Silicon-based aerogel as well as preparation method and application thereof

Abstract

The invention discloses a silicon-based aerogel and a preparation method and application thereof, the silicon-based aerogel contains the following preparation raw materials: monohydroxy silane, water, a dialdehyde compound, a pH value regulator and a polyhydroxy polymer, relative to 100 parts by weight of the polyhydroxy polymer, the content of the monohydroxy silane is 125-360 parts by weight; the content of the dialdehyde compound is 100 to 200 parts by weight; the content of the water is 500 to 600 parts by weight. The polyhydroxy polymer is used as a framework structure of the silicon-based aerogel, so that the silicon-based aerogel has excellent flexibility; silicon dioxide and a main chain of the polyhydroxy polymer form a C-O-Si chemical bond, so that powder falling of the aerogel is avoided. The silicon dioxide in the silicon-based aerogel is grafted on the main chain of the polyhydroxy polymer, and the skeleton has excellent extension performance, so that the nanopore channel is not easy to damage in the drying process, and the thermal conductivity of the silicon-based aerogel is low.

Description

Technical Field

[0001] The present invention relates to the technical field of gel materials, and in particular to a silicon-based aerogel and its preparation method and application. Background Art

[0002] An aerogel is a nano-porous solid material formed by replacing the liquid phase in a gel with gas by a certain drying method. Aerogels have excellent heat insulation properties. An inch-thick aerogel is equivalent to the heat insulation function of 20-30 ordinary glasses.

[0003] However, pure silica aerogel has a low density and a high porosity, resulting in low strength and high brittleness, making it difficult to be used as a bulk heat insulation material in practical applications. In related technologies, to solve the problem of high brittleness of aerogels, pouring methods, immersion methods, and spraying methods are mainly used in the composite stage of aerogels and fiber felts, and supercritical drying methods and atmospheric pressure drying methods are mainly used for drying. Among them, the pouring, spraying, and immersion composite methods will cause the aerogel precursor and fiber to be either unevenly compounded or overloaded with liquid, resulting in problems such as powder shedding, high raw material loss, long production cycle, and high thermal conductivity in the later products;

[0004] Therefore, it is necessary to provide an aerogel with low thermal conductivity, good mechanical properties, and no powder shedding. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, in the first aspect of the present invention, a silicon-based aerogel is proposed. The silicon-based aerogel has low thermal conductivity, good mechanical properties, and no powder shedding.

[0006] In the second aspect of the present invention, a preparation method of the silicon-based aerogel is also provided.

[0007] In the third aspect of the present invention, an application of the silicon-based aerogel is also provided.

[0008] According to the embodiment of the first aspect of the present invention, the provided silicon-based aerogel contains the following preparation raw materials:

[0009] Mono-hydroxy silane, water, dialdehyde compounds, pH value regulators, and polyhydroxy polymers. Relative to 100 parts by weight of the polyhydroxy polymer, the content of the mono-hydroxy silane is 125-360 parts by weight; the content of the dialdehyde compound is 100-200 parts by weight; the content of the water is 500-600 parts by weight.

[0010] The silicon-based aerogel according to the embodiment of the present invention has at least the following beneficial effects:

[0011] The silica-based aerogel provided by the present invention has low thermal conductivity, good mechanical properties and no powder shedding. This is because the present invention uses a polyhydroxy polymer as the framework structure of the silica-based aerogel, which has excellent flexibility and can be bent; a dialdehyde compound is used as the cross-linking agent between the polyhydroxy polymer and the monohydroxy silane to generate a macromolecular silane, and a C-O-Si chemical bond is formed between the silicon dioxide and the main chain of the polyhydroxy polymer, avoiding powder shedding of the aerogel and facilitating the preparation of composite materials by post-processing. In addition, since the silicon dioxide in the silica-based aerogel is grafted onto the main chain of the polyhydroxy polymer and the framework has excellent extensibility, the nanopores are not easily damaged during the drying process, resulting in low thermal conductivity of the silica-based aerogel.

[0012] According to some embodiments of the present invention, the monohydroxy silane is prepared by hydrolyzing a silicon source, an alcohol solvent and water under acidic conditions.

