Carboxymethyl cellulose-based aerogel and preparation method and application thereof

Abstract

The application discloses a kind of aerogel based on carboxymethyl cellulose and its preparation method and application.The preparation method of the aerogel based on carboxymethyl cellulose of the application includes the following steps: 1) carboxymethyl cellulose is dispersed with water to prepare carboxymethyl cellulose solution, then injected into mold for directional freezing, then freeze-drying, to obtain carboxymethyl cellulose aerogel matrix;2) carboxymethyl cellulose aerogel matrix is immersed in iron salt ethanol solution or iron salt ethanol-water solution for ion crosslinking, then dried, to obtain the aerogel based on carboxymethyl cellulose.The aerogel based on carboxymethyl cellulose of the application has excellent compression resilience in air and water, its raw material is abundant, low in cost, easy to obtain, and its preparation method is simple and easy to operate, suitable for large-scale industrial production and application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aerogel materials, in particular to an aerogel based on carboxymethyl cellulose and a preparation method and application thereof. BACKGROUND

[0002] Aerogel is a kind of high-dispersed solid material with porous structure formed by colloidal particles or polymer molecules through physical or chemical cross-linking, which has the advantages of rich pores, large specific surface area, light weight, etc., and has broad application prospects in aerospace, military, construction, environmental protection, flexible devices and other fields. Aerogel can be divided into inorganic aerogel and organic aerogel according to composition: inorganic aerogel generally has the disadvantages of easy breakage and poor elasticity, and the mechanical properties are difficult to fully meet the requirements of practical application. Organic aerogel has excellent flexibility and elasticity, and has more promising application prospect than inorganic aerogel, but since its raw materials are mostly petroleum-based compounds such as polyurethane, it does not meet the strategic direction of sustainable development. Therefore, under the background of the continuous depletion of petrochemical resources and the increasingly serious environmental problems, it is of great significance to develop aerogel based on biomass resources.

[0003] Cellulose is the most widely distributed and abundant natural high-molecular polysaccharide in nature, and cellulose-based aerogel made of cellulose has the advantages of biodegradability, non-toxicity, renewability, etc., and is an ideal substitute for non-renewable petroleum-based aerogel. However, since the cellulose chains in cellulose-based aerogel form dynamic hydrogen bonds, the structure will collapse seriously after the aerogel is deformed, which will lead to problems such as poor structural stability and insufficient elasticity of the aerogel, greatly limiting the practical application of cellulose-based aerogel. In addition, most of the existing cellulose-based aerogels have strong hydrophilicity, which makes it difficult for them to maintain stable performance in high-humidity / underwater environments for a long time, and their practical application scenarios are greatly limited.

[0004] Therefore, it is of great significance to develop a cellulose-based aerogel that has excellent compression resilience in air and water, is non-toxic and environmentally friendly, and meets the strategic direction of sustainable development. SUMMARY

[0005] The purpose of the present application is to provide an aerogel based on carboxymethyl cellulose and a preparation method and application thereof.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A preparation method of an aerogel based on carboxymethyl cellulose comprises the following steps:

[0008] 1) Disperse carboxymethyl cellulose with water to prepare a carboxymethyl cellulose solution, then inject it into a mold for directional freezing, and then perform freeze-drying to obtain a carboxymethyl cellulose aerogel matrix;

[0009] 2) immersing the carboxymethyl cellulose aerogel matrix into an ethanol solution of iron salt or an ethanol-water solution of iron salt for ion crosslinking, and then drying, to obtain the carboxymethyl cellulose-based aerogel.

[0010] Preferably, the mass ratio of the carboxymethyl cellulose in step 1) to the iron salt in step 2) is 1:1-35.

[0011] Further preferably, the mass ratio of the carboxymethyl cellulose in step 1) to the iron salt in step 2) is 1:5-15.

[0012] Preferably, the mass fraction of the carboxymethyl cellulose in the carboxymethyl cellulose solution in step 1) is 1%-5%.

[0013] Preferably, the mold cavity of the mold in step 1) is rectangular, and the material of the mold is polytetrafluoroethylene.

