Montmorillonite-based flame-retardant heat-insulating composite aerogel as well as preparation method and application thereof

Abstract

The invention discloses montmorillonite-based flame-retardant and heat-insulating composite aerogel as well as a preparation method and application thereof, and belongs to the field of flame-retardant and heat-insulating materials. The preparation method comprises the following steps: adding chitosan into an acetic acid solution of sodium alginate for reaction to obtain a sodium alginate-chitosan composite aerogel solution; the preparation method comprises the following steps: uniformly mixing a sodium alginate-chitosan composite aerogel solution with a montmorillonite solution to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution, and carrying out freeze drying treatment on the montmorillonite-sodium alginate-chitosan composite aerogel solution to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; the montmorillonite-sodium alginate-chitosan composite aerogel precursor is subjected to heating and drying treatment, and the montmorillonite-sodium alginate-chitosan composite aerogel is obtained. The montmorillonite-sodium alginate-chitosan composite aerogel material prepared by the preparation method disclosed by the invention has excellent mechanical properties and flame-retardant and heat-insulating properties.

Description

Technical Field

[0001] The present invention relates to the technical field of flame - retardant and heat - insulating materials, and particularly relates to a montmorillonite - based flame - retardant and heat - insulating composite aerogel, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the large density, poor thermal insulation performance, high production cost, poor mechanical properties of traditional heat - insulating materials, and the fact that they may contain a large amount of harmful substances, endangering the human living environment and life safety, it is urgent to explore an aerogel with rich raw material sources, low price, environmental friendliness, excellent heat - preservation performance, and good mechanical properties. Sodium alginate is a natural polymer polysaccharide compound extracted from seaweed, with advantages such as natural source, good heat - insulating performance, biodegradability, and wide applicability, and is expected to play an important role in the field of heat - insulating materials. The heat - insulating material made of sodium alginate not only has excellent heat - insulating effects, but also is beneficial to environmental protection and sustainable development. Chitosan is a natural biopolymer derived from the shells of crustaceans, with advantages such as good processability, environmental friendliness, renewable property, heat - insulating performance, and biocompatibility. It contains a large number of cationic amino groups and hydroxyl groups, which can provide active sites for many reactions. However, since both sodium alginate and chitosan are biomass materials, their thermal stability and flame retardancy are poor, affecting their applications.

[0003] In order to further improve the thermal stability and flame retardancy of sodium alginate - chitosan composite aerogels, researchers have begun to consider introducing flame retardants. In this modification scheme, the flame retardant can effectively improve the fire resistance of the material, slow down the heat diffusion during a fire, and prevent the material from degrading in a high - temperature environment, thus greatly broadening its application scope in the field of high - temperature heat insulation.

[0004] Based on this, the present invention aims to propose an aerogel material based on the composite of sodium alginate and chitosan, further optimize the thermal stability and flame retardancy of the material by introducing a flame retardant, and further reduce the production cost, so that it has a wide application prospect. Summary of the Invention

[0005] In order to solve the problem of poor thermal stability and flame retardant performance of the composite aerogel material prepared from sodium alginate and chitosan, the present invention provides a montmorillonite - based flame - retardant and heat - insulating composite aerogel, a preparation method thereof, and an application thereof. The preparation method provided by the present invention is based on the cross - linking effect of chitosan and sodium alginate to form a three - dimensional framework network structure, introduce the flame retardant montmorillonite (MMT, Montmorillonite), and prepare the montmorillonite - sodium alginate - chitosan composite aerogel through freeze - drying technology.

[0006] To achieve the above - mentioned purpose, the present invention provides the following technical solutions: The present invention provides a method for preparing a montmorillonite-based flame-retardant and heat-insulating composite aerogel, comprising: Adding chitosan to an acetic acid solution of sodium alginate for reaction to obtain a sodium alginate-chitosan composite aerogel solution; Mixing the sodium alginate-chitosan composite aerogel solution with a montmorillonite solution evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution, subjecting the montmorillonite-sodium alginate-chitosan composite aerogel solution to freeze-drying treatment to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor, and subjecting the montmorillonite-sodium alginate-chitosan composite aerogel precursor to heat-drying treatment to obtain a montmorillonite-sodium alginate-chitosan composite aerogel.

[0007] In the acetic acid solution of sodium alginate, the mass ratio of sodium alginate to the acetic acid solution is 1:(40 - 70); wherein, the mass concentration of the acetic acid solution is 0.05% - 0.1%.

[0008] The mass ratio of chitosan to sodium alginate is 1:(2 - 2.5).

[0009] The mass ratio of the sodium alginate-chitosan composite aerogel solution to the montmorillonite solution is (1 - 3):1; the mass concentration of the sodium alginate-chitosan composite aerogel solution is 2% - 3.5%, and the mass concentration of the montmorillonite solution is 2% - 3.5%.

[0010] The freeze-drying treatment is specifically as follows: ultrasonically dispersing the montmorillonite-sodium alginate-chitosan composite aerogel solution, then placing it in an environment at -50 to -60 °C for freezing for 10 - 12 h to obtain a frozen product, and then placing the frozen product in a vacuum environment at -50 to -60 °C and 3 - 5 Pa for drying for 60 - 72 h.