[0013] According to some embodiments of the present invention, the molar ratio of water to the silicon source is 0.1 to 1:1. For example, the molar ratio of water to the silicon source can be 0.1:1, 0.2:1, 0.3:1, 0.5:1, 0.7:1, 0.8:1 or 1:1. Thus, when the molar ratio of water to the silicon source is within the above range, the prepared monohydroxy silane can reduce the thermal conductivity of the silica-based aerogel.

[0014] According to some embodiments of the present invention, the silicon source includes at least one of tetramethyl orthosilicate, methyltriethyl orthosilicate, dimethyldiethyl orthosilicate, tetra-isopropyl orthosilicate, tetra-tert-butyl orthosilicate, tetrahexyl orthosilicate, ethyl silicate, propyl silicate or butyl silicate.

[0015] According to some embodiments of the present invention, the polyhydroxy polymer is selected from polyvinyl alcohol, cellulose or a combination thereof.

[0016] According to some embodiments of the present invention, if the degree of polymerization of the polyvinyl alcohol is too low, the strength of the silica-based aerogel will be affected. If the degree of polymerization of the polyvinyl alcohol is too high, the viscosity will be too high, which is not conducive to the operation of the reaction. Therefore, the degree of polymerization of the polyvinyl alcohol is 200 to 2000. All individual values and sub-ranges from 200 to 2000 are included. For example, the degree of polymerization of the polyvinyl alcohol can be 200, 300, 400, 500, 600, 700, 800, 900, 1100, 1300, 1500, 1700, 1900, 2000 or any range value composed of any two of them.

[0017] According to some embodiments of the present invention, the degree of alcoholysis of the polyvinyl alcohol is 60% to 95%, including all individual values and sub-ranges from 60% to 95%. For example, the degree of polymerization of the polyvinyl alcohol can be 60%, 70%, 85%, 90%, 90%, or a range value composed of any two of them. For example, the degree of alcoholysis of the polyvinyl alcohol is 85% to 90%. Thus, when the degree of alcoholysis is within the above range, it has a more appropriate hydroxyl content, which can avoid the polycondensation reaction between adjacent hydroxyl groups and dialdehyde compounds.

[0018] According to some embodiments of the present invention, the dialdehyde compound includes at least one of glyoxal, succinaldehyde, glutaraldehyde, or methylglyoxal. Thus, the role of the dialdehyde compound is to act as a cross-linking agent for the polyhydroxy polymer and the monohydroxy silane, and the silicon dioxide forms a C-O-Si chemical bond with the main chain of the polyhydroxy polymer, avoiding powdering of the silica aerogel.

[0019] According to some embodiments of the present invention, the alcohol solvent includes at least one of ethanol, methanol, propanol, benzyl alcohol, or isopropanol. Thus, the alcohol solvent provides a solubilizing effect and promotes the dissolution of the monohydroxy silane in water.

[0020] According to some embodiments of the present invention, the pH value regulator includes an acid regulator and a base regulator.

[0021] According to some embodiments of the present invention, the acid regulator includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0022] According to some embodiments of the present invention, the base regulator includes at least one of sodium hydroxide, potassium hydroxide, or ammonia water.

[0023] According to the second aspect embodiment of the present invention, a method for preparing a silica aerogel is provided, including the following steps:

[0024] S1. Perform a first reaction on the monohydroxy silane, water, and the dialdehyde compound to obtain intermediate I;

[0025] S2. Under alkaline conditions, mix the polyhydroxy polymer and water to obtain mixture I; perform a second reaction on intermediate I and mixture I to obtain intermediate II;

[0026] S3. Adjust the solution of intermediate II to an acidic environment for a third reaction, and adjust it to an alkaline environment for a fourth reaction to obtain a wet gel;

[0027] S4. Subject the wet gel to aging, solvent replacement, and drying in sequence to obtain the silica aerogel;

[0028] Among them, in the step S2, the pH value of the alkaline condition is 8 to 10;

[0029] In step S3, the pH value of the acidic environment is 2 to 6;

[0030] In step S3, the pH value of the alkaline environment is 7.1 to 9.

[0031] The preparation method of the silica-based aerogel according to the embodiment of the present invention has at least the following beneficial effects:

[0032] In the present invention, by using a dialdehyde compound as a cross-linking agent for mono-hydroxy silane and poly-hydroxy polymer to generate a macromolecular silane, silicon dioxide is grafted onto the main chain of the poly-hydroxy polymer, and the skeleton has excellent extensibility. Therefore, the nano-pore channels are not easily damaged during the drying process, and the finally obtained aerogel has a low thermal conductivity, high compressive strength and high toughness, and there is no problem of powder shedding.

