Flexible flame-retardant aerogels, articles thereof, and methods of making the same

Abstract

The present application relates to aerogel materials, chemical synthesis and flexible thermal sealing technical field, specifically to flexible flame-retardant aerogel, its product and their preparation method; including matrix dispersion liquid preparation, low-temperature crosslinking aging, directional freezing and atmospheric pressure sublimation drying, and flexible fabric composite packaging and other steps; the method combines modified natural polymer, two-dimensional nanomaterial, amino-containing and aldehyde-containing siloxane precursor and microencapsulated phase change material; its core is to use the Schiff base reaction of amino and aldehyde group and the construction of double crosslinking network at low temperature by siloxane polycondensation, and cooperate with the sublimation drying of cold nitrogen flow under atmospheric pressure; the present application does not use the traditional high-temperature thermal crosslinking and high-pressure supercritical CO2 drying process, uses low-temperature covalent crosslinking and atmospheric pressure sublimation technology to solve the problems of high energy consumption and difficult to scale production, effectively avoids the brittle fracture and pulverization failure of the material in a wide temperature range, and greatly improves the flame-retardant, thermal insulation and phase change heat storage buffering performance of the product.

Description

Technical Field

[0001] This invention relates to the fields of aerogel materials, chemical synthesis, and flexible thermal insulation and sealing technology, specifically to flexible flame-retardant gels, their products, and their preparation methods. Background Technology

[0002] Flexible flame-retardant gels have broad application prospects in aerospace, new energy battery thermal runaway protection and industrial pipeline insulation due to their thermal conductivity being less than 0.030 W / m·K and meeting specific flame-retardant ratings. However, existing flexible flame-retardant gel technologies generally suffer from the following technical defects: existing technologies generally rely on high-temperature vacuum crosslinking or high-temperature thermal imidization treatment at 150-200℃ to build a crosslinking network, resulting in high process energy consumption and making it difficult to achieve continuous large-scale production. To prevent capillary forces from causing skeletal collapse in the three-dimensional porous network during drying, traditional processes heavily rely on supercritical CO2 drying technology. This technology requires high-pressure equipment and involves complex procedures. Existing aerogels have limitations in their mechanical and phase change thermal storage functions when dealing with alternating environments across a wide temperature range from ultra-low to high temperatures, making them prone to brittle fracture or structural pulverization. Existing flexible insulation jackets lack a synergistic coupling mechanism between thermal insulation and phase change thermal storage, and edge sealing processes struggle to balance flexibility and weather resistance. Summary of the Invention

[0003] The purpose of this invention is to provide a flexible flame-retardant gel, its products, and their preparation methods, aiming to solve the problems of high energy consumption and difficulty in large-scale production due to reliance on high-temperature crosslinking and supercritical drying in existing technologies; easy brittleness and powdering of finished products over a wide temperature range; lack of synergistic heat insulation and heat storage; and difficulty in achieving both flexibility and weather resistance in edge sealing. Specifically, the technical solution of this invention is as follows: A method for preparing flexible flame-retardant gels includes: Step 1: Dissolve the modified natural polymer in deionized water and tert-butanol, add two-dimensional nanomaterials, and disperse by ultrasonication at 300W-450W for 25min-40min and shearing at 1000r / min-1600r / min for 20min-25min to obtain the matrix dispersion. Step 2: At 25-60℃, amino-containing silane precursor and aldehyde-containing silane precursor are added dropwise to the system. The pH is adjusted to 4.5-5.5 using an acidic regulator. Composite flame retardant and microencapsulated phase change material are added. After stirring, the mixture is allowed to stand for 3-8 hours to age and obtain hydrogel. Step 3: Directional freeze the hydrogel at -60℃ to -40℃ for 3h-5h, introduce dry cold nitrogen gas at -20℃ to 0℃ with a dew point below -40℃, and sublimate and dry at normal pressure for 44h-60h to obtain a flexible flame-retardant gel.