[0011] The heat-drying is specifically as follows: placing the montmorillonite-sodium alginate-chitosan composite aerogel precursor in a vacuum environment at 50 - 60 °C for drying for 4 - 6 h.

[0012] The present invention also provides a montmorillonite-based flame-retardant and heat-insulating composite aerogel, which is prepared according to the above method for preparing a montmorillonite-based flame-retardant and heat-insulating composite aerogel.

[0013] In the montmorillonite-based flame-retardant and heat-insulating composite aerogel, chitosan and sodium alginate crosslink to form a three-dimensional skeleton network structure, and montmorillonite is evenly attached to the three-dimensional skeleton network structure, and there is a hydrogen bond interaction between montmorillonite and sodium alginate and chitosan.

[0014] In the montmorillonite-based flame-retardant and heat-insulating composite aerogel, the mass proportion of montmorillonite is 25 - 50%.

[0015] The present invention also provides the application of the above-mentioned montmorillonite-based flame-retardant and heat-insulating composite aerogel, and the montmorillonite-based flame-retardant and heat-insulating composite aerogel is applied in the field of flame-retardant and heat-insulating materials.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention specifically provides a preparation method of a montmorillonite-sodium alginate-chitosan composite aerogel. Based on the cross-linking effect of cationic chitosan and anionic sodium alginate, a three-dimensional skeleton grid structure is formed, which can enhance the skeleton support strength of the composite aerogel; a flame retardant montmorillonite is introduced into the composite aerogel, and the montmorillonite is well dispersed in the sodium alginate and chitosan gel system. The montmorillonite adheres to the skeleton structure to play a coating role, and there is an interaction force between the montmorillonite and sodium alginate and chitosan, and there is a strong hydrogen bond effect, which can improve its flame retardant performance and thermal stability. Then, the montmorillonite-sodium alginate-chitosan composite aerogel is prepared by freeze-drying technology, making the production process more environmentally friendly and the cost lower.

[0017] The montmorillonite-sodium alginate-chitosan composite aerogel material prepared by the method provided by the present invention has a high compression modulus and specific compression modulus, so that the composite aerogel has excellent mechanical properties. When the montmorillonite-sodium alginate-chitosan composite aerogel is subjected to a combustion experiment, it can achieve self-extinguishing when leaving the fire, showing a strong and effective flame retardant performance; then, an insulation test is carried out, and under the condition of long-term heating, the temperature change can be kept small. The excellent properties of the composite aerogel prepared by the present invention enable it to provide better protection in a high-temperature environment and meet the high-standard requirements for flame-retardant and heat-insulating materials; it has a wide application prospect in the fields of thermal insulation, flame retardancy, and heat insulation materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is a flowchart for the preparation of the montmorillonite-based flame-retardant and heat-insulating composite aerogel of the present invention; Figure 2 It is a physical picture of the montmorillonite-based flame-retardant and heat-insulating composite aerogel prepared by the present invention; Figure 3 It is an SEM (Search Engine Marketing, scanning electron microscope) image of the sodium alginate-chitosan composite aerogel prepared in Comparative Example 1; Figure 4SEM image of montmorillonite-sodium alginate-chitosan composite aerogel-30% prepared in Example 2; Figure 5 SEM image of montmorillonite-sodium alginate-chitosan composite aerogel-50% prepared in Example 6; Figure 6 Mechanical property comparison chart of montmorillonite-sodium alginate-chitosan composite aerogel; Figure 7 Vertical burning experiment of montmorillonite-sodium alginate-chitosan composite aerogel. Among them, (a) is the combustion process diagram of sodium alginate-chitosan composite aerogel, (b) is the combustion process diagram of montmorillonite-sodium alginate-chitosan composite aerogel-30%, and (c) is the combustion process diagram of montmorillonite-sodium alginate-chitosan composite aerogel-50%; Figure 8 Heat insulation performance experiment of montmorillonite-sodium alginate-chitosan composite aerogel-30% prepared in Example 2. Among them, (a) is the thermal infrared image at 30 s, (b) is the thermal infrared image at 10 min, and (c) is the thermal infrared image at 30 min. Detailed implementation manners

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0021] In the present invention, the term "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0022] In the present invention, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or its similar expression below refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b, or c", or "at least one (item) of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0023] It should be understood that in various embodiments of the present invention, the magnitudes of the serial numbers of the above processes do not imply the order of execution. Some or all of the steps may be executed in parallel or sequentially. The execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

[0024] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "the", and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0025] The weights of the relevant components mentioned in the specification of the embodiments of the present invention not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the contents of the relevant components in the specification of the embodiments of the present invention are enlarged or reduced in proportion, they are within the scope disclosed in the specification of the embodiments of the present invention. Specifically, the mass described in the specification of the embodiments of the present invention can be mass units well-known in the chemical engineering field such as μg, mg, g, kg, etc.

