An atmospheric-pressure drying aerogel for electromagnetic shielding and a preparation method thereof

Abstract

The present invention discloses an atmospheric-pressure drying aerogel for electromagnetic shielding and a preparation method thereof, belonging to the technical field of aerogel preparation. First, a carbon nanotube dispersion liquid and a cellulose nanofiber solution oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical are mixed evenly to form a suspension; then a cationic guar gum solution is added to the suspension and mixed evenly, and then an iron ion solution is added and mixed evenly to form a TOCNF / CGG / CNT / Fe<supgt;3+< / supgt> hydrogel; finally, the TOCNF / CGG / CNT / Fe<supgt;3+< / supgt> hydrogel is subjected to freeze-thaw cycles and solvent replacement to obtain an atmospheric-pressure drying aerogel. The atmospheric-pressure drying aerogel prepared by the present invention has good electromagnetic shielding performance and good mechanical properties, and can be used in fields such as aerospace, national defense, and the next generation of wearable flexible electronic products, having a wide market application prospect.

Description

Technical Field

[0001] The present invention relates to an atmospheric pressure drying aerogel for electromagnetic shielding and a preparation method thereof, belonging to the technical field of aerogel preparation. Background Art

[0002] With the rapid development of modern social electronic information technology, intelligent electronic devices have emerged into daily life. From household appliances to satellite communications, they have brought great convenience to our daily life and work. However, serious electromagnetic pollution and electromagnetic interference (EMI) problems have also emerged. It not only affects the normal operation of electronic devices, causing communication system obstacles, but also endangers human health. In addition, electromagnetic wave leakage may also endanger information security. Therefore, the shielding of electromagnetic waves is particularly important.

[0003] Aerogels are widely used in electromagnetic shielding materials due to their excellent properties such as high porosity, high specific surface area and low density. Most traditional gel drying methods use processes such as supercritical drying and freeze drying for drying preparation. Carbon dioxide (CO2), carbon monoxide (CO) and ethanol are usually used as suitable supercritical fluids for nanocellulose gels under supercritical drying. However, the critical temperature of ethanol is higher than 200 °C, which brings danger to the use of ethanol as a supercritical fluid and challenges to large-scale production. Moreover, due to the cumbersome supercritical drying process and long production cycle, the development of supercritical drying is limited. Freeze drying is the most commonly used method to remove the solvent in the nanocellulose gel and control the internal network structure of the aerogel to prevent collapse. However, due to the slow freezing speed and the need to use a cold source with a higher temperature, it takes extra time to form larger pores, limiting its application. Therefore, supercritical drying and freeze drying usually require specific equipment and conditions, a long drying cycle, high costs, certain danger coefficients and large energy consumption, which greatly limit their application and development.

[0004] The principle of atmospheric pressure drying is a drying method that uses one or more solvents with low surface tension to replace the pore solution in the wet gel and makes the gel surface hydrophobic through modification to prevent excessive shrinkage deformation and structural collapse during drying. Since the atmospheric pressure drying process is simple to operate, has low production costs, low energy consumption, does not require high temperature and high pressure conditions, has a low danger coefficient and is easy to prepare on a large scale, it is an emerging method for drying aerogels. However, during the atmospheric pressure drying process, due to the action of capillary force, the aerogel may shrink and its density may increase, affecting its pore structure and properties; and if not handled properly, the porous structure of the aerogel may collapse during drying, resulting in performance degradation; in addition, the aerogel prepared by atmospheric pressure drying is more brittle and has lower mechanical strength.

[0005] For example, Patent CN 116234282 A discloses an anisotropic nanofiber / carbon nanotube unidirectional aerogel composite material and its preparation method, which uses nanofibers and carbon nanotubes as raw materials and prepares an aerogel material through an atmospheric pressure drying method; however, its cross-linking strength is weak, and its nanostructured aerogel still faces challenges in obtaining high mechanical strength and good flexibility, including the bendability and even stretchability of the aerogel;

[0006] The literature (Li X, He P, Ma R, et al. Modulation of composite hydrogel consisting of TEMPO-oxidized cellulose nanofibers and cationic guar gum[J]. International Journal of Biological Macromolecules: Structure, Function and Interactions, 2023:241.) discloses the preparation of an all-polysaccharide hydrogel composed of TEMPO-oxidized cellulose nanofibers (TOCN) and cationic guar gum (CGG), but it is necessary to regulate the carboxylate content of TOCN, the number of freeze-thaw cycles, and the increase in solid content to increase the cross-linking density of the hydrogel, thereby enhancing the structural characteristics and properties of the TOCN / CGG hydrogel. Summary of the Invention

[0007] [Technical Problem]

[0008] Aerogels prepared by conventional methods have problems such as high density, insufficient flexibility, poor electromagnetic shielding effect, and insufficient mechanical strength;

[0009] Aerogels prepared by atmospheric pressure drying are brittle and have weak mechanical strength.

