Composite aerogel and preparation method thereof

Abstract

The invention relates to the technical field of composite aerogel, in particular to composite aerogel and a preparation method thereof. The method comprises the following steps: (1-1) adding nanofibers and cellulose into a dispersion solvent A to obtain a dispersion liquid A; wherein the diameter of the nanofiber is 100 to 500 nm, and the length-diameter ratio of the nanofiber is 50 to 300; and (1-2) carrying out aging, solvent replacement, freezing and optional fumigation treatment on the dispersion liquid A to obtain the composite aerogel. According to the preparation method of the composite aerogel provided by the invention, nanofibers with specific sizes are compounded with cellulose, so that the mechanical property of the composite aerogel can be remarkably improved, and the heat insulation property of the composite aerogel can be greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite aerogel, and particularly relates to a composite aerogel and a preparation method thereof. BACKGROUND

[0002] Cellulose is the most abundant natural polymer on earth, and cellulose aerogel material developed by using its excellent biocompatibility, degradability, low density, and renewable advantages has broad application prospects in the fields of drug release, cosmetics, and catalysis. Cellulose aerogel is the third generation of aerogel developed after inorganic aerogel and organic aerogel. Since cellulose contains many active hydroxyl groups, a three-dimensional porous structure can be formed by physical cross-linking of intramolecular and intermolecular hydrogen bonds in the preparation process without using a cross-linking agent, so that the preparation process of the aerogel is relatively simple.

[0003] However, cellulose aerogel also has its own defects: since many hydroxyl groups on cellulose cannot form effective hydrogen bonds, the mechanical properties of cellulose aerogel are poor, such as low strength, poor toughness, and easy to break. In addition, the pore size and density of cellulose aerogel are large, resulting in a high thermal conductivity of 0.04 W / m·K.

[0004] In CN106009031A, cellulose is dissolved in a mixed solution of NaOH, polyvinyl alcohol and water, and after heating, freezing, regeneration treatment in an acid solution and drying, high-strength cellulose aerogel is obtained, and the elastic modulus and toughness thereof reach 1.03 MPa and 245 kJ / m 3 , respectively. CN103709435A discloses a preparation method of light and high-strength cellulose aerogel. A cellulose solution is configured, and then the cellulose solution is frozen and thawed for 1-100 cycles to obtain a cellulose solution after cycle treatment. Then, the cellulose solution after cycle treatment is added to an acid solution to gel, displace and dry, and light and high-strength cellulose aerogel is obtained. The maximum load of the cellulose aerogel prepared by the method can reach 50 N-200 N, but both of the two methods need acid-base reaction conditions, have high requirements for equipment corrosion resistance, and are easy to pollute the environment.

[0005] A preparation method of cellulose / polyurethane composite aerogel is disclosed in CN103012835A, which comprises the following steps: step one, dissolving cellulose by using a cellulose green dissolution system, and then preparing a cellulose wet gel; step two, performing solvent exchange on the cellulose wet gel obtained in step one to obtain a cellulose organic wet gel containing an organic solvent; step three, dissolving an isocyanate resin and a catalyst in the organic solvent; step four, immersing the cellulose wet gel obtained in step two into the solution prepared in step three to obtain a cellulose / polyurethane composite wet gel; and step five, drying the cellulose / polyurethane composite wet gel obtained in step four to obtain the cellulose / polyurethane composite aerogel. Although the cellulose / polyurethane composite aerogel prepared by the method has excellent mechanical properties, the method has defects such as complex preparation process, long cycle, and additional addition of an organic catalyst due to hydrolysis and polycondensation reaction of the polymer precursor.

[0006] Therefore, it is urgent to provide a method for preparing cellulose aerogel with good mechanical properties and low thermal conductivity. SUMMARY

[0007] The present application aims to solve the problems of poor mechanical properties and high thermal conductivity of cellulose aerogel in the prior art, and provides a composite aerogel and a preparation method thereof.

[0008] To achieve the above-mentioned purpose, the first aspect of the present application provides a method for preparing a composite aerogel, wherein the method comprises the following steps:

[0009] (1-1) adding nanofibers and cellulose into a dispersion solvent A to obtain a dispersion liquid A; wherein the diameter of the nanofibers is 100-500 nm, and the aspect ratio is 50-300;

[0010] (1-2) performing aging, solvent replacement, freezing and optional fumigation treatment on the dispersion liquid A to obtain a composite aerogel.

[0011] The second aspect of the present application provides a method for preparing a composite aerogel, wherein the method comprises the following steps:

[0012] (2-1) adding nanofibers, cellulose derivatives and a crosslinking agent into a dispersion solvent B to obtain a dispersion liquid B; wherein the diameter of the nanofibers is 100-500 nm, and the aspect ratio is 50-300; the dispersion solvent B is selected from water, acetone and the dispersion solvent A;

[0013] (2-2) when the dispersion solvent B is water, the dispersion B is subjected to aging, freezing and optional fumigation treatment to obtain a composite aerogel; when the dispersion solvent B is acetone or the dispersion solvent A, the dispersion B is subjected to aging, solvent replacement, freezing and optional fumigation treatment to obtain a composite aerogel.

