CN114805910A - A kind of preparation method of superhydrophobic, heat insulating aerogel - Google Patents

Abstract

The invention relates to the field of natural polymer materials and heat insulation materials, in particular to a preparation method of super-hydrophobic and heat-insulating aerogel. The invention combines the directional freezing method and the chemical vapor deposition method, the directional freezing method enables the aerogel to have a layered/porous oriented structure, the aerogel is endowed with excellent heat insulation performance, the structure and the performance are adjusted by changing the concentration of chitosan, an aldehyde cross-linking agent is not needed, the aerogel is more green and environment-friendly, and in addition, the chemical vapor deposition hydrophobic modified reinforced material has water resistance. The process is simple and environment-friendly, the consumed time is short, the obtained chitosan aerogel is low in thermal conductivity and has anisotropy, the thermal conductivity of the anisotropy enables the chitosan aerogel to be axially insulated, radially radiated and more uniform in heat transfer, and the damage of local heating to the aerogel is prevented.

Description

A kind of preparation method of superhydrophobic, heat insulating aerogel

technical field

The invention relates to the field of natural polymer materials and thermal insulation materials, in particular to a method for preparing a superhydrophobic and thermal insulation aerogel.

Background technique

In recent years, my country's building energy consumption is increasing day by day, which has become a chronic disease restricting sustainable development. Thermal management materials with excellent thermal insulation properties are one of the means to solve the problem of building energy consumption.

Aerogel is a new type of porous material with low density, high porosity, high specific surface area and other characteristics, which also endows aerogel with low thermal conductivity and can be widely used in thermal insulation materials. field. The most typical aerogel material is silica aerogel, but the production process of silica aerogel takes a long time, the precursors used are mostly silicone precursors, and the supercritical drying method is used, which is costly and difficult. Industrial mass production, and the brittleness of silica aerogel itself also limits its application in the field of thermal insulation building materials.

Organic aerogel materials, especially biomass organic aerogel materials (such as cellulose, chitin, chitosan, fructose, etc.), have been highly valued by scholars in recent years. Compared with traditional metal organic compound precursors, cellulose, chitin, chitosan and other biological macromolecules are abundant in nature, and have the advantages of green environmental protection, renewable, biodegradable, in the field of energy and environmental protection materials. It has very important practical significance and application prospects.

Chitosan is the product of deacetylation of chitin, and its content in nature is second only to cellulose. It is called the second largest natural polymer material, and because of its amino active group, it has stronger chemical modification, The activity of chemical coordination is considered to be a more promising material than cellulose. At present, there are few studies on the use of chitosan to prepare thermal insulation materials, and the method of supercritical drying is usually used. Freeze-drying is a method for preparing porous lightweight aerogel materials. The solvent is removed by vacuum sublimation, which can retain the integrity of the chemical skeleton. It is an alternative method with low equipment requirements, lower cost and safer. In addition, because chitosan has strong hydrophilicity, the material will be corroded by water vapor in a high humidity environment, resulting in a significant decrease in mechanical strength. Therefore, it is still necessary to find a suitable hydrophobic modification method to enhance the hydrophobicity of chitosan aerogels.

SUMMARY OF THE INVENTION

In order to improve the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a super-hydrophobic, heat-insulating aerogel, which has the advantages of simple synthesis process, green environmental protection, and anisotropic layered/honeycomb The size of the microstructure can be adjusted, the thermal conductivity is low, and the hydrophobicity is strong. The aerogel of the present invention is an anisotropic thermal insulation material with radial thermal insulation and axial heat dissipation, and the larger the anisotropy ratio, the better the thermal insulation effect. The method has a wide range of raw materials and is degradable, the method is simple and easy to operate, and the cost is low; and by controlling the concentration of chitosan, the viscosity of the system can be changed, and then the growth mode of ice crystals can be adjusted to obtain aerogels with different densities, different cross-linking degrees and different structures. .

To achieve the above object, the present invention adopts the following technical scheme to realize:

A kind of preparation method of aerogel, described method comprises the steps:

(1) Mix and disperse natural polymer material with catalyst and deionized water to prepare slurry;

(2) freezing and forming the slurry in a directional freezing device to obtain a cryogel; the directional freezing device has a temperature gradient in the vertical direction;

(3) vacuum freeze-drying the obtained cryogel to obtain a completely dried aerogel.

The present invention also provides a method for preparing a hydrophobic aerogel, the method comprising the following steps:

(4) Hydrophobically modify the above-mentioned aerogel by chemical vapor deposition.

According to the present invention, in step (1), the natural polymer material is selected from at least one of cellulose, chitin, chitosan, starch, gelatin and the like.

