CN117384418A - A kind of bio-based airgel thermal insulation material and its preparation method and application - Google Patents

Abstract

The invention provides a bio-based aerogel heat insulation material, and a preparation method and application thereof, and belongs to the technical field of aerogel preparation. Mixing low acyl gellan gum with water to obtain gellan gum solution, cooling to obtain gellan gum hydrogel, soaking in metal salt solution or acid solution to harden to obtain hardened gum, wherein the metal salt solution comprises calcium chloride solution, aluminum nitrate solution or zirconium oxychloride solution, the acid solution comprises hydrochloric acid solution or nitric acid solution, soaking the hardened gum in organic solvent solution to obtain organic gel, and drying the organic gel to obtain the bio-based aerogel heat insulation material. According to the invention, the mechanical property of the gel can be further enhanced after the gel is soaked in the polyvalent metal salt solution or the dilute acid solution; the thermal conductivity of the aerogel prepared by the method is lower than that of air (25 mW/(m.K)), and the aerogel has a wide application prospect in the field of heat preservation and heat insulation.

Description

A kind of bio-based airgel thermal insulation material and its preparation method and application

Technical field

The invention relates to the field of airgel preparation, and in particular to a bio-based airgel thermal insulation material and its preparation method and application.

Background technique

Aerogel is an open porous material with a three-dimensional nanostructure. It has unique physical properties such as low density, high specific surface area, high porosity, and low thermal conductivity. It has many applications in the fields of thermal insulation, catalysis, drug release, adsorption, etc. Huge application prospects. Despite these excellent properties of aerogels, currently few aerogel materials can be used in practical applications due to insufficient mechanical strength. Silica aerogels have lower thermal conductivity but poor mechanical properties. Compared with silica aerogels, organic aerogels have better moldability and better mechanical properties than traditional silica aerogels. However, the synthesis process of organic aerogels is complex and usually involves some toxic solvents and raw materials, which can easily cause environmental pollution problems. Therefore, aerogels based on natural polymers with good biocompatibility, abundant resources, and biodegradability have received widespread attention. Pure natural polymer-based aerogels also have the disadvantage of unclear mechanical properties. Therefore, using natural polymer materials to prepare an environmentally friendly, super-insulating, and high-mechanical-strength aerogel is currently a major technical difficulty.

Gellan Gum (GG) is a water-soluble anionic polysaccharide, a new microbial polysaccharide derived from Sphingomonas paucimobilis, which is produced by fermentation of microorganisms under aerobic conditions. Gellan gum is non-toxic and has good biocompatibility and biodegradability. Gellan gum has important applications in food, biomedicine, and industry.

Chinese patent CN108465459A discloses a method of preparing composite aerogel by mixing gellan gum and graphene oxide and freeze-drying. The pore size of the composite aerogel is tens to hundreds of microns, and does not have the unique nanometer properties of aerogels. Porous structure and high specific surface area. Its microscopic morphology also does not have a nanoskeleton structure. Chinese patent CN108421081A discloses a multi-component composite aerogel material made by mixing chitosan, sodium alginate, gellan gum, etc. Among them, the matrix of the airgel is mainly obtained by anionic and cationic cross-linking between chitosan and sodium alginate, and gellan gum only plays an auxiliary role. The method of preparing nanoporous aerogels using gellan gum itself as a matrix has never been disclosed.

Contents of the invention

In order to solve the above problems, the present invention provides a bio-based airgel thermal insulation material and its preparation method and application.

In order to achieve the above objects, the present invention provides the following technical solutions:

The invention provides a preparation method of bio-based airgel thermal insulation material, which includes the following steps:

1) Mix low acyl gellan gum and water to obtain a gellan gum solution;

2) Cool the gellan gum solution obtained in step 1) to obtain gellan gum hydrogel;

3) Soak the gellan gum hydrogel obtained in step 2) in a metal salt solution or acid solution to harden to obtain a hardened glue;

The metal salt solution includes calcium chloride solution, aluminum nitrate solution or zirconium oxychloride solution;

The acid solution includes hydrochloric acid solution or nitric acid solution;

4) Soak the hardened gel obtained in step 3) into an organic solvent solution to obtain an organic gel;

5) Dry the organic gel obtained in step 4) to obtain a bio-based airgel thermal insulation material.

