CN117447763A - Preparation method and application of flame-retardant and heat-insulating bio-based aerogel - Google Patents

Abstract

A preparation method and application of flame-retardant heat-insulating bio-based aerogel relate to the field of flame-retardant heat-insulating materials, and in particular relate to a preparation method and application of flame-retardant heat-insulating bio-based aerogel. The problems that the mechanical property and the flame retardant property are not compatible, the light weight and the porosity are reduced in the existing bio-based aerogel are solved. The method comprises the following steps: 1. pre-freezing the sodium alginate solution, and freeze-drying to obtain sodium alginate aerogel; 2. immersing sodium alginate aerogel in a calcium source solution, and pre-crosslinking; 3. preparing a hydroxyapatite premix solution; 4. adding the pre-mixed hydroxyapatite solution into the pre-crosslinked sodium alginate aerogel, reacting, freeze-drying and aging to obtain the SA@HAP-24 aerogel. The aerogel disclosed by the invention is multifunctional biological base aerogel integrating heat preservation, high strength, water resistance and fire resistance. The flame-retardant heat-insulating bio-based aerogel is applied to fireproof and flame-retardant materials.

Description

Preparation method and application of flame-retardant and heat-insulating bio-based aerogel

Technical field

The invention relates to the field of flame-retardant and heat-insulating materials, and in particular to a preparation method and application of a flame-retardant and heat-insulating bio-based aerogel.

Background technique

As humans continue to pay attention to energy conservation and safety, thermal insulation materials have been widely used in building insulation, aerospace, fire rescue and other fields. At present, thermal insulation materials are mainly divided into two categories: inorganic thermal insulation materials and organic thermal insulation materials. Among them, organic insulation materials (such as polystyrene, expanded polystyrene boards, polyurethane foam, etc.) are widely used in the field of building insulation due to their low density, low thermal conductivity, and easy construction. However, traditional organic insulation materials are mostly derived from petrochemical-based materials and have shortcomings such as flammability, environmental pollution, and difficulty in recycling and reuse, which pose a huge threat to human life and property safety and the environment. As the global energy crisis and environmental issues become increasingly prominent, the development of biodegradable, fire-safe, bio-based organic insulation materials that are in line with current sustainable development strategies has become a top priority today.

Bio-based aerogels among organic thermal insulation materials have excellent application prospects in the field of thermal insulation materials due to their unique three-dimensional network porous structure, which determines their low density, high porosity, and low thermal conductivity. However, traditional bio-based airgel raw materials are mainly based on cellulose, lignin, chitosan, alginate and other bio-based raw materials and their derivatives. These elements are mainly composed of C, H, and O elements, so they are extremely It is easy to burn and has a fast burning rate. Therefore, flame retardant treatment is required in most application fields.

Sodium alginate (SA) is a non-flammable polysaccharide extracted from seaweed, consisting of blocks linked by β-D-mannuronic acid (M) and α-L-guluronic acid (G) Linear copolymer. Due to its unique structural unit, the homopolymerized G block in SA can achieve ionic cross-linking with metal ions (Cu ²⁺ , Ca ²⁺ , Al ^3+, etc.) to form an "egg box structure" without changing the gel structure. In this case, it can better strengthen the gel network and improve its mechanical and flame retardant properties. As a salt polymer, SA itself has certain flame retardant properties compared to most natural polymers, but it is far from meeting the standards for flame retardant material applications. At the same time, SA airgel is difficult to use on a large scale in practical applications due to its poor mechanical strength. In order to solve this type of problem, researchers have learned to add flame retardants or reinforcing materials to lightweight SA aerogels to improve the flame retardant or mechanical properties of the material, such as introducing intumescent flame retardant systems, inorganic clay (ATP), Fiber (kapok fiber) and other inorganic fillers. However, the simple filling of flame retardants results in the inability to balance the mechanical and flame retardant properties of the material, and the lightweight and porosity of SA aerogel materials are significantly reduced, thus limiting the wide application of multifunctional SA aerogels.

