and provide a polyimide aerogel foam composite material and its preparation method, so as to overcome the problems of heavy weight and limited thermal insulation performance of polyimide aerogel foam materials in the prior art. The preparation method of polyimide aerogel foam composite material provided in this application can prepare polyimide aerogel foam composite material with low density and good thermal insulation performance, and the preparation process is simple.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] First, this application provides a method for preparing a polyimide aerogel foam composite material, comprising the following steps:

[0009] S1. An aromatic dianhydride is esterified with a hydroxyl compound containing active hydrogen, an aromatic diamine is added, and a polycondensation reaction is carried out to obtain a polyimide precursor. Then, the precursor is ground to obtain a polyimide precursor powder.

[0010] S2. Mix silicate, C1~C4 alcohol and water, adjust the pH value to 1~3 with the first pH adjuster, stir the reaction to obtain aerogel precursor solution;

[0011] S3. The aerogel precursor solution is mixed with the polyimide precursor powder, the pH value is adjusted to 7-8 with a second pH adjuster, and then the mixture is sheared at high speed to form a paste to obtain a paste sol.

[0012] S4. Add surfactant, foaming nucleating agent and reinforcing fiber to the paste sol, mix evenly, and then let it stand to react, completing the transformation from sol to gel, and obtain wet gel;

[0013] S5. The wet gel is foamed and dried in a supercritical environment, and then cured at high temperature to obtain a polyimide aerogel foam composite material.

[0014] Preferably, in step S3, the high-speed shearing rotation speed is 5000~8000 r / min, and the time is 30~60 min.

[0015] Preferably, the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, and benzophenone tetracarboxylic dianhydride.

[0016] Preferably, the aromatic dianhydride is selected from one or more of pyromellitic dianhydride (PMDA), 3,3,4,4,-biphenyltetracarboxylic dianhydride (BPDA), 3,3,4,4,-diphenyl ether tetracarboxylic dianhydride (ODPA), and 3,3,4,4,-benzophenone tetracarboxylic dianhydride (BTDA).

[0017] Preferably, the aromatic diamine is selected from one or more of m-phenylenediamine, p-phenylenediamine, diaminodiphenyl ether, diaminodiphenylmethane, diaminodiphenol, and diaminodibenzophenone.

[0018] Preferably, the hydroxyl compound containing active hydrogen is selected from ethanol or methanol.

[0019] Preferably, in step S1, the mass ratio of the aromatic dianhydride, the hydroxyl compound containing active hydrogen, and the aromatic diamine is 100:20~30:35~69.

[0020] Preferably, in step S3, the mass ratio of the aerogel precursor solution to the polyimide precursor powder is 1:0.5~2.5.

[0021] Preferably, the silicate ester is selected from tetraethyl orthosilicate or methyl orthosilicate.

[0022] Preferably, the C1-C4 alcohol is ethanol.

[0023] Preferably, the mass ratio of the silicate ester, the C1-C4 alcohol, and water is 1:4-6:8-11.

[0024] Preferably, in step S1, the esterification reaction and the polycondensation reaction are carried out in a polar organic solvent; the polar organic solvent is selected from one or more of N,N,-dimethylformamide, N,N,-dimethylacetamide, tetrahydrofuran, N-methyl-2-pyrrolidone and dimethyl sulfoxide.

[0025] Preferably, in step S1, after the polycondensation reaction is completed, the solvent is removed by distillation to obtain polyimide precursor powder.

[0026] Preferably, the particle size of the polyimide precursor powder is 50~150μm.

[0027] Preferably, in step S1, the esterification reaction is carried out at a temperature of 45-60°C for 2-3 hours.

[0028] Preferably, in step S1, the temperature of the polycondensation reaction is 45~60℃ and the time is 3~4h.

[0029] Preferably, in step S2, the stirring rate of the stirring reaction is 300~1000 r / min, and the reaction time is 50~90 min.

[0030] Preferably, the first pH adjuster is selected from dilute hydrochloric acid solution; the second pH adjuster is selected from dilute ammonia solution.

[0031] Preferably, the first pH adjuster is a dilute hydrochloric acid solution with a concentration of 0.2 mol / L; the second pH adjuster is a dilute ammonia solution with a concentration of 0.1 mol / L.

[0032] Preferably, the surfactant is selected from one or more of sodium dodecyl sulfate, Tween 20, and sodium dodecylbenzene sulfonate.

