Biomass-based radiation refrigeration fireproof composite material and preparation method thereof

Abstract

The invention relates to a biomass-based radiation refrigeration fireproof composite material and a preparation method thereof, and belongs to the technical field of macromolecular fireproof composite materials. In order to solve the problem that an existing fireproof coating cannot give consideration to both thermal management and fireproof performance, the invention provides a biomass-based radiation refrigeration fireproof composite material which comprises magnesium-aluminum hydrotalcite powder, cellulose nanofibers and a hydrophobic adhesive. According to the invention, a brick-mud hierarchical structure with a shell-like structure is constructed through electrostatic self-assembly, and the mechanical strength and toughness of the material are improved. The optical performance is improved through a multi-stage scattering interface constructed through CNF, and the solar spectral reflectivity is as high as 95.6%. The emissivity of the atmosphere window wave band reaches 94.9%, the radiation refrigeration power reaches 138.54 W / m < 2 >, and the thermal management performance is far better than that of a traditional fireproof coating. The inherent flame retardant property of Mg-Al LDH is combined with the enhancement effect of CNF, so that the material is endowed with excellent flame retardant property and good thermal stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polymer fireproof composite materials, and particularly relates to a biomass-based radiation refrigeration fireproof composite material and a preparation method thereof. BACKGROUND

[0002] With the intensification of global climate change and the acceleration of urbanization, there is an increasing demand for high-performance coatings in the fields of construction and industry. Existing fireproof coatings mainly adopt an intumescent flame-retardant system, the core components of which are a "trinity" system composed of ammonium polyphosphate, pentaerythritol and melamine. Such coatings have significant deficiencies in terms of thermal management, environmental friendliness and functionality, especially low thermal reflection efficiency, which leads to a sharp increase in building energy consumption in extreme high-temperature weather in summer, intensifying the urban heat island effect, and industrial equipment also faces the risk of coating aging, failure and even fire under high-temperature working conditions.

[0003] Radiation refrigeration technology, as a passive cooling strategy, has attracted widespread attention in recent years. This technology directly dissipates heat in the form of thermal radiation to the low-temperature outer space through the high solar reflectance (> 90%) and high emissivity in the mid-infrared band (8-13 μm) of the coating material, thereby achieving zero-energy consumption cooling. At present, radiation refrigeration coatings based on polymers (such as PVDF, PDMS) or inorganic particles (such as TiO2, BaSO4) have made some progress, but their application is still limited by single-function design. Most studies focus on improving the optical performance of the coating, but ignore its fireproof performance, and the high content of organic components in the coating will release a large amount of flammable gas under fire conditions, intensifying the spread of fire. In addition, radiation refrigeration coatings usually require the coating to have high optical uniformity and surface flatness, which is fundamentally contradictory to the required intumescent carbon layer structure of fireproof coatings. These factors make it difficult for existing radiation refrigeration technology to be directly applied to the fireproof field. SUMMARY

[0004] To solve the problem that existing fireproof coatings cannot balance thermal management and fireproof performance, the application provides a biomass-based radiation refrigeration fireproof composite material and a preparation method thereof.

[0005] The technical scheme of the application is as follows:

[0006] A biomass-based radiation refrigeration fireproof composite material, comprising the following components in mass percentage: magnesium-aluminum hydrotalcite powder 40%-70%, cellulose nanofiber 20%-50% and hydrophobic adhesive 10%-20%.

[0007] Further, the hydrophobic adhesive is at least one of water-based polyurethane emulsion, acrylate emulsion or silicone resin.

[0008] A preparation method of a biomass-based radiation refrigeration fireproof composite material, comprising the following steps:

[0009] Step one, using hydrothermal method to synthesize magnesium-aluminum hydrotalcite powder;

[0010] Step two, mixing the magnesium-aluminum hydrotalcite powder prepared in step one, cellulose nanofiber water dispersion and hydrophobic adhesive and ultrasonic treatment to obtain a uniform and stable composite coating;

[0011] Step three, coating the composite coating prepared in step two on the surface of the base material to form a wet film;

[0012] Step four, pre-curing the wet film obtained in step three to obtain a fireproof composite material.