According to the present invention, in step (1), the catalyst is selected from acids, such as at least one of dilute hydrochloric acid, acetic acid, phosphoric acid, and the like.

According to the present invention, in step (1), the mass ratio of the natural polymer material, the catalyst and the deionized water is 1-10:0.5-2:100, such as 1-10:1:100.

According to the present invention, in step (2), the directional freezing device is a directional freezing device commonly used in the art that can realize a temperature gradient in the vertical direction. Exemplarily, as shown in FIG. 1 , the directional freezing device includes a mold and a cooling stage, wherein the material of the bottom plate of the mold is a material with good thermal conductivity, such as copper, and the material of the side wall of the mold is For materials with low thermal conductivity and certain chemical stability, such as polytetrafluoroethylene, the outer side of the side wall preferably needs to be further insulated with thermal insulation foam. Preferably, the directional freezing device further includes a temperature control system, which can realize the control of the temperature gradient in the vertical direction, such as using a thermocouple and a PID feedback heating device to realize precise control of the freezing temperature.

According to the present invention, in step (2), the temperature of the freeze forming is -200°C to 0°C, and the cold source is liquid nitrogen, frozen ethanol, frozen acetone, refrigerator, and the like.

According to the present invention, in step (2), the freezing molding time is 10 to 120 min, and the freezing molding rate is adjusted by controlling different cooling table temperatures, such as -100°C to -40°C. , for example, -100°C, -90°C, -80°C, -70°C, -60°C, -50°C, -40°C.

According to the present invention, in step (2), the larger the temperature gradient, the better, the change of the temperature gradient can affect the mechanical properties of the aerogel, but has little effect on the thermal conductivity, and the greater the temperature gradient, the better the aerogel's mechanical properties. The smaller the pore size, the stronger the mechanical properties.

According to the present invention, in step (3), in the freeze-drying process, the freeze-drying temperature is -50--20°C, the freeze-drying pressure is 1-100 Pa, and the freeze-drying time is 10-100 h.

According to the present invention, in step (4), the raw materials used in the chemical vapor deposition method are methyltriethoxysilane, methyltrimethoxysilane, dimethyldiethoxysilane, dimethyldimethylsilane Silicone reagents such as oxysilane, hexadecyltrimethoxysilane, and hexadecyltrimethoxysilane.

Further, the dosage of the modified organosilicon reagent is 0.1-1 wt% of the aerogel material.

Preferably, the chemical vapor deposition method adopts a temperature of 50 to 100° C., a pressure of 100 to 1000 Pa, and a time of 1 to 5 hours. The container is a sealed stainless steel or glass product that can be evacuated.

Beneficial effects of the present invention:

The invention has wide raw material sources, low cost, green and renewable, simple and efficient preparation process and short time-consuming, and is an efficient method for preparing block heat-insulating hydrophobic aerogel.

The aerogel prepared by the invention can simply adjust the viscosity of the system by adjusting the experimental parameters (the concentration of chitosan) to affect the growth of ice crystals, thereby effectively regulating the structure, so as to change the thermal properties and mechanical properties, without aldehyde cross-linking It is more green and environmentally friendly, and retains the amino group of chitosan, which has further functionalization ability and development value.

The aerogel prepared by the invention has structural anisotropy and performance anisotropy, can achieve thermal insulation in the radial direction, and can achieve effective heat dissipation in the axial direction, so that its thermal insulation ability is better than that of the same thermal conductivity (same as the radial direction) The isotropic material has good application value in the field of thermal insulation materials.

The aerogel prepared by the invention has strong hydrophobicity, which enables the material to have properties such as self-cleaning and waterproofing, and can be used normally in a high humidity environment.

To sum up, the present invention proposes an anisotropic chitosan aerogel with low density, high porosity, low thermal conductivity, high specific modulus and strong hydrophobicity, and its preparation method and application. Specifically, the present invention is Combining directional freezing and chemical vapor deposition methods, the directional freezing method makes the aerogels have a layered/porous oriented structure, which endows excellent thermal insulation properties, and adjusts the structure and properties by changing the chitosan concentration, without the need for aldehydes Cross-linking agent, more green and environmentally friendly, in addition, chemical vapor deposition hydrophobically modified to enhance the water resistance of the material. The process is simple and environmentally friendly, takes less time, and the obtained chitosan aerogel has low thermal conductivity and anisotropy. This anisotropic thermal conductivity enables axial heat insulation, radial heat dissipation, and thermal conductivity The heat is more uniform, preventing damage to the aerogel by localized heating.

