A method for preparing breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsion.

Abstract

This invention discloses a method for preparing breathable, fully flexible, and heat-insulating boron nitride aerogel material based on a high internal phase emulsion, comprising the following steps: Step 1, preparing a stabilizer; Step 2, preparing a high internal phase emulsion; Step 3, preparing a porous polymer aerogel with ultra-low density; Step 4, preparing a breathable, fully flexible, and heat-insulating boron nitride aerogel material. This invention uses a high internal phase emulsion as a matrix, combining it with boron nitride aerogel to effectively control the mechanical properties, density, porosity, and thermal conductivity of the aerogel material. By combining boron nitride micron and / or nanobelts that interweave and entwine to form a composite three-dimensional porous network structure, the resulting aerogel material has an internal structure in which fibers are uniformly dispersed within the mesh of a three-dimensional framework, with interwoven fibers forming pores. This improves the mechanical strength of the aerogel material while imparting flexibility and breathability, and its low thermal conductivity effectively insulates against heat transmission.

Description

Technical Field

[0001] This invention belongs to the field of boron nitride aerogel material preparation technology, specifically relating to a method for preparing breathable, fully flexible, and heat-insulating boron nitride aerogel material based on a high internal phase emulsion. Background Technology

[0002] Aerogels are unique solid materials composed of an interconnected three-dimensional solid network and numerous air-filled pores. They extend the structural features and physicochemical properties of nanoscale building blocks to the macroscopic scale, combining typical aerogel characteristics such as high porosity, large surface area, and low density with the specific properties of various components. More importantly, aerogels, due to their lightweight, high-efficiency thermal insulation, and resistance to high-temperature oxidation, have wide applications in national defense, equipment insulation, aerospace, oil pipelines, and special environments. Traditional high-temperature resistant aerogel insulation materials have certain deficiencies in high-temperature resistance, thermal insulation, and mechanical properties. Furthermore, aerogels themselves are extremely brittle, and cracks, defects, and powder shedding are unavoidable during the preparation process, significantly impacting their performance. Therefore, the preparation process requires not only low thermal conductivity and sustained high-temperature resistance, but also high strength, high-efficiency thermal insulation, and a green and flexible manufacturing process. Thus, constructing bulk materials that exhibit excellent thermal insulation performance in extreme environments is essential.

[0003] Aerogel preparation techniques have evolved, with gelation being a crucial process as it largely determines the final morphology of the aerogel. Traditional gelation follows the classic sol-gel process, forming a disordered yet continuous colloidal network. With a deeper understanding of aerogels, the high internal phase emulsion template method has attracted significant attention from researchers due to its simple preparation process, low solvent consumption, low energy consumption during drying, and the ability to incorporate chemical reactants and nanoparticles to form stable colloidal systems. The unique high internal phase emulsion method combines the advantages of emulsions and gels, making the foam structure and gel state of the high internal phase emulsion itself an ideal template for preparing high-porosity aerogels.

[0004] Boron nitride is a crystal composed of equal numbers of nitrogen and boron atoms, with a hexagonal crystal system, exhibiting excellent insulation, chemical stability, and thermal stability. Boron nitride materials can be used to prepare porous aerogels, effectively combining the advantages of both boron nitride and aerogels. The resulting boron nitride aerogel possesses an excellent internally interconnected network structure and high-temperature resistance, making it a novel type of non-oxide aerogel.

[0005] Boron nitride aerogel oxidizes to form boron oxide at around 900℃, which further leads to a rapid decrease in the high-temperature stability of boron nitride. At the same time, its thermal insulation and mechanical properties also have certain defects. Given the application requirements of boron nitride aerogel in high-temperature insulation, it is urgent to improve the structure and chemical composition of boron nitride aerogel to obtain high-temperature resistant aerogel materials with higher comprehensive performance.

[0006] Therefore, there is a need for a method to prepare breathable, fully flexible, heat-insulating boron nitride aerogel materials using high internal phase emulsions as templates, so as to achieve the goals of simple process, controllable structure, green and environmentally friendly process, and low cost, and to give full play to the advantages of aerogels. Summary of the Invention

[0007] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing breathable, fully flexible, heat-insulating boron nitride aerogel materials based on a high internal phase emulsion. This method utilizes a high internal phase emulsion template method, mixing polymerizable monomers and crosslinking agents to obtain an oil phase, then adding treated mullite fibers. Subsequently, an aqueous solution containing boron and nitrogen sources is added. Polymerization is then carried out using a polymeric free radical initiator and heating, resulting in a tightly bonded network structure formed by the polymeric monomers and the mullite fibers. This produces a three-dimensional porous network structure of intertwined boron nitride nanoribbons and / or microribbons. After thermal decomposition, a flexible heat-insulating aerogel material is obtained, exhibiting low thermal conductivity and density, and achieving excellent thermal insulation and high-temperature resistance.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing breathable, fully flexible, heat-insulating boron nitride aerogel material based on a high internal phase emulsion, characterized in that the method includes the following steps:

[0009] Step 1: Preparation of stabilizer: At room temperature, disperse mullite fibers in vinyltriethoxysilane, mix and shake, the solution turns clear, and the stabilizer is obtained;

[0010] Step 2: Preparation of high internal phase emulsion: At room temperature, polymerizable monomers, crosslinking agents and co-crosslinking agents are mixed to obtain an oil phase. Then, boron source small molecules, nitrogen source small molecules and solvent are mixed to obtain an aqueous phase. The aqueous phase is then added dropwise to the oil phase, followed by the addition of the stabilizer and initiator prepared in Step 1 and shaken to obtain a high internal phase emulsion.