[0004] Preferably, the modified natural polymer is carboxymethyl cellulose or sodium alginate, or a mixture of the two; the two-dimensional nanomaterial is graphene oxide, reduced graphene oxide, aminated graphene oxide, or MXene, or a mixture thereof.

[0005] Preferably, the amino-containing silane precursor is 3-aminopropyltriethoxysilane; the aldehyde-containing silane precursor is p-formylphenyltrimethoxysilane; and the composite flame retardant is a polyphosphate and borate ester complex.

[0006] Preferably, in step two, the acidity regulator is glacial acetic acid.

[0007] Preferably, in step three, the temperature of the dry cold nitrogen gas is between -10°C and 0°C.

[0008] Preferably, a method for preparing a flexible flame-retardant gel product includes the following steps: Step A, preparing a flexible flame-retardant gel using the preparation method described in any one of claims 1-5; Step B, slicing the flexible flame-retardant gel to obtain an aerogel core material; Step C, laminating the aerogel core material between two layers of flexible fabric, applying a sealant to the seams and edges for pressing and sealing, and curing at room temperature for 24 hours to obtain the flexible flame-retardant gel product.

[0009] Preferably, in step C, the flexible fabric is a high-silica fiber cloth, a polytetrafluoroethylene-coated high-silica glass fiber cloth, or a basalt fiber cloth.

[0010] Preferably, in step C, the sealant is a room temperature vulcanized modified silicone rubber with a temperature resistance range of -50°C to 250°C.

[0011] Preferably, a flexible flame-retardant gel product is prepared by the method for preparing a flexible flame-retardant gel product as described in any of the above preferred embodiments.

[0012] The beneficial effects of this invention are as follows: This invention utilizes low-temperature crosslinking and atmospheric pressure drying with cold nitrogen gas flow for sublimation drying, eliminating the need for high-pressure supercritical equipment and high-temperature vacuum ovens, effectively reducing energy consumption and shortening the production cycle. The product also possesses excellent flame retardant and heat insulation properties. By adding microencapsulated phase change materials, the product also has phase change heat storage function, providing thermal buffering during equipment start-up and shutdown or drastic changes in ambient temperature, thereby improving the temperature stability of the system. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below; the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0014] Example 1: This embodiment provides a flexible flame-retardant gel and a flexible thermal insulation sleeve, specifically including the following steps; S1. Preparation of matrix dispersion: Mix 700 mL of deionized water with 300 mL of tert-butanol and stir at room temperature for 10 min to obtain a mixed solvent; add 20 g of sodium alginate to the mixed solvent and stir until completely dissolved, then add 0.50 g of monolayer Ti3C2T x MXene solid component; ultrasonically dispersed at 300W-450W for 25min-40min and sheared at 1000r / min-1600r / min for 20min-25min to obtain matrix dispersion; this dark brown matrix dispersion serves as a uniform dispersion medium for subsequent crosslinking reactions, ensuring the uniform distribution of multifunctional components within it, thereby improving the structural uniformity of the overall material; The preferred ultrasonic treatment power is 400W. If it is below 300W, the peeling will be insufficient, and if it is above 450W, it will easily lead to polymer degradation. The preferred shear dispersion speed is 1500 r / min. If the speed is below 1000 r / min, the dispersion will be uneven, and if it is above 1600 r / min, it will easily damage the polymer chains. The mass ratio of two-dimensional nanomaterials to modified natural polymers is 2.5%. S2. Low-temperature crosslinking and introduction of multifunctional components: The uniform dark brown matrix dispersion was heated to 45°C, and 15g of 3-aminopropyltriethoxysilane and 18g of p-formylphenyltrimethoxysilane were added dropwise under mechanical stirring, with the addition time controlled at 20min; the mass ratio of 3-aminopropyltriethoxysilane to p-formylphenyltrimethoxysilane was 15:18. Under this ratio, the Schiff base reaction of the amino and aldehyde groups reached a complete crosslinking state, and the crosslinking network was dense; Deviation from this ratio will result in unreacted monomer residues or a loose network. The pH of the system was adjusted to 5.0 using glacial acetic acid. 12g of ammonium polyphosphate, 5g of tributyl borate, and 15g of paraffin-silica microcapsule phase change material were then added. This amount of addition provides an effective buffer against the latent heat of phase change without compromising the mechanical support properties of the gel skeleton. After stirring for 20 minutes, the mixture was poured into a stainless steel mold and aged at 50°C for 4 hours to obtain a highly elastic hydrogel. This highly elastic hydrogel has a three-dimensional network structure, which can effectively bind the solvent and provide stable mechanical support for subsequent drying, preventing structural collapse. S3, Directional Freezing and Normal Pressure Sublimation Drying: The highly elastic hydrogel was placed in a directional freezing mold and frozen at -50℃ for 4 hours; after demolding, the frozen sample was placed in a normal pressure drying chamber, and 0℃ dry cold nitrogen gas was introduced at a flow rate of 5L / min, with the dew point controlled at -50℃, and continuously purged for 48 hours to obtain a flexible flame-retardant hydrogel. S4. Encapsulation of the flexible insulation sleeve: Cut the flexible flame-retardant gel into 10mm thick sheets and sandwich them between two 0.5mm thick polytetrafluoroethylene-coated high-silica glass fiber cloths; leave a 20mm overlap area at the edge, uniformly coat the inside of the overlap area with two-component addition-type room temperature vulcanizing modified silicone rubber, and cold press and bond them with 0.2MPa pressure, and cure at room temperature for 24h to obtain a detachable flexible insulation sleeve.