Description of drawings

Figure 1 is a schematic diagram of a directional freezing device.

In Figure 1, 1 refers to the mold with PTFE tube as the side wall and copper as the bottom plate, 2 refers to the PID control heating device and thermocouple temperature measurement, 3 refers to the freezing pool and cold source, 4 refers to is the insulating foam, 5 refers to the prepared solution, 6 refers to the copper cold stage, and 7 refers to the frozen aerogel obtained by directional freezing.

Figure 2 is a schematic diagram of anisotropy of thermal conductivity and compressive strength.

Figure 3 shows the wettability of the chitosan aerogels before modification (left) and after modification (right) in Example 1.

FIG. 4 is a scanning electron microscope (SEM) and dimensional diagram of Example 8. FIG.

FIG. 5 is a scanning electron microscope (SEM) image of Example 1. FIG.

FIG. 6 is a scanning electron microscope (SEM) image of Comparative Example 1. FIG.

7 is a scanning electron microscope (SEM) of Example 4 (right), Example 11 (left), and Example 12 (middle).

FIG. 8 is an infrared thermal image of Example 1 (right) and Comparative Example 1 (left).

Detailed ways

The preparation method of the present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are only for illustrating and explaining the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the intended protection scope of the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

The thermal conductivity and compressive strength tests used in the following examples were obtained by the following test methods: Axial thermal conductivity was tested by FOX200 (USA, TA instrument), and radial thermal conductivity was tested by QTM500 (Japan). , Kyoto Electronics KEM), and the compressive strength was tested by a universal testing machine (China, Sansi Taijie) (QJ 2755-1995).

The directional freezing device used in the following embodiments includes a mold 1, a temperature control device 2, a freezing pool 3, a thermal insulation material 4, a configuration solution 5, and a copper cold stage 6, and the copper cold stage 6 is built in the freezing pool 3. Among them, the mold 1 is built on the copper cold stage 6 in the freezing pool 3, and the temperature of the copper cold stage 6 is monitored and maintained by the temperature control device 2 at a preset temperature.

Example 1

(1) Weigh 1 g of chitosan, dissolve it in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid, stir mechanically for 24 hours after mixing, and let stand for 5 hours to obtain a slurry.

(2) Using liquid nitrogen as the cold source, pour the prepared slurry into the mold and put it into the above-mentioned directional freezing device, add liquid nitrogen, and keep the liquid nitrogen at a certain height in the cold source pool (liquid nitrogen can be added during the freezing process). ), while using thermocouple temperature measurement and PID feedback heating device to control the temperature of the cold stage to maintain at -100 ℃, a temperature gradient is formed between the slurry at the top of the mold and the slurry at the bottom of the mold, and this state is maintained for about 30 minutes until the slurry is completely frozen ( The upper surface of the solution is completely frozen).

(3) The cryogel prepared above was placed in a freeze dryer, the pressure was adjusted to 60Pa, and the duration was 48 hours to obtain a completely dried chitosan aerogel product.

(4) Put the above-mentioned dried aerogel in a glass vacuum desiccator, add methyltriethoxysilane (quality 0.2g) and deionized water (0.2g) at the same time, the vacuum degree is 100Pa, put The reaction was carried out in a constant temperature oven at 60° C. for 5 hours, and dried in a vacuum drying oven for 2 hours to obtain a superhydrophobic chitosan aerogel product.

The wettability of the chitosan aerogel obtained in step (3) of Example 1 and the superhydrophobic chitosan aerogel obtained in step (4) was tested. The results are shown in Figure 3, where the left picture is before modification and the right picture is after modification. It can be seen from Figure 3 that the hydrophobicity of the modified chitosan aerogel is greatly improved.

Example 2

The preparation steps in this example are the same as those in Example 1, except that 2 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 3

The preparation steps in this example are the same as those in Example 1, except that 3 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 4

The preparation steps in this example are the same as those in Example 1, except that 4 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 5

The preparation steps in this example are the same as those in Example 1, except that 5 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 6

The preparation steps of this example are the same as those of Example 1, except that 6 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 7

The preparation steps of this example are the same as those of Example 1, except that 7 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 8

The preparation steps in this example are the same as those in Example 1, except that 8 g of chitosan is weighed and dissolved in 100 mL of deionized water with a mass fraction of 1% glacial acetic acid.

Example 9

Other operations are the same as in Example 2, except that step (2): the temperature of the cold stage is controlled to -40°C.

Example 10

Other operations are the same as in Example 2, except that step (2): the temperature of the cold stage is controlled to -80°C.

Example 11

Other operations are the same as in Example 4, except that step (2): the temperature of the cold stage is controlled to -40°C.

