Hydrophobic silica aerogel thermal insulation blanket and method of making

Abstract

This invention discloses a hydrophobic silica aerogel thermal insulation felt and its preparation method. The hydrophobic silica aerogel thermal insulation felt comprises a fiber felt and a hydrophobic silica aerogel layer; the aerogel layer comprises: 30-40 parts silica sol, 30-40 parts chitosan-metal salt complex solution, 0.1-0.2 parts crosslinking agent, and 0.1-0.5 parts gelling agent; the silica sol comprises: 8-15 parts tetraethoxysilane, 0.1-0.5 parts methyltrimethoxysilane, pH adjuster, 16-25 parts anhydrous ethanol, and 2-7 parts water; the chitosan-metal salt complex solution comprises: 0.2-1 parts oligochitosan, 1-3 parts zirconium nitrate pentahydrate, pH adjuster, 0-0.3 parts hydroxyl-containing anti-precipitant, and 30-45 parts water. This invention uses fiber felt as a matrix, and impregnates it in composite silica sol to allow the composite silica sol to penetrate and form an aerogel layer. This gives the heat insulation felt both the super heat insulation of aerogel and the flexibility of fiber felt, while significantly improving its hydrophobicity and greatly extending its service life.

Description

Technical Field

[0001] This invention relates to the field of thermal insulation materials, and more particularly to a hydrophobic silica aerogel thermal insulation felt and its preparation method. Background Technology

[0002] In today's society, high-efficiency thermal insulation materials, with their superior thermal insulation and energy-saving performance, have become key elements in promoting sustainable energy utilization and the development of high-end equipment. From building envelopes to aerospace thermal protection systems, thermal insulation materials are ubiquitous, supporting society's needs for energy conservation, emission reduction, and exploration in extreme environments. However, due to the inherent physical limitations of traditional thermal insulation materials—their thermal conductivity is difficult to further reduce due to their solid framework and the convection of gas within pores—their thermal conductivity cannot meet the ever-growing demand for ultra-efficient thermal insulation. Therefore, developing new material systems with "super thermal insulation" performance has become crucial.

[0003] In existing technologies, researchers have successfully prepared aerogel materials with nanoporous network structures by controlling the hydrolysis and condensation process of silica precursors and combining it with supercritical drying technology. These materials exhibit thermal conductivity as low as 0.015 W / (m·K), demonstrating significant potential. However, their inherent brittleness and poor mechanical strength make them difficult to directly apply as bulk materials in engineering, limiting their use in harsh environments such as vibration and load-bearing conditions. To address this, some researchers have proposed combining aerogels with fiber reinforcements (such as ceramic fibers and nonwoven fabrics) to improve their flexibility and strength. Although the matrix of this composite material possesses ultra-low thermal conductivity, it still faces the challenge of significant structural shrinkage during atmospheric pressure drying, which restricts its low-cost large-scale production. Furthermore, its hydrophobic stability and long-term durability are also affected by environmental factors. For example, prolonged high-temperature and high-humidity environments may cause hydrophobic groups to fail, leading to moisture absorption collapse and a decline in thermal insulation performance, which may affect the longevity of its thermal insulation properties. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a hydrophobic silica aerogel thermal insulation felt and its preparation method. This invention uses fiber felt as a matrix, impregnating it in a composite silica sol to allow the sol to penetrate. Following gelation, aging, solvent replacement, and supercritical drying, an aerogel layer is formed on the surface of the fiber felt and the surface of its internal pores. This results in a thermal insulation felt that possesses both the superior thermal insulation properties of aerogel and the flexibility of fiber felt. Furthermore, after modification, its hydrophobicity is significantly improved, greatly extending its service life.

[0005] The specific technical solution of this invention is as follows: First, a hydrophobic silica aerogel insulation felt, characterized in that it includes a fiber felt and a hydrophobic silica aerogel layer attached to the surface of the fiber felt and the surface of its internal pores.

[0006] The hydrophobic silica aerogel layer comprises the following raw materials in parts by weight: 30-40 parts silica sol, 30-40 parts chitosan-metal salt complex solution, 0.1-0.2 parts crosslinking agent, and 0.1-0.5 parts gelling agent.

