High-flexibility high-temperature-resistant silicon-based aerogel and preparation method thereof

Abstract

The invention provides high-flexibility high-temperature-resistant silicon-based aerogel and a preparation method thereof. The preparation method of the silicon-based aerogel comprises the following steps: (1) uniformly mixing polyvinyl alcohol, methyltrimethoxysilane and glutaraldehyde, adjusting the pH value of a system to 4-5, stirring for 1.5-2 hours at normal temperature, adjusting the pH value of the system to 8-9, standing to obtain wet gel, and aging and drying to obtain gel; (2) soaking the gel obtained in the step (1) into an ethanol solution of aluminum isopropoxide, reacting at 55-65 DEG C for 3.5-6 hours, and taking out the gel; and (3) immersing the system obtained in the step (2) into an aqueous solution of zirconium oxychloride, and reacting at 75-85 DEG C for 1.5-3 hours. The silicon-based aerogel obtained through the preparation method has good brittleness and good high-temperature resistance, and the problem that the brittleness and the high-temperature resistance of traditional aerogel cannot be considered at the same time is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aerogels, and more particularly, to a high-flexibility high-temperature-resistant silicon-based aerogel and a preparation method thereof. BACKGROUND

[0002] The common problem of ambient drying aerogel powder is high brittleness (crushing after compression deformation > 80%) and insufficient hydrophobicity (contact angle < 130°), which leads to particle breakage during transportation and use. Traditional modification methods (such as hexamethyldisilazane) require high-temperature treatment (> 120℃), which is energy-consuming and easy to cause particle agglomeration.

[0003] The current mainstream production process still has some problems in practice: insufficient flexibility: fiber reinforcement easily leads to a decrease in porosity, low chemical bonding strength, and easy powder loss during drying; temperature resistance limitation: single metal oxide deposition easily causes lattice diffusion with SiO2 at high temperatures, leading to interface failure; complex process: multiple steps of solvent replacement or supercritical drying are required, which is high in cost and difficult to scale up.

[0004] CN115108809A introduces a preparation method of a high-temperature-resistant modified silica aerogel thermal insulation composite material. The method uses fiber reinforcement, which easily leads to a decrease in porosity, low chemical bonding strength, and easy powder loss during drying. SUMMARY

[0005] The first object of the present application is to provide a preparation method of a silicon-based aerogel, which has low density, low thermal conductivity, high hydrophobicity, and high elasticity.

[0006] The preparation method of the silicon-based aerogel provided by the present application comprises the following steps: (1) uniformly mix polyvinyl alcohol, methyltrimethoxysilane, and glutaraldehyde, adjust the pH of the system to 4-5, stir at room temperature for 1.5-2 h, then adjust the pH of the system to 8-9, and stand to obtain a wet gel, which is aged and dried to obtain a gel; (2) immerse the gel obtained in step (1) in an isopropyl alcohol aluminum ethanolic solution, react at 55-65℃ for 3.5-6 h, and take out the gel; (3) immerse the gel obtained in step (2) in a zirconium oxychloride aqueous solution, react at 75-85℃ for 1.5-3 h.

[0007] The present application prepares a gel from polyvinyl alcohol PVA, methyltrimethoxysilane MTMS and glutaraldehyde GA, then the obtained gel is immersed in an ethanol solution of aluminum isopropyl alcohol for reaction, and then immersed in an aqueous solution of aluminum oxychloride for reaction, so that the obtained silica-based aerogel has good brittleness (good elongation at break, low drying shrinkage) and good high-temperature resistance (no agglomeration occurs at high temperature), solving the problem that traditional aerogels cannot have both brittleness and high-temperature resistance. Although traditional silica aerogels have high-temperature resistance, they are inherently brittle, and the traditional silica aerogels will sinter and densify at high temperature (> 800℃), losing the porous structure, and the silica-based aerogel prepared by the present application effectively solves this problem.

[0008] The silica-based aerogel prepared by the preparation method provided by the present application can also achieve the same compressive strength, bending failure load and tensile strength effect without using fiber reinforcement, and has low powder falling rate.