[0014] The third aspect of the present application provides a composite aerogel prepared by the method of the first aspect of the present application.

[0015] Through the above technical solutions, the present application has the following beneficial technical effects:

[0016] 1) The preparation method of the composite aerogel provided in the present application can significantly improve the mechanical properties of the composite aerogel and greatly improve the thermal insulation performance of the composite aerogel by compounding nanofibers with specific sizes and cellulose or cellulose derivatives.

[0017] 2) The preparation method of the composite aerogel provided in the present application can further improve the toughness and elastic modulus of the composite aerogel through fumigation treatment.

[0018] 3) The composite aerogel provided in the present application has excellent mechanical properties, good toughness, large elastic modulus and is not easy to break, and has low thermal conductivity, good thermal insulation performance, wide application prospect and is suitable for industrialization. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values disclosed in this document are not limited to the precise values recited as the exact dimensions are not critical to the present application. The ranges and values should be interpreted as being approximate such that modest variation from the recited values of the ranges and values is intended to be within the scope of the application. The ranges and values of numerical parameters include all values from and including the lower and upper values of the ranges, and values within ranges defined by the minimum and maximum values. These ranges and values are to be interpreted as being approximate such that modifications of less than 1% either way are within the scope of the application. The disclosure is also drawn to individual values within these ranges and values.

[0020] The first aspect of the present application provides a preparation method of a composite aerogel, wherein the method comprises the following steps:

[0021] (1-1) adding nanofibers and cellulose into a dispersion solvent A to obtain a dispersion A; wherein the diameter of the nanofibers is 100-500 nm, and the aspect ratio is 50-300;

[0022] (1-2) subjecting the dispersion A to aging, solvent replacement, freezing and optional fumigation treatment to obtain a composite aerogel.

[0023] In the present application, the inventors have found that compounding nanofibers with specific sizes and cellulose can significantly improve the mechanical properties of the composite aerogel and greatly improve the thermal insulation performance of the composite aerogel.

[0024] In step (1-1):

[0025] In a preferred embodiment of the present application, the nanofiber is selected from one or more of polystyrene nanofiber, polyethylene terephthalate nanofiber, polyurethane nanofiber, polyimide nanofiber, polyethylene nanofiber, polypropylene nanofiber, polyvinyl chloride nanofiber, chlorinated polyvinyl chloride nanofiber, polyvinylidene chloride nanofiber, polyamide nanofiber, polyvinylidene fluoride nanofiber, polyacrylonitrile nanofiber, preferably selected from one or more of polystyrene nanofiber, polyethylene terephthalate nanofiber, polyimide nanofiber.

[0026] In the present application, the source of the nanofiber is not particularly limited, and the nanofiber can be a commercially available product or prepared by a method known in the art. For example, the nanofiber can be prepared by electrospinning using plastic as raw material.

[0027] In a preferred embodiment of the present application, the method for preparing the nanofiber comprises the following sub-steps:

[0028] (a) dissolving the plastic in an organic solvent to obtain a homogeneous solution;

[0029] (b) electrospinning the homogeneous solution to obtain the nanofiber.

[0030] Preferably, the plastic is selected from one or more of polystyrene, polyethylene terephthalate, polyurethane, polyimide, polyethylene, polypropylene, polyvinyl chloride, chlorinated polyvinyl chloride, polyvinylidene chloride, polyamide, polyvinylidene fluoride, polyacrylonitrile, preferably selected from one or more of polystyrene, polyethylene terephthalate, polyimide.

[0031] In the present application, the plastic can be a new plastic or a waste plastic. In order to reduce the production cost of the composite cellulose aerogel and realize the resource utilization of waste plastic, it is preferred to use waste plastic to prepare the nanofiber.

[0032] Preferably, the organic solvent is selected from one or more of toluene, xylene, tetrahydronaphthalene, decahydronaphthalene, 1-chloronaphthalene, hexadecane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, cyclohexanone, methyl ethyl ketone, carbon disulfide, dichloroethane, trichloromethane, tetrachloroethane, ethyl acetate, butyl acetate, chlorobenzene, epichlorohydrin, dimethyl sulfoxide, trifluoroacetic acid, hexafluoroisopropanol, o-chlorophenol, m-cresol, formic acid, phenol, triethyl phosphate, sulfolane. In the present application, the organic solvent capable of dissolving the plastic can be selected according to the specific type of plastic, which will not be described one by one.

[0033] Preferably, the mass ratio of the plastic and the organic solvent is 1:5-45, preferably 1:10-30. In the present application, when the mass ratio of the plastic and the organic solvent is within the above range, the solubility of the plastic can be improved as much as possible under the premise of reducing the amount of the organic solvent, which helps to improve the spinning effect of electrospinning.

