Flexible thermal insulation polyimide aerogel and polyimide composite aerogel with active fire extinguishing function and preparation method thereof

Abstract

The present application relates to a kind of flexible heat-insulating polyimide aerogel and polyimide composite aerogel with active fire extinguishing function and its preparation method, belong to aerogel technical field.Flexible heat-insulating polyimide aerogel is obtained by mixing polyamide acid and amino functionalized SiO2 Nanoparticles PAA / SiO2 Aerogel, PAA / SiO2 Aerogel is subjected to thermal imidization treatment, with good heat insulation performance.Polyimide composite aerogel with active fire extinguishing function is coated with perfluorohexanone microcapsule on the surface of flexible heat-insulating polyimide aerogel, with good heat insulation, fire extinguishing and flame-retardant performance.

Description

Technical Field

[0001] This invention belongs to the field of aerogel technology, specifically relating to a flexible heat-insulating polyimide aerogel and a polyimide composite aerogel with active fire extinguishing function, and the preparation method thereof. Background Technology

[0002] Polyimide (PI) aerogels exhibit unique advantages in the field of thermal insulation and protection due to their excellent thermal stability, ultra-low thermal conductivity, and lightweight properties. However, traditional PI aerogels often face problems such as poor intrinsic flexibility and brittleness in practical applications, and lack the ability to proactively respond to fire risks, making it difficult to meet the stringent requirements of flexibility and functional integration in high-end thermal management scenarios.

[0003] Perfluorohexanone (PFH) is a small-molecule liquid that is prone to leakage and migration, making it unstable and easily lost before reaching the fire trigger temperature. This makes it difficult to meet the requirements of on-demand release and timely response in fire protection. Therefore, microencapsulation technology is necessary to encapsulate PFH within wall materials, fundamentally inhibiting its volatilization at room temperature and reducing loss. This achieves effective storage and controlled release upon thermal triggering, thereby fully leveraging its high-efficiency fire extinguishing performance.

[0004] Currently, heat insulation materials and fire extinguishing materials are used separately, and there is no existing technology that combines heat insulation materials and fire extinguishing materials. Summary of the Invention

[0005] The purpose of this invention is to provide a polyimide composite aerogel with active fire extinguishing function, which has good heat insulation and fire extinguishing effects.

[0006] A second objective of this invention is to provide a flexible, heat-insulating polyimide aerogel.

[0007] The third objective of this invention is to provide a method for preparing a polyimide composite aerogel with active fire extinguishing function.

[0008] The fourth objective of this invention is to provide a method for preparing flexible thermally insulating polyimide aerogel.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing flexible thermal insulation polyimide aerogel includes the following steps: adding polyamic acid to water and simultaneously adding a neutralizing agent, 3-aminopropyltriethoxysilane, to obtain a polyamic acid solution; then adding amino-functionalized SiO2 nanoparticles; mixing evenly and injecting into a mold; freeze-drying to obtain PAA / SiO2 aerogel; and subjecting the PAA / SiO2 aerogel to thermal imidization treatment to obtain PI / SiO2 composite aerogel.

[0010] Furthermore, the mass fractions of the amino-functionalized SiO2 nanoparticles relative to the PAA solid content are 5 wt%, 10 wt%, and 15 wt%, respectively.

[0011] Furthermore, the thermal imidization treatment is performed by holding at 100 ℃, 150 ℃, 200 ℃, 250 ℃ and 300 ℃ for 30-90 min each.

[0012] Further, the preparation method of the polyamic acid includes the following steps: dissolving p-phenylenediamine (1,4-phenylenediamine) in an organic solvent and adding biphenyltetracarboxylic dianhydride in batches to form oligomers, then adding 2,2-bis[4-(4-aminophenoxy)phenyl]propane and reacting at 0°C, and finally obtaining white polyamic acid powder by adding water to precipitate, washing and filtering, freeze drying and grinding.