[0033] According to some embodiments of the present invention, the acidic environment, alkaline environment or alkaline condition in the present invention refers to adjusting the pH value by using the pH value regulator of the present invention.

[0034] According to some embodiments of the present invention, the mono-hydroxy silane is prepared by the following method:

[0035] Mix a silicon source, an alcohol solvent and water, adjust the pH value of the solution to 2 to 6 by using a pH value regulator, and carry out a fifth reaction to remove the alcohol solvent, thereby obtaining the mono-hydroxy silane. Thus, the role of the mono-hydroxy silane is to react with the dialdehyde compound and graft onto the macromolecular chain of the poly-hydroxy polymer to form a molecule with a silane side chain on the macromolecular chain.

[0036] According to some embodiments of the present invention, the temperature of the aging is 30 to 50 °C. Among them, for example, the aging temperature is 30 °C, 35 °C, 40 °C, 45 °C or 50 °C.

[0037] According to some embodiments of the present invention, the time of the aging is 24 to 48 h. Among them, for example, the time of the aging is 24 h, 30 h, 36 h, 42 h or 48 h. Thus, after the aging step, the aerogel is denser and has higher strength.

[0038] According to some embodiments of the present invention, the drying is carried out by using 2 the method of supercritical drying. Thus, by using the method of supercritical drying, the wet gel structure of the present invention will not damage the nano-bubble pore structure during the drying process, and the thermal conductivity is lower.

[0039] According to some embodiments of the present invention, the method of 2 supercritical drying by using at least meets one of the following conditions:

[0040] i The temperature is 30 to 50 °C;

[0041] ii The pressure is 6 to 10 MPa;

[0042] iii The time is 3 to 8 h.

[0043] According to some embodiments of the present invention, the molar ratio of the mono-hydroxy silane and the dialdehyde compound is 0.8 to 2:1.

[0044] According to some embodiments of the present invention, the temperature of the first reaction is 10 to 25 °C.

[0045] According to some embodiments of the present invention, the time of the first reaction is 2 to 6 h.

[0046] According to some embodiments of the present invention, the time of the second reaction is 0.5 to 2 h.

[0047] According to some embodiments of the present invention, the temperature of the second reaction is 40 to 60 °C.

[0048] According to some embodiments of the present invention, the time of the third reaction is 0.5 to 2 h.

[0049] According to some embodiments of the present invention, the time of the fourth reaction is 1 to 3 h.

[0050] The third aspect of the present invention provides a refrigerator, including a heat insulation material, and the heat insulation material is the silicon-based aerogel as described above.

[0051] Since the application adopts all the technical solutions of the silicon-based aerogel in the above embodiments, therefore, it has at least the technical effects brought by the technical solutions of the above embodiments. That is, the refrigerator has good heat preservation and heat insulation effects.

[0052] Other features and advantages of the present invention will be described in the following description, and some of them will be obvious from the description, or will be understood by implementing the present invention. Detailed Embodiments

[0053] The following will clearly and completely describe the concept of the present invention and the technical effects produced in combination with the embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0054] In the description of the present invention, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0055] In some embodiments of the present invention, a silica-based aerogel is provided, and the silica-based aerogel contains the following preparation raw materials:

[0056] Mono-hydroxy silane, water, dialdehyde compounds, pH value regulator, and polyhydroxy polymer. With respect to 100 parts by weight of the polyhydroxy polymer, the content of the mono-hydroxy silane is 125 to 360 parts by weight; the content of the dialdehyde compound is 100 to 200 parts by weight; the content of the water is 500 to 600 parts by weight.

[0057] It can be understood that: The silica-based aerogel provided by the present invention has low thermal conductivity, good mechanical properties, and no powder shedding. This is because the present invention uses a polyhydroxy polymer as the skeleton structure of the silica-based aerogel, which has excellent flexibility and can be bent; uses a dialdehyde compound as the cross-linking agent for the polyhydroxy polymer and mono-hydroxy silane to generate a macromolecular silane, and silicon dioxide forms a C-O-Si chemical bond with the main chain of the polyhydroxy polymer, avoiding powder shedding of the aerogel and facilitating the preparation of composite materials in post-processing. In addition, since the silicon dioxide in the silica-based aerogel is grafted onto the main chain of the polyhydroxy polymer and the skeleton has excellent extensibility, the nanopores are not easily damaged during the drying process, resulting in low thermal conductivity of the silica-based aerogel.