[0013] Further, the preparation method of the magnesium-aluminum hydrotalcite powder in step one is as follows: taking Mg(NO3)2·6H2O and Al(NO3)3·9H2O as metal sources, hexamethylenetetramine HMT as a precipitating agent and a structure directing agent, and the molar ratio of Mg:Al:HMT being 2-4:1:2.6-5.2, dissolving Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT in deionized water to form a transparent solution, adjusting the pH of the system to 9-10 with lye, and then transferring it into a high-pressure reaction kettle for hydrothermal reaction at 120-180°C for 9-18h, and then centrifuging, washing and drying the reaction product to obtain white powder of magnesium-aluminum hydrotalcite.

[0014] Further, the solid content of the cellulose nanofiber water dispersion in step two is 5-20wt%.

[0015] Further, the mixing in step two is specifically dispersing the magnesium-aluminum hydrotalcite powder in the cellulose nanofiber water dispersion, stirring at a speed of 200-500rpm for 30-60min, then adding the hydrophobic adhesive and continuing to stir for 10-30min.

[0016] Further, the ultrasonic treatment in step two has an ultrasonic power of 200-400W and a time of 10-20min.

[0017] Further, the coating in step three is blade coating, spin coating, roller coating or spraying, the base material is metal, ceramic, polymer or wood, and the thickness of the wet film is 300-500μm.

[0018] Further, the pre-curing treatment in step four is drying at 80-120°C for 1-3h.

[0019] Further, the fireproof composite material obtained in step four has a shell-like layered brick-mud structure, and has a reflectivity of not less than 92% in the solar spectrum band and an emissivity of not less than 90% in the atmospheric window band.

[0020] Advantages of the present application:

[0021] The present application provides a biomass-based radiative cooling fireproof composite material based on magnesium-aluminum hydrotalcite (Mg-Al LDH) and cellulose nanofiber (CNF). The material constructs a Mg-Al LDH / CNF heterojunction interface through electrostatic self-assembly, in which the carboxyl groups of CNF form strong electrostatic interactions with the LDH layers, significantly improving the LDH exfoliation dispersion. Using inorganic magnesium-aluminum hydrotalcite as "bricks" and biomass-based cellulose nanofiber as "mortar", combined with a hydrophobic adhesive, a "brick-mortar" hierarchical structure with a shell-like structure is successfully constructed, significantly improving the mechanical strength and toughness of the fireproof composite material.

[0022] The fireproof composite material constructed by CNF has significantly improved optical performance, with a solar spectrum band (0.3-2.5 μm) reflectivity of up to 95.6%. The emissivity in the atmospheric window band (8-13 μm) also reached 94.9%, and this high reflectivity and high emissivity ensured the daytime radiative cooling capacity of the fireproof composite material. Outdoor test results show that the temperature in the area covered by the coating can be reduced by 10.4°C compared to the ambient temperature, and the theoretical radiative cooling power can reach 138.54 W / m 2 , far exceeding the thermal management performance of traditional fireproof coatings.

[0023] The magnesium-aluminum hydrotalcite in the fireproof composite material of the present application has natural fireproof performance, and its layered structure can form a protective carbonized layer at high temperatures to inhibit flame spread. The inherent flame retardant properties of Mg-Al LDH combined with the reinforcing effect of CNF together give the fireproof composite material excellent flame retardant performance and good thermal stability. These characteristics ensure that the coating can maintain structural integrity and performance stability in long-term outdoor or high-temperature harsh environments. Under the action of a fire source, the fireproof composite material can maintain structural stability and not burn within 90 seconds, fully demonstrating its application potential in high-temperature environments. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 SEM image of the fireproof composite material obtained in Example 2;

[0025] Figure 2 Zeta potential comparison chart of the Mg-Al LDH and CNF aqueous solution in Example 2;

[0026] Figure 3 UV-Vis-NIR reflectance, infrared emission spectrum of the fireproof composite material obtained in Example 2, pure CNF coating and pure Mg-Al LDH coating;

[0027] Figure 4The ultraviolet-visible-near infrared reflectance spectrum of the fireproof composite material obtained in Example 2 at different incident angles;

[0028] Figure 5 The comparison diagram of the daytime temperature curve and the ambient temperature curve of the fireproof composite material obtained in Example 2;

[0029] Figure 6 The temperature difference curve of the daytime temperature and the ambient temperature of the fireproof composite material obtained in Example 2;

[0030] Figure 7 The fire resistance performance test diagram of the fireproof composite material obtained in Example 2 at different combustion times. DETAILED DESCRIPTION

[0031] The technical solutions of the present application are further described below in combination with examples, but are not limited thereto, and any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application shall be covered in the protection scope of the present application. The process equipment or device not specifically mentioned in the following examples is the conventional equipment or device in the art, and if not specifically indicated, the raw materials used in the examples of the present application are commercially available; if not specifically indicated, the technical means used in the examples of the present application are conventional means well known to those skilled in the art.