[0013] Furthermore, the preparation method of the amino-functionalized SiO2 nanoparticles includes the following steps: preparing a SiO2 suspension, slowly adding 3-aminopropyltriethoxysilane to the SiO2 suspension, adjusting the pH to 4-5 and stirring continuously for 6-18 hours, washing and centrifuging after the reaction is completed, collecting the solid product, drying it, and obtaining the amino-functionalized SiO2 nanoparticles.

[0014] The flexible thermal insulation polyimide aerogel is prepared by the aforementioned method for preparing flexible thermal insulation polyimide aerogel.

[0015] The preparation method of polyimide composite aerogel with active fire extinguishing function includes the following steps: preparing sodium alginate solution, adding glycerin, then adding perfluorohexanone microcapsules, stirring to disperse the perfluorohexanone microcapsules evenly, obtaining perfluorohexanone microcapsule coating, and coating it on the surface of the flexible heat-insulating polyimide aerogel.

[0016] Furthermore, the preparation method of the perfluorohexanone microcapsules includes the following steps: adding urea-formaldehyde resin solution to perfluorohexanone emulsion, adjusting the pH to 2.5-3.0, heating to 35-45 ℃ to solidify and form, filtering, washing, and drying to obtain perfluorohexanone microcapsules.

[0017] Furthermore, the perfluorohexanone microcapsules account for 40 wt%, 50 wt%, 60 wt%, 70 wt%, and 80 wt% of the solid content of the sodium alginate solution, respectively.

[0018] The polyimide composite aerogel with active fire extinguishing function is prepared by the method described above.

[0019] The beneficial effects of this invention are: The flexible thermal insulation polyimide aerogel of the present invention introduces flexible diamine and functionalized SiO2 to form a uniform three-dimensional network with oriented pores, chemical cross-linking and physical entanglement synergistic enhancement, and successfully constructs a PI / SiO2 composite aerogel with a double cross-linked network, which has good thermal insulation effect.

[0020] The polyimide composite aerogel with active fire extinguishing function of the present invention has perfluorohexanone microcapsules coated on flexible heat-insulating polyimide aerogel, which has good heat insulation and active fire extinguishing effects. Attached Figure Description

[0021] Figure 1 SEM images of PI / SiO2 composite aerogels with different SiO2 contents are shown below. (a) is the SEM image of PI, (b) is the SEM image of PI / SiO2-5 composite aerogel, (c) is the SEM image of PI / SiO2-10 composite aerogel, (d) is the SEM image of PI / SiO2-15 composite aerogel, and (e) is the SEM image of PI / SiO2-20 composite aerogel. Figure 2 FT-IR images of PI / SiO2 composite aerogels with different SiO2 contents; Figure 3 The thermal insulation properties of aerogels are shown in (a), where (b) is the thermal insulation properties of PI / SiO2-10 aerogel and (c) is the thermal insulation properties of PI / SiO2 aerogels with different NH2-SiO2 contents in a nitrogen atmosphere. Figure 4 The mechanical properties of PI / SiO2-10 aerogel are shown in (a) flexural properties, (b) radial compressive strength, and (c) radial compressive strength. Figure 5 SEM image of perfluorohexanone microcapsules; Figure 6 FT-IR images of perfluorohexanone microcapsules and urea-formaldehyde resin wall materials; Figure 7 To show the thermal insulation performance of PI / SiO2 coated with different PFH microcapsule contents, (a) is the axial thermal conductivity; (b) is the radial thermal conductivity; and (c) is the axial and radial temperature difference at 1 minute and 20 minutes. Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0023] Example 1 The method for preparing flexible thermal insulation PI aerogel in this embodiment includes the following steps: S1: Preparation of functionalized SiO2: 3 g of SiO2 nanoparticles were weighed and dispersed in 30 mL of ethanol to form a uniform SiO2 suspension. Then, 1.5 g of 3-aminopropyltriethoxysilane (3-APTES) was slowly added dropwise to the SiO2 suspension. The pH of the system was adjusted to 4-5 with acetic acid, and the mixture was stirred continuously at room temperature for 12 h. After the reaction was complete, the product was filtered and washed with ethanol, then centrifuged at 8000 rpm for 10 min, repeated 5 times. The resulting solid product was collected and dried in a 60 ℃ oven for 24 h to obtain amino-functionalized SiO2 nanoparticles, denoted as NH2-SiO2.

