A reinforced silica aerogel composite material and its preparation method

Abstract

This invention relates to the field of silica aerogel technology and discloses an enhanced silica aerogel composite material and its preparation method. Specifically, isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers are grafted onto the surface of amino-functionalized aramid fibers, amino-functionalized E-type glass fibers, and amino-functionalized mullite ceramic fibers via isocyanate-amino addition reaction to obtain alkyl long-chain POSS-type ethoxysilane functionalized composite fibers. Using tetraethyl orthosilicate as a precursor, silica sol is first generated through hydrolysis-condensation reaction. Then, the silica sol is modified by alkyl long-chain POSS-type ethoxysilane functionalized composite fibers through silanol condensation reaction. Finally, after aging and molding processes, an enhanced silica aerogel composite material is obtained, exhibiting a compressive strength ≥1.8MPa and a water contact angle >150°, demonstrating excellent mechanical and hydrophobic properties.

Description

Technical Field

[0001] This invention relates to the field of silica aerogel technology, specifically to an enhanced silica aerogel composite material and its preparation method. Background Technology

[0002] Silica aerogel is composed of a nanoscale porous structure and has a low density (3-500 mg / cm³). 3 High specific surface area (400-1500 m²) 2 New types of thermal insulation materials, characterized by high porosity (80-99.8%) and low thermal conductivity (0.01-0.03 W / (m·K)), have shown great application potential in thermal insulation fields such as construction, aerospace, and new energy. However, pure silica aerogel has poor mechanical properties, low toughness, and high brittleness, making it prone to breakage during drying or under external force, which limits its practical application in engineering.

[0003] Composite fiber reinforcement technology is a common method to improve the mechanical properties of silica aerogels. Among them, aramid fibers (excellent toughness and temperature resistance), ceramic fibers (excellent high-temperature stability), and glass fibers (good overall performance and low cost) are all ideal reinforcing materials for improving aerogel properties. However, conventional fibers are usually bonded to the porous aerogel matrix by weak forces, resulting in interfacial gaps that can easily lead to fiber reinforcement failure and defects such as powder shedding, cracking, and breakage in aerogel composites.

[0004] Furthermore, silica aerogels are mainly prepared via the sol-gel method. The resulting aerogels are rich in hydroxyl groups on their surface, making them highly susceptible to moisture absorption when exposed to humid environments for extended periods. This not only leads to increased thermal conductivity, deterioration of insulation performance, and increased load on the aerogel, but can also cause cracking or even failure, significantly shortening its service life. Therefore, hydrophobic modification of silica aerogels is crucial. Summary of the Invention

[0005] This invention utilizes aramid fibers, mullite ceramic fibers, and glass fibers to synergistically reinforce and modify silica aerogel. Addressing the issues of weak interfacial bonding between the fibers and the porous aerogel matrix and the easy water absorption of silica aerogel, a binding agent (isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer) with both a rigid POSS structure and hydrophobic alkyl long chains was developed. This agent is grafted onto the fiber surface through chemical bonding and embedded into the silica aerogel network through silanol condensation. This achieves strong interfacial bonding between the fibers and the aerogel matrix, as well as hydrophobic modification of the aerogel. The resulting reinforced silica aerogel composite material exhibits excellent mechanical and hydrophobic properties.

[0006] A method for preparing an enhanced silica aerogel composite material includes the following steps:

[0007] Step 1: Synthesize isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers;

[0008] Step 2: Isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers are grafted onto the surface of amino-functionalized fibers via isocyanate-amino addition reaction to obtain alkyl long-chain POSS-type ethoxysilane functionalized composite fibers.

[0009] The amino-functionalized fibers include amino-functionalized aramid fibers, amino-functionalized E-type glass fibers, and amino-functionalized mullite ceramic fibers, with a corresponding mass ratio of (3-5):(1-2):(1-3).

