A hydrophobic nanocellulose aerogel and preparation method thereof
Hydrophobic nanocellulose aerogel is prepared by the sol-gel method, and the independently developed silicon-based hydrophobic regulator is coupled with nanocellulose to solve the problem of nanocellulose aerogel's easy water absorption, achieving excellent hydrophobicity and anti-deformation stability, making it suitable for flexible and load-bearing products.
Patent Information
- Application Number
- CN202411870823.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-18
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2044-12-18
AI Technical Summary
Nanocellulose aerogels easily absorb water, resulting in decreased mechanical properties and increased thermal conductivity, which limits their application. Existing hydrophobic treatment methods have problems such as coating shedding or increased brittleness.
Hydrophobic nanocellulose aerogel was prepared by the sol-gel method. By introducing a self-developed silicon-based hydrophobic regulator to couple with the nanocellulose macromolecular chain, the water absorption was reduced and the toughness was enhanced. The silicon-based hydrophobic regulator was made by reacting undecenyl alcohol with perfluorododecyltrichlorosilane, introducing a branched terminal alkenyl chain and adding γ-mercaptopropyltriethoxysilane to form a multi-branched ethoxysilane modification.
The aerogel has excellent hydrophobicity and anti-deformation stability, maintains a stable pore structure, is suitable for flexible and load-bearing products, and improves the thermal insulation effect.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of aerogels, and in particular relates to a hydrophobic nanocellulose aerogel and a preparation method thereof. Background Art
[0002] Aerogel is an ultralight solid material with a 3D network skeleton and a highly interconnected porous structure. Traditional inorganic aerogels, such as silica aerogel, have the characteristics of large specific surface area and high porosity, as well as many excellent properties such as extremely low thermal conductivity. However, they have disadvantages such as harsh preparation conditions and high brittleness. Nanocellulose aerogel, a new type of organic aerogel, is an ultralight solid material with good toughness, environmental protection, and biorenewable advantages. It combines the low density, high specific surface area, and low thermal conductivity of highly porous aerogels and has great application potential in energy storage, thermal, water purification, optics, and electricity.
[0003] However, the surface of nanocellulose contains a large number of hydroxyl groups, which makes its aerogel easy to absorb water. After absorbing water, the aerogel will swell and soften, resulting in a decrease in the mechanical properties of the aerogel. Water enters the pores of the aerogel, resulting in an increase in thermal conductivity and a reduction in the thermal insulation effect of the aerogel. Therefore, the high water absorption of nanocellulose aerogel greatly limits its application. In the existing technology, the hydrophobic treatment of nanocellulose aerogel mainly includes two technical means. The first is the external coating method, which coats the surface of the aerogel product with a hydrophobic material, which can effectively reduce the hydrophilicity of the aerogel material. However, the coating material has insufficient bonding performance with the pores and falls off during long-term use, causing the performance of the product to gradually deteriorate. The second is the internal modification method, which improves the overall hydrophobicity of the gel material by introducing dopants such as fluoride. However, the introduction of fluoride increases the brittleness of the aerogel. During the deformation process, the aerogel pore structure is prone to collapse, which greatly limits its application in flexible products and load-bearing products. Summary of the Invention
[0004] In order to solve the technical problems mentioned in the background technology, the purpose of the present invention is to provide a hydrophobic nanocellulose aerogel and a preparation method thereof.
[0005] The purpose of the present invention can be achieved through the following technical solutions:
[0006] A method for preparing a hydrophobic nanocellulose aerogel comprises the following steps:
[0007] Step S1, co-hydrolysis: preparing a dispersion of nanocellulose and an ethanol solution, adding a silicon-based hydrophobicity control agent and ethyl orthosilicate, and adjusting the pH to 3-4.5 with formic acid. Stirring at 30-50 rpm for 0.8-1.3 hours to obtain a precursor solution.
