A method for high-temperature preparation of aerogels by a template method

Abstract

The application belongs to the field of aerogel material preparation, and discloses a method for preparing aerogel by a template method at high temperature. In the method, a water-soluble inorganic salt is used as a template, a base material is dispersed into the inorganic salt template and adhered to the surface of the inorganic salt template, the structure of the base material is fixed, the inorganic salt template is washed away with water, and normal pressure drying is performed, so that a hierarchical pore aerogel is obtained. The method has simple equipment, convenient operation, and an environmentally-friendly preparation process. Aerogels of different materials, composite materials and morphologies can be prepared by the method, and the aerogels have stable structures, uniform internal structures and small densities.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of aerogel material preparation, and particularly relates to a method for preparing aerogel at high temperature by a template method. BACKGROUND

[0002] Aerogel is a kind of dry gel material with air as a dispersion medium, and is the solid with the smallest density in the world, which has a very broad application prospect in many fields such as aerospace, environmental protection, energy storage, biological medicine and catalytic system. Generally, the preparation process of aerogel mainly includes two steps: the first step is to prepare a gel through a sol-gel process; and the second step is to replace the liquid in the gel with gas to obtain the aerogel. The liquid in the gel is usually an organic solvent, and the preparation of sol-gel inevitably uses a large amount of organic solvent. Before drying, a long time of solvent replacement is generally required, which is not only high in cost but also not friendly to the environment. The drying methods mainly include supercritical drying, freeze drying and atmospheric drying. The supercritical drying is high in cost and high in danger, the freeze drying is long in drying period and high in energy consumption, and if the atmospheric drying is used to obtain the aerogel in the prior art, the structure of the aerogel is easy to collapse and deform. Therefore, how to reduce the preparation time of the aerogel, ensure green and pollution-free, reduce the preparation cost and ensure the quality of the aerogel has become a key problem. SUMMARY

[0003] The purpose of the application is to solve the problems of the prior art, and to provide a preparation method of aerogel which is simple in equipment, convenient in operation and environmentally friendly in process. The technical scheme is as follows:

[0004] In the first aspect, the application provides a preparation method of aerogel, which includes the following steps:

[0005] S1-1, uniformly mixing an inorganic salt and a base material to obtain a solid I;

[0006] S2-1, adding the solid I into water to obtain a solid II;

[0007] S3-1, tightly pressing and drying the solid II to obtain a solid III;

[0008] S4-1, finally immersing the solid III in water to remove the inorganic salt, and drying to obtain the aerogel;

[0009] The base material includes a first base material and a second base material, the first base material is at least one of polyethylene, nanofiber, chopped fiber and fiber pulp, the melting point of the first base material is 100-300 DEG C, and the second base material is at least one of nanofiber, chopped fiber and fiber pulp.

[0010] In the present application, a water-soluble inorganic salt is used as a template, and a nanofiber, a chopped fiber, and a fiber pulp that are insoluble in water are used as a base material. The base material is dispersed into the template, the structure of the base material is fixed, the template is removed, and normal pressure drying is performed, so that a porous base material, i.e., an aerogel, is obtained. On the one hand, the preparation method of the aerogel in the present application has a simple process, is easy to operate, and has a short preparation period, and is suitable for large-scale and rapid production of aerogels. On the other hand, only water is used as a solvent in the preparation process of the aerogel, and no organic solvent is used in the entire process, so that the cost is low and the process is green and safe. In addition, the drying method is normal pressure drying, which is low in cost and easy to implement. On the other hand, the preparation method in the present application has great versatility. By changing the type of the base material and the ratio of the base material to the inorganic salt, aerogels with different materials and different morphologies can be prepared. In addition, the aerogel has a stable structure, a uniform internal structure, and a small density.

[0011] Preferably, the mass ratio of the first base material to the base material is 10:100-40:100. That is, the weight percentage of the base material with a melting point of 100-300℃ in the total weight of the base material is 10%-40%, so that the base material with a melting point of 100-300℃ can improve the structural strength of the aerogel without affecting the heat resistance of the aerogel.

[0012] Preferably, the inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate. The inorganic salt selected in the present application has good water solubility, is easy to be pressure cast with the base material, ensures that the solid formed after pressure casting has high hardness after drying, and is easier to remove the inorganic salt template to prepare the aerogel. In addition, the inorganic salt selected in the present application has a high melting point, so that the template formed by the inorganic salt will not deform during the drying process to affect the structure of the aerogel.