[0058] In some embodiments of the present invention, the mono-hydroxy silane is prepared by hydrolyzing a silicon source, an alcohol solvent, and water under acidic conditions.

[0059] In some embodiments of the present invention, the molar ratio of the water to the silicon source is 0.1 to 1:1. For example, the molar ratio of the water to the silicon source is 0.1:1, 0.2:1, 0.3:1, 0.5:1, 0.7:1, 0.8:1, or 1:1.

[0060] It can be understood that when the molar ratio of the water to the silicon source is within the above range, the prepared mono-hydroxy silane can reduce the thermal conductivity of the silica-based aerogel.

[0061] In some embodiments of the present invention, the silicon source includes at least one of tetramethyl orthosilicate, methyltriethyl orthosilicate, dimethyldiethyl orthosilicate, tetra-isopropyl orthosilicate, tetra-tert-butyl orthosilicate, tetrahexyl orthosilicate, ethyl silicate, propyl silicate or butyl silicate.

[0062] In some embodiments of the present invention, the polyhydroxy polymer is selected from polyvinyl alcohol, cellulose or a combination thereof.

[0063] In some embodiments of the present invention, if the degree of polymerization of the polyvinyl alcohol is too low, it will affect the strength of the silica aerogel. If the degree of polymerization of the polyvinyl alcohol is too high, the viscosity will be too high, which is not conducive to the operation of the reaction. Therefore, the degree of polymerization of the polyvinyl alcohol is 200 to 2000. All individual values and sub-ranges from 200 to 2000 are included. For example, the degree of polymerization of the polyvinyl alcohol is 200, 300, 400, 500, 600, 700, 800, 900, 1100, 1300, 1500, 1700, 1900, 2000 or any range value composed of any two of them.

[0064] In some embodiments of the present invention, the degree of alcoholysis of the polyvinyl alcohol is 60% to 95%. All individual values and sub-ranges from 60% to 95% are included. For example, the degree of alcoholysis of the polyvinyl alcohol is 60%, 70%, 85%, 90%, 90% or any range value composed of any two of them. For example, the degree of alcoholysis of the polyvinyl alcohol is 85% to 90%. Thus, when the degree of alcoholysis is within the above range, it has a more appropriate hydroxyl content and can avoid the polycondensation reaction between adjacent hydroxyl groups and dialdehyde compounds.

[0065] In some embodiments of the present invention, the dialdehyde compound includes at least one of glyoxal, succinaldehyde, glutaraldehyde or methylglyoxal. Thus, the role of the dialdehyde compound is to act as a crosslinking agent for the polyhydroxy polymer and the monohydroxy silane, and a C-O-Si chemical bond is formed between the silicon dioxide and the main chain of the polyhydroxy polymer to avoid powder falling of the aerogel.

[0066] In some embodiments of the present invention, the alcohol solvent includes at least one of ethanol, methanol, propanol, benzyl alcohol or isopropyl alcohol. It can be understood that the alcohol solvent provides a solubilizing effect and promotes the dissolution of the monohydroxy silane in water.

[0067] In some embodiments of the present invention, the pH value regulator includes an acid regulator and a base regulator.

[0068] In some embodiments of the present invention, the acid regulator includes at least one of hydrochloric acid, sulfuric acid, nitric acid.

[0069] In some embodiments of the present invention, the base regulator includes at least one of sodium hydroxide, potassium hydroxide or ammonia water.

[0070] A method for preparing a silicon-based aerogel according to an embodiment of the second aspect of the present invention includes the following steps:

[0071] S1. Perform a first reaction on a monohydroxy silane, water, and a dialdehyde compound to obtain intermediate I;

[0072] S2. Under alkaline conditions, mix a polyhydroxy polymer and water to obtain mixture I; perform a second reaction on intermediate I and mixture I to obtain intermediate II;

[0073] S3. Adjust the solution of intermediate II to an acidic environment for a third reaction, and then adjust the solution of intermediate II to an alkaline environment for a fourth reaction to obtain a wet gel;

[0074] S4. Subject the wet gel to aging, solvent replacement, and drying in sequence to obtain the silicon-based aerogel;

[0075] Wherein, in step S2, the pH value of the alkaline condition is 8-10;

[0076] In step S3, the pH value of the acidic environment is 2-6;

[0077] In step S3, the pH value of the alkaline environment is 7.1-9.