[0009] In a preferred embodiment of the present application, in step (1), the mass ratio of polyvinyl alcohol, methyltrimethoxysilane and glutaraldehyde is (0.8-1.2):(1.8-2.1):(1.0-1.8), preferably 1:(1.8-2.1):(1.0-1.8). In the present application, if the amount of polyvinyl alcohol PVA is too small, the obtained product has very low gel strength and poor mechanical properties, and if the amount of polyvinyl alcohol PVA is too large, the obtained product has increased density, low hydrophobicity and poor heat resistance. When the proportion of methyltrimethoxysilane is too large, the obtained product has uneven structure and is prone to cracking. When the proportion of glutaraldehyde GA is too small, the obtained product has low strength and is prone to cracking, and has very low porosity, and when the proportion of glutaraldehyde GA is too large, the obtained gel is brittle and has low specific surface area.

[0010] In step (1) of the present application, when the pH value is too large (weakly acidic) in the acidic pH value (4-5), condensation is greater than hydrolysis, and complete hydrolysis cannot be achieved; when the pH value is too large (strongly acidic), subsequent gel crosslinking is difficult.

[0011] In step (1) of the present application, after the acid is adjusted to be acidic (pH=4-5) and reacted at room temperature for 1.5-2h, the hydrolysis reaction is completely, which can effectively ensure that the performance of the final product reaches the best. After the reaction is completed, the pH of the system is adjusted to 8-9, and when the pH value is adjusted to be too large (the stronger the alkalinity), the condensation rate is too fast, the gel density is large, and the final product has small pores; and when the pH value of the system is adjusted to be too small (the alkalinity is too weak, and the closer to neutral), the gel time is long, the specific surface area is small, and the product has large pores.

[0012] In a preferred embodiment of the present application, the step of "aging" in step (1) comprises: adding ethanol and aging for 24h~48h, and the amount of ethanol used can be the amount commonly used in the art for aging with ethanol, usually just enough to immerse the gel.

[0013] In the present application, the preparation method provided by the present application only needs to be dried under normal pressure. In a preferred embodiment of the present application, the step of "drying" in step (1) comprises: drying at 60℃~70℃ under normal pressure for 12h~15h. In this drying step, too long drying time will cause the obtained gel to shrink and crack. In an alternative embodiment of the present application, if the aging step is performed by adding ethanol, the ethanol needs to be removed before drying after the aging is completed.

[0014] In a preferred embodiment of the present application, in step (2), the concentration of the ethanol solution of aluminum isopropoxide is 0.08mol / L~0.12mol / L. In the steps given in the present application, the concentration value of aluminum isopropoxide is important for the performance of the obtained product. If the concentration value of the ethanol solution of aluminum isopropoxide is too low, the modification effect of the obtained product is poor, and the mechanical and thermal stability performance is not significantly improved. If the concentration value is too high, the obtained product has a large density, the modification is not uniform, and the porosity and specific surface area decrease. In the present application, on the basis of ensuring the above concentration value, the amount of the ethanol solution of aluminum isopropoxide only needs to be just enough to immerse the aerogel. At the same time, in this step, the applicant has found through a large number of experiments that when the reaction time is short, the modification effect is not obvious, and the mechanical property improvement is limited, and at the same time, the surface energy may change slightly to affect the hydrophobicity. When the reaction time is too long, the aluminum isopropoxide may not only deposit on the skeleton, but also nucleate, grow in the pores, form an excessively thick aluminum oxide coating or independent aluminum oxide particles, and seriously block the nanometer pores of the gel, causing the product to crack during the drying process. When the reaction temperature is too low, the reaction rate is slow. When the reaction temperature is too high, the reaction rate is extremely fast, the reaction is difficult to control, and at the same time, the aluminum isopropoxide will undergo severe hydrolysis and condensation, and may not have time to uniformly bond with the silicon network before precipitating as aluminum oxide particles. At the same time, rapid evaporation of the solvent will cause the gel to shrink and crack.

