Low-thermal-conductivity hydrophobic aerogel felt and preparation method thereof

Abstract

The invention provides a low-thermal-conductivity hydrophobic aerogel felt and a preparation method thereof. The preparation method of the low-thermal-conductivity hydrophobic aerogel felt comprises the following steps: S1, mixing a silica sol solution in an alkaline state with a glass fiber felt, and curing; and S2, putting the cured glass fiber felt obtained in the step S1 into an ethanol solution of hexamethyldisiloxane, adjusting the pH value of the system to 8-9, and modifying at 70-75 DEG C for 5-6 hours. In the modification process, the pH value of the system is adjusted to 8-9, and meanwhile, the specific modifier hexamethyldisiloxane is used, so that the reaction of the silica sol, the glass fiber felt and the modifier hexamethyldisiloxane is more complete, the prepared aerogel structure is more complete, and the stability, the heat insulation performance and the hydrophobic performance of the aerogel felt are considered.

Description

Technical Field

[0001] The invention relates to the technical field of synthesis of silicon dioxide aerogel felt, and more specifically to a low thermal conductivity and hydrophobic aerogel felt and a preparation method thereof. Background Art

[0002] With the increasing demand for high-performance thermal insulation materials in modern industry and construction, traditional materials have shown limitations in meeting specific needs. Aerogel composites have attracted widespread attention due to their light weight, excellent thermal insulation performance and hydrophobic properties, and have gradually become a research hotspot for the new generation of high-performance thermal insulation materials. Aerogel, as an ultra-lightweight, porous material with excellent thermal insulation properties, has been used in many fields, such as thermal insulation, oil-water separation, sound absorption and noise reduction. Glass fiber felt is known for its high strength, high temperature resistance and corrosion resistance, and is often used in composite materials and engineering applications.

[0003] In order to improve the hydrophobicity of aerogel felt in the prior art, hexamethyldisilazane is generally used as an aerogel modifier. However, hexamethyldisilazane is volatile at room temperature and is sensitive to water. It reacts with water to produce silanol and ammonia, resulting in the hydrophobicity and thermal insulation properties of the obtained aerogel felt being always unsatisfactory and unable to effectively take both into account. Summary of the invention

[0004] In order to solve or partially solve the problems existing in the prior art, the present invention provides a low thermal conductivity and hydrophobic aerogel felt and a preparation method thereof. The aerogel felt obtained by the preparation method provided by the present invention has good hydrophobicity and thermal insulation performance.

[0005] The preparation method provided by the present invention comprises the following steps:

[0006] S1, mixing the alkaline silica sol solution with the glass fiber felt and curing;

[0007] S2, placing the cured glass fiber felt obtained in step S1 into an ethanol solution of hexamethyldisiloxane, adjusting the pH of the system to 8-9, and modifying at 70-75° C. for 5-6 hours.

[0008] The applicant of the present invention has found that by mixing an alkaline silica sol solution with a glass fiber felt, and then using hexamethyldisiloxane instead of hexamethyldisilazane to hydrophobically modify the aerogel in an alkaline environment after curing, the hydrophobic properties of the obtained aerogel glass fiber felt can be effectively improved, and the performance of the aerogel glass fiber felt (also referred to as aerogel felt in the present invention) to maintain stability in a humid environment can be improved. At the same time, while ensuring the thermal insulation performance of the aerogel, the hydrophobic properties of the aerogel felt are improved, and the density of the aerogel felt is reduced.

[0009] In the present invention, there is no other special regulation on the glass fiber mat (ie, glass fiber mat), and any commercially available one may be used.

[0010] In a preferred embodiment of the present invention, in step S2, the mass fraction of the ethanol solution of hexamethyldisiloxane is 2.2% to 2.8%. When the concentration of the modifier is too low, the qualified modification effect cannot be achieved, so that the sample strongly absorbs water. In consideration of the need to save costs in actual production, the minimum modifier concentration is 2.2% while ensuring that the product's hydrophobicity and various performances meet the standards.

[0011] In a specific embodiment of the present invention, in step S2, an alkaline reagent such as sodium hydroxide can be used to adjust the pH of the system to 8-9. In a preferred embodiment of the present invention, a sodium hydroxide aqueous solution with a mass fraction of 6% is used.

[0012] In the scheme of the present invention, in step S2, the modification time only needs 5 to 6 hours. In the prior art, the modification time usually requires at least 7 hours to achieve a good modification effect, but the preparation method provided by the present invention only needs 5 to 6 hours (preferably only 5 hours) to obtain a good modification effect of the present invention (that is, each property of the obtained aerogel felt meets the performance requirements of the present invention, including hydrophobicity, thermal conductivity, etc.).

[0013] In a preferred embodiment of the present invention, while ensuring that the water repellency and various performance indicators of the obtained product meet the standards, in step S2, the mass ratio of the cured glass fiber felt to the ethanol solution of hexamethyldisiloxane is 1:(4-5).

