Preparation method and application of degradable nanofiber aerogel with high toughness and low thermal conductivity

Abstract

The invention relates to a preparation method of degradable nano fiber aerogel with high toughness and low thermal conductivity. The preparation method comprises the following steps: 1) stirring and mixing a konjac glucomannan powder raw material and a sodium carbonate solution, and removing acetyl to obtain a deacetylated konjac glucomannan solution; (2) heating the konjac glucomannan solution obtained in the step (1) to obtain konjac glucomannan hydrogel; and 3) gradually soaking the konjac glucomannan hydrogel obtained in the step 2) in an organic solvent with the concentration from low to high to obtain organic gel with nanofibers, and further performing supercritical drying to obtain the nanofiber and nanopore double-nano aerogel. The degradable nanofiber aerogel with high toughness and low thermal conductivity is applied to thermal insulation materials. The thermal conductivity of the aerogel prepared by the method is 15-35 mW / (m.K) under a room temperature environment condition, and the aerogel has a relatively great application prospect in the field of heat preservation and heat insulation.

Description

Technical Field

[0001] The invention relates to the technical field of aerogel preparation, in particular to a preparation method and application of a degradable high-toughness and low-thermal conductivity nanofiber aerogel, belonging to the field of chemistry. Background Art

[0002] Aerogel is a solid three-dimensional material composed of nano-colloidal particles that aggregate to form a nano-skeleton and nano-porous network structure, and the pores are filled with gas dispersion medium. Due to its unique characteristics such as low density, high specific surface area, high porosity, and low thermal conductivity, aerogel is widely used, especially in the fields of thermal insulation, adsorption, and catalysis. However, traditional SiO 2 Aerogels are brittle and fragile because the connection between particles is very weak and they cannot withstand mechanical tension and large loads. Polymer aerogels developed from petrochemical materials are usually non-degradable and the process is complicated. Therefore, environmentally friendly, widely available, and biodegradable biomass polysaccharide aerogel materials are favored by many researchers. Thanks to its special microstructure and physical properties, polysaccharide-based nanofiber aerogels have more structural and performance advantages and great application value. They are widely used in thermal insulation, sewage treatment, tissue repair, drug delivery and other fields. (Linfeng Chen, Xiaoxiao Yu, et al. Renewable biomass-based aerogels: from structural design to functional regulation [J]. Chemical Society Reviews, 2024, 53, 7489.). Therefore, using biomass polysaccharide materials to prepare an environmentally friendly and degradable high-toughness, low-thermal conductivity nanofiber aerogel is of great significance in the field of aerogels.

[0003] Konjac Glucomannan (KGM) is a water-soluble neutral polysaccharide extracted from the tuber of the konjac plant. It is well-known for its gelation that depends on alkali and heat treatment. As a natural and multifunctional food additive and health supplement, KGM is widely used in the food, medicine and cosmetics industries due to its high viscosity and good gel-forming properties, showing broad application prospects in many fields. In current research, KGM hydrogels are weak gels, and common KGM-based aerogels are composite materials, mostly macroporous aerogels obtained by freeze-drying (Chinese patents CN115530222A, CN115490910A). There are few reports on the method of preparing nanofibers and nanoporous double-nanostructure (nanofiber diameter 20-90 nm, nanopore diameter 10-50 nm) aerogels using KGM itself as the matrix. Summary of the invention

[0004] The purpose of the present invention is to provide a degradable high-toughness and low-thermal conductivity nanofiber and nanoporous double-nano aerogel and a preparation method and application thereof.

[0005] In order to achieve the above-mentioned purpose of the invention, the following technical scheme is adopted: a method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel, comprising the following steps: Step 1) mixing the konjac glucomannan powder raw material with a sodium carbonate solution to remove the acetyl group to obtain a deacetylated konjac glucomannan solution; Step 2) heating the konjac glucomannan solution obtained in step 1) to obtain a konjac glucomannan hydrogel; Step 3) The konjac glucomannan hydrogel obtained in step 2) is gradually immersed in organic solvents with concentrations ranging from low to high to obtain an organic gel with nanofibers, and further supercritical drying is performed to obtain nanofibers and nanoporous double-nano aerogels.

[0006] Furthermore, the concentration of the sodium carbonate solution in step 1) is 0.01 to 0.06 mol / L.

[0007] Furthermore, the concentration of the konjac glucomannan solution in step 1) is 10 to 60 mg / mL; and the stirring mixing time is 1 to 3 min.

[0008] Furthermore, in step 2), the heating temperature is 85°C to 95°C, and the heating time is 0.5 to 1.5 h.