[0034] Preferably, the operation condition of the dissolving includes: the dissolving temperature is 40-160℃, preferably 60-130℃; the dissolving time is 30-300min, preferably 60-180min. In the present application, the specific operation condition of the dissolving can be adjusted according to the specific type of the plastic and the organic solvent, so as to ensure that the plastic can be quickly dissolved in the organic solvent.

[0035] Preferably, the operation condition of the electrospinning includes: the spinning voltage is 12-25KV, preferably 15-20KV; the receiving distance is 10-30cm, preferably 15-20cm; the flow rate of the electrospinning liquid is 0.5-1.5mL / h, preferably 0.8-1.2mL / h.

[0036] In a preferred embodiment of the present application, the diameter of the nanofiber is 100-300nm, and the aspect ratio is 100-250.

[0037] In the present application, the inventors have found that, when the nanofiber is too slender, the nanofiber filament cannot provide sufficient toughness, and in the process of homogeneous dispersion, the nanofibers are easily entangled, the cohesion and friction force increase, and finally the mechanical properties of the prepared composite aerogel are reduced; when the nanofiber is too thick, the density of the prepared composite aerogel increases, the porosity decreases, which leads to the increase of the thermal conductivity and the decrease of the heat insulation performance. When the size of the nanofiber is within the above limited range, the mechanical properties and the heat insulation performance of the composite aerogel are better.

[0038] In a preferred embodiment of the present application, the cellulose is derived from herbaceous plants or woody plants, preferably from one or more of weeds, leaves, wood chips, bamboo, hemp, cotton, straw, coconut shell, and bagasse, for example, the cellulose can be wood fiber, bamboo fiber, cotton fiber (such as defatted cotton), hemp fiber, crop straw cellulose, and sugarcane cellulose (obtained by delignification and hemicellulose extraction from bagasse powder).

[0039] In a preferred embodiment of the present application, the dispersion solvent A is selected from one or more of N-methylmorpholine-N-oxide aqueous solution, N,N dimethylacetamide / LiCl (mass ratio of 90-95:5-10), 1,3-dimethyl-2-imidazolidinone / LiCl (mass ratio of 90-95:5-10), dimethyl sulfoxide / LiCl (mass ratio of 90-95:5-10), [Emim]OAc, [Bmim]OAc, [Omim]OAc, [Amim]Cl, [Bmim]Cl, [Emim]Cl, [Hmim]Cl, [C4mpy]Cl, [Bmim]Br, [Amim]HCOO, [Bmim]HCOO, preferably selected from one or more of [Emim]OAc, [Bmim]OAc, [Omim]OAc, [Amim]Cl, [Bmim]Cl, [Emim]Cl, [Hmim]Cl, [C4mpy]Cl, [Bmim]Br, [Amim]HCOO, [Bmim]HCOO.

[0040] In a preferred embodiment of the present application, the mass ratio of the nanofiber, cellulose and dispersion solvent A is 0.05-1.5:0.3-2.5:100, preferably 0.2-1:0.5-2:100.

[0041] In the present application, the inventors have found that, when the amount of nanofiber is too large, the cross-linking degree between the cellulose framework is weakened, resulting in a decrease in the mechanical properties of the composite aerogel framework and adversely affecting the thermal insulation performance of the composite aerogel; when the amount of nanofiber is too small, the mechanical properties of the composite aerogel are adversely affected; when the mass ratio of nanofiber and cellulose is within the above range, the composite aerogel has good mechanical properties and beneficial thermal insulation performance.

[0042] In a preferred embodiment of the present application, the nanofiber and cellulose are added to the dispersion solvent A for homogeneous dispersion to obtain dispersion liquid A. The operating conditions of the homogeneous dispersion include a homogenization speed of 3000-20000 rpm, preferably 5000-15000 rpm, and a homogenization time of 10-60 min, preferably 20-40 min.

[0043] In the present application, the cellulose can be dissolved in the dispersion solvent A, but the nanofiber cannot be dissolved in the dispersion solvent A. The homogeneous dispersion operation can improve the dispersibility of the nanofiber in the dispersion liquid A, which helps to improve the comprehensive performance of the composite aerogel.

[0044] In step (1-2),

[0045] In one embodiment of the present application, in order to remove the bubbles in the dispersion A, further improve the uniformity of the dispersion, preferably, the dispersion A is subjected to ultrasonic treatment before the aging of the dispersion A; wherein the operation conditions of the ultrasonic treatment include: the ultrasonic power is 200-1000w, preferably 500-700w; the ultrasonic time is 10-50min, preferably 20-40min.

[0046] In one embodiment of the present application, the operation conditions of the aging treatment include: the aging temperature is 25-50℃, preferably 30-40℃; the aging time is 4-48h, preferably 24-36h.

[0047] In the present application, the aging treatment can promote the construction of three-dimensional network structure of the nanofiber and the cellulose, enrich the pore structure, and help to further improve the mechanical stability and thermal insulation performance of the composite aerogel.

