Low-shrinkage biomass-based curdlan nanofiber aerogel and preparation method thereof

Abstract

The biomass-based curdlan nanofiber aerogel material is prepared from curdlan as a raw material, nanofiber aerogel fibers are in nanoscale, and the preparation method comprises the following steps: 1) stirring and mixing curdlan and water to obtain a curdlan water dispersion; (2) stirring, heating and cooling the curdlan water dispersion liquid obtained in the step (1) to obtain curdlan water gel; (3) soaking the curdlan hydrogel obtained in the step (2) in an organic solvent, and carrying out polar gradient alcohol solvent exchange to obtain organogel; the polar gradient alcohol solvent exchange means that an alcohol solvent with relatively high polarity is replaced by an alcohol solvent with relatively low polarity; 4, the organic gel obtained in the step 3 is subjected to supercritical drying, and then the biomass-based nanofiber aerogel is obtained.The biomass-based curdlan nanofiber aerogel material is applied to heat preservation and heat insulation materials.The preparation method is simple and reliable.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiber aerogel preparation, in particular to a biomass-based curdlan nanofiber aerogel and a preparation method thereof, and belongs to the technical field of chemistry. Background Art

[0002] Aerogel is a three-dimensional open porous material with a porous nano-skeleton. With its unique physical properties such as low density, high specific surface area, high porosity and low thermal conductivity, it shows great application potential in the fields of thermal insulation, catalysis, drug release, adsorption, etc. At present, a variety of organic and inorganic aerogel materials have been developed, such as silica aerogel, carbon aerogel and natural and artificial polymer aerogel. However, aerogel materials also face many challenges: poor mechanical properties, complex synthesis process, and some materials are non-degradable or involve toxic solvents and raw materials, which are easy to cause environmental pollution. Therefore, the development of aerogels based on natural polymers with good biocompatibility, abundant resources and biodegradability has become a research hotspot. This not only provides a new idea for solving the brittleness problem of aerogel materials, but also has important significance in environmental protection and sustainable development. Curdlan (CUR) is a water-insoluble polysaccharide with a triple helical structure composed of β-glucan, which is produced by microbial fermentation and has unique gel properties. It is dispersible in cold water and can form a thermoreversible or thermoirreversible colloid after heating. Curdlan has excellent biocompatibility, stability and water retention. It is mainly used in the food industry as a coagulant, thickener, water-retaining agent, film-forming agent and adhesive. At present, the research on curdlan is still centered on the field of hydrogels and the preparation of aerogels using freeze-drying (Liu Xiaoying et al. Research Progress on Curdlan-based Hydrogels and Their Applications [J]. Food Science, 2023, 44(17): 248-257.), and although the aerogels prepared by freeze-drying have a low shrinkage rate (Chinese patent CN116854982A), they do not have the characteristics of nanofibers and continuous nanoporous aerogels (Chinese patent CN115770555A). Therefore, the preparation of low-shrinkage biomass-based nanofiber aerogels has become a technical problem that needs to be solved in this field. . Summary of the invention

[0003] The object of the present invention is to provide a biomass-based curdlan nanofiber aerogel material and a preparation method and application thereof.

[0004] In order to achieve the above-mentioned invention purpose, the following technical scheme is adopted: a biomass-based curdlan nanofiber aerogel material, which is made of curdlan as a raw material, the nanofiber aerogel fiber is nanoscale, the diameter is less than 40 nanometers; the pore size is nanopore, the pore size is less than 50 nanometers; the porosity is 85-98%; the specific surface area is 140-260m 2 / g; The thermal conductivity is 16 - 33 mW / (m·K).

[0005] A preparation method of a biomass-based curdlan nanofiber aerogel material, the biomass-based curdlan nanofiber aerogel material is as described above, and the preparation method is as follows: Step 1): Stir and mix curdlan with water to obtain a curdlan aqueous dispersion; Step 2): Stir, heat and cool the curdlan aqueous dispersion obtained in step 1) to obtain a curdlan hydrogel; Step 3): Immerse the curdlan hydrogel obtained in step 2) in an organic solvent for polar gradient alcohol solvent exchange to obtain an organogel; the polar gradient alcohol solvent exchange refers to replacing a polar alcohol solvent with a less polar alcohol solvent; Step 4): After supercritical drying of the organogel obtained in step 3), a biomass-based nanofiber aerogel is obtained.

