Flame-retardant bio-based benzoxazine aerogel composite phase change material and preparation method thereof

Abstract

The present invention relates to a flame-retardant bio-based benzoxazine aerogel composite phase change material and a preparation method, and belongs to the technical field of composite functional materials. The method comprises the following steps: the aerogel composite phase change material is composed of a support material and a phase change material. The support material is prepared by a directional freeze-drying process using a bio-based benzoxazine monomer synthesized by a "one-pot method" as a flame retardant, a natural polymer as a cross-linked network and a functional filler. The prepared support material has an ordered layered porous network structure. Due to the hydrogen bonding effect between the functional filler and the active groups in the natural polymer, the functional filler is uniformly dispersed in the support material, giving the support material excellent properties. The phase change material is introduced into the support material by vacuum impregnation to prepare an aerogel composite phase change material, wherein the phase change material is uniformly distributed in the porous network of the support material. The present invention prepares an aerogel composite phase change material that integrates flame retardancy, heat insulation, photothermal conversion and energy storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite functional materials, and in particular relates to a flame-retardant bio-based benzoxazine aerogel composite phase change material and a preparation method thereof. Background Art

[0002] Phase change materials, as an emerging energy storage material, have the advantages of zero energy consumption and no pollution. Among them, solid-liquid phase change materials have been widely used in energy-saving buildings, thermal management, and solar energy utilization due to their advantages such as adjustable phase change temperature, high heat storage density, low supercooling, and high economic benefits. However, they have inherent problems such as low thermal conductivity, flammability, and easy leakage above the melting point, which hinder their practical application in the field of thermal management. Their low thermal conductivity will lead to slow heat transfer during application, affecting the efficiency of the phase change process; their flammability will cause a certain fire risk during use; and their easy leakage above the melting point will easily cause short circuits in electronic devices when combined with them. Therefore, it is necessary to prepare a composite phase change material with high thermal conductivity, flame retardancy, and good shape stability to promote its widespread application in the field of thermal management.

[0003] As a high-performance thermosetting resin with excellent thermal stability, good chemical stability, and outstanding mechanical properties, benzoxazine has broad application prospects in the field of phase change energy storage. However, traditional petroleum-based benzoxazines suffer from problems such as high curing temperature, easy shrinkage upon curing, complex synthesis process, and environmental pollution, which seriously limit their widespread application. Its high curing temperature not only increases production costs but also has adverse effects on the processing of some heat-sensitive materials. The easy shrinkage upon curing has a serious impact on applications requiring extremely high dimensional accuracy. The complex synthesis process increases the difficulty and cost of synthesis. At the same time, the use of high-boiling-point, highly polar solvents (such as dimethylacetamide and dimethyl sulfoxide), volatile solvents (such as acetone and ethanol), and byproducts produced during the synthesis, use, and disposal of benzoxazine can cause serious environmental damage, limiting its further development. Summary of the Invention

[0004] To overcome the shortcomings of the aforementioned prior art, the present invention provides a flame-retardant bio-based benzoxazine aerogel composite phase change material and a method for preparing the same. This aerogel composite phase change material utilizes a simple freeze-drying process to prepare an aerogel composite material composed of a one-pot synthesized bio-based benzoxazine monomer, a natural polymer, and a functional filler. Subsequently, the phase change material is introduced into the aerogel composite material by vacuum impregnation. This aerogel composite phase change material not only addresses the low thermal conductivity, leakage, and flammability issues of conventional solid-liquid phase change materials, but also addresses the high curing temperature, shrinkage during curing, complex synthesis process, and environmental pollution associated with conventional petroleum-based benzoxazine.

[0005] First, a bio-based benzoxazine monomer synthesized via a one-pot method replaces traditional petroleum-based benzoxazine, and the aerogel composite material preparation process uses water as a solvent instead of a high-boiling, highly polar solvent. This process is simple to operate, environmentally friendly, and imparts excellent flame retardancy to the aerogel composite phase change material. Second, the use of a biocompatible natural polymer as a cross-linking network not only enhances the mechanical properties of the aerogel composite but also improves its anti-leakage capability. Furthermore, hydrogen bonding between the functional filler and the active groups in the natural polymer allows the functional filler to be uniformly dispersed throughout the aerogel composite, imparting not only excellent properties such as thermal conductivity and photothermal conversion but also further enhancing its mechanical strength. This technological breakthrough has promoted the development of aerogel composite phase change materials in areas such as thermal management and solar energy utilization.