[0078] It can be understood that: in the present invention, by using a dialdehyde compound as a cross-linking agent for a monohydroxy silane and a polyhydroxy polymer to generate a macromolecular silane, silicon dioxide is grafted onto the main chain of the polyhydroxy polymer, and the skeleton has excellent extensibility. Therefore, nanopores are not easily damaged during the drying process, and the finally obtained silicon-based aerogel has a low thermal conductivity, high compressive strength, and high toughness, and there is no problem of powder shedding.

[0079] In step S2, limiting the pH value of the alkaline condition to 8-10 is more conducive to the progress of the polycondensation reaction. In step S3, limiting the pH value of the acidic environment to 2-6 is more conducive to the hydrolysis reaction. In step S3, limiting the pH value of the alkaline environment to 7.1-9 is more conducive to the polycondensation reaction, improving the cross-linking strength between gel ions and perfecting the skeleton structure of the gel.

[0080] In some embodiments of the present invention, the monohydroxy silane is prepared by the following method:

[0081] Mix a silicon source, an alcohol solvent, and water, adjust the pH value of the solution to 2-6 using a pH value regulator, perform a fifth reaction, and remove the alcohol solvent to obtain the monohydroxy silane. Thus, the role of the monohydroxy silane is to facilitate the grafting of the silane into the polyhydroxy polymer.

[0082] In some embodiments of the present invention, the reaction temperature of the fifth reaction is 15 to 25 °C. For example, the reaction temperature of the fifth reaction is 15 °C, 20 °C, 22 °C, 23 °C or 25 °C.

[0083] In some embodiments of the present invention, the reaction time of the fifth reaction is 0.5 to 2 h. For example, the reaction time of the fifth reaction is 0.5 h, 1 h, 1.5 h or 2 h. It can be understood that within the above reaction time range, the hydrolysis reaction is complete.

[0084] In some embodiments of the present invention, the aging temperature is 30 to 50 °C. It includes all individual values and sub-ranges from 30 °C to 50 °C. For example, the aging temperature is 30 °C, 35 °C, 40 °C, 45 °C, 50 °C or any range composed of any two of them.

[0085] In some embodiments of the present invention, the aging time is 24 to 48 h. It includes all individual values and sub-ranges from 24 h to 48 h. For example, the aging time is 24 h, 30 h, 36 h, 42 h, 48 h or any range composed of any two of them.

[0086] Thus, after the aging step, the silica aerogel is denser and has higher strength.

[0087] In some embodiments of the present invention, the drying is carried out by the method of CO 2 supercritical drying. Thus, by adopting the method of supercritical drying, the wet gel structure of the present invention will not destroy the nano-porous structure during the drying process, and the thermal conductivity is lower.

[0088] In some embodiments of the present invention, the method of CO 2 supercritical drying satisfies at least one of the following conditions:

[0089] i The temperature is 30 to 50 °C;

[0090] ii The pressure is 6 to 10 MPa;

[0091] iii The time is 3 to 8 h.

[0092] In some embodiments of the present invention, the molar ratio of the mono-hydroxy silane to the dialdehyde compound is 0.8 to 2:1.

[0093] In some embodiments of the present invention, the reaction temperature of the first reaction is 10 to 25 °C. It includes all individual values and sub-ranges from 10 °C to 25 °C. For example, the reaction temperature of the first reaction is 10 °C, 15 °C, 20 °C, 25 °C or any range value composed of any two of them.

[0094] In some embodiments of the present invention, the reaction time of the first reaction is 2 to 6 h, including all individual values and sub-ranges from 2 to 6. For example, the reaction time of the first reaction is 2 h, 3 h, 4 h, 5 h, 6 h, or a range value composed of any two of them.