[0008] Step S2, gelation: heating the precursor solution to 40-50°C, neutralizing it with ammonia water under ultrasonic oscillation, and then stirring it at 60-90 rpm for 1.5-2 hours to obtain a composite gel;
[0009] Step S3, freeze drying: the composite gel is transferred into a mold, frozen in liquid nitrogen for 5 minutes, and then transferred into a freeze dryer for freeze drying to obtain a hydrophobic nanocellulose aerogel.
[0010] Furthermore, the feeding ratio of nanocellulose, silicon-based hydrophobicity regulating agent and ethyl orthosilicate is 50g:4.2-6.8g:2.9-3.5g.
[0011] Furthermore, the solid content of the dispersion is 1.5-2.2 wt %, and the volume fraction of the ethanol solution is 20-30 vol %.
[0012] Furthermore, the freeze-drying parameters are: temperature of -50°C, vacuum degree of 100Pa, and time of 72h; or temperature of -60°C, vacuum degree of 10Pa, and time of 48h.
[0013] The silicon-based hydrophobicity regulating agent is prepared by the following steps:
[0014] Step A1: Undecyl alcohol and anhydrous tetrahydrofuran are mixed, and dry nitrogen is introduced into the mixture. The temperature of the water bath is controlled at 10±2°C, and stirring is applied at 60-90 rpm. Perfluorododecyltrichlorosilane is slowly added and the reaction is carried out for 2.5-3 hours. Then, triethylamine is added and mixed, and the temperature is raised to 55-70°C. The reaction is continued for 1.2-1.8 hours. After the reaction is completed, the tetrahydrofuran is removed by rotary evaporation, and the substrate is washed with water and dried to obtain an intermediate;
[0015] Furthermore, the feed ratio of perfluorododecyltrichlorosilane, undecenol, triethylamine and anhydrous tetrahydrofuran is 10 mmol: 32-35 mmol: 2-3 mL: 35-50 mL, and the active chlorosilane group of perfluorododecyltrichlorosilane is fully substituted and etherified with undecenol to introduce an alkyl chain of a branched terminal olefin group.
[0016] Step A2: Mix the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide, heat to 50-70°C, stir at 120-150 rpm, and use 150-200 W / m 2 The mixture was irradiated with ultraviolet light and reacted for 6-8 hours. After the reaction was completed, water was added and vacuum rotary evaporation was carried out to remove dimethylacetamide to obtain a silicon-based hydrophobicity regulating agent.
[0017] Furthermore, the feed ratio of the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide is 10mmol:30mmol:60-80mg:50-60mL. Under ultraviolet initiation, γ-mercaptopropyltriethoxysilane is added to the terminal alkenyl group of the intermediate to introduce multi-branched ethoxysilane modification.
[0018] Beneficial effects of the present invention:
[0019] The present invention is based on nanocellulose and adopts a sol-gel method to prepare an aerogel material. A self-developed silicon-based hydrophobicity regulating agent is introduced into the sol to regulate the voids of the aerogel and at the same time give the aerogel good anti-deformation stability. The silicon-based hydrophobicity regulating agent is etherified by replacing the active chlorosilane in the molecules of undecyl alcohol and perfluorododecyltrichlorosilane, and an alkyl chain of a branched terminal olefin group is introduced to prepare an intermediate. Then, γ-mercaptopropyltriethoxysilane is subjected to ultraviolet-induced addition to the terminal olefin group of the intermediate to introduce multi-branched ethoxysilane for modification. The silicon-based hydrophobicity regulating agent is co-hydrolyzed with ethyl orthosilicate and then coupled with the hydroxyl groups on the nanocellulose macromolecular chain to effectively reduce the water absorption of the nanocellulose molecules. The fluorine structure The introduction greatly reduces the surface energy of the aerogel pore wall. In addition, the pores of the aerogel are tiny, and under surface tension, it is difficult for water to infiltrate the aerogel, thus having excellent hydrophobicity. Compared with the existing fluorine-containing silane doping, the fluorine structure of the silicon-based hydrophobic regulator is located in the center of the molecule, and the long-chain alkyl at the end plays a bridging support role. First, it avoids the segregation and aggregation of the fluorine structure in the gel, resulting in uneven pores after drying, affecting the thermal insulation effect of the aerogel and the stability of the pore structure. Second, the long-chain alkyl has a toughening effect, improving the toughness of the aerogel pore wall, and can maintain the stability of the pore properties under certain deformation conditions, maintaining a stable thermal insulation effect, and has broad application prospects in flexible products and load-bearing products. DETAILED DESCRIPTION
[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.