[0033] Preferably, the foaming nucleating agent is selected from one or more of nano-clay, nano-calcium carbonate, and nano-diatomaceous earth.

[0034] Preferably, the particle size of the foaming nucleating agent is 100~500nm.

[0035] Preferably, the reinforcing fiber is selected from one or more of chopped glass fiber or chopped carbon fiber.

[0036] Preferably, the reinforcing fiber is a short-cut fiber with a fiber length of 3~12mm.

[0037] Preferably, in step S4, the mass ratio of the paste sol, surfactant, foaming nucleating agent, and reinforcing fiber is 300~450:2~3:1:2~3.

[0038] Preferably, in step S5, carbon dioxide is used as the supercritical fluid in the supercritical environment.

[0039] Preferably, the foaming and drying conditions include: first, maintaining the temperature and pressure at 140~150℃ and 7~8Mpa for 1~2 hours; then, maintaining the temperature and pressure at 170~180℃ and 8~10Mpa for 2~5 hours.

[0040] Preferably, the high-temperature curing treatment is performed at a temperature of 220~250℃ for 3~6 hours.

[0041] Based on a general inventive concept, this application also provides a polyimide aerogel foam composite material obtained according to the above preparation method.

[0042] Preferably, the density of the polyimide aerogel foam composite material is 5~8 kg / m³. 3 .

[0043] Preferably, the thermal conductivity of the polyimide aerogel foam composite material is 0.023~0.028 W / m·K.

[0044] Preferably, the limiting oxygen index of the polyimide aerogel foam composite material is 44%~47%.

[0045] Preferably, the 5% thermal weight loss temperature of the polyimide aerogel foam composite material is 420~432℃.

[0046] Compared with the prior art, this application has the following advantages:

[0047] This case utilizes a one-step method to achieve in-situ composite of polyimide foam and silica aerogel. First, polyimide precursor powder and silica aerogel precursor solution are mixed under high-speed shearing to form a paste, resulting in a relatively uniform dispersion of the precursor powder. This method overcomes the defects of direct powder foaming, where uneven powder interstices lead to large and unevenly distributed pores. In a high-temperature supercritical environment, small-molecule gases in the paste are uniformly encapsulated, forming a foam with fine and uniform pores after foaming. Simultaneously, the aerogel precursor gel is uniformly dispersed within the foam and, under the action of supercritical fluid, displaces the solvent, forming a nanoporous three-dimensional network structure. This nanonetwork is locked within the polyimide pores, leveraging the aerogel's extremely low thermal conductivity to significantly improve overall thermal insulation performance. Furthermore, it reduces powder shedding from the composite material. Furthermore, the introduction of silica aerogel as an inorganic phase into the organic polyimide matrix not only improves the temperature and flame resistance of the composite material, but also provides mechanical support for the aerogel with the polyimide foam skeleton, overcoming the defects of low strength and inability to be used independently of pure aerogel, and achieving a synergistic improvement of low density, high thermal insulation and good mechanical properties; this composite material has broad application prospects.

[0048] Furthermore, this application completes foaming, gelation, and solvent replacement in one step within the same supercritical environment, eliminating the need to prepare foam first, then impregnate and dry, thus greatly simplifying the process and reducing energy consumption and costs. Detailed Implementation

[0049] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0050] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit, combined with any other point or individual value, or combined with other lower or upper limits to form an unspecified range.

[0051] Those skilled in the art will understand that the order in which the steps are written in the various embodiments or examples does not imply a strict execution order and does not limit the implementation process in any way. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but sequentially is preferred.

[0052] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized using conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available. The raw material information used in the various embodiments and comparative examples of this application is as follows:

[0053] Nano clay: with a particle size of 100~500nm, and its main component is montmorillonite.

[0054] Nano calcium carbonate: Particle size is 100~500nm.

[0055] Nano-diatomite: Particle size is 100~500nm.

[0056] Short-cut glass fiber: fiber length is 3~12mm.

[0057] Short-cut carbon fiber: fiber length is 3~12mm.

[0058] Example 1

[0059] (1) Preparation of polyimide precursor powder: 500 parts by weight of N,N,-dimethylacetamide was heated to 50°C, and then 200 parts by weight of 3,3,4,4,-benzophenone tetracarboxylic dianhydride (BTDA) and 50 parts by weight of ethanol were added to carry out esterification reaction for 3 h; then 135 parts by weight of 4,4-diaminodiphenyl ether was added and reacted for 4 h to obtain a homogeneous solution of polyimide precursor; the solvent was removed by distillation, vacuum dried, and then ground and screened to obtain polyimide precursor powder with a particle size of 50~150 μm.