[0048] In one preferred embodiment of the present application, the operation of the solvent replacement includes: adding the replacement solvent to the dispersion A and standing to obtain the composite wet gel.

[0049] In the present application, after adding the replacement solvent to the dispersion A, the nanofiber and the cellulose form the composite wet gel and precipitate under the action of the replacement solvent. Through the operation of the solvent replacement, the replacement solvent can penetrate into the composite wet gel, which helps to improve the subsequent freezing effect.

[0050] In one preferred embodiment of the present application, the replacement solvent is selected from water and / or tert-butyl alcohol, preferably tert-butyl alcohol.

[0051] In one preferred embodiment of the present application, the operation of the solvent replacement includes: the replacement temperature is room temperature, the replacement time is 3-15h, preferably 6-12h, and the replacement times is 3-10 times, preferably 5-8 times.

[0052] In one preferred embodiment of the present application, the operation conditions of the freezing include: the freezing temperature is -80℃ to -10℃, preferably -60℃ to -30℃; the freezing time is 5-25h, preferably 10-15h.

[0053] In the present application, after the freezing is completed, the frozen product can be dried, and the drying is selected from one or more of freeze drying, supercritical carbon dioxide drying, and vacuum freeze drying. The frozen product obtained after the freeze drying is the composite aerogel with excellent mechanical properties and thermal insulation performance.

[0054] In a preferred embodiment of the present application, the dispersion A is subjected to solvent replacement, freezing and fumigation treatment in sequence to obtain a composite aerogel. In the present application, the fumigation treatment can further promote the formation of a three-dimensional network structure in the composite aerogel, enrich the micro-pores of the composite aerogel, and help to further improve the toughness and elastic modulus of the composite aerogel.

[0055] In a preferred embodiment of the present application, the fumigation treatment comprises: contacting the frozen product after freezing with a fumigation solvent to perform fumigation, thereby obtaining a composite aerogel; wherein the fumigation solvent is selected from the organic solvent, and the boiling point of the fumigation solvent is 100-200℃, preferably 130-170℃. In the present application, the frozen product can be subjected to a drying treatment, such as freeze-drying, supercritical carbon dioxide drying or vacuum freeze-drying, prior to the fumigation treatment.

[0056] In a preferred embodiment of the present application, the fumigation solvent is selected from one or more of toluene, xylene, tetrahydronaphthalene, decahydronaphthalene, 1-chloronaphthalene, hexadecane, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, cyclohexanone, methyl ethyl ketone, carbon disulfide, dichloroethane, trichloromethane, tetrachloroethane, ethyl acetate, butyl acetate, chlorobenzene, epichlorohydrin, dimethyl sulfoxide, trifluoroacetic acid, hexafluoroisopropanol, o-chlorophenol, m-cresol, formic acid, phenol, triethyl phosphate, and sulfolane.

[0057] In the present application, when the nanofiber is a polystyrene nanofiber, the fumigation solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, toluene, xylene, cyclohexanone, and butyl acetate, preferably cyclohexanone. When the nanofiber is a polyethylene terephthalate nanofiber, the fumigation solvent is one or more of tetrachloroethane, phenol, and o-chlorophenol, preferably a mixed solvent of tetrachloroethane and phenol, further preferably a mixed solvent of tetrachloroethane and phenol in a volume ratio of 1:1-3.

[0058] When the nanofiber is a polyurethane nanofiber or / and a polyimide nanofiber, the fumigation solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, preferably N,N-dimethylformamide; when the nanofiber is a polyethylene nanofiber and / or a polypropylene nanofiber, the fumigation solvent is toluene and / or xylene, preferably xylene.

[0059] When the nanofiber is one or more of polyvinyl chloride nanofiber, chlorinated polyvinyl chloride nanofiber, and polyvinylidene chloride nanofiber, the fumigation solvent is one or more of tetrachloroethane, chlorobenzene, epichlorohydrin, cyclohexanone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, and preferably is cyclohexanone. When the nanofiber is polyamide nanofiber, the fumigation solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, formic acid, and phenol, and preferably is formic acid.

[0060] When the nanofiber is polyvinylidene fluoride nanofiber, the fumigation solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, and preferably is N,N-dimethylformamide. When the nanofiber is polyacrylonitrile nanofiber, the fumigation solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide, and preferably is N,N-dimethylformamide.

[0061] In a preferred embodiment of the present application, the operation conditions of the fumigation treatment are as follows: the fumigation temperature is 50-100℃, preferably 60-90℃; and the fumigation time is 0.5-4h, preferably 1-2h. In the present application, the fumigation temperature and the fumigation time are more optimal when they are within the above typical ranges.