[0021] Example 1: Preparation of hydrophobic nanocellulose aerogel. The specific implementation process is as follows:
[0022] (1) Preparation of silicon-based hydrophobicity regulator
[0023] Step A1: Mix undecylenol and anhydrous tetrahydrofuran, introduce dry nitrogen protection, control the temperature of the water bath at 10±2°C, apply stirring at 90 rpm, slowly add perfluorododecyltrichlorosilane and react for 2.5 hours, then add triethylamine, mix well, and raise the temperature to 70°C, and continue the reaction for 1.2 hours. The feed ratio of perfluorododecyltrichlorosilane, undecylenol, triethylamine and anhydrous tetrahydrofuran is 10 mmol:35 mmol:3 mL:50 mL. After the reaction, remove tetrahydrofuran by rotary evaporation, wash the substrate with water, and dry it to obtain an intermediate.
[0024] Step A2: Mix the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide, heat to 70°C, stir at 150 rpm, and use 150W / m 2 The reaction was carried out under ultraviolet irradiation for 6 hours, wherein the feed ratio of the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide was 10 mmol: 30 mmol: 60 mg: 60 mL, and the photoinitiator was selected from photoinitiator 1173. After the reaction was completed, water was added and the dimethylacetamide was removed by vacuum rotary evaporation to obtain a silicon-based hydrophobic regulator.
[0025] (2) Preparation of hydrophobic nanocellulose aerogel
[0026] Step S1, co-hydrolysis: prepare an ethanol solution (aqueous solution) with a volume fraction of 20 vol%, mix the nanocellulose and the ethanol solution, control the solid content to 1.5 wt%, and ultrasonically disperse at 33 kHz for 10 min to prepare a dispersion, then add a silicon-based hydrophobic regulator and ethyl orthosilicate to the dispersion, adjust the pH to 3 with formic acid, and stir at 50 rpm for 0.8 h, wherein the feed ratio of nanocellulose, silicon-based hydrophobic regulator and ethyl orthosilicate is 50 g:4.2 g:3.5 g, and the nanocellulose is selected from TL-002 type raw material to obtain a precursor solution.
[0027] Step S2, gelation: the precursor solution was heated to 50° C., ultrasonically oscillated at 20 kHz, neutralized by adding ammonia water, and then stirred at 90 rpm for 1.5 h to obtain a composite gel.
[0028] Step S3, freeze drying: the composite gel was transferred into a mold, frozen in liquid nitrogen for 5 minutes, and then transferred into a freeze dryer. The freeze drying parameters were set as follows: temperature of -50°C, vacuum degree of 100 Pa, and time of 72 hours to obtain hydrophobic nanocellulose aerogel.
[0029] Example 2, preparation of hydrophobic nanocellulose aerogel, the specific implementation process is as follows:
[0030] (1) Preparation of silicon-based hydrophobicity regulator
[0031] Step A1: Mix undecylenol and anhydrous tetrahydrofuran, introduce dry nitrogen protection, control the temperature of the water bath at 10±2°C, apply stirring at 60 rpm, slowly add perfluorododecyltrichlorosilane and react for 3 hours, then add triethylamine, mix well, and raise the temperature to 55°C, and continue the reaction for 1.8 hours. The feed ratio of perfluorododecyltrichlorosilane, undecylenol, triethylamine and anhydrous tetrahydrofuran is 10 mmol:32 mmol:2 mL:35 mL. After the reaction, remove tetrahydrofuran by rotary evaporation, wash the substrate with water, and dry it to obtain an intermediate.