[0007] The silica sol comprises the following raw materials in parts by weight: 8-15 parts of tetraethoxysilane (TEOS), 0.1-0.5 parts of methyltrimethoxysilane (MTMS), pH adjuster, 16-25 parts of anhydrous ethanol, and 2-7 parts of water.

[0008] The chitosan-metal salt complex solution comprises the following raw materials in parts by weight: 0.2-1 parts of oligochitosan, 1-3 parts of zirconium nitrate pentahydrate, pH adjuster, 0.1-0.3 parts of hydroxyl-containing anti-precipitant, and 30-45 parts of water.

[0009] The proportions of each raw material in the above hydrophobic silica aerogel layer, silica sol, and chitosan-metal salt complex solution are calculated separately.

[0010] In the hydrophobic silica aerogel insulation felt of the present invention, silica sol is the core of forming the aerogel skeleton, wherein TEOS, as a silicon source, forms a silica network through hydrolysis and condensation; zirconium nitrate pentahydrate can introduce zirconium element to improve the high-temperature stability and mechanical strength of the aerogel; chitosan, as an organic modifying component, can improve the flexibility of the aerogel, and its molecular chain spatial structure can fix the hydrophobic methyl groups on the surface of silica sol during supercritical drying, thus helping to optimize the hydrophobic properties of the insulation felt; pH adjuster is used to regulate the hydrolysis rate of TEOS to ensure uniform gel structure; hydroxyl-containing anti-precipitant can be adsorbed on the surface of chitosan during the preparation process to form steric hindrance, effectively preventing the aggregation of small particles and the formation of precipitation, thereby preventing the formation of precipitation in the chitosan-metal salt complex suspension and ensuring the stability of the composite system.

[0011] As a reinforcing skeleton, fiber mat can significantly improve the mechanical strength of aerogel insulation mat and avoid the problem of high brittleness of aerogel. The synergistic effect of crosslinking agent and gelation accelerator can accelerate the gelation process of silica sol on the surface and inside of fiber mat, ensuring that aerogel and fiber mat are tightly bonded.

[0012] Preferably, the fiber felt is a mullite fiber felt, which has high temperature resistance, excellent mechanical properties, and good compatibility with aerogel.

[0013] Preferably, the crosslinking agent includes one or more of glutaraldehyde and sodium tripolyphosphate. This promotes the crosslinking of chitosan and the silica network, thereby improving structural stability.

[0014] Preferably, the gelling agent includes one or more of epichlorohydrin, KH-550, and KH-560. These gelling agents not only promote gelation but also have a coupling effect, enhancing the bonding force between the aerogel and the fiber mat.

[0015] Preferably, the molecular weight of the oligochitosan is 1000-3000.

[0016] The reason for choosing oligomeric chitosan is that its amino and hydroxyl groups are more fully exposed on its chain segments, resulting in higher reactivity and better compatibility with other materials. However, when the molecular weight of chitosan is too low, although the amino and hydroxyl groups are more fully exposed, the segment entanglement ability weakens, and the coordination force with zirconium ions deteriorates, making it difficult to form a stable three-dimensional cross-linked network. This leads to a loose aerogel framework, forming more pore defects and increasing the thermal conductivity. When medium-polymer chitosan is chosen, the increased rigidity of the molecular chain reduces water solubility, making it prone to molecular chain aggregation. This results in large particles that block the nanopores of the aerogel, leading to an increase in thermal conductivity. Therefore, the molecular weight of chitosan needs to be controlled within the range of 1000-3000 to achieve a balance of reactivity, solubility, and dispersibility, forming a stable cross-linked network without clogging pores or damaging the hydrophobic structure.

[0017] Preferably, the anti-settling agent is polyvinyl alcohol 2000.

[0018] Polyvinyl alcohol 2000 contains a large number of hydroxyl groups on its molecular chain, which can adsorb onto the surface of chitosan to form steric hindrance, effectively preventing the aggregation of small particles and the formation of precipitation. If it is replaced with an anti-precipitant without hydroxyl groups, it will not be able to form hydrogen bonds with the chitosan-zirconium ion complex to build steric hindrance, which will cause the complex to aggregate and form large particles that block the nanopores. The composite silica sol is prone to delamination, and the porous structure is easily destroyed after drying. The interfacial bonding is loose, and it cannot effectively inhibit the shrinkage of the silica aerogel network after high temperature, ultimately leading to a decrease in thermal insulation, hydrophobicity, and tensile strength.