[0062] The second aspect of the present application provides a preparation method of a composite aerogel, wherein the method comprises the following steps:

[0063] (2-1) adding nanofiber, cellulose derivative, and crosslinking agent into dispersion solvent B to obtain dispersion liquid B; wherein the diameter of the nanofiber is 100-500nm, and the aspect ratio is 50-300; the dispersion solvent B is selected from water, acetone, or the dispersion solvent A;

[0064] (2-2) when the dispersion solvent B is water, the dispersion liquid B is subjected to aging, freezing, and optional fumigation treatment to obtain a composite aerogel; when the dispersion solvent B is acetone or the dispersion solvent A, the dispersion liquid B is subjected to aging, dissolution replacement, freezing, and optional fumigation treatment to obtain a composite aerogel.

[0065] In the present application, compared with cellulose, the number of hydroxyl groups on the molecular chain of the cellulose derivative is reduced, and by adding the crosslinking agent, nanofibers of a specific size can be combined with the cellulose derivative, which not only significantly improves the mechanical properties of the composite aerogel, but also greatly improves the thermal insulation performance of the composite aerogel.

[0066] In step (2-1):

[0067] In a preferred embodiment of the present application, the nanofibers and the dispersion solvent A are the same as the nanofibers and the dispersion solvent A described in the first aspect of the present application.

[0068] In a preferred embodiment of the present application, the cellulose derivative is selected from one or more of carboxylated cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose acetate butyrate.

[0069] In the present application, compared with cellulose, the number of hydroxyl groups on the molecular chain of the cellulose derivative is less, and by adding the crosslinking agent, the combination between the nanofibers and the cellulose derivative can be more sufficient, and the mechanical properties of the prepared composite aerogel can be obviously improved.

[0070] In a preferred embodiment of the present application, the crosslinking agent is selected from one or more of polyethylene glycol diglycidyl ether, citric acid, 1,4-butanediol diglycidyl ether, epichlorohydrin, and preferably is polyethylene glycol diglycidyl ether.

[0071] In a preferred embodiment of the present application, the mass ratio of the nanofibers, the cellulose derivative, the crosslinking agent and the dispersion solvent B is 0.05-1.5:0.3-2.5:0.05-1:100, and preferably is 0.2-1:0.5-2:0.1-0.6:100.

[0072] In the present application, the inventors have found through research that when the mass ratio of the nanofibers, the cellulose derivative, the crosslinking agent and the dispersion solvent B is within the above range, the prepared composite aerogel can have good mechanical properties and excellent thermal insulation performance.

[0073] In a preferred embodiment of the present application, the nanofibers, the cellulose derivative and the crosslinking agent are added to the dispersion solvent B for homogeneous dispersion to obtain a dispersion liquid B. Preferably, the operation conditions of the homogeneous dispersion include: a homogeneous speed of 3000-20000 rpm, and preferably 5000-15000 rpm; a homogeneous time of 10-60 min, and preferably 20-40 min.

[0074] In the present application, the cellulose derivative can be dissolved in the dispersion solvent B, but the nanofibers cannot be dissolved in the dispersion solvent B, and the homogeneous dispersion operation can improve the dispersibility of the nanofibers in the dispersion liquid B, which helps to improve the comprehensive performance of the composite aerogel.

[0075] In step (2-2):

[0076] In one embodiment of the present invention, before aging the dispersion B, in order to remove air bubbles in the dispersion and further improve the uniformity of dispersion, it is preferable to first subject the dispersion B to ultrasonic treatment; wherein, the operating conditions of the ultrasonic treatment include: ultrasonic power of 200-1000w, preferably 500-700w; ultrasonic time of 10-50min, preferably 20-40min.

[0077] In one embodiment of the present invention, the aging, dissolution and replacement, freezing and fumigation treatments in step (2-2) are the same as the aging, dissolution and replacement, freezing and fumigation treatments in step (1-2) of the first aspect of the present invention, and will not be described in detail hereafter.

[0078] A third aspect of the present invention provides a composite aerogel prepared using the method described in the first aspect of the present invention.

[0079] In a preferred embodiment of the present invention, the composite aerogel has a toughness of 450-530 kJ / m. 3 The preferred value is 495-515 kJ / m 3 The elastic modulus is 0.8-1.3 MPa, preferably 1.05-1.2 MPa; the thermal conductivity is 0.03-0.04 W / m·k, preferably 0.031-0.035 W / m·k.

[0080] The present invention will be described in detail below through embodiments.

[0081] Example 1

[0082] (1-1) Add waste polystyrene to tetrahydrofuran and stir at 60°C for 60 min until the waste polystyrene is fully dissolved to obtain a homogeneous solution; wherein the mass ratio of waste polystyrene to tetrahydrofuran is 1:20.

[0083] The above homogeneous solution was placed in a spinneret and electrospinned under the conditions of a spinning voltage of 15kV, a receiving distance of 18cm, and an electrospinning solution flow rate of 0.8mL / h to obtain nanofibers with a diameter of 300nm and an aspect ratio of 200.

