Boron nitride / aramid nanofiber aerogel and preparation method thereof

Abstract

The application provides a boron nitride / aramid nanofiber aerogel and a preparation method thereof, and comprises the following steps: dispersing chopped aramid fibers and boron nitride nanobelt powder in an organic solvent to react, so as to obtain aramid nanofiber / boron nitride hydrogel; and performing liquid nitrogen directional freezing and freeze-drying treatment on the aramid nanofiber / boron nitride hydrogel, so as to obtain the boron nitride / aramid nanofiber aerogel; the boron nitride aerogel (inorganic aerogel) and the aramid nanofiber aerogel (organic aerogel) are effectively integrated together; due to the hydrogen bond effect, the flexible boron nitride nanobelt with a high aspect ratio is firmly locked by the aramid fibers; after the filtration and liquid nitrogen directional freezing operation, the boron nitride / aramid nanofiber aerogel is assembled into a lamellar structure inside, so that a multifunctional integrated aerogel with heat insulation, elasticity, flexibility, flame retardation and thermal stability is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of thermal insulation and flexible materials, and particularly relates to a boron nitride / aramid nanofiber aerogel and a preparation method thereof. BACKGROUND

[0002] Aerogels are attractive due to their low density and thermal conductivity, high porosity and large specific surface area, which makes them can be applied in various fields, such as aerospace, electronics, energy storage and conversion, environmental remediation and biomedical, etc. In the past few years, inorganic aerogels (such as carbon-based, ceramic-based and metal-based aerogels), polymer-based aerogels and organic aerogels have dominated the development of aerogels. However, due to the drawbacks of traditional inorganic aerogels such as easy oxidation, inherent brittleness and difficult processing, their application in thermal insulation and mechanical elasticity is severely limited. Although polymer-based aerogels have excellent performance in flexibility, ultra-lightness, etc., they have poor environmental stability and are prone to decomposition, which limits their application fields. Studies have shown that effectively integrating the characteristics of inorganic aerogels and organic aerogels into an aerogel with excellent elasticity and thermal insulation performance is the future direction of development, but so far, there have been few studies on such aerogels.

[0003] Aramid fiber, a kind of fiber material developed by American DuPont Company in the 1960s, is one of the world's three high-tech fibers along with carbon fiber and ultra-high molecular weight polyethylene fiber, and has excellent mechanical properties, high strength, high modulus, good thermal stability and chemical stability, friction resistance, flame resistance and other characteristics, and is widely used in civilian and national defense and military fields.

[0004] Aramid nanofiber aerogel prepared by using short-cut aramid fiber has low thermal conductivity, excellent flame retardancy, thermal stability and high specific strength, and has broad application prospects in supercapacitors, wearable materials, thermal insulation and the like; aramid nanofiber aerogel makes up for the shortcomings of traditional polymer aerogels in poor thermal stability, and is expected to be used in high-temperature fields (> 200℃); however, the pure aramid nanofiber aerogel prepared at present has poor mechanical resilience, and is not suitable for serving in fields that require thermal insulation, flexibility and elasticity at the same time.

[0005] However, the cross-linking agent is mainly composed of organic polymers, and cannot enhance the mechanical elasticity of aramid nanofiber aerogel at high temperature.

[0006] In recent years, boron nitride nanobelt has attracted attention due to its length of tens to hundreds of microns, high aspect ratio and thermal stability, and the aerogel prepared by using boron nitride nanobelt can exhibit excellent flexibility, elasticity and thermal stability.

[0007] If a kind of organic aerogel (aramid nanofiber aerogel) and inorganic aerogel (boron nitride aerogel) is designed to be set in an aerogel, the heat insulation, flexibility, elasticity, flame retardant and other performances of organic aerogel and inorganic aerogel are set in an aerogel, to meet the application requirements in more fields. However, there is no related aerogel reported and patented. SUMMARY

[0008] The present application aims to provide a boron nitride / aramid nanofiber aerogel and a preparation method thereof, which solves the above problems in the prior art.

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0010] The present application provides a preparation method of a boron nitride / aramid nanofiber aerogel, comprising the following steps:

[0011] The chopped aramid fibers and boron nitride nanobelt powder are dispersed in an organic solvent to react, to obtain aramid nanofiber / boron nitride hydrogel;

[0012] The aramid nanofiber / boron nitride hydrogel is subjected to directional freezing and freeze-drying treatment with liquid nitrogen, to obtain boron nitride / aramid nanofiber aerogel.