[0060] (2) Preparation of aerogel precursor solution: Tetraethyl orthosilicate (at a weight ratio of tetraethyl orthosilicate:water:ethanol of 1:5:8) was added to an aqueous solution of ethanol, and the pH of the solution was adjusted to 1.5 with 0.2 mol / L dilute hydrochloric acid. The solution was stirred and dispersed for 60 min at a rate of 300 r / min to form an aerogel precursor solution.

[0061] (3) Preparation of paste gel: 100 parts by weight of polyimide precursor powder were added to 200 parts by weight of aerogel precursor solution. Then, the pH of the solution was adjusted to 7 with 0.1 mol / L dilute ammonia water. The solution was sheared at high speed for 30 min at 5000 r / min to form a paste sol.

[0062] (4) Dispersion of additives and wet gel: Add 2 parts by weight of sodium dodecyl sulfate, 1 part by weight of nano clay and 3 parts by weight of chopped glass fiber to the above paste sol. After stirring and dispersing at 6000 r / min for 10 min, let it stand in the mold for 1 h to complete the transformation from sol to gel and form wet gel.

[0063] (5) Foaming and supercritical drying: The mold containing the wet gel was placed in a supercritical reactor for gradient heating foaming and gradient supercritical drying: First, the temperature was increased to 140℃ at a rate of 5℃ / min, the pressure in the reactor was controlled at 7MPa, and the temperature and pressure were maintained for 2h; then, the temperature was increased to 180℃ at a rate of 5℃ / min, the pressure in the reactor was increased to 10MPa, and the temperature and pressure were maintained for 4h. During the heating, the polyimide precursor began to lose small molecules and form imide rings. At the same time, the melt strength increased, and bubbles were formed under the action of the surfactant sodium dodecyl sulfate. Meanwhile, the wet gel in the bubble wall also lost solution and became a nanoporous three-dimensional network structure, thus obtaining polyimide aerogel foam.

[0064] (6) Post-curing treatment: The obtained polyimide aerogel foam is cured at 240℃ for 5h to obtain polyimide aerogel composite material.

[0065] Example 2

[0066] (1) Preparation of polyimide precursor powder: 500 parts by weight of N,N,-dimethylacetamide was heated to 45°C, and then 200 parts by weight of 3,3,4,4,-diphenyl ether tetracarboxylic dianhydride (ODPA) and 60 parts by weight of ethanol were added to carry out esterification reaction for 3 h; then 70 parts by weight of p-phenylenediamine were added and reacted for 3 h to obtain a homogeneous solution of polyimide precursor; the solvent was then removed by distillation, vacuum dried, and then ground and screened to obtain polyimide precursor powder with a particle size of 50~150 μm.

[0067] (2) Preparation of aerogel precursor solution: Tetraethyl orthosilicate (at a weight ratio of tetraethyl orthosilicate:water:ethanol of 1:4:9) was added to the ethanol solution, and the pH of the solution was adjusted to 2 with 0.2mol / L dilute hydrochloric acid. The solution was stirred and dispersed for 50min at a rate of 500r / min to form an aerogel precursor solution.

[0068] (3) Preparation of paste gel: Add 150 parts by weight of polyimide precursor powder to 200 parts by weight of aerogel precursor solution, and then control the pH of the mixed solution to 7 with 0.1 mol / L dilute ammonia water; shear at high speed for 40 min at 5000 r / min to form paste sol.

[0069] (4) Dispersion of additives and wet gel: Add 2 parts by weight of Tween 20, 1 part by weight of nano calcium carbonate and 3 parts by weight of short carbon fiber to the above paste sol. Stir and disperse at 500 r / min for 10 min, and then let stand in the mold for 2 h to complete the transformation from sol to gel and form wet gel.