[0015] Example 2: This embodiment provides a flexible flame-retardant gel and a flexible thermal insulation sleeve, specifically including the following steps; S1. Preparation of matrix dispersion: Mix 750 mL of deionized water with 250 mL of tert-butanol; add 18 g of carboxymethyl cellulose and, after it dissolves, add 0.90 g of graphene oxide solid powder; sonicate at 350 W for 40 min, and shear disperse at 1200 r / min for 25 min to obtain the matrix dispersion; this matrix dispersion serves as the basic medium for subsequent crosslinking reactions, effectively preventing the aggregation of nanomaterials and ensuring the uniformity of the overall material structure; The preferred ultrasonic power here is 350W, and the preferred shear dispersion speed is 1200 r / min. If the speed is lower than 1000 r / min, the dispersion will be uneven, and if it is higher than 1600 r / min, the polymer molecular chains will be easily damaged. The mass ratio of two-dimensional nanomaterials to modified natural polymers is 5.0%. S2. Low-temperature crosslinking and introduction of multifunctional components: The matrix dispersion is heated to 60°C, and 14g of 3-aminopropyltriethoxysilane and 16g of p-formylphenyltrimethoxysilane are added dropwise in sequence; wherein the mass ratio of 3-aminopropyltriethoxysilane to p-formylphenyltrimethoxysilane is 14:16, which can ensure that the number of dynamic covalent bonds is moderate and avoid the network being loose; The pH of the system was adjusted to 4.6 using glacial acetic acid; 11g of ammonium polyphosphate, 4g of trimethyl borate and 12g of paraffin microcapsule phase change material were added to balance the heat storage and insulation properties; after stirring for 25 min, the mixture was poured into a mold and aged at 60℃ for 3 h to obtain a hydrogel; the hydrogel constructed a stable interpenetrating network structure, providing the necessary mechanical support and molding basis for the porous framework of the aerogel; S3. Directional freezing and atmospheric pressure sublimation drying: The hydrogel was directionally frozen at -40℃ for 5h, then placed in an atmospheric pressure drying chamber, and dried cold nitrogen gas at -8℃ with a flow rate of 4L / min and a dew point of -42℃ was introduced and purged for 54h to obtain a flexible flame-retardant gel. S4. Encapsulation of flexible insulation sleeve: Cut flexible flame-retardant gel into 10mm core material, composite it between two layers of basalt fiber cloth, and use room temperature vulcanized modified silicone rubber to coat and press the joints and edges. Curing at room temperature for 24 hours yields a flexible insulation sleeve.