[0013] Preferably, the chopped aramid fibers and boron nitride nanobelt powder are dispersed in an organic solvent to react, to obtain aramid nanofiber / boron nitride hydrogel, and the specific method is as follows:

[0014] The chopped aramid fibers are washed and dried, and then the dried chopped aramid fibers, boron nitride nanobelt powder, alkali and deionized water are dissolved in an organic solvent to obtain a dark red solution;

[0015] Deionized water is added to the dark red solution and stirred thoroughly to obtain initial aramid nanofiber / boron nitride hydrogel;

[0016] The initial aramid nanofiber / boron nitride hydrogel is subjected to suction filtration to obtain aramid nanofiber / boron nitride hydrogel.

[0017] Preferably, the mass ratio of the chopped aramid fibers to alkali is 2:3 to 5:7; the volume ratio of the deionized water to the organic solvent is 1:25 to 3:100; the solid-liquid ratio of the use amount of the chopped aramid fibers to the organic solvent is (0.2-1) g:(50-600) ml; and the mass of the boron nitride nanobelt powder is 10% to 70% of the total mass of the boron nitride / aramid nanofiber aerogel.

[0018] Preferably, the length of the chopped aramid fibers is 3-15 mm, and the diameter is 0.2-0.25 mm.

[0019] Preferably, the method for preparing the boron nitride nanoribbon powder comprises the following steps:

[0020] Dissolving melamine and boric acid in a co-solvent to obtain a melamine diborate solution;

[0021] Freeze-drying the melamine diborate solution to obtain a melamine diborate aerogel;

[0022] Pyrolyzing the melamine diborate aerogel under a high-temperature atmosphere to obtain the boron nitride nanoribbon powder.

[0023] A boron nitride / aramid nanofiber aerogel prepared by the method.

[0024] Preferably, the boron nitride / aramid nanofiber aerogel is a three-dimensional lamellar porous network.

[0025] Preferably, the boron nitride / aramid nanofiber aerogel has a density of 5-80 mg / mL.

[0026] Preferably, the boron nitride / aramid nanofiber aerogel has a porosity of 1-97%.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] The present application uses pyrolysis of melamine diborate aerogel to prepare boron nitride nanoribbon powder, then disperses the short aramid fibers and the boron nitride nanoribbon powder in an organic solvent, and obtains the boron nitride / aramid nanofiber aerogel through the filtration operation, liquid nitrogen directional freezing and freeze-drying method. The high aspect ratio boron nitride nanoribbon is uniformly dispersed in the aramid nanofiber and has a strong binding effect on the aramid nanofiber, and a multifunctional hybrid aerogel with heat insulation, elasticity, flexibility, flame retardation, thermal stability and other properties is obtained.

[0029] Further, compared with the pure aramid nanofiber aerogel prepared by the prior art, the present application uniformly disperses the boron nitride nanoribbon in the aramid nanofiber aerogel, which can significantly improve the compression resilience and flame retardation performance of the aramid nanofiber aerogel, and the obtained boron nitride / aramid nanofiber aerogel has multifunctional properties such as heat insulation, elasticity, flexibility, flame retardation and thermal stability. Specifically:

[0030] (1) The aramid nanofiber aerogel as a matrix makes the material have excellent thermal insulation performance. The aramid nanofibers in the aerogel are intertwined with each other. Due to the hydrogen bond effect, the boron nitride nanobelt is firmly locked by the aramid nanofiber and assembled into a lamellar structure. During the filtration operation and the liquid nitrogen directional freezing process, ice crystals parallel to the interlayer are formed, so that the prepared hybrid aerogel forms a multilayer stacking structure in the Z-axis direction. This structure enhances the phonon scattering in the heat transfer process, hinders the effective conduction of heat, and significantly improves the thermal insulation performance of the material. At the same time, because the boron nitride nanobelt has flame retardant and self-extinguishing properties, the boron nitride / aramid nanofiber aerogel has excellent flame retardant performance.

[0031] (2) The boron nitride nanobelt is uniformly dispersed in the aramid nanofiber aerogel, and the flexible boron nitride nanobelt with high aspect ratio plays a binding role on the aramid nanofiber. The aramid nanofiber arranged in the interlayer is tightly wound with the boron nitride nanobelt, so that the boron nitride / aramid nanofiber aerogel exhibits excellent elasticity and flexibility.

[0032] (3) The excellent elasticity and flexibility make the boron nitride / aramid nanofiber aerogel have potential application value in the fields of thermal insulation, wearable materials, flexibility, etc.