[0026] Montmorillonite is a relatively typical layered silicate clay, which has unique excellent properties and can form a composite material with a polymer. After modification with montmorillonite, the flame retardancy, mechanical properties, barrier properties, thermal stability, etc. of the composite material can be significantly improved. At the same time, while improving the properties of the composite material, its low density, high porosity and other characteristics can also be retained. Therefore, it can be introduced into the aerogel system as a flame retardant.

[0027] As Figure 1 shown, the embodiments of the present invention provide a preparation method of a montmorillonite-based flame retardant and heat insulation composite aerogel. The specific steps include adding chitosan to an acetic acid solution of sodium alginate for reaction to obtain a sodium alginate-chitosan composite aerogel solution; mixing the sodium alginate-chitosan composite aerogel solution with a montmorillonite solution evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution, subjecting the montmorillonite-sodium alginate-chitosan composite aerogel solution to freeze-drying treatment to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor, and subjecting the montmorillonite-sodium alginate-chitosan composite aerogel precursor to heat-drying treatment to obtain a montmorillonite-sodium alginate-chitosan composite aerogel.

[0028] The preparation method provided by the embodiments of the present invention is based on the cross-linking effect of cationic chitosan and anionic sodium alginate to form a three-dimensional framework network structure, which can enhance the framework support strength of the composite aerogel. At the same time, montmorillonite is well dispersed in the sodium alginate and chitosan gel system. Montmorillonite adheres to the framework structure to play a coating role. There are interaction forces between montmorillonite and sodium alginate and chitosan, and there are strong hydrogen bond interactions, which can improve its flame retardancy and thermal stability.

[0029] In some embodiments, the mass ratio of sodium alginate to acetic acid in the acetic acid solution of sodium alginate is 1:(40 - 70); wherein, the mass concentration of the acetic acid solution is 0.05% - 0.1%. The concentration of the acetic acid solution of sodium alginate needs to be moderate. If the concentration is too high, the viscosity of the solution will be high, which is not conducive to subsequent reactions; if the concentration is too low, the stability and viscosity of the colloid will be affected, and an ideal structure cannot be formed.

[0030] In some embodiments, the mass ratio of chitosan to sodium alginate is 1:(2 - 2.5). Chitosan and sodium alginate are cross-linked. A suitable reaction ratio can obtain an ideal three-dimensional framework network. Excessive chitosan or sodium alginate will cause the mechanical properties of the material to decrease, and insufficient dosage will cause incomplete cross-linking, resulting in a relatively loose three-dimensional framework.

[0031] In some embodiments, the mass ratio of the sodium alginate-chitosan composite aerogel solution to the montmorillonite solution is (1 - 3):1; the mass concentration of the sodium alginate-chitosan composite aerogel solution is 2% - 3.5%, and the mass concentration of the montmorillonite solution is 2% - 3.5%. The mass proportion of montmorillonite in the composite aerogel affects the microstructure, mechanical properties, flame retardancy, etc. of the composite aerogel. Therefore, montmorillonite needs to be added in an appropriate amount. If the addition amount of montmorillonite is too small, the expected flame retardant effect cannot be achieved. If the addition amount of montmorillonite is too large, agglomeration will occur, affecting the interfacial strength, which is not conducive to the full dispersion of montmorillonite into the mixed solution, and to a certain extent, the structural stability is damaged. At the same time, sodium alginate and chitosan cross-link with each other and cannot separate more groups to form hydrogen bond interactions with montmorillonite. Therefore, excessive addition of montmorillonite will reduce the mechanical properties of the composite aerogel.

[0032] In some embodiments, before freeze-drying the montmorillonite-sodium alginate-chitosan composite aerogel solution, ultrasonic dispersion is carried out for 40 - 50 minutes to remove possible bubbles in the solution.

[0033] In some embodiments, the freeze-drying treatment is specifically as follows: ultrasonically disperse the montmorillonite-sodium alginate-chitosan composite aerogel solution, and then place it in an environment at -50 to -60 °C for freezing for 10 to 12 h to obtain a frozen product. Then, place the frozen product in a vacuum environment at -50 to -60 °C and 3 to 5 Pa for drying for 60 to 72 h. Freeze-drying the montmorillonite-sodium alginate-chitosan composite aerogel solution can cause the ice crystals in the composite aerogel to sublimate in a vacuum environment, forming a complex three-dimensional skeleton grid structure inside the composite aerogel. This structure helps to improve the strength of the composite aerogel material, retain the original morphology, and improve the heat insulation performance. The heat-drying treatment is specifically as follows: place the montmorillonite-sodium alginate-chitosan composite aerogel precursor in a vacuum environment at 50 to 60 °C for drying for 4 to 6 h. In some embodiments of the present invention, the combined use of freeze-drying and heat-drying can avoid the collapse of the aerogel structure by first performing low-temperature freeze-drying treatment, and then optimize the performance of the aerogel through heat treatment. At the same time, since freeze-drying takes a long time, heat treatment can be used to accelerate the removal of residual solvents in the subsequent process, improving the efficiency. The combined use of freeze-drying and heat-drying is a strategy that takes into account both structural integrity and process economy.