[0011] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 is polymerized in an oil bath. The product is then freeze-dried for the first time to obtain a porous polymer aerogel with ultra-low density. The porous polymer aerogel is then subjected to low-temperature treatment to induce boron nitride to self-assemble into an aerogel precursor composed of micro- and nanofibers. After a second freeze-drying, a boron nitride aerogel precursor composed of micro- and nanobelts is obtained.

[0012] Step 4: Preparation of breathable, flexible, and heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro- and nano-belts obtained in Step 3 is placed in a tube furnace for heating and then naturally cooled to room temperature to obtain the breathable, flexible, and heat-insulating boron nitride aerogel material.

[0013] This invention uses a mixture of polymerizable monomers, crosslinking agents, and co-crosslinking agents as an oil phase, which provides a stable three-dimensional porous gel framework structure as the main support structure after polymerization. A mixture of boron source molecules, nitrogen source molecules, and solvent is used as an aqueous phase. The aqueous phase is added dropwise to the oil phase, followed by the addition of stabilizers and initiators, to form a high internal phase emulsion, which is then polymerized. This makes the three-dimensional porous gel framework structure more permeable. After polymerization, a low-temperature treatment is performed to further promote the self-assembly process of boron nitride fibers. Under low-temperature conditions, the nitrogen and boron sources contained in the aqueous phase further crystallize on the three-dimensional porous gel framework structure to form boron nitride micro / nano ribbons, which are tightly bonded to and intertwined with mullite fibers, forming a micro / nano ribbon-like fiber gel. The system is then freeze-dried to remove moisture, and finally, through high-temperature pyrolysis, a breathable, fully flexible, and heat-insulating boron nitride aerogel material is obtained.

[0014] This invention uses mullite fibers, which have structural reinforcement and stabilizing functions, as a stabilizer for high internal phase emulsions. The mullite fibers modified with vinyltriethoxysilane contain a stacked structure, which improves their mechanical strength and thermal insulation properties. They can quickly diffuse and accumulate at the oil-water interface, stabilizing the entire system to form a stable high internal phase emulsion. An initiator is used to initiate free radical polymerization. This invention adds the aqueous phase dropwise to the oil phase, allowing the oil phase to encapsulate as much water as possible. At the same time, it avoids directly adding mullite fibers to the oil phase to prevent overheating and direct polymerization of the oil phase.

[0015] In this invention, the mixture obtained under high-speed oscillation is observed to be highly viscous, exhibiting a jelly-like emulsion. After standing, the test tube is inverted for observation, and the system loses its fluidity, thus obtaining a high internal phase emulsion.

[0016] The above-described method for preparing a breathable, fully flexible, heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that the mass of mullite fibers in the stabilizer solution in step one is 1% to 5% of the volume of vinyltriethoxysilane, where the mass unit is mg and the volume unit is μL. In this invention, mullite fibers serve as the main structural stabilizer for the fibrous structure of the aerogel, and the main function of triethoxysilane is to modify the surface of the mullite fibers, making them contain siloxane bonds on the surface, thereby promoting the stability of the oil-water interface.

[0017] The above-mentioned method for preparing breathable, fully flexible, and heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that, in step two, the polymerizable monomer is octadecyl acrylate, the crosslinking agent is ethylene glycol dimethacrylate, the co-crosslinking agent is trimethylolpropane trimethacrylate, the boron source molecule is selected from one or more of boric acid, boric anhydride, and sodium borate, the nitrogen source molecule is selected from one or more of urea, melamine, and polyvinylimide, the solvent is selected from one or more of distilled water, ethanol, and tert-butanol, and the initiator is azobisisobutyronitrile.

[0018] The above-mentioned method for preparing breathable, fully flexible, heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that, in step two, the mass fractions of polymerizable monomers, crosslinking agents, and co-crosslinking agents in the oil phase are all 8.3% to 75.0%, the mass of the boron source is 21% to 42% of the volume of the aqueous phase, the mass of the nitrogen source is 21% to 42% of the volume of the aqueous phase, the mass of the stabilizer is 4% to 5% of the volume of the oil phase, and the mass of the initiator is 1% to 2% of the volume of the oil phase, wherein the unit of mass is mg and the unit of volume is μL. This invention achieves optimal polymerizable monomers and their ratio to crosslinking agents by controlling the mass fractions of polymerizable monomers, crosslinking agents, and co-crosslinking agents in the oil phase, and by using vinyltriethoxysilane-modified mullite fibers as a high internal phase emulsion stabilizer. By optimizing the stabilizer content, the stabilizer content is reduced from the commonly reported 5%–20% to 1%–5%, resulting in a highly efficient and stable high internal phase emulsion. Furthermore, by controlling the mass of boron and nitrogen sources and maintaining a molar ratio of 2:1, this invention enables more effective formation of the micro / nano structure of boron nitride aerogel. This suitable ratio also promotes good flexibility of boron nitride after thermal decomposition. Finally, by controlling the mass of the initiator to trigger subsequent polymerization reactions, and by controlling the doping amount of mullite fibers to control the quantity of mullite fibers in the lightweight insulating aerogel, this invention further controls the mass fractions of nitrogen and boron sources in the aqueous phase to further adjust the crystallinity of the boron nitride fiber micro / nano ribbons, ensuring the density and insulation effect of the lightweight, high-temperature resistant insulating aerogel.