[0009] Furthermore, the organic solvent solution in step 3) includes one or more of ethanol solution, methanol solution and isopropanol solution. The volume concentration of the organic solvent is 30-100%.

[0010] Furthermore, the soaking in step 3) is performed 1 to 3 times for 8 to 12 hours, and the organic solvent needs to be replaced each time the soaking is performed.

[0011] Further; step 3) the obtained aerogel consists of nanofibers and nanopores, the nanofiber diameter is 20 to 100 nanometers, the nanopore diameter is 10 to 50 nanometers, the porosity is 85% to 95%, and the thermal conductivity is 15 to 35 mW / (m·K) at room temperature.

[0012] Furthermore, the drying method in step 3) is supercritical carbon dioxide drying, and the pressure during the drying process is 15 MPa and the temperature is 50°C.

[0013] A degradable high-toughness and low-thermal conductivity nanofiber aerogel, wherein the degradable high-toughness and low-thermal conductivity nanofiber aerogel is prepared by the above-mentioned preparation method, and the degradable high-toughness and low-thermal conductivity nanofiber aerogel is used in thermal insulation materials.

[0014] 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, and the raw material konjac glucomannan is a natural polymer, which has good biocompatibility, is environmentally friendly, has abundant resources and is biodegradable; (2) The konjac glucomannan raw material of the present invention can form a stable hydrogel after being treated with a certain concentration of sodium carbonate solution and heated; (3) The mechanical properties of the konjac glucomannan hydrogel of the present invention can be enhanced by soaking in gradient concentration organic solvents; (4) The thermal conductivity of the aerogel prepared by the present invention is 15 to 35 mW / (m·K) at room temperature, and has great application prospects in the field of thermal insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a physical picture of the aerogel material prepared according to the present invention.

[0016] Figure 2 The nitrogen adsorption isotherm and pore size distribution diagram of the aerogel material prepared in Example 2.

[0017] Figure 3 This is a scanning electron microscope image of the aerogel material prepared in Example 2.

[0018] Figure 4 This is the thermal conductivity diagram of KGM-1~KGM-5 aerogel materials.

[0019] Figure 5 This is the compression stress-strain curve of KGM-1~KGM-5 aerogel materials. DETAILED DESCRIPTION

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] Unless otherwise specified, the "room temperature" or "normal temperature" mentioned in the present invention is 25±2°C.

[0022] The present invention provides a method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel, comprising the following steps: Step 1) mixing the konjac glucomannan powder raw material with a sodium carbonate solution to remove the acetyl group to obtain a deacetylated konjac glucomannan solution; Step 2) heating the konjac glucomannan solution obtained in step 1) to obtain a konjac glucomannan hydrogel; Step 3) The hydrogel obtained in step 2) is gradually immersed in organic solvents with concentrations ranging from low to high to obtain an organic gel with nanofibers, and further supercritical drying is performed to obtain nanofibers and nanoporous double-nano aerogels.

[0023] In the present invention, the konjac glucomannan solution is prepared by mixing konjac glucomannan and sodium carbonate solution, and the konjac glucomannan solution is a uniform solution.

[0024] The concentration of the sodium carbonate solution is 0.01 to 0.06 mol / L, preferably 0.015 to 0.04 mol / L, and more preferably 0.02 to 0.03 mol / L.

[0025] In the present invention, the heating temperature is 85°C to 95°C, preferably 88°C to 93°C, and more preferably 90°C to 92°C.

[0026] The heating time is 0.5 to 1.5 h, preferably 0.75 to 1.25 h, and more preferably 0.9 to 1 h.

[0027] In the present invention, the organic solvent comprises one or more of ethanol solution, methanol solution and isopropanol solution, preferably one or two of ethanol solution and methanol solution; the volume concentration of the organic solvent is 30-100%, preferably 50-90%, and more preferably 70-80%.

[0028] In the present invention, the soaking times are 1 to 5 times, preferably 2 to 4 times, and more preferably 3 times; the soaking time is 5 to 12 hours, preferably 6 to 10 hours, and more preferably 7 to 8 hours, and the organic solvent needs to be replaced each time the soaking is performed.

[0029] In the present invention, the drying preferably includes supercritical liquid carbon dioxide drying, which can maintain the original nanofiber structure of the gel to the greatest extent and improve the thermal insulation performance of the aerogel sample. Those skilled in the art can follow the conventional operation of the supercritical liquid carbon dioxide drying method.