[0016] Example 3: This embodiment provides a flexible flame-retardant gel and a flexible thermal insulation sleeve, specifically including the following steps; S1. Preparation of matrix dispersion: Mix 650 mL of deionized water with 350 mL of tert-butanol; add 12 g of sodium alginate and 8 g of carboxymethyl cellulose, stir to dissolve, and then add 0.10 g of monolayer Ti3C2T. x MXene and 0.20 g graphene oxide were used; the mixture was ultrasonically treated at 450 W for 35 min and sheared at 1600 r / min for 20 min to obtain a matrix dispersion. The matrix dispersion effectively dispersed the components, providing a good precursor system for the subsequent construction of a continuous and dense three-dimensional network. The ultrasonic treatment power was 450W, and the shear dispersion speed was 1600 r / min, ensuring efficient exfoliation and uniform dispersion of the nanomaterials, avoiding uneven dispersion below 1000 r / min or damage to the molecular chains above 1600 r / min. The total mass ratio of the two-dimensional nanomaterials to the modified natural polymer was 1.5%. S2. Low-temperature crosslinking and introduction of multifunctional components: The matrix dispersion is heated to 35°C, and 16g of 3-aminopropyltriethoxysilane and 17g of p-formylphenyltrimethoxysilane are added dropwise in sequence; the mass ratio of 3-aminopropyltriethoxysilane to p-formylphenyltrimethoxysilane is 16:17, which can effectively adjust the crosslinking density of the system and avoid deviation from this ratio, resulting in unreacted monomer residues; The pH of the system was adjusted to 5.3 using glacial acetic acid; 10g of ammonium polyphosphate, 6g of triphenyl borate and 18g of fatty acid ester microcapsule phase change material were added to optimize the phase change heat storage performance; after stirring for 20 min, the mixture was poured into a mold and aged at 40℃ for 5 h to obtain a hydrogel; the hydrogel fixed the internal pore structure through organic and inorganic dual cross-linking, which effectively improved the overall skeleton's anti-shrinkage ability during the subsequent drying process; S3. Directional freezing and atmospheric pressure sublimation drying: The hydrogel was directionally frozen at -60℃ for 3h, then placed in an atmospheric pressure drying chamber, and dried cold nitrogen gas at -5℃ with a flow rate of 6L / min and a dew point of -55℃ was introduced and purged for 44h to obtain a flexible flame-retardant gel. S4. Encapsulation of flexible insulation sleeve: Cut flexible flame-retardant gel into 8mm core material, composite it between two layers of high silica fiber cloth, and use room temperature vulcanized modified silicone rubber to press and seal the edges and seams. Curing at room temperature for 24 hours yields a flexible insulation sleeve.

[0017] Example 4: This embodiment provides a flexible flame-retardant gel and a flexible thermal insulation sleeve, specifically including the following steps; S1. Preparation of matrix dispersion: Mix 800 mL of deionized water with 200 mL of tert-butanol; add 20 g of sodium alginate, and after it dissolves, add 0.10 g of monolayer Ti3C2T. x MXene was subjected to ultrasonic treatment at 300W for 25 min and sheared dispersion at 1000 r / min for 20 min to obtain a matrix dispersion; the mass ratio of two-dimensional nanomaterials to modified natural polymers was 0.5%. S2. Low-temperature crosslinking and introduction of multifunctional components: The matrix dispersion was kept at 25°C, and 13g of 3-aminopropyltriethoxysilane and 15g of p-formylphenyltrimethoxysilane were added dropwise in sequence. This mass ratio ensures the density and stability of the crosslinking network. The pH of the system was adjusted to 5.5 using glacial acetic acid. 12g of ammonium polyphosphate, 5g of tributyl borate and 10g of paraffin microcapsule phase change material were added. After stirring for 15 min, the mixture was poured into a mold and aged at 25°C for 8 h to obtain a hydrogel. S3. Directional freezing and atmospheric pressure sublimation drying: The hydrogel was directionally frozen at -45℃ for 5h, then placed in an atmospheric pressure drying chamber, and dried cold nitrogen gas at -10℃ with a flow rate of 5L / min and a dew point of -45℃ was introduced and purged for 60h to obtain a flexible flame-retardant gel. S4. Encapsulation of the flexible insulation sleeve: The obtained aerogel is sliced ​​into 10mm core material and laminated between two layers of high silica fiber cloth. The joints and edges are sealed with room temperature vulcanized modified silicone rubber and cured at room temperature for 24 hours to obtain the flexible insulation sleeve.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that p-formylphenyltrimethoxysilane in step S2 is omitted, while the other operating steps and process parameters are exactly the same as in Example 1.