[0014] Preferably, the directional freezing in step 1) is performed at a temperature of -210°C to -150°C, and the directional freezing time is 0.5 h-1 h.

[0015] Preferably, the directional freezing in step 1) comprises the following operation: performing directional freezing by tightly attaching one side of the mold to a cold source.

[0016] Preferably, the cold source is an iron container containing liquid nitrogen.

[0017] Preferably, the freeze-drying in step 1) is performed at a temperature of -60°C to -50°C, and the freeze-drying time is 24 h-72 h.

[0018] Preferably, the iron salt in step 2) is at least one of ferric chloride, ferric nitrate, and ferric bromide.

[0019] Preferably, the mass fraction of the iron salt in the ethanol solution of the iron salt in step 2) is 0.5%-10%.

[0020] Preferably, the mass fraction of the iron salt in the ethanol-water solution of the iron salt in step 2) is 0.5%-10%, and the mass fraction of ethanol is ≥60% and <99.5%.

[0021] Preferably, the ion crosslinking in step 2) is performed at a temperature of 20°C-25°C, and the ion crosslinking time is 1 h-6 h.

[0022] Preferably, the drying mode in step 2) is vacuum drying.

[0023] Preferably, the vacuum drying is performed at a temperature of 20°C-35°C.

[0024] A carboxymethyl cellulose-based aerogel made by the above preparation method.

[0025] A pressure sensor, the pressure sensing material used contains the above carboxymethyl cellulose-based aerogel.

[0026] The principle of the present application: the carboxymethyl cellulose solution is first directionally frozen, the layered structure is controlled by the ice crystal growth at a gradient temperature, a carboxymethyl cellulose aerogel matrix with layered and anisotropic structure is formed, then it is soaked in an ethanol solution of iron salt or an ethanol-water solution of iron salt (ethanol plays the role of transporting Fe 3+ while maintaining the aerogel form, and the synergistic effect of ethanol and water can improve the permeability of the iron salt solution) 3+ The coordination bond between Fe And the carboxyl group in the aerogel realizes ionic crosslinking to form a stable network structure, and reduces the hydrogen bond between celluloses, reduces the intermolecular adhesion, thereby improving the elasticity of the aerogel, and finally endows the aerogel with high elasticity, and the aerogel has excellent compression resilience in air and water.

[0027] The carboxymethyl cellulose-based aerogel of the present application has excellent compression resilience in air and water, and has the advantages of abundant raw material source, low cost, easy to obtain, simple and easy to operate, and is suitable for large-scale industrial production and application.

[0028] Specifically:

[0029] 1) The carboxymethyl cellulose-based aerogel of the present application is made of carboxymethyl cellulose as the main raw material, and the carboxymethyl cellulose has the advantages of abundant source, low cost, easy to obtain, etc., and the intermolecular interaction between carboxymethyl cellulose can form anisotropic carboxymethyl cellulose aerogel by directional freezing;

[0030] 2) The present application introduces Fe 3+ into the carboxymethyl cellulose aerogel matrix by ionic crosslinking, and prepares an aerogel with excellent compression resilience in air and water, which is safe and non-toxic;

[0031] 3) The carboxymethyl cellulose-based aerogel of the present application has high resilience, and has excellent compression resilience in air and water, and is suitable for pressure sensors;

[0032] 4) The preparation method of the carboxymethyl cellulose-based aerogel of the present application is simple and easy to operate, does not require special production equipment, has low production cost, and is suitable for large-scale industrial production and application. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 SEM image of the carboxymethyl cellulose-based aerogel in Example 1.

[0034] Figure 2 SEM image of the carboxymethyl cellulose-based aerogel in Comparative Example 1.

[0035] Figure 3 Graph of compression resilience test results of the carboxymethyl cellulose-based aerogel in Example 1 and Comparative Example 1.

[0036] Figure 4 Graph of compression resilience test results of the carboxymethyl cellulose-based aerogel in Example 1 in air environment / underwater environment.

[0037] Figure 5 Graph of stability test results of the carboxymethyl cellulose-based aerogel in Example 1, Comparative Example 1 and Comparative Example 2 in underwater environment.