[0019] Preferably, the pH adjuster includes one or more of hydrochloric acid, glacial acetic acid, and formic acid.

[0020] Secondly, a method for preparing a hydrophobic silica aerogel insulation felt includes the following steps: 1) Preparation of silica sol: Tetraethoxysilane, methyltrimethoxysilane, anhydrous ethanol and water are mixed and stirred evenly. A pH adjuster is added to lower the pH to 2-2.5, and the mixture is stirred evenly to obtain silica sol.

[0021] 2) Preparation of chitosan-metal salt complex suspension: Add oligochitosan to 20-25 parts of water, add pH adjuster to adjust the pH of the system to 4-6, stir evenly to obtain oligochitosan suspension; then add zirconium nitrate pentahydrate to 10-20 parts of water and stir evenly, then add dropwise to the oligochitosan suspension, react, add anti-precipitant, stir evenly, let stand to defoam, and obtain chitosan-metal salt complex suspension.

[0022] In step 2), chitosan and zirconium nitrate pentahydrate are combined through coordination bonding. The active groups in the oligomeric chitosan molecules provide lone pairs of electrons, and the zirconium ions dissociated from the zirconium nitrate pentahydrate act as the central ion to accept electrons, thus forming a stable coordination structure. This invention combines chitosan and zirconium nitrate pentahydrate with silica sol in the form of a chitosan-metal salt complex because it offers better stability. This invention found that if chitosan and zirconium nitrate pentahydrate are added to silica sol alone, the zirconium ions of the zirconium nitrate pentahydrate easily hydrolyze with water, forming zirconium hydroxide precipitate. However, the method of this invention effectively avoids the stratification of the composite silica sol and also makes the zirconium element distribution more uniform.

[0023] 3) Mix and stir the silica sol and chitosan-metal salt complex solution to obtain a composite silica sol; immerse the fiber felt in the composite silica sol, add crosslinking agent and gelation accelerator, and after gel formation, perform aging, solvent replacement and supercritical drying to obtain a hydrophobic silica aerogel insulation felt.

[0024] Preferably, in step 2), the reaction conditions are: room temperature and 5-8 hours.

[0025] Preferably, in step 3), the mass ratio of the fiber felt to the composite silica sol is 5:95-10:90.

[0026] The mass ratio of fiber felt to composite silica sol is also crucial. If the proportion of fiber felt is too high, the composite silica sol may not be able to fully wet the surface and internal pores of the fiber felt, resulting in insufficient aerogel coverage, a reduced proportion of nanopores, and decreased thermal insulation performance. Conversely, if the proportion of fiber felt is too low, although the composite silica sol can fully encapsulate the fibers, improving thermal insulation and hydrophobicity, the aerogel itself is brittle and lacks sufficient fiber skeleton support, leading to a sharp drop in tensile strength. Furthermore, without sufficient fiber skeleton support at high temperatures, it is prone to collapse, resulting in an increased rate of change in thermal conductivity after high-temperature resistance.

[0027] Preferably, in step 3), the aging temperature is 20-50℃ and the time is 24-48h.

[0028] Preferably, in step 3), the solvent used for solvent replacement is anhydrous ethanol, and the solvent replacement is performed 3-5 times, each time for 8-12 hours.

[0029] Preferably, in step 3), the supercritical drying is supercritical CO2 drying, with a temperature of 40-50℃, a pressure of 8-10MPa, and a drying time of 4-10h.

[0030] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention uses flexible fiber felt as the matrix and the sol fully penetrates between the fiber felt through the simple impregnation process. Its heat insulation efficiency is 2-4 times that of traditional heat insulation materials. Therefore, only 1 / 3 of the traditional materials are needed to achieve the same effect.

[0031] (2) This invention utilizes the excellent flexibility and tensile strength of fiber felt to solve the problems of aerogel being fragile and difficult to process. It can not only improve the thermal insulation performance to a certain extent, but also give aerogel better toughness and operability.

[0032] (3) The present invention combines chitosan with silica sol, which makes the aerogel insulation felt more hydrophobic, making it difficult for water molecules to penetrate into the material, thus ensuring the long-term stability of its thermal insulation performance. Furthermore, the introduction of organic components enhances the flexibility of the aerogel.