[0010] Step 3: Preparation of reinforced silica aerogel composite material, the preparation process is as follows:

[0011] Using tetraethyl orthosilicate as a precursor, silica sol is generated through a hydrolysis-condensation reaction.

[0012] An enhanced silica aerogel composite material was prepared by modifying silica sol through a silanol condensation reaction using alkyl long-chain POSS-type ethoxysilane functionalized composite fibers, followed by aging and molding processes.

[0013] Preferably, the method for preparing the isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer is as follows:

[0014] Using methyltrimethoxysilane and trimethoxysilane as raw materials, a hydrolysis-condensation method was adopted. The hydrolysis and condensation reaction of methyltrimethoxysilane and trimethoxysilane was catalyzed by concentrated hydrochloric acid, and the molar ratio of methyltrimethoxysilane to trimethoxysilane was controlled at 3.01-3.05:1 to generate hexamethylPOSS.

[0015] The reaction involves a nucleophilic substitution reaction between the -NH2 functional group of (3-aminopropyl)dimethylethoxysilane and the bromine functional group of an alkyl bromide monomer, with the molar ratio of (3-aminopropyl)dimethylethoxysilane to the alkyl bromide monomer controlled at 1:0.91-0.95, to generate intermediate I; wherein the alkyl bromide monomer is one of 1-bromooctane, 1-bromononane, 1-bromodecane, 1-bromoundecane, and 1-bromododecane.

[0016] Intermediate II is generated by a nucleophilic substitution reaction between the -NH- functional group of intermediate I and the bromine functional group of 3-bromopropene, with the molar ratio of intermediate I to 3-bromopropene controlled at 1:1.01-1.05.

[0017] Intermediate III is generated by the addition reaction of the alkenyl functional group of intermediate II with the Si-H functional group of hexamethylPOSS, and the molar ratio of intermediate II to hexamethylPOSS is controlled to be 0.91-0.95:1.

[0018] An addition reaction is carried out between the Si-H functional group of intermediate III and the alkenyl functional group of isocyanate methacrylate, and the molar ratio of intermediate III to isocyanate methacrylate is controlled to be 1:1.01-1.05, to generate an isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer.

[0019] Preferably, when the alkyl bromide monomer is 1-bromodecane, the isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer obtained isocyanate-based POSS-type decaalkylated ethoxysilane monomer.

[0020] Preferably, the amino-functionalized aramid fiber is prepared by treating aramid fibers with a diameter of 10-12 μm and a length of 5-8 mm with ammonia plasma.

[0021] Preferably, the amino-functionalized E-type glass fiber is prepared by modifying 8-12 parts by weight of hydrophilic glass fiber with a diameter of 8-12 μm and a length of 7-10 mm by 0.5-2 parts by weight of silane coupling agent KH-540 through a silanol-hydroxyl dehydration condensation reaction.

[0022] Preferably, the amino-functionalized mullite ceramic fiber is prepared by modifying 8-12 parts by weight of hydrophilic mullite ceramic fiber with a diameter of 8-10 μm and a length of 7-10 mm by 0.5-2 parts by weight of silane coupling agent KH-540 through a silanol-hydroxyl dehydration condensation reaction.

[0023] Preferably, the mass ratio of isocyanate-based POSS-type decaalkylated ethoxysilane monomer to amino-functionalized fiber in the alkyl long-chain POSS-type ethoxysilane functionalized composite fiber is 1:(4-8).

[0024] The raw materials for the reinforced silica aerogel composite material prepared according to the above method include: 45 parts by weight of tetraethyl orthosilicate and 10-20 parts by weight of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber.

[0025] Beneficial effects:

[0026] Based on molecular design mechanisms, this invention synthesizes isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers.

[0027] Isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers were grafted onto the surface of amino-functionalized aramid fibers, amino-functionalized E-type glass fibers, and amino-functionalized mullite ceramic fibers via isocyanate-amino addition reaction to obtain alkyl long-chain POSS-type ethoxysilane functionalized composite fibers.