Preferably, the volume ratio of the mass of low acyl gellan gum to water in step 1) is 40~1600mg:20ml. Preferably, the mixing conditions in step 1) include: the temperature is 50~130°C and the time is 30 minutes.

Preferably, the cooling time of step 2) is 1 hour, and the temperature is 0~40°C.

Preferably, the concentration of the metal salt solution in step 3) is 0.01~0.1 mol/L.

Preferably, the concentration of the acid solution in step 3) is 0.5 mol/L.

Preferably, the soaking time in step 3) is 8 hours.

Preferably, the organic solvent solution in step 4) includes ethanol, methanol or acetone;

The soaking conditions include: soaking three times, each soaking time is 8 hours, and the organic solvent solution is replaced each time.

The present invention also provides bio-based airgel thermal insulation materials obtained by the preparation method described in the above technical solution.

The present invention also provides the application of the bio-based airgel thermal insulation material described in the above technical solution in thermal insulation.

The beneficial effects of the present invention are:

(1) The preparation method of the present invention is simple and reliable. The raw material gellan gum is a natural polymer. The raw material is environmentally friendly, rich in resources, has good biocompatibility, and is biodegradable;

(2) In the present invention, the mechanical properties of the gel can be further enhanced by soaking in a multivalent metal salt solution or a dilute acid solution;

(3) The mechanical properties of the aerogel prepared by the present invention are stronger than most of the current pure natural polymer-based aerogels, and the shape is plastic. It overcomes the shortcomings of the current pure natural polymer-based aerogels with unclear mechanical properties. Conducive to practical applications;

(4) The thermal conductivity of the aerogel prepared by the present invention under environmental conditions is lower than that of air (25 mW/(m·K)), and it has great application prospects in the field of thermal insulation.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the embodiments will be briefly introduced below.

Figure 1 is a schematic diagram of the preparation method of the present invention;

Figure 2 shows the rheological frequency scans of gellan gum hydrogels of different concentrations without soaking and soaking in ZrOCl ₂ ·8H ₂ O solution;

Figure 3 is a scanning electron microscope image of GG-1 aerogel;

Figure 4 is a scanning electron microscope image of GG-2 aerogel;

Figure 5 is a scanning electron microscope image of GG-4 aerogel;

Figure 6 is a scanning electron microscope image of GG-6 aerogel;

Figure 7 is a scanning electron microscope image of GG-8 aerogel;

Figure 8 shows the nitrogen adsorption isotherm and pore size distribution diagram of GG-1 aerogel;

Figure 9 shows the nitrogen adsorption isotherm and pore size distribution diagram of GG-2 aerogel;

Figure 10 shows the nitrogen adsorption isotherm and pore size distribution diagram of GG-4 aerogel;

Figure 11 shows the nitrogen adsorption isotherm and pore size distribution diagram of GG-6 aerogel;

Figure 12 shows the nitrogen adsorption isotherm and pore size distribution diagram of GG-8 aerogel;

Figure 13 shows the compressive stress-strain curves of GG-1, GG-2, GG-4, GG-6, and GG-8 aerogels;

Figure 14 shows the maximum compressive stress and Young's modulus corresponding to the aerogel in Figure 12;

Figure 15 shows the thermal conductivity diagrams of GG-1, GG-2, GG-4, GG-6, and GG-8 aerogels.

In the above figure, GG-1 means that the concentration of the gellan gum solution is 1% (w/w), GG-2 means that the concentration of the gellan gum solution is 2% (w/w), and GG-4 is Refers to the concentration of gellan gum removal solution being 4% (w/w), GG-6 refers to the concentration of gellan gum removal solution being 6% (w/w), GG-8 refers to the concentration of gellan gum removal solution is 8%(w/w).

Detailed ways

The invention provides a preparation method of bio-based airgel thermal insulation material, which includes the following steps:

1) Mix low acyl gellan gum and water to obtain a gellan gum solution;

2) Cool the gellan gum solution obtained in step 1) to obtain gellan gum hydrogel;

3) Soak the gellan gum hydrogel obtained in step 2) in a metal salt solution or acid solution to harden to obtain a hardened glue;

The metal salt solution includes calcium chloride solution, aluminum nitrate solution or zirconium oxychloride solution;

The acid solution includes hydrochloric acid solution or nitric acid solution;

4) Soak the hardened gel obtained in step 3) into an organic solvent solution to obtain an organic gel;

5) Dry the organic gel obtained in step 4) to obtain a bio-based airgel thermal insulation material.