[0095] In some embodiments of the present invention, the time of the second reaction is 0.5 to 2 h, including all individual values and sub-ranges from 0.5 to 2. For example, the reaction time of the second reaction is 0.5 h, 1 h, 1.5 h, 2 h, or a range value composed of any two of them.

[0096] In some embodiments of the present invention, the temperature of the second reaction is 40 to 60 °C, including all individual values and sub-ranges from 40 °C to 60 °C. For example, the reaction temperature of the second reaction is 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, or a range value composed of any two of them.

[0097] In some embodiments of the present invention, the time of the third reaction is 0.5 to 2 h, including all individual values and sub-ranges from 0.5 to 2. For example, the reaction time of the third reaction is 0.5 h, 1 h, 1.5 h, 2 h, or a range value composed of any two of them.

[0098] In some embodiments of the present invention, the time of the fourth reaction is 1 to 3 h, including all individual values and sub-ranges from 1 to 3. For example, the reaction time of the second reaction is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or a range value composed of any two of them.

[0099] The third aspect of the present invention provides a refrigerator, including a heat insulation material, and the heat insulation material includes the silicon-based aerogel of the present invention.

[0100] It can be understood that: since the refrigerator adopts all the technical solutions of the silicon-based aerogel in the above embodiments, therefore, it has at least the technical effects brought by the technical solutions of the above embodiments. That is, the refrigerator has good heat preservation and heat insulation effects.

[0101] Unless otherwise specified, the reagent information used in the specific implementation is as follows:

[0102] Polyhydroxy polymer A: KURARAY PVAL 3-88 from Japan, with a degree of alcoholysis of 87% to 89% and a degree of polymerization of 250;

[0103] Polyhydroxy polymer B: KURARAY PVAL3-80 from Japan, with a degree of alcoholysis of 78% to 82% and a degree of polymerization of 500;

[0104] Polyhydroxy polymer C: KURARAY PVL-L-8 from Japan, with a degree of alcoholysis of 69% to 72% and a degree of polymerization of 1500;

[0105] Dialdehyde compounds: Glutaraldehyde, commercially available;

[0106] Crosslinking agent A: Two-component waterborne crosslinking agent SJ-2605 from Shuiji New Materials Co., Ltd.;

[0107] Crosslinking agent B: One-component waterborne crosslinking agent SJ-1805 from Shuiji New Materials Co., Ltd.;

[0108] pH value regulator: Hydrochloric acid, ammonia water, commercially available;

[0109] Silicon source: Tetraethyl orthosilicate, commercially available.

[0110] The technical solution of the present invention will be better understood by combining specific embodiments below.

[0111] Example 1

[0112] This example provides a silica aerogel, the formulation content is shown in the composition of Example 1 in Table 1, and it is prepared according to the following method:

[0113] Preparation of monohydroxy silane: Water, tetraethyl orthosilicate and ethanol were mixed in a molar ratio of 1:1:2, the pH value of the mixed solution was adjusted to 3.0 with hydrochloric acid, stirred at room temperature for 1 h, and ethanol was removed by heating to obtain monohydroxy silane;

[0114] S1. Dissolve the monohydroxy silane in water, add glutaraldehyde, and stir to make it react fully to obtain intermediate I;

[0115] S2. Add polyhydroxy polymer A to water, heat to fully dissolve, then stir to lower the temperature to 50 °C, adjust the pH value of the solution to 8.0, and add it to the intermediate I mixture, and react for 1 h; to obtain intermediate II;

[0116] S3. Adjust the pH value of the solution of intermediate II to 3.0 with hydrochloric acid, stir for 0.5 h; then adjust the pH value of the solution to 10.0 with ammonia water, and let it stand for 2 h to obtain a wet gel;

[0117] S4. Age the wet gel at 40 °C for 24 h, perform solvent replacement once with absolute ethanol, and perform drying for 5 h under the conditions of supercritical drying process with CO 2 at a temperature of 40 °C and a pressure of 8.0 MPa to obtain a silica aerogel.