[0019] The above-mentioned method for preparing breathable, fully flexible, heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that the volume ratio of the oil phase and the water phase in step two is 220:1600-4800. This invention uses mullite fiber as a stabilizer. This system meets the limitations of traditional high internal phase emulsions, requiring an internal phase volume fraction greater than 74% to form a stable high internal phase emulsion. The water content of the high internal phase emulsion can be widely controlled from 86.9% to 95.2%, broadening the application range of the internal phase volume of the high internal phase emulsion. By initiating the polymerization of the continuous phase in the system, the dispersed phase volume fraction exists as a pore-forming agent in the system. Simultaneously, nitrogen and boron sources in the aqueous phase are attached to the organic framework structure formed by the aerogel. Orientation and crystallization occur at a lower temperature, and boron nitride aerogel is formed by freeze-drying. This aerogel possesses the properties of both boron nitride and aerogel. The content of nitrogen and boron sources plays a decisive role in the density, strength, porosity, and thermal conductivity of the aerogel. After continuous phase polymerization, the dispersed phase is removed by drying, and high-temperature pyrolysis effectively reduces the density of the aerogel material, increases the porosity of the aerogel, and reduces the thermal conductivity of the aerogel.

[0020] The above-mentioned method for preparing breathable, fully flexible, and heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that the preparation process of the aqueous phase in step two is as follows: small molecules of boron source and small molecules of nitrogen source are dissolved in a solvent, then heated to 80℃~85℃ and continuously stirred to obtain a clear aqueous phase; the aqueous phase is added dropwise to the oil phase while maintaining the temperature of the aqueous phase at 35℃~40℃. This invention uses high temperature and continuous stirring to ensure complete dissolution and obtain a clear aqueous phase. In this invention, the temperature of the aqueous phase is maintained at 35℃~40℃ when it is added dropwise to the oil phase to prevent the nitrogen source and its precipitation due to excessively low temperature.

[0021] The above-mentioned method for preparing breathable, fully flexible, and heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that the polymerization process in step three is as follows: prepolymerization at 45℃~65℃ for 6h~8h, followed by further polymerization at 75℃~95℃ for 12h~20h; the first and second freeze-drying times are both greater than 24h, and the low-temperature treatment is held at -5℃ for more than 10h. This invention achieves prepolymerization and polymerization through gradient temperature control, followed by placing the polymerized material in a room temperature environment and performing a first freeze-drying and low-temperature treatment. The purpose is to allow the nitrogen and boron sources to self-assemble into interwoven micro / nanofibers at low temperatures. Finally, a second freeze-drying is performed to remove the aqueous phase from the system, yielding a micro / nanofiber ribbon-like fiber gel.

[0022] The method described above for preparing breathable, fully flexible, and thermally insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that the heating process in step four involves heating to 1000℃~1200℃ at a heating rate of 5℃ / min~10℃ / min and then holding at that temperature for 3h~4h. This invention, by controlling the heating parameters, makes the aerogel network structure more permeable while further promoting the tight bonding between the glass fiber and the three-dimensional skeleton structure, resulting in a lightweight, breathable, and thermally insulating aerogel.

[0023] The above-mentioned method for preparing a breathable, fully flexible, heat-insulating boron nitride aerogel material based on a high internal phase emulsion is characterized in that the density of the breathable, fully flexible, heat-insulating boron nitride aerogel material in step four is 60 mg / cm³. 3 ~220mg / cm 3 The porosity is not less than 82.9%, the thermal conductivity is not greater than 29 mW / (m·K), and it can withstand a high temperature of 1200℃ for more than 20 minutes. The breathable, fully flexible, heat-insulating boron nitride aerogel material prepared by this invention has a wide density control range, as well as a relatively low thermal conductivity and good breathability.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. This invention utilizes a high internal phase emulsion template method, mixing polymerizable monomers, crosslinking agents, and co-crosslinking agents to obtain an oil phase. An aqueous phase containing nitrogen and boron sources, a stabilizer, and an initiator are then added and mixed to form a high internal phase emulsion. Polymerization allows the network structure formed by the polymer monomers to tightly bond with mullite fibers. The emulsion is then placed at a low temperature, allowing the nitrogen and boron sources in the aqueous phase to assemble, forming boron nitride fiber micro / nanobelts. Through freeze-drying and high-temperature pyrolysis, a breathable, fully flexible, and heat-insulating boron nitride aerogel material is obtained. This material possesses low thermal conductivity and density, achieving excellent high-temperature insulation and breathability. It also allows for precise control of porosity, pore size, and thermal conductivity, while maintaining excellent mechanical properties, thus broadening the application range of aerogel products and enabling heat insulation applications in extreme high-temperature environments.