[0038] Figure 6 Actual image of the carboxymethyl cellulose-based aerogel in Example 1 and Comparative Example 4.

[0039] Figure 7 Compression cycle curve of the carboxymethyl cellulose-based aerogel in Example 1, Comparative Example 2 and Comparative Example 3.

[0040] Figure 8 Compression curve of the carboxymethyl cellulose-based aerogel in Examples 1-3.

[0041] Figure 9 Graph of sensing performance test results of the carboxymethyl cellulose-based aerogel in Example 1. DETAILED DESCRIPTION

[0042] The present application will be further explained and described with reference to the following specific examples.

[0043] Example 1:

[0044] A carboxymethyl cellulose-based aerogel is prepared as follows:

[0045] 1) 0.1 g of carboxymethyl cellulose is added to 9.9 g of deionized water, and stirred at 50°C to fully dissolve to prepare a 1% carboxymethyl cellulose solution by mass fraction. The carboxymethyl cellulose solution is injected into a rectangular polytetrafluoroethylene mold, and one side of the mold is tightly attached to an iron vessel containing liquid nitrogen (cooling temperature range: -210°C to -196°C) for directional freezing for 0.5 h. The carboxymethyl cellulose aerogel matrix is obtained by placing the mold in a freeze dryer and freeze-drying at -50°C for 24 h.

[0046] 2) The carboxymethyl cellulose aerogel matrix was immersed in an ethanol-water solution of iron salt prepared by 1g of ferric chloride, 80g of ethanol and 19g of deionized water. The solution was soaked at room temperature for 1 hour and then dried in a vacuum drying oven at 20°C for 6 hours to obtain a carboxymethyl cellulose-based aerogel (denoted as A1).

[0047] The scanning electron microscope (SEM) image of the carboxymethyl cellulose-based aerogel (A1) in this embodiment is shown below. Figure 1 (SEM images with 3 different magnifications are shown).

[0048] Depend on Figure 1 It can be seen that the carboxymethyl cellulose-based aerogel in this embodiment has a layered structure, and there are obvious cross-links between the layers, forming a stable network structure.

[0049] In addition, the carboxymethyl cellulose-based aerogel in this embodiment was immersed in an ethanol-water solution for stability testing. The test showed that the layered structure of the aerogel was not damaged, indicating that it has good stability.

[0050] Example 2:

[0051] A carboxymethyl cellulose-based aerogel is prepared as follows:

[0052] 1) Add 0.3g of carboxymethyl cellulose to 9.7g of deionized water and stir at 55℃ to dissolve completely to prepare a 3% carboxymethyl cellulose solution. Then, inject the carboxymethyl cellulose solution into a rectangular polytetrafluoroethylene mold and place one side of the mold against an iron container filled with liquid nitrogen (cooling temperature range -210℃ to -196℃) for directional freezing for 0.5h. Then, place it in a freeze dryer and freeze dry at -50℃ for 36h to obtain a carboxymethyl cellulose aerogel matrix.

[0053] 2) The carboxymethyl cellulose aerogel matrix was immersed in an ethanol-water solution of iron salt prepared by 2g of ferric chloride, 60g of ethanol and 38g of deionized water. The solution was soaked at room temperature for 3 hours and then dried in a vacuum drying oven at 25°C for 6 hours to obtain a carboxymethyl cellulose-based aerogel (denoted as A2).

[0054] Example 3:

[0055] A carboxymethyl cellulose-based aerogel is prepared as follows:

[0056] 1) 0.5 g of carboxymethyl cellulose was added to 9.5 g of deionized water, and stirred at 60°C until dissolved to form a 5% carboxymethyl cellulose solution by mass fraction. The carboxymethyl cellulose solution was injected into a polytetrafluoroethylene mold with a rectangular cavity, and one side of the mold was tightly attached to an iron container containing liquid nitrogen (cooling temperature range: -210°C to -196°C) for directional freezing for 0.5 h. The frozen product was then placed in a freeze dryer and freeze-dried at -50°C for 48 h to obtain a carboxymethyl cellulose aerogel matrix.