[0010] [Technical Solution]

[0011] To solve the above problems, the present invention first mixes a carbon nanotube (CNT) dispersion liquid and a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) solution evenly to form a suspension; then adds a cationic guar gum (CGG) solution to the suspension and mixes evenly, and then adds an iron ion (Fe 3+ ) solution and continues to mix evenly to form a TOCNF / CGG / CNT / Fe 3+ hydrogel; finally, the TOCNF / CGG / CNT / Fe 3+The hydrogel is subjected to freeze-thaw cycles and solvent replacement to obtain an atmospheric pressure dried aerogel. The atmospheric pressure dried aerogel prepared by the present invention has good electromagnetic shielding performance and good mechanical properties, and can be used in fields such as aerospace, national defense, and next-generation wearable flexible electronic products, having broad market application prospects.

[0012] The first object of the present invention is to provide a method for preparing an atmospheric pressure dried aerogel for electromagnetic shielding, comprising the following steps:

[0013] (1) Mix a carbon nanotube (CNT) dispersion and a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) solution evenly to form a suspension;

[0014] (2) Add a cationic guar gum (CGG) solution to the suspension and mix evenly, then add an iron ion (Fe 3+ ) solution and continue to mix evenly to form a TOCNF / CGG / CNT / Fe 3+ hydrogel;

[0015] (3) Subject the TOCNF / CGG / CNT / Fe 3+ hydrogel to freeze-thaw cycles, solvent replacement, and drying to obtain an atmospheric pressure dried aerogel.

[0016] In an embodiment of the present invention, in step (1), the mass concentration of the carbon nanotube (CNT) dispersion is 12-16%, and the solvent is water.

[0017] In an embodiment of the present invention, in step (1), the mass concentration of the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) solution is 1-3%, and the solvent is water.

[0018] In an embodiment of the present invention, in step (1), the mass ratio of the carbon nanotube (CNT) dispersion to the 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) solution is 0.7-0.9:7.5.

[0019] In an embodiment of the present invention, in step (1), the even mixing is achieved by ultrasonic mixing, the power of the ultrasonic wave is 300-500 W; the time of the ultrasonic wave is 5-15 min.

[0020] In an embodiment of the present invention, in step (2), the mass concentration of the cationic guar gum (CGG) solution is 1-3%; the solvent is water.

[0021] In an embodiment of the present invention, in step (2), the mass ratio of cationic guar gum (CGG) in the cationic guar gum (CGG) solution, TEMPO-oxidized cellulose nanofibers (TOCNF) in the TEMPO-oxidized cellulose nanofibers (TOCNF) solution in step (1), and carbon nanotubes (CNT) in the carbon nanotubes (CNT) dispersion in step (1) is 4:1 - 3:1.5 - 24.

[0022] In an embodiment of the present invention, in step (2), the iron ion (Fe 3+ ) solution is an iron salt solution, the solvent is water, the iron salt is ferric chloride, and the mass concentration is 0.5 - 1.5%.

[0023] In an embodiment of the present invention, in step (2), the mass ratio of the cationic guar gum (CGG) solution to the iron ion (Fe 3+ ) solution is 1 - 2:1 - 2.

[0024] In an embodiment of the present invention, in step (3), the freeze-thaw cycle is to freeze the TOCNF / CGG / CNT / Fe 3+ hydrogel at -20 to -30 °C for 20 - 30 h, and perform 1 - 4 freeze-thaw cycles.

[0025] In an embodiment of the present invention, in step (3), the solvent replacement is to thaw and melt the frozen hydrogel in absolute ethanol; then perform solvent replacement with ethanol and isopropanol, and the time for each replacement is 4 - 8 h.