[0032] Step A2: Mix the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide, heat to 50°C, stir at 120 rpm, and use 200 W / m 2 The reaction was carried out under ultraviolet irradiation for 8 hours, wherein the feed ratio of the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide was 10 mmol: 30 mmol: 80 mg: 50 mL, and the photoinitiator was selected from photoinitiator 1173. After the reaction was completed, water was added and the dimethylacetamide was removed by vacuum rotary evaporation to obtain a silicon-based hydrophobic regulator.
[0033] (2) Preparation of hydrophobic nanocellulose aerogel
[0034] Step S1, co-hydrolysis: prepare an ethanol solution (aqueous solution) with a volume fraction of 30 vol%, mix the nanocellulose and the ethanol solution, control the solid content to 2.2 wt%, and ultrasonically disperse at 33 kHz for 10 min to prepare a dispersion, then add a silicon-based hydrophobic regulator and ethyl orthosilicate to the dispersion, adjust the pH to 4.5 with formic acid, and stir at 30 rpm for 1.3 h, wherein the feed ratio of nanocellulose, silicon-based hydrophobic regulator and ethyl orthosilicate is 50 g:6.8 g:2.9 g, and the nanocellulose is selected from TL-002 type raw material to obtain a precursor solution.
[0035] Step S2, gelation: the precursor solution was heated to 40° C., ultrasonically oscillated at 20 kHz, neutralized by adding ammonia water, and then stirred at 60 rpm for 2 h to obtain a composite gel.
[0036] Step S3, freeze drying: the composite gel was transferred into a mold, frozen in liquid nitrogen for 5 minutes, and then transferred into a freeze dryer. The freeze drying parameters were set as follows: temperature of -60°C, vacuum degree of 10 Pa, and time of 48 hours to obtain hydrophobic nanocellulose aerogel.
[0037] Example 3, preparation of hydrophobic nanocellulose aerogel, the specific implementation process is as follows:
[0038] (1) Preparation of silicon-based hydrophobicity regulator
[0039] Step A1: Mix undecylenol and anhydrous tetrahydrofuran, introduce dry nitrogen protection, control the temperature of the water bath at 10±2°C, apply stirring at 60 rpm, slowly add perfluorododecyltrichlorosilane and react for 3 hours, then add triethylamine, mix well, and raise the temperature to 65°C, and continue the reaction for 1.5 hours. The feed ratio of perfluorododecyltrichlorosilane, undecylenol, triethylamine and anhydrous tetrahydrofuran is 10 mmol:33 mmol:3 mL:40 mL. After the reaction, remove tetrahydrofuran by rotary evaporation, wash the substrate with water, and dry it to obtain an intermediate.
[0040] Step A2: Mix the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide, raise the temperature to 60°C, stir at 150 rpm, and use 180 W / m 2 The reaction was carried out under ultraviolet irradiation for 7.5 hours, wherein the feed ratio of the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide was 10 mmol: 30 mmol: 60 mg: 60 mL, and the photoinitiator was selected from photoinitiator 1173. After the reaction was completed, water was added and the dimethylacetamide was removed by vacuum rotary evaporation to obtain a silicon-based hydrophobic regulator.
[0041] (2) Preparation of hydrophobic nanocellulose aerogel
[0042] Step S1, co-hydrolysis: prepare an ethanol solution (aqueous solution) with a volume fraction of 30 vol%, mix the nanocellulose and the ethanol solution, control the solid content to 1.8 wt%, and ultrasonically disperse at 33 kHz for 10 min to prepare a dispersion, then add a silicon-based hydrophobic regulator and ethyl orthosilicate to the dispersion, adjust the pH to 3.5 with formic acid, and stir at 50 rpm for 1.1 h, wherein the feed ratio of nanocellulose, silicon-based hydrophobic regulator and ethyl orthosilicate is 50 g:5.5 g:3.2 g, and the nanocellulose is selected from TL-002 type raw material to obtain a precursor solution.
[0043] Step S2, gelation: the precursor solution was heated to 40° C., ultrasonically oscillated at 20 kHz, neutralized by adding ammonia water, and then stirred at 90 rpm for 1.7 h to obtain a composite gel.