[0028] Using tetraethyl orthosilicate as a precursor, silica sol is first generated through hydrolysis-condensation reaction. Then, the silica sol is modified by alkyl long-chain POSS-type ethoxysilane functionalized composite fibers through silanol condensation reaction. Finally, after aging and molding processes, an enhanced silica aerogel composite material is obtained.

[0029] The reinforced silica aerogel composite material prepared by this invention has a compressive strength ≥1.8MPa and a water contact angle >150°, exhibiting excellent mechanical and hydrophobic properties. Detailed Implementation

[0030] Example 1:

[0031] The specific process for synthesizing isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers is as follows:

[0032] Process 1: Using methyltrimethoxysilane (CAS No. 1185-55-3) and trimethoxysilane (CAS No. 2487-90-3) as raw materials, a hydrolysis-condensation method is employed. The hydrolysis and condensation reaction of methyltrimethoxysilane and trimethoxysilane is catalyzed by concentrated hydrochloric acid, and the molar ratio of methyltrimethoxysilane to trimethoxysilane is controlled at 3.03:1, to generate hexamethylPOSS, whose chemical structural formula is as follows:

[0033] ;

[0034] Process 2: A nucleophilic substitution reaction occurs between the -NH2 functional group of (3-aminopropyl)dimethylethoxysilane (CAS No. 18306-79-1) and the bromine functional group of an alkyl bromide monomer, with the molar ratio of (3-aminopropyl)dimethylethoxysilane to the alkyl bromide monomer controlled at 1:0.94, to generate intermediate I, whose chemical structural formula is as follows:

[0035] ;

[0036] The alkyl bromide monomer can be selected from one of 1-bromooctane, 1-bromononane, 1-bromodecane, 1-bromoundecane, and 1-bromododecane;

[0037] Process 3: A nucleophilic substitution reaction occurs between the -NH- functional group of intermediate I and the bromine functional group of 3-bromopropene, with the molar ratio of intermediate I to 3-bromopropene controlled at 1:1.02, to generate intermediate II, whose chemical structural formula is as follows:

[0038] ;

[0039] Process 4: An addition reaction occurs between the alkenyl functional group of intermediate II and the Si-H functional group of hexamethylPOSS, and the molar ratio of intermediate II to hexamethylPOSS is controlled at 0.94:1 to generate intermediate III, whose chemical structural formula is as follows:

[0040] ;

[0041] Step 5: An addition reaction occurs between the Si-H functional group of intermediate III and the alkenyl functional group of isocyanate methacrylate, with the molar ratio of intermediate III to isocyanate methacrylate controlled at 1:1.03, to generate an isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer. Its chemical structural formula is as follows:

[0042] ;

[0043] Based on this, when 1-bromodecane is chosen as the alkyl bromide monomer, an isocyanate-based POSS-type decaalkylated ethoxysilane monomer is synthesized, with the following chemical structural formula:

[0044] ;

[0045] The specific experimental steps for synthesizing isocyanate-based POSS-type decaalkylated ethoxysilane monomers are as follows:

[0046] Under nitrogen protection, 100 mL of anhydrous ethanol, 5 mL of deionized water, and 4 mL of concentrated hydrochloric acid were added to a three-necked flask and stirred at room temperature for 5 min. Then, 20 mL of a mixed solution of methyltrimethoxysilane and trimethoxysilane (prepared from 12.3 g of methyltrimethoxysilane, 3.7 g of trimethoxysilane, and 20 mL of anhydrous ethanol) was added dropwise to the three-necked flask. The mixture was heated to 50 °C and stirred for 4 h. After cooling to room temperature, the mixture was stirred for 40 h. The mixture was filtered, washed with a 1:1 volume ratio of tetrahydrofuran and methanol, and dried to obtain hexamethylPOSS.