[0006] In order to achieve the above object, the present invention adopts the following preparation method to be realized:

[0007] S1. Mixing a bio-based benzoxazine monomer and deionized water, stirring and dissolving the mixture to obtain a benzoxazine monomer solution;

[0008] S2, adding a phosphorus-containing acid catalyst to the benzoxazine monomer solution prepared in step S1, stirring and dissolving to obtain a benzoxazine sol;

[0009] S3, adding a certain amount of natural polymer to the benzoxazine sol prepared in step S2, stirring and dissolving, to obtain a golden mixed sol;

[0010] S4, adding the functional filler to the golden mixed sol prepared in step S3, stirring to dissolve, and ultrasonically mixing to obtain a mixed sol system; then, freezing the mixed sol system to obtain a frozen molded body; then, freeze-drying the frozen molded body to obtain an incompletely solidified aerogel composite material;

[0011] S5. Place the incompletely cured aerogel composite material prepared in step S4 into an oven for drying to obtain an aerogel composite material; then, immerse the aerogel composite material in a molten phase change material to obtain a flame retardant bio-based benzoxazine aerogel composite phase change material.

[0012] Furthermore, in step S1, the bio-based benzoxazine monomer has the following structure:

[0013]

[0014] Furthermore, in Formula I, R1 is one of the following structures:

[0015]

[0016] Furthermore, in Formula I, Formula I1-2, Formula I1-3 and Formula I1-4, R2 is one of the following structures:

[0017]

[0018] Furthermore, the stirring and dissolving in step S1 is carried out under the following conditions: a temperature of 30-80°C, a rotation speed of 200-600 rpm, and a time of 5-30 min; and the solid content of benzoxazine in the benzoxazine monomer solution in step S1 is 2-12%.

[0019] Furthermore, the stirring and dissolving in step S2 is carried out under the following conditions: a temperature of 30-80°C, a rotation speed of 400-800 rpm, and a time of 20-60 min; the phosphorus-containing acid catalyst in step S2 is any one of phosphoric acid, orthophosphoric acid, phytic acid, hypophosphorous acid, phosphorous acid, metaphosphorous acid, phosphite, and pyrophosphoric acid; and the mass ratio of the phosphorus-containing acid catalyst to the benzoxazine monomer in step S2 is (0.1-0.5):1.

[0020] Furthermore, the stirring and dissolving in step S3 is specifically carried out under the following conditions: a temperature of 30-80° C., a rotation speed of 400-800 rpm, and a time of 30-70 min; the natural polymer in step S3 is any one of chitosan, chitin, frankincense, agarose, glycogen, collagen, silk fibroin, hyaluronic acid, guar gum, cellulose, lignin, starch, alginate, pectin, and carrageenan; and in step S3, the solid content mass ratio of the natural polymer to the benzoxazine solution is (0.5-3):9.

[0021] Furthermore, the stirring and dissolving in step S4 is carried out under the following conditions: a temperature of 30-80°C, a rotation speed of 400-800 rpm, and a time of 5-20 min; the ultrasonic treatment is carried out under the following conditions: a power of 300 W, an ultrasonic treatment for 10-30 min at room temperature; the freezing is carried out in a directional freezing mold, the freezing source is ethanol, the temperature is -60 to -80°C, and the freezing time is 20-40 min; the freeze drying is carried out in a freeze dryer at a pressure of 2-15 Pa, a temperature of -40 to -60°C, and a time of 36-72 h;

[0022] Furthermore, the functional filler in step S4 is a thermally conductive filler, any one of carbon black, carbon nanotubes, boron nitride, graphene, carbon fiber staple fibers, melanin, polyaniline, polypyrrole, titanium nitride, silver nanowires, mesoporous Prussian blue nanoparticles, titanium dioxide, black phosphorus nanosheets, and polydopamine; the mass ratio of the natural polymer, benzoxazine, and functional filler in step S4 is 2:9:(0.05-0.2).

[0023] Furthermore, the drying temperature in step S5 is 80-120°C, the immersion environment is under vacuum conditions with a vacuum degree of 0.075-0.09 MPa, the temperature is 80-120°C, and the immersion time is 12-36 hours. The phase change material in step S5 is any one of stearyl alcohol, cetyl alcohol, beeswax, paraffin, myristyl alcohol, sodium acetate trihydrate, polyethylene glycol, lauric acid, palmitic acid, and stearic acid.