[0044] Step S3, freeze drying: the composite gel was transferred into a mold, frozen in liquid nitrogen for 5 minutes, and then transferred into a freeze dryer. The freeze drying parameters were set as follows: temperature of -60°C, vacuum degree of 10 Pa, and time of 48 hours to obtain hydrophobic nanocellulose aerogel.
[0045] Example 4, preparation of hydrophobic nanocellulose aerogel, the specific implementation process is as follows:
[0046] (1) Preparation of silicon-based hydrophobicity regulator
[0047] Step A1: Mix undecylenol and anhydrous tetrahydrofuran, introduce dry nitrogen protection, control the temperature of the water bath at 10±2°C, apply stirring at 90 rpm, slowly add perfluorododecyltrichlorosilane and react for 3 hours, then add triethylamine, mix well, and raise the temperature to 65°C, and continue the reaction for 1.5 hours. The feed ratio of perfluorododecyltrichlorosilane, undecylenol, triethylamine and anhydrous tetrahydrofuran is 10 mmol:35 mmol:2.5 mL:40 mL. After the reaction, remove tetrahydrofuran by rotary evaporation, wash the substrate with water, and dry it to obtain an intermediate.
[0048] Step A2: Mix the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide, raise the temperature to 65°C, stir at 150 rpm, and use 200 W / m 2 The reaction was carried out under ultraviolet irradiation for 6.5 hours, wherein the feed ratio of the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide was 10 mmol: 30 mmol: 80 mg: 60 mL, and the photoinitiator was selected from photoinitiator 1173. After the reaction was completed, water was added and the dimethylacetamide was removed by vacuum rotary evaporation to obtain a silicon-based hydrophobic regulator.
[0049] (2) Preparation of hydrophobic nanocellulose aerogel
[0050] Step S1, co-hydrolysis: prepare an ethanol solution (aqueous solution) with a volume fraction of 20 vol%, mix the nanocellulose and the ethanol solution, control the solid content to 1.5 wt%, and ultrasonically disperse at 33 kHz for 10 min to prepare a dispersion, then add a silicon-based hydrophobic regulator and ethyl orthosilicate to the dispersion, adjust the pH value to 4 with formic acid, and stir at 30 rpm for 1.2 h, wherein the feed ratio of nanocellulose, silicon-based hydrophobic regulator and ethyl orthosilicate is 50 g:6.2 g:3 g, and the nanocellulose is selected from TL-002 type raw material to obtain a precursor solution.
[0051] Step S2, gelation: the precursor solution was heated to 50° C., ultrasonically oscillated at 20 kHz, neutralized by adding ammonia water, and then stirred at 90 rpm for 1.8 h to obtain a composite gel.
[0052] Step S3, freeze drying: the composite gel was transferred into a mold, frozen in liquid nitrogen for 5 minutes, and then transferred into a freeze dryer. The freeze drying parameters were set as follows: temperature of -60°C, vacuum degree of 10 Pa, and time of 48 hours to obtain hydrophobic nanocellulose aerogel.
[0053] Comparative Example 1 refers to Example 3, except that an equal amount of the silicon-based hydrophobicity regulating agent is replaced with ethyl orthosilicate during the implementation process, and the rest of the implementation process is exactly the same.
[0054] Comparative Example 2, in combination with the prior art, refers to Example 3, and during the implementation process, an equal amount of the silicon-based hydrophobicity regulating agent is replaced with perfluorooctyltrimethoxysilane, and the rest of the implementation process is exactly the same.
[0055] Samples were taken from the aerogel material prepared as above, and the basic physical properties of the aerogel samples were tested, as shown in Table 1:
[0056] Table 1 Basic physical properties of examples and comparative examples
[0057]
[0058] The test results in Table 1 show that the surface water contact angle of the aerogel prepared in the example is higher than 130°, showing excellent hydrophobicity, high porosity, small pore size, low thermal conductivity, and excellent thermal insulation performance.