[0047] The 1H NMR spectrum of hexamethylPOSS is characterized as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.14 (s, 18H), 2.82 (s, 2H);

[0048] Under nitrogen protection, 3.2 g of (3-aminopropyl)dimethylethoxysilane and 30 mL of anhydrous tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 30 mL of anhydrous tetrahydrofuran solution containing 4.2 g of 1-bromodecane and 1.5 mL of triethylamine were added dropwise to the three-necked flask. The mixture was heated to 60 °C and stirred for 5 h. After cooling to room temperature, the solvent was removed by rotary evaporation. The mixture was washed with anhydrous ethanol and dried to obtain intermediate I.

[0049] Under nitrogen protection, 4.5 g of intermediate I and 40 mL of anhydrous tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 10 mL of anhydrous tetrahydrofuran solution containing 1.8 g of 3-bromopropene and 1.1 mL of triethylamine were added dropwise to the three-necked flask. The mixture was heated to 70 °C and stirred for 5 h. After cooling to room temperature, the solvent was removed by rotary evaporation. The mixture was washed with anhydrous ethanol and dried to obtain intermediate II.

[0050] Under nitrogen protection, 5.1 g of hexamethylPOSS and 50 mL of anhydrous tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 30 mL of anhydrous tetrahydrofuran solution containing 3.2 g of intermediate II and 5 drops of castor catalyst were added dropwise to the three-necked flask. The mixture was heated to 70 °C and stirred for 6 h. After cooling to room temperature, the solvent was removed by rotary evaporation. The mixture was washed with anhydrous ethanol and dried to obtain intermediate III.

[0051] Under nitrogen protection, 4.2 g of intermediate III and 40 mL of anhydrous tetrahydrofuran were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 10 mL of anhydrous tetrahydrofuran solution containing 1.6 g of isocyanate methacrylate and 3 drops of caster catalyst were added dropwise to the three-necked flask. The mixture was heated to 50 °C and stirred for 10 h. After cooling to room temperature, the solvent was removed by rotary evaporation. The mixture was washed with anhydrous ethanol and dried to obtain isocyanate-based POSS-type decaalkylated ethoxysilane monomer.

[0052] The 1H NMR characterization of isocyanate-based POSS-type decaalkylated ethoxysilane monomers is as follows: 1 H NMR (CDCl3, 400MHz) δ: 0.09 (s, 18H), 0.18 (s, 6H), 0.60-0.63 (t, 2H), 0.75-0.78 (t, 2H), 0.87-0.91 (t, 3H), 0.95-0.97 (d, 2H), 1.06 -1.11(m, 6H), 1.23-1.65(m, 20H), 2.36-2.50(m, 7H), 3.29-3.33(t, 2H), 3.65-3.71(m, 2H), 4.44-4.48(t, 2H).

[0053] Example 2:

[0054] The preparation steps for alkyl long-chain POSS-type ethoxysilane functionalized composite fibers are as follows:

[0055] The first step is to prepare amino-functionalized aramid fibers: Aramid fibers are modified by ammonia plasma to introduce amino groups onto the fiber surface, thus obtaining amino-functionalized aramid fibers. The specific preparation method is as follows: Aramid fibers (diameter 10-12μm, length 5-8mm) are placed in acetone solvent, ultrasonically washed for 30min, and then soaked for 24h. They are repeatedly washed with deionized water until there is no irritating odor, dried, and placed in a cold plasma treatment chamber. The chamber pressure is evacuated to 2Pa, and ammonia gas is introduced at a flow rate of 3L / min to maintain a pressure of 8Pa. The chamber is then evacuated to 2Pa. The ammonia gas is rinsed three times. Ammonia gas is introduced into the treatment chamber again to maintain a chamber pressure of 30Pa. The radio frequency plasma power supply (frequency 13.56MHz) is started, and the treatment power is set to 80W and the treatment time to 30s to obtain amino-functionalized aramid fibers.