[0026] In an embodiment of the present invention, in step (3), the drying is carried out at 60 - 70 °C for 1 - 2 h.

[0027] The second object of the present invention is the atmospheric-pressure drying aerogel for electromagnetic shielding prepared by the method of the present invention.

[0028] The third object of the present invention is the application of the atmospheric-pressure drying aerogel for electromagnetic shielding of the present invention in the fields of aerospace, national defense, or next-generation flexible wearable electronic devices.

[0029] The fourth object of the present invention is to provide an electromagnetic shielding material that uses the atmospheric-pressure drying aerogel for electromagnetic shielding of the present invention.

[0030] [Beneficial effects]

[0031] (1) The present invention uses a method of regulating the use structure of biomass raw materials and surface engineering to enhance atmospheric pressure drying to prepare lightweight and porous aerogels for electromagnetic interference shielding work. This method is an important method for preparing aerogel shielding materials with simple operation, mild conditions, no chemical cross-linking, recyclability, and high efficiency.

[0032] (2) The TOCNF used in the present invention is formed by the interaction of hydrogen bonds with CNT, and can create a hybrid double network composed of hydrophobic CNT and hydrophilic TOCNF. The carboxylic acid groups on TOCNF and the quaternary ammonium cations on CGG, as well as Fe 3+ can immediately form a hydrogel through non-covalent interactions (electrostatic interactions and hydrogen bonds) after coming into contact with each other without the help of any cross-linking agent.

[0033] (3) The present invention can enhance the mechanical strength of the gel through freeze-thaw cycles and solvent replacement to resist the problem of pore structure collapse caused by capillary forces during atmospheric pressure drying.

[0034] (4) The present invention solves the bottleneck problems in the preparation process of biomass aerogels by atmospheric pressure drying method and its application research in electromagnetic shielding materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the preparation mechanism diagram of the atmospheric pressure drying aerogel for electromagnetic shielding in the present invention.

[0036] Figure 2 is the physical diagram of the atmospheric pressure drying aerogel for electromagnetic shielding in Example 1.

[0037] Figure 3 is the scanning electron microscope image of the atmospheric pressure drying aerogel for electromagnetic shielding in Example 1, where (a) is 300μm and (b) is 100μm.

[0038] Figure 4 is the electromagnetic shielding performance diagram of the atmospheric pressure drying aerogel for electromagnetic shielding in Examples 1-4. DETAILED DESCRIPTION OF THE INVENTION

[0039] The following are the preferred embodiments of the present invention. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0040] Test method:

[0041] 1. Mechanical property test:

[0042] The test is carried out using a servo material multi-functional high and low temperature control testing machine, model AI-700-NGD.

[0043] 2. Electromagnetic shielding effect test:

[0044] Use a network vector analyzer, model AV3620, to conduct tests in the X-band (8.2 - 12.4 GHz).

[0045] Raw materials used in the examples:

[0046] Carbon nanotube (CNT) dispersion: with a mass concentration of 14%, and water as the solvent; purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd.

[0047] TOCNF solution: A solution of 2,2,6,6 - tetramethylpiperidine - 1 - oxyl (TEMPO) - oxidized cellulose nanofibers (TOCNF), with a mass concentration of 2%, a carboxyl content of 2.4 mmol / g, and water as the solvent; purchased from Tianjin Wood Elf Biotechnology Co., Ltd.

[0048] Cationic guar gum (CGG): powder, degree of substitution 1.7 mmol / g, purchased from Shanghai Macklin Biochemical Co., Ltd.

[0049] Ferric chloride: solid particles, purity 99.5%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0050] In the examples, the solutions not specifically indicating the solvent are water - based solvents, and the % not specifically indicating the meaning refers to mass percentage.