[0006] Furthermore; the concentration of the curdlan aqueous dispersion is 30 - 100 mg / mL; the temperature of the mixing is 20°C - 30°C, the stirring speed is 400 - 600 r / min, and the time is 30 min.

[0007] Furthermore; the heating temperature of the curdlan aqueous dispersion is 90°C - 100°C, and the time is 1 h; the stirring speed in step 2) is 200 - 400 r / min; the cooling temperature in step 2) is 0°C - 25°C.

[0008] Furthermore; the organic solvent includes ethanol, methanol, and isopropanol.

[0009] Furthermore; the number of immersions in step 3) is 1 - 5 times, the time is 5 - 10 h, and the organic solvent needs to be replaced each time.

[0010] An application of a biomass-based curdlan nanofiber aerogel material, the biomass-based curdlan nanofiber aerogel material is as described above, and it is applied to thermal insulation materials.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method of the present invention is simple and reliable, the raw material is pure curdlan, without other additives, and curdlan is a natural polymer, which is environmentally friendly, rich in resources, has good biocompatibility, and is biodegradable, and has great application prospects in the biomedical field; (2) After washing and exchanging with gradient alcohol solvents, the linear shrinkage rate of the nanofiber aerogel is effectively reduced in the present invention; (3) The linear shrinkage rate (0% - 8%) of the nanofiber aerogel prepared by the present invention is less than that of the silica aerogel, achieving a high level in the field of biopolymers (nanofiber aerogel). (4) The fibers and pore sizes of the nanofiber aerogel prepared by the present invention are at the nanoscale, with the nanofiber diameter being 10 - 40 nanometers and the pores being relatively small. (5) The nanofiber aerogel prepared by the present invention has a high specific surface area, which is 140 - 260 m 2 / g; the specific surface area is relatively large. (6) The nanofiber aerogel prepared by the present invention has a low thermal conductivity (16 - 33 mW / (m·K)) at room temperature and has great application prospects in the field of thermal insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a physical picture of the nanofiber aerogel material prepared by the present invention.

[0013] Figure 2 This is a scanning electron microscope image of the CUR-6 nanofiber aerogel prepared by the present invention.

[0014] Figure 3 This is the nitrogen adsorption isotherm and pore size distribution diagram of the CUR-6 nanofiber aerogel.

[0015] Figure 4 This is the thermal conductivity diagram of the CUR-3 - CUR-8 nanofiber aerogels.

[0016] Figure 5 This is the compression stress-strain curve diagram of the CUR-3 - CUR-8 nanofiber aerogels.

[0017] Figure 6 This is the curve diagram of the shrinkage rate. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0019] In the present invention, "room temperature" and "normal temperature" are both calculated as 25 ± 2°C unless otherwise specified.

[0020] In the present invention, the curdlan aqueous dispersion is prepared by mixing curdlan and water, and the aqueous dispersion is a milky white suspension with a certain viscosity. In the present invention, the water is preferably deionized water. In a specific embodiment of the present invention, the curdlan is purchased from Shanghai Yuanye (manufacturer), S11046, BR type. In the present invention, the mass ratio of curdlan to the volume of water is preferably 600-1200 mg:20 ml, specifically 600 mg:20 ml, 800 mg:20 ml, 1000 mg:20 ml, 1200 mg:20 ml, 1600 mg:20 ml. The linear shrinkage rate of the gel of the present invention is measured by measuring the samples before and after drying, accurately measuring three times with an electronic caliper, and taking the average value.

[0021] Example 1 Add 600 mg of curdlan powder to 20 mL of deionized water at room temperature, and carry out magnetic stirring at 450 r / min for 30 min to form a uniform curdlan aqueous dispersion. Heat the above aqueous dispersion by stirring in a water bath at a water bath temperature of 95 °C for 1 h, and the stirring speed is 200 r / min until the curdlan is dissolved in deionized water to form a translucent solution. Transfer the above aqueous solution to a conventional mold and cool it at room temperature for 30 min to obtain a curdlan hydrogel. Then soak the hydrogel in an anhydrous methanol solution for 8 h. Then soak the soaked hydrogel in anhydrous ethanol three times to remove water, 8 h each time, and change the solution each time. Treat the obtained alcohol gel by supercritical liquid carbon dioxide drying method to obtain the final nanofiber aerogel sample (CUR-3).