[0024] S2: Preparation of polyamic acid (PAA): 100 g of anhydrous N-methylpyrrolidone (NMP) was poured into a three-necked flask, followed by the addition of 1.6 g of p-phenylenediamine (1,4-phenylenediamine) (PPDA). The mixture was mechanically stirred under nitrogen protection until completely dissolved, forming a clear and homogeneous solution. Next, 4.45 g of biphenyltetracarboxylic dianhydride (BPDA) was added in batches to the homogeneous solution. The reaction system was placed in an ice-water bath with temperature control, and the mixture was stirred continuously at 0 °C for 5 h to allow BPDA and PPDA to fully react and form oligomers. Subsequently, 6 g of BAPP was added in batches, and the reaction was continued at 0 °C with stirring for 3 h. Finally, 4.38 g of BPDA was added in batches to the reaction system, and the mixture was stirred continuously at 0 °C for 3 h to allow the polymerization reaction to reach completion, ultimately yielding a homogeneous and viscous PAA solution. Deionized water was then slowly added to the PAA solution to induce the precipitation of white crystalline solids. The precipitate was washed, filtered, freeze-dried, and then ground to obtain white PAA powder.

[0025] S3: Preparation of PI / SiO2: PAA powder was slowly added to water under magnetic stirring, while triethylamine was added dropwise as a neutralizing agent to completely dissolve the PAA powder, resulting in a homogeneous PAA solution with a solid content of 2.5 wt%. NH2-SiO2 nanoparticles were then added and thoroughly mixed to obtain a homogeneous PAA / SiO2 composite sol, which was then injected into a mold. Liquid nitrogen was conducted to the bottom of the mold using a copper block, causing the aerogel to be directionally frozen from bottom to top, forming a vertical channel. The frozen sample was then placed in a freeze dryer and dried for 48 h to obtain PAA / SiO2 aerogel. The obtained PAA / SiO2 aerogel was placed in a tube furnace and subjected to thermal imidization treatment at 100 ℃, 150 ℃, 200 ℃, 250 ℃, and 300 ℃ for 60 min each, finally yielding the PI / SiO2 composite aerogel. The mass fraction of NH2-SiO2 relative to the solid content of PAA was 10wt%, and the resulting sample was named PI / SiO2-10.

[0026] The polyimide composite aerogel with active fire extinguishing function in this embodiment includes the following steps: S1: Preparation of urea-formaldehyde resin: 6.5 g of urea was added to a 37% formaldehyde solution, followed by the addition of an equal volume of water. After complete dissolution under continuous stirring, the pH of the system was adjusted to 9.5 with a 5 wt% NaOH solution. The reaction was then carried out at 75 ℃ and 1000 rpm for 1 h to obtain a urea-formaldehyde resin solution.

[0027] S2: Preparation of the PFH emulsion system: Dissolve 2.06 g of sodium dodecylbenzenesulfonate (SDBS) in 100 mL of water, then add perfluorohexanone (PFH) solution to the SDBS deionized water solution. Stir continuously at 1000 rpm for 20 min until a homogeneous and stable emulsion system is formed. Then adjust the pH of the system to neutral to obtain the final product.

[0028] S3: Preparation of microcapsules. In step S1, the urea-formaldehyde resin solution was cooled to room temperature and then diluted with water to control the volume fraction of the wall material at 10%. This diluted solution was then added to the PFH emulsion system in step S5. After adjusting the pH to 2.5-3.0 with acetic acid, the reaction system was heated to 35 °C and reacted for 1 h. The temperature was then further increased to 45 °C and reacted for 4 h to promote further solidification of the shell. After the reaction, the product was separated by filtration and repeatedly washed with water until the system was neutral. Finally, the obtained product was dried to obtain PFH microcapsules. The encapsulation rate of the PFH core material in the microcapsules was 67.35%.