Contents of the invention

The present invention is to solve the problems of existing bio-based aerogels that do not take into account the mechanical properties and flame-retardant properties, and are lightweight and have reduced porosity, and provide a preparation method and application of flame-retardant and heat-insulating bio-based aerogels.

The preparation method of flame-retardant and heat-insulating bio-based aerogel of the present invention includes the following steps:

1. Pre-freeze the sodium alginate solution for 3 to 6 hours, then freeze-dry for 72 to 90 hours, and then take it out after freeze-drying to obtain sodium alginate aerogel (SA);

2. Soak the sodium alginate aerogel with calcium source solution, pre-crosslink it, and then remove excess calcium source solution;

3. At room temperature, add the phosphorus source solution to the calcium source solution. Continue stirring after the phosphorus source solution is completely poured in. After stopping stirring, the hydroxyapatite premixed solution will be obtained;

4. Add the hydroxyapatite premixed solution to the pre-crosslinked sodium alginate aerogel to completely submerge the sodium alginate aerogel. After sealing, react in a 35°C water bath for 24 hours. After the reaction time is over, Pre-freeze the sample for 3 to 6 hours, then freeze-dry for 72 to 90 hours. After freeze-drying, take it out and place it in an oven at 80°C for aging for 18 to 30 hours to obtain SA@HAP-24 aerogel.

Further, the preparation method of the sodium alginate solution in step one is: dissolving sodium alginate in deionized water to prepare a sodium alginate solution with a mass fraction of 2%.

Furthermore, the pre-crosslinking time in step two is 15 to 20 minutes.

Further, the calcium source solution in step 2 is CaCl ₂ aqueous solution, the concentration is 0.3 mol/L, and the pH is 10.50±0.2.

Further, the phosphorus source solution in step three is (NH ₄ ) ₂ HPO ₄ aqueous solution, the concentration is 0.3 mol/L, and the pH is 10.50±0.2.

Further, the volume ratio of the calcium source solution and the phosphorus source solution in step three is 5:3.

Further, the stirring time in step three is 10 to 15 minutes.

The present invention provides a fireproof material containing the bio-based aerogel described in any one of the above.

The application of the flame-retardant and heat-insulating bio-based aerogel of the present invention in fire prevention and flame retardancy.

Beneficial effects of the present invention:

The present invention uses biomass sodium alginate (SA) aerogel as a matrix, and successfully prepares a composite material through surface calcification and in-situ growth of hydroxyapatite (HAP) on the surface without destroying the structure of the internal sodium alginate aerogel. A multi-functional bio-based aerogel integrating thermal insulation, high strength, water resistance and fire protection. It has good biocompatibility and degradability. While maintaining the original internal structure and thermal insulation performance of SA airgel, the preparation method is simple and easy to implement. It solves the problems of traditional bio-based aerogels such as flammability, low mechanical strength, water resistance, significantly reduced thermal insulation performance and lightness.

The SA@HAP-24 aerogel prepared by the present invention is a white lightweight material with a porous structure and a density of only 0.038g·cm ^-1 . Compared with pure SA aerogel, the surface of the SA aerogel wears It has a layer of protective armor with a bone-like structure, so it not only ensures the internal structure of SA airgel, but also makes it have excellent water resistance.

Thermogravimetric analysis tests show that compared with pure SA aerogel, the initial thermal decomposition temperature of SA@HAP aerogel is significantly higher, and the residual carbon mass at 800°C is 43.5wt%, showing excellent self-composition Carbon properties have a certain inhibitory effect on the exchange of flammable volatiles and gases. Due to the introduction of the HAP structure on the surface of the SA@HAP airgel, the pyrophosphate and Ca ²⁺ produced during the decomposition process effectively promote the degradation and carbonization of the SA@HAP airgel material, thereby creating a dense state in the condensed phase. And the hard carbon layer plays an excellent shielding role.