[0022] Example 2 Add 800 mg of curdlan powder to 20 mL of deionized water at room temperature, and carry out magnetic stirring at 450 r / min for 30 min to form a uniform curdlan aqueous dispersion. Heat the above aqueous dispersion by stirring in a water bath at a water bath temperature of 95 °C for 1 h, and the stirring speed is 200 r / min until the curdlan is dissolved in deionized water to form a translucent solution. Transfer the above aqueous solution to a conventional mold and cool it at room temperature for 30 min to obtain a curdlan hydrogel. Then soak the hydrogel in an anhydrous methanol solution for 8 h. Then soak the soaked hydrogel in anhydrous ethanol three times to remove water, 8 h each time, and change the solution each time. Treat the obtained alcohol gel by supercritical liquid carbon dioxide drying method to obtain the final nanofiber aerogel sample (CUR-4).

[0023] Example 3 Add 1000 mg of curdlan powder to 20 mL of deionized water at room temperature, and perform magnetic stirring at 450 r / min for 30 min to form a uniform curdlan aqueous dispersion. Stir and heat the above aqueous dispersion in a water bath at a water bath temperature of 95 °C for 1 h, and the stirring speed is 200 r / min until the curdlan is dissolved in deionized water to form a translucent solution. Transfer the above aqueous solution to a conventional mold and cool it at room temperature for 30 min to obtain a curdlan hydrogel. Then soak the hydrogel in an anhydrous methanol solution for 8 h. Then soak the soaked hydrogel in anhydrous ethanol 3 times to remove water, 8 h each time, and change the solution each time. Treat the obtained alcogel by supercritical liquid carbon dioxide drying method to obtain the final nanofiber aerogel sample (CUR-5).

[0024] Example 4 Add 1200 mg of curdlan powder to 20 mL of deionized water at room temperature, and perform magnetic stirring at 450 r / min for 30 min to form a uniform curdlan aqueous dispersion. Stir and heat the above aqueous dispersion in a water bath at a water bath temperature of 95 °C for 1 h, and the stirring speed is 200 r / min until the curdlan is dissolved in deionized water to form a translucent solution. Transfer the above aqueous solution to a conventional mold and cool it at room temperature for 30 min to obtain a curdlan hydrogel. Then soak the hydrogel in an anhydrous methanol solution for 8 h. Then soak the soaked hydrogel in anhydrous ethanol 3 times to remove water, 8 h each time, and change the solution each time. Treat the obtained alcogel by supercritical liquid carbon dioxide drying method to obtain the final nanofiber aerogel sample (CUR-6).

[0025] Example 5 Add 1600 mg of curdlan powder to 20 mL of deionized water at room temperature, and perform magnetic stirring at 450 r / min for 30 min to form a uniform curdlan aqueous dispersion. Stir and heat the above aqueous dispersion in a water bath at a water bath temperature of 95 °C for 1 h, and the stirring speed is 200 r / min until the curdlan is dissolved in deionized water to form a translucent solution. Transfer the above aqueous solution to a conventional mold and cool it at room temperature for 30 min to obtain a curdlan hydrogel. Then soak the hydrogel in an anhydrous methanol solution for 8 h. Then soak the soaked hydrogel in anhydrous ethanol 3 times to remove water, 8 h each time, and change the solution each time. Treat the obtained alcogel by supercritical liquid carbon dioxide drying method to obtain the final nanofiber aerogel sample (CUR-8).

[0026] Changing the anhydrous ethanol in the above examples to anhydrous isopropanol can also obtain similar results.

[0027] The nanofiber aerogels obtained from the above 5 exemplary embodiments were subjected to thermal conductivity testing, scanning electron microscopy testing, surface area testing, and pore size testing. The specific results are shown in the attached drawings and Table 1. It can be seen from the results that by using this method, a heat-insulating nanofiber aerogel material with a small shrinkage rate can be obtained, and the thermal conductivity of the nanofiber aerogel first decreases and then increases with the increase in the concentration of curdlan. The thermal conductivities shown in multiple different examples are lower than the thermal conductivity of air (25 mW / (m·K)). Therefore, the nanofiber aerogel prepared by the present invention has great application prospects in the field of thermal insulation.