[0033] (4) In this invention, chitosan and zirconium nitrate pentahydrate are combined with silica sol in the form of chitosan-metal salt complex. This can avoid the formation of zirconium hydroxide precipitate due to the hydrolysis of zirconium ions and water in zirconium nitrate pentahydrate, thereby effectively avoiding the layering of composite silica sol, resulting in better stability and more uniform zirconium element distribution. Attached Figure Description

[0034] Figure 1 Electron micrograph of the aerogel insulation felt prepared in Example 1 (1 μm scale bar). Figure 2 Electron micrograph of the aerogel insulation felt prepared in Example 1 (30 μm scale bar). Figure 3 Electron micrograph of the aerogel insulation felt prepared in Example 1 (100 μm scale bar). Detailed Implementation

[0035] Example 1 Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0036] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0037] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0038] like Figure 1-3 The images shown are electron microscope (EM) images of the hydrophobic silica aerogel insulation felt prepared in Example 1 at different scales. Wherein: observe Figure 3 (100μm scale) The skeletal structure of the fiber felt can be clearly observed. The mullite fibers are distributed in an interlaced network, forming the supporting matrix of the material. Aerogel particles are uniformly coated on the surface of the mullite fibers and fill the pores between the mullite fibers, forming a porous structure of "mullite fiber-aerogel". This is the core structural feature of the thermal insulation fiber felt, and the existence of pores also provides the basis for thermal insulation performance.

[0039] observe Figure 2 (30μm scale) It can be observed that the aerogel is not a single particle, but is attached to the surface of the mullite fiber in the form of aggregates. The aggregates are formed by the aggregation of nano-sized aerogel particles, with tiny pores between the particles. The surface of the mullite fiber is completely covered by the aerogel layer, with no obvious exposed areas, indicating that the composite effect of aerogel and mullite fiber is good. This coating structure can reduce the thermal conductivity of mullite fiber and improve the overall thermal insulation.

[0040] observe Figure 1 (1μm scale) The aerogel itself exhibits a nanoporous structure, formed by the accumulation of tiny nanoparticles with a high proportion of voids between particles. These mesopores effectively suppress thermal convection of gas molecules, while the nanoscale particles also reduce heat radiation transfer. This is the key microscopic reason for the high thermal insulation properties of aerogels. Furthermore, in Figure 1No obvious large-sized cracks or defects were observed, indicating that the nanoporous structure of the aerogel prepared in Example 1 has good integrity and can effectively ensure the thermal insulation performance of the aerogel insulation felt.

[0041] Comparative Example 1 The difference from Example 1 is that zirconium nitrate pentahydrate was not added to the composite silica sol; all other raw materials and steps remained the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0042] 0.33g of oligochitosan with a molecular weight of 2000 was added to 39.6g of deionized water, and then 0.33ml of glacial acetic acid was added to adjust the pH of the system to about 4. The mixture was stirred evenly at room temperature to obtain an oligochitosan suspension. Then 0.25g of polyvinyl alcohol 2000 was added, and the mixture was stirred for 2 hours. After standing to remove foam, a chitosan suspension was obtained.

[0043] Finally, the silica sol and chitosan suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0044] Comparative Example 2 The difference from Example 1 is that chitosan was not added to the composite silica sol, while the other raw materials and steps were the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0045] Add 0.33 ml of glacial acetic acid to 21.6 g of deionized water and stir until homogeneous at room temperature. Then add 1.2 g of zirconium nitrate pentahydrate to 18 g of deionized water and stir until homogeneous. Slowly add this solution dropwise to the above solution and stir at room temperature for 7 hours. Then add 0.25 g of polyvinyl alcohol 2000. Continue stirring for 2 hours, and after standing to remove foam, the metal salt solution is obtained.

[0046] Finally, the silica sol and metal salt solution were mixed and stirred for 1.5 hours to obtain a composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain a hydrophobic silica aerogel insulation felt.

[0047] Comparative Example 3 The difference from Example 1 is that conventional drying (drying at 80°C for 12 hours) is used instead of supercritical CO2 drying, while the other raw materials and steps remain the same. Specifically, this includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0048] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0049] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried at 80℃ for 12 hours to obtain the hydrophobic silica aerogel insulation felt.