Due to the growth of HAP on the surface of SA airgel, SA@HAP airgel has excellent flame retardant properties. Only one layer of HAP needs to be grown, and its limiting oxygen index can reach 50.1%. The vertical combustion test has passed UL-94V-0. level, achieving the effect of extinguishing immediately after leaving the fire. In addition, HAP grows on the surface of the material through Ca ²⁺ , which overcomes the problems of traditional additive flame retardants such as poor water resistance and easy precipitation. Due to the micro-crosslinking on the surface of the airgel, the SA airgel is given a layer of protection. Armor, thereby preparing high-performance flame-retardant bio-based SA@HAP composites.

The SA@HAP aerogel prepared by the invention has broad application prospects in building insulation, fire-fighting suits and spacecraft insulation layers.

Description of the drawings

Figure 1 is a road map for the preparation of surface microcalcified SA aerogels;

Figure 2 shows the preparation route diagram of SA@HAP-24 aerogel;

Figure 3 shows the water resistance properties of SA aerogel and SA@HAP aerogel;

Figure 4 shows the TG and DTG curves of SA aerogel and SA@HAP aerogel under _N2 atmosphere;

Figure 5 shows the ATR-FTIR spectra of SA, HAP and SA@HAP aerogels;

Figure 6 is the SEM image of the SA airgel surface;

Figure 7 is an enlarged view of Figure 6;

Figure 8 shows the pore size distribution of SA airgel;

Figure 9 is the SEM image of the surface of SA@HAP airgel;

Figure 10 is an enlarged view of Figure 9;

Figure 11 shows the pore size distribution of SA@HAP airgel;

Figure 12 shows the XRD analysis of the surface of HAP and SA@HAP aerogels;

Figure 13 shows the heat release rate (HRR) curves of SA and SA@HAP airgel;

Figure 14 shows the total heat release (THR) curves of SA and SA@HAP aerogels.

Detailed ways

The technical solution of the present invention is not limited to the specific implementations listed below, but also includes any combination of specific implementations.

Specific Embodiment One: The preparation method of flame-retardant and insulating bio-based aerogel in this embodiment includes the following steps:

1. Pre-freeze the sodium alginate solution for 3 to 6 hours, then freeze-dry for 72 to 90 hours, and then take it out after freeze-drying to obtain sodium alginate aerogel (SA);

2. Soak the sodium alginate aerogel with calcium source solution, pre-crosslink it, and then remove excess calcium source solution;

3. At room temperature, add the phosphorus source solution to the calcium source solution. Continue stirring after the phosphorus source solution is completely poured in. After stopping stirring, the hydroxyapatite premixed solution will be obtained;

4. Add the hydroxyapatite premixed solution to the pre-crosslinked sodium alginate aerogel to completely submerge the sodium alginate aerogel. After sealing, react in a 35°C water bath for 24 hours. After the reaction time is over, Pre-freeze the sample for 3 to 6 hours, then freeze-dry for 72 to 90 hours. After freeze-drying, take it out and place it in an oven at 80°C for aging for 18 to 30 hours to obtain SA@HAP-24 aerogel.

Compared with the current traditional petrochemical-based thermal insulation materials, the SA@HAP airgel prepared in this embodiment uses bio-based raw materials as the matrix, has good biocompatibility and degradability, and maintains the interior of the original SA airgel. While having excellent structure and thermal insulation properties, the preparation method is simple and easy to implement, and has good application prospects. At the same time, due to the growth of HAP on the surface of the SA airgel, the SA@HAP airgel has excellent flame retardant properties, with a limiting oxygen index of up to 50.1%. The vertical combustion test passed the UL-94V-0 level, achieving flame retardancy. Instant extinguishing effect. In addition, HAP grows on the surface of the material through Ca ²⁺ , which overcomes the problems of traditional additive flame retardants such as poor water resistance and easy precipitation. Due to the micro-crosslinking on the surface of the airgel, the SA airgel is given a layer of protection. Armor, thereby preparing high-performance flame-retardant bio-based SA@HAP composites.