[0029] S4: Preparation of microcapsule coating: Weigh 0.2 g of sodium alginate and dissolve it in 10 mL of deionized water. Stir until completely dissolved to obtain a homogeneous solution with viscosity. Add glycerol to this solution to obtain the sodium alginate system, which is used to regulate the flexibility of subsequent film formation. Then, disperse the prepared PFH microcapsule sample in the sodium alginate system and stir thoroughly until uniformly dispersed. This is ready for subsequent coating operations. The mass fraction of the microcapsules relative to the sodium alginate solution solid content is 70 wt%. The prepared coating is coated on the surface of PI / SiO2-10 aerogel, and the resulting sample is named PI / PFH-70.

[0030] Example 2 The preparation method of flexible thermal insulation PI aerogel in this embodiment is largely the same as that in Example 1, except that the mass fraction of NH2-SiO2 relative to the solid content of PAA is 5 wt%. The resulting sample is named PI / SiO2-5.

[0031] Example 3 The preparation method of flexible thermal insulation PI aerogel in this embodiment is largely the same as that in Example 1, except that the mass fraction of NH2-SiO2 relative to the solid content of PAA is 15 wt%. The resulting sample is named PI / SiO2-15.

[0032] Example 4 The polyimide composite aerogel with active fire extinguishing function in this embodiment is largely the same as that in Example 1, except that the mass fraction of the microcapsules relative to the sodium alginate solution solid content is 40 wt%. The resulting sample is named PI / PFH-40.

[0033] Example 5 The polyimide composite aerogel with active fire extinguishing function in this embodiment is largely the same as that in Example 1, except that the mass fraction of the microcapsules relative to the sodium alginate solution solid content is 50 wt%. The resulting sample is named PI / PFH-50.

[0034] Example 6 The polyimide composite aerogel with active fire extinguishing function in this embodiment is largely the same as that in Example 1, except that the mass fraction of the microcapsules relative to the sodium alginate solution solid content is 60 wt%. The resulting sample is named PI / PFH-60.

[0035] Example 7 The polyimide composite aerogel with active fire extinguishing function in this embodiment is largely the same as that in Example 1, except that the mass fraction of the microcapsules relative to the sodium alginate solution solid content is 80 wt%. The resulting sample is named PI / PFH-80.

[0036] Comparative Example 1 The preparation method of this comparative example flexible thermal insulation PI aerogel is largely the same as that of Example 1, except that the mass fraction of NH2-SiO2 relative to the solid content of PAA is 0 wt%. The resulting sample is named PI.

[0037] Comparative Example 2 The preparation method of this comparative example of flexible thermal insulation PI aerogel is largely the same as that of Example 1, except that the mass fraction of NH2-SiO2 relative to the solid content of PAA is 20 wt%. The resulting sample is named PI / SiO2-20.