[0057] 2) The carboxymethyl cellulose aerogel matrix was immersed in an ethanol solution of iron salt prepared from 4 g of ferric chloride and 96 g of ethanol, and soaked at room temperature for 4 h. The product was then placed in a vacuum drying oven and dried at 35°C for 6 h to obtain a carboxymethyl cellulose-based aerogel (denoted as A3).

[0058] Comparative Example 1:

[0059] A carboxymethyl cellulose-based aerogel (without ion crosslinking) was prepared as follows:

[0060] 0.1 g of carboxymethyl cellulose was added to 9.9 g of deionized water, and stirred at 50°C until dissolved to form a 1% carboxymethyl cellulose solution by mass fraction. The carboxymethyl cellulose solution was injected into a polytetrafluoroethylene mold with a rectangular cavity, and one side of the mold was tightly attached to an iron container containing liquid nitrogen (cooling temperature range: -210°C to -196°C) for directional freezing for 0.5 h. The frozen product was then placed in a freeze dryer and freeze-dried at -50°C for 24 h to obtain a carboxymethyl cellulose-based aerogel (denoted as B1; same as the carboxymethyl cellulose aerogel matrix in Example 1).

[0061] The SEM image of the carboxymethyl cellulose-based aerogel (B1) in this comparative example is shown in Figure 2 (including SEM images with three different magnifications).

[0062] It can be seen that: Figure 2 The carboxymethyl cellulose-based aerogel in the comparative example has a very regular layered structure, but the crosslinking density between the layers is low, indicating that the directional freezing process can form a carboxymethyl cellulose aerogel matrix with a layered structure, and ion crosslinking can further form a stable network structure.

[0063] Comparative Example 2:

[0064] A carboxymethyl cellulose-based aerogel (without adding iron salt) was prepared as follows:

[0065] The carboxymethyl cellulose aerogel matrix (same as Example 1) was immersed in an ethanol aqueous solution prepared from 80 g of ethanol and 20 g of deionized water, soaked at room temperature for 1 h, and then dried in a vacuum drying oven at 20 °C for 6 h to obtain a carboxymethyl cellulose-based aerogel (denoted as B2).

[0066] Comparative Example 3:

[0067] A carboxymethyl cellulose-based aerogel (refrigerator freezing was used) was prepared as follows:

[0068] 1) 0.1 g of carboxymethyl cellulose was added to 9.9 g of deionized water, and stirred at 50 °C until completely dissolved to prepare a carboxymethyl cellulose solution with a mass fraction of 1%. The carboxymethyl cellulose solution was then injected into a polytetrafluoroethylene mold with a rectangular shape, and the mold was placed in a refrigerator (temperature about -21 °C) for 24 h of freezing, and then placed in a freeze dryer for 24 h of freeze drying at -50 °C to obtain a carboxymethyl cellulose aerogel matrix.

[0069] 2) The carboxymethyl cellulose aerogel matrix was immersed in an iron salt ethanol-aqueous solution prepared from 1 g of ferric chloride, 80 g of ethanol, and 19 g of deionized water, soaked at room temperature for 1 h, and then dried in a vacuum drying oven at 20 °C for 6 h to obtain a carboxymethyl cellulose-based aerogel (denoted as B3).

[0070] Comparative Example 4:

[0071] A carboxymethyl cellulose-based aerogel (without adding ethanol) was prepared as follows:

[0072] The carboxymethyl cellulose aerogel matrix (same as Example 1) was immersed in an iron salt aqueous solution prepared from 1 g of ferric chloride and 99 g of deionized water, soaked at room temperature for 1 h, and then dried in a vacuum drying oven at 20 °C for 6 h to obtain a carboxymethyl cellulose-based aerogel (denoted as B4).

[0073] Compression performance, underwater stability, and sensing performance tests of the aerogels:

[0074] 1) The carboxymethyl cellulose-based aerogels in Example 1 and Comparative Example 1 (denoted as CMC / Fe 3+ The aerogels and CMC aerogels in Example 1 and Comparative Example 1 (denoted as CMC / Fe Figure 3(a is the carboxymethyl cellulose-based aerogel in Comparative Example 1, b is the carboxymethyl cellulose-based aerogel in Example 1) shown.