[0024] Furthermore, the flame-retardant bio-based benzoxazine aerogel composite phase change material includes a support material and a phase change material; the support material is composed of a bio-based benzoxazine monomer synthesized by a "one-pot method" as a flame retardant, a natural polymer as a cross-linked network, and a functional filler; the support material has an ordered layered porous network structure; the aerogel composite phase change material has a dense structure, wherein the phase change material is evenly distributed in the porous network of the support material.

[0025] Furthermore, the flame-retardant bio-based benzoxazine aerogel composite phase change material has a maximum compressive strength of up to 19.92 MPa, a maximum phase change enthalpy of up to 210.48 J / g, a maximum thermal conductivity of 1.653 (W / mK), a maximum thermal insulation efficiency of 58%, a minimum residual carbon rate of 23.4%, a maximum peak heat release rate, an average heat release rate, and a total heat release rate reduced by 46%, 63%, and 40%, respectively. The maximum light-to-heat conversion efficiency reaches 94%, and the aerogel composite phase change material has a mass retention rate of 99.28% after heating at 90°C for 30 minutes.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention uses bio-based raw materials to synthesize a new water-soluble benzoxazine monomer with carbohydrate functional groups through a simple "one-pot method". This monomer replaces the traditional petroleum-based benzoxazine, and the preparation process is simple, low-cost, and environmentally friendly.

[0028] 2. The flame-retardant bio-based benzoxazine aerogel composite phase change material disclosed in the present invention is prepared using a directional freeze-drying process. The flame retardant is a bio-based benzoxazine monomer synthesized using a one-pot method, and a natural polymer is used as a cross-linked network and functional filler. The prepared support material has an ordered layered porous network structure. The aerogel composite material preparation process uses water as a solvent instead of a high-boiling point, highly polar solvent, reducing environmental pollution and health risks. It also imparts excellent flame retardancy to the aerogel composite phase change material, with a minimum residual carbon rate of 23.4%. The peak heat release rate, average heat release rate, and total heat release rate are reduced by 46%, 63%, and 40%, respectively. This achieves a combination of low cost, environmental friendliness, and high performance, providing a sustainable solution for applications in multiple fields.

[0029] 3. The aerogel phase-change composite material prepared by this invention exhibits excellent properties. Hydrogen bonding between the functional filler and the active groups in the natural polymer allows the functional filler to be uniformly dispersed throughout the aerogel composite, endowing the aerogel composite with exceptional properties, including thermal conductivity (up to 1.653 W / mK), excellent latent heat of phase change (melting enthalpy up to 210.48 J / g), mechanical properties (compressive strength up to 19.92 MPa), and photothermal conversion (photothermal conversion rate up to 94%). Furthermore, the aerogel composite phase-change material exhibits excellent leakage resistance, with a mass retention rate of 99.28% after heating at 90°C for 30 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart for preparing the flame-retardant bio-based benzoxazine aerogel composite phase change material of the present invention;

[0031] Figure 2 (a) is the NMR image of the flame-retardant bio-based benzoxazine prepared in Example 1; Figure 2 (b) is a graph showing the water solubility of the flame-retardant bio-based benzoxazine prepared in Example 1;

[0032] Figure 3 (a) and (b) are SEM images of the aerogel composite material prepared in Example 1 and the flame-retardant bio-based benzoxazine aerogel composite phase change material, respectively;

[0033] Figure 4 Mechanical properties of flame-retardant bio-based benzoxazine aerogel composite phase change materials prepared in Examples 1 to 3 and Comparative Example 4;

[0034] Figure 5 This is a flame retardant image of the flame retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1;

[0035] Figure 6(a) and (b) are the heat insulation-temperature rise diagram and heat insulation-temperature drop diagram of the flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1 and Comparative Example 4, respectively;

[0036] Figure 7 This is a photothermal conversion diagram of the flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1 and Comparative Example 4; DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The preparation flow chart of the present invention is as follows: Figure 1 shown.

[0038] Example 1

[0039] S1. Mix 3.6 g of a bio-based benzoxazine monomer having the structures of Formulas I1-2 and I2-1 with 36.4 ml of deionized water. Stir at a temperature of 50°C and a speed of 200 rpm for 10 min until the benzoxazine monomer solution is completely dissolved. The solid content of benzoxazine in the benzoxazine monomer solution is 9%.