[0038] Scanning electron microscope (SEM) images of PI, PI / SiO2-5, PI / SiO2-10, PI / SiO2-15, and PI / SiO2-20 samples were obtained. The results are as follows: Figure 1 As shown. From Figure 1It can be seen that all samples successfully constructed a typical anisotropic hierarchical porous structure: in the axial section along the freezing direction, parallel vertically oriented channels are observed, interconnected to form regular directional channels; while in the radial section perpendicular to the freezing direction, a honeycomb-like porous morphology is exhibited. This anisotropic structural characteristic indicates that the liquid nitrogen directional freezing process effectively guides the directional growth of ice crystals, thereby forming a pore structure with consistent orientation. Further comparison of the microstructure under different SiO2 addition amounts reveals that the SiO2 content has a significant impact on the pore size of the aerogel. As the SiO2 addition amount increases from 0 wt% to 10 wt%, the pore size of the aerogel gradually decreases. When the SiO2 addition was 0 wt%, the pore size was relatively large and the pore walls were relatively smooth. When the SiO2 addition increased to 5 wt%, the pore size decreased slightly, and fine nanoparticles began to adhere to the pore wall surface. When the SiO2 addition reached 10 wt%, the pores became further refined, the nanoparticles distributed on the pore wall surface became more dense, and the pore structure became more compact. This indicates that the introduction of SiO2 nanoparticles played a role in regulating the pore size to some extent. However, as the SiO2 addition further increased to 15 wt% and 20 wt%, the pore size of the aerogel showed an increasing trend, even exceeding that of the pure sample without filler. This phenomenon can be attributed to the following reasons: First, excessive nanoparticles agglomerate in the sol, and the large agglomerates formed disrupt the normal nucleation and growth process of ice crystals; second, the high addition amount led to a significant increase in the system viscosity, which inhibited the nucleation efficiency of ice crystals, resulting in a reduction in the number of nuclei, while a small number of ice crystals preferentially grew to form large pores.

[0039] FT-IR was tested for PI, PI / SiO2-5, PI / SiO2-10, PI / SiO2-15, and PI / SiO2-20, such as... Figure 2 As shown, with the increase of NH2-SiO2 content, the concentration at 1097 cm⁻¹... -1 The Si-O bond absorption peak gradually increases, indicating that NH2-SiO2 has been successfully introduced into the aerogel matrix. Furthermore, the characteristic absorption peak of PI appears in the spectrum: 1775 cm⁻¹. -1 Location (asymmetric C=O stretching vibration), 1716 cm -1 At (symmetric C=O stretching vibration) and 1361 cm -1 (CN stretching vibration). The clear appearance of these characteristic peaks clearly indicates that the precursor PAA has been completely converted into PI through a thermal imidization process. This complete imidization transformation is a prerequisite for ensuring that the aerogel has good thermal stability and mechanical properties.

[0040] The thermal insulation properties of aerogels PI, PI / SiO2-5, PI / SiO2-10, PI / SiO2-15, and PI / SiO2-20 were tested, such as... Figure 3 As shown, a 10 mm thick aerogel can insulate the palm from a temperature difference of 10.2 °C. Comparative tests were conducted under extreme liquid nitrogen cryogenic conditions. Without insulation, water in a vial suspended 10 mm above a copper block froze rapidly within 8 minutes. However, when a 10 mm thick PI / SiO2-10 aerogel was placed between the vial and the copper block, the water in the vial remained unfrozen after 30 minutes. Furthermore, the thermal stability of the aerogel was investigated. The temperature of pure PI aerogel was 518 °C after a 5 wt% weight loss, while the temperature reached 539 °C after adding 10 wt% NH2-SiO2. This indicates that the introduction of NH2-SiO2 significantly improved the thermal stability of the material.

[0041] The mechanical properties of PI / SiO2-10 aerogel were tested, such as... Figure 4 As shown, from Figure 4 This demonstrates its excellent flexibility and resilience. The pure PI aerogel (containing BAPP) exhibited a compressive strength of 0.129 MPa in the first cycle; after 50 cycles, its strength decreased to 0.115 MPa, with a retention rate of 89.1%. This indicates that the introduction of BAPP is key to improving the material's elasticity and fatigue resistance: its unique paddle-shaped twisted molecular structure generates steric hindrance, effectively preventing the tight packing of rigid chain segments; simultaneously, the ether bonds within it act as flexible units, providing excellent mobility for the molecular chains. This "rigid-flexible" molecular configuration fosters a dynamically reversible physical entanglement network. This network efficiently dissipates energy through molecular chain de-entanglement under stress and spontaneously recovers after unloading, thus simultaneously endowing the material with excellent flexibility and elastic recovery at the molecular level. The introduction of NH2-SiO2 resulted in synergistic enhancement; the PI / SiO2-10 sample's first-cycle compressive strength increased to 0.205 MPa, and the strength retention rate after 50 cycles was 90.2%. This indicates that NH2-SiO2 not only enhances the initial compressive strength through interfacial bonding, but also effectively inhibits damage accumulation under cyclic loading, and synergistically enhances the overall fatigue resistance with the flexible chain network.