[0070] (5) Foaming and supercritical drying: The mold containing the wet gel was placed in a supercritical reactor for gradient heating foaming and gradient supercritical drying: First, the temperature was increased to 150°C at a rate of 5°C / min, the pressure in the reactor was controlled at 7 MPa, and the temperature and pressure were maintained for 2 hours; then, the temperature was increased to 180°C at a rate of 5°C / min, the pressure in the reactor was increased to 9 MPa, and the temperature and pressure were maintained for 4 hours. During the heating, the polyimide precursor began to lose small molecules and form imide rings. At the same time, the melt strength increased, and bubbles were formed under the action of surfactants. Meanwhile, the wet gel in the bubble wall also lost solution and became a nanoporous three-dimensional network structure, thus obtaining polyimide aerogel foam.

[0071] (6) Post-curing treatment: The obtained polyimide aerogel foam is kept at 250°C for 3 hours to obtain polyimide aerogel composite material.

[0072] Example 3

[0073] (1) Preparation of polyimide precursor powder: 500 parts by weight of N,N,-dimethylacetamide was heated to 60°C, and 200 parts by weight of 3,3,4,4,-biphenyltetracarboxylic dianhydride (BPDA) and 40 parts by weight of ethanol were added for esterification reaction for 3 h; then 138 parts by weight of 4,4-diaminodiphenyl ether were added and reacted for 3 h to obtain a homogeneous solution of polyimide precursor. The solvent was removed by distillation, and the solution was dried under vacuum. Then it was ground and screened to obtain polyester ammonium salt precursor powder with a particle size of 50~150 μm.

[0074] (2) Preparation of aerogel precursor solution: Tetraethyl orthosilicate (at a weight ratio of tetraethyl orthosilicate:water:ethanol of 1:6:11) was added to the ethanol solution, and the pH of the solution was adjusted to 2 with 0.2mol / L dilute hydrochloric acid. The solution was stirred and dispersed for 60min at a rate of 400r / min to form an aerogel precursor solution.

[0075] (3) Preparation of paste-like gel: 250 parts by weight of polyimide precursor powder were added to 200 parts by weight of aerogel precursor solution. Then, the pH of the mixed solution was adjusted to 8 with 0.1 mol / L dilute ammonia water and sheared at high speed for 40 min at 6000 r / min to form a paste-like sol.

[0076] (4) Dispersion of additives and wet gel: Add 3 parts by weight of sodium dodecylbenzenesulfonate, 1 part by weight of nano diatomaceous earth and 2 parts by weight of short carbon fiber to the above paste sol. Stir and disperse evenly for 5 minutes at 500 r / min, and then let stand in the mold for 2 hours to complete the transformation from sol to gel and form wet gel.

[0077] (5) Foaming and supercritical drying: The mold containing the wet gel was placed in a supercritical reactor for gradient heating foaming and gradient supercritical drying: First, the temperature was increased to 150°C at a rate of 5°C / min, the pressure in the reactor was controlled at 8 MPa, and the temperature and pressure were maintained for 2 hours; then, the temperature was increased to 175°C at a rate of 5°C / min, the pressure in the reactor was increased to 10 MPa, and the temperature and pressure were maintained for 5 hours. During the heating, the polyimide precursor began to lose small molecules and form imide rings. At the same time, the melt strength increased, and bubbles were formed under the action of surfactants. Meanwhile, the wet gel in the bubble wall also lost solution and became a nanoporous three-dimensional network structure, thus obtaining polyimide aerogel foam.

[0078] (6) Post-curing treatment: The obtained polyimide aerogel foam is kept at a high temperature of 240°C for 4 hours to obtain polyimide aerogel composite material.

[0079] Performance testing

[0080] Density test: The density of the polyimide foam prepared in the above embodiments and the commercially available polyimide foam were tested according to the method specified in GB / T6343-2009.

[0081] Thermal conductivity test: The thermal conductivity of the polyimide foam prepared in the above embodiments and the commercially available polyimide foam were tested according to the method specified in GB / T10294-2008.

[0082] Thermogravimetric analysis: Thermogravimetric analysis was performed on the polyimide foam prepared in the above embodiments and commercially available polyimide foam to obtain the temperature at which the polyimide foam lost 5% of its weight.

[0083] Oxygen Limiting Index: The oxygen limiting index of the polyimide foam prepared in the above embodiments and commercially available polyimide foam were tested according to the method specified in GB / T2406.2-2009.