[0040] S2. Add 1.8 g of phosphoric acid to the benzoxazine monomer solution prepared in step S1, stir at a temperature of 50°C and a speed of 500 rpm for 20 min to obtain a benzoxazine sol; wherein the mass ratio of phosphoric acid to benzoxazine monomer is 0.5:1.

[0041] S3. Add 0.8 g of chitosan to the benzoxazine sol prepared in step S2, stir at a temperature of 50°C and a rotation speed of 600 rpm for 30 min to obtain a golden mixed sol; wherein the solid content mass ratio of the natural polymer chitosan to the benzoxazine solution is 2:9.

[0042] S4. Add 0.66 g of carbon nanotubes to the golden mixed sol prepared in step S3, stir at a temperature of 50°C, a rotation speed of 500 rpm, stir for 10 min, and ultrasonically mix at room temperature with an ultrasonic power of 300 W for 10 min to obtain a mixed sol system; then, place the mixed sol system in a directional freezing mold, freeze at -70°C for 40 min to obtain a frozen molded body; then, freeze-dry the frozen molded body under a vacuum environment at a pressure of 2 Pa, a temperature of -40°C, and a freezing time of 72 h to obtain an incompletely solidified aerogel composite material; wherein the mass ratio of natural polymer chitosan, benzoxazine, and functional filler is 2:9:0.15.

[0043] S5. Place the uncured aerogel composite material prepared in step S4 in an oven for drying at a temperature of 80°C for 24 h to obtain an aerogel composite material; then place the aerogel composite material in a molten stearyl alcohol phase change material and vacuum impregnate it to obtain a flame-retardant bio-based benzoxazine aerogel composite phase change material at a pressure of 0.08 MPa, a temperature of 80°C, and an impregnation time of 24 h.

[0044] The flame retardant bio-based benzoxazine prepared in Example 1 was analyzed by nuclear magnetic resonance hydrogen spectroscopy using a Bruker AVANCE III HD 400 nuclear magnetic resonance spectrometer. Figure 2 As shown in (a), δ=3.63 and δ=4.85 correspond to the -CH2 protons of -Ar-CH2-N and -O-CH2-N- on the oxazine ring in PBa, respectively, indicating the presence of an oxazine ring in the structure and proving the successful preparation of benzoxazine. Figure 2 (b) Demonstrates the water solubility of flame-retardant bio-based benzoxazines at room temperature.

[0045] The flame-retardant bio-based benzoxazine aerogel and the flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1 were observed using a scanning electron microscope. Figure 3 (a) is a SEM image of the aerogel composite material prepared in Example 1. The aerogel composite material presents a channel-type ordered vertical layered porous network structure. Figure 3 (b) is an SEM image of the flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1. The phase change material in the flame-retardant bio-based benzoxazine aerogel composite phase change material penetrates into the three-dimensional layered porous structure of the aerogel composite material, making the substances more tightly bonded.

[0046] Examples 2-4

[0047] Examples 2 to 4 provide a method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material. Compared with Example 1, the difference is that the mass ratios of benzoxazine, chitosan, and carbon nanotubes in S4 are 2:9:0.05, 2:9:0.1, and 2:9:0.2, respectively. The rest is the same as Example 1 and will not be repeated here. A flame-retardant bio-based benzoxazine aerogel composite phase change material is obtained.

[0048] Example 5

[0049] S1. Mix 3.6 g of a bio-based benzoxazine monomer containing structures Ⅰ1-4 and Ⅰ2-3 with 36.4 ml of deionized water. Stir at 40°C and 300 rpm for 15 minutes until the monomer is completely dissolved to form a benzoxazine monomer solution. The solid content of benzoxazine in the benzoxazine monomer solution is 9%.

[0050] S2. Add 1.8 g of phytic acid to the benzoxazine monomer solution prepared in step S1, stir at a temperature of 55°C and a rotation speed of 400 rpm for 25 min to obtain a benzoxazine sol; wherein the mass ratio of phytic acid to benzoxazine monomer is 0.5:1.

[0051] S3. Add 0.8 g of lignin to the benzoxazine sol prepared in step S2, stir at a temperature of 40°C and a rotation speed of 700 rap, and stir for 40 min to obtain a golden mixed sol; wherein the solid content mass ratio of the natural polymer lignin to the benzoxazine solution is 2:9.