[0051] Example 1

[0052] A method for preparing an atmospheric - pressure - dried aerogel for electromagnetic shielding, comprising the following steps:

[0053] (1) Mix 0.804 g of a 14% mass - concentration carbon nanotube (CNT) dispersion and 7.5 g of a 2% mass - concentration solution of 2,2,6,6 - tetramethylpiperidine - 1 - oxyl (TEMPO) - oxidized cellulose nanofibers (TOCNF), and ultrasonicate for 10 min at 400 W to form a suspension;

[0054] (2) Add 15 g of a 2% mass - concentration aqueous solution of cationic guar gum (CGG) to the suspension and mix evenly, then add 15 g of a 1% mass - concentration aqueous solution of ferric chloride and continue to mix evenly to form a TOCNF / CGG / CNT / Fe 3+ hydrogel;

[0055] (3) The TOCNF / CGG / CNT / Fe 3+The hydrogel was frozen in a refrigerator at -25°C for 24 h, and underwent three freeze-thaw cycles. The sample frozen in the last cycle was thawed and melted in absolute ethanol for 12 h; then the solvent was replaced twice with ethanol and isopropanol, with each replacement lasting 6 h; the replaced hydrogel was dried in an oven at 65°C for 1.5 h to obtain an atmospheric pressure dried aerogel;

[0056] Among them, the mass ratio of CNT, TOCNF, and CGG is 1.5:2:4, that is, the solid content of CNT in the aerogel is 20%.

[0057] Example 2

[0058] Adjust the mass of the carbon nanotube (CNT) dispersion in step (1) of Example 1 to 2.143 g, and keep the others the same as in Example 1 to obtain an atmospheric pressure dried aerogel; among them, the mass ratio of CNT, TOCNF, and CGG is 4:2:4, that is, the solid content of CNT in the aerogel is 40%.

[0059] Example 3

[0060] Adjust the mass of the carbon nanotube (CNT) dispersion in step (1) of Example 1 to 4.821 g, and keep the others the same as in Example 1 to obtain an atmospheric pressure dried aerogel; among them, the mass ratio of CNT, TOCNF, and CGG is 9:2:4, that is, the solid content of CNT in the aerogel is 60%.

[0061] Example 4

[0062] Adjust the mass of the carbon nanotube (CNT) dispersion in step (1) of Example 1 to 12.857 g, and keep the others the same as in Example 1 to obtain an atmospheric pressure dried aerogel; among them, the mass ratio of CNT, TOCNF, and CGG is 24:2:4, that is, the solid content of CNT in the aerogel is 80%.

[0063] The obtained atmospheric pressure dried aerogel was subjected to performance tests, and the test results are as follows:

[0064] Figure 4 It is the electromagnetic shielding performance diagram of the atmospheric pressure dried aerogel used for electromagnetic shielding in Examples 1-4. From Figure 4 it can be seen that: when the solid content of CNT in the aerogel is 20% (Example 1), the electromagnetic shielding performance can reach 7.3 dB; when the solid content of CNT in the aerogel is 40% (Example 2), the electromagnetic shielding performance can reach 16.5 dB; when the solid content of CNT in the aerogel is 60% (Example 3), the electromagnetic shielding performance can reach 28.2 dB; when the solid content of CNT in the aerogel is 80% (Example 4), the electromagnetic shielding performance can reach 43.6 dB.

[0065] The test results of the mechanical properties of the atmospheric pressure dried aerogel are as follows:

[0066] Under a compressive strain of 60%, the compressive stress of Example 1 was 0.79 MPa; the compressive stress of Example 2 was 0.85 MPa; the compressive stress of Example 3 was 0.96 Mpa; the compressive stress of Example 4 was 1.05 MPa.

[0067] Example 5

[0068] Adjust the amount of the aqueous solution of cationic guar gum (CGG) in step (2) of Example 4 to 20 g; keep the others the same as Example 4 to obtain the aerogel.

[0069] Example 6

[0070] Adjust the amount of the aqueous solution of cationic guar gum (CGG) in step (2) of Example 4 to 10 g; keep the others the same as Example 4 to obtain the aerogel.

[0071] Example 7

[0072] Adjust the amount of the aqueous solution of ferric chloride in step (2) of Example 4 to 20 g; keep the others the same as Example 4 to obtain the aerogel.

[0073] Example 8

[0074] Adjust the amount of the aqueous solution of ferric chloride in step (2) of Example 4 to 10 g; keep the others the same as Example 4 to obtain the aerogel.

[0075] Comparative Example 1

[0076] Adjust step (2) of Example 4 to:

[0077] Add 30 g of an aqueous solution of cationic guar gum (CGG) with a mass concentration of 2% to the suspension and mix evenly to form a TOCNF / CGG / CNT hydrogel;

[0078] Keep the others the same as Example 4 to obtain the aerogel.