[0019] Comparative Example 2: The difference between this comparative example and Example 1 is that glacial acetic acid is not used to adjust the pH in step S2, and the system is naturally strongly alkaline. Other operating steps and process parameters are exactly the same as in Example 1.

[0020] Comparative Example 3: The difference between this comparative example and Example 1 is that only 1000 mL of deionized water is used as the solvent in step S1, and tert-butanol is not added. The other operating steps and process parameters are exactly the same as in Example 1.

[0021] Comparative Example 4: The difference between this comparative example and Example 1 is that the addition of 0.50g of monolayer Ti3C2T is omitted in step S1. x The solid component dispersion of MXene contained solids, and the other operating steps and process parameters were exactly the same as in Example 1.

[0022] Comparative Example 5: The difference between this comparative example and Example 1 is that the paraffin-silica microcapsule phase change material is omitted in step S2, while the other operating steps and process parameters are exactly the same as in Example 1.

[0023] Comparative Example 6: The difference between this comparative example and Example 1 is that the dew point of the dry cold nitrogen gas introduced in step S3 is adjusted to -20°C, while the other operating steps and process parameters are exactly the same as in Example 1.

[0024] Performance Testing and Datasheets Thermal conductivity was tested using the steady-state plate method at 25℃; latent heat of phase change was tested using differential scanning calorimetry; limiting oxygen index was tested according to GB / T2406.2, and vertical burning was evaluated according to UL94; low-temperature bending performance was tested by 180° reciprocating bending at -50℃; high-temperature insulation performance was measured by measuring the temperature of the unexposed surface after continuous burning with a 600℃ alcohol torch for 30 minutes; density was tested according to relevant national standards; volume shrinkage was calculated by measuring the dimensional changes of the sample before and after burning at 600℃. Table 1. Performance test results of the examples and comparative examples. As can be seen from the comparison of the test results of Example 1 and Comparative Example 1 in Table 1, after omitting the aldehyde-containing silane precursor, the thermal conductivity increased, the number of low-temperature bending cycles decreased, the temperature of the unexposed surface increased, and the volume shrinkage rate increased. The underlying mechanism is that in Example 1, amino and aldehyde groups can form Schiff base bonds, while silanol condensation forms a Si-O-Si network. Organic and inorganic crosslinking together improve the continuity and toughness of the skeleton. In Comparative Example 1, the lack of aldehyde components results in insufficient dynamic covalent bonds. The gel skeleton mainly relies on single silane condensation and hydrogen bonding for maintenance, leading to a decrease in network integrity. After drying, the pore walls are prone to thickening and local collapse, thus increasing the thermal conductivity from 0.022 W / m·K to 0.033 W / m·K. The decrease in crosslinking density also makes the material prone to cracking when bent at -50°C, reducing the cycle life from 500 to 180 times. At high temperatures, the continuous carbon layer and ceramicized layer are difficult to maintain stably, causing the back-fired surface temperature to rise to 196°C and the volume shrinkage rate to increase to 15.8%. As can be seen from the comparison of the test results of Example 1 and Comparative Example 2 in Table 1, failure to adjust the pH of the system to the range of 4.5 to 5.5 will lead to a decrease in thermal conductivity, flame retardancy rating and bending resistance. The underlying mechanism is that the weakly acidic environment in Example 1 is conducive to the condensation reaction of aminosiloxanes and aldehyde-containing siloxanes, and also conducive to the hydrolysis of silane precursors to generate silanols; when the neutral conditions are maintained in Comparative Example 2, the Schiff base formation rate decreases, the silane hydrolysis and condensation process is insufficient, and the interpenetrating network formed during the hydrogel aging stage is loose; the structure is not able to resist capillary action and local stress during the sublimation process at normal pressure, resulting in a decrease in the uniformity of the pore structure and an increase in the thermal conductivity to 0.030 W / m·K; the insufficient network stability also weakens the continuity of the char layer during combustion, causing UL94 to drop from V-0 to V-1 and the back-fire surface temperature to rise to 184°C; As can be seen from the comparison of the test results of Example 1 and Comparative Example 3 in Table 1, after omitting the tert-butanol co-solvent, the density of the material increases