[0052] S4. Add 0.66 g of polypyrrole to the golden mixed sol prepared in step S3, stir at a temperature of 60°C, a rotation speed of 600 rpm, stir for 20 min, and ultrasonically mix at room temperature with an ultrasonic power of 300 W for 15 min to obtain a mixed sol system; then, place the mixed sol system in a directional freezing mold, freeze at -60°C for 30 min to obtain a frozen molded body; then, freeze-dry the frozen molded body under a vacuum environment at a pressure of 23 Pa, a temperature of -50°C, and a freezing time of 64 h to obtain an incompletely solidified aerogel composite material; wherein the mass ratio of the natural polymer polypyrrole, benzoxazine, and functional filler is 2:9:0.15.

[0053] S5. Place the uncured aerogel composite material prepared in step S4 in an oven and dry it at a temperature of 90°C for 20 h to obtain an aerogel composite material. Subsequently, place the aerogel composite material in molten myristyl alcohol phase change material and vacuum impregnate it to obtain a flame-retardant bio-based benzoxazine aerogel composite phase change material at a pressure of 0.075 MPa, a temperature of 90°C, and an impregnation time of 18 h.

[0054] Comparative Examples 1-4

[0055] Comparative Examples 1 to 4 provide a method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material. Compared with Example 1, the difference is that in S3, the mass ratio of the solid content of the benzoxazine solution to the natural polymer is 9:0.5, 9:1, 9:1.5, and 9:2; no functional filler is added in S4, and the rest is the same as Example 1 and will not be repeated here to obtain a flame-retardant bio-based benzoxazine aerogel composite phase change material.

[0056] The mechanical properties of the flame retardant bio-based benzoxazine aerogel composite phase change material prepared in Examples 1 to 3 and Comparative Example 4 were tested using a universal tensile testing machine. The results are as follows: Figure 4 As shown in the figure, with the increase of carbon nanotube functional fillers, the mechanical properties of the flame retardant bio-based benzoxazine aerogel composite phase change material show an increasing trend (the compressive stress at 80% maximum compressive strain increases from 14.18 MPa to 19.92 MPa), and the compressive strength of the material in comparative example 4 is increased by 186%, indicating that the functional fillers form a rigid support network in the aerogel, which improves the deformation resistance and inhibits pore collapse by dispersing stress; at the same time, mechanical strengthening does not sacrifice flame retardancy / thermal conductivity, reflecting the advantages of filler-matrix collaborative design, and providing a new strategy for high-strength and lightweight energy storage materials.

[0057] A TA Instruments Q20 differential scanning calorimeter was used to measure the temperature at 10 °C min −1 The melting and crystallization behaviors of a flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Examples 1 to 3 and Comparative Example 4 were measured at a ramp rate, and the melting enthalpy and crystallization enthalpy of the samples were calculated. The test results are shown in Table 1.

[0058] The initial mass of a flame-retardant bio-based benzoxazine aerogel composite phase change material (PCM) prepared in Examples 1-3 and Comparative Example 4, with a standard size (20 mm × 20 mm × 20 mm), was accurately weighed. The material was then placed in a 90°C constant temperature environment and heated for 1 hour. The sample mass was recorded every 5 minutes. The leakage behavior of the PCM in the molten state was quantitatively characterized by calculating the mass loss rate. The test results are shown in Table 1.

[0059] Table 1 Phase change properties of different embodiments and comparative examples

[0060]

[0061] As shown in Table 1, the phase change performance data show that the introduction of functional fillers creates more thermal pathways within the aerogel composite, further facilitating heat transfer within the phase change components. This improves the phase change enthalpy (from 164.10 J / g to 210.48 J / g) and thermal conductivity (from 0.72 W / mK to 0.94 W / mK) of the flame-retardant bio-based benzoxazine aerogel composite phase change material. The enthalpy efficiency reaches as high as 80%, indicating that the material can absorb or release more thermal energy during the phase change process, significantly improving energy efficiency. The three-dimensional network structure of the support material provides uniform support for the phase change material, reducing agglomeration of the lower phase change material. After heating at 90°C for 30 minutes, the mass retention rate of the aerogel composite phase change material reaches 99.28%. The excellent packaging stability and structural integrity during the phase change process enhance the material's safety and service life.