[0015] In the present application, this step is one of the core points of the present application. In a preferred embodiment of the present application, in step (3), the concentration of the aqueous solution of zirconium oxychloride is 0.04 mol / L to 0.08 mol / L. The amount of the aqueous solution of zirconium oxychloride is 400 mL to 500 mL. In this step, too little amount and too low concentration of the aqueous solution of zirconium oxychloride will result in low strength, large shrinkage, high density, low porosity, and poor thermal insulation performance of the aerogel, and even the formation of a complete block body. Too much amount and too high concentration of the aqueous solution of zirconium oxychloride will result in the plugging of the aerogel pore, the increase of the density, the possible cracking, and the decrease of the specific surface area. At the same time, in this step (3), too short reaction time will limit the improvement of the mechanical strength and the thermal stability, and the specific surface area may be slightly reduced due to slight plugging of the surface. Too long reaction time will increase the density of the product, and uneven excessive deposition may cause cracking during the drying process. Too high reaction temperature will destroy the fine nano-network of the gel, resulting in the collapse or crushing of the overall structure. High density, low porosity, and poor thermal insulation performance.

[0016] As mentioned above, the preparation method provided by the present application is particularly suitable for preparing aerogels under normal pressure drying. That is, after the gel after the reaction with the aqueous solution of zirconium oxychloride is taken out, it is dried under normal pressure. The drying conditions are preferably 3 to 5℃ / min to 450 to 550℃ in air under normal pressure for 2 to 3.5h. In this drying step, when the heating rate is low, the obtained aerogel has high density, low specific surface area, and poor thermal insulation performance, but the structure may be more uniform and the risk of cracking is lower. If the heating rate is high, the obtained aerogel is prone to cracking and crushing, the yield is very low, and the mechanical properties and ultra-low thermal conductivity are destroyed. When the drying temperature is low, the obtained aerogel has low strength, poor stability (may further shrink later), and impure chemical composition. When the drying temperature is too high, the obtained aerogel has small porosity and specific surface area, and the product may be glassy. Too short drying time will result in suboptimal performance of the obtained aerogel, possible defects, and poor stability. Too long drying time will result in a certain degree of loss of the specific surface area and porosity of the obtained aerogel, and a slight decrease in the thermal insulation performance.

[0017] Another object of the present application is to provide the silicon-based aerogel obtained by the above preparation method.

[0018] The silicon-based aerogel obtained by the present application has a thermal conductivity of 0.020 (W / m*k), and a density of only 0.017g / cm 3 ~0.035g / cm 3 While the density of the ceramic fiber sheet is 0.050g / cm 3 at the same thermal conductivity. The silicon-based aerogel obtained by the present application can replace the traditional ceramic fiber sheet in the field of new energy battery thermal insulation, and can effectively improve the safety and energy density of the battery pack.

[0019] That is, still another object of the present application is to provide the use of the above-mentioned silica-based aerogel in the preparation of thermal insulation materials for new energy batteries.

[0020] The present application has the following beneficial effects: The silica-based aerogel obtained by using polyvinyl alcohol and methyltrimethoxysilane and glutaraldehyde as raw materials, and then sequentially immersing the obtained gel in an isopropyl alcohol solution of aluminum alcohol and a zirconium oxychloride aqueous solution to obtain the silica-based aerogel solves the contradiction between the brittleness and high-temperature failure of traditional aerogels. The silica-based aerogel obtained by the present application still has good stability at high temperatures above 800℃ (preferably 1000℃), the porosity is basically unchanged, and the porous structure does not change.

[0021] The present application sequentially deposits Al2O3 and ZrO2 double metal oxide layers on the surface of the aerogel obtained by using polyvinyl alcohol and methyltrimethoxysilane and glutaraldehyde as raw materials, which significantly improves the high-temperature resistance of the final silica-based aerogel layer. Experiments show that after the silica-based aerogel obtained by the present application is heat-treated at 1000℃, the volume shrinkage rate of the aerogel powder is less than 8%, and the thermal conductivity is less than 0.035 W / (m·K).

[0022] 2、The specific surface area of the silica-based aerogel obtained by the present application is greater than 600m 2 / g, the porosity is about 99%, the compression deformation rate is more than 30%, and the powder loss rate is less than 1% (preferably less than 0.6%). At the same time, compared with traditional silica aerogels, the elongation at break of the silica-based aerogel of the present application is increased by at least 300% (the elongation at break is preferably more than 10%, and further preferably 15%), and the dry shrinkage rate is reduced to less than 5% (preferably as low as 2%, and further preferably 1%).