[0032] Example 1

[0033] The present embodiment provides a preparation method of a biomass-based radiation refrigeration fireproof composite material, and the steps are as follows:

[0034] Step one, synthesis of magnesium-aluminum hydrotalcite powder by hydrothermal method: Mg(NO3)2·6H2O and Al(NO3)3·9H2O are used as metal sources, hexamethylenetetramine HMT is used as precipitating agent and structure directing agent, and the molar ratio of Mg:Al:HMT is 2:1:2.6, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT are dissolved in deionized water to form a transparent solution, the pH of the system is adjusted to 9.5 with lye, then transferred into a high-pressure reaction kettle, and hydrothermal reaction is carried out at 120℃ for 12h, and the reaction product is centrifuged, washed and vacuum dried at 60℃ to obtain white powder of magnesium-aluminum hydrotalcite.

[0035] Step two, take the solid content of 20wt% cellulose nanofiber water dispersion; according to the weight portion, take 4 portions of the magnesium-aluminum hydrotalcite powder prepared in step one, 15 portions of cellulose nanofiber water dispersion and 1 portion of water-based polyurethane emulsion; first disperse the magnesium-aluminum hydrotalcite powder in the cellulose nanofiber water dispersion, stir at a speed of 400 rpm for 40 min; then add the water-based polyurethane emulsion and continue stirring for 20 min; finally, ultrasonic dispersion is carried out under a power of 300 W for 15 min to obtain a uniform and stable composite coating;

[0036] Step three, the composite coating prepared in step two is coated on the surface of the aluminum plate substrate in the form of scraping to form a wet film with a thickness of 500 μm;

[0037] Step four, the wet film obtained in step three is placed in a 60℃ air drying oven for pre-curing for 2h to obtain a fireproof composite material.

[0038] Example 2

[0039] The present embodiment provides a preparation method of a biomass-based radiation refrigeration fireproof composite material, the steps of which are as follows:

[0040] Step one, synthesis of magnesium-aluminum hydrotalcite powder by hydrothermal method: taking Mg(NO3)2·6H2O and Al(NO3)3·9H2O as metal sources, and hexamethylenetetramine HMT as precipitating agent and structure directing agent, the molar ratio of Mg:Al:HMT is 2:1:2.6, dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT in deionized water to form a transparent solution, adjust the pH of the system to 9.5 with alkali, then transfer it into a high-pressure reaction kettle, and react at 120℃ for 12h, the reaction product is centrifuged, washed and dried at 60℃ under vacuum to obtain white powder of magnesium-aluminum hydrotalcite.

[0041] Step two, take the solid content of 20wt% cellulose nanofiber water dispersion; according to the weight portion, take 4 portions of the magnesium-aluminum hydrotalcite powder prepared in step one, 15 portions of cellulose nanofiber water dispersion and 1 portion of water-based polyurethane emulsion; first disperse the magnesium-aluminum hydrotalcite powder in the cellulose nanofiber water dispersion, stir at a speed of 400 rpm for 40 min; then add the water-based polyurethane emulsion and continue stirring for 20 min; finally, ultrasonic dispersion is carried out under a power of 300 W for 15 min to obtain a uniform and stable composite coating;

[0042] Step three, the composite coating prepared in step two is coated on the surface of the aluminum plate substrate in the form of scraping to form a wet film with a thickness of 500 μm;

[0043] Step four, the wet film obtained in step three is placed in a 60℃ air drying oven for pre-curing for 2h to obtain a fireproof composite material.