[0118] Examples 2 to 4

[0119] Examples 2 to 4 provide a series of silica aerogels, the formulation contents are shown in the compositions of Examples 2 to 4 in Table 1 respectively, and they are prepared according to the following method:

[0120] Preparation of monohydroxy silane: Water, tetraethyl orthosilicate and ethanol were mixed in a molar ratio of 1:1:2, and the pH value of the mixed solution was adjusted to 3.0 with hydrochloric acid, stirred at room temperature for 1 h, and ethanol was removed by heating to obtain monohydroxy silane;

[0121] S1. Dissolve the monohydroxy silane in water, add glutaraldehyde, and stir to make it react fully to obtain intermediate I;

[0122] S2. Add the polyhydroxy polymer A to water, heat until it is fully dissolved, stir to lower the temperature to 50 °C, adjust the pH value of the solution to 8.0, add it to the intermediate I mixture, and react for 1 h to obtain intermediate II;

[0123] S3. Adjust the pH value of the intermediate II solution to 3.0 with hydrochloric acid, stir for 0.5 h, then adjust the pH value of the solution to 10.0 with ammonia water, and let it stand for 2 h to obtain a wet gel;

[0124] S4. Age the wet gel at 40 °C for 24 h, perform solvent replacement once with absolute ethanol, and perform supercritical drying under the conditions of a temperature of 40 °C and a pressure of 8.0 MPa for 5 h to obtain a silica aerogel. 2 Table 1 Examples 1 - 4 (parts by weight)

[0125] Table 1 Examples 1 - 4 (parts by weight)

[0126] Example 1 Example 2 Example 3 Example 4 monohydroxy silane 360 180 125 360 dicarboxaldehyde compound 200 172 100 172 water in step S1 360 360 373 360 water in step S2 200 200 207 200 polyhydroxy polymer A 100 100 100 100

[0127] Examples 5 - 8

[0128] Examples 5 - 8 provide a series of silica aerogels, whose formulation contents and preparation methods are basically the same as those of Example 1. The difference lies in the data in Table 2.

[0129] Table 2 Examples 5 - 8

[0130] Example 5 Example 6 Example 7 Example 8 molar ratio of water to tetraethyl orthosilicate 0.3:1 0.7:1 2:1 3:1

[0131] Example 9

[0132] This example provides a silica aerogel, whose component dosages and preparation method are the same as those of Example 1. The difference is that polyhydroxy polymer B is used to replace polyhydroxy polymer A in Example 1.

[0133] Example 10

[0134] This example provides a silica aerogel, whose component dosages and preparation method are the same as those of Example 1. The difference is that polyhydroxy polymer C is used to replace polyhydroxy polymer A in Example 1.

[0135] Comparative Example 1

[0136] Comparative Example 1 provides a silica aerogel, with the same component dosages and preparation method as in Example 1, except that crosslinking agent A is used to replace glutaraldehyde in Example 1.

[0137] Comparative Example 2

[0138] Comparative Example 2 provides a silica aerogel, with the same component dosages and preparation method as in Example 1, except that crosslinking agent B is used to replace glutaraldehyde in Example 1.

[0139] Comparative Example 3

[0140] Comparative Example 3 provides a silica aerogel, and its preparation steps are as follows:

[0141] Weigh 4 g of tetraethyl orthosilicate and 1 g of methyltrimethoxysilane, add 60 g of absolute ethanol and 2 g of deionized water, and stir well until dissolved to obtain a mixed solution A; Ultrasonicate microcrystalline cellulose for 10 min, exchange it in an ethanol solvent for 10 h, and dry it to obtain pretreated microcrystalline cellulose. Then immerse 0.1 g of the pretreated and dried microcrystalline cellulose into the above mixed solution, stir in a 40 °C water bath for 2 h, then add a 0.5 mol / L hydrochloric acid solution to adjust the pH of the solution to 4.0, continue stirring for 8 h for hydrolysis, and then add a 5 mol / L ammonia water solution to adjust the pH of the solution to 8.0 for gelation, and let it stand at room temperature to form a wet gel; Pour the above wet gel into 100 mL of absolute ethanol for aging treatment, with an aging temperature of 70 °C and an aging time of 15 h; Take out the gel after aging treatment, add it to a mixed solution B with a volume ratio of trimethylchlorosilane:absolute ethanol:n - hexane of 1:1:9 for surface modification treatment. After standing for 10 h, wash the wet gel with n - hexane. Finally, vacuum freeze - dry the modified wet gel at 30 - 70 °C, and then dry it in a forced - air drying oven at 160 °C for 24 h to obtain a heat - insulating silica aerogel composite material for packaging.