[0026] 2. This invention proposes a novel strategy for preparing high internal phase emulsions based on mullite fibers as stabilizers. Employing a high internal phase emulsion template method, the transformation from a "gel state" to a "composite aerogel" is achieved through free radical-initiated polymerization. This improved preparation method differs from the complex and time-consuming sol-gel process, offering a simpler preparation process with fewer restrictions on raw materials. Furthermore, an organic polymer framework can be used as a reinforcing structure, along with supporting reinforcement structures. This allows boron nitride fibers to interpenetrate and interweave within the mesh of the three-dimensional framework, forming a three-dimensional network structure. This effectively exhibits the excellent flexibility and connectivity of the fibers, achieving uniform formation of boron nitride micro / nanofiber bands from the inside out within the aerogel.

[0027] 3. The high internal phase emulsion template method used in this invention is based on the use of novel stabilizers. Nitrogen and boron sources are cleverly dissolved in the aqueous phase. The non-covalent bonds between the components cause them to spontaneously arrange and assemble, realizing the role of supramolecular assembly in the preparation of inorganic materials. Due to the control process in the wet chemistry stage, the method of preparing boron nitride aerogel using high internal phase emulsion as template has diversity and tunability in specific properties, endowing the aerogel with corresponding properties. The method is simple to operate, has low equipment requirements, and is suitable for large-scale production.

[0028] 4. The present invention provides a novel method for preparing boron nitride aerogel. The prepared flexible boron nitride micro-nano aerogel exhibits good flexibility in the range of -196℃ to 1200℃, avoiding the limitation that traditional boron nitride aerogel can only withstand about 900℃. The aerogel material obtained by this method has good flexibility and also exhibits compressive, shear, and bending properties.

[0029] 5. This invention uses mullite fiber as a high internal phase emulsion stabilizer, and finds that its content can be between 1% and 5%, breaking through the lowest limit previously reported at home and abroad. The explored system forms a stable high internal phase emulsion, and the water content of the high internal phase emulsion can be controlled in a wide range from 86.9% to 95.2%. This breakthrough in internal phase volume broadens the application range of high internal phase emulsions. By initiating continuous phase polymerization, the water content plays a decisive role in the density and porosity of porous aerogel materials. Because water does not participate in polymerization, increasing the water content can effectively reduce the density of porous aerogel materials and increase the porosity of aerogels, but does not significantly reduce the thermal conductivity of aerogels.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the preparation of a breathable, fully flexible, heat-insulating boron nitride aerogel material according to the present invention.

[0032] Figure 2 This is a scanning electron microscope image of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 1 of the present invention.

[0033] Figure 3 This is a test image showing the high flexibility of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 6 of the present invention.

[0034] Figure 4 This is a scanning electron microscope image of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 6 of the present invention.

[0035] Figure 5The image shows the X-ray diffraction pattern of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 6 of this invention.

[0036] Figure 6 The image shows the Raman spectrum of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 6 of this invention.

[0037] Figure 7 This is an elemental distribution diagram of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 6 of the present invention.

[0038] Figure 8 This is a schematic diagram illustrating the high-temperature thermal insulation effect of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in Example 6 of the present invention.

[0039] Figure 9 The image shows a physical sample of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared by scale-up testing using the method described in Example 6 of this invention. Detailed Implementation

[0040] Figure 1 This is a flowchart illustrating the preparation of a breathable, fully flexible, heat-insulating boron nitride aerogel material according to the present invention. Figure 1 As can be seen from the diagram, this invention first mixes the oil phase and the water phase, which are immiscible and form an interface. Then, a stabilizer and an initiator are added and the mixture is shaken and mixed to form a high internal phase emulsion, which allows the mullite fibers and the three-dimensional network structure of the aerogel to be fully entangled. Then, a porous polymer aerogel material is obtained through staged heating polymerization. Subsequently, a supramolecular assembly process is carried out through a first freeze-drying and low-temperature treatment to form a boron nitride precursor material with an internal phase structure composed of micro- and nano-ribbons. Then, freeze-drying is performed to remove the water phase from the entire system. Finally, high-temperature thermal decomposition is carried out by heating to obtain a thermally insulating aerogel with a three-dimensional network structure formed by boron nitride micro- and nano-ribbons, namely, a breathable and fully flexible thermally insulating boron nitride aerogel material. The right side of the breathable and fully flexible thermally insulating boron nitride aerogel material is an enlarged view of a single boron nitride micro- and nano-ribbon, and the right side of the enlarged view of a single boron nitride micro- and nano-ribbon is a ball-and-stick model of a single boron nitride fiber.

[0041] Example 1

[0042] This embodiment includes the following steps:

[0043] Step 1: Preparation of stabilizer: At room temperature, 5 mg of mullite fiber is dispersed in 5 mL of vinyltriethoxysilane, mixed and shaken, and after 100 min, the solution turns clear, thus obtaining the stabilizer.

[0044] Step 2: Preparation of high internal phase emulsion: At room temperature, 160 μL of octadecyl acrylate, 40 μL of ethylene glycol dimethacrylate, and 20 μL of trimethylolpropane trimethacrylate were mixed to obtain an oil phase. Then, 1.2 g of boric acid and 1.2 g of melamine in a molar ratio of 1:2 were dissolved in 5.7 mL of distilled water. The mixture was then heated to 85 °C and stirred continuously until the system became transparent, yielding an aqueous phase. 1600 μL of the aqueous phase at 40 °C was then added dropwise to 220 μL of the oil phase, followed by the addition of 10 μL of the stabilizer prepared in Step 1 and 2 mg of azobisisobutyronitrile (AIBN) and shaken. A whitish gel-like emulsion was obtained. After standing, the test tube was inverted for observation. The system lost its fluidity, yielding a high internal phase emulsion.