[0013] In a second aspect, the present application provides a preparation method of an aerogel, which includes the following steps:

[0014] S1-2, uniformly mixing the inorganic salt and the base material to obtain a solid I;

[0015] S2-2, adding the solid I into water to obtain a solid II;

[0016] S3-2, further compacting and drying the solid II to obtain a solid III;

[0017] S4-2, then immersing the solid III into a binder, drying to obtain a solid IV;

[0018] S5-2, finally immersing the solid IV into water to remove the inorganic salt, and drying to obtain an aerogel;

[0019] Preferably, the base material includes at least one of a nanofiber, a chopped fiber, and a fiber pulp.

[0020] In this application, water-soluble inorganic salts are used as templates, and water-insoluble nanofibers, chopped fibers, and fiber pulp are used as substrates. The substrates are dispersed in the template, and an adhesive is added to make the substrate structure more stable. After removing the template and drying under normal pressure, a porous substrate, i.e., aerogel, is obtained. The adhesive can be dissolved in a small amount of organic solvent first, and then the solid III can be impregnated with the adhesive. The soaking time in the adhesive is 0.5h-2h, so that the organic solvent evaporates, thereby better fixing the structure of the substrate in the solid IV.

[0021] Preferably, the adhesive comprises at least one of polyacrylic acid, polyurethane, polyimide, and polyetherimide. The melting point of the adhesive used is lower than the decomposition temperature or glass transition temperature of the substrate. More preferably, the melting point of the adhesive is 100°C-300°C.

[0022] Preferably, the adhesive concentration is less than 10%. When the adhesive concentration is too high, the adhesive has poor fluidity and cannot fully impregnate the solid; when the adhesive concentration is too low, the resulting solid structure has poor strength.

[0023] Preferably, the chopped fibers have a diameter of less than 500 micrometers and a length of less than 3 centimeters. Placing the mixture of inorganic salt and substrate in water effectively removes the inorganic salt template. When chopped fibers are used as the substrate, the diameter and length of the chopped fibers are controlled to allow for better crushing and mixing with the inorganic salt.

[0024] Thirdly, this application also provides a method for preparing aerogel, comprising the following steps:

[0025] S1-3. Crush the inorganic salt to obtain solid I;

[0026] S2-3. Add solid I to water to obtain solid II;

[0027] S3-3. Then, press and dry solid II to obtain solid III;

[0028] S4-3. Then, immerse solid III in the polymer solution and dry it to obtain solid IV;

[0029] S5-3. Finally, immerse solid IV in water to remove inorganic salts, and then dry to obtain aerogel.

[0030] In this application, after forming an inorganic salt template, a polymer solution is dispersed into and contacts the inorganic salt template to form an aerogel structure. Since the polymer itself has a certain degree of adhesion, no additional adhesive is needed to fix the aerogel structure. Finally, the inorganic salt template is removed to obtain the aerogel. This preparation method uses simple equipment, is easy to operate, and has low energy consumption. The preparation process is environmentally friendly, and the inorganic salt can be recycled and reused. By controlling the ratio of inorganic salt to polymer and selecting different polymer types, aerogels of different materials, composite materials, and morphologies can be prepared. The prepared aerogels have stable structures, uniform internal structures, and low density.

[0031] Preferably, the polymer concentration in the polymer solution is less than 30%, and the polymer molecular weight is greater than 10,000. The concentration of the polymer solution can control the density of the aerogel; the higher the polymer solution concentration, the greater the density of the obtained aerogel.

[0032] Fourthly, this application also provides an aerogel prepared by any of the above-described preparation methods. This aerogel has a stable structure, uniform internal structure, and low density.

[0033] The beneficial effects achieved by this application are: the preparation method is simple, easy to operate, and has a short preparation cycle, making it suitable for large-scale rapid production of aerogels; moreover, only water is used as a solvent in the preparation process of aerogels, which is low-cost and green and safe, and the drying method using atmospheric pressure drying is low-cost and relatively easy to implement; and aerogels of different materials and morphologies can be prepared, and the prepared aerogels have stable structures, uniform internal structures, and low density. Attached Figure Description

[0034] Figure 1 The diagram shown is a flowchart of the aerogel preparation method provided by the first preparation method of this application;

[0035] Figure 2 The diagram shows a flowchart of the aerogel preparation method provided by the second preparation method of this application;

[0036] Figure 3 The flowchart shown is a process for preparing aerogel according to the third preparation method of this application;

[0037] Figure 4 The image shown is a scanning electron microscope image of the aerogel provided by the first preparation method of this application;

[0038] Figure 5 The image shown is a scanning electron microscope image of the aerogel prepared by the second method of this application;

[0039] Figure 6 The image shown is a scanning electron microscope image of the aerogel prepared by the third preparation method of this application. Detailed Implementation

[0040] The present invention and its technical effects will be clearly and completely described below with reference to embodiments and accompanying drawings, so as to fully understand the purpose, solution and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The same reference numerals used throughout the drawings indicate the same or similar parts.