[0033] (4) The present application has the characteristics of thermal insulation, elasticity, flame retardant, thermal stability, etc. as a flexible thermal insulation material, compared with the traditional pure aramid nanofiber aerogel, it has high elasticity, excellent flame retardant performance and flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the optical photo of the boron nitride / aramid nanofiber aerogel prepared in Example 1 of the present application;

[0035] Figure 2 is the SEM photo of the boron nitride / aramid nanofiber aerogel prepared in Example 1 of the present application;

[0036] Figure 3 is the TEM photo of the boron nitride / aramid nanofiber aerogel prepared in Example 1 of the present application;

[0037] Figure 4 is the mechanical property of the boron nitride / aramid nanofiber aerogel prepared in Example 1 of the present application;

[0038] Figure 5 is the thermal insulation performance of the boron nitride / aramid nanofiber aerogel prepared in Example 1 of the present application;

[0039] Figure 6 is the flame retardant performance of the boron nitride / aramid nanofiber aerogel prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0040] The application will be further described in detail below with reference to the examples.

[0041] The application provides a boron nitride / aramid nanofiber aerogel with thermal insulation, elasticity, flexibility, flame retardation and thermal stability, and a preparation method thereof.

[0042] The aramid fibers and the boron nitride aerogel are uniformly dispersed in an organic solvent, and the boron nitride / aramid nanofiber aerogel is prepared by filtration operation, directional freezing in liquid nitrogen and freeze drying.

[0043] The boron nitride / aramid nanofiber aerogel has a three-dimensional lamellar porous network, which is composed of aramid nanofibers and boron nitride nanobands.

[0044] The main elements of the boron nitride / aramid nanofiber aerogel are carbon, boron, nitrogen and oxygen.

[0045] The internal microstructure of the boron nitride / aramid nanofiber aerogel is a lamellar structure composed of aramid fibers and boron nitride.

[0046] The density of the boron nitride / aramid nanofiber aerogel is 5-80 mg / mL.

[0047] The thermal conductivity of the boron nitride / aramid nanofiber aerogel is 30-47 mW / m·k.

[0048] The boron nitride / aramid nanofiber aerogel has excellent flame retardation.

[0049] The porosity of the boron nitride / aramid nanofiber aerogel is 1-97%.

[0050] Specifically, the application provides a preparation method of a boron nitride / aramid nanofiber aerogel, which comprises the following steps:

[0051] Step 1) preparing a melamine diborate solution:

[0052] The melamine and boric acid are dissolved in a cosolvent to obtain a melamine diborate solution.

[0053] Step 2) freeze drying treatment is performed on the melamine diborate solution to obtain a melamine diborate aerogel.

[0054] Step 3) pyrolysis of the melamine diborate aerogel under a high-temperature atmosphere to obtain boron nitride nanoband powder.

[0055] Step 4) washing the short aramid fiber with ethanol, and then drying the washed short aramid fiber in an oven.

[0056] Step 5) dissolving the dried short aramid fiber, boron nitride nanoribbon powder, alkali and deionized water in an organic solvent to obtain a dark red solution.

[0057] Step 6) adding deionized water to the dark red solution and stirring to obtain aramid nanofiber / boron nitride hydrogel.

[0058] Step 7) pouring the aramid nanofiber / boron nitride hydrogel into a Buchner funnel, and washing with ethanol and deionized water respectively by suction filtration to obtain washed aramid nanofiber / boron nitride hydrogel.

[0059] Step 8) treating the washed aramid nanofiber / boron nitride hydrogel by liquid nitrogen directional freezing and freeze-drying to obtain boron nitride / aramid nanofiber aerogel.

[0060] Specifically:

[0061] The molar ratio of melamine to boric acid in step 1) is 1:4-4:1.

[0062] The co-solvent includes water and an organic solvent, and the organic solvent is at least one of methanol, ethanol, isopropanol, n-butanol or t-butanol, wherein the volume ratio of water to the organic solvent is 7:5-9:13.

[0063] The concentration of the melamine diborate solution is 10-30 mg / ml.

[0064] In step 2), a vacuum freeze-drying process is selected, and the vacuum freeze-drying treatment time is 12-48 h.

[0065] In step 3), the pyrolysis temperature is 600-1400°C, and the high-temperature pyrolysis time is 0.5-5 h.

[0066] The atmosphere is one or a mixture of any two of ammonia, argon and nitrogen.

[0067] In step 4), the length of the short aramid fiber is 3-15 mm, and the diameter is 0.2-0.25 mm.

[0068] The drying temperature of the short aramid fiber is 60-100°C, and the drying time is 1-2 h.