[0044] Example 3

[0045] The present embodiment provides a preparation method of a biomass-based radiation refrigeration fireproof composite material, the steps are as follows:

[0046] Step one, magnesium-aluminum hydrotalcite powder was synthesized by hydrothermal method: Mg(NO3)2·6H2O and Al(NO3)3·9H2O were used as metal sources, hexamethylenetetramine HMT was used as precipitant and structure directing agent, and the molar ratio of Mg:Al:HMT was 2:1:2.6, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT were dissolved in deionized water to form a transparent solution, the pH of the system was adjusted to 9.5 with alkali, then it was transferred into a high-pressure reaction kettle and hydrothermal reaction was carried out at 120℃ for 12h, the reaction product was centrifuged, washed and vacuum dried at 60℃ to obtain white powder of magnesium-aluminum hydrotalcite.

[0047] Step two, 20wt% cellulose nanofiber water dispersion was taken, 4 parts of magnesium-aluminum hydrotalcite powder prepared in step one, 25 parts of cellulose nanofiber water dispersion and 1 part of water-based polyurethane emulsion were weighed; first, the magnesium-aluminum hydrotalcite powder was dispersed in the cellulose nanofiber water dispersion, and stirred at a speed of 400rpm for 40min; then the water-based polyurethane emulsion was added and stirred for 20min; finally, ultrasonic dispersion was carried out under the power of 300W for 15min to obtain a uniform and stable composite coating;

[0048] Step three, the composite coating prepared in step two was coated on the surface of the aluminum plate substrate by scraping to form a wet film with a thickness of 500μm;

[0049] Step four, the wet film obtained in step three was placed in a 60℃ air drying oven for pre-curing for 2h to obtain a fireproof composite material.

[0050] Comparative Example 1

[0051] The present comparative example provides a preparation method of a biomass-based radiation refrigeration fireproof composite material, the steps are as follows:

[0052] Step one, magnesium-aluminum hydrotalcite powder was synthesized by hydrothermal method: Mg(NO3)2·6H2O and Al(NO3)3·9H2O were used as metal sources, hexamethylenetetramine HMT was used as precipitant and structure directing agent, and the molar ratio of Mg:Al:HMT was 2:1:2.6, Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT were dissolved in deionized water to form a transparent solution, the pH of the system was adjusted to 9.5 with alkali, then it was transferred into a high-pressure reaction kettle and hydrothermal reaction was carried out at 120℃ for 12h, the reaction product was centrifuged, washed and vacuum dried at 60℃ to obtain white powder of magnesium-aluminum hydrotalcite.

[0053] Step two, take the solid content of 20wt% cellulose nanofiber water dispersion; according to the weight portion, take 4 portions of the magnesium-aluminum hydrotalcite powder prepared in step one, 5 portions of cellulose nanofiber water dispersion and 1 portion of water-based polyurethane emulsion; first disperse the magnesium-aluminum hydrotalcite powder in the cellulose nanofiber water dispersion, stir at a speed of 400 rpm for 40 min; then add the water-based polyurethane emulsion and continue stirring for 20 min; finally, ultrasonic dispersion is carried out under a power of 300 W for 15 min to obtain a uniform and stable composite coating;

[0054] Step three, the composite coating prepared in step two is coated on the surface of the aluminum plate substrate in the form of scraping to form a wet film with a thickness of 500 μm;

[0055] Step four, the wet film obtained in step three is placed in a 60°C air drying oven for pre-curing for 2h to obtain a fireproof composite material.

[0056] Comparative example 2

[0057] This comparative example provides a preparation method of a biomass-based radiation cooling fireproof composite material, the steps of which are as follows:

[0058] Step one, magnesium-aluminum hydrotalcite powder is synthesized by a hydrothermal method: Mg(NO3)2·6H2O and Al(NO3)3·9H2O are used as metal sources, hexamethylenetetramine HMT is used as a precipitating agent and a structure directing agent, and the molar ratio of Mg:Al:HMT is 2:1:2.6; Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT are dissolved in deionized water to form a transparent solution; the pH of the system is adjusted to 9.5 with lye, then transferred into a high-pressure reaction kettle, and reacted at 120°C for 12h; the reaction product is centrifuged, washed, and vacuum dried at 60°C to obtain white powder magnesium-aluminum hydrotalcite.