[0041] For ease of understanding, the English abbreviations and related technical terms used in the embodiments of this application will be explained and described below.

[0042] Aerogels are a class of dry gel materials dispersed in air. They are the least dense solids in the world and are considered to be materials obtained by replacing the liquid component with gas in a gel structure. Aerogels possess a unique three-dimensional porous structure, combining excellent properties such as low density, high specific surface area, high porosity, low thermal conductivity, low dielectric constant, and high temperature resistance. They have broad application prospects in many fields such as aerospace, environmental protection, energy storage, biomedicine, and catalytic systems.

[0043] In this application, water-soluble inorganic salts are used as templates, and water-insoluble nanofibers, chopped fibers, fiber pulp and polymer solutions are used as substrates. The substrates are dispersed inside and on the surface of the template, and the substrates fill the pores of the template. After the substrate structure is fixed, the template is washed away with water and dried under normal pressure to obtain a porous substrate, i.e., aerogel.

[0044] Please see Figure 1 , Figure 1 This is a flowchart of the aerogel preparation method provided by the first preparation method of this application. The aerogel preparation method of this application includes steps S1-1, S2-1, S3-1, and S4-1. Detailed steps are as follows:

[0045] S1-1. Mix the inorganic salt with the substrate to obtain solid I;

[0046] S2-1. Add solid I to water to obtain solid II;

[0047] S3-1. Then, press and dry solid II to obtain solid III;

[0048] S4-1. Finally, solid III is immersed in water to remove inorganic salts, and then dried to obtain aerogel.

[0049] The substrate includes a first substrate and a second substrate. The first substrate is at least one of polyethylene, nanofibers, chopped fibers and fiber pulp. The melting point of the first substrate is 100℃-300℃. The second substrate is at least one of nanofibers, chopped fibers and fiber pulp.

[0050] The substrate is the main material of the target aerogel. In this embodiment, nanofibers refer to linear materials with a diameter at the nanometer scale and a relatively large length. Chopped fibers are short fibers, and fiber pulp is a fibrous aggregate obtained from plant fibers through chemical and mechanical processing. The properties and uses of the prepared aerogel are related to the choice of substrate. After the substrate is made into an aerogel, some of its own properties are retained. For example, aerogels prepared from high-temperature resistant substrates often also possess high-temperature resistant properties.

[0051] The substrate can incorporate one or more nanofibers as needed. For example, if it is difficult to achieve the properties of high temperature resistance and high thermal conductivity using only one type of nanofiber, high temperature resistant nanofibers and high thermal conductivity nanofibers can be selected simultaneously as the substrate. Similarly, the substrate can also include one or more chopped fibers, or the substrate can include one or more fiber pulps. In other embodiments, the substrate can also include multiple nanofibers, multiple chopped fibers, and multiple fiber pulps.

[0052] In step S1-1, the inorganic salt and the substrate are crushed and mixed evenly. The substrate and inorganic salt are dispersed and mixed evenly by crushing to obtain an aerogel with uniform pores. The inorganic salt and the substrate can be directly mixed and crushed, or the inorganic salt and the substrate can be added and crushed in batches, or the inorganic salt and the substrate can be crushed separately and then mixed. In this embodiment, the inorganic salt is first crushed to the micron level, then mixed into the substrate, and then crushed and mixed again to obtain solid I.

[0053] In step S2-1, water is added to solid I to slightly dissolve the inorganic salts, resulting in a dissolution rate of 2%-10% of the inorganic salts. In one embodiment, the amount of water added can be 2%, 4%, 6%, 8%, 10%, etc., depending on the properties of the inorganic salts, the moisture content of the substrate, and the requirements for aerogel performance. In one embodiment, when fiber pulp is selected as the substrate, step S2-1 can be omitted during aerogel preparation because the fiber pulp contains a certain amount of moisture.

