Preparation method of silicon dioxide aerogel felt with high elasticity

Abstract

The invention provides a preparation method of a silicon dioxide aerogel felt with high elasticity. The preparation method of the silicon dioxide aerogel felt comprises the following steps: 1) mixing a silicon source, ethanol and water, hydrolyzing under an acidic condition to obtain hydrolysate, adding a basic catalyst, and carrying out condensation polymerization to obtain sol; the silicon source is selected from propyl triethoxy silane and tetraethoxy silane; (2) adding elastomer fibers into the sol obtained in the step (1), and uniformly mixing to obtain mixed sol; and 3) immersing a fiber felt in the mixed sol, taking out the fiber felt after dipping, curing, adding an ethanol solution of propyltriethoxysilane, aging, and drying to obtain the silicon dioxide aerogel felt. The silicon dioxide aerogel felt obtained by the invention has the advantages of good hydrophobicity, high elasticity, small heat conductivity coefficient and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of silica aerogels, and more specifically, to a method for preparing a silica aerogel mat with high elasticity. Background Technology

[0002] Aerogels are porous nanomaterials with excellent properties such as low thermal conductivity and good insulation. Silica aerogels are frequently used and widely applied in pipe insulation, building insulation, and other fields. However, most commercially available silica aerogels are brittle and have poor mechanical properties, limiting their application. To address this mechanical property issue, silica aerogels prepared via the sol-gel method using methyl-containing silicon source groups, such as methyltrimethoxysilane (MTMS) or methyltriethoxysilane (MTES), and tetraethoxysilane, exhibit a certain degree of flexibility and are currently widely used in silica aerogel mats. However, their mechanical strength still does not meet the required standards. Therefore, the preparation of silica aerogel mats with superior mechanical properties is a current research hotspot.

[0003] Currently, most aerogel felts on the market are too hard, have low elastic modulus, are not suitable for roll forming, and involve complicated and time-consuming processes, resulting in significant costs in industrial production. Summary of the Invention

[0004] To at least partially or completely solve the problems in the prior art, this invention uses propyltriethoxysilane and tetraethoxysilane as silicon sources to prepare a precursor solution via a sol-gel method. Elastomer fibers (preferably polyurethane electrospun fibers) are added to the precursor solution to obtain a mixed sol, which is then impregnated with a fiber felt. Subsequently, the resulting aerogel felt is impregnated in a composite solution of propyltriethoxysilane and ethanol. The resulting aerogel felt has better elasticity, good hydrophobicity, low thermal conductivity, and excellent performance.

[0005] The method for preparing silica aerogel mat provided by the present invention includes the following steps: 1) A silicon source, ethanol and water are mixed and hydrolyzed under acidic conditions to obtain a hydrolysate. An alkaline catalyst is then added to carry out a polycondensation reaction to obtain a sol. The silicon source is propyltriethoxysilane and tetraethoxysilane. 2) Add elastomer fibers to the sol obtained in step 1) and mix well to obtain a mixed sol; 3) Immerse the fiber felt in the mixed sol, remove the fiber felt after impregnation, cure it, then add an ethanol solution of propyltriethoxysilane for aging, and dry it to obtain the final product.

[0006] The preparation method provided by this invention does not use highly irritating liquids such as those containing amines or chlorine as modifiers, making it suitable for industrial production.

[0007] In a preferred embodiment of the present invention, in step 1), the molar ratio of propyltriethoxysilane to tetraethoxysilane is 1.6:2.4~2.2:1.8. In this preparation method, if the proportion of propyl is too small, the resulting aerogel felt will have fewer propyl groups on its surface, resulting in poor hydrophobicity and elasticity; if the proportion of propyl is too large, it will hinder the formation of the gel skeleton structure and cause gelation difficulties.

[0008] In a preferred embodiment of the present invention, in step 1), the molar ratio of the silicon source (propyltriethoxysilane and tetraethoxysilane) to ethanol is 1:5 to 1:13. In the preparation method of the present invention, if the amount of ethanol is too small, the resulting aerogel is too hard and has a high density, resulting in poor performance of the aerogel felt; while if the amount of ethanol is too large, gelation is difficult, and the performance of the resulting aerogel felt is not improved.

[0009] In a preferred embodiment of the present invention, in step 1), the molar ratio of the silicon source (propyltriethoxysilane and tetraethoxysilane) to water is 1:2 to 1:5. In the preparation method of the present invention, if the amount of water is too small, the hydrolysis reaction cannot be carried out; if the amount of water is too large, the performance of the resulting aerogel felt is not improved.