[0069] In step 5), the alkali is at least one of sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide and sodium amide, and is preferably at least one of sodium hydroxide and potassium hydroxide, but is not limited thereto; and the organic solvent is at least one of dimethyl sulfoxide, ethanol, sulfolane, ethyl acetate and ethyl methyl sulfone, but is not limited thereto.

[0070] The mass ratio of the short-cut aramid fiber and alkali is 2:3-5:7, and the volume ratio of deionized water and organic solvent is 1:25-3:100;

[0071] 0.2-1g of short-cut aramid fiber is added with 50-600ml of organic solvent, and is fully stirred for 4-8h at a rotating speed of 100r / min-1000r / min.

[0072] The mass of the boron nitride nanobelt powder is 10%-70% of the total mass of the boron nitride / aramid nanofiber aerogel.

[0073] In step 6), the stirring time is 4-8h, and the rotating speed is 100r / min-1000r / min; and the volume ratio between the deionized water and the dark red liquid is 1:3-5:9.

[0074] In step 7), the aramid nanofiber / boron nitride hydrogel is cleaned with ethanol and deionized water for 3-5 times, respectively, and the total volume of the cleaned aramid nanofiber / boron nitride hydrogel is 80-100ml.

[0075] In step 8), the aramid nanofiber / boron nitride hydrogel is subjected to liquid nitrogen directional freezing and freeze-drying treatment to obtain the boron nitride / aramid nanofiber aerogel, and the specific process is as follows:

[0076] The cleaned aramid nanofiber / boron nitride hydrogel is transferred into a directional freezing mold, and is placed in an environment filled with liquid nitrogen for 30-50min, and is subjected to liquid nitrogen directional freezing from bottom to top.

[0077] The aramid nanofiber / boron nitride hydrogel subjected to liquid nitrogen directional freezing is subjected to freeze-drying for 12-48h to obtain the boron nitride / aramid nanofiber aerogel.

[0078] In summary, the multifunctional integrated boron nitride / aramid nanofiber aerogel prepared by the application not only has thermal stability and heat insulation performance, but also improves the poor flexibility of the aramid nanofiber aerogel, enhances the flame retardant performance of the aramid nanofiber aerogel, and expands the application field of the aramid nanofiber aerogel.

[0079] The technical solutions of the application are further described in detail below through several embodiments and in combination with the accompanying drawings.

[0080] Embodiment 1:

[0081] 0.4838g of melamine and 0.4762g of boric acid are weighed, and are sequentially added into 48ml of a t-butyl alcohol / distilled water co-solvent, wherein the ratio of t-butyl alcohol to distilled water is 7:5, to obtain a melamine di-boric acid solution with a concentration of 20mg / mL. The solution is transferred into a vacuum freeze dryer for treatment for 24h to obtain melamine di-boric acid aerogel.

[0082] The melamine diboric acid aerogel was transferred to a tube furnace and subjected to high-temperature heat treatment at 1100℃ for 3 hours in an ammonia / nitrogen atmosphere to obtain boron nitride nanoribbon powder.

[0083] Weigh 0.23g of chopped aramid fiber, wash it with ethanol, and then place the washed chopped aramid fiber in an oven to dry at 60℃ for 1 hour.

[0084] Weigh 0.345g of potassium hydroxide and dissolve it in 2ml of deionized water. Add 0.026g of boron nitride nanoribbon powder and 0.23g of cleaned and dried chopped aramid fiber to the solution. Then add 50ml of dimethyl sulfoxide and stir for 4 hours at room temperature and pressure at a speed of 150r / min to obtain a dark red solution.

[0085] Add 150 ml of deionized water to the dark red solution and stir thoroughly for 4 h at a speed of 150 r / min to obtain aramid nanofiber / boron nitride hydrogel.

[0086] The aramid nanofiber / boron nitride hydrogel was poured into a Buchner funnel and filtered. It was then washed three times with ethanol and three times with deionized water to make the hydrogel neutral. The volume of the washed aramid nanofiber / boron nitride hydrogel was 80 ml.

[0087] The cleaned aramid nanofibers / boron nitride hydrogel were transferred into a directional freezing mold and placed on the surface of a specific device filled with liquid nitrogen for 30 minutes, and then directionally frozen from bottom to top with liquid nitrogen.

[0088] The aramid nanofiber / boron nitride hydrogel, after being directionally frozen by liquid nitrogen, was transferred to a vacuum freeze dryer and treated for 24 hours to obtain boron nitride / aramid nanofiber aerogel.