[0054] In step S3-1, the size and shape of the mold can be adjusted according to the product, and this application does not impose any restrictions on this. Solid II is die-cast in the mold. By pressing solid II tightly, the inorganic salts and substrate in solid III can form a dense structure. By drying solid II, the moisture content in the obtained solid III is reduced. At the same time, a portion of the substrate with a melting point of 100℃-300℃ melts to fix the structure of the substrate in solid III. Here, the melting point in this application refers to the temperature at which the substrate begins to melt.

[0055] In one embodiment, solid II can be dried directly in the mold after being compressed, or it can be dried after being removed from the mold; this application does not impose any restrictions on this. In one embodiment, the drying temperature of solid II after compression is 80℃-120℃, and the drying time is 2h-5h.

[0056] In one embodiment, the substrate with a melting point of 100°C-300°C can also be replaced by organic material powder, which also has a melting point of 100°C-300°C.

[0057] In step S4-1, solid III is immersed in water, where the inorganic salts dissolve and are removed. The spaces previously occupied by inorganic salts are replaced by water. After drying to remove the water, the spaces previously occupied by inorganic salts are replaced by air, thus obtaining a hierarchical porous aerogel. Notably, the dissolved inorganic salts in the water can be recycled and reused during the immersion of solid III in water.

[0058] In this embodiment, firstly, water is added to solid I to dissolve some inorganic salts, so that solid II can be better die-cast in step S3-1, while ensuring that the obtained solid III has high hardness. Secondly, by selecting some substrates with low melting points, these substrates will melt during heating and drying to fix the structure of the substrate. Solid III has high hardness and the substrate structure is relatively fixed, so that after removing inorganic salts in step S4-1, the integrity of the structure can be guaranteed by drying under normal pressure, avoiding aerogel shrinkage, deformation and collapse.

[0059] In this embodiment, aerogels of different densities can be designed by setting different ratios of substrate and inorganic salt.

[0060] The aerogel preparation method in this application is simple, easy to operate, and has a short preparation cycle, making it suitable for large-scale rapid production of aerogels. On the one hand, only water is used as a solvent in the aerogel preparation process, and no organic solvents are used throughout the process, resulting in low cost and environmental safety. At the same time, the atmospheric pressure drying method is low-cost and relatively easy to implement. On the other hand, the preparation method in this application has great versatility. By changing the type of substrate and the ratio of substrate to inorganic salt, aerogels with different materials and morphologies can be prepared. Moreover, the aerogel structure is stable, with a uniform internal structure and low density.

[0061] In one embodiment, the mass ratio of the first substrate to the substrate is greater than 10:100 to 40:100. That is, the weight of the portion of the substrate with a melting point of 100℃-300℃ accounts for 10%-40% of the total weight of the substrate, so that the portion of the substrate with a melting point of 100℃-300℃ can improve the strength of the aerogel structure without affecting the heat resistance of the aerogel.

[0062] In one embodiment, the mass ratio of chopped polyethylene (PE) fibers with a melting point of 110°C to the substrate is 1:9. This mass ratio refers to the percentage of chopped PE fibers with a melting point of 110°C in the total substrate. A higher amount of chopped PE fibers with a melting point of 110°C allows for better fixation of the substrate structure during melting, but this can also lead to poorer heat resistance in the prepared aerogel. Conversely, too little chopped PE fibers with a melting point of 110°C results in poor fixation of the substrate structure, potentially causing deformation and collapse of the aerogel structure. In this embodiment, by controlling the mass ratio of chopped PE fibers with a melting point of 110°C to the substrate to 1:9, the chopped PE fibers with a melting point of 110°C can improve the structural strength of the aerogel without affecting its heat resistance.

[0063] In this embodiment, the inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate. The inorganic salt selected in this application has good water solubility and is easy to die-cast together with the substrate, ensuring that the solid III formed after die-casting has high hardness after drying. Furthermore, it is easier to remove the inorganic salt template by immersing the solid III in water to form an aerogel. At the same time, the inorganic salt selected in this application has a high melting point, so that the template formed by the inorganic salt will not deform during the drying process and affect the structure of the aerogel.

[0064] In one embodiment, the inorganic salt can be at least one of potassium salt and sodium salt.

[0065] In one embodiment, the inorganic salt has a melting point above 200°C. In other embodiments, the inorganic salt has a melting point above 500°C, and the inorganic salt may also be other water-soluble salts.