[0059] Step two, take the solid content of 20wt% cellulose nanofiber water dispersion; according to the weight portion, take 4 portions of the magnesium-aluminum hydrotalcite powder prepared in step one, 5 portions of cellulose nanofiber water dispersion and 1 portion of water-based polyurethane emulsion; first disperse the magnesium-aluminum hydrotalcite powder in the cellulose nanofiber water dispersion, stir at a speed of 400 rpm for 40 min; then add the water-based polyurethane emulsion and continue stirring for 20 min; finally, ultrasonic dispersion is carried out under a power of 300 W for 15 min to obtain a uniform and stable composite coating;

[0060] Step three, the composite coating prepared in step two is coated on the surface of the aluminum plate substrate in the form of scraping to form a wet film with a thickness of 500 μm;

[0061] Step four, the wet film obtained in step three is placed in a 60°C air drying oven for pre-curing for 2h to obtain a fireproof composite material.

[0062] The solar reflectance, infrared emissivity and refrigeration power of the fireproof composite materials prepared in Examples 1-3 and Comparative Example, Comparative Example 2 were tested, and the results are shown in Table 1.

[0063] Table 1

[0064]

[0065] As can be seen from the data in Table 1, with the increase of the content of CNF, the solar reflectance of the composite fireproof material shows a significant upward trend, which helps to reduce the absorption of solar radiation, thereby reducing the temperature of the material surface. At the same time, although the atmospheric window emissivity fluctuates slightly under different proportions, it remains at a high level, all reaching more than 94%, showing the excellent performance of the composite material in terms of infrared radiation emission. Based on the fact that both the solar reflectance and the atmospheric window emissivity are at a high level, the radiation refrigeration power of the composite fireproof material is also significantly enhanced, reaching a maximum of 139.00 W / m 2 This further proves the excellent ability of the biomass-based radiation refrigeration fireproof composite material prepared in the present application in terms of thermal management. Especially in outdoor environments with high temperatures or strong sunlight, the material can achieve significant cooling effect through efficient reflection of sunlight and emission of infrared radiation, providing double protection for fire safety and thermal comfort.

[0066] Figure 1 The scanning electron microscope image of the fireproof composite material obtained in Example 2 is shown in Figure 1. As shown in Figure 1, the fireproof composite material shows a brick mortar structure mode similar to a shell structure. CNF acts as a "mortar" role and is coated and dispersed in the interlayer of Mg-Al LDH. The formation of this shell-like structure provides more interfaces, promoting light scattering and reflection, thereby improving the radiation refrigeration performance of the fireproof composite material. The addition of CNF effectively adjusts the optical properties of the material system and increases the light scattering interface. Figure 1

[0067] The Zeta potential comparison chart of the Mg-Al LDH and CNF aqueous solutions in Example 2 is shown in Figure 2. As shown in Figure 2, the Zeta potential of the pure Mg-Al LDH aqueous solution is positive, and the Zeta potential of the pure CNF aqueous solution is negative. Due to the electrostatic interaction between the two, CNF is uniformly distributed in the interlayer of Mg-Al LDH. Figure 2 Figure 2 The ultraviolet-visible-near infrared reflectance and infrared emission spectrum of the fireproof composite material obtained in Example 2, the pure CNF coating and the pure Mg-Al LDH coating is shown in Figure 3.

[0068] Figure 3 Figure 4 ​​UV-Vis-NIR reflectance spectra of the fireproof composite obtained in Example 2 at different incident angles; as shown in Figure 3 , Figure 4 The addition of CNF significantly enhances the light scattering ability of the fireproof composite, especially in the visible and near-infrared regions, with a reflectance close to twice that of pure Mg-Al LDH. CNF achieves a reflectance of up to 95.6% and an infrared emissivity of 94.9% by increasing the scattering interface in the system. The reflectance of the fireproof composite changes little at different incident angles, and it still maintains good light reflection performance regardless of the change in illumination angle.

[0069] Figure 5 Comparison chart of daytime temperature curve and ambient temperature curve of the fireproof composite obtained in Example 2; Figure 6 Temperature difference curve of daytime temperature and ambient temperature of the fireproof composite obtained in Example 2; The test was conducted on the roof of the College of Materials, Northeast Forestry University (North Latitude 45°72'03", East Longitude 126°63'46"). An aluminum foil-wrapped polystyrene foam box was used as the outer shell during the test process to enhance the heat insulation effect, and a polyethylene (PE) film was placed on top to form a sealed air cavity to reduce the interference of non-radiative heat transfer. The entire device was erected on a high shelf above the ground to minimize the influence of ground thermal convection and ensure the stability and accuracy of the test data. As shown in Figure 5 and Figure 6 Between 09:00 and 16:00, the temperature of the fireproof composite decreased significantly compared to the ambient temperature, especially when the solar radiation intensity was high, the temperature of the fireproof composite maintained at around 30°C, which was much lower than the surrounding environment temperature (35-45°C). During the period from 09:00 to 14:00, the temperature difference between the coating and the environment maintained between 5.4°C and 10.4°C, which proved the good radiative cooling performance of the composite fireproof material.