Specific Embodiment Two: The difference between this embodiment and Specific Embodiment One is that the preparation method of the sodium alginate solution in step one is: dissolving sodium alginate in deionized water to prepare a sodium alginate solution with a mass fraction of 2%. Others are the same as the first embodiment.

Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the pre-crosslinking time in step two is 15 to 20 minutes. Others are the same as the first or second embodiment.

Specific embodiment four: The difference between this embodiment and one of the specific embodiments one to three is that the calcium source solution in step two is a CaCl ₂ aqueous solution, the concentration is 0.3 mol/L, and the pH is 10.50±0.2. Others are the same as one of the first to third embodiments.

Specific embodiment five: The difference between this embodiment and one of the specific embodiments one to four is that in step three, the phosphorus source solution is (NH ₄ ) ₂ HPO ₄ aqueous solution, with a concentration of 0.3 mol/L and a pH of 10.50±0.2. Others are the same as one of the first to fourth embodiments.

Specific Embodiment Six: The difference between this embodiment and one of the specific embodiments one to five is that the volume ratio of the calcium source solution and the phosphorus source solution in step three is 5:3. Others are the same as one of the specific embodiments one to five.

Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that the stirring time in step three is 10 to 15 minutes. Others are the same as one of the specific embodiments one to six.

Specific Embodiment 8: The fireproof material of this embodiment contains the bio-based aerogel described in any of the above specific embodiments.

Specific Embodiment 9: Application of the flame-retardant and insulating bio-based aerogel of this embodiment in fire prevention and flame retardancy.

The embodiments of the present invention are described in detail below. The following examples are implemented on the premise of the technical solution of the present invention and provide detailed implementation plans and specific operating processes. However, the protection scope of the present invention is not limited to the following implementations. example.

Example 1:

The preparation method of flame-retardant and insulating bio-based aerogel in this embodiment includes the following steps:

Step 1: Preparation of SA airgel and surface microcalcification

Dissolve 2g of sodium alginate powder in 98g of deionized water to prepare a sodium alginate solution with a mass fraction of 2wt%. Stir and disperse evenly at a constant speed at room temperature of 25°C. Pour into a mold and pre-freeze in a freezing equipment for 6 hours. Then, freeze-dry for 72 hours, take it out after freeze-drying, and dry at 60°C for 4 hours under normal pressure to obtain sodium alginate aerogel (SA);

At room temperature of 25°C, dissolve CaCl ₂ in distilled water to prepare a 0.3 mol/L CaCl ₂ solution (calcium source solution); dissolve (NH ₄ ) ₂ HPO ₄ in distilled water to prepare a 0.3 mol/L (NH ₄ ) solution. ₂ HPO ₄ solution (phosphorus source solution); adjust the pH values of the CaCl ₂ solution and (NH ₄ ) ₂ HPO ₄ solution to 10.50 respectively with 25% volume fraction of ammonia water;

Pour an appropriate amount of calcium source solution into the mold, place the sodium alginate aerogel in the mold so that the sodium alginate aerogel is completely immersed in the calcium source solution, pre-crosslink for 15 minutes, and then pour out the excess calcium source solution. out, thereby obtaining SA aerogel with surface microcalcification. The preparation route diagram of SA aerogel with surface microcalcification is shown in Figure 1.

Step 2: Preparation of SA@HAP airgel

According to the chemical reaction equation and chemical formula of hydroxyapatite, it can be seen that its Ca/P is 1.67. At room temperature, place 50 mL of calcium source solution in a beaker, slowly add 30 mL of phosphorus source solution under vigorous stirring at 800 r/min, and continue stirring for 10 min after the phosphorus source solution is completely poured in. After stopping stirring, the hydroxyapatite preform is obtained. mixture.