In the present invention, low acyl gellan gum is mixed with water to obtain a gellan gum solution. In the present invention, the water is preferably deionized water. In a specific embodiment of the present invention, the low acyl gellan gum is purchased from Maclean (manufacturer), G821481 gellan gum, biotechnology grade, low acyl type. In the present invention, the volume ratio of the mass of the low acyl gellan gum to water is preferably 40 to 1600 mg: 20 ml, specifically 200 mg: 20 ml, 400 mg: 20 ml, 800 mg: 20 ml, 1200 mg: 20 ml, 1600 mg: 20 ml. In the present invention, the mixing conditions preferably include: a temperature of 80°C to 120°C and a time of 30 min; the temperature is preferably 95°C. In the present invention, the gellan gum solution is a uniform and transparent solution.

In the present invention, the obtained gellan gum solution is cooled to obtain gellan gum hydrogel. In the present invention, the cooling time is preferably 1 hour, and the temperature is preferably 0 to 40°C. In the present invention, the obtained gellan gum solution is preferably placed in a conventional mold for cooling.

In the present invention, the obtained gellan gum hydrogel is soaked in a metal salt solution or an acid solution and hardened to obtain a hardened glue; the metal salt solution includes calcium chloride solution, aluminum nitrate solution or zirconium oxychloride solution; the acid solution Including hydrochloric acid solution or nitric acid solution. In the present invention, the concentration of the metal salt solution is preferably 0.01~0.1 mol/L. In the present invention, when the metal salt solution is preferably a calcium chloride solution, the concentration is 0.1 mol/L; when the metal salt solution is preferably an aluminum nitrate solution, the concentration is 0.01 mol/L; when the metal salt solution is preferably an aluminum nitrate solution, the concentration is 0.01 mol/L. When the solution is preferably a zirconium oxychloride solution, the concentration is 0.1 mol/L. In the present invention, the concentration of the acid solution is preferably 0.5 mol/L. In the present invention, the soaking time is preferably 8 hours, and the temperature is preferably 0 to 40°C.

In the present invention, the obtained hardened glue is soaked in an organic solvent solution to obtain an organic gel. In the present invention, the organic solvent solution preferably includes ethanol, methanol or acetone. In the present invention, the soaking conditions preferably include: soaking 3 times, each soaking time is 8 hours, replacing the organic solvent solution with each soaking, and replacing the water solvent in the gel with an alcohol solvent to facilitate subsequent supercritical processes. dry.

In the present invention, the obtained organic gel is dried to obtain a bio-based airgel thermal insulation material. In the present invention, the drying preferably includes supercritical liquid carbon dioxide drying method, and those skilled in the art can follow the routine.

The present invention also provides bio-based airgel thermal insulation materials obtained by the preparation method described in the above technical solution. In the present invention, the microscopic morphology of the bio-based airgel insulation material is that nanofibers are interwoven to form a nanoporous structure, the diameter of the nanofibers is 10-100 nanometers, the average pore diameter of the nanopores is 20-70 nanometers, and the material's The specific surface area is 200-600m ² /g. In the present invention, when the bio-based airgel insulation material is compressed to 90%, the airgel stress reaches more than 2 MPa, and the Young's modulus is not less than 1 MPa. In the present invention, the thermal conductivity of the bio-based airgel insulation material is 15-50 mW/(m·K).

The present invention also provides the application of the bio-based airgel thermal insulation material described in the above technical solution in thermal insulation.

In order to further illustrate the present invention, the present invention is described in detail below with reference to the examples, but they should not be understood as limiting the protection scope of the present invention.

Example 1

Add 200 mg of low acyl gellan gum to 20 ml of deionized water, and then stir at 80°C for 30 min until the low acyl gellan gum is completely dissolved to obtain a uniform and transparent solution. Pour the above solution into the mold, cool and let stand for 1 hour to obtain the hydrogel. The hydrogel was then soaked in 0.1 M ZrOCl ₂ ·8H ₂ O solution (the volume ratio of ZrOCl ₂ ·8H ₂ O solution to hydrogel was greater than 5) for 8 h. Then soak the soaked hydrogel in absolute ethanol (the volume ratio of absolute ethanol to hydrogel is greater than 5) three times for 8 hours each time, and replace the solution with each soak. The resulting alcohol gel was dried using supercritical liquid carbon dioxide to obtain the final aerogel sample (GG-1).