[0066] In this embodiment, solid II is placed in a mold, pressed, and dried (i.e., step S3-1), with a pressing pressure of 0.5 kg / cm². 2 -1kg / cm 2 The compression time is 0.5 minutes to 1 minute. By compressing solid II, the inorganic salts and substrate in solid III can form a dense structure. When the compression pressure decreases, the compression time can be increased to allow the inorganic salts and substrate to form a dense structure better; when the compression time is shortened, the compression pressure can be increased to allow the inorganic salts and substrate to form a dense structure better.

[0067] In one embodiment, the pressure during compaction is 0.5 kg / cm². 2 The pressing time is 1 minute.

[0068] In one embodiment, the pressure during compaction is 0.8 kg / cm². 2The compression time is 0.8 minutes.

[0069] In one embodiment, the pressure during clamping is 1 kg / cm². 2 The pressing time is 0.5 minutes.

[0070] In other embodiments, different compression pressures and compression times can be selected depending on the specific substrate and the desired properties of the aerogel.

[0071] In this embodiment, solid III is immersed in water to remove inorganic salts, and then dried under normal pressure to obtain an aerogel (i.e., step S4-1). Solid III is immersed in water 3-4 times, with the amount of water added each time being 4-5 times the mass of solid III. The total immersion time for solid III is 5-10 hours. Using a method of adding water in small amounts multiple times to remove the inorganic salt template ensures more thorough removal of the inorganic salts and saves water. The specific amount of water added each time can be determined based on the solubility of the inorganic salts in water.

[0072] In one embodiment, step S3-1 includes: adding water to solid III, the mass of which is 4 times the mass of solid III; soaking for two hours; pouring out the soaked water; adding new water to solid III; repeating the water addition 4 times; removing solid III; and drying it under normal pressure to obtain an aerogel.

[0073] In one embodiment, step S4-1 includes: adding water to solid III to immerse solid III, soaking for 1 hour, pouring out the soaking water, adding new water to solid III to immerse solid III again, repeating the water addition 5 times, removing solid III, and drying it under normal pressure to obtain aerogel.

[0074] In one embodiment, when solid III removes inorganic salts, hot water, stirring, or extraction can be used to accelerate the removal of inorganic salts.

[0075] In this embodiment, solid III is immersed in water to remove inorganic salts, and then dried at atmospheric pressure to obtain an aerogel (i.e., step S4-1). The drying temperature at atmospheric pressure is 80℃-120℃, and the drying time is 2h-5h. The drying temperature and drying time are determined according to the properties of the substrate or the characteristics of the aerogel. For example, when the substrate is not suitable for drying at too high a temperature, the drying time can be extended to obtain the aerogel; or when prolonged drying will damage the aerogel structure, the drying temperature can be increased to reduce the drying time.

[0076] In one embodiment, the drying temperature for atmospheric pressure drying is 80°C, and the drying time is 5 hours.

[0077] In one embodiment, the drying temperature for atmospheric pressure drying is 90°C, and the drying time is 4 hours.

[0078] In one embodiment, the drying temperature for atmospheric pressure drying is 100°C, and the drying time is 3 hours.

[0079] In one embodiment, the drying temperature for atmospheric pressure drying is 110°C, and the drying time is 2.5 hours.

[0080] In one embodiment, the drying temperature for atmospheric pressure drying is 120°C, and the drying time is 2 hours.

[0081] In one embodiment, the inorganic salt has a solubility greater than 10 g / 100 g water, and the substrate has a solubility less than 0.5 g / 100 g water. In another embodiment, the inorganic salt is soluble in water, and the substrate is insoluble or only slightly soluble in water.

[0082] In this embodiment, the chopped fibers have a diameter of less than 500 micrometers and a length of less than 3 centimeters. When using chopped fibers as the substrate, the diameter and length of the chopped fibers are controlled to allow for better crushing and mixing with the inorganic salts. A scanning electron microscope image of the prepared aerogel is shown below. Figure 4 As shown.

[0083] Example 1

[0084] A method for preparing an aerogel includes the following steps:

[0085] 20g of sodium chloride was crushed to the micron level, mixed with 0.2g of chopped fibers and 0.1g of nylon (melting point 220℃-260℃), and crushed and mixed again to obtain solid I;

[0086] Add 2 mL of water to solid I and stir well to obtain solid II;

[0087] Solid II was placed in a mold at 1 kg / cm³. 2 After being pressed under pressure for 0.5 minutes, it was dried at 100°C for 2 hours to obtain solid III;

[0088] Solid III was soaked in water for 2 hours, then the water was changed and the soaking was repeated 3 times. After soaking, it was removed and dried at 100℃ and normal pressure for 4 hours to obtain an aerogel with a density of 52 mg / cm³. 3 .