[0010] In a specific embodiment of the present invention, in step 1), the "acidic condition" refers to a system pH of 2-3, preferably pH 2. In this invention, if the system pH is too low, a larger amount of alkaline catalyst is required for subsequent condensation, leading to particle aggregation and increased aerogel density. Conversely, if the system pH is too high, effective hydrolysis cannot be achieved, resulting in poor hydrophobicity of the aerogel felt. In a specific embodiment of the present invention, the "acidic condition" can be achieved by adding an acidic catalyst. The acidic catalyst includes, but is not limited to, sulfuric acid, acetic acid, nitric acid, hydrochloric acid, and cationic resins.

[0011] In a specific embodiment of the present invention, in step 1), the hydrolysis temperature is 50℃~70℃, and the hydrolysis time is 8h~24h. When the hydrolysis time is too short, the hydrophobicity of the resulting aerogel is poor.

[0012] In a preferred embodiment of the present invention, in step 1), the alkaline catalyst can be sodium hydroxide, ammonia, potassium hydroxide, tetramethylamine hydroxide, etc. In an optional embodiment, sodium hydroxide is added in the form of a sodium hydroxide solution, and the mass fraction of the sodium hydroxide solution can be 12%. In a preferred embodiment, the mass ratio of the alkaline catalyst to the hydrolysate in step 1) is 1:60 to 1:75. In the preparation method of the present invention, when the amount of alkaline catalyst is too large, the particles agglomerate, resulting in a high density aerogel; when the amount of alkaline catalyst is too small, the sol does not form a gel, i.e., the aerogel structure cannot be formed.

[0013] In a specific embodiment of the present invention, in step 1), the reaction temperature of the polycondensation reaction can be 50℃~60℃. In this preparation method, when the polycondensation temperature is too low, the aerogel framework structure formation effect is poor, and the hydrophobicity is poor; when the polycondensation temperature is too high, the sol-gel process is too fast, and the aerogel framework structure is unstable. The reaction time is usually 1~2 minutes, and the polycondensation reaction time is usually sufficient to allow the alkaline catalyst to be uniformly dispersed in the hydrolysate.

[0014] In a preferred embodiment of the present invention, in step 2), the elastomer fiber is a polyurethane electrospun fiber, a polycaprolactone fiber, or a polylactic acid-caprolactone copolymer fiber. In this step, the elastic recovery rate of the elastomer fiber is not less than 90%, and the elongation at break is not less than 500%. In a preferred embodiment, the elastomer fiber is preferably a polyurethane electrospun fiber.

[0015] In a preferred embodiment of the present invention, in step 2), the mass ratio of the elastomer fiber is 0.5% to 10% of the mass of the fiber felt. In this step, if too much elastomer fiber is used, the thermal conductivity of the aerogel felt will increase and the thermal insulation performance will deteriorate, while if too little is used, there will be little improvement in mechanical properties.

[0016] In this invention, the fiber felt in step 3) can be glass fiber needle-punched felt, ceramic fiber felt, polyester fiber felt, or carbon fiber felt, preferably glass fiber needle-punched felt. In a preferred embodiment of this invention, in step 3), the density of the fiber felt is 0.2~0.4 g / cm³. 3 The porosity is 80-90%. The applicant found that when the density of the fiber felt used is too low, the mechanical properties of the resulting aerogel felt are poor; when the density is too high, the aerogel composite effect is poor, and the thermal insulation performance of the resulting product is poor. When the porosity is too small, the aerogel is unevenly distributed during composite, resulting in uneven thermal insulation of the resulting product; when the porosity is too large, the compressibility of the final composite aerogel felt deteriorates. In a specific embodiment of the present invention, the thickness of the fiber felt used in step 3) can be 5mm-10mm.

[0017] In a specific embodiment of the present invention, in step 3), the mixed sol is used to immerse the fiber felt, meaning the fiber felt needs to be completely soaked in the mixed sol. Therefore, the fiber felt used in this step should be of a specification sufficient to allow it to be soaked in the mixed sol. In this step, the glass fiber needled felt is typically immersed in the mixed sol for about 1 to 2 minutes, and then the glass fiber needled felt is removed after impregnation.

[0018] In a specific embodiment of the present invention, in step 3), curing can be performed at 50°C. When the sol on the surface of the fiber felt is solid, i.e., the sol has gelled, the curing can be judged to be complete.

[0019] In a preferred embodiment of the present invention, in step 3), the mass ratio of the propyltriethoxysilane ethanol solution to the hydrolysate in step 1) is 1:(4~6). In this step, the amount of propyltriethoxysilane ethanol solution used is such that the propyltriethoxysilane ethanol solution covers the cured gel surface by at least 5 cm.

[0020] In a preferred embodiment of the present invention, in step 3), the mass ratio of propyltriethoxysilane to ethanol in the propyltriethoxysilane ethanol solution is 1:3 to 1:6. Within this mass ratio range, the resulting silica aerogel felt exhibits the best performance.