Pour 50mL of hydroxyapatite premixed solution into the SA airgel mold containing surface microcalcification, so that the SA airgel is completely immersed, seal the mold and place it in a 35°C water bath for reaction for 24 hours; wait for the reaction time After the completion, put the sample into the freezing equipment to pre-freeze for 6 hours, continue to freeze-dry for 72 hours, take out the sample after freeze-drying, and age it at 80°C for 24 hours to prepare the SA aerogel with HAP grown on the surface, which is recorded as SA@HAP -24 airgel. The preparation route diagram of SA@HAP-24 aerogel is shown in Figure 2.

Pure SA aerogel was used as a control. The preparation method of pure SA aerogel was as shown in step 1 above.

The comparison results of the water resistance properties of SA aerogel and SA@HAP-24 aerogel prepared in this example are shown in Figure 3. It can be seen that after being placed in water for 5 minutes, most of the SA aerogel has been dissolved, and the SA@HAP-24 aerogel of the present invention does not appear to dissolve. One day after being placed in water, the SA aerogel had completely dissolved, while the SA@HAP-24 aerogel of the present invention still did not dissolve. Compared with pure SA aerogel, SA@HAP aerogel exhibits excellent water resistance.

The TG and DTG curves of SA aerogel and SA@HAP aerogel under _N2 atmosphere are shown in Figure 4. The thermogravimetric analysis (TGA) test in Figure 4 shows that the residual carbon mass of the SA@HAP aerogel at 800°C is 43.5wt%, which shows that the SA@HAP aerogel has excellent self-carbon-forming properties. In addition, The porous structure of SA@HAP airgel is retained, which shows good insulation effect against heat.

The total reflection Fourier transform infrared spectrum (ATR-FTIR) diagrams of SA, HAP and SA@HAP gas are shown in Figure 5. It can be seen from the FTIR spectrum: the absorption peaks at 1600cm ^-1 and 1405cm ^-1 are attributed to the vibration characteristic peaks of the carboxyl groups in SA, 1020cm ^-1 is the stretching vibration peak of CO, and the broad absorption band at 3260cm ^-1 It belongs to the stretching vibration of the hydroxyl group in SA. Compared with the SA airgel sample, due to the introduction of calcium ions, the carboxyl absorption peaks (1625 cm ^-1 and 1440 cm ^-1 ) of the SA@HAP airgel obviously shift to larger wave numbers. In addition, the characteristic peaks at 960 cm ^-1 and 1050 cm ^-1 correspond to the ν ₁ symmetric stretching vibration and ν ₃ asymmetric stretching vibration of PO of the phosphate group, which proves the successful generation of HAP on the SA aerogel surface. At the same time, the -OH group absorption peak (3120cm ^-1 ) on the surface of SA@HAP aerogel was obviously blue-shifted due to the hydrogen bond formed between HAP and SA, which further proved that HAP successfully grew on the surface of SA.

The SEM image of the SA aerogel surface is shown in Figure 6, the enlarged image in Figure 6 is shown in Figure 7, and the pore size distribution of the SA aerogel is shown in Figure 8. The surface scanning electron microscope (SEM) test of SA airgel shows that the SA airgel material has a uniform pore structure as a whole, the pore walls are relatively smooth and flat, and the pore diameter is concentrated in 60-80 μm.

The SEM image of the surface of SA@HAP airgel is shown in Figure 9, the enlarged view in Figure 9 is shown in Figure 10, and the pore size distribution of SA@HAP airgel is shown in Figure 11. It can be seen that with the calcification and growth of HAP, HAP beads obviously grow in situ on the surface of the airgel, and as the degree of cross-linking of the airgel increases, the pore size decreases slightly to 45-70 μm. Further research showed that after microcalcification and HAP growth on the surface of SA airgel, it only acted on the surface of the airgel and did not damage the internal three-dimensional porous structure.