[0084] Add 0.5g of the above nanofibers and 1.0g of degreased cotton to 100g of [Amim]Cl, and homogenize them at 10000rpm for 30min to obtain dispersion A;

[0085] (1-2) The dispersion liquid A was treated with ultrasonic waves at a power of 500 w for 30 min, and after removing the bubbles, it was aged at 35 °C for 30 h. Then, t-butyl alcohol was slowly added to the dispersion liquid A for solvent replacement, the replacement time was 8 h, and the replacement number was 6 times. Then, it was first frozen at -30 °C for 12 h, and then vacuum freeze-dried at -196 °C for 48 h. Then, it was fumigated with cyclohexanone vapor at 65 °C for 1 h to obtain a composite cellulose aerogel.

[0086] Example 2

[0087] (1-1) The waste polyimide was added to N,N-dimethylformamide, and stirred at 90 °C for 100 min until the waste polyimide was fully dissolved to obtain a homogeneous solution; wherein the mass ratio of waste polyimide to N,N-dimethylformamide was 1:30;

[0088] The above homogeneous solution was placed into a spinning nozzle, and electrospinning was carried out under the conditions of a spinning voltage of 20 kV, a receiving distance of 20 cm, and an electrospinning liquid flow rate of 1.0 mL / h to obtain nanofibers with a diameter of 250 nm and an aspect ratio of 150;

[0089] 0.4 g of the above nanofibers and 1.2 g of the absorbent cotton were added to 100 g of [Bmim]Cl, and homogenously dispersed at a rotation speed of 10,000 rpm for 30 min to obtain a dispersion liquid A;

[0090] (1-2) The dispersion liquid A was treated with ultrasonic waves at a power of 500 w for 30 min, and after removing the bubbles, it was aged at 40 °C for 24 h. Then, t-butyl alcohol was slowly added to the dispersion liquid A for solvent replacement, the replacement time was 6 h, and the replacement number was 8 times. Then, it was first frozen at -30 °C for 12 h, and then vacuum freeze-dried at -196 °C for 48 h. Then, it was fumigated with N,N-dimethylformamide vapor at 70 °C for 1.5 h to obtain a composite cellulose aerogel.

[0091] Example 3

[0092] (1-1) The waste polyethylene terephthalate was added to trifluoroacetic acid, and stirred at 60 °C for 60 min until the waste polyethylene terephthalate was fully dissolved to obtain a homogeneous solution; wherein the mass ratio of waste polyethylene terephthalate to trifluoroacetic acid was 1:10;

[0093] The above homogeneous solution was placed into a spinning nozzle, and electrospinning was carried out under the conditions of a spinning voltage of 18 kV, a receiving distance of 15 cm, and an electrospinning liquid flow rate of 1.2 mL / h to obtain nanofibers with a diameter of 200 nm and an aspect ratio of 250;

[0094] 0.8 g of the above nanofiber and 1.5 g of the defatted cotton were added to 100 g of [Emim]Cl, and homogenously dispersed at a rotation speed of 10,000 rpm for 30 min to obtain dispersion liquid A;

[0095] (1-2) The dispersion liquid A was ultrasonically treated at a power of 500 w for 30 min, and after removing the bubbles, was aged at 30°C for 36 h. Then, t-butyl alcohol was slowly added to the dispersion liquid A for solvent replacement, the replacement time was 12 h, and the replacement was performed 5 times. Then, the dispersion liquid was first frozen at -30°C for 12 h, and then vacuum freeze-dried at -196°C for 48 h. Then, the dispersion liquid was fumed in a mixed solvent of tetrachloroethane and phenol (volume ratio of 1:1) at 70°C for 1 h to obtain the composite cellulose aerogel.

[0096] Example 4

[0097] (1-1) 0.15 g of polyacrylonitrile nanofiber (commercially available, diameter of 400 nm, aspect ratio of 50) and 0.4 g of cellulose (obtained by delignification and hemicellulose extraction from sugar cane bagasse powder) were added to 100 g of a mixed solvent of dimethyl sulfoxide / LiCl with a mass ratio of 92:8, and homogenously dispersed at a rotation speed of 3,000 rpm for 60 min to obtain dispersion liquid A;

[0098] (1-2) The dispersion liquid A was ultrasonically treated at a power of 200 w for 50 min, and after removing the bubbles, was aged at 50°C for 12 h. Then, water was slowly added to the dispersion liquid A for solvent replacement, the replacement time was 4 h, and the replacement was performed 10 times. Then, the dispersion liquid was first frozen at -30°C for 12 h, and then vacuum freeze-dried at -196°C for 48 h. Then, the dispersion liquid was fumed in N,N-dimethylformamide at 100°C for 0.5 h to obtain the composite cellulose aerogel.