[0042] SEM images of perfluorohexanone microcapsules, such as... Figure 5As shown in the figure, the overall morphology and local structural features of the microcapsules can be clearly observed. The prepared microcapsules exhibit a relatively regular spherical structure. Furthermore, the figure preliminarily indicates that the microcapsule particle size is mainly distributed in the tens of micrometers, with a relatively uniform overall particle size distribution, suggesting good stability in the emulsification process. Further observation of the local morphology of individual microcapsules reveals that the surface of the microcapsules is generally smooth and dense, with no obvious cracks or pores observed. This indicates that the urea-formaldehyde prepolymer underwent a sufficient condensation reaction under acidic conditions, forming a continuous and dense shell structure. This is beneficial for improving the microcapsule's coating ability on the PFH core material and reducing the volatilization loss of the core material.

[0043] FT-IR spectra of perfluorohexanone microcapsules and urea-formaldehyde resin wall materials, as shown in the figure. Figure 6 As shown, the structural characteristics of the two can be clearly distinguished, and the successful encapsulation by PFH can be verified. First, both exhibit a common absorption peak at the following wavenumber: 3319 cm⁻¹ -1 (NH stretching vibration), 2960cm -1 (CH stretching vibration), 1630cm -1 (Urea bond C=O stretching vibration) and 1540cm -1 (NH stretching vibrations), these are characteristic absorptions of urea-formaldehyde resin wall materials. Secondly, the microcapsule samples at 1706 cm⁻¹... -1 A new absorption peak appeared at 1000-1300 cm⁻¹, corresponding to the stretching vibration of the C=O group in PFH, which directly proves that PFH was successfully encapsulated inside the microcapsule. Further observation at 1000-1300 cm⁻¹... -1 Significant differences can be observed in the fingerprint area. The absorption of aldehyde resin in this region is mainly due to its own structure: 1200-1260 cm⁻¹ -1 The absorption at 1100-1150 cm⁻¹ is attributed to the CN bond stretching vibration (amide III band). -1 The weak absorption at the peak corresponds to the COC ether bond stretching vibration in the polyether segment, while the remaining regions exhibit CC skeletal vibrations. The overall peak shape is flat, with no obvious strong absorption characteristics. In contrast, the microcapsule sample loaded with perfluorohexanone shows a significant increase in absorption intensity within the same wavenumber range. This change is a typical characteristic of numerous CF bond stretching vibrations superimposed on the intrinsic absorption of urea-formaldehyde resin, fully demonstrating the introduction of perfluorohexanone into the microcapsule system.

[0044] The thermal insulation properties of PI / PFH-40, PI / PFH-50, PI / PFH-60, PI / PFH-70, and PI / PFH-80 aerogels were tested, such as... Figure 7 As shown. From Figure 7It can be seen that the three-dimensional porous structure of PI / SiO2 aerogel is the core source of its excellent thermal insulation performance, while the microcapsule coating only acts on the material surface and does not destroy the intrinsic porous structure of the aerogel. The prepared coated composite aerogel fully retains the intrinsic thermal insulation advantages of the aerogel while introducing highly efficient flame-retardant and fire-extinguishing components.

[0045] The flame retardant properties of PI / PHF-70 aerogel were tested, and the results are shown in Table 1.

[0046] Table 1 Flame retardant properties of PI / PHF-70 aerogel

[0047] PI / PFH-70 improves all core flame retardant indicators: ignition time is reduced from 8 seconds to 70 seconds, and flame resistance is increased by 775%, providing ample escape time in the early stages of a fire; peak heat release rate is increased from 195.98 kW / m³. 2 Reduced to 52.25 kW / m 2 The heat release rate decreased by 73.3%, significantly reducing the risk of heat spread and flashover; the time to reach the peak heat release rate was delayed from 26 s to 266 s, a delay of 923%, significantly slowing down the heat release during combustion; pTHR decreased from 21.74 MJ / m³. 2 It dropped to 12.10 MJ / m 2 The decrease was 44.3%, and the total heat release during the fire was significantly reduced; pTSP decreased from 0.065m. 2 Reduced to 0.003m 2 The rate of decrease was as high as 95.4%, and the harm of tobacco poisoning was basically eliminated.