[0034] An embodiment of the present invention also provides a montmorillonite-based flame-retardant and heat-insulating composite aerogel prepared according to the above method. The physical object of the montmorillonite-based flame-retardant and heat-insulating composite aerogel is as Figure 2 shown. In the montmorillonite-based flame-retardant and heat-insulating composite aerogel, chitosan and sodium alginate crosslink to form a three-dimensional skeleton grid structure, and montmorillonite is uniformly attached to the three-dimensional skeleton grid structure. There is a hydrogen bond interaction between montmorillonite and sodium alginate and chitosan. Among them, the mass ratio of montmorillonite in the montmorillonite-based flame-retardant and heat-insulating composite aerogel is 25 to 50%. The montmorillonite-based flame-retardant and heat-insulating composite aerogel has excellent mechanical properties, flame-retardant properties, and heat-insulating properties, and can be applied to the field of flame-retardant and heat-insulating materials.

[0035] In the following examples, unless otherwise specified, all materials used can be obtained through ordinary channels; the testing methods used are conventional methods in the art.

[0036] Example 1 Dissolve 0.9 g of sodium alginate powder in 36.2 g of 0.08% acetic acid solution, and obtain a sodium alginate acetic acid solution after magnetic stirring for 60 min. Then, slowly add 0.4 g of chitosan powder to the sodium alginate acetic acid solution, and magnetic stir for 60 min. After the reaction is complete, obtain a uniformly mixed sodium alginate-chitosan composite aerogel solution with a mass concentration of 3.5%; 0.43 g of montmorillonite powder was added to 12.07 g of deionized aqueous solution, and magnetically stirred to obtain a montmorillonite solution with a mass concentration of 3.4%. The above sodium alginate-chitosan composite aerogel solution and montmorillonite solution were mixed and magnetically stirred for 120 min to be uniformly mixed, obtaining a montmorillonite-sodium alginate-chitosan composite aerogel solution; The montmorillonite-sodium alginate-chitosan composite aerogel solution was poured into a mold, placed in an ultrasonic disperser and ultrasonically dispersed for 40 min. Then the montmorillonite-sodium alginate-chitosan composite aerogel solution was placed in the freezing chamber of a freeze dryer and frozen at -50 °C for 10 h to obtain a frozen product. The frozen product was dried under the conditions of low temperature (-50 °C) and vacuum (5 Pa) for 72 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; The montmorillonite-sodium alginate-chitosan composite aerogel precursor was placed in a vacuum drying oven at 55 °C and dried for 6 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel-25%, and the mass ratio of montmorillonite in the montmorillonite-sodium alginate-chitosan composite aerogel was 25%.

[0037] Example 2 0.49 g of sodium alginate powder was dissolved in 34.3 g of 0.05% acetic acid solution, and magnetically stirred for 60 min to obtain an acetic acid solution of sodium alginate. Then 0.21 g of chitosan powder was slowly added to the acetic acid solution of sodium alginate and magnetically stirred for 60 min. After the reaction was complete, a uniformly mixed sodium alginate-chitosan composite aerogel solution with a mass concentration of 2% was obtained; 0.3 g of montmorillonite powder was added to 14.7 g of deionized aqueous solution, and magnetically stirred to obtain a montmorillonite solution with a mass concentration of 2%. The above sodium alginate-chitosan composite aerogel solution and montmorillonite solution were mixed and magnetically stirred for 120 min to be uniformly mixed, obtaining a montmorillonite-sodium alginate-chitosan composite aerogel solution; The montmorillonite-sodium alginate-chitosan composite aerogel solution was poured into a mold, placed in an ultrasonic disperser and ultrasonically dispersed for 40 min. Then the montmorillonite-sodium alginate-chitosan composite aerogel solution was placed in the freezing chamber of a freeze dryer and frozen at -58 °C for 12 h to obtain a frozen product. The frozen product was dried under the conditions of low temperature (-58 °C) and vacuum (3 Pa) for 72 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; The montmorillonite-sodium alginate-chitosan composite aerogel precursor was placed in a vacuum drying oven at 50 °C and dried for 4 h to obtain montmorillonite-sodium alginate-chitosan composite aerogel-30%, and the mass ratio of montmorillonite in the montmorillonite-sodium alginate-chitosan composite aerogel was 30%.

[0038] Example 3 Dissolve 0.75 g of sodium alginate powder in 30 g of 0.08% acetic acid solution, and obtain the acetic acid solution of sodium alginate after magnetic stirring for 60 min. Then slowly add 0.325 g of chitosan powder into the acetic acid solution of sodium alginate, and magnetic stir for 60 min. After the reaction is complete, a uniformly mixed sodium alginate-chitosan composite aerogel solution with a mass concentration of 3.5% is obtained; Add 0.58 g of montmorillonite powder into 16.92 g of deionized water solution, and magnetic stir to obtain a montmorillonite solution with a mass concentration of 3.3%; mix the above sodium alginate-chitosan composite aerogel solution and montmorillonite solution, and magnetic stir for 120 min to mix evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution; Pour the montmorillonite-sodium alginate-chitosan composite aerogel solution into a mold, place it in an ultrasonic disperser and ultrasonically disperse for 50 min. Then place the montmorillonite-sodium alginate-chitosan composite aerogel solution in the freezing ice chamber of a freeze dryer, freeze at -60 °C for 10 h to obtain a frozen product, and dry the frozen product under the conditions of low temperature (-60 °C) and vacuum (4 Pa) for 60 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; The montmorillonite-sodium alginate-chitosan composite aerogel precursor was placed in a vacuum drying oven at 60 °C and dried for 5 h to obtain montmorillonite-sodium alginate-chitosan composite aerogel-35%, and the mass ratio of montmorillonite in the montmorillonite-sodium alginate-chitosan composite aerogel was 35%.