[0021] In a specific embodiment of the present invention, in step 3), the aging step is preferably carried out at 65~75℃ for 8~48h. In the present invention, if the aging temperature is too low or the aging time is too short, the skeleton structure produced by the aerogel microparticles is poor, resulting in hydrophilicity of the aerogel felt. If the aging temperature is too high, it exceeds the boiling point of ethanol. Drying can be a commonly used drying step in the art, for example, supercritical drying can be used (the drying pressure can be 17MPa).

[0022] Another object of the present invention is to provide a silica aerogel felt obtained by the above preparation method.

[0023] The beneficial effects of this invention are: 1. This invention uses propyltriethoxysilane and tetraethoxysilane as silicon sources to prepare a precursor solution via a sol-gel method. Elastomer fibers (preferably polyurethane electrospun fibers) are added to the precursor solution to obtain a mixed sol. A fiber felt is then immersed in this mixed solution. The combination of fine and coarse fibers enhances the skeletal structure of the fiber felt, absorbing deformation energy and preventing the propagation of cracks (cracks that occur on the felt surface during deformation). Subsequently, the resulting aerogel felt is immersed in a composite solution of propyltriethoxysilane and ethanol. The resulting aerogel exhibits better elasticity without compromising thermal insulation performance. Compared to aerogel felts prepared by other methods (typically, commercially available aerogel felts have a compression rebound rate of 80%~95% and a compression modulus less than 1 MPa), the aerogel felt obtained by this invention has a compression rebound rate of no less than 98% (preferably no less than 99%) and a compression modulus of 4 MPa or higher (preferably 5.5 MPa or higher), making it widely applicable in noise reduction, thermal insulation, and other fields.

[0024] 2. The aerogel felt obtained by this invention has a water repellency of up to 99% (for the test method of water repellency, please refer to GB / T 10299-2011 Test Method for Water Repellency of Thermal Insulation Materials), and a thermal conductivity of less than 0.030 (W / (m·K).

[0025] 3. The preparation method of aerogel felt provided by this invention uses less organic solvent (existing technologies for preparing hydrophobic aerogels usually require highly irritating and corrosive gases / liquids such as amines and chlorine as modifiers. Conventional atmospheric pressure drying processes and some supercritical drying processes also require silazane or trimethylchlorosilane as modifiers, while the preparation method provided by this invention does not require them), making it green and environmentally friendly. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in further detail below with reference to examples. The following typical examples and comparative examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0027] Example 1 S1: Add 0.4 mol tetraethoxysilane, 0.4 mol propyltriethoxysilane, 7.2 mol ethanol and 3.2 mol aqueous solution to a round-bottom flask and hydrolyze for 24 h at 70 °C and pH of approximately 2 to obtain the hydrolysate.

[0028] S2: Add 9.24g of 12% sodium hydroxide aqueous solution dropwise to the hydrolysate from step S1, and carry out polycondensation and stirring reaction at 50℃ for 1min to obtain sol.

[0029] S3: Add 5.5g of polyurethane electrospun textile fiber (commercially available TPU thermoplastic polyurethane fiber, elastic recovery rate >90%, diameter 1000-2000nm) to the obtained sol, mix well to obtain a mixed sol, and impregnate 500g of glass fiber needle-punched felt (density 100kg / m³) with the mixed sol. 3 After immersing the glass fiber / polyurethane fiber / silica aerogel composite material (with a thickness of 5 mm, a porosity of 85%, and a thermal conductivity of 0.04 W / m·K at 25℃) in the sol-gel for approximately 1-2 minutes, remove the material and place it in an oven at 50℃ for 30 minutes to cure the sol-gel. Then, add a mixed solution consisting of 22.18 g of propyltriethoxysilane and 88.7 g of ethanol, ensuring the mixed solution covers the cured gel surface by at least 5 cm. Aging modification is then performed at 75℃ for 12 hours.

[0030] S4: After aging, CO2 supercritical drying (drying pressure of 17 MPa) is carried out to obtain silica aerogel felt with high elasticity.

[0031] Example 2 S1: Add 0.36 mol tetraethoxysilane, 0.44 mol propyltriethoxysilane, 7.2 mol ethanol and 3.2 mol aqueous solution to a round-bottom flask and hydrolyze for 24 h at 70 °C and pH of approximately 2 to obtain the hydrolysate.

[0032] S2: Add 9.24g of 12% sodium hydroxide aqueous solution dropwise to the hydrolysate from step S1, and carry out polycondensation and stirring reaction at 50℃ for 1min to obtain sol.