[0014] In a preferred embodiment of the present invention, while ensuring that the hydrophobicity and various performance indicators of the obtained product meet the standards, in step S1, the mass ratio of the alkaline silica sol solution to the glass fiber felt is (6-7): 1. At the same time, the applicant found that if the ratio is too large, the obtained product will suffer from severe powder loss, and if the ratio is too small, the obtained product will have poor thermal conductivity.

[0015] In a preferred embodiment of the present invention, in step S1, the method for preparing the alkaline silica sol solution comprises the following steps:

[0016] Mix tetraethoxysilane, ethanol and water, adjust the pH of the system to 2-3, and hydrolyze at 50-55°C for 4-8 hours. After the reaction, add sodium hydroxide solution until the pH of the system reaches 7.2-8, and stir rapidly to obtain an alkaline silica sol solution.

[0017] In a preferred embodiment of the present invention, in the preparation method of the silica sol solution in an alkaline state, concentrated hydrochloric acid is used to adjust the pH of the system to 2-3. Compared with using other acids to adjust the pH value of the system, the use of concentrated hydrochloric acid can also act as a catalyst, thereby improving the performance of the final aerogel felt.

[0018] In a specific embodiment of the present invention, in the preparation method of the alkaline silica sol solution, the sodium hydroxide solution in the step of "adding sodium hydroxide solution until the pH of the system reaches 7.2-8" is usually a sodium hydroxide aqueous solution, and its concentration can be a conventional concentration, for example, its mass fraction can be 3%.

[0019] In a preferred embodiment of the present invention, in step S1, the mass ratio of tetraethoxysilane, ethanol, and water is 1:(8-9):(2.5-3.5). In the scheme provided by the present invention, the inventors have found through experiments that too much or too little ethanol will result in too high a thermal conductivity of the final product, too little water will result in incomplete hydrolysis, resulting in the final product's various properties failing to meet the required standards of the present invention, and too little water will result in a higher density of the final product.

[0020] In a specific embodiment of the present invention, the preparation method further comprises drying the modified glass fiber mat obtained in step S2, preferably supercritical drying, for example, drying at 15 MPa and 55°C.

[0021] The preparation method of the aerogel felt provided by the invention has a short modification time and the obtained aerogel structure is more complete.

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

[0023] Compared with the prior art, the present invention adjusts the solution pH to 8-9 in the modification step, so that the reaction of the composite material (the material obtained after the silica sol and the glass fiber felt are cured) with the modifier hexamethyldisiloxane is more complete, the modification time is short, and the prepared aerogel structure is more complete. While ensuring the thermal insulation performance of the aerogel (the thermal conductivity is at least not higher than 0.018w / (m*k), and further preferably in the range of 0.015w / (m*k) to 0.018w / (m*k)), the hydrophobicity of the aerogel felt is improved (the hydrophobicity is as high as 99%, and the volume water absorption rate is not higher than 1.5%), and the low density (not higher than 195kg / m 3 ). DETAILED DESCRIPTION

[0024] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. In the present invention, if there is no special explanation, "%" means mass percentage.

[0025] Example 1

[0026] This embodiment provides an aerogel felt, comprising the following steps:

[0027] (1) Take 1 mol of tetraethoxysilane, 8 mol of anhydrous ethanol and 2.5 mol of water in a three-necked flask and stir evenly.

[0028] (2) Concentrated hydrochloric acid was added to the mixed system to adjust the pH to pH = 2, and hydrolysis was carried out at 50°C for 8 hours.

[0029] (3) After the hydrolysis reaction is completed, add 3% mass fraction sodium hydroxide aqueous solution to the system until the pH of the system is ＝ 8. Stir evenly to obtain an alkaline silica sol solution.

[0030] (4) Cut the glass fiber mat into 13 cm*13 cm squares, place the cut glass fiber mat in a tray, and then pour the alkaline silica sol solution obtained in step (3) into the tray so that the glass fiber mat is completely soaked in the silica sol solution, wherein the mass ratio of the glass fiber mat to the alkaline silica sol solution is 1:6.

[0031] (5) Take out the soaked glass fiber felt in step (4) and place it in a clean tray separately for curing at room temperature until the glass fiber felt is completely cured.

[0032] (6) After the curing is complete, a 2.2% by mass hexamethyldisiloxane ethanol solution is added, and the pH of the system is adjusted to 8 using a 6% by mass sodium hydroxide aqueous solution, and the modification is carried out at 70-72° C. for 5 hours. The mass ratio of the completely cured glass fiber felt to the ethanol solution of hexamethyldisiloxane with a pH of 8 is 1:4.

[0033] (7) After the modification reaction is completed, supercritical drying is carried out at 15 MPa and 55°C to obtain a sample.

[0034] Example 2

[0035] This embodiment provides an aerogel felt, comprising the following steps:

[0036] (1) Take 1 mol of tetraethoxysilane, 9 mol of anhydrous ethanol and 3.5 mol of water in a three-necked flask and stir evenly.