[0089] To illustrate the beneficial effects of the method of this application, embodiments 1-2, 1-3, 1-4, and 1-5 have also been provided. Please refer to Table 1. The methods of embodiments 1-2, 1-3, 1-4, and 1-5 in Table 1 are the same as those of embodiment 1, but one parameter is different, as detailed in Table 1.

[0090] Table 1. Effects of different parameters on aerogel density

[0091]

[0092] Please see Figure 2 , Figure 2 This is a flowchart of the preparation of aerogel provided by the second preparation method of this application. The difference between the second preparation method and the first preparation method is that, in the second preparation method, after solid II is placed in a mold, pressed and dried to obtain solid III, the second preparation method further includes a step of immersing the pressed and dried solid III in an adhesive and then taking it out and drying it. In addition, the second preparation method does not limit the melting point of the substrate.

[0093] Specifically, the second preparation method includes steps S1-2, S2-2, S3-2, and S4-2. The detailed steps are as follows:

[0094] S1-2. Mix the inorganic salt with the substrate to obtain solid I;

[0095] S2-2. Then add solid I to water to obtain solid II;

[0096] S3-2. Then, press and dry solid II to obtain solid III;

[0097] S4-2. Then, solid III is immersed in the adhesive and dried to obtain solid IV.

[0098] S5-2. Finally, solid IV is immersed in water to remove inorganic salts, and then dried to obtain aerogel.

[0099] The substrate includes at least one of nanofibers, chopped fibers, and fiber pulp.

[0100] In one embodiment, the adhesive concentration is less than 10%, and the immersion time of solid III in the adhesive is 0.5h-2h. The adhesive impregnates solid III to better fix the structure of the substrate in solid IV. If a polyamic acid (PAA) solution is used as the adhesive, the process of immersing solid III in the adhesive and then removing it for high-temperature treatment is also called imidization.

[0101] In one embodiment, the adhesive includes at least one selected from polyacrylic acid, polyurethane, polyimide, and polyetherimide. In one embodiment, the melting point of the adhesive is lower than the decomposition temperature or glass transition temperature of the substrate. In one embodiment, the melting point of the adhesive is 100°C-300°C.

[0102] In one embodiment, the adhesive can be dissolved in a small amount of organic solvent, and then solid III can be immersed in the adhesive solution, removed and dried to allow the organic solvent to evaporate, thereby obtaining solid IV.

[0103] It should be noted that the preparation conditions, substrate and inorganic salt selection, and parameter settings of the aerogel preparation method in the first preparation method are also applicable to the implementation methods in the second preparation method, and will not be repeated here.

[0104] Example 2

[0105] A method for preparing an aerogel includes the following steps:

[0106] 20g of sodium chloride was crushed to the micron level, mixed with 0.2g of chopped aramid fiber, and crushed and mixed again to obtain solid I;

[0107] Add 2 mL of water to solid I and stir well to obtain solid II;

[0108] Solid II was added to the mold at 1 kg / cm³. 2 After being pressed under pressure for 0.5 minutes, it was dried at 100℃ for 2 hours to obtain solid III. Solid III was removed from the mold and soaked in a 5% polyacrylic acid solution. After being soaked through, it was dried at normal pressure to obtain solid IV.

[0109] Solid IV was immersed in water for 2 hours, then the water was changed and the immersion was repeated 3 times. Solid IV was then removed and dried at 100℃ and normal pressure for 4 hours to obtain an aerogel with a density less than 15 mg / cm³. 3 The scanning electron microscope image of the prepared aerogel is shown below. Figure 5 As shown.

[0110] To illustrate the beneficial effects of the method in this application, embodiments 2-2, 2-3, 2-4, and 2-5 have also been provided. Please refer to Table 2. The methods in embodiments 2-2, 2-3, 2-4, and 2-5 in Table 2 are the same as those in embodiment 2, but one parameter is different, as detailed in Table 2.