[0039] Example 4 Dissolve 0.59 g of sodium alginate powder in 29.7 g of 0.05% acetic acid solution, and obtain the acetic acid solution of sodium alginate after magnetic stirring for 60 min. Then slowly add 0.24 g of chitosan powder into the acetic acid solution of sodium alginate, and magnetic stir for 60 min. After the reaction is complete, a uniformly mixed sodium alginate-chitosan composite aerogel solution with a mass concentration of 2.7% is obtained; Add 0.55 g of montmorillonite powder to 19.45 g of deionized aqueous solution, and stir magnetically to obtain a montmorillonite solution with a mass concentration of 2.75%; mix the above sodium alginate-chitosan composite aerogel solution and montmorillonite solution, and stir magnetically for 120 min to mix evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution; Pour the montmorillonite-sodium alginate-chitosan composite aerogel solution into a mold, place it in an ultrasonic disperser and disperse it ultrasonically for 45 min. Then, place the montmorillonite-sodium alginate-chitosan composite aerogel solution in the freezing chamber of a freeze dryer and freeze it at -58 °C for 12 h to obtain a frozen product. Dry the frozen product under the conditions of low temperature (-58 °C) and vacuum (4 Pa) for 65 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; Place the montmorillonite-sodium alginate-chitosan composite aerogel precursor in a vacuum drying oven at 55 °C and dry it for 5 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel-40%, and the mass fraction of montmorillonite in the montmorillonite-sodium alginate-chitosan composite aerogel is 40%.

[0040] Example 5 Dissolve 0.447 g of sodium alginate powder in 26.83 g of 0.1% acetic acid solution, stir magnetically for 60 min to obtain a sodium alginate acetic acid solution, and then slowly add 0.223 g of chitosan powder to the sodium alginate acetic acid solution, stir magnetically for 60 min, and wait for the reaction to complete to obtain a uniformly mixed sodium alginate-chitosan composite aerogel solution with a mass concentration of 2.5%; Add 0.55 g of montmorillonite powder to 21.95 g of deionized aqueous solution, stir magnetically to obtain a montmorillonite solution with a mass concentration of 2.4%; mix the above sodium alginate-chitosan composite aerogel solution and montmorillonite solution, and stir magnetically for 120 min to mix evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution; Pour the montmorillonite-sodium alginate-chitosan composite aerogel solution into a mold, place it in an ultrasonic disperser and disperse it ultrasonically for 50 min. Then, place the montmorillonite-sodium alginate-chitosan composite aerogel solution in the freezing chamber of a freeze dryer and freeze it at -55 °C for 11 h to obtain a frozen product. Dry the frozen product under the conditions of low temperature (-55 °C) and vacuum (3 Pa) for 70 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; The montmorillonite-sodium alginate-chitosan composite aerogel precursor was placed in a vacuum drying oven at 50 °C and dried for 6 h to obtain montmorillonite-sodium alginate-chitosan composite aerogel-45%, where the mass ratio of montmorillonite in the montmorillonite-sodium alginate-chitosan composite aerogel was 45%.

[0041] Example 6 0.35 g of sodium alginate powder was dissolved in 24.5 g of 0.05% acetic acid solution, and after magnetic stirring for 60 min, an acetic acid solution of sodium alginate was obtained. Then, 0.15 g of chitosan powder was slowly added to the acetic acid solution of sodium alginate, and magnetic stirring was carried out for 60 min. After the reaction was complete, a uniformly mixed sodium alginate-chitosan composite aerogel solution with a mass concentration of 2% was obtained; 0.5 g of montmorillonite powder was added to 24.5 g of deionized water solution, and magnetic stirring was carried out to obtain a montmorillonite solution with a mass concentration of 2%. The above sodium alginate-chitosan composite aerogel solution and montmorillonite solution were mixed, and magnetic stirring was carried out for 120 min to mix evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution; The montmorillonite-sodium alginate-chitosan composite aerogel solution was poured into a mold, placed in an ultrasonic disperser and ultrasonically dispersed for 40 min. Then, the montmorillonite-sodium alginate-chitosan composite aerogel solution was placed in the freezing chamber of a freeze dryer and frozen at -58 °C for 12 h to obtain a frozen product. The frozen product was dried under the conditions of low temperature (-58 °C) and vacuum (3 Pa) for 72 h to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor; The montmorillonite-sodium alginate-chitosan composite aerogel precursor was placed in a vacuum drying oven at 50 °C and dried for 4 h to obtain montmorillonite-sodium alginate-chitosan composite aerogel-50%, where the mass ratio of montmorillonite in the montmorillonite-sodium alginate-chitosan composite aerogel was 50%.