The XRD analysis curves of HAP and SA@HAP surfaces are shown in Figure 12. Analysis shows that the crystal planes of HAP powder at (002), (211), (300), (310), and (213) are completely consistent with JCPDF:09-0432, and the high-intensity diffraction peaks of its crystal planes indicate that it is prepared by this method. HAP has a good crystalline state. The XRD pattern of the surface of SA@HAP-24 aerogel, through the index diffraction peak, is almost the same as JCPDF:00-055-0592, with (211), (300), and (310) being the main crystal planes respectively. Comparing the spectra of HAP, it can be seen that when HAP is grown onto the SA surface, as the growth time increases, the (300) crystal plane absorption intensity gradually increases, indicating that the growth of HAP on the SA airgel surface grows along the c-axis direction through crystal attachment. , making the HAP on the surface of SA airgel have excellent stability.

Combining the analysis results of FTIR, SEM and XRD spectra, it is known that hydroxyapatite (HAP) has successfully grown on the surface of SA airgel through Ca ²⁺ linkage, proving the successful preparation of SA@HAP airgel material.

The performance analysis of the SA@HAP aerogel prepared in this example is as follows:

(1) Thermal insulation performance and mechanical properties

Table 1 shows the thermal insulation performance and mechanical property test results of SA aerogel and SA@HAP aerogel. It can be seen from Table 1 that the thermal conductivity of SA aerogel is 0.02585W/(m·K), which is smaller than the thermal conductivity of air, 0.0267W/(m·K). When HAP is grown on the surface of SA, the thermal conductivity of SA@HAP aerogel increases slightly, but still remains at a low level, with a thermal conductivity of only 0.03144W/(m·K), which shows that the thermal conductivity of SA@HAP aerogel After surface microcalcification and surface growth of HAP, the original structure inside the SA airgel is not completely destroyed, so that it still has excellent thermal insulation properties.

For pure SA aerogel, since there are only intermolecular interactions in its structure, the compressive strength is only 0.15MPa. After microcalcification and HAP growth on the SA surface, a layer of bionic reinforced armor was worn on the SA surface through metal coordination and hydrogen bonding, which effectively improved the mechanical strength of the SA aerogel, making the SA@HAP aerogel The compressive strength has increased to 1.95MPa, which is nearly 13 times higher than pure SA, and the elastic modulus has been increased 20 times. Therefore, SA@HAP aerogel exhibits good mechanical properties and structural strength.

Table 1 Thermal insulation properties and mechanical properties of aerogels

(2) Flame retardant performance and combustion behavior test

In order to analyze the influence of surface growth of HAP on the flame retardant performance and combustion behavior of SA airgel, the properties of SA and SA@HAP airgel materials were analyzed through vertical combustion test, limiting oxygen index and cone calorimetry test. As shown in Table 2, pure SA aerogel will burn rapidly when exposed to fire, and will continue to smolder when it is away from the flame until it is completely burned out. With the growth of HAP on the surface, the SA@HAP aerogel sample could not be ignited within 15 seconds and successfully passed the V-0 level of UL-94, with an LOI value of 50.1%. This bio-based aerogel showed Excellent flame retardant properties.

Table 2 Test numbers of flame retardant properties of three types of aerogels

The heat release rate (HRR) and total heat release (THR) curves of SA and SA@HAP aerogels are shown in Figure 13 and Figure 14 respectively. Curve a in the figure represents SA, and curve b represents SA@HAP. It can be seen that pure SA aerogel will quickly release a large amount of heat once exposed to high thermal radiation conditions, with a peak value of 91.81kW/m ² and a total heat release of 10.56MJ/m ² . With the microcalcification of the surface and the growth of HAP, due to the carbonization promoted by pyrophosphate and Ca ²⁺ during the decomposition of HAP, a dense and hard protective carbon layer is formed on the surface of the material, allowing SA@HAP to condense. The heat release rate and total heat release of the glue were reduced to 31.45kW/m ² and 4.96MJ/m ² respectively, making the SA@HAP airgel exhibit excellent fire safety performance.