[0050] Comparative Example 4 The difference from Example 1 is that yttrium nitrate pentahydrate is used instead of zirconium nitrate pentahydrate, while the other raw materials and steps are the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0051] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of yttrium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0052] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0053] Comparative Example 5 The difference from Example 1 is that the amount of oligochitosan with a molecular weight of 2000 is reduced to 0.1g, while the remaining raw materials and steps are the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0054] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0055] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0056] Comparative Example 6 The difference from Example 1 is that the amount of oligochitosan with a molecular weight of 2000 is increased to 1.2g, while the remaining raw materials and steps are the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0057] 1.2 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was then added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0058] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0059] Comparative Example 7 The difference from Example 1 is that the amount of zirconium nitrate pentahydrate is reduced to 0.5g, while the remaining raw materials and steps are the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0060] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 0.5 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0061] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0062] Comparative Example 8 The difference from Example 1 is that the amount of zirconium nitrate pentahydrate is increased to 3.6g, while the remaining raw materials and steps are the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0063] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 3.6 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0064] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0065] Comparative Example 9 The difference from Example 1 is that the 2000 molecular weight oligochitosan is replaced with a 500 molecular weight ultra-oligochitosan, while the other raw materials and steps remain the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0066] 0.33 g of ultra-oligomeric chitosan with a molecular weight of 500 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain an oligomeric chitosan suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the oligomeric chitosan suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0067] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0068] Comparative Example 10 The difference from Example 1 is that the oligochitosan with a molecular weight of 2000 is replaced with a medium-molecular-weight chitosan with a molecular weight of 8000; all other raw materials and steps remain the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0069] 0.33 g of medium-polymer chitosan with a molecular weight of 8000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain an oligomeric chitosan suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the oligomeric chitosan suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0070] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0071] Comparative Example 11 The difference from Example 1 is that polyvinyl alcohol 2000 is not added when preparing the chitosan-metal salt complex suspension; all other raw materials and steps are the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0072] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to about 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was then added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0073] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0074] Comparative Example 12 The difference from Example 1 is that, in preparing the chitosan-metal salt complex suspension, polyvinyl alcohol 2000 (containing a large number of hydroxyl groups) was replaced with an equal weight of aqueous polyamide wax slurry (containing no hydroxyl groups), while the remaining raw materials and steps remained the same. Specifically, this includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0075] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of aqueous polyamide wax paste was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0076] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 45g of the composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0077] Comparative Example 13 The difference from Example 1 is that, after preparing the zirconium nitrate solution and chitosan suspension, they are not first prepared into a complex suspension, but are directly added separately to the silica sol. All other raw materials and steps remain the same. Specifically, this includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0078] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to about 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. Then, 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly to obtain a zirconium nitrate solution.

[0079] Finally, silica sol, oligochitosan suspension, zirconium nitrate solution, and 0.25g of polyvinyl alcohol 2000 were mixed and stirred for 1.5h to obtain composite silica sol. 5g of mullite fiber felt was immersed in 45g of composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4h until gel formation, then aged at 30℃ for 36h. The mixture was replaced four times with anhydrous ethanol (10h each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5h to obtain hydrophobic silica aerogel insulation felt.

[0080] Comparative Example 14 The difference from Example 1 is that the ratio of fiber felt to composite silica sol is increased from 1:9 to 3:17, specifically including: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0081] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0082] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 15g of mullite fiber felt was immersed in 85g of composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, and then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol 4 times (10 hours each time), and finally dried with supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0083] Comparative Example 15 The difference from Example 1 is that the ratio of fiber felt to composite silica sol is reduced from 1:9 to 3:97, while the remaining raw materials and steps remain the same. Specifically, it includes: Mix 10.4g TEOS, 0.25g MTMS, 18.4g anhydrous ethanol and 3.6g deionized water, stir for 3.5h, add 0.83g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 22h to obtain silica sol.

[0084] 0.33 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 21.6 g of deionized water, and then 0.33 ml of glacial acetic acid was added to adjust the pH of the system to approximately 4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.2 g of zirconium nitrate pentahydrate was added to 18 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.25 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0085] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 h to obtain the composite silica sol. 3 g of mullite fiber felt was immersed in 97 g of the composite silica sol, and 0.15 g of glutaraldehyde and 0.3 g of epichlorohydrin were added. The mixture was allowed to stand for 4 h until gel formation, then aged at 30 °C for 36 h. The mixture was replaced with anhydrous ethanol four times (10 h each time), and finally dried under supercritical CO2 at 45 °C and 9 MPa for 5 h to obtain the hydrophobic silica aerogel insulation felt.