[0033] S3: Add 5.5g of polyurethane electrospun textile fiber (commercially available TPU thermoplastic polyurethane fiber, elastic recovery rate >90%, diameter 1000-2000nm) to the obtained sol, mix well to obtain a mixed sol, and immerse 500g of glass fiber needle-punched felt (density 100kg / m³) in the mixed sol. 3 After immersing the glass fiber / polyurethane fiber / silica aerogel composite material (with a thickness of 5 mm, a porosity of 85%, and a thermal conductivity of 0.04 W / m·K at 25℃) in the sol-gel for approximately 1-2 minutes, remove the material and place it in an oven at 50℃ for 30 minutes to cure the sol-gel. Then, add a mixed solution consisting of 22.18 g of propyltriethoxysilane and 88.7 g of ethanol, ensuring the mixed solution covers the cured gel surface by at least 5 cm. Aging modification is then performed at 75℃ for 12 hours.

[0034] S4: After aging, CO2 supercritical drying (drying pressure of 17 MPa) is carried out to obtain silica aerogel felt with high elasticity.

[0035] Example 3 The method provided in this embodiment is the same as that provided in Embodiment 1, except that the same mass of ceramic fiber felt (density 200 kg / m³) is used in step S3. 3 (80% porosity, 10mm thickness) to replace glass fiber needled felt.

[0036] Comparative Example 1 The method provided in this comparative example is the same as that in Example 1, except that: In step S3, 150g of ethanol solution is used instead of the mixed solution consisting of 22.18g of propyltriethoxysilane and 88.7g of ethanol.

[0037] Comparative Example 2 The method provided in this comparative example is the same as that in Example 1, except that: Step S3: Impregnate 500g of glass fiber needled felt (density 100kg / m³) with the obtained sol. 3After immersing the glass fiber / polyurethane fiber / silica aerogel composite material (5 mm thick, 80% porosity, and 0.04 W / m·K thermal conductivity at 25℃) in the sol-gel for approximately 1-2 minutes, remove the material and place it in an oven at 50℃ for 30 minutes to cure the sol-gel. Then, add a mixed solution consisting of 22.18 g of propyltriethoxysilane and 88.7 g of ethanol, ensuring the mixed solution covers the cured gel surface by at least 5 cm. Aging modification is then performed at 75℃ for 12 hours.

[0038] Performance Characterization The silica aerogel felts obtained in the examples and comparative examples were subjected to performance tests. The test method for compression resilience is as described in Appendix C of GB / T 34336-2017 Nanoporous Aerogel Composite Insulation Products. The test method for elastic modulus is as described in ASTM D1621 / ISO 3386. The test method for thermal conductivity is as described in GB / T 10294-2008 (Determination of Steady-State Thermal Resistance and Related Properties of Insulation Materials) Protective Hot Plate Method. The test results are shown in Table 1.

[0039] Table 1 ; Finally, the method of this invention is merely a preferred embodiment and is not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a silica aerogel felt, characterized in that, Includes the following steps: 1) A silicon source, ethanol and water are mixed and hydrolyzed under acidic conditions to obtain a hydrolysate. An alkaline catalyst is then added to carry out a polycondensation reaction to obtain a sol. The silicon source is propyltriethoxysilane and tetraethoxysilane. 2) Add elastomer fibers to the sol obtained in step 1) and mix well to obtain a mixed sol; 3) Immerse the fiber felt in the mixed sol, remove the fiber felt after impregnation, cure it, then add an ethanol solution of propyltriethoxysilane for aging, and dry it to obtain the final product.

2. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of propyltriethoxysilane to tetraethoxysilane is 1.6:2.4~2.2:1.

8.

3. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of the silicon source, ethanol and water is 1:(5~13):(2~5).

4. The preparation method according to claim 1, characterized in that, In step 2), the elastomer fiber is polyurethane electrospun fiber, polycaprolactone fiber or polylactic acid-caprolactone copolymer fiber, preferably polyurethane electrospun fiber.

5. The preparation method according to claim 1 or 4, characterized in that, In step 2), the amount of elastomeric fiber added is 0.5% to 10% of the amount of fiber felt used.

6. The preparation method according to claim 1, characterized in that, In step 3), the fiber felt is glass fiber needle-punched felt, ceramic fiber felt, polyester fiber felt or carbon fiber felt.

7. The preparation method according to claim 1 or 6, characterized in that, In step 3), the density of the fiber felt is 0.2~0.4 g / cm³. 3 The porosity is 80-90%.

8. The preparation method according to claim 1, characterized in that, In step 3), the mass ratio of the ethanol solution of propyltriethoxysilane to the hydrolysate in step 1) is 1:(4~6).

9. The preparation method according to claim 1 or 8, characterized in that, In step 3), the mass ratio of propyltriethoxysilane to ethanol in the propyltriethoxysilane ethanol solution is 1:3 to 1:

6.

10. The silica aerogel felt obtained by the preparation method according to any one of claims 1 to 9.