[0045] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 was prepolymerized in an oil bath at 60°C for 8 hours, and then the temperature was raised to 90°C for 15 hours for further polymerization. The product was then freeze-dried for the first time for 24 hours to obtain porous polymer aerogel with ultra-low density. The porous polymer aerogel was then placed in a refrigerator at -5°C for 10 hours, and then freeze-dried for the second time for 24 hours to obtain boron nitride aerogel precursor composed of micro-nano ribbons.

[0046] Step 4: Preparation of breathable, fully flexible, heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro-nano ribbons obtained in Step 3 is placed in a tube furnace and heated to 1200℃ at a heating rate of 10℃ / min, and then kept at that temperature for 4 hours. After that, it is naturally cooled to room temperature to obtain the breathable, fully flexible, heat-insulating boron nitride aerogel material.

[0047] The density of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment was measured to be 0.17 g / cm³. 3 It has a porosity of 85.4%, a thermal conductivity of 28 mW / (m·K), and can withstand a high temperature of 1200℃ for more than 20 minutes.

[0048] In this embodiment, the boron source may also be one or more of boric acid, boric anhydride, and sodium borate; the nitrogen source may also be one or more of urea, melamine, and polyvinylimide; and the solvent may also be one or more of distilled water, ethanol, and tert-butanol.

[0049] Figure 2 This is a scanning electron microscope image of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment. Figure 2 As can be seen from the image, the internal microstructure of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment is composed of intertwined nanoribbons or microribbons.

[0050] Example 2

[0051] This embodiment includes the following steps:

[0052] Step 1: Preparation of stabilizer: At room temperature, 4 mg of mullite fiber was dispersed in 5 mL of vinyltriethoxysilane, mixed and shaken, and after 150 min, the solution turned clear, thus obtaining the stabilizer.

[0053] Step 2: Preparation of high internal phase emulsion: At room temperature, 160 μL of octadecyl acrylate, 40 μL of ethylene glycol dimethacrylate, and 20 μL of trimethylolpropane trimethacrylate were mixed to obtain an oil phase. Then, 2.4 g of boric acid and 2.4 g of melamine in a molar ratio of 1:2 were dissolved in 5.7 mL of distilled water. The mixture was then heated to 80 °C and stirred continuously until the system became transparent, yielding an aqueous phase. 1600 μL of the aqueous phase at 35 °C was then added dropwise to 220 μL of the oil phase, followed by 9 μL of the stabilizer prepared in Step 1 and 3 mg of azobisisobutyronitrile (AIBN). The mixture was shaken, resulting in a whitish gel-like emulsion. After standing, the test tube was inverted for observation. The system lost its fluidity, yielding a high internal phase emulsion.

[0054] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 was prepolymerized in an oil bath at 55°C for 8 hours, and then the temperature was raised to 85°C for further polymerization for 16 hours. The product was then freeze-dried for the first time for 24 hours to obtain porous polymer aerogel with ultra-low density. The porous polymer aerogel was then placed in a refrigerator at -5°C for 10 hours, and then freeze-dried for the second time for 24 hours to obtain boron nitride aerogel precursor composed of micro-nano ribbons.

[0055] Step 4: Preparation of breathable, flexible, and heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro- and nano-belts obtained in Step 3 is placed in a tube furnace, heated to 1100℃ at a heating rate of 5℃ / min, and held at that temperature for 3 hours. Then it is naturally cooled to room temperature to obtain the breathable, flexible, and heat-insulating boron nitride aerogel material.

[0056] The density of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment was measured to be 0.14 g / cm³. 3 It has a porosity of 88.4%, a thermal conductivity of 28.7 mW / (m·K), and can withstand a high temperature of 1200℃ for more than 20 minutes.

[0057] In this embodiment, the boron source may also be one or more of boric acid, boric anhydride, and sodium borate; the nitrogen source may also be one or more of urea, melamine, and polyvinylimide; and the solvent may also be one or more of distilled water, ethanol, and tert-butanol.

[0058] Example 3

[0059] This embodiment includes the following steps:

[0060] Step 1: Preparation of stabilizer: At room temperature, 3 mg of mullite fiber was dispersed in 5 mL of vinyltriethoxysilane, mixed and shaken, and after 80 min, the solution turned clear, thus obtaining the stabilizer.

[0061] Step 2: Preparation of high internal phase emulsion: At room temperature, 160 μL of octadecyl acrylate, 40 μL of ethylene glycol dimethacrylate, and 20 μL of trimethylolpropane trimethacrylate were mixed to obtain an oil phase. Then, 2.0 g of boric acid and 2.0 g of melamine in a molar ratio of 1:2 were dissolved in 5.7 mL of distilled water. The mixture was then heated to 82 °C and stirred continuously until the system became transparent, yielding an aqueous phase. 2000 μL of the aqueous phase at 40 °C was then added dropwise to 220 μL of the oil phase, followed by 11 μL of the stabilizer prepared in Step 1 and 4 mg of azobisisobutyronitrile (AIBN). The mixture was shaken, resulting in a whitish gel-like emulsion. After standing, the test tube was inverted for observation. The system lost its fluidity, yielding a high internal phase emulsion.