[0086] Example 2 Mix 12g TEOS, 0.15g MTMS, 24g anhydrous ethanol and 3g deionized water, stir for 4 hours, add 0.92g hydrochloric acid, adjust the pH to 2.2, and continue stirring for 20 hours to obtain silica sol.

[0087] 0.3 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 25 g of deionized water, and then 0.8 ml of glacial acetic acid was added to adjust the pH of the system to approximately 5. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 1.5 g of zirconium nitrate pentahydrate was added to 12 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 6 hours, and then 0.15 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0088] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 5g of mullite fiber felt was immersed in 95g of the composite silica sol, and 0.18g of glutaraldehyde and 0.4g of epichlorohydrin were added. The mixture was allowed to stand for 5 hours until gel formation, then aged at 35℃ for 40 hours. The mixture was replaced with anhydrous ethanol four times (10 hours each time), and finally dried under supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0089] Example 3 Take 22.5g TEOS, 0.75g MTMS, 37.5g anhydrous ethanol and 10.5g deionized water, mix them, stir for 3.5h, add 2.1g hydrochloric acid, adjust the pH to 2.4, and continue stirring for 22h to obtain silica sol.

[0090] 1.5 g of chitosan oligosaccharide with a molecular weight of 2000 was added to 49 g of deionized water, and then 1.6 ml of glacial acetic acid was added to adjust the pH of the system to approximately 5.4. The mixture was stirred evenly at room temperature to obtain a chitosan oligosaccharide suspension. 4.5 g of zirconium nitrate pentahydrate was then added to 28.5 g of deionized water and stirred evenly. This solution was then slowly added dropwise to the chitosan oligosaccharide suspension. The mixture was reacted at room temperature for 7 hours, and then 0.45 g of polyvinyl alcohol 2000 was added. The mixture was stirred for another 2 hours, and after standing to remove foam, a chitosan-metal salt complex suspension was obtained.

[0091] Finally, the silica sol and chitosan-metal salt complex suspension were mixed and stirred for 1.5 hours to obtain the composite silica sol. 10g of mullite fiber felt was immersed in 90g of composite silica sol, and 0.15g of glutaraldehyde and 0.3g of epichlorohydrin were added. The mixture was allowed to stand for 4 hours until gel formation, and then aged at 30℃ for 36 hours. The mixture was replaced with anhydrous ethanol 4 times (10 hours each time), and finally dried with supercritical CO2 at 45℃ and 9MPa for 5 hours to obtain the hydrophobic silica aerogel insulation felt.

[0092] Performance testing The silica aerogel insulation felts prepared in each embodiment and comparative example were tested for thermal conductivity, hydrophobicity (contact angle), tensile strength, and high-temperature stability (rate of change of thermal conductivity after being placed at 300℃ for 24 hours). The results are shown in Table 1. Table 1 The data comparison in the table above shows that: Compared with Example 1, Comparative Example 1 did not add zirconium nitrate pentahydrate, and the high temperature stability and tensile strength of the aerogel decreased significantly, indicating that zirconium nitrate pentahydrate can effectively improve the mechanical properties and high temperature stability of the material.

[0093] Compared to Example 1, Comparative Example 7 reduced the amount of zirconium nitrate pentahydrate. The reduced zirconium ions led to a corresponding decrease in zirconium dioxide formation. These nanoparticles are the cross-linking nodes of the network; insufficient content results in a loose network structure, a sharp drop in mechanical properties, and increased collapse of the aerogel pores after high-temperature resistance, leading to a higher rate of change in thermal conductivity. Conversely, Comparative Example 8 increased the amount of zirconium nitrate pentahydrate. This caused zirconium ions to easily aggregate, damaging the aerogel surface roughness and resulting in decreased hydrophobicity. It also blocked the aerogel nanopores, disrupting the core thermal insulation structure of "air trapped in nanopores," thus increasing the thermal conductivity.

[0094] Compared with Example 1, in Comparative Example 4, yttrium nitrate pentahydrate was used instead of zirconium nitrate pentahydrate, and the water contact angle decreased slightly. This is because the hydroxyl groups on the surface of yttrium trioxide generated by the decomposition of yttrium nitrate are more active and more easily adsorb water molecules in the environment, thus weakening the hydrophobic effect of the thermal insulation felt.