[0111] Table 2. Effects of different parameters on aerogel density

[0112]

[0113]

[0114] Please see Figure 3 , Figure 3This is a flowchart of the preparation of aerogel provided by the third preparation method of this application. The difference between the third preparation method and the first preparation method is that the substrate in the first preparation method includes at least one of nanofibers, chopped fibers and fiber pulp, while in the third preparation method the substrate is selected from polymer solution; and in the first preparation method the substrate and inorganic salt are crushed and mixed together and co-cast into shape, while in the third preparation method the inorganic salt is crushed and cast into shape first, and then immersed in the substrate (i.e. polymer solution) to disperse the substrate into the inorganic salt template.

[0115] Specifically, the preparation method of aerogel in the third preparation method of this application includes steps S1-3, S2-3, S3-3, S4-3, and S5-3. The detailed steps are as follows:

[0116] S1-3. Crush the inorganic salt to obtain solid I;

[0117] S2-3. Add solid I to water to obtain solid II;

[0118] S3-3. Then, press and dry solid II to obtain solid III;

[0119] S4-3. Then, immerse solid III in the polymer solution and dry it to obtain solid IV;

[0120] S5-3. Finally, immerse solid IV in water to remove inorganic salts, and then dry to obtain aerogel.

[0121] In this process, steps S1-3, S2-3, and S3-3 form an inorganic salt template. In step S4-3, the polymer solution substrate is dispersed into and contacts the inorganic salt template to form an aerogel structure. Since the polymer itself has a certain degree of adhesion, in this embodiment, no adhesive is needed to fix the aerogel structure. In step S5-3, the inorganic salt template is removed to obtain the aerogel.

[0122] In this preparation method, the equipment used in the aerogel preparation process is simple, easy to operate, and has low energy consumption. The preparation process is environmentally friendly, and the inorganic salts can be recycled and reused. By controlling the ratio of inorganic salts to polymers and selecting different polymer types, aerogels of different materials, composite materials, and morphologies can be prepared. The prepared aerogels have stable structures, uniform internal structures, and low densities. The density of the hierarchical porous aerogel prepared using polyurethane (PU) solution as a substrate is less than 60 mg / cm³. 3 The scanning electron microscope image of the prepared aerogel is shown below. Figure 6 As shown.

[0123] In this embodiment, the polymer concentration in the polymer solution is less than 30%, and the molecular weight of the polymer is greater than 10,000.

[0124] In one embodiment, the polymer concentration in the polymer solution is 30%, and the polymer molecular weight is 50,000.

[0125] In one embodiment, the polymer concentration in the polymer solution is 20%, and the polymer molecular weight is 40,000.

[0126] In one embodiment, the polymer concentration in the polymer solution is 15%, and the polymer molecular weight is 30,000.

[0127] In one embodiment, the polymer concentration in the polymer solution is 10%, and the polymer molecular weight is 20,000.

[0128] In one embodiment, the polymer concentration in the polymer solution is 5%, and the polymer molecular weight is 10,000.

[0129] In this embodiment, solid II is placed in a mold, pressed, and dried (i.e., step S3-3), with a pressing pressure of 0.5 kg / cm². 2 -1kg / cm 2 The pressing time is 0.5 minutes to 1 minute.

[0130] In this embodiment, the immersion time of solid III in the polymer solution is 0.5h-2h.

[0131] In this embodiment, solid IV is immersed in water to remove inorganic salts, and then dried under normal pressure to obtain an aerogel. Solid IV is immersed in water 3-4 times, and the amount of water added each time is 4-5 times the mass of solid IV. The total immersion time of solid IV is 5h-10h. The drying temperature under normal pressure is 80℃-120℃, and the drying time is 2h-5h.

[0132] Example 3

[0133] A method for preparing an aerogel includes the following steps:

[0134] 20g of sodium chloride was crushed to the micron level to obtain solid I;

[0135] Add 2 mL of water to solid I and stir well to obtain solid II;

[0136] Solid II was placed in a mold at 1 kg / cm³. 2 After being pressed under pressure for 0.5 minutes, it was dried at 100°C for 2 hours to obtain solid III;

[0137] Solid III was immersed in a 30% polyurethane solution and soaked thoroughly. After being removed and dried, solid IV was obtained.

[0138] Solid IV was immersed in water for 2 hours, then the water was changed and the immersion was repeated 3 times. Solid IV was then removed and dried at 100℃ and normal pressure for 4 hours to obtain an aerogel with a density of 58 mg / cm³. 3 .

[0139] To illustrate the beneficial effects of the method of this application, Examples 3-2, 3-3, 3-4, and 3-5 were also provided. Please refer to Table 3. The methods of Examples 3-2, 3-3, 3-4, and 3-5 in Table 3 are the same as those in Example 3, but the concentration of polyurethane is different. See Table 3 for details.