[0056] The second step is to prepare amino-functionalized glass fiber: The silanol functional groups obtained by the hydrolysis of silane coupling agent KH-540 (3-aminopropyltrimethoxysilane) undergo a dehydration condensation reaction with the hydroxyl functional groups abundant on the surface of hydrophilic glass fiber to obtain amino-functionalized glass fiber. The specific preparation method is as follows: 10g of hydrophilic E-type glass fiber (diameter 8-12μm, length 7-10mm), 10mL of deionized water, and 90mL of anhydrous ethanol are added to a three-necked flask. The mixture is ultrasonically dispersed for 1h and stirred at room temperature for 2h. Then, 10mL of an ethanol aqueous solution containing 1g of silane coupling agent KH-540 (volume ratio of anhydrous ethanol to deionized water is 4:1) and 2 drops of glacial acetic acid are added dropwise to the three-necked flask. The mixture is heated to 60℃ and stirred for 5h. After cooling to room temperature, the mixture is filtered and separated. The fibers are repeatedly washed with deionized water and dried to obtain amino-functionalized glass fiber.

[0057] The third step is to prepare amino-functionalized mullite ceramic fibers: The silanol functional groups obtained by the hydrolysis reaction of the silane coupling agent KH-540 (3-aminopropyltrimethoxysilane) undergo a dehydration condensation reaction with the hydroxyl functional groups abundant on the surface of the mullite ceramic fibers to obtain amino-functionalized mullite ceramic fibers. The specific preparation method is the same as that for the preparation experiment of amino-functionalized glass fibers, except that hydrophilic mullite ceramic fibers (diameter 8-10 μm, length 7-10 mm) are used instead of hydrophilic E-type glass fibers (diameter 8-12 μm, length 7-10 mm).

[0058] The preparation method of hydrophilic mullite ceramic fiber is as follows: 20g of mullite ceramic fiber (diameter 8-10μm, length 7-10mm) and 200mL of sodium hydroxide aqueous solution (10wt%) are added to a round bottom flask, ultrasonically dispersed for 10min, heated to 60℃ and stirred for 2h, filtered and separated, repeatedly washed with deionized water, and dried to obtain hydrophilic mullite ceramic fiber;

[0059] The fourth step is the preparation of alkyl long-chain POSS-type ethoxysilane functionalized composite fibers: An addition reaction is achieved between the isocyanate groups in the isocyanate-based POSS-type decaalkylated ethoxysilane monomer and the amino functional groups on the surface of amino-functionalized aramid fibers, amino-functionalized glass fibers, and amino-functionalized mullite ceramic fibers. This grafting modification of aramid fibers, glass fibers, and mullite ceramic fibers by the isocyanate-based POSS-type decaalkylated ethoxysilane monomer yields alkyl long-chain POSS-type ethoxysilane functionalized composite fibers. The specific preparation method is as follows: Under nitrogen protection, ... 8g of amino-functionalized aramid fiber, 3g of amino-functionalized glass fiber, 4g of amino-functionalized mullite ceramic fiber, and 150mL of anhydrous tetrahydrofuran were added to a three-necked flask. The mixture was ultrasonically dispersed for 1h and stirred at room temperature for 2h. Then, 10mL of anhydrous tetrahydrofuran solution containing 3g of isocyanate-based POSS-type decaalkylated ethoxysilane monomer and 2 drops of dibutyltin dilaurate (catalyst) were added dropwise to the three-necked flask. The mixture was heated to 50℃ and stirred for 6h. After cooling to room temperature, the mixture was filtered and separated. The fibers were washed with anhydrous ethanol and dried to obtain alkyl long-chain POSS-type ethoxysilane functionalized composite fibers.