[0062] The flame retardant performance of a flame retardant bio-based benzoxazine aerogel composite phase change material prepared in Examples 1 to 3 and Comparative Example 4 was tested using an FTT iCone classic cone calorimeter (35 kWm- 2 The test results are shown in Table 2. At the same time, a butane torch with a flame temperature of 1200°C was used to burn the flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1 for 5 seconds. The combustion process is shown in Table 2. Figure 5 shown.

[0063] Table 2 Flame retardant properties of different embodiments and comparative examples

[0064]

[0065] As shown in Examples 1 to 3 and Comparative Example 4 in Table 2, as the content of carbon nanotube functional fillers increases, the flame retardant performance parameters of the bio-based benzoxazine aerogel composite phase change material show regular changes: the peak heat release rate, average heat release rate, and the final value of the total heat release rate all decrease significantly. This phenomenon clearly confirms the enhancement of the flame retardant performance of the composite phase change material. The chitosan polysaccharide component and the carbon nanotube functional filler in the composite phase change material can form a dense carbon layer protection structure under the synergistic catalytic effect. This carbonized layer can effectively isolate heat transfer, thereby playing an excellent heat barrier role. In addition, as Figure 5 As shown in the figure, the flame-retardant bio-based benzoxazine aerogel composite phase change material was burned under a butane torch at a flame temperature of 1200°C for 5 seconds without showing any obvious burning marks and self-extinguished within 1 second, indicating that it has excellent flame retardant properties.

[0066] The photothermal conversion performance of a flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1 and Comparative Example 4 was tested using a CEL-S500-T5 simulated sunlight xenon lamp light source. The radiation intensity in the experiment was 200 mW·cm -2 Each sample was irradiated at different radiation intensities for 33 minutes and then cooled naturally at room temperature. The temperature changes during the entire experiment were recorded using an infrared thermal imaging system and the temperature-time curve was obtained using computer software. The test results are shown in Figure 2. Figure 3 As shown in the figure, Example 1 exhibits excellent photothermal performance under a light intensity of 200 mW·cm⁻², and its surface temperature can quickly rise to 115°C, demonstrating efficient photothermal conversion capabilities. After the light source is turned off at 33 minutes, the surface temperature of the material quickly drops to 38°C, indicating that it has good thermal responsiveness and heat dissipation properties. In contrast, Comparative Example 4 can only reach 69°C under the same lighting conditions, and the temperature rise is significantly lower. In addition, due to the introduction of carbon nanotube functional fillers, Example 1 exhibits excellent photothermal conversion efficiency and thermal conductivity during both heating and cooling processes, further highlighting its advantages in photothermal applications.

[0067] The thermal insulation performance of the flame-retardant bio-based benzoxazine aerogel composite phase change material prepared in Example 1 and Comparative Example 4 was tested using an Infra Tec Vano Cam-HD research980 infrared thermal imaging system. The surface temperature changes of Example 1 and Comparative Example 4 at a constant temperature of 90°C for 30 minutes and within 30 minutes after stopping heating are shown in Figure 2. Figure 4 As shown. Compared with the blank group, the aerogel composite phase change materials of Example 1 and Comparative Example 4 both showed significant temperature regulation performance under high temperature environment, but Example 1 was better than Comparative Example 4. When exposed to a heat source, the surface temperature of the material showed a slow upward trend, which was mainly attributed to the stearyl alcohol component converting thermal energy into latent heat storage through a phase change process. As the heating time increases, the thermal buffering effect becomes more significant, and after 30 minutes, the temperature difference between the material surface and the hot stage can reach 50°C. After the heating is stopped, the temperature regulation mechanism of the composite phase change material is more prominent: when the ambient temperature drops sharply, the stored latent heat is continuously released, effectively slowing down the temperature drop rate, and showing excellent thermal insulation performance. This feature is reflected in the fact that the surface temperature of the material is always higher than the hot stage temperature, which confirms its good thermal energy storage and release capabilities.

