Silica aerogel composite material with high hydrophobicity and preparation method thereof

Abstract

This invention discloses a method for preparing a silica aerogel composite material with high hydrophobicity, comprising: first, preparing a silica precursor solution; then, preparing a wet gel by sol-gel process and composite with fiber felt; next, completing isothermal hydrophobic modification and aging by CO₂ pressurization-assisted methylsilyl hydrophobic modifier; and finally, obtaining the target composite material by supercritical CO₂ drying. This invention utilizes the dual effects of CO₂ catalysis and pressurization to achieve uniform and efficient hydrophobic modification of the entire pore structure of the aerogel material. The resulting composite material has a thermal conductivity as low as 0.0155 W / (m·K) and a 2-hour water absorption rate as low as 1.7%, achieving both excellent thermal insulation and moisture resistance. Furthermore, it requires a small amount of modifier, has strong process controllability, and is suitable for industrial-scale production.

Description

Technical Field

[0001] This invention belongs to the technical field of aerogel material preparation, specifically relating to a silica aerogel composite material with high hydrophobicity and its preparation method. Background Technology

[0002] Silica aerogel possesses a unique three-dimensional network nanoporous structure and is one of the lightest known solid materials. Its excellent properties, including lightweight, low thermal conductivity, high insulation, and high temperature resistance, make it highly advantageous in various fields such as building insulation, industrial pipeline insulation, and aerospace. However, in high-humidity environments, the numerous silanol groups (≡Si-OH) on the surface of the silica aerogel framework readily combine with water molecules, leading to a significant decrease in the material's moisture absorption and insulation performance, and even structural collapse. This severely limits its large-scale application in humid environments.

[0003] To address the hydrophobic modification problem of silica aerogels, existing technologies mainly fall into two categories: in-situ modification and two-step modification. For example, the invention patent with authorization announcement number CN117776191B introduces an alkyl-containing organosilicon source for co-hydrolysis during the preparation of the silica precursor solution, allowing hydrophobic alkyl groups to grow in situ and form a RO-Si≡ structure, thus imparting hydrophobicity to the material. The invention patent application with publication number CN120398069A discloses a method for simultaneously hydrophobically modifying silica aerogels using hexamethyldisiloxane and hexamethyldisilazane as dual modifiers. The (CH3)3-Si-OH generated by the hydrolysis of the modifiers combines with the HO-Si≡ on the framework surface to form an R3-Si-O-Si≡ hydrophobic structure.

[0004] While the two modification methods mentioned above can impart hydrophobicity to silica aerogels to some extent, they both have insurmountable technical defects: In the in-situ modification process, the introduction of alkyl-containing organosilicon sources with large steric hindrance during the hydrolysis stage will significantly hinder the normal hydrolysis and condensation reaction of the silicon source, leading to an increase in defects in the aerogel skeleton structure, which ultimately causes a significant increase in the thermal conductivity of the material, losing its core advantage of low thermal conductivity; while the conventional two-step modification method can balance low thermal conductivity and surface hydrophobicity to some extent, the hydrophobic modification reaction can only be carried out on the surface of the material, and the modifier is difficult to penetrate into the three-dimensional nanopores of the aerogel, resulting in a large number of hydrophilic silanol groups remaining inside the material, resulting in the problem of "hydrophobic surface and hydrophilic interior", and moisture absorption failure will still occur when used in a humid environment for a long time. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a highly hydrophobic silica aerogel composite material and its preparation method that achieves efficient hydrophobic modification of the material with uniform internal and external properties without damaging the three-dimensional network structure of the aerogel and ensuring the material's low thermal conductivity, while reducing the amount of modifier used, simplifying the process, and improving industrial adaptability.

[0006] This invention is achieved through the following technical solution: A method for preparing a silica aerogel composite material with high hydrophobicity includes the following steps: Preparation of S1 silica precursor solution: Mix organosilicon source, ethanol and acidic substance, and hydrolyze under constant temperature to obtain silica precursor solution; Preparation of S2 silica aerogel fiber felt composite wet gel: The alkaline gel catalyst and the silica precursor solution obtained in step S1 are placed in a constant temperature container and mixed evenly. Fiber felt is added until it is completely wetted and allowed to stand to gel, so as to obtain a wet gel state silica aerogel fiber felt composite material. S3 Pressure-assisted hydrophobic modification: The wet gel composite material obtained in step S2 is placed in a constant temperature sealed device containing alcohol solvent. Methyl silicone hydrophobic modifier and CO2 gas are introduced into the sealed device. The pressure in the sealed device is adjusted to a preset value. The device is kept at a constant temperature for solvent replacement and hydrophobic modification aging. S4 Supercritical CO2 Drying: The wet gel composite material modified and aged in step S3 is placed in a high-pressure drying kettle, and solvent replacement drying is performed using supercritical CO2 fluid drying technology to obtain a highly hydrophobic silica aerogel composite material.