[0042] Comparative Example 1 0.35 g of sodium alginate powder was dissolved in 49.5 g of 0.05% acetic acid solution, and after magnetic stirring for 60 min, an acetic acid solution of sodium alginate was obtained. Then, 0.15 g of chitosan powder was slowly added to the acetic acid solution of sodium alginate, and magnetic stirring was carried out for 60 min. After the reaction was complete, a uniformly mixed sodium alginate-chitosan composite aerogel solution was obtained; Pour the sodium alginate-chitosan composite aerogel solution into an aerogel mold, place it in an ultrasonic disperser and disperse it ultrasonically for 40 min. Then, place the sodium alginate-chitosan composite aerogel solution in the freezing chamber of a freeze dryer and freeze it at -58 °C for 12 h to obtain a frozen product. Dry the frozen product under the conditions of low temperature (-58 °C) and vacuum (3 Pa) for 72 h to obtain a sodium alginate-chitosan composite aerogel precursor; Place the sodium alginate-chitosan composite aerogel precursor in a vacuum drying oven at 50 °C and dry it for 4 h to obtain a sodium alginate-chitosan composite aerogel.

[0043] Perform the following performance tests on the composite aerogels prepared in Examples 1-6 and Comparative Example 1 above: Use a scanning electron microscope (SEM) to characterize the surface morphology of the composite aerogels prepared in the above examples and comparative examples. As Figure 3 shown, it can be observed that the composite aerogel formed by the cross-linking of sodium alginate and chitosan in the sodium alginate-chitosan composite aerogel prepared in Comparative Example 1 presents a three-dimensional skeleton grid structure, containing many irregular pores, with different pore sizes and a porous structure with interconnected pores. This interconnected grid structure confirms that due to the occurrence of the cross-linking of sodium alginate and chitosan cations and anions, the skeleton support strength of the composite aerogel is enhanced, and the collapse phenomenon that occurs during the preparation of pure chitosan aerogel can be avoided. As Figure 4 shown, it can be observed that in the montmorillonite-sodium alginate-chitosan composite aerogel-30% prepared in Example 2, montmorillonite is well dispersed in the sodium alginate and chitosan gel system, adheres to the skeleton structure, plays a coating role, and there is an interaction force with sodium alginate and chitosan, with a strong hydrogen bond effect, which can improve its flame retardancy and thermal stability to a certain extent. As Figure 5 shown, it can be observed that in the montmorillonite-sodium alginate-chitosan composite aerogel-50% prepared in Example 6, there is a phenomenon of a large amount of aggregation of montmorillonite on the three-dimensional skeleton grid structure formed by sodium alginate and chitosan. This is mainly because the reduction of the sodium alginate and chitosan gel system makes it impossible to allocate more groups to form hydrogen bonds with excessive montmorillonite, resulting in a large amount of montmorillonite being piled up together and unable to be evenly dispersed. The porous skeleton structure is occupied by montmorillonite groups, and the aggregation phenomenon of surface montmorillonite is not conducive to improving the mechanical properties of the composite aerogel.

[0044] As Figure 6As shown in the figure, the mechanical properties of the composite aerogels prepared in the above examples and comparative examples were characterized, and the characterization quantities included the compression modulus and the specific compression modulus. The compression modulus was calculated from the slope of the stress-strain curve of the composite aerogel in the linear deformation stage, and the specific compression modulus was the ratio of the compression modulus of the composite aerogel to its density. The compression modulus and specific compression modulus of the sodium alginate-chitosan composite aerogel without montmorillonite were 117.86 KPa and 4333.17 m 2 / s 2 ; when the montmorillonite addition increased to 25%, the mechanical properties were enhanced. The compression modulus and specific compression modulus of the montmorillonite-sodium alginate-chitosan composite aerogel-25% were 150.68 KPa and 5245.68 m 2 / s 2 ; when the montmorillonite addition increased to 30%, the best mechanical properties were obtained. The compression modulus and specific compression modulus of the montmorillonite-sodium alginate-chitosan composite aerogel-30% were 170.37 KPa and 5648.71 m 2 / s 2 ; when the montmorillonite addition increased to 35%, the mechanical properties were enhanced. The compression modulus and specific compression modulus of the montmorillonite-sodium alginate-chitosan composite aerogel-35% were 160.15 KPa and 5066.29 m 2 / s 2 ; when the montmorillonite addition increased to 40%, the mechanical properties were enhanced. The compression modulus and specific compression modulus of the montmorillonite-sodium alginate-chitosan composite aerogel-40% were 143.24 KPa and 4466.13 m 2 / s 2 ; when the montmorillonite addition increased to 45%, the mechanical properties were enhanced. The compression modulus and specific compression modulus of the montmorillonite-sodium alginate-chitosan composite aerogel-45% were 125.25 KPa and 3866.55 m 2 / s 2 ; when further adding montmorillonite to 50%, the compression modulus and specific compression modulus of the montmorillonite-sodium alginate-chitosan composite aerogel-50% decreased to 105.88 KPa and 3369.83 m 2 / s 2 . It can be concluded that adding an appropriate amount of montmorillonite can enhance the mechanical properties of the composite aerogel, and both the compression modulus and the specific compression modulus show an increasing trend.