[0028]

[0029] Figure 1 Figure 7 is a physical photograph of the nanofiber aerogel prepared in the embodiment of the present invention. It can be seen that the nanofiber aerogel prepared by the present invention is white and opaque.

[0030] Figure 2 The electron micrograph shows that all the nanofiber aerogels are composed of nanofibers tightly wound together, having a fine nanostructure, and the diameter of the nanofibers is 15 - 30 nm.

[0031] Figure 3 It can be seen that the specific surface area of the nanofiber aerogel is about 180 m 2 g -1 2, and the average pore size is 5 - 15 nm, further proving that the nanofiber aerogel belongs to mesoporous materials and has a fine nanostructure.

[0032] Figure 4 The thermal conductivity of the nanofiber aerogel was measured. It can be seen that with the increase in the concentration of curdlan, the thermal conductivity of the nanofiber aerogel first decreases and then increases, showing a "U" - shaped trend. Among them, the thermal conductivity of CUR - 6 is the lowest (16 mW / (m·K)). Therefore, the nanofiber aerogel prepared by the present invention also has great application prospects in the field of thermal insulation.

[0033] Figure 6 It can be seen that the shrinkage rate of the curdlan alcohol gel decreases regularly with the increase in concentration, which is due to the influence of the increase in fiber density at high concentrations. After being prepared into a nanofiber aerogel by supercritical carbon dioxide drying, the shrinkage rate will further increase, but generally still shows a regularity similar to that of the alcohol gel, and the shrinkage rates are all below 8%.

[0034] Table 1 Performance test table of the nanofiber aerogel prepared in the embodiment. Repeating the above - mentioned embodiment multiple times, the obtained results are similar, indicating that the preparation method of this method has good repeatability.

Claims

1. A biomass-based curdlan nanofiber aerogel material, made from curdlan as a raw material, characterized by: Nanofiber aerogel fibers are nanometer-sized, with a diameter of less than 40 nanometers; the pore size is nanopores, with a pore size of less than 50 nanometers; the porosity is 85-98%; the specific surface area is 140-260m 2 / g; The thermal conductivity is 16~33 mW / (m·K).

2. A method for preparing a biomass-based curdlan nanofiber aerogel material, wherein the biomass-based curdlan nanofiber aerogel material is as described in claim 1, characterized in that The preparation method is as follows: Step 1) mixing curdlan with water to obtain a curdlan dispersion; Step 2) stirring, heating and cooling the curdlan glue dispersion obtained in step 1) to obtain a curdlan glue gel; Step 3) soaking the curdlan hydrogel obtained in step 2) in an organic solvent to perform polar gradient alcohol solvent exchange to obtain an organic gel; the polar gradient alcohol solvent exchange refers to replacing the alcohol solvent with a smaller polarity with the alcohol solvent with a larger polarity; Step 4) The organic gel obtained in step 3) is subjected to supercritical drying to obtain a biomass-based nanofiber aerogel.

3. The method for preparing a biomass-based nanofiber aerogel according to claim 2, characterized in that: The concentration of the curdlan dispersion is 30 to 100 mg / mL; The mixing temperature is 20° C. to 30° C., the stirring speed is 400 to 600 r / min, and the mixing time is 30 min.

4. The method for preparing a biomass-based nanofiber aerogel according to claim 2, characterized in that: The curdlan dispersion is heated at a temperature of 90°C to 100°C for 1 hour; the stirring speed in step 2) is 200 to 400 r / min; and the cooling temperature in step 2) is 0°C to 25°C.

5. The method for preparing a biomass-based nanofiber aerogel according to claim 2, characterized in that: The organic solvent includes ethanol, methanol and isopropanol.

6. The method for preparing a biomass-based nanofiber aerogel according to claim 3, characterized in that: The soaking times in step 3) are 1 to 5 times for 5 to 10 hours, and the organic solvent needs to be replaced each time the soaking is performed.

7. An application of a biomass-based curdlan nanofiber aerogel material, wherein the biomass-based curdlan nanofiber aerogel material is as described in claim 1, characterized in that Used in thermal insulation materials.

Images