[0007] Further, in step S1, the organosilicon source is any one of tetraethyl orthosilicate, methyl orthosilicate, and polymethyl silicate; the acidic substance is one or more of hydrochloric acid, nitric acid, and acetic acid; the volume ratio of organosilicon source to ethanol is 1:5; the pH value of the mixed system is adjusted to 2-5 by the acidic substance; the constant temperature of the hydrolysis reaction is 35-45℃; and the reaction time is 1-2 hours.

[0008] Furthermore, in step S2, the volume ratio of the alkaline gel catalyst to the silica precursor solution is 1:10, the constant temperature of the mixing system is 35~45℃, the stirring time is 2min, and the gelation time is 5~10min.

[0009] Furthermore, the alkaline gel catalyst is one or both of ammonia solution and ammonium fluoride solution; the fiber mat is any one of ceramic fiber paper, glass fiber surface mat, melamine foam, pre-oxidized fiber mat, and glass fiber mat.

[0010] Furthermore, in step S3, the temperature of the constant temperature sealing device is controlled at 35~45℃, and the solvent replacement and hydrophobic modification aging time is 12~24h.

[0011] Furthermore, the sealing device is a high-pressure stainless steel sealed container with a manual control valve; the alcohol solvent is either methanol or ethanol; and the methylsilyl hydrophobic modifier is hexamethyldisilazane.

[0012] Furthermore, the pressure inside the sealing device is adjusted to 0.3~0.5MPa using CO2 gas.

[0013] Furthermore, the volume ratio of the alcohol solvent to the methylsilyl hydrophobic modifier is 200:1.

[0014] Furthermore, in step S4, the process parameters for supercritical CO2 fluid drying are: drying pressure 14 MPa, drying temperature 50~60℃, CO2 flow rate 2300 kg / h, and drying cycle time 8~10 h.

[0015] Furthermore, the composite material has a thermal conductivity ≤0.016W / (m・K) and a 2h mass water absorption rate ≤2%, exhibiting uniform hydrophobic properties both inside and out.

[0016] The beneficial effects of this invention are: 1. This invention addresses the core defects of existing technologies while balancing low thermal conductivity and high hydrophobicity: It employs a process of gelation followed by pressure modification, avoiding the hindrance of the hydrolysis-condensation reaction by the alkyl silicon source in in-situ modification, thus ensuring the integrity of the three-dimensional network pore structure of the aerogel and maintaining an extremely low thermal conductivity. Simultaneously, CO2 pressure-assisted modification solves the problems of conventional two-step modifiers failing to penetrate into the material and uneven hydrophobicity, achieving highly efficient hydrophobic modification of the entire pore structure inside and outside the material, and significantly reducing the material's water absorption rate.

[0017] 2. Innovatively utilizing the dual effects of CO2 to improve modification efficiency and reduce modification costs: On the one hand, CO2 can react with water in the wet gel system to generate carbonic acid, providing a protic acid catalyst for the rapid hydrolysis of hexamethyldisilazane to generate active (CH3)3-Si-OH. It can also consume the ammonia produced in the hydrolysis reaction, disrupting the hydrolysis equilibrium and further accelerating the hydrolysis rate, thus improving the modification reaction efficiency. On the other hand, CO2 pressurization can reduce the surface tension of the system, promoting the rapid penetration of the active hydrophobic groups generated by hydrolysis into the interior of the aerogel nanopores. These groups then undergo a complete esterification reaction with the exposed ≡Si-OH on the framework, forming a stable Si-O-Si(CH3)3 hydrophobic structure, achieving uniform hydrophobic modification both internally and externally. Simultaneously, this process can significantly reduce the amount of hydrophobic modifier used, substantially lowering production costs.

[0018] 3. Strong process controllability and suitability for industrial production: The process steps of this invention are continuous, the parameter range is clear, no complex equipment is required, the modification and solvent replacement are carried out simultaneously, the production cycle is shortened, the prepared product has stable performance and good batch consistency, and it has excellent industrial promotion value.