[0059] The sample was subjected to a dynamic cyclic compression test using an electronic universal material testing machine. The compression rate was 10 mm / min, and the compression strain was set to 50%. After the cyclic compression reached the set test number, the residual compressive stress and thermal conductivity change rate of the sample were calculated, as shown in Table 2.
[0060] Table 2 Dynamic cycle compression results of the embodiments and comparative examples
[0061]
[0062] From the test results in Table 2, it can be seen that after dynamic cyclic compression, the aerogel prepared in Example has a high residual compressive stress and a low decrease in the rate of change of thermal conductivity, indicating that the aerogel material in Example has excellent compression toughness and can maintain a stable pore structure during deformation.
[0063] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
[0064] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.
Claims
1. A hydrophobic nanocellulose aerogel, characterized in that It is prepared by sequentially co-hydrolyzing, gelling and freeze-drying nanocellulose, silicon-based hydrophobicity regulator and ethyl orthosilicate; The silicon-based hydrophobic control agent is prepared by the following steps: Step A1: Undecyl alcohol and anhydrous tetrahydrofuran are mixed, and dry nitrogen is introduced into the mixture. The temperature of the water bath is controlled at 10±2°C, and stirring is applied at 60-90 rpm. Perfluorododecyltrichlorosilane is slowly added and the reaction is carried out for 2.5-3 hours. Triethylamine is then added and mixed, and the temperature is raised to 55-70°C. The reaction is continued for 1.2-1.8 hours. After the reaction is completed, tetrahydrofuran is removed by rotary evaporation. The substrate is washed with water and dried to obtain an intermediate, wherein the feed ratio of perfluorododecyltrichlorosilane, undecyl alcohol, triethylamine and anhydrous tetrahydrofuran is 10 mmol:32-35 mmol:2-3 mL:35-50 mL; Step A2: Mix the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide, heat to 50-70°C, stir at 120-150 rpm, and use 150-200 W / m 2 The reaction was carried out under ultraviolet irradiation for 6-8 hours. After the reaction was completed, water was added and the dimethylacetamide was removed by vacuum rotary evaporation to obtain a silicon-based hydrophobic regulator, wherein the feed ratio of the intermediate, γ-mercaptopropyltriethoxysilane, photoinitiator and dimethylacetamide was 10 mmol: 30 mmol: 60-80 mg: 50-60 mL.
2. The method for preparing a hydrophobic nanocellulose aerogel according to claim 1, characterized in that: The details are as follows: Step S1, co-hydrolysis: nanocellulose and ethanol solution are mixed to form a dispersion, a silicon-based hydrophobicity control agent and ethyl orthosilicate are added, the mixture is acidified with formic acid and stirred for 0.8-1.3 hours to obtain a precursor solution; Step S2, gelation: heating the precursor solution to 40-50°C, neutralizing it with ammonia water under ultrasonic oscillation, and then stirring it for 1.5-2 hours to obtain a composite gel; Step S3, freeze drying: the composite gel is transferred into a mold, frozen with liquid nitrogen to set the shape, and then freeze dried to obtain a hydrophobic nanocellulose aerogel.
3. The method for preparing a hydrophobic nanocellulose aerogel according to claim 2, characterized in that: The feeding ratio of nanocellulose, silicon-based hydrophobic regulator and ethyl orthosilicate is 50g:4.2-6.8g:2.9-3.5g.
4. The method for preparing a hydrophobic nanocellulose aerogel according to claim 3, characterized in that: The solid content of the dispersion is 1.5-2.2 wt %, and the volume fraction of the ethanol solution is 20-30 vol %.
5. The method for preparing a hydrophobic nanocellulose aerogel according to claim 4, characterized in that: The pH value of the precursor solution is 3-4.
5.
6. The method for preparing a hydrophobic nanocellulose aerogel according to claim 4, characterized in that: The freeze-drying parameters are: temperature of -50°C, vacuum degree of 100Pa, time of 72h; or temperature of -60°C, vacuum degree of 10Pa, time of 48h.