[0070] Figure 7 Fire resistance test chart of the fireproof composite obtained in Example 2 at different burning times, as shown in Figure 7 The fireproof composite film did not burn within 90s and maintained good structural stability. Mg-Al LDH, as a material with natural flame retardancy, its layered structure helps to form a protective carbonized layer at high temperatures, effectively reducing the spread of flames.

Claims

1. A biomass-based radiation-cooled fireproof composite material, characterized in that, It includes the following components by weight percentage: 40%~70% magnesium-aluminum hydrotalcite powder, 20%~50% cellulose nanofibers, and 10%~20% hydrophobic adhesive.

2. The biomass-based radiation-cooled fireproof composite material according to claim 1, characterized in that, The hydrophobic adhesive is at least one of waterborne polyurethane emulsion, acrylate emulsion, or silicone resin.

3. A method for preparing a biomass-based radiation-cooled fire-resistant composite material as described in claim 1 or 2, characterized in that, The steps are as follows: Step 1: Synthesize magnesium-aluminum hydrotalcite powder using a hydrothermal method; Step 2: Mix the magnesium-aluminum hydrotalcite powder, cellulose nanofiber aqueous dispersion and hydrophobic adhesive obtained in Step 1 and ultrasonically treat them to obtain a uniform and stable composite coating. Step 3: Apply the composite coating obtained in Step 2 to the surface of the substrate material to form a wet film; Step 4: Pre-curing treatment is performed on the wet film obtained in Step 3 to obtain the fireproof composite material.

4. The preparation method of the biomass-based radiation cooling fireproof composite material according to claim 3, characterized in that, The preparation method of magnesium-aluminum hydrotalcite powder in step one is as follows: using Mg(NO3)2·6H2O and Al(NO3)3·9H2O as metal sources, and hexamethylenetetramine (HMT) as precipitant and structure directing agent, the Mg:Al:HMT molar ratio is 2~4:1:2.6~5.

2. Mg(NO3)2·6H2O, Al(NO3)3·9H2O and HMT are dissolved in deionized water to form a transparent solution. After adjusting the pH of the system to 9~10 with alkaline solution, the solution is transferred to a high-pressure reactor and hydrothermally reacted at 120~180℃ for 9~18h. The reaction product is centrifuged, washed and dried to obtain white powdered magnesium-aluminum hydrotalcite.

5. The method for preparing the biomass-based radiation-cooled fireproof composite material according to claim 3 or 4, characterized in that, The solid content of the cellulose nanofiber aqueous dispersion in step two is 5~20wt%.

6. The preparation method of the biomass-based radiation cooling fireproof composite material according to claim 3, characterized in that, The mixing process in step two involves first dispersing magnesium-aluminum hydrotalcite powder in an aqueous dispersion of cellulose nanofibers and stirring at 200-500 rpm for 30-60 minutes; then adding a hydrophobic adhesive and continuing to stir for 10-30 minutes.

7. The preparation method of the biomass-based radiation cooling fireproof composite material according to claim 3, characterized in that, The ultrasonic power for the ultrasonic treatment in step two is 200~400W, and the time is 10~20min.

8. The preparation method of the biomass-based radiation cooling fireproof composite material according to claim 3, characterized in that, The coating in step three can be applied by scraping, spin coating, roller coating, or spraying. The substrate material can be metal, ceramic, polymer, or wood, and the thickness of the wet film is 300~500μm.

9. The preparation method of the biomass-based radiation cooling fireproof composite material according to claim 3, characterized in that, The pre-curing treatment described in step four involves drying at 80~120℃ for 1~3 hours.

10. The preparation method of the biomass-based radiation-cooled fireproof composite material according to claim 3, characterized in that, The fireproof composite material obtained in step four has a shell-like layered brick-mud structure, with a reflectivity of not less than 92% in the solar spectrum band and an emissivity of not less than 90% in the atmospheric window band.

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