[0019] 4. Excellent product performance and wide range of applications: The silica aerogel composite material prepared by this invention has a thermal conductivity as low as 0.0155W / (m・K) and a water absorption rate as low as 1.7% in 2 hours. It has excellent thermal insulation and moisture resistance properties and can be widely used in many fields such as industrial insulation, building insulation, and cold chain transportation in high humidity environments. Attached Figure Description

[0020] The present invention will now be described in further detail with reference to the accompanying drawings.

[0021] Figure 1 This is a process flow diagram of the preparation method described in this invention.

[0022] Figure 2 This is a schematic diagram of the CO2 pressurized modification reaction principle described in this invention.

[0023] Figure 3 This is a diagram showing the surface hydrophobic state of Example 1.

[0024] Figure 4 This is a diagram showing the surface hydrophobic state of Comparative Example 1.

[0025] Figure 5 This is a diagram showing the surface hydrophobic state of Comparative Example 2. Detailed Implementation

[0026] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0027] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Example 1

[0028] This embodiment provides a method for preparing a silica aerogel composite material with high hydrophobicity, the specific steps of which are as follows: Preparation of S1 silica precursor solution: Take 1L of tetraethyl orthosilicate and 5L of anhydrous ethanol and mix them evenly. Add hydrochloric acid to adjust the pH of the mixture to 3. Place it under constant temperature of 35~45℃ and heat and stir for 1h to allow tetraethyl orthosilicate to be fully hydrolyzed, and obtain a clear and transparent silica precursor solution. Preparation of S2 silica aerogel fiber felt composite wet gel: Ammonia solution and silica precursor solution obtained in step S1 are added to a constant temperature gel frame at 35~45℃ at a volume ratio of 1:10. The mixture is stirred and mixed for 2 minutes. Glass fiber felt is then placed in the mixture until it is completely soaked and saturated with the solution. The mixture is kept at a constant temperature and allowed to stand for 5~10 minutes to complete the gelation process and obtain wet gel silica aerogel fiber felt composite material. S3 Pressure-assisted hydrophobic modification: The wet gel composite material obtained in step S2 was placed in a high-pressure stainless steel sealed container at 40°C containing ethanol solvent. Hexamethyldisilazane and CO2 gas were introduced into the sealed container, wherein the volume ratio of ethanol to hexamethyldisilazane was 200:1. The pressure inside the sealed container was adjusted to 0.4 MPa by CO2 gas. The container was kept at a constant temperature for solvent replacement and hydrophobic modification aging for 24 hours. S4 Supercritical CO2 Drying: The wet gel composite material modified and aged in step S3 was placed in a high-pressure drying kettle and solvent replacement drying was carried out using supercritical CO2 fluid drying technology. The drying pressure was set to 14 MPa, the drying temperature to 50~60℃, the CO2 flow rate to 2300 kg / h, and the drying cycle time to 10 h. After drying, a highly hydrophobic silica aerogel composite material was obtained.

[0029] Comparative Example 1 This comparative example uses an existing in-situ hydrophobic modification process to prepare silica aerogel composite materials. The specific steps are as follows: 1 L of tetraethyl orthosilicate, 5 L of anhydrous ethanol, and 0.2 L of methyltrimethoxysilane are mixed evenly, 100 mL of deionized water is added, and the pH of the mixture is adjusted to 3 with hydrochloric acid. The mixture is placed at a constant temperature of 35-45℃ and heated and stirred for 5 h until fully hydrolyzed to obtain a silica precursor sol. Ammonia solution and the above precursor sol are added to a gelation frame at a volume ratio of 1:10 at 35-45℃ and stirred for 2 min. Glass fiber mat of the same specifications as in Example 1 is placed in the mixture until it is completely wetted, and the mixture is kept at a constant temperature for 5-10 min to complete gelation. The resulting wet gel is placed in an ethanol solvent at 35-45℃ and aged for 24 h. It is then dried using the same supercritical CO2 drying process as in Example 1 to obtain the in-situ hydrophobic modified silica aerogel composite material.