[0062] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 is prepolymerized in an oil bath at 50°C for 8 hours, and then the temperature is raised to 95°C for 12 hours for further polymerization. The product is then freeze-dried for the first time for 24 hours to obtain porous polymer aerogel with ultra-low density. The porous polymer aerogel is then placed in a refrigerator at -5°C for 10 hours, and then freeze-dried for the second time for 24 hours to obtain boron nitride aerogel precursor composed of micro-nano ribbons.

[0063] Step 4: Preparation of breathable, fully flexible, heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro-nano ribbons obtained in Step 3 is placed in a tube furnace and heated to 1150℃ at a heating rate of 7℃ / min, and then held at that temperature for 3.5h. After that, it is naturally cooled to room temperature to obtain the breathable, fully flexible, heat-insulating boron nitride aerogel material.

[0064] The density of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment was measured to be 0.15 g / cm³. 3 It has a porosity of 82.9%, a thermal conductivity of 28.9 mW / (m·K), and can withstand a high temperature of 1200℃ for more than 20 minutes.

[0065] In this embodiment, the boron source may also be one or more of boric acid, boric anhydride, and sodium borate; the nitrogen source may also be one or more of urea, melamine, and polyvinylimide; and the solvent may also be one or more of distilled water, ethanol, and tert-butanol.

[0066] Example 4

[0067] This embodiment includes the following steps:

[0068] Step 1: Preparation of stabilizer: At room temperature, 2 mg of mullite fiber was dispersed in 5 mL of vinyltriethoxysilane, mixed and shaken, and after 50 min, the solution turned clear, thus obtaining the stabilizer.

[0069] Step 2: Preparation of high internal phase emulsion: At room temperature, 160 μL of octadecyl acrylate, 40 μL of ethylene glycol dimethacrylate, and 20 μL of trimethylolpropane trimethacrylate were mixed to obtain an oil phase. Then, 2.4 g of boric acid and 2.4 g of melamine in a molar ratio of 1:2 were dissolved in 5.7 mL of distilled water. The mixture was then heated to 83 °C and stirred continuously until the system became transparent, yielding an aqueous phase. 3000 μL of the aqueous phase at 37 °C was then added dropwise to 220 μL of the oil phase, followed by the addition of 10 μL of the stabilizer prepared in Step 1 and 2 mg of azobisisobutyronitrile (AIBN) and shaken. A whitish gel-like emulsion was formed. After standing, the test tube was inverted for observation. The system lost its fluidity, yielding a high internal phase emulsion.

[0070] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 was prepolymerized in an oil bath at 45°C for 7 hours, and then the temperature was raised to 75°C for 20 hours for further polymerization. The product was then freeze-dried for 24 hours to obtain porous polymer aerogel with ultra-low density. The porous polymer aerogel was then placed in a refrigerator at -5°C for 10 hours, and then freeze-dried for 24 hours to obtain boron nitride aerogel precursor composed of micro-nano ribbons.

[0071] Step 4: Preparation of breathable, flexible, and heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro- and nano-belts obtained in Step 3 is placed in a tube furnace and heated to 1200℃ at a heating rate of 8℃ / min, and then kept at that temperature for 4 hours. After that, it is naturally cooled to room temperature to obtain the breathable, flexible, and heat-insulating boron nitride aerogel material.

[0072] The density of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment was measured to be 0.1 g / cm³. 3 It has a porosity of 92%, a thermal conductivity of 28.4 mW / (m·K), and can withstand a high temperature of 1200℃ for more than 20 minutes.

[0073] In this embodiment, the boron source may also be one or more of boric acid, boric anhydride, and sodium borate; the nitrogen source may also be one or more of urea, melamine, and polyvinylimide; and the solvent may also be one or more of distilled water, ethanol, and tert-butanol.

[0074] Example 5

[0075] This embodiment includes the following steps:

[0076] Step 1: Preparation of stabilizer: At room temperature, 1 mg of mullite fiber is dispersed in 5 mL of vinyltriethoxysilane, mixed and shaken, and after 30 min, the solution turns clear, thus obtaining the stabilizer.

[0077] Step 2: Preparation of high internal phase emulsion: At room temperature, 160 μL of octadecyl acrylate, 40 μL of ethylene glycol dimethacrylate, and 20 μL of trimethylolpropane trimethacrylate were mixed to obtain an oil phase. Then, 2.4 g of boric acid and 2.4 g of melamine in a molar ratio of 1:2 were dissolved in 5.7 mL of distilled water. The mixture was then heated to 81 °C and stirred continuously until the system became transparent, yielding an aqueous phase. 4400 μL of the aqueous phase at 35 °C was then added dropwise to 220 μL of the oil phase, followed by the addition of 10 μL of the stabilizer prepared in Step 1 and 2 mg of azobisisobutyronitrile (AIBN) and shaken. A whitish gel-like emulsion was formed. After standing, the test tube was inverted for observation. The system lost its fluidity, yielding a high internal phase emulsion.

[0078] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 was prepolymerized in an oil bath at 65°C for 6 hours, and then the temperature was raised to 80°C for further polymerization for 18 hours. The product was then freeze-dried for the first time for 24 hours to obtain a porous polymer aerogel with ultra-low density. The porous polymer aerogel was then placed in a refrigerator at -5°C for 10 hours, and then freeze-dried for the second time for 24 hours to obtain a boron nitride aerogel precursor composed of micro-nano ribbons.