Claims

1. A method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material, characterized in that: The method comprises the following steps: S1. Mixing a bio-based benzoxazine monomer and deionized water, stirring and dissolving the mixture to obtain a benzoxazine monomer solution; S2, adding a phosphorus-containing acid catalyst to the benzoxazine monomer solution prepared in step S1, stirring and dissolving to obtain a benzoxazine sol; S3, adding a natural polymer to the benzoxazine sol prepared in step S2, stirring and dissolving, to obtain a golden mixed sol, wherein the natural polymer is any one of chitosan and lignin; S4, adding a functional filler to the golden mixed sol prepared in step S3, stirring to dissolve, and ultrasonically mixing to obtain a mixed sol system; then, placing the mixed sol system in a mold, freezing it, and obtaining a frozen molded body; then, freeze-drying the frozen molded body to obtain an incompletely solidified aerogel composite material, wherein the functional filler is a thermally conductive filler; S5. Place the uncured aerogel composite material prepared in step S4 in an oven for drying to obtain an aerogel composite material; then place the aerogel composite material in a molten phase change material and perform vacuum impregnation to obtain a flame-retardant bio-based benzoxazine aerogel composite phase change material, wherein the phase change material is a solid-liquid phase change material; the bio-based benzoxazine monomer has the following structure: ； In formula I, R1 has the following structure: ； The structure of R2 in formula I and R1 is as follows: 。 2. The method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 1, characterized in that: The stirring and dissolving in step S1 is carried out under the following specific conditions: a temperature of 30-80° C., a rotation speed of 200-600 rpm, and a time of 5-30 min; and the solid content of benzoxazine in the benzoxazine monomer solution in step S1 is 2%-12%.

3. The method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 1, characterized in that: The stirring and dissolving in step S2 is carried out under the following specific conditions: a temperature of 30-80°C, a rotation speed of 400-800 rpm, and a time of 20-60 min; the phosphorus-containing acid catalyst in step S2 is any one of phosphoric acid, orthophosphoric acid, phytic acid, hypophosphorous acid, phosphorous acid, metaphosphorous acid, phosphite, and pyrophosphoric acid; and the mass ratio of the phosphorus-containing acid catalyst to the benzoxazine monomer in step S2 is (0.1-0.5):

1.

4. The method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 1, characterized in that: The stirring and dissolving in step S3 is carried out under the following conditions: a temperature of 30-80° C., a rotation speed of 400-800 rpm, and a time of 30-70 min; in step S3, the solid content mass ratio of the natural polymer to the benzoxazine solution is (0.5-3):

9.

5. The method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 1, characterized in that: The stirring and dissolving in step S4 is specifically performed under the following conditions: a temperature of 30-80°C, a rotation speed of 400-800 rpm, and a time of 5-15 min; the ultrasound is specifically performed under the following conditions: a power of 300 W, room temperature, and ultrasound for 10-30 min; the freezing is specifically performed under the following conditions: a freezing source of ethanol, a temperature of -60 to -80°C, and a freezing time of 20-40 min; and the freeze-drying is specifically performed in a freeze dryer under the following conditions: a pressure of 2-15 Pa, a temperature of -40 to -60°C, and a freezing time of 36-72 h.

6. The method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 1, characterized in that: The thermally conductive filler in step S4 is any one of carbon black, carbon nanotubes, boron nitride, graphene, carbon fiber staple fibers, melanin, polyaniline, polypyrrole, titanium nitride, silver nanowires, mesoporous Prussian blue nanoparticles, titanium dioxide, black phosphorus nanosheets, and polydopamine; the mass ratio of the natural polymer, benzoxazine, and functional filler in step S4 is 2:9:(0.05-0.2).

7. The method for preparing a flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 1, characterized in that: The drying described in step S5 has the following specific conditions: a temperature of 80-120°C and a time of 12-36 h; the vacuum impregnation has the following specific conditions: a pressure of 0.075-0.09 MPa, a temperature of 80-120°C, and a time of 12-36 h; the solid-liquid phase change material in step S5 is any one of stearyl alcohol, cetyl alcohol, beeswax, paraffin, myristyl alcohol, sodium acetate trihydrate, polyethylene glycol, lauric acid, palmitic acid, and stearic acid.

8. A flame retardant bio-based benzoxazine aerogel composite phase change material, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 7.

9. The flame-retardant bio-based benzoxazine aerogel composite phase change material according to claim 8, characterized in that: The aerogel composite phase change material includes a support material and a phase change material; the support material is composed of a bio-based benzoxazine monomer synthesized by a "one-pot method" as a flame retardant, a natural polymer as a cross-linked network, and a functional filler; the support material has an ordered layered porous network structure; the aerogel composite phase change material has a dense structure, wherein the phase change material is evenly distributed in the porous network of the support material.

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