Compared with traditional petrochemical-based insulation materials and bio-based airgel materials, SA@HAP airgel exhibits excellent mechanical, water resistance and fire safety properties. The main reasons are: 1) SA@HAP airgel is completely derived from biological matrix , has good biocompatibility and degradability, and is of great significance for alleviating the current energy and environmental crisis. 2) By subjecting the SA airgel to surface microcalcification and surface HAP growth, the SA airgel is penetrated with a layer of "artificial skeleton" that strengthens and maintains the skeleton structure, thus endowing the SA@HAP airgel with excellent water resistance and mechanical properties. 3) Due to the introduction of the HAP structure on the surface of SA@HAP aerogel, the pyrophosphate and Ca ²⁺ produced during the decomposition process effectively promote the degradation and carbonization of SA@HAP aerogel material, thus in the condensed phase Produces a dense and hard carbon layer, which exerts an excellent shielding effect. 4) In the gas phase, since SA@HAP releases a large amount of non-flammable gases (such as H ₂ O, CO _2, etc.) during the combustion process, it effectively plays a dilution role in the gas phase. Therefore, SA@HAP aerogel obtains excellent water resistance, mechanical and fire safety properties.

Claims (9)

1. A method for preparing flame-retardant and insulating bio-based aerogels, characterized in that the method includes the following steps: 1. Pre-freeze the sodium alginate solution for 3 to 6 hours, then freeze-dry for 72 to 90 hours, and then take it out after freeze-drying to obtain sodium alginate aerogel; 2. Soak the sodium alginate aerogel with calcium source solution, pre-crosslink it, and then remove excess calcium source solution; 3. At room temperature, add the phosphorus source solution to the calcium source solution. Continue stirring after the phosphorus source solution is completely poured in. After stopping stirring, the hydroxyapatite premixed solution will be obtained; 4. Add the hydroxyapatite premixed solution to the pre-crosslinked sodium alginate aerogel to completely submerge the sodium alginate aerogel. After sealing, react in a 35°C water bath for 24 hours. After the reaction time is over, Pre-freeze the sample for 3 to 6 hours, then freeze-dry for 72 to 90 hours. After freeze-drying, take it out and place it in an oven at 80°C for aging for 18 to 30 hours to obtain SA@HAP-24 aerogel. 2. The preparation method of a kind of flame-retardant and heat-insulating bio-based aerogel according to claim 1, characterized in that the preparation method of the sodium alginate solution in step one is: dissolving the sodium alginate in deionized water to prepare the quality Fraction 2% sodium alginate solution. 3. The preparation method of a flame-retardant and heat-insulating bio-based aerogel according to claim 2, characterized in that the pre-crosslinking time in step two is 15 to 20 minutes. 4. The preparation method of a kind of flame-retardant and heat-insulating bio-based aerogel according to claim 3, characterized in that the calcium source solution in step 2 is _CaCl2 aqueous solution, the concentration is 0.3mol/L, and the pH is 10.50±0.2 . 5. The preparation method of a flame-retardant and heat-insulating bio-based aerogel according to claim 4, characterized in that in step three, the phosphorus source solution is (NH ₄ ) ₂ HPO ₄ aqueous solution with a concentration of 0.3 mol/L. The pH is 10.50±0.2. 6. The preparation method of a flame-retardant and heat-insulating bio-based aerogel according to claim 5, characterized in that the volume ratio of the calcium source solution and the phosphorus source solution in step three is 5:3. 7. The preparation method of flame-retardant and heat-insulating bio-based aerogel according to claim 6, characterized in that the stirring time in step three is 10 to 15 minutes. 8. A fireproof material, characterized by containing the bio-based aerogel according to any one of claims 1 to 7. 9. Application of the flame-retardant and insulating bio-based aerogel according to any one of claims 1 to 7 in fire prevention and flame retardancy.