Claims

1. A method for preparing flexible thermally insulating polyimide aerogel, characterized in that, Includes the following steps: Polyamic acid was added to water along with a neutralizing agent to obtain a polyamic acid solution. Then, amino-functionalized SiO2 nanoparticles were added, mixed evenly, injected into a mold, and freeze-dried to obtain PAA / SiO2 aerogel. The PAA / SiO2 aerogel was then subjected to thermal imidization treatment to obtain PI / SiO2 composite aerogel.

2. The method for preparing flexible thermal insulation polyimide aerogel according to claim 1, characterized in that, The mass fractions of the amino-functionalized SiO2 nanoparticles relative to the PAA solid content were 5 wt%, 10 wt%, and 15 wt%, respectively.

3. The method for preparing flexible thermal insulation polyimide aerogel according to claim 1, characterized in that, The thermal imidization treatment was performed by holding the temperature at 100 ℃, 150 ℃, 200 ℃, 250 ℃ and 300 ℃ for 30-90 min at each temperature.

4. The method for preparing flexible thermal insulation polyimide aerogel according to claim 1, characterized in that, The preparation method of the polyamic acid includes the following steps: dissolving p-phenylenediamine (1,4-phenylenediamine) in an organic solvent and adding biphenyltetracarboxylic dianhydride in batches to form oligomers, then adding 2,2-bis[4-(4-aminophenoxy)phenyl]propane and reacting at 0°C, and finally obtaining white polyamic acid powder by adding water to precipitate, washing and filtering, freeze drying and grinding.

5. The method for preparing flexible thermal insulation polyimide aerogel according to claim 1, characterized in that, The preparation method of the amino-functionalized SiO2 nanoparticles includes the following steps: preparing a SiO2 suspension, slowly adding 3-aminopropyltriethoxysilane to the SiO2 suspension, adjusting the pH to 4-5 and stirring continuously for 6-18 hours, washing and centrifuging after the reaction, collecting the solid product, drying it, and obtaining the amino-functionalized SiO2 nanoparticles.

6. Flexible thermal insulating polyimide aerogel, characterized in that, It is prepared by the method for preparing flexible thermal insulation polyimide aerogel according to any one of claims 1-5.

7. A method for preparing polyimide composite aerogel with active fire extinguishing function, characterized in that, Includes the following steps: Prepare a sodium alginate solution and add glycerin, then add perfluorohexanone microcapsules, stir to disperse the perfluorohexanone microcapsules evenly, and obtain a perfluorohexanone microcapsule coating, which is then coated on the surface of the flexible heat-insulating polyimide aerogel as described in claim 6.

8. The method for preparing the polyimide composite aerogel with active fire extinguishing function according to claim 7, characterized in that, The preparation method of the perfluorohexanone microcapsules includes the following steps: adding urea-formaldehyde resin solution to perfluorohexanone emulsion, adjusting the pH to 2.5-3.0, heating to 35-45 ℃ to solidify and form, filtering, washing, and drying to obtain perfluorohexanone microcapsules.

9. The method for preparing the polyimide composite aerogel with active fire extinguishing function according to claim 7, characterized in that, The perfluorohexanone microcapsules accounted for 40 wt%, 50 wt%, 60 wt%, 70 wt%, and 80 wt% of the solid content of the sodium alginate solution, respectively.

10. A polyimide composite aerogel with active fire extinguishing function, characterized in that, It is prepared by the method for preparing polyimide composite aerogel with active fire extinguishing function as described in any one of claims 7-9.

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