[0099] Example 5

[0100] (1-1) 1.2 g of polyvinyl chloride nanofiber (commercially available, diameter of 100 nm, aspect ratio of 300) and 2.2 g of cellulose (obtained by delignification and hemicellulose extraction from sugar cane bagasse powder) were added to 100 g of a mixed solution of N,N-dimethylacetamide / LiCl with a mass ratio of 92:8, and homogenously dispersed at a rotation speed of 20,000 rpm for 10 min to obtain dispersion liquid A;

[0101] (1-2) The dispersion liquid A was subjected to ultrasonic treatment at a power of 1000 w for 10 min, and after removing the bubbles, was aged at 50°C for 12 h, and then solvent replacement was performed by slowly adding water to the dispersion liquid A, the replacement time was 15 h, and the replacement number was 3 times; and then, freezing was performed at -30°C for 12 h, and vacuum freeze-drying was performed at -196°C for 48 h, and then fumigation was performed at 55°C for 3 h in cyclohexanone vapor, to obtain a composite cellulose aerogel.

[0102] Example 6

[0103] (2-1) 0.4 g of polyethylene terephthalate nanofiber (same as Example 3), 0.8 g of carboxylated cellulose, and 0.2 g of polyethylene glycol diglycidyl ether were added to 100 g of [Amim]Cl, and homogenously dispersed at a rotation speed of 10000 rpm for 30 min to obtain a dispersion liquid B;

[0104] (2-2) The dispersion liquid B was subjected to ultrasonic treatment at a power of 500 w for 30 min, and after removing the bubbles, was aged at 35°C for 30 h, and then solvent replacement was performed by slowly adding t-butyl alcohol to the dispersion liquid B, the replacement time was 8 h, and the replacement number was 6 times; and then, freezing was performed at -30°C for 12 h, and vacuum freeze-drying was performed at -196°C for 48 h, and then fumigation was performed at 70°C for 1 h in a mixed solvent of tetrachloroethane and phenol (volume ratio of 1:1) vapor, to obtain a composite cellulose aerogel.

[0105] Example 7

[0106] (2-1) 0.6 g of polystyrene nanofiber (same as Example 1), 1.2 g of carboxymethyl cellulose, and 0.3 g of polyethylene glycol diglycidyl ether were added to 100 g of deionized water, and homogenously dispersed at a rotation speed of 10000 rpm for 30 min to obtain a dispersion liquid B;

[0107] (2-2) The dispersion liquid B was subjected to ultrasonic treatment at a power of 500 w for 30 min, and after removing the bubbles, was aged at 35°C for 30 h, and then, freezing was performed at -30°C for 12 h, and vacuum freeze-drying was performed at -196°C for 48 h, and then fumigation was performed at 65°C for 1 h in cyclohexanone vapor, to obtain a composite cellulose aerogel.

[0108] Example 8

[0109] The same as Example 1, except that fumigation was omitted.

[0110] Comparative Example 1

[0111] Compared with Example 5, the difference is that the diameter of the commercially available polyvinyl chloride nanofiber is 50 nm, and the aspect ratio is 500.

[0112] Comparative Example 2

[0113] Compared with Example 5, the difference lies in that the diameter of the commercially available polyvinyl chloride nanofiber is 800 nm, and the aspect ratio is 30.

[0114] Comparative Example 3

[0115] Compared with Example 5, the difference lies in that the addition amount of the polyvinyl chloride nanofiber is 2.5 g.

[0116] Test Example

[0117] The toughness, elastic modulus and thermal conductivity of the composite cellulose aerogels prepared in Examples 1-7 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1. Among them, the toughness and elastic modulus were tested by a universal mechanical testing machine, and the thermal conductivity was tested by a thermal conductivity tester.

[0118] Table 1

[0119] Examples Toughness kJ / m 3 ]] Elastic modulus MPa Thermal conductivity coefficient W / m-k Example 1 498 1.07 0.033 Example 2 499 1.08 0.033 Example 3 507 1.10 0.034 Example 4 461 0.87 0.030 Example 5 480 0.94 0.038 Example 6 512 1.19 0.031 Example 7 510 1.17 0.032 Example 8 474 0.90 0.031 Comparative Example 1 385 0.66 0.039 Comparative Example 2 494 1.06 0.045 Comparative Example 3 426 0.75 0.046

[0120] It can be known by comparing Example 1 and Example 8 that fumigation treatment helps to further improve the toughness and elastic modulus of the composite aerogel.

[0121] It can be known by comparing Example 5 and Comparative Example 1 that the nanofiber is too long and thin, and in the process of homogenization and dispersion, the nanofibers are easy to entangle, the cohesion and friction force increase, and the distribution is uneven, which finally leads to a significant decrease in the mechanical properties of the prepared composite aerogel.

[0122] It can be known by comparing Example 5 and Comparative Example 2 that the nanofiber is too short and thick, the density of the prepared composite aerogel increases, the porosity decreases, which leads to an increase in the thermal conductivity and a decrease in the heat insulation performance.

[0123] It can be known by comparing Example 5 and Comparative Example 3 that the addition amount of the nanofiber is too large, and the mechanical properties and heat insulation performance of the composite aerogel skeleton decrease. This may be because the excessive nanofiber weakens the cross-linking degree between the cellulose skeleton, thereby leading to a decrease in the mechanical properties and heat insulation performance of the composite aerogel skeleton.