[0075] It can be seen from Figure 3 that the carboxymethyl cellulose-based aerogel in Comparative Example 1 cannot recover to the original thickness after compression, while the carboxymethyl cellulose-based aerogel in Example 1 can recover to the original thickness, having excellent compression resilience.

[0076] 2) The carboxymethyl cellulose-based aerogel in Example 1 (the shape of the sample is a cuboid, and the size specification is 30mm x 25mm x 10mm) was placed in an air environment / underwater environment, and was pressed to a deformation degree ε of 70% along the length direction, and then the pressure was removed. After the length of the sample remained stable, the deformation degree of the sample was tested, and the compression resilience test results of the aerogel in the air environment / underwater environment are shown in Figure 4 .

[0077] It can be seen from Figure 4 that the carboxymethyl cellulose-based aerogel in Example 1 can recover to the original length after compression in the air environment / underwater environment, having excellent compression resilience.

[0078] 3) The carboxymethyl cellulose-based aerogels in Example 1, Comparative Example 1 and Comparative Example 2 were respectively immersed in deionized water, and continuously soaked for 72h. The dissolution of the aerogel was observed, and the stability test results of the aerogel in the underwater environment are shown in Figure 5 (Each small graph in the figure is from left to right Comparative Example 1, Comparative Example 2 and Example 1, marked as a, b and c).

[0079] It can be seen from Figure 5 that the carboxymethyl cellulose-based aerogels in Comparative Example 1 and Comparative Example 2 are completely dissolved after being soaked in the underwater environment for 2h, while the carboxymethyl cellulose-based aerogel in Example 1 has not obviously dissolved after being soaked in the underwater environment for 72h, having excellent underwater stability.

[0080] 4) The actual photos of the carboxymethyl cellulose-based aerogels in Example 1 and Comparative Example 4 are shown in Figure 6 (the upper part is a surface graph, and the lower part is a cross-sectional graph).

[0081] It can be seen from Figure 6It can be seen that in Comparative Example 4, since ethanol was not used, large pores were generated inside the aerogel, and the original layered structure was destroyed. The reason is that the carboxymethyl cellulose aerogel that has not undergone ionic cross-linking will dissolve in water. When soaked in an iron salt aqueous solution, the outer layer will undergo cross-linking and hardening, while the inner layer will dissolve due to the rapid penetration of water molecules, and the structure will be destroyed. In contrast, in Example 1, ethanol was added, and the internal layered structure of the aerogel remained intact and elastic.

[0082] 5) The carboxymethyl cellulose-based aerogels (rectangular in shape, each measuring 30mm × 25mm × 10mm) from Examples 1, 2, and 3 were placed on a compression pan and subjected to compression tests using a universal tensile testing machine (KYD-2000NS, China). The compression rate was set to 20mm / min. The compression cycle curves of the aerogels obtained are shown below. Figure 7 (a is Comparative Example 2, b is Comparative Example 3, c is Example 1) as shown.

[0083] Depend on Figure 7 It can be seen that: the compression curve of the carboxymethyl cellulose-based aerogel (without added iron salt) in Comparative Example 2 has a very large hysteresis, and its stress quickly becomes 0 after unloading, indicating that the aerogel cannot recover in time after the external force is removed, and its compression resilience is very poor; the stress of the carboxymethyl cellulose-based aerogel in Comparative Example 3 (which was frozen in a refrigerator) did not immediately become 0 after the external force was unloaded, indicating that the aerogel has a certain degree of compression resilience, but judging from the hysteresis area in its compression curve, its compression resilience is still not good enough; the hysteresis area in the compression curve of the carboxymethyl cellulose-based aerogel in Example 1 is the smallest, and the stress gradually decreases to 0 during the unloading process, indicating that the aerogel has excellent compression resilience.