[0037] (2) Concentrated hydrochloric acid was added to the mixed system to adjust the pH to pH = 3, and hydrolyzed at 55°C for 4 hours.

[0038] (3) After the hydrolysis reaction is completed, add 3% mass fraction sodium hydroxide aqueous solution to the system until the pH of the system is ＝ 7.2, stir rapidly to obtain an alkaline silica sol solution.

[0039] (4) Cut the glass fiber mat into 13 cm*13 cm squares, place the cut glass fiber mat in a tray, and then pour the alkaline silica sol solution obtained in step (3) into the tray so that the glass fiber mat is completely soaked in the silica sol solution, wherein the mass ratio of the glass fiber mat to the alkaline silica sol solution is 1:6.

[0040] (5) Take out the soaked glass fiber felt in step (4) and place it in a clean tray separately for curing at room temperature until the glass fiber felt is completely cured.

[0041] (6) After the curing is complete, a 2.8% by mass hexamethyldisiloxane ethanol solution is added, and the pH of the system is adjusted to 9 using a 6% by mass sodium hydroxide aqueous solution, and the modification is carried out at 73-75° C. for 5 hours. The mass ratio of the completely cured glass fiber felt to the 9% by mass hexamethyldisiloxane ethanol solution is 1:4.

[0042] (7) After the modification reaction is completed, supercritical drying is carried out at 15 MPa and 55°C to obtain a sample.

[0043] The properties of the aerogel felt obtained in the example were measured, and the results obtained are shown in Table 1.

[0044] Among them, the water repellency is based on the spray test method:

[0045] 1. Prepare the sample: After weighing the mass, thickness, length and width of the sample, place the aerogel glass fiber felt sample on a specific test device, ensuring that the sample is at a certain angle (45°) to the horizontal plane.

[0046] 2. Spraying treatment: Spray the sample with a water flow of 0.5 L / min for 1 h.

[0047] 3. Measure mass change: After spraying, weigh the mass of the sample immediately and record the data.

[0048] 4. Calculate the hydrophobicity: By comparing the mass difference before and after spraying, combined with parameters such as the volume of the sample and the density of water, the hydrophobicity of the sample can be calculated.

[0049] Among them, the thermal conductivity is measured using a thermal conductivity instrument.

[0050] Among them, the method for testing volume water absorption is:

[0051] 1. Prepare the sample: weigh the mass, thickness, length and width of the sample.

[0052] 2. Immersion treatment: Place the sample 2 cm underwater to ensure that the sample is completely submerged. The sample can be smoothly moved underwater using auxiliary tools such as wire mesh and fixed to prevent the sample from moving.

[0053] 3. Standing and weighing: After the sample has been standing in water for a period of time (120 minutes), take out the sample and lift a corner to stand (10 minutes) to remove excess water on the surface. Then weigh it and record the mass after water absorption.

[0054] 4. Calculate the water absorption: By comparing the mass difference before and after water absorption, the volume water absorption rate of the sample can be calculated. The smaller the volume water absorption rate, the better the hydrophobicity of the material.

[0055] Among them, the density measurement method is: weigh the mass, thickness, length and width of the sample, calculate the volume of the sample, and divide the mass by the volume to get the density.

[0056] Table 1 Performance of aerogel felt

[0057] <![CDATA[Density / kg / m 3 > Water repellency / % Thermal conductivity / w / (m*k) Volume water absorption / % Example 1 189 99 0.018 1.4 Example 2 183 99 0.017 1.2

[0058] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a low thermal conductive hydrophobic aerogel felt, characterized in that: The steps include: S1, mixing the alkaline silica sol solution with the glass fiber felt and curing; S2, placing the cured glass fiber felt obtained in step S1 into an ethanol solution of hexamethyldisiloxane, adjusting the pH of the system to 8-9, and modifying at 70-75° C. for 5-6 hours.

2. The preparation method according to claim 1, characterized in that: In step S2, the mass fraction of the hexamethyldisiloxane ethanol solution is 2.2-2.8%.

3. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of the cured glass fiber felt to the ethanol solution of hexamethyldisiloxane is 1:(4-5).

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S1, the mass ratio of the alkaline silica sol solution to the glass fiber felt is (6-7):

1.

5. The preparation method according to any one of claims 1 to 3, characterized in that: In step S1, the method for preparing the alkaline silica sol solution comprises the following steps: Mix tetraethoxysilane, ethanol and water, adjust the pH of the system to 2-3, hydrolyze at 50-55°C for 4-8h, and after the reaction, add sodium hydroxide solution dropwise until the pH of the system reaches 7.2-8, stir rapidly to obtain the product.

6. The preparation method according to claim 5, characterized in that: The mass ratio of tetraethoxysilane, ethanol and water is 1:(8-9):(2.5-3.5).

7. The preparation method according to any one of claims 1 to 6, characterized in that Also includes: After modification, supercritical drying is performed.

8. The low thermal conductive hydrophobic aerogel felt obtained by the preparation method according to any one of claims 1 to 7.