[0084] The performance test results of each polyimide foam are shown in Table 1:

[0085] Table 1 Performance Measurement of Various Polyimide Foams

[0086] performance Example 1 Example 2 Example 3 A commercially available PI foam <![CDATA[Density (kg / m 3 )]]> 5 7 8 10 Thermal conductivity (w / m·k) 0.028 0.025 0.023 0.043 5% thermogravimetric temperature (°C) 420 425 432 381 Limiting oxygen index (%) 45 44 47 37

[0087] As shown in Table 1, the polyimide aerogel composite material provided in this application has high high-temperature resistance and outstanding thermal insulation performance. It represents a significant performance improvement over existing products on the market and can meet the high-temperature thermal insulation requirements of advanced industries such as aerospace, military, and new energy.

[0088] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method of making a polyimide aerogel foam composite, characterized by, Includes the following steps: S1. An aromatic dianhydride is esterified with a hydroxyl compound containing active hydrogen, an aromatic diamine is added, and a polycondensation reaction is carried out to obtain a polyimide precursor. Then, the precursor is ground to obtain a polyimide precursor powder. S2. Mix silicate, C1~C4 alcohol and water, adjust the pH value to 1~3 with the first pH adjuster, stir the reaction to obtain aerogel precursor solution; S3. The aerogel precursor solution is mixed with the polyimide precursor powder, the pH value is adjusted to 7-8 with a second pH adjuster, and then the mixture is sheared at high speed to form a paste to obtain a paste sol. S4. Add surfactant, foaming nucleating agent and reinforcing fiber to the paste sol, mix evenly, and then let it stand to react, completing the transformation from sol to gel, and obtain wet gel; S5. The wet gel is foamed and dried in a supercritical environment, and then cured at high temperature to obtain a polyimide aerogel foam composite material.

2. The production method according to claim 1, characterized by, In step S3, the high-speed shearing speed is 5000~8000 r / min and the time is 30~60 min.

3. The preparation method according to claim 1, characterized in that, The aromatic dianhydride is selected from one or more of pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, and benzophenone tetracarboxylic dianhydride; The aromatic diamine is selected from one or more of m-phenylenediamine, p-phenylenediamine, diaminodiphenyl ether, diaminodiphenylmethane, diaminodiphenol, and diaminodibenzophenone. The hydroxyl compound containing active hydrogen is selected from ethanol or methanol.

4. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the aromatic dianhydride, the hydroxyl compound containing active hydrogen, and the aromatic diamine is 100:20~30:35~69; In step S3, the mass ratio of the aerogel precursor solution to the polyimide precursor powder is 1:0.5~2.

5.

5. The preparation method according to claim 1, characterized in that, The silicate ester is selected from tetraethyl orthosilicate or methyl orthosilicate; the mass ratio of the silicate ester, the C1~C4 alcohol and water is 1:4~6:8~11.

6. The preparation method according to claim 1, characterized in that, In step S1, the esterification reaction and the polycondensation reaction are carried out in a polar organic solvent; the polar organic solvent is selected from one or more of N,N,-dimethylformamide, N,N,-dimethylacetamide, tetrahydrofuran, N-methyl-2-pyrrolidone and dimethyl sulfoxide; In step S1, the esterification reaction is carried out at a temperature of 45-60°C for 2-3 hours. In step S1, the polycondensation reaction is carried out at a temperature of 45-60°C for 3-4 hours. In step S2, the stirring rate of the stirring reaction is 300~1000 r / min, and the reaction time is 50~90 min.

7. The preparation method according to claim 1, characterized in that, The first pH adjuster is selected from dilute hydrochloric acid solution; the second pH adjuster is selected from dilute ammonia solution.

8. The preparation method according to claim 1, characterized in that, The surfactant is selected from one or more of sodium dodecyl sulfate, Tween 20 and sodium dodecylbenzene sulfonate; the foaming nucleating agent is selected from one or more of nano clay, nano calcium carbonate and nano diatomaceous earth; the reinforcing fiber is selected from one or more of chopped glass fiber or chopped carbon fiber.

9. The preparation method according to claim 1, characterized in that, In step S5, carbon dioxide is used as the supercritical fluid in the supercritical environment. The foaming and drying conditions include: first, maintaining the temperature and pressure at 140~150℃ and 7~8Mpa for 1~2 hours; then, maintaining the temperature and pressure at 170~180℃ and 8~10Mpa for 2~5 hours. The curing temperature for the high-temperature treatment is 220~250℃, and the curing time is 3~6h.

10. A polyimide aerogel foam composite material obtained by the preparation method according to any one of claims 1 to 9.