[0140] Table 3. Effect of polyurethane concentration on aerogel density

[0141] Example Polyurethane (PU) solubility % Aerogel density mg / cm 3 ]] 3 30 58 3-2 20 47 3-3 15 41 3-4 10 36 3-5 5 22

[0142] As can be seen from the table, the aerogels prepared by the method of this application all have relatively low densities, and the density of the aerogel can be controlled by adjusting the concentration of the polymer. The higher the polyurethane concentration, the greater the density of the obtained aerogel.

[0143] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. Any embodiment that achieves the technical effects of the present invention using the same means should fall within the protection scope of the present invention. Within the protection scope of the present invention, various modifications and variations can be made to the technical solutions and / or implementation methods.

Claims

1. A method for preparing an aerogel, characterized in that, Includes the following steps: S1 1. Mix the inorganic salt with the substrate to obtain solid I; S2 1. Add solid I to water to dissolve 2%-10% of the inorganic salts, and obtain solid II; S3 1. Then, compact and dry solid II. The pressure during compaction should be 0.5 kg / cm². 2 1kg / cm 2 The compaction time is 0.5 minutes. 1 minute, drying temperature 80℃ Drying temperature: 120℃, drying time: 2 hours After 5 hours, solid III was obtained; S4 1. Finally, solid III was immersed in water to remove inorganic salts, and then dried to obtain aerogel; The substrate includes a first substrate and a second substrate, wherein the mass ratio of the first substrate to the second substrate is 10:

100. 40:100; the first substrate is nylon or polyester, and the melting point of the first substrate is 100℃. 300℃; the second substrate is chopped fiber; The inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate, and the melting point of the inorganic salt is higher than 200°C. The solubility of inorganic salts is greater than 10g / 100g water, and the solubility of the substrate is less than 0.5g / 100g water.

2. A method for preparing an aerogel, characterized in that, Includes the following steps: S1 2. Mix the inorganic salt with the substrate to obtain solid I; S2 2. Add solid I to water to dissolve 2%-10% of the inorganic salts, and obtain solid II; S3 2. Then, compact solid II and dry it. The pressure during compaction is 0.5 kg / cm². 2 1kg / cm 2 The compaction time is 0.5 minutes. 1 minute, drying temperature 80℃ Drying temperature: 120℃, drying time: 2 hours After 5 hours, solid III was obtained; S4 2. Then, solid III is immersed in the adhesive and dried to obtain solid IV; S5 2. Finally, solid IV is immersed in water to remove inorganic salts, and then dried to obtain aerogel; The substrate includes at least one of nanofibers, chopped fibers, and fiber pulp; The inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate, and the melting point of the inorganic salt is higher than 200°C. The solubility of inorganic salts is greater than 10g / 100g water, and the solubility of the substrate is less than 0.5g / 100g water; The adhesive comprises at least one of polyacrylic acid, polyurethane, polyimide, and polyetherimide, and the adhesive has a melting point of 100°C. At 300℃, with an adhesive concentration of less than 10%, the soaking time of solid III in the adhesive is 0.5 hours. 2h.

3. The preparation method according to claim 2, characterized in that, The chopped fibers have a diameter of less than 500 micrometers and a length of less than 3 centimeters.

4. A method for preparing an aerogel, characterized in that, The method for preparing the aerogel includes the following steps: S1 3. Crush the inorganic salt to obtain solid I; S2 3. Add solid I to water to dissolve 2%-10% of the inorganic salts, and obtain solid II; S3 3. Then, compact solid II and dry it. The pressure during compaction is 0.5 kg / cm². 2 1kg / cm 2 The compaction time is 0.5 minutes. 1 minute, drying temperature 80℃ Drying temperature: 120℃, drying time: 2 hours After 5 hours, solid III was obtained; S4 3. Then, immerse solid III in the polymer solution for 0.5-2 hours, dry it, and obtain solid IV; S5 3. Finally, solid IV is immersed in water to remove inorganic salts, and then dried to obtain aerogel; The inorganic salt includes at least one of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate, and the melting point of the inorganic salt is higher than 200°C. The solubility of inorganic salts is greater than 10g / 100g water, and the solubility of the substrate is less than 0.5g / 100g water; The polymer solution is a polyurethane solution.

5. An aerogel, characterized in that, By claim 1 Prepared by any one of the preparation methods described in item 2.

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