[0084] 6) The carboxymethyl cellulose-based aerogels from Examples 1-3 (samples were cuboid in shape, each measuring 30mm × 25mm × 10mm) were placed on a compression pan, and then a compression test was performed using a universal tensile testing machine (KYD-2000NS, China). The compression rate was set to 20mm / min. The compression curves of the aerogels obtained are shown below. Figure 8 As shown.

[0085] Depend on Figure 8It is known that the ethanol content in the iron salt solution has a significant impact on the compressibility of the aerogel. As the ethanol content increases from 60% (A2) to 80% (A1), the compression resilience of the aerogel increases. This is because excessive water content in the iron salt solution enhances the movement of carboxymethyl cellulose in the system, which is not conducive to the maintenance of the layered structure. When the iron salt solution is completely free of water (A3), the flocculation effect of ethanol on carboxymethyl cellulose molecules makes it difficult for the iron salt solution to disperse inside the aerogel, which is not conducive to cross-linking. Therefore, the elasticity will decrease.

[0086] 7) The carboxymethyl cellulose-based aerogel from Example 1 (the samples were cuboid in shape, each measuring 30mm × 25mm × 10mm) was sandwiched between two copper foils to assemble pressure sensor A and pressure sensor B. Pressure sensor A was then attached to the wrist of a tester in an air environment, with the wrist repeatedly bent and straightened. Pressure sensor B was attached to the finger joints of a tester in an underwater environment, with the finger joints repeatedly bent and straightened. The real-time resistance changes of the aerogel in the air / underwater environments were recorded using a benchtop digital multimeter (VC8165, China). The resulting aerogel sensing performance test results are as follows: Figure 9 (a represents the air environment, and b represents the underwater environment) as shown.

[0087] Depend on Figure 9 It can be seen that the pressure sensor assembled from the carboxymethyl cellulose aerogel in Example 1 can effectively monitor the activities of human body parts such as wrists and fingers in air / underwater environments, indicating that the carboxymethyl cellulose aerogel of the present invention is suitable as a pressure sensing material for pressure sensors.

[0088] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a carboxymethylcellulose-based aerogel, characterized by, The preparation method comprises the following steps: 1) dispersing carboxymethyl cellulose in water to prepare a carboxymethyl cellulose solution, injecting the solution into a mold for directional freezing, and then performing freeze drying to obtain a carboxymethyl cellulose aerogel matrix; 2) immersing the carboxymethyl cellulose aerogel matrix in an ethanol solution of an iron salt or an ethanol-water solution of an iron salt for ion crosslinking, and then performing drying to obtain the carboxymethyl cellulose-based aerogel.

2. The method of claim 1, wherein: The mass ratio of the carboxymethyl cellulose in step 1) to the iron salt in step 2) is 1:1-35.

3. The method of claim 1, wherein: The mass fraction of the carboxymethyl cellulose in the carboxymethyl cellulose solution in step 1) is 1%-5%.

4. The method of any one of claims 1 to 3, wherein: The directional freezing in step 1) is performed at a temperature of -210 ℃ to -150 ℃, and the directional freezing time is 0.5 h-1 h.

5. The method of any one of claims 1-3, wherein: The freeze drying in step 1) is performed at a temperature of -60 ℃ to -50 ℃, and the freeze drying time is 24 h-72 h.

6. The method of claim 1, wherein: The mass fraction of the iron salt in the ethanol solution of the iron salt in step 2) is 0.5%-10%, and the mass fraction of the iron salt in the ethanol-water solution of the iron salt in step 2) is 0.5%-10%, and the mass fraction of ethanol is ≥60% and <99.5%.

7. The method of any one of claims 1-3 and 6, wherein: The ion crosslinking in step 2) is performed at a temperature of 20 ℃-25 ℃, and the ion crosslinking time is 1 h-6 h.

8. The method of any one of claims 1-3 and 6, wherein: The drying mode in step 2) is vacuum drying.

9. A carboxymethylcellulose-based aerogel, characterized in that, The carboxymethyl cellulose-based aerogel prepared by any one of the preparation methods in claims 1-8.

10. A pressure sensor, characterized by The pressure sensing material comprises the carboxymethyl cellulose-based aerogel in claim 9.

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