[0095] Compared with Example 1, no chitosan was added in Comparative Example 2, resulting in a decrease in the water contact angle and a deterioration in hydrophobicity. This indicates that the chitosan molecular chains can fix the hydrophobic methyl groups on the surface of silica sol and form complexes with Zr ions to promote the uniform dispersion of ZrO2. Without chitosan, the hydrophobic structure is incomplete and ZrO2 aggregates.

[0096] Compared to Example 1, Comparative Example 5 reduced the amount of chitosan added. Insufficient chitosan resulted in fewer crosslinking sites and poorer ZrO2 dispersion, leading to increased network defects and consequently lower tensile strength. The rate of change in thermal conductivity after high-temperature resistance also increased. Conversely, Comparative Example 6 increased the amount of chitosan added. Excessive chitosan agglomerates, clogging nanopores and damaging the surface hydrophobic microstructure. Therefore, the results showed a decrease in both the hydrophobicity and thermal insulation properties of the insulation felt.

[0097] Compared to Example 1, Comparative Example 9 used ultra-low-molecular-weight chitosan. When the molecular weight of chitosan is too low, although the amino and hydroxyl groups are more fully exposed, the segmental entanglement ability weakens, and the coordination binding force with zirconium ions deteriorates, making it impossible to form a stable three-dimensional cross-linked network. This results in a loose aerogel framework, forming more pore defects, and thus increasing the thermal conductivity. Comparative Example 10 used medium-molecular-weight chitosan. Medium-molecular-weight chitosan molecules have strong rigidity and poor water solubility, making them prone to molecular chain aggregation. This forms large-sized particles that block the nanopores of the aerogel, leading to an increase in thermal conductivity. Therefore, the molecular weight of chitosan needs to be controlled within the range of 1000-3000 to achieve a balance of reactivity, solubility, and dispersibility, forming a stable cross-linked network without blocking pores or damaging the hydrophobic structure.

[0098] Compared with Example 1, in Comparative Example 3, conventional drying was used instead of supercritical CO2 drying, which destroyed the porous structure of the aerogel, significantly increased the thermal conductivity, and reduced the high-temperature stability, indicating that supercritical drying is the key process to ensure thermal insulation performance.

[0099] Compared with Example 1, in Comparative Example 11, the overall performance was significantly worse because polyvinyl alcohol 2000 was not added when preparing the chitosan-metal salt complex suspension. This is because the polyvinyl alcohol molecular chain contains a large number of hydroxyl groups, which can be adsorbed on the surface of the chitosan-zirconium ion complex to form steric hindrance and avoid aggregation. Without it, the complex aggregates and precipitates, the composite silica sol separates, the porous structure is destroyed after drying, the interfacial bonding is loose, and the shrinkage of the silica aerogel network cannot be effectively inhibited after high temperature, thus the overall performance is reduced.

[0100] Compared with Example 1, in Comparative Example 12, polyvinyl alcohol 2000 was replaced with an equal weight of aqueous polyamide wax slurry when preparing the chitosan-metal salt complex suspension. The aqueous polyamide wax slurry anti-settling agent does not contain hydroxyl groups and cannot form hydrogen bonds with the chitosan-zirconium ion complex to build steric hindrance, which leads to the complex agglomeration to form large particles that block the nanopores. The composite silica sol is prone to stratification, and the porous structure is easily destroyed after drying. The interfacial bonding is loose, and it cannot effectively inhibit the shrinkage of the silica aerogel network after high temperature. Therefore, the thermal insulation, hydrophobicity and tensile strength are all reduced.

[0101] Compared with Example 1, in Comparative Example 13, after preparing the zirconium nitrate solution and chitosan suspension, the two were not first prepared into a complex suspension, but were directly added to the silica sol separately. This operation process causes the zirconium ions to hydrolyze and precipitate first, failing to form a stable complex with chitosan. This results in uneven dispersion of the system, the formation of high-density aggregates, and the lack of stable cross-linking sites in the network structure. These aggregates are prone to breakage under stress and cannot effectively suppress the collapse of the silica aerogel network at high temperatures, thus degrading performance.