[0023] 3、The preparation method provided by the present application uses normal pressure drying, which can effectively reduce the production cost and is suitable for large-scale production. DETAILED DESCRIPTION

[0024] The specific implementation of the present application will be further described in detail below in conjunction with examples. The following typical examples and comparative examples are used to illustrate the present application, but are not used to limit the scope of the present application. In the present application, normal temperature is 25-30℃.

[0025] Example 1 S1: 50.27g of PVA was dissolved in water, 101.34g of MTMS and 75.86g of glutaraldehyde were added, and stirring was carried out at normal temperature for 2h until uniform.

[0026] S2: The pH was adjusted to 5 with acetic acid, and stirring was continued at normal temperature for 2h.

[0027] S3: After the completion of the stirring in S2, ammonia water was added dropwise until the pH was 8.5, and the gel was allowed to stand.

[0028] S4: 500 mL of ethanol (which covered the gel to be aged) was added to the gel obtained in step S3, and the mixture was aged for 24 h.

[0029] S5: The ethanol in the system of S4 was removed, and the gel was dried at 60°C under normal pressure for 12 h to obtain a dried gel.

[0030] S6: The gel obtained in step S5 was immersed in 500 mL of a 0.1 mol / L aluminum isopropoxide ethanol solution (which completely covered the gel), and the mixture was reacted at 60°C for 4 h, and then the gel was taken out.

[0031] S7: The gel obtained in step S6 was again immersed in 450 mL of a 0.05 mol / L zirconium oxychloride aqueous solution, and the mixture was reacted at 80°C for 2 h, and then the gel was taken out.

[0032] S8: The gel obtained in step S7 was heated to 500°C at a rate of 5°C / min under normal pressure in air, and was kept at this temperature for 2 h to obtain a final product.

[0033] Comparative Example 1 S1: 50.27 g of PVA was dissolved in water, and 101.34 g of MTMS and 75.86 g of glutaraldehyde were added, and the mixture was stirred at room temperature for 2 h until it was uniform.

[0034] S2: The pH was adjusted to 5 with acetic acid, and the stirring was continued at room temperature for 2 h.

[0035] S3: After the completion of the stirring in S2, ammonia water was added dropwise until the pH was 8.5, and the gel was allowed to stand.

[0036] S4: 500 mL of ethanol was added to the gel obtained in step S3, and the mixture was aged for 24 h.

[0037] S5: The ethanol in the system of S4 was removed, and the gel was dried at 60°C under normal pressure for 12 h to obtain a dried gel.

[0038] S6: The gel obtained in step S5 was immersed in 500 mL of a 0.1 mol / L aluminum isopropoxide ethanol solution, and the mixture was reacted at 60°C for 4 h, and then the gel was taken out.

[0039] S7: The gel obtained in step S6 was heated to 500°C at a rate of 5°C / min in air, and was kept at this temperature for 2 h to obtain a final product.

[0040] Comparative Example 2 S1: 50.27 g of PVA was dissolved in water, and 101.34 g of MTMS, 75.86 g of glutaraldehyde, 8.05 g of zirconium oxychloride, and 10.22 g of aluminum isopropoxide were added, and the mixture was stirred at room temperature for 2 h until it was uniform.

[0041] S2: Adjust the pH to 5 with acetic acid, continue stirring at room temperature for 2h.

[0042] S3: After the completion of the stirring in S2, add ammonia water dropwise to pH = 8.5, and let the gel stand.

[0043] S4: Add 500 mL of ethanol to the gel obtained in step S3 and age for 24h.

[0044] S5: Remove the ethanol in the S4 system and dry at 60°C under normal pressure for 12h to obtain a dry gel.

[0045] S6: Heat the gel obtained in step S5 to 500°C at a rate of 5°C / min in air under normal pressure, and keep the temperature for 2h to obtain the final product.

[0046] Comparative Example 3 S1: Mix 204.75g of tetraethoxysilane, 178.25g of methyltriethoxysilane, 960.24g of ethanol, and 108.46g of water, and after stirring, add 2mL of 1mol / l dilute hydrochloric acid, and stir and heat for 8h.