Example 12

Other operations are the same as in Example 4, except that step (2): the temperature of the cold stage is controlled to -80°C.

Comparative Example 1

Other operations are the same as in Example 1, except that step (2):

A low-temperature refrigerator -80°C was used as the cold source, and the prepared slurry was put into the refrigerator for freezing. Since there was no temperature gradient, the prepared samples were randomly frozen samples.

Table 1 Thermal conductivity and compressive strength of chitosan aerogels prepared in Examples 1-12 and Comparative Example 1

FIG. 4 is a scanning electron microscope (SEM) and size chart of the chitosan aerogel obtained in Example 8. FIG. It can be seen that the structure of the obtained chitosan aerogel has anisotropy, which is a honeycomb structure perpendicular to the freezing direction and a layered structure parallel to the freezing direction.

FIG. 5 is a scanning electron microscope (SEM) image of the chitosan aerogel obtained in Example 1. FIG. It can be seen that the structure of the obtained chitosan aerogel has anisotropy, which is a honeycomb structure perpendicular to the freezing direction and a layered structure parallel to the freezing direction.

FIG. 6 is a scanning electron microscope (SEM) image of the chitosan aerogel obtained in Comparative Example 1. FIG. It can be seen that the structure of randomly frozen aerogels is disordered and isotropic.

7 is a scanning electron microscope (SEM) of Example 4 (right), Example 11 (left), and Example 12 (middle). It can be seen that with the increase of the freezing temperature gradient, the pore size is smaller and the pore size distribution range is narrower.

FIG. 8 is an infrared thermal image of Example 1 (right) and Comparative Example 1 (left). It can be seen that when the bottom surface is heated, the temperature distribution of Example 1 with anisotropic structure prepared by the directional freezing method is more uniform, which can prevent the material properties from being changed due to local heating.

The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a preparation method of aerogel, described method comprises the steps: (1) Mix and disperse natural polymer material with catalyst and deionized water to prepare slurry; (2) freezing and forming the slurry in a directional freezing device to obtain a cryogel; the directional freezing device has a temperature gradient in the vertical direction; (3) vacuum freeze-drying the obtained cryogel to obtain a completely dried aerogel. 2. a preparation method of hydrophobic aerogel, described method comprises the steps: (4) Hydrophobically modify the above-mentioned aerogel by chemical vapor deposition. 3. The preparation method according to claim 1, wherein, in step (1), the natural polymer material is selected from at least one of cellulose, chitin, chitosan, starch and gelatin. Preferably, in step (1), the catalyst is selected from an acid, and the acid is at least one of dilute hydrochloric acid, acetic acid and phosphoric acid. 4. The preparation method according to claim 1 or 3, wherein, in step (1), the mass ratio of the natural polymer material, catalyst and deionized water is 1～10:0.5～2:100, such as 1 ~10:1:100. 5. according to the preparation method described in any one of claim 1,3-4, wherein, in step (2), described directional freezing device comprises mould, cold stage, wherein, the material of the bottom plate of described mould is thermal conductivity A good material, such as copper, the material of the side wall of the mold is a material with low thermal conductivity and certain chemical stability, such as polytetrafluoroethylene, and the outer side of the side wall preferably needs to be further insulated. Foam for insulation. Preferably, the directional freezing device further includes a temperature control system, which can control the temperature gradient in the vertical direction. 6. The preparation method according to any one of claims 1, 3-5, wherein, in step (2), the temperature of the freeze forming is -200 ℃～0 ℃, and the cold source is liquid nitrogen, frozen ethanol, Freeze acetone or freezer. 7. The preparation method according to any one of claims 1, 3-6, wherein, in step (2), the freeze-forming time is 10-120 min. 8. The preparation method according to any one of claims 1, 3-7, wherein, in step (3), in the freeze-drying process, the freeze-drying temperature is -50～-20°C, and the freeze-drying pressure It is 1～100Pa, and the freeze-drying time is 10～100h. 9. The preparation method according to claim 2, wherein, in step (4), the raw materials used in the chemical vapor deposition method are methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane At least one of ethoxysilane, dimethyldimethoxysilane, hexadecyltrimethoxysilane, and hexadecyltrimethoxysilane. Preferably, the dosage of the modified organosilicon reagent is 0.1-1 wt% of the aerogel material. 10. The preparation method according to claim 2, wherein, the temperature used in the chemical vapor deposition method is 50-100 ° C, the pressure is 100-1000 Pa, the time is 1-5 h, and the container is a sealed stainless steel that can be evacuated or Glass product.

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