[0045] The reasons for the improvement of the mechanical properties of the aerogel by adding montmorillonite can be explained as follows: On the one hand, the addition of montmorillonite leads to an increase in the density of the composite aerogel. Since the density of the aerogel affects its mechanical properties, the increase in density enhances the mechanical properties of the aerogel to a certain extent. On the other hand, when montmorillonite is initially added, it is fully dispersed in the composite aerogel system. There is a hydrogen bond interaction between montmorillonite, sodium alginate, and chitosan, which can better support the skeleton structure of the aerogel, thus improving the mechanical strength. When the composite aerogel with added montmorillonite is compressed, it is necessary to first overcome the ionic force between sodium alginate and chitosan, and at the same time, overcome the hydrogen bond molecular force with montmorillonite. Therefore, adding montmorillonite enhances the mechanical properties of the composite aerogel. However, when an excessive amount of montmorillonite is added, its compressive modulus and specific compressive modulus tend to decrease. This shows that montmorillonite needs to be added in an appropriate amount. The continuous increase in the mechanical properties of the composite aerogel cannot be achieved by adding montmorillonite because the excessive addition of montmorillonite will cause it to agglomerate, affecting the interfacial strength, making it difficult for montmorillonite to be fully dispersed in the mixed solution, and to a certain extent, destroying the structural stability. At the same time, sodium alginate and chitosan crosslink with each other and cannot separate more groups to form hydrogen bond interactions with montmorillonite. Therefore, the excessive addition of montmorillonite will reduce the mechanical properties of the composite aerogel.

[0046] Vertical burning experiments were carried out on the composite aerogels prepared in the above examples and comparative examples. The sodium alginate-chitosan composite aerogel prepared in Comparative Example 1, the montmorillonite-sodium alginate-chitosan composite aerogel-30% prepared in Example 2, and the montmorillonite-sodium alginate-chitosan composite aerogel-50% prepared in Example 6 were respectively placed above the flame of an alcohol lamp and burned for 14 s. Then, the alcohol lamp was removed, and their combustion changes were observed and their self-extinguishing times were recorded. The results are as Figure 7 shown. At the same time, the mass loss rate was calculated based on the mass change before and after combustion, and the results are shown in Table 1.

[0047] From Figure 7As can be observed from (a)-(c), during the 14-s combustion process, the sodium alginate-chitosan composite aerogel exhibited a relatively strong combustion phenomenon, while the montmorillonite-sodium alginate-chitosan composite aerogel-50% hardly burned. After the sodium alginate-chitosan composite aerogel was removed from the alcohol lamp, it showed a strong smoldering effect and self-extinguished after about 16 s; as the montmorillonite addition increased, the self-extinguishing time of the composite aerogel became shorter and shorter. When the montmorillonite addition was 50%, it directly self-extinguished after the alcohol lamp was removed, showing a strong and effective flame retardant property. To more intuitively demonstrate the flame retardant property of the montmorillonite-based composite aerogel, the mass loss rates of several composite aerogels were calculated. From Table 1, it can be obtained that the mass loss rate of the sodium alginate-chitosan composite aerogel was 47.9%, indicating its weak flame retardant performance; the mass loss rate of the montmorillonite-sodium alginate-chitosan composite aerogel-25% was 39.5%, the mass loss rate of the montmorillonite-sodium alginate-chitosan composite aerogel-30% was 37.7%, the mass loss rate of the montmorillonite-sodium alginate-chitosan composite aerogel-35% was 35.5%, the mass loss rate of the montmorillonite-sodium alginate-chitosan composite aerogel-40% was 32.2%, the mass loss rate of the montmorillonite-sodium alginate-chitosan composite aerogel-45% was 27.5%, and the mass loss rate of the montmorillonite-sodium alginate-chitosan composite aerogel-50% was 24.1%. As the montmorillonite addition increased, the combustion mass loss rate of the composite aerogel gradually decreased, indicating that the addition of montmorillonite could significantly improve its flame retardant property and the flame retardant performance of the montmorillonite-based composite aerogel was optimized.

[0048] The addition of montmorillonite can significantly improve the flame retardant performance of the composite aerogel, mainly because the inorganic nanoparticle montmorillonite has excellent flame retardant and heat resistance properties and is an effective charring agent. During combustion, montmorillonite can form an isolation layer on the surface of the aerogel material, blocking the transmission of oxygen and heat in the aerogel and slowing down the spread of the flame, thus playing a role in protecting the underlying aerogel.