[0047] S2: After the completion of the hydrolysis of the sol in S1, stir at room temperature while adding ammonia water dropwise to control the pH of the sol at 7-7.5, and immerse the sol with the added alkali solution into the pre-cut glass fiber short fibers (about 1cm in length), stir uniformly, and let the gel stand.

[0048] S3: Add 1000mL of ethanol to the aerogel obtained in S2 to ensure that the product is completely immersed, age in a 60°C water bath for 24h, and remove the ethanol after aging.

[0049] S4: Super-critically dry the product obtained after removing the ethanol in S3 to obtain the final product.

[0050] Performance Characterization The silicon-based aerogel products obtained in the examples and comparative examples were tested for performance: The test standard for the thermal conductivity was ISO 22007-2.

[0051] The test method for the powder drop rate was to use a vibrating sieve shaker, vibrate at 1800rpm for 2min, and measure the change in mass before and after.

[0052] The test method for the volume shrinkage rate was to measure the change in volume before and after heating in a muffle furnace at a rate of 10°C / min to 1000°C and keeping the temperature for two hours.

[0053] The calculation method of porosity is (1-(product density value / 2.2))*100%, 2.2 is the density of silicon dioxide; the test method of porosity after 1000℃ treatment is to use a muffle furnace to heat to 1000℃ at 10℃ / min, keep warm for two hours, and then measure the porosity again.

[0054] The test method of specific surface area is referred to GB / T 19587.

[0055] The test method of elongation at break is referred to GB / T 3923.1-2013.

[0056] The test method of dry shrinkage rate is to measure the volume V1 of wet gel before drying of the sample, measure the volume V2 of the gel after drying at normal pressure, and the dry shrinkage rate is equal to ((V1-V2) / V1)*100%.

[0057] The test method of density is GB / T 5211.4.

[0058] The test method of compressive strength, bending failure load and tensile strength is GB / T 34336-2017.

[0059] The test results are shown in Table 1 and Table 2.

[0060] Table 1 ; Table 2 ; Finally, the method of the present application is only a preferred embodiment, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a silica-based aerogel, characterized by, Comprising the following steps: (1) mixing polyvinyl alcohol, methyltrimethoxysilane and glutaraldehyde, adjusting the pH of the system to 4-5, stirring for 1.5-2 hours, then adjusting the pH of the system to 8-9, standing to obtain a wet gel, aging and drying to obtain a gel; (2) immersing the gel obtained in step (1) in an isopropyl alcohol aluminum ethanolic solution, reacting at 55-65℃ for 3.5-6 hours, and taking out the gel; (3) immersing the gel obtained in step (2) in a zirconium oxychloride aqueous solution, reacting at 75-85℃ for 1.5-3 hours.

2. The production method according to claim 1, characterized by, In step (1), the mass ratio of polyvinyl alcohol, methyltrimethoxysilane and glutaraldehyde is (0.8-1.2):(1.8-2.1):(1.0-1.8).

3. The production method according to claim 1, characterized by, In step (1), the "drying" step includes drying at 60-70℃ under normal pressure for 12-15 hours.

4. The method of claim 1, wherein, In step (2), the concentration of the isopropyl alcohol aluminum ethanolic solution is 0.08-0.12 mol / L.

5. The preparation method according to claim 1, characterized in that, In step (3), the concentration of the zirconium oxychloride aqueous solution is 0.04-0.08 mol / L.

6. The production method according to claim 1 or 5, characterized by, In step (3), the amount of the zirconium oxychloride aqueous solution is 400-500 mL.

7. The production method according to claim 1, characterized by, Further comprising: taking out the gel after the reaction in step (3) is completed, and drying under normal pressure.

8. The preparation method according to claim 7, characterized in that, Further comprising drying the obtained system under normal pressure at a temperature increasing rate of 3-5℃ / min to 450-550℃ for 2-3.5 hours.

9. The silica-based aerogel obtained by the preparation method of any one of claims 1-8.

10. The use of the silica-based aerogel of claim 9 in the preparation of a heat insulation material for a new energy battery.