[0079] Step 4: Preparation of breathable, flexible, and heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro- and nano-belts obtained in Step 3 is placed in a tube furnace, heated to 1200℃ at a heating rate of 6℃ / min, and held at that temperature for 4 hours. Then it is naturally cooled to room temperature to obtain the breathable, flexible, and heat-insulating boron nitride aerogel material.

[0080] The density of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment was measured to be 0.08 g / cm³. 3 It has a porosity of 93.8%, a thermal conductivity of 26.3 mW / (m·K), and can withstand a high temperature of 1200℃ for more than 20 minutes.

[0081] In this embodiment, the boron source may also be one or more of boric acid, boric anhydride, and sodium borate; the nitrogen source may also be one or more of urea, melamine, and polyvinylimide; and the solvent may also be one or more of distilled water, ethanol, and tert-butanol.

[0082] Example 6

[0083] This embodiment includes the following steps:

[0084] Step 1: Preparation of stabilizer: At room temperature, 5 mg of mullite fiber is dispersed in 5 mL of vinyltriethoxysilane, mixed and shaken, and after 150 min, the solution turns clear, thus obtaining the stabilizer.

[0085] Step 2: Preparation of high internal phase emulsion: At room temperature, 160 μL of octadecyl acrylate, 40 μL of ethylene glycol dimethacrylate, and 20 μL of trimethylolpropane trimethacrylate were mixed to obtain an oil phase. Then, 2.4 g of boric acid and 2.4 g of melamine in a molar ratio of 1:2 were dissolved in 5.7 mL of distilled water. The mixture was then heated to 80 °C and stirred continuously until the system became transparent, yielding an aqueous phase. 4800 μL of the aqueous phase at 40 °C was then added dropwise to 220 μL of the oil phase, followed by the addition of 10 μL of the stabilizer prepared in Step 1 and 2 mg of azobisisobutyronitrile (AIBN) and shaken. A whitish gel-like emulsion was formed. After standing, the test tube was inverted for observation. The system lost its fluidity, yielding a high internal phase emulsion.

[0086] Step 3: Preparation of porous polymer aerogel with ultra-low density: The high internal phase emulsion obtained in step 2 was prepolymerized in an oil bath at 60°C for 8 hours, and then the temperature was raised to 90°C for 15 hours for further polymerization. The product was then freeze-dried for the first time for 24 hours to obtain porous polymer aerogel with ultra-low density. The porous polymer aerogel was then placed in a refrigerator at -5°C for 10 hours, and then freeze-dried for the second time for 24 hours to obtain boron nitride aerogel precursor composed of micro-nano ribbons.

[0087] Step 4: Preparation of breathable, fully flexible, heat-insulating boron nitride aerogel material: The boron nitride aerogel precursor composed of micro-nano ribbons obtained in Step 3 is placed in a tube furnace and heated to 1200℃ at a heating rate of 10℃ / min, and then kept at that temperature for 4 hours. After that, it is naturally cooled to room temperature to obtain the breathable, fully flexible, heat-insulating boron nitride aerogel material.

[0088] The density of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment was measured to be 0.06 g / cm³. 3 It has a porosity of 94.3%, a thermal conductivity of 27.8 mW / (m·K), and can withstand a high temperature of 1200℃ for more than 20 minutes.

[0089] In this embodiment, the boron source may also be one or more of boric acid, boric anhydride, and sodium borate; the nitrogen source may also be one or more of urea, melamine, and polyvinylimide; and the solvent may also be one or more of distilled water, ethanol, and tert-butanol.

[0090] Figure 3This is a test image showing the high flexibility of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment. Figure 3 As can be seen from the figure, the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment has good flexibility. The lower right corner of the figure indicates that the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment can be used as a flexible felt or rolled into a corresponding pattern.

[0091] Figure 4 This is a scanning electron microscope image of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment. Figure 4 As can be seen, the internal microstructure of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment consists of intertwined nanoribbons or microribbons. Figure 4 and Figure 3 The comparison shows that the difference between Example 1 and Example 6 lies in the different contents of boron and nitrogen sources in the aqueous phase. The laboratory results show that the microstructure and fiber length of the aerogel are not very correlated with the change in boron nitride content. It can also be seen that the internal microstructure is still composed of intertwined nanoribbons or microribbons. The material is interconnected from top to bottom and has good permeability. Furthermore, the test shows that the pressure drop at both ends of the material is small, which proves that the material has good air permeability.

[0092] Figure 5 The X-ray diffraction pattern of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment is shown below. Figure 5 As can be seen from the data, the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment exhibits 100 and 002 crystal planes at approximately 25° and 43°, which conforms to the Bragg diffraction law. The breathable, fully flexible, heat-insulating boron nitride aerogel material has high crystallinity and conforms to the XRD standard card of hexagonal boron nitride.

[0093] Figure 6 The image shows the Raman spectrum of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment, combined with... Figure 5 XRD and Figure 6 It can be seen that the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment has high crystallinity, exhibiting the same characterization results as hexagonal boron nitride. In the figure, E2g represents the asymmetric stretching mode, 1367.5 cm⁻¹. -1 This indicates that this is a typical Raman spectrum of a hexagonal boron nitride aerogel.