[0079] Comparative Example 2

[0080] Adjust step (2) of Example 4 to:

[0081] Add 30 g of an aqueous solution of ferric chloride with a mass concentration of 1% to the suspension and mix evenly to form a TOCNF / Fe 3+ / CNT hydrogel;

[0082] Keep the others the same as Example 4 to obtain the aerogel.

[0083] Comparative Example 3

[0084] Adjust step (2) of Example 4 to:

[0085] 15 g of an aqueous solution of ferric chloride with a mass concentration of 1% was added to the suspension and mixed evenly, and then 15 g of an aqueous solution of cationic guar gum (CGG) with a mass concentration of 2% was added and mixed evenly to form a TOCNF / CGG / CNT / Fe 3+ hydrogel;

[0086] Other conditions were the same as in Example 4 to obtain an aerogel.

[0087] Comparative Example 4

[0088] Step (2) of Example 4 was omitted, and other conditions were the same as in Example 4 to obtain an aerogel.

[0089] The obtained aerogel was subjected to performance testing, and the test results are as follows:

[0090] Table 1

[0091] Example Electromagnetic shielding performance (dB) Compressive stress (MPa) Example 4 43.6 1.05 Example 5 40.2 1.03 Example 6 37.8 0.75 Example 7 39.5 0.98 Example 8 36.2 0.69 Comparative Example 1 34.2 0.58 Comparative Example 2 33.5 0.42 Comparative Example 3 35.7 0.65 Comparative Example 4 29.8 0.2

[0092] Comparative Example 5

[0093] In step (2) of Example 4, the cationic guar gum was adjusted to guar gum, and other conditions were the same as in Example 4 to obtain an aerogel.

[0094] It was found that: Guar gum cannot crosslink with TOCNF to form a hydrogel like cationic guar gum.

[0095] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing atmospheric pressure dried aerogel for electromagnetic shielding, characterized in that: The steps include: (1) mixing a carbon nanotube (CNT) dispersion and a cellulose nanofiber (TOCNF) solution oxidized by TEMPO to form a suspension; (2) Add cationic guar gum CGG solution to the suspension and mix well, then add iron ions Fe 3+ The solution continues to mix evenly to form TOCNF / CGG / CNT / Fe 3+ Hydrogel; (3) TOCNF / CGG / CNT / Fe 3+ The hydrogel was subjected to freeze-thaw cycles, solvent replacement, and drying to obtain atmospheric pressure dry aerogel; The mass ratio of the cationic guar gum CGG in the cationic guar gum CGG solution in step (2), the cellulose nanofibers TEMPO-oxidized by 2,2,6,6-tetramethylpiperidin-1-oxyl free radicals TOCNF solution in step (1), and the carbon nanotubes CNT in the carbon nanotube CNT dispersion in step (1) is 4:1-3:24; In step (2), the cationic guar gum CGG solution and the iron ion Fe 3+ The mass ratio of the solution is 1-2:1; the mass concentration of the cationic guar gum CGG solution is 1-3%; the iron ion Fe in step (2) 3+ The mass concentration of the solution is 0.5-1.5%.

2. The method according to claim 1, characterized in that The solvent of the cationic guar gum CGG solution in step (2) is water.

3. The method according to claim 1, characterized in that: Step (2) Iron ion Fe 3+ The solution is an iron salt solution, the solvent is water, and the iron salt is ferric chloride.

4. The method according to claim 1, characterized in that The freeze-thaw cycle in step (3) is to convert TOCNF / CGG / CNT / Fe 3+ The hydrogel was frozen at -20 to -30 °C for 20-30 h and subjected to 1-4 freeze-thaw cycles.

5. The method according to claim 1, characterized in that: In step (3), the solvent replacement is to place the hydrogel that has been frozen through a freeze-thaw cycle in anhydrous ethanol to thaw and melt; then, ethanol and isopropanol are used for solvent replacement, and each replacement takes 4-8 hours.

6. Normal pressure dried aerogel for electromagnetic shielding prepared by the method according to any one of claims 1 to 5.

7. Application of the atmospheric pressure dried aerogel for electromagnetic shielding as claimed in claim 6 in the fields of aerospace, national defense or next generation flexible wearable electronic devices.

8. An electromagnetic shielding material, characterized in that: The atmospheric pressure dried aerogel for electromagnetic shielding as claimed in claim 6 is used.

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