[0142] Comparative Example 4

[0143] Comparative Example 4 provides a silica aerogel, with the same component dosages and preparation method as in Example 1, except that Comparative Example 4 does not contain polyhydroxy polymer A.

[0144] Performance testing

[0145] The silica aerogels prepared in Examples 1 - 10 and Comparative Examples 1 - 4 of the present invention were respectively tested for thermal conductivity, compressive strength, density, and powder - shedding rate:

[0146] The powder loss rate test method refers to GB / T 20810-2018, the thermal conductivity test method refers to GB / T 10295-2008, the compressive strength test method refers to GB / T 8813-2008, and the density test method refers to GBT 6343-2009. The results are shown in Table 3.

[0147] Table 3 Data of Examples 1-10 and Comparative Examples 1-4

[0148]

[0149] As can be seen from Table 3 above, the silica-based aerogel provided by the embodiments of the present invention has low thermal conductivity, high compressive strength, and extremely low powder loss rate. From the data of Comparative Examples 1-2, it can be seen that when using conventional cross-linking agents, their thermal conductivity and powder loss rate are both lower than those of the silica-based aerogel provided by the present invention, and the effect is not good. From the experimental data of Comparative Example 3, it can be seen that the silica-based aerogel prepared in Comparative Example 3 has a relatively high thermal conductivity and poor heat preservation performance. From Comparative Example 4, when there is a lack of polyhydroxy polymer, the powder loss rate of Comparative Example 4 is very high and the compressive strength is also very low.

[0150] The above has made a detailed description in combination with the embodiments of the present invention, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the purpose of the present invention.

Claims

1. A silica-based aerogel, characterized in that, the silica-based aerogel contains the following preparation raw materials: monohydroxy silane, water, dialdehyde compounds, pH regulators and polyhydroxy polymers. Relative to 100 parts by weight of the polyhydroxy polymer, the content of the monohydroxy silane is 125 - 360 parts by weight; the content of the dialdehyde compounds is 100 - 200 parts by weight; the content of the water is 500 - 600 parts by weight.

2. The silica-based aerogel according to claim 1, characterized in that, the monohydroxy silane is prepared by hydrolyzing a silicon source, an alcohol solvent and water under acidic conditions.

3. The silica-based aerogel according to claim 2, characterized in that, the molar ratio of the water to the silicon source is 0.1 - 1:

1.

4. The silica-based aerogel according to claim 1, characterized in that, the polyhydroxy polymer is selected from polyvinyl alcohol, cellulose or a combination thereof.

5. The silica-based aerogel according to claim 4, characterized in that, the degree of polymerization of the polyvinyl alcohol is 200 - 2000.

6. The silica-based aerogel according to claim 1, characterized in that, the dialdehyde compounds include at least one of glyoxal, succinaldehyde, glutaraldehyde or methylglyoxal.

7. The silica-based aerogel according to claim 1, characterized in that, the alcohol solvent includes at least one of ethanol, methanol, propanol, benzyl alcohol or isopropanol.

8. A method for preparing the silica-based aerogel according to any one of claims 1 - 7, characterized in that, it includes the following steps: S1. Perform a first reaction on the monohydroxy silane, water and dialdehyde compounds to obtain intermediate I; S2. Under alkaline conditions, mix the polyhydroxy polymer and water to obtain mixture I; perform a second reaction on intermediate I and mixture I to obtain intermediate II; S3. Adjust the solution of intermediate II to an acidic environment for a third reaction, and adjust it to an alkaline environment for a fourth reaction to obtain a wet gel; S4. Subject the wet gel to aging, solvent replacement and drying in sequence to obtain the silica-based aerogel; wherein, in step S2, the pH value of the alkaline condition is 8 - 10; in step S3, the pH value of the acidic environment is 2 - 6; in step S3, the pH value of the alkaline environment is 7.1 - 9.

9. The method for preparing the silica-based aerogel according to claim 8, characterized in that, the monohydroxy silane is prepared by the following method: Mix the silicon source, the alcohol solvent and water, adjust the pH value of the solution to 2 - 6 with a pH regulator, perform a fifth reaction, and remove the alcohol solvent to obtain the monohydroxy silane.

10. A refrigerator, including a heat insulation material, characterized in that, the heat insulation material includes the silica-based aerogel according to any one of claims 1 - 7.

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