[0030] In the present invention, the microscopic morphology of the nanofiber and nanoporous double-nano aerogel material is that the nanofibers are aggregated to form a nanoporous network structure; the diameter of the nanofiber is 20 to 90 nm, preferably 40 to 70 nm, and more preferably 50 to 60 nm; The pore size of the nanopore is 10 to 50 nm, preferably 15 to 40 nm, and more preferably 20 to 30 nm. In the present invention, the specific surface area of ​​the nanofiber and nanoporous double nano aerogel material is 200 to 400 m 2 / g, the porosity is 85% to 95%, and the thermal conductivity is 15 to 35 mW / (m·K).

[0031] The present invention also provides degradable high-toughness and low-thermal conductivity nanofiber aerogel prepared by the above preparation method.

[0032] The present invention also provides application of the above-mentioned degradable high-toughness and low-thermal conductivity nanofiber aerogel in thermal insulation.

[0033] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0034] Example 1 200 mg of konjac glucomannan was added to 20 ml of 0.01 M sodium carbonate solution, and then stirred at room temperature for 10 min until the konjac glucomannan was completely dissolved to obtain a uniform mixed solution. The above solution was poured into a mold and heated at 90 ° C for 1 h to obtain a hydrogel. The hydrogel was then soaked in a methanol aqueous solution for 2 times, with the concentrations of 30%, 50%, and 70% respectively, and then soaked in anhydrous methanol for 3 times to remove moisture, and finally soaked in anhydrous ethanol for 2 times, each time for 8 hours, and the solution was changed each time. The obtained ethanol gel was treated by supercritical liquid carbon dioxide drying to obtain the final aerogel sample (KGM-1).

[0035] Example 2 400 mg of konjac glucomannan was added to 20 ml of 0.02 M sodium carbonate solution, and then stirred at room temperature for 10 min until the konjac glucomannan was completely dissolved to obtain a uniform mixed solution. The above solution was poured into a mold and heated at 90 ° C for 1 h to obtain a hydrogel. The hydrogel was then soaked in a methanol aqueous solution for 2 times, with the concentrations of 30%, 50%, and 70% respectively, and then soaked in anhydrous methanol for 3 times to remove moisture, and finally soaked in anhydrous ethanol for 2 times, each time for 8 hours, and the solution was changed each time. The obtained ethanol gel was treated by supercritical liquid carbon dioxide drying to obtain the final aerogel sample (KGM-2).

[0036] Example 3 600 mg of konjac glucomannan was added to 20 ml of 0.03 M sodium carbonate solution, and then stirred at room temperature for 10 min until the konjac glucomannan was completely dissolved to obtain a uniform mixed solution. The above solution was poured into a mold and heated at 90 ° C for 1 h to obtain a hydrogel. The hydrogel was then soaked in a methanol aqueous solution for 2 times, with the concentrations of 30%, 50%, and 70% respectively, and then soaked in anhydrous methanol for 3 times to remove moisture, and finally soaked in anhydrous ethanol for 2 times, each time for 8 hours, and the solution was changed each time. The obtained ethanol gel was treated by supercritical liquid carbon dioxide drying to obtain the final aerogel sample (KGM-3).

[0037] Example 4 800 mg of konjac glucomannan was added to 20 ml of 0.04 M sodium carbonate solution, and then stirred at room temperature for 10 min until the konjac glucomannan was completely dissolved to obtain a uniform mixed solution. The above solution was poured into a mold and heated at 90 ° C for 1 h to obtain a hydrogel. The hydrogel was then soaked in a methanol aqueous solution for 2 times, with the concentrations of 30%, 50%, and 70% respectively, and then soaked in anhydrous methanol for 3 times to remove moisture, and finally soaked in anhydrous ethanol for 2 times, each time for 8 hours, and the solution was changed each time. The obtained ethanol gel was treated by supercritical liquid carbon dioxide drying to obtain the final aerogel sample (KGM-4).

[0038] Example 5 1200 mg of konjac glucomannan was added to 20 ml of 0.06 M sodium carbonate solution, and then stirred at room temperature for 10 min until the konjac glucomannan was completely dissolved to obtain a uniform mixed solution. The above solution was poured into a mold and heated at 90 ° C for 1 h to obtain a hydrogel. The hydrogel was then soaked in a methanol aqueous solution for 2 times, with the concentrations of 30%, 50%, and 70% respectively, and then soaked in anhydrous methanol for 3 times to remove moisture, and finally soaked in anhydrous ethanol for 2 times, each time for 8 hours, and the solution was changed each time. The obtained ethanol gel was treated by supercritical liquid carbon dioxide drying to obtain the final aerogel sample (KGM-5).