[0030] Comparative Example 2 This comparative example uses a conventional two-step modification process to prepare silica aerogel composite materials. The specific steps are as follows: S1-S2 are completely consistent with Example 1, and wet gel-state silica aerogel fiber felt composite material is obtained; S3 is atmospheric pressure hydrophobic modification: the obtained wet gel-state composite material is placed in a container containing ethanol solvent at a constant temperature of 40°C, and an equal amount of hexamethyldisilazane as in Example 1 is added, wherein the volume ratio of ethanol to hexamethyldisilazane is 200:1, and the modification is carried out under atmospheric pressure for 24 hours; S4 is dried using the same supercritical CO2 drying process as in Example 1, to obtain the conventional two-step modified silica aerogel composite material.

[0031] The performance of the silica aerogel composite materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 was tested, and the test results are shown in Table 1 below:

[0032] Table 1 As can be seen from the test data in Table 1 above, the composite material prepared in Example 1 of the present invention has a lower thermal conductivity than Comparative Example 1 and Comparative Example 2, and its 2-hour mass water absorption rate is significantly lower than that of the two comparative examples. It achieves a balance between low thermal conductivity and high hydrophobicity, and solves the core technical problems of increased thermal conductivity and uneven hydrophobicity in conventional two-step methods in the prior art. It has outstanding beneficial effects.

[0033] The scope of protection of this invention is not limited to the technical solutions disclosed in the specific embodiments. Any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of this invention shall fall within the scope of protection of this invention.

Claims

1. A method for preparing a silica aerogel composite material with high hydrophobicity, characterized in that: Includes the following steps: S1. Preparation of silica precursor solution: Mix organosilicon source, ethanol and acidic substance, and hydrolyze under constant temperature to obtain silica precursor solution; S2. Preparation of silica aerogel fiber felt composite wet gel: The alkaline gel catalyst and the silica precursor solution obtained in step S1 are placed in a constant temperature container and mixed evenly. Fiber felt is added until it is completely wetted and allowed to stand to gel, so as to obtain a wet gel state silica aerogel fiber felt composite material. S3, Pressure-assisted hydrophobic modification: The wet gel composite material obtained in step S2 is placed in a constant temperature sealed device containing alcohol solvent. Methyl silicone hydrophobic modifier and CO2 gas are introduced into the sealed device. The pressure inside the sealed device is adjusted to a preset value. The device is kept at a constant temperature for solvent replacement and hydrophobic modification aging. S4. Supercritical CO2 drying: The wet gel composite material modified and aged in step S3 is placed in a high-pressure drying kettle and dried by solvent displacement using supercritical CO2 fluid drying technology to obtain a highly hydrophobic silica aerogel composite material.

2. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 1, characterized in that: In step S1, the organosilicon source is any one of tetraethyl orthosilicate, methyl orthosilicate, and polymethyl silicate; the acidic substance is one or more of hydrochloric acid, nitric acid, and acetic acid; the volume ratio of organosilicon source to ethanol is 1:5; the pH value of the mixed system is adjusted to 2-5 by the acidic substance; the constant temperature of the hydrolysis reaction is 35-45℃; and the reaction time is 1-2 hours.

3. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 1, characterized in that: In step S2, the volume ratio of alkaline gel catalyst to silica precursor solution is 1:10, the constant temperature of the mixing system is 35~45℃, the stirring time is 2min, and the gelation time is 5~10min.

4. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 3, characterized in that: The alkaline gel catalyst is one or both of ammonia solution and ammonium fluoride solution; the fiber mat is any one of ceramic fiber paper, glass fiber surface mat, melamine foam, pre-oxidized fiber mat, and glass fiber mat.

5. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 1, characterized in that: In step S3, the temperature of the constant temperature sealing device is controlled at 35~45℃, and the solvent replacement and hydrophobic modification aging time is 12~24h.

6. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 5, characterized in that: The sealing device is a high-pressure stainless steel sealed tank with a manual control valve; the alcohol solvent is either methanol or ethanol; and the methylsilyl hydrophobic modifier is hexamethyldisilazane.

7. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 5, characterized in that: The pressure inside the sealing device is adjusted to 0.3~0.5MPa using CO2 gas.

8. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 6, characterized in that: The volume ratio of the alcohol solvent to the methylsilyl hydrophobic modifier is 200:

1.

9. The method for preparing a silica aerogel composite material with high hydrophobicity according to claim 1, characterized in that: In step S4, the process parameters for supercritical CO2 fluid drying are: drying pressure 14 MPa, drying temperature 50~60℃, CO2 flow rate 2300 kg / h, and drying cycle time 8~10 h.

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