significantly, and the thermal conductivity, back surface temperature and shrinkage rate all deteriorate significantly. The underlying mechanism is that tert-butanol in Example 1 has low surface tension and high atmospheric pressure sublimation driving force. After freezing, it can form a eutectic or mixed crystal structure with water that is more conducive to sublimation migration, and the collapse stress on the skeleton during the drying stage is small. In Comparative Example 3, only water is used as a solvent. After freezing, the ice crystal sublimation rate is slow, the residence time at the sublimation interface is prolonged, and the stress on the pore walls is more obvious, resulting in increased skeleton shrinkage and pore blockage. The density increases to 0.108 g / cm³, and the thermal conductivity increases to 0.041 W / m·K. The structural collapse also weakens the integrity of the heat insulation layer during flame burning, causing the temperature on the unexposed surface to rise to 221°C and the volume shrinkage rate to reach 21.3%. As can be seen from the comparison of the test results of Example 1 and Comparative Example 4 in Table 1, the low-temperature flexibility, flame retardancy rating and high-temperature thermal insulation performance all decreased after omitting the two-dimensional nanomaterials. The underlying mechanism is that the MXene surface in Example 1 contains polar groups such as hydroxyl groups, which can form a stable interface with sodium alginate and siloxane network, playing a role in stress transfer and skeleton reinforcement; the two-dimensional sheets can also extend the diffusion path of heat and combustible small molecules, improving the integrity of the char layer; in Comparative Example 4, without this reinforcing phase, the skeleton is prone to local cracking under bending load and temperature change, and the number of bending cycles at -50℃ decreased from 500 to 260; the char layer density was insufficient during flame burning, UL94 dropped to V-1, and the temperature of the unexposed side rose to 168℃; As can be seen from the comparison of the test results of Example 1 and Comparative Example 5 in Table 1, the latent heat of phase change decreased significantly after omitting the microcapsule phase change material, while the thermal conductivity and flame retardant properties changed little. The underlying mechanism is that the microcapsule phase change material in Example 1 is uniformly distributed in the porous framework, absorbing heat in the phase change temperature range and providing a thermal buffer effect, thus achieving a latent heat of phase change of 35.8 J / g; Comparative Example 5 does not contain this component, and the phase change heat absorption unit is basically missing, with a latent heat of phase change of only 2.1 J / g; Since the remaining framework structure, flame retardant system, and drying conditions remain unchanged, the thermal conductivity and flame retardant rating are still close to those of Example 1; This indicates that the microcapsule phase change material mainly contributes to the heat storage performance and has little impact on the basic thermal insulation and flame retardant performance; As can be seen from the comparison of the test results of Example 1 and Comparative Example 6 in Table 1, after the dew point of dry cold nitrogen was increased from -50℃ to -20℃, the thermal conductivity, flame retardancy rating and bending resistance all decreased. The underlying mechanism is that in Example 1, the low dew point cold nitrogen gas can continuously reduce the partial pressure of water vapor around the sample, maintaining a stable sublimation driving force, which allows the frozen solvent to migrate rapidly out of the pores. In Comparative Example 6, the increased moisture content of the gas flow weakens the sublimation driving force, making it easy for local recondensation or uneven sublimation to occur inside the sample, resulting in pore wall adhesion and collapse. After the pore structure is destroyed, the density increases to 0.094 g / cm³, and the thermal conductivity increases to 0.036 W / m·K. The decrease in skeleton integrity also reduces the number of low-temperature bending cycles to 210 and increases the shrinkage rate after flame burning to 16.7%. Based on the data from Examples 1 to 4, it can be seen that, within the scope of this invention, a flexible flame-retardant gel with low thermal conductivity, flame retardancy, low-temperature bending resistance, and heat storage properties can be obtained by combining modified natural polymers, two-dimensional nanomaterials, two-component siloxane precursors, composite flame retardants, microencapsulated phase change materials, and atmospheric pressure freeze-drying conditions. The parameter combination used in Example 1 is relatively coordinated in terms of network uniformity, pore structure maintenance, and functional component matching, so all comprehensive indicators meet the set technical effect requirements.