[0094] Figure 7 This is an elemental distribution map of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment. Figure 7 As can be seen from the image, the elemental distribution and composition of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment include nitrogen, boron, and oxygen.

[0095] Figure 8 This is a schematic diagram illustrating the high-temperature thermal insulation effect of the breathable, fully flexible, thermally insulating boron nitride aerogel material prepared in this embodiment. Figure 8 It can be seen that when the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared in this embodiment is subjected to a high-temperature continuous heating test, the material can resist ablation and is flame-retardant at a high temperature of 1200℃. Furthermore, when the heat source is removed, no oxidation, blackening, or structural breakage occurs on the surface of the aerogel material.

[0096] Figure 9 The image shows a physical sample of the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared using the method described in this embodiment for scale-up testing. Figure 9 As can be seen, the breathable, fully flexible, heat-insulating boron nitride aerogel material prepared through scale-up experiments has excellent properties that allow for scale-up preparation, and the corresponding shapes can be prepared according to the mold.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsions, characterized in that, The method comprises the following steps: Step one, preparation of stabilizer: disperse mullite fibers in vinyl triethoxysilane at room temperature, mix and shake to obtain the stabilizer; Step two, preparation of high internal phase emulsion: mix polymerizable monomer, crosslinking agent and co-crosslinking agent to obtain oil phase at room temperature, then mix boron source small molecule, nitrogen source small molecule and solvent to obtain water phase, then add water phase drop by drop into oil phase, then add stabilizer prepared in step one and initiator and shake to obtain high internal phase emulsion; Step three, preparation of porous polymer aerogel with ultra-low density: polymerize high internal phase emulsion obtained in step two in an oil bath, then perform first freeze drying on the product to obtain porous polymer aerogel with ultra-low density, then perform low temperature treatment on the porous polymer aerogel, then perform second freeze drying to obtain boron nitride aerogel precursor composed of micro-nano strips; the low temperature treatment is to keep the temperature below-5℃ for more than 10h; Step four, preparation of breathable full-flexible thermal insulation boron nitride aerogel material: place boron nitride aerogel precursor composed of micro-nano strips obtained in step three into a tube furnace to heat, then naturally cool to room temperature to obtain the breathable full-flexible thermal insulation boron nitride aerogel material.

2. The method for preparing a breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsions according to claim 1, characterized in that The mass of mullite fibers in the stabilizer solution in step one is 1% to 5% of the volume of vinyl triethoxysilane, wherein the unit of mass is mg and the unit of volume is μL.

3. The method for preparing a breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsion according to claim 1, characterized in that, The polymerizable monomer in step two is octadecyl acrylate, the crosslinking agent is ethylene glycol dimethacrylate, the co-crosslinking agent is trimethylolpropane trimethacrylate, the boron source small molecule is selected from one or more than two of boric acid, boric anhydride and sodium borate, the nitrogen source small molecule is selected from one or more than two of urea, melamine and polyvinyl imine, the solvent is selected from one or more than two of distilled water, ethanol and tert-butanol, and the initiator is azobisisobutyronitrile.

4. The method for preparing a breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsions according to claim 1, characterized in that, The mass fraction of polymerizable monomer, crosslinking agent and co-crosslinking agent in the oil phase in step two is 8.3% to 75.0%, the mass of boron source is 21% to 42% of the volume of water phase, the mass of nitrogen source is 21% to 42% of the volume of water phase, the mass of stabilizer is 4% to 5% of the volume of oil phase, and the mass of initiator is 1% to 2% of the volume of oil phase, wherein the unit of mass is mg and the unit of volume is μL.

5. The method for preparing a breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsions according to claim 1, characterized in that The volume ratio of oil phase to water phase in step two is 220:1600 to 4800.

6. The method of claim 1, wherein the method of preparing a full-flexible thermal insulation boron nitride aerogel material based on high internal phase emulsion is characterized by, The preparation process of water phase in step two is: dissolve boron source small molecule and nitrogen source small molecule in solvent, then heat to 80℃ to 85℃ and continuously stir to obtain water phase; the temperature of water phase is kept at 35℃ to 40℃ when water phase is added drop by drop into oil phase.

7. The method of claim 1, wherein the method of preparing a full-flexible thermal insulation boron nitride aerogel material based on high internal phase emulsion is characterized by, The polymerization process in step three is: pre-polymerize at 45℃ to 65℃ for 6h to 8h, then further polymerize at 75℃ to 95℃ for 12h to 20h; the time of first freeze drying and second freeze drying is both greater than 24h.

8. The method for preparing a breathable, fully flexible, thermally insulating boron nitride aerogel material based on high internal phase emulsions according to claim 1, characterized in that The heating process in step four is heating to 1000-1200℃ at a temperature increasing rate of 5-10℃ / min and then holding for 3-4h.

9. The method of claim 1, wherein the method of preparing a fully flexible and breathable boron nitride aerogel material based on high internal phase emulsion is characterized by, The density of the breathable full-flexible thermal insulation boron nitride aerogel material in step four is 60 mg / cm 3 220 mg / cm 3 The porosity is not less than 82.9%, the thermal conductivity is not greater than 29 mW / (m·K), and the high temperature resistance is 1200℃ for more than 20 minutes.

Images