[0060] Example 3:

[0061] A reinforced silica aerogel composite material I was prepared, the raw materials of which included: 45 parts by weight of tetraethyl orthosilicate and 15 parts by weight of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber. The preparation process is as follows:

[0062] (1) Preparation of silica sol: Using tetraethyl orthosilicate as a precursor, silica sol is generated through hydrolysis-condensation reaction. The specific preparation steps are as follows: 45g of tetraethyl orthosilicate, 20mL of anhydrous ethanol and 5mL of deionized water are added to the reaction vessel and stirred for 10min. The pH of the system is adjusted to 3.0 using 0.1mol / L hydrochloric acid aqueous solution. The temperature is raised to 40℃ and stirred for 2h to obtain transparent and uniform silica sol.

[0063] The viscosity of the silica sol was determined to be 5.0 mPa·s according to the standard GB / T 10247-2008 "Viscosity Measurement Method".

[0064] (2) Preparation of composite fiber modified wet gel I: Silica sol is modified using alkyl long-chain POSS-type ethoxysilane functionalized composite fibers. The silanol functional groups obtained by the hydrolysis of ethoxy groups on the surface of the alkyl long-chain POSS-type ethoxysilane functionalized composite fibers undergo a dehydration condensation reaction with the silanol functional groups abundant in the silica sol to obtain composite fiber modified wet gel I. The specific preparation steps are as follows:

[0065] 15g of alkyl long-chain POSS type ethoxysilane functionalized composite fiber, 80mL of anhydrous ethanol and 30mL of deionized water were added to a dispersion tank, ultrasonically dispersed for 40min, stirred at room temperature for 30min, and allowed to stand for 45min without sedimentation to obtain fiber dispersion.

[0066] The fiber dispersion was slowly injected into the silica sol prepared in process (1), stirred for 20 min to mix evenly, and the pH of the system was adjusted to 8.0 using 0.5 mol / L ammonia water. After stirring for 10 min, it was quickly poured into a mold of a preset shape, heated to 50℃ and kept at a constant temperature for 10 h to obtain composite fiber modified wet gel I.

[0067] (3) Preparation of reinforced silica aerogel composite material I: The composite fiber modified wet gel I was aged and dried to obtain reinforced silica aerogel composite material I. The specific preparation steps are as follows: The composite fiber modified wet gel I was immersed in anhydrous ethanol and aged at 50°C for 60 hours. The ethanol was replaced every 12 hours. After aging, supercritical CO2 drying was used. The temperature was set at 40°C, the pressure at 8MPa, and the drying time at 12 hours. The material was then naturally cooled to room temperature to obtain reinforced silica aerogel composite material I.

[0068] Example 4:

[0069] The preparation of reinforced silica aerogel composite material II includes 45 parts by weight of tetraethyl orthosilicate and 10 parts by weight of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber. The preparation process is the same as that of reinforced silica aerogel composite material I, except that 10g of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber is used instead of 15g of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber.

[0070] Example 5:

[0071] The preparation of reinforced silica aerogel composite material III includes 45 parts by weight of tetraethyl orthosilicate and 20 parts by weight of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber. The preparation process is the same as that of reinforced silica aerogel composite material I, except that 20g of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber is used instead of 15g of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber.

[0072] Comparative Example 1:

[0073] The silica aerogel composite material a was prepared by means of raw materials including 45 parts by weight of tetraethyl orthosilicate and 15 parts by weight of composite fiber a. The preparation process was the same as that of the preparation experiment of reinforced silica aerogel composite material I. The only difference was that 15g of alkyl long chain POSS type ethoxysilane functionalized composite fiber was replaced by 15g of composite fiber a.

[0074] The preparation method of composite fiber a is as follows: 8g of aramid fiber, 3g of hydrophilic E-type glass fiber, 4g of hydrophilic mullite ceramic fiber and 150mL of anhydrous ethanol are added to a three-necked flask, ultrasonically dispersed for 1h, stirred at room temperature for 2h, filtered and separated, and dried to obtain composite fiber a.