[0039] Example 6 1200 mg of konjac glucomannan was added to 20 ml of 0.06 M sodium carbonate solution, and then stirred at room temperature for 10 min until the konjac glucomannan was completely dissolved to obtain a uniform mixed solution. The above solution was poured into a mold and heated at 90 ° C for 1 h to obtain a hydrogel. Then the hydrogel was soaked in methanol aqueous solution twice in sequence, with the concentrations of 30%, 50%, and 70% respectively, and then soaked in anhydrous ethanol for 3 times to remove moisture, and finally soaked in anhydrous isopropanol twice, each time for 8 hours, and the solution was changed each time. The obtained isopropanol gel was treated by supercritical liquid carbon dioxide drying to obtain the final aerogel sample.

[0040] The aerogels obtained in the above five embodiments were subjected to thermal conductivity test, specific surface area and pore size test, scanning electron microscope test and compression test. The specific results are shown in the accompanying drawings and Table 1. It can be seen from the results that a nanofiber konjac aerogel thermal insulation material can be obtained by adopting the present method, which also has great application prospects in the field of thermal insulation.

[0041]

[0042] Figure 1 This is a photo of the aerogel prepared in Example 1 of the present invention.

[0043] Figure 2 It can be seen that the specific surface area of ​​aerogel is 270 m 2 / g, and the average pore size is 10-50 nm, proving that the aerogel is a mesoporous material with a fine nanopore structure. (The specific surface area and average pore size obtained by nitrogen adsorption isotherm have a mature calculation formula, which is a well-known technology)

[0044] Figure 3The scanning electron microscope image shows that KGM aerogel is composed of nanofibers tightly wound together to form a fine nano three-dimensional structure with interconnected pores. The diameter of the nanofibers is about 50 nm.

[0045] Figure 4 The thermal conductivity of the aerogel was measured, and it can be seen that with the increase in the concentration of the konjac glucomannan solution, the thermal conductivity of the aerogel first decreases and then increases, showing a "U"-shaped trend, among which the thermal conductivity of KGM-2 is the lowest. Therefore, the aerogel prepared by the present invention has a great application prospect in the field of thermal insulation.

[0046] Figure 5 The compressive stress-strain curve of the aerogel was measured, and the elastic modulus was calculated by fitting the curve at 0-3% strain. The mechanical strength of the aerogel increased with the increase of the concentration of konjac glucomannan solution. It can be seen that the prepared konjac glucomannan aerogel has good mechanical properties.

Claims

1. A method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel, characterized in that: The following steps are involved: Step 1) mixing the konjac glucomannan powder raw material with a sodium carbonate solution to remove the acetyl group to obtain a deacetylated konjac glucomannan solution; Step 2) heating the konjac glucomannan solution obtained in step 1) to obtain a konjac glucomannan hydrogel; Step 3) The konjac glucomannan hydrogel obtained in step 2) is gradually immersed in organic solvents with concentrations ranging from low to high to obtain an organic gel with nanofibers, and further supercritical drying is performed to obtain nanofibers and nanoporous double-nano aerogels.

2. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: The concentration of the sodium carbonate solution in step 1) is 0.01-0.06 mol / L.

3. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: In the step 1), the concentration of the konjac glucomannan solution is 10-60 mg / mL; and the stirring mixing time is 1-3 min.

4. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: In the step 2), the heating temperature is 85°C to 95°C, and the heating time is 0.5 to 1.5 h.

5. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: The organic solvent solution in step 3) includes one or more of ethanol solution, methanol solution and isopropanol solution. The volume concentration of the organic solvent is 30-100%.

6. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: The soaking in step 3) is performed 1 to 3 times for 8 to 12 hours, and the organic solvent needs to be replaced each time the soaking is performed.

7. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: Step 3) The obtained aerogel consists of nanofibers and nanopores, the diameter of the nanofibers is 20 to 100 nanometers, the diameter of the nanopores is 10 to 50 nanometers, the porosity is 85% to 95%, and the thermal conductivity is 15 to 35 mW / (m·K) at room temperature.

8. The method for preparing a degradable high-toughness and low-thermal conductivity nanofiber aerogel according to claim 1, characterized in that: The drying method in step 3) is supercritical carbon dioxide drying, and the pressure during the drying process is 15 MPa and the temperature is 50°C.

9. A degradable high-toughness and low-thermal conductivity nanofiber aerogel, wherein the degradable high-toughness and low-thermal conductivity nanofiber aerogel is prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The degradable high-toughness and low-thermal conductivity nanofiber aerogel is used in thermal insulation materials.

Images