[0124] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

Claims

1. A method for preparing a composite aerogel, characterized in that, The method includes the following steps: (1-1) Nanofibers and cellulose are added to dispersion solvent A to obtain dispersion A; wherein the diameter of the nanofibers is 100-500 nm and the aspect ratio is 50-300. (1-2) The dispersion A is subjected to aging, solvent replacement, freezing and optional fumigation treatment to obtain composite aerogel.

2. A method for preparing a composite aerogel, characterized in that, The method includes the following steps: (2-1) Nanofibers, cellulose derivatives and crosslinking agents are added to dispersion solvent B to obtain dispersion B; wherein, the diameter of the nanofibers is 100-500 nm and the aspect ratio is 50-300; the dispersion solvent B is selected from water, acetone or the dispersion solvent A; (2-2) When the dispersion solvent B is water, the dispersion B is subjected to aging, freezing and optional fumigation treatment to obtain a composite aerogel; when the dispersion solvent B is acetone or dispersion solvent A, the dispersion B is subjected to aging, dissolution and displacement, freezing and optional fumigation treatment to obtain a composite aerogel.

3. The method according to claims 1 and 2, wherein, The nanofibers are selected from one or more of the following: polystyrene nanofibers, polyethylene terephthalate nanofibers, polyurethane nanofibers, polyimide nanofibers, polyethylene nanofibers, polypropylene nanofibers, polyvinyl chloride nanofibers, chlorinated polyvinyl chloride nanofibers, polyvinylidene chloride nanofibers, polyamide nanofibers, polyvinylidene fluoride nanofibers, and polyacrylonitrile nanofibers. Preferably, the nanofibers have a diameter of 200-300 nm and an aspect ratio of 100-250.

4. The method according to claims 1 and 2, wherein, The dispersing solvent A is selected from one or more of the following: N-methylmorpholine-N-oxide aqueous solution, N,N-dimethylacetamide / LiCl, 1,3-dimethyl-2-imidazolium ketone / LiCl, dimethyl sulfoxide / LiCl, [Emim]OAc, [Bmim]OAc, [Omim]OAc, [Amim]Cl, [Bmim]Cl, [Emim]Cl, [Hmim]Cl, [C4mpy]Cl, [Bmim]Br, [Amim]HCOO, and [Bmim]HCOO.

5. The method according to claim 1, wherein, The cellulose is derived from herbaceous or woody plants, preferably from one or more of weeds, leaves, sawdust, bamboo, hemp, cotton, straw, coconut shells, and bagasse. Preferably, the mass ratio of the nanofibers, cellulose and dispersing solvent A is 0.05-1.5:0.3-2.5:100, and more preferably 0.2-1.0:0.5-2.0:

100.

6. The method according to claim 2, wherein, The cellulose derivative is selected from one or more of carboxylated cellulose, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, cellulose acetate, and cellulose acetate butyrate. Preferably, the crosslinking agent is selected from one or more of polyethylene glycol diglycidyl ether, citric acid, 1,4-butanediol diglycidyl ether, and epichlorohydrin; Preferably, the mass ratio of the nanofibers, cellulose derivatives, crosslinking agent and dispersing solvent B is 0.05-1.5:0.3-2.5:0.05-1.0:100, and more preferably 0.2-1.0:0.5-2.0:0.1-0.6:

100.

7. The preparation method according to any one of claims 1-6, wherein, The operating conditions for the aging treatment include: an aging temperature of 25-50℃, preferably 30-40℃; and an aging time of 4-48h, preferably 24-36h.

8. The method according to any one of claims 1-7, wherein, The solvent replacement operation includes: adding a replacement solvent to dispersion A or dispersion B to perform replacement, thereby obtaining a composite wet gel; Preferably, the displacement solvent is selected from one or more of water and / or tert-butanol; Preferably, the solvent replacement operation includes: a replacement temperature of room temperature, a replacement time of 3-15 hours, preferably 6-12 hours, and 3-10 replacements, preferably 5-8 replacements.

9. The method according to any one of claims 1-8, wherein, The freezing operation conditions include: a freezing temperature of -80°C to -10°C, preferably -60°C to -30°C; and a freezing time of 5-25 hours, preferably 10-15 hours.

10. The method according to any one of claims 1-9, wherein, The fumigation process includes: contacting the frozen product with a fumigation solvent to fumigate, thereby obtaining a composite aerogel; wherein the fumigation solvent is selected from organic solvents capable of dissolving the nanofibers and the boiling point of the fumigation solvent is 100-200℃, preferably 130-170℃. Preferably, the operating conditions for the fumigation treatment include: a fumigation temperature of 50-100℃, more preferably 60-90℃; and a fumigation time of 0.5-4h, more preferably 1-2h.

11. A composite aerogel prepared by the method according to any one of claims 1-10.