Example 2

Add 400 mg of low acyl gellan gum to 20 ml of deionized water, and then stir at 95°C for 30 min until the low acyl gellan gum is completely dissolved to obtain a uniform and transparent solution. Pour the above solution into the mold, cool and let stand for 1 hour to obtain a hydrogel. The hydrogel was then soaked in 0.1 M _CaCl solution (the volume ratio of _CaCl solution to hydrogel was greater than 5) for 8 h. Then soak the soaked hydrogel in methanol (the volume ratio of methanol to hydrogel is greater than 5) 3 times, 8 hours each time, and replace the solution with each soak. The resulting alcohol gel was dried using supercritical liquid carbon dioxide to obtain the final aerogel sample (GG-2).

Example 3

Add 800 mg of low acyl gellan gum to 20 ml of deionized water, and then stir at 120°C for 30 min until the low acyl gellan gum is completely dissolved to obtain a uniform and transparent solution. Pour the above solution into the mold, cool and let stand for 1 hour to obtain a hydrogel. The hydrogel was then soaked in 0.5 M HCl solution (the volume ratio of HCl solution to hydrogel was greater than 5) for 8 h. Then soak the soaked hydrogel in acetone (the volume ratio of acetone to hydrogel is greater than 5) 3 times, 8 hours each time, and replace the solution with each soak. The obtained acetone gel was processed by supercritical liquid carbon dioxide drying method to obtain the final aerogel sample (GG-4).

Example 4

Add 1200 mg of low acyl gellan gum to 20 ml of deionized water, and then stir at 120°C for 30 min until the low acyl gellan gum is completely dissolved to obtain a uniform and transparent solution. Pour the above solution into the mold, cool and let stand for 1 hour to obtain the hydrogel. The hydrogel was then soaked in 0.01 M Al(NO ₃ ) ₃ solution (the volume ratio of Al(NO ₃ ) ₃ solution to hydrogel was greater than 5) for 8 h. Then soak the soaked hydrogel in absolute ethanol (the volume ratio of ethanol to hydrogel is greater than 5) three times, 8 hours each time, and replace the solution with each soak. The resulting alcohol gel was dried using supercritical liquid carbon dioxide to obtain the final aerogel sample (GG-6).

Example 5

Add 1600 mg of low acyl gellan gum to 20 ml of deionized water, and then stir at 120°C for 30 min until the low acyl gellan gum is completely dissolved to obtain a uniform and transparent solution. Pour the above solution into the mold, cool and let stand for 1 hour to obtain the hydrogel. The hydrogel was then soaked in 0.5 M HNO ₃ solution (the volume ratio of HNO _{3 3} solution to hydrogel was greater than 5) for 8 h. Then soak the soaked hydrogel in absolute ethanol (the volume ratio of absolute ethanol to hydrogel is greater than 5) three times, 8 hours each time, and replace the solution with each soak. The resulting alcohol gel was dried using supercritical liquid carbon dioxide to obtain the final aerogel sample (GG-8).

The aerogels obtained in the above five embodiments were subjected to electron microscope scanning, surface area testing, pore size testing, and compression testing. The specific results are as shown in the accompanying drawings. It can be seen from the results that using this method, an aerogel with excellent mechanical properties can be obtained. gel, and the mechanical strength of the aerogel increases as the concentration of low acyl gellan gum solution increases. The maximum compressive stress of GG-8 aerogel is as high as 45.60 MPa, and the compressive Young's modulus is as high as 35.736 MPa. In addition, the thermal conductivity of the GG-2 aerogel is 24.5 mW/(m·K), which is lower than the thermal conductivity of air under ambient conditions (25 mW/(m·K)). Therefore, the aerogel prepared in the present invention also has great application prospects in the field of thermal insulation.

In order to verify that the mechanical properties of the gel can be further enhanced by soaking in multivalent metal salt solution or dilute acid solution, rheology was performed on gellan gum hydrogels of different concentrations without soaking and soaking in ZrOCl ₂ ·8H ₂ O solution. test. From the rheological frequency scan chart in Figure 2, it can be seen that the storage modulus of the hydrogel soaked in ZrOCl ₂ ·8H ₂ O solution has increased by 1-2 orders of magnitude at each concentration. Therefore, it can be explained that the mechanical properties of the hydrogel are enhanced after immersion in multivalent metal salt solution or dilute acid solution. (The hollow pattern in Figure 2 represents the gellan gum hydrogel that has not been soaked in ZrOCl ₂ ·8H ₂ O solution. The concentration increases from bottom to top; the solid pattern represents the gellan gum hydrogel after soaking in ZrOCl ₂ ·8H ₂ O solution. , the concentration increases sequentially from bottom to top. The same pattern represents the same concentration of gellan gum hydrogel.)