[0102] Compared to Example 1, in Comparative Example 14, the ratio of fiber felt to composite silica sol was increased from 1:9 to 3:17. The excessively high proportion of fiber felt prevented the composite silica sol from fully wetting the surface and internal pores of the fiber felt, resulting in insufficient aerogel coverage and a reduced proportion of nanopores, thus decreasing thermal insulation performance. Conversely, in Comparative Example 15, the ratio of fiber felt to composite silica sol was decreased from 1:9 to 3:97. While the low proportion of fiber felt allowed the composite silica sol to fully encapsulate the fibers, improving thermal insulation and hydrophobicity, the aerogel itself was brittle and lacked sufficient fiber skeleton support, leading to a sharp drop in tensile strength. Furthermore, the lack of sufficient fiber skeleton support at high temperatures made it prone to collapse, resulting in an increased rate of change in thermal conductivity after high-temperature resistance.

Claims

1. A hydrophobic silica aerogel insulation felt, characterized in that: Includes fiber felt and hydrophobic silica aerogel layer attached to the surface of the fiber felt and the surface of its internal pores; The hydrophobic silica aerogel layer comprises the following raw materials in parts by weight: 30-40 parts silica sol, 30-40 parts chitosan-metal salt complex solution, 0.1-0.2 parts crosslinking agent, and 0.1-0.5 parts gelling agent; The silica sol comprises the following raw materials in parts by weight: 8-15 parts tetraethoxysilane, 0.1-0.5 parts methyltrimethoxysilane, pH adjuster, 16-25 parts anhydrous ethanol, and 2-7 parts water. The chitosan-metal salt complex solution comprises the following raw materials in parts by weight: 0.2-1 parts of oligochitosan, 1-3 parts of zirconium nitrate pentahydrate, pH adjuster, 0.1-0.3 parts of hydroxyl-containing anti-precipitant, and 30-45 parts of water.

2. The hydrophobic silica aerogel insulation felt according to claim 1, characterized in that: The fiber felt is a mullite fiber felt.

3. The hydrophobic silica aerogel insulation felt according to claim 1, characterized in that: The crosslinking agent includes one or more of glutaraldehyde and sodium tripolyphosphate; The gelling agent includes one or more of epichlorohydrin, KH-550, and KH-560.

4. The hydrophobic silica aerogel insulation felt according to claim 1, characterized in that: The molecular weight of the oligochitosan is 1000-3000; The anti-settling agent is polyvinyl alcohol 2000; The pH adjuster includes one or more of hydrochloric acid, glacial acetic acid, and formic acid.

5. A method for preparing a hydrophobic silica aerogel thermal insulation felt according to any one of claims 1-4, characterized in that... include: (1) Mix tetraethoxysilane, methyltrimethoxysilane, anhydrous ethanol and water evenly, add pH adjuster to lower pH to 2-2.5, stir evenly, and obtain silica sol; (2) Add oligochitosan to 20-25 parts of water, add pH adjuster to adjust the pH of the system to 4-6, stir evenly to obtain oligochitosan suspension; then add zirconium nitrate pentahydrate to 10-20 parts of water and stir evenly, then add dropwise to oligochitosan suspension, react, add anti-precipitant, stir evenly, let stand to defoam, and obtain chitosan-metal salt complex suspension; (3) Mix and stir the silica sol and chitosan-metal salt complex solution to obtain composite silica sol; immerse the fiber felt in the composite silica sol, add crosslinking agent and gelation agent, and after the gel is formed, perform aging, solvent replacement and supercritical drying to obtain hydrophobic silica aerogel insulation felt.

6. The preparation method according to claim 5, characterized in that: In step (2), the reaction conditions are: room temperature and 5-8 hours.

7. The preparation method according to claim 5, characterized in that: In step (3), the mass ratio of the fiber felt to the composite silica sol is 5:95-10:

90.

8. The preparation method according to claim 5 or 7, characterized in that: In step (3), the aging temperature is 20-50℃ and the time is 24-48h.

9. The preparation method according to claim 5, characterized in that: In step (3), the solvent used for solvent replacement is anhydrous ethanol, and the solvent replacement is performed 3-5 times, each time for 8-12 hours.

10. The preparation method according to claim 5, characterized in that: In step (3), the supercritical drying is supercritical CO2 drying, with a temperature of 40-50℃, a pressure of 8-10MPa, and a drying time of 4-10h.

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