[0049] Table 1 Mass loss rates of the composite aerogels in the examples and comparative examples

[0050] The heat insulation performance of the composite aerogel prepared in Example 2 above was experimentally tested. At room temperature of 22 °C, the montmorillonite-sodium alginate-chitosan composite aerogel-30% prepared in Example 2 was placed on a stable heat source at a temperature of 100 °C. Three temperature measurement points (Tp1, Tp2, and Tp3) were selected on the sample, and then an infrared thermometer was used to record the changes in the surface temperature of the composite aerogel at three time points (30 s, 10 min, and 30 min). The experimental results are as Figure 8 shown. From Figure 8It can be seen from (a) that at 30 s, the three temperature measurement points of montmorillonite-sodium alginate-chitosan composite aerogel-30% rose to 24.2 °C, 24.8 °C, and 24.6 °C respectively; when placed at the heat source for 10 min, from Figure 8 It can be seen from (b) that the three temperature measurement points of montmorillonite-sodium alginate-chitosan composite aerogel-30% rose to 31 °C, 31.9 °C, and 31.2 °C respectively; then continue heating, from Figure 8 It can be seen from (c) that at 30 min, the three temperature measurement points of montmorillonite-sodium alginate-chitosan composite aerogel-30% rose to 33.4 °C, 34.8 °C, and 32.4 °C respectively. The surface temperature of montmorillonite-sodium alginate-chitosan composite aerogel-30% gradually stabilized at 10 min after heating and was not much different from the temperature measured after 30 min of heating. Thus, it can be shown that montmorillonite-sodium alginate-chitosan composite aerogel has excellent heat insulation performance, and the remarkable feature of this performance lies in its extremely high porosity structure, which enables the gaseous air in the composite aerogel to play an important role. During the heat conduction process, the gaseous air provides a large thermal resistance, effectively preventing the transfer of heat, and the heat can only be transferred through the relatively sparse solid phase structure, thus slowing down the heat transfer process to the surface of the composite aerogel.

[0051] In the ranges and any values disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In the following text, in principle, the various technical solutions can be combined with each other to obtain new technical solutions, and this should also be regarded as specifically disclosed herein.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still modify the specific implementation manners of the present invention or make equivalent substitutions. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of the claims of the present invention pending approval.

Claims

1. A preparation method of a montmorillonite-based flame-retardant and heat-insulating composite aerogel, characterized in that, Including: Adding chitosan to an acetic acid solution of sodium alginate for reaction to obtain a sodium alginate-chitosan composite aerogel solution; Mixing the sodium alginate-chitosan composite aerogel solution with a montmorillonite solution evenly to obtain a montmorillonite-sodium alginate-chitosan composite aerogel solution, subjecting the montmorillonite-sodium alginate-chitosan composite aerogel solution to freeze-drying treatment to obtain a montmorillonite-sodium alginate-chitosan composite aerogel precursor, and subjecting the montmorillonite-sodium alginate-chitosan composite aerogel precursor to heat-drying treatment to obtain a montmorillonite-sodium alginate-chitosan composite aerogel.

2. The preparation method of a montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 1, characterized in that In the acetic acid solution of sodium alginate, the mass ratio of sodium alginate to the acetic acid solution is 1:(40 - 70); wherein, the mass concentration of the acetic acid solution is 0.05% - 0.1%.

3. The preparation method of a montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 1, wherein, The mass ratio of chitosan to sodium alginate is 1:(2 - 2.5).

4. The preparation method of a montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 1, characterized in that, The mass ratio of the sodium alginate-chitosan composite aerogel solution to the montmorillonite solution is (1 - 3):1; the mass concentration of the sodium alginate-chitosan composite aerogel solution is 2% - 3.5%, and the mass concentration of the montmorillonite solution is 2% - 3.5%.

5. The preparation method of a montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 1, characterized in that, The freeze-drying treatment is specifically: ultrasonically dispersing the montmorillonite-sodium alginate-chitosan composite aerogel solution, then placing it in an environment at -50 to -60 °C for freezing for 10 - 12 h to obtain a frozen product, and then placing the frozen product in a vacuum environment at -50 to -60 °C and 3 - 5 Pa for drying for 60 - 72 h.

6. The preparation method of a montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 1, wherein, The heat-drying is specifically: placing the montmorillonite-sodium alginate-chitosan composite aerogel precursor in a vacuum environment at 50 - 60 °C for drying for 4 - 6 h.

7. A montmorillonite-based flame-retardant and heat-insulating composite aerogel, characterized in that, The montmorillonite-based flame-retardant and heat-insulating composite aerogel is prepared according to the preparation method of the montmorillonite-based flame-retardant and heat-insulating composite aerogel according to any one of claims 1 - 6.

8. A montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 7, characterized in that, In the montmorillonite-based flame-retardant and heat-insulating composite aerogel, chitosan and sodium alginate crosslink to form a three-dimensional skeleton network structure, and montmorillonite is uniformly attached to the three-dimensional skeleton network structure, and there is a hydrogen bond interaction between montmorillonite and sodium alginate and chitosan.

9. The montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 7, wherein The mass proportion of montmorillonite in the montmorillonite-based flame-retardant and heat-insulating composite aerogel is 25% - 50%.

10. Use of the montmorillonite-based flame-retardant and heat-insulating composite aerogel according to claim 7, characterized in that, The montmorillonite-based flame-retardant and heat-insulating composite aerogel is applied in the field of flame-retardant and heat-insulating materials.

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