The electron microscopy image in Figure 3-7 shows that all aerogels are tightly entangled with nanofibers and have a fine nanostructure. The diameter of the nanofibers is about 15 nm. There is not much difference in the morphology of GG-1 and GG-2 aerogels. It can be seen that the nanofiber roots are clearly defined. However, in the scanning electron microscope images of GG-4, GG-6, and GG-8 aerogels, there are The phenomenon of multiple fibers being bundled makes the pore walls of the airgel porous structure thicker.

Figures 8 and 12 show that the specific surface area of the aerogel is around 400 m ² g ^-1 and the average pore diameter is 17-35 nm, which further proves that the aerogel is a mesoporous material with a fine nanostructure.

It can be seen in Figures 13 and 14 that when the airgel is compressed to 90%, as the concentration of the gellan gum solution increases, the mechanical properties of the airgel increase accordingly. It may be because as the concentration of gellan gum solution increases, the skeleton density of the aerogel increases. It can also be seen from the scanning electron microscope that the pore walls of the aerogel become thicker, which can dissipate energy more effectively. Among them, the maximum compressive stress of GG-8 is as high as 45.60 MPa. The Young's modulus of the airgel can be obtained through the elastic deformation in the early stage of compression of the airgel. It can be seen that the Young's modulus of GG-8 is as high as 35.74 MPa, which is higher than the Young's modulus of most natural polymer-based aerogels. The quantity should be high.

Figure 15 measures the thermal conductivity of aerogel. It can be seen that as the concentration of gellan gum solution increases, the thermal conductivity of aerogel first decreases and then increases, showing a "U" shaped trend. Among them, GG-2 has the lowest thermal conductivity (24.5 mW/(m·K)), which is lower than the thermal conductivity of air under ambient conditions (25 mW/(m·K)). Therefore, the aerogel prepared in the present invention also has great application prospects in the field of thermal insulation.

Table 1 Performance data of airgel prepared in Examples 1-5

The above example was repeated many times and the results obtained were similar, indicating that the preparation method of this method has good repeatability.

Although the above embodiments describe the present invention in detail, they are only part of the embodiments of the present invention, not all embodiments. People can also obtain other embodiments based on this embodiment without any inventive step. These embodiments All belong to the protection scope of the present invention.

Claims (5)

1. The preparation method of the bio-based aerogel heat insulation material is characterized by comprising the following steps of:

1) Mixing low-acyl gellan gum with water to obtain gellan gum solution;

2) Cooling the gellan gum solution obtained in the step 1) to obtain gellan gum hydrogel;

3) Soaking the gellan gum hydrogel obtained in the step 2) in a metal salt solution to harden to obtain hardened gum;

the metal salt solution is an aluminum nitrate solution or a zirconium oxychloride solution; the concentration of the metal salt solution is 0.01-0.1 mol/L;

the acid solution is nitric acid solution; the concentration of the acid solution is 0.5mol/L;

4) Soaking the hardened glue obtained in the step 3) in an organic solvent solution to obtain organic gel;

5) Drying the organic gel obtained in the step 4) to obtain a bio-based aerogel heat insulation material;

the mass-to-water volume ratio of the low acyl gellan gum in the step 1) is 40-160 mg:20ml;

the mixing conditions in the step 1) comprise: the temperature is 50-130 ℃ and the time is 30min;

and 2) cooling for 1h at the temperature of 0-40 ℃.

2. The method according to claim 1, wherein the soaking time in step 3) is 8 hours.

3. The method of claim 1, wherein the step 4) organic solvent solution comprises ethanol, methanol, or acetone;

the soaking conditions include: soaking for 3 times, wherein the soaking time is 8 hours, and the organic solvent solution is replaced each time.

4. The bio-based aerogel thermal insulation material obtained by the preparation method of any one of claims 1 to 3.

5. The use of the biobased aerogel insulation of claim 4 for thermal insulation.