[0025] The above are merely specific embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any conventional modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing flexible flame-retardant gel, characterized in that, include: Step 1: Dissolve the modified natural polymer in deionized water and tert-butanol, add two-dimensional nanomaterials, and disperse by ultrasonication at 300W-450W for 25min-40min and shearing at 1000r / min-1600r / min for 20min-25min to obtain the matrix dispersion. Step 2: At 25-60℃, amino-containing silane precursor and aldehyde-containing silane precursor are added dropwise to the system. The pH is adjusted to 4.5-5.5 using an acidic regulator. Composite flame retardant and microencapsulated phase change material are added. After stirring, the mixture is allowed to stand for 3-8 hours to age and obtain hydrogel. Step 3: Directional freeze the hydrogel at -60℃ to -40℃ for 3h-5h, introduce dry cold nitrogen gas at -20℃ to 0℃ with a dew point below -40℃, and sublimate and dry at normal pressure for 44h-60h to obtain a flexible flame-retardant gel.

2. The method for preparing the flexible flame-retardant gel according to claim 1, characterized in that, The modified natural polymer is carboxymethyl cellulose or sodium alginate, or a mixture of the two; the two-dimensional nanomaterial is graphene oxide, reduced graphene oxide, aminated graphene oxide, or MXene, or a mixture thereof.

3. The method for preparing the flexible flame-retardant gel according to claim 1, characterized in that, The amino-containing silane precursor is 3-aminopropyltriethoxysilane; the aldehyde-containing silane precursor is p-formylphenyltrimethoxysilane; and the composite flame retardant is a complex of ammonium polyphosphate and borate ester.

4. The method for preparing the flexible flame-retardant gel according to claim 1, characterized in that, In step two, the acidity regulator is glacial acetic acid.

5. The method for preparing the flexible flame-retardant gel according to claim 1, characterized in that, In step three, the temperature of the dry cold nitrogen gas is between -10°C and 0°C.

6. A method for preparing a flexible flame-retardant gel product, characterized in that, Includes the following steps: Step A: Prepare a flexible flame-retardant gel using the preparation method described in any one of claims 1-5; Step B: Slice the flexible flame-retardant gel to obtain an aerogel core material; Step C: Composite the aerogel core material between two layers of flexible fabric, apply a sealant to the seams and edges, and press and seal the surfaces. After curing at room temperature for 24 hours, obtain a flexible flame-retardant gel product.

7. The method for preparing the flexible flame-retardant gel product according to claim 6, characterized in that, In step C, the flexible fabric is a high-silica fiber cloth, a polytetrafluoroethylene-coated high-silica glass fiber cloth, or a basalt fiber cloth.

8. The method for preparing the flexible flame-retardant gel product according to claim 6, characterized in that, In step C, the sealant is a room temperature vulcanized modified silicone rubber with a temperature resistance range of -50°C to 250°C.

9. A flexible flame-retardant gel product, characterized in that, It is prepared by the method for preparing flexible flame-retardant gel products according to any one of claims 6-8.

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