[0075] Comparative Example 2:

[0076] The silica aerogel composite material b was prepared by means of 45 parts by weight of tetraethyl orthosilicate and 15 parts by weight of composite fiber b. The preparation process was the same as that of the preparation experiment of reinforced silica aerogel composite material I. The only difference was that 15g of alkyl long chain POSS type ethoxysilane functionalized composite fiber was replaced by 15g of composite fiber b.

[0077] The preparation method of composite fiber b is as follows: 8g of aramid fiber, 3g of hydrophilic E-type glass fiber, 4g of hydrophilic mullite ceramic fiber and 150mL of anhydrous ethanol are added to a three-necked flask, ultrasonically dispersed for 1h, stirred at room temperature for 2h, and then 10mL of an ethanol aqueous solution containing 3g of methyltrimethoxysilane (a commonly used hydrophobic modifier for the surface treatment of silica aerogel and hydrophilic fibers) is added dropwise to the three-necked flask (the volume ratio of anhydrous ethanol to deionized water is 4:1). The mixture is heated to 60℃ and stirred for 5h, cooled to room temperature, filtered and separated, repeatedly washed with deionized water, and dried to obtain composite fiber b.

[0078] Performance testing:

[0079] (1) Mechanical property test: The sample was cut into 10mm×10mm×8mm (length×width×thickness) size. The parallelism of the upper and lower surfaces of the sample was controlled to be ≤0.1mm and the thickness deviation was ≤0.2mm. The sample was tested for compression performance using a CMT4104 universal testing machine. The thickness direction was the direction of force, the compression speed was 1mm / min, and the compression strength (i.e., the compressive strength) of the sample at 20% deformation was recorded.

[0080] (2) Hydrophobicity test: The water contact angle of the sample was tested using a JC2000 contact angle meter. The specific test steps were as follows: the sample was placed stably on the stage of the contact angle meter, and 4 μL of pure water was dropped onto the sample surface using a micro syringe (the test environment temperature was controlled at 25℃ and the relative humidity was maintained at 50%). When the droplet was stable, the water contact angle of the sample surface was measured.

[0081] The results of the above performance experiments are shown in Table 1.

[0082] Table 1. Experimental results of the performance of reinforced silica aerogel composites

[0083] Sample type performance indicators Reinforced silica aerogel composite material I Reinforced silica aerogel composite material II Reinforced silica aerogel composite material III Comparative Example 1 Comparative Example 2 Compressive strength (MPa) 2.3 1.8 2.5 1.0 1.1 Water contact angle (°) 155.2 150.6 158.3 0 (Water droplets are absorbed) 102.8

[0084] A comprehensive analysis of the above experimental results leads to the following conclusions:

[0085] (1) This invention utilizes self-developed isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers to modify aramid fibers, glass fibers and mullite ceramic fibers. The resulting reinforced silica aerogel composite material has a compressive strength ≥1.8MPa, which is a significant improvement in mechanical properties compared to conventional silica aerogel composite materials.

[0086] (2) The water contact angle of the enhanced silica aerogel composite material prepared in this invention is >150°, which is a superhydrophobic material.

Claims

1. A method for preparing an enhanced silica aerogel composite material, characterized in that, Includes the following steps: Step 1: Synthesize isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers, whose chemical structural formula is as follows: ； Step 2: Isocyanate-based POSS-type alkyl long-chain ethoxysilane monomers are grafted onto the surface of amino-functionalized fibers via isocyanate-amino addition reaction to obtain alkyl long-chain POSS-type ethoxysilane functionalized composite fibers. The amino-functionalized fibers include amino-functionalized aramid fibers, amino-functionalized E-type glass fibers, and amino-functionalized mullite ceramic fibers, with a corresponding mass ratio of (3-5):(1-2):(1-3). Step 3: Preparation of reinforced silica aerogel composite material, the preparation process is as follows: Using tetraethyl orthosilicate as a precursor, silica sol is generated through a hydrolysis-condensation reaction. An enhanced silica aerogel composite material was prepared by modifying silica sol through a silanol condensation reaction using alkyl long-chain POSS-type ethoxysilane functionalized composite fibers, followed by aging and molding processes.

2. The method for preparing an enhanced silica aerogel composite material according to claim 1, characterized in that, The method for preparing the isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer is as follows: Using methyltrimethoxysilane and trimethoxysilane as raw materials, a hydrolysis-condensation method was adopted. The hydrolysis and condensation reaction of methyltrimethoxysilane and trimethoxysilane was catalyzed by concentrated hydrochloric acid, and the molar ratio of methyltrimethoxysilane to trimethoxysilane was controlled at 3.01-3.05:1 to generate hexamethylPOSS. The reaction involves a nucleophilic substitution reaction between the -NH2 functional group of (3-aminopropyl)dimethylethoxysilane and the bromine functional group of an alkyl bromide monomer, with the molar ratio of (3-aminopropyl)dimethylethoxysilane to the alkyl bromide monomer controlled at 1:0.91-0.95, to generate intermediate I; wherein the alkyl bromide monomer is one of 1-bromooctane, 1-bromononane, 1-bromodecane, 1-bromoundecane, and 1-bromododecane. Intermediate II is generated by a nucleophilic substitution reaction between the -NH- functional group of intermediate I and the bromine functional group of 3-bromopropene, with the molar ratio of intermediate I to 3-bromopropene controlled at 1:1.01-1.

05. Intermediate III is generated by the addition reaction of the alkenyl functional group of intermediate II with the Si-H functional group of hexamethylPOSS, and the molar ratio of intermediate II to hexamethylPOSS is controlled to be 0.91-0.95:

1. An addition reaction is carried out between the Si-H functional group of intermediate III and the alkenyl functional group of isocyanate methacrylate, and the molar ratio of intermediate III to isocyanate methacrylate is controlled to be 1:1.01-1.05, to generate an isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer.

3. The method for preparing an enhanced silica aerogel composite material according to claim 2, characterized in that, When the alkyl bromide monomer is 1-bromodecane, the chemical structural formula of the isocyanate-based POSS-type alkyl long-chain ethoxysilane monomer obtained is as follows: 。 4. The method for preparing an enhanced silica aerogel composite material according to claim 1, characterized in that, The amino-functionalized aramid fiber is prepared by treating aramid fibers with a diameter of 10-12 μm and a length of 5-8 mm with ammonia plasma.

5. The method for preparing an enhanced silica aerogel composite material according to claim 1, characterized in that, The amino-functionalized E-type glass fiber is prepared by modifying 8-12 parts by weight of hydrophilic glass fiber with a diameter of 8-12 μm and a length of 7-10 mm by 0.5-2 parts by weight of silane coupling agent KH-540 through a silanol-hydroxyl dehydration condensation reaction.

6. The method for preparing an enhanced silica aerogel composite material according to claim 1, characterized in that, The amino-functionalized mullite ceramic fiber is prepared by modifying 8-12 parts by weight of hydrophilic mullite ceramic fiber with a diameter of 8-10 μm and a length of 7-10 mm by 0.5-2 parts by weight of silane coupling agent KH-540 through a silanol-hydroxyl dehydration condensation reaction.

7. The method for preparing an enhanced silica aerogel composite material according to claim 1, characterized in that, The mass ratio of isocyanate-based POSS-type decaalkylated ethoxysilane monomer to amino-functionalized fiber in the alkyl long-chain POSS-type ethoxysilane functionalized composite fiber is 1:(4-8).

8. A reinforced silica aerogel composite material prepared by the method according to any one of claims 1-7, characterized in that, The raw materials for the reinforced silica aerogel composite material include: 45 parts by weight of tetraethyl orthosilicate and 10-20 parts by weight of alkyl long-chain POSS-type ethoxysilane functionalized composite fiber.

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