[0089] The boron nitride / aramid nanofiber aerogel contains 10% boron nitride nanoribbon powder as the total amount of boron nitride / aramid nanofiber aerogel.

[0090] Test results show that the thermal conductivity can reach 36.1 mW / m·K, and the density is 9.623 mg / cm³. 3 .Depend on Figure 1 It is evident that boron nitride / aramid nanofiber aerogels can be prepared in large quantities. Figure 2 , Figure 3 It is evident that the microstructure of the prepared boron nitride / aramid nanofiber aerogel shows boron nitride dispersed within the aramid fibers. (From...) Figure 4 As can be seen, boron nitride / aramid nanofiber aerogels possess excellent elasticity. (The text abruptly ends here, likely due to an incomplete sentence or missing information.) Figure 5 It is evident that boron nitride / aramid nanofiber aerogel possesses excellent thermal insulation properties. (From...) Figure 6It can be seen that the boron nitride / aramid nanofiber aerogel has flame retardant properties.

[0091] Example 2:

[0092] 0.4838g of melamine and 0.4762g of boric acid were weighed and added to 48mL of a t-butanol / distilled water co-solvent, wherein the ratio of t-butanol to distilled water was 7:5, to obtain a melamine di-boric acid solution with a concentration of 20mg / mL. The solution was transferred to a vacuum freeze dryer for processing for 24h to obtain melamine di-boric acid aerogel.

[0093] The melamine di-boric acid aerogel was transferred to a tube furnace and heated to 1100℃ in an ammonia / nitrogen environment for high-temperature heat treatment for 3h to obtain boron nitride nanobelt powder.

[0094] 0.23g of chopped aramid fiber was weighed, washed with ethanol, and then placed in an oven for drying, with a drying temperature of 60℃ and a drying time of 1h.

[0095] 0.345g of potassium hydroxide was dissolved in 2ml of deionized water, 0.099g of boron nitride nanobelt powder and 0.23g of washed and dried chopped aramid fiber were added, and 50ml of dimethyl sulfoxide was added, stirred at room temperature and normal pressure for 4h at a speed of 150r / min to obtain a dark red solution.

[0096] 150ml of deionized water was added to the dark red solution, stirred thoroughly for 4h at a speed of 150r / min to obtain aramid nanofiber / boron nitride hydrogel. The aramid nanofiber / boron nitride hydrogel was poured into a Buchner funnel and subjected to suction filtration, washed with ethanol and deionized water for 3 times respectively, and the pH of the hydrogel was neutral. The volume of the washed aramid nanofiber / boron nitride hydrogel was 80ml.

[0097] The washed aramid nanofiber / boron nitride hydrogel was transferred to a directional freezing mold, placed on the surface of a specific device filled with liquid nitrogen for 30min, and subjected to liquid nitrogen directional freezing from bottom to top. The aramid nanofiber / boron nitride hydrogel after liquid nitrogen directional freezing was transferred to a vacuum freeze dryer for processing for 24h to obtain boron nitride / aramid nanofiber aerogel.

[0098] The content of boron nitride nanobelt powder in the boron nitride / aramid nanofiber aerogel was 30% of the total amount of the boron nitride / aramid nanofiber aerogel.

[0099] The test results show that the thermal conductivity value is 38.3mW / m·k, the density is 13.757mg / cm 3 , and the mechanical properties are stable.

[0100] Example 3:

[0101] Weigh 0.4838g melamine, 0.4762g boric acid, and add them into 48mL of t-butyl alcohol / distilled water co-solvent in turn, wherein the ratio of t-butyl alcohol to distilled water is 7:5, to obtain a melamine diborate solution with a concentration of 20mg / mL. Transfer it to a vacuum freeze dryer for processing for 24h to obtain melamine diborate aerogel.

[0102] Transfer the melamine diborate aerogel to a tube furnace, and heat it to 1100℃ in an ammonia / nitrogen environment for high-temperature heat treatment for 3h to obtain boron nitride nanobelt powder.

[0103] Weigh 0.23g short aramid fiber, clean it with ethanol, and then place the cleaned and dried short aramid fiber in an oven for drying, with a drying temperature of 60℃ and a drying time of 1h.

[0104] Weigh 0.345g potassium hydroxide into 2ml deionized water, add 0.23g boron nitride nanobelt powder and 0.23g cleaned and dried short aramid fiber to it, and then add 50ml dimethyl sulfoxide to it, stir at room temperature and normal pressure for 4h at a speed of 150r / min to obtain a dark red solution.

[0105] Add 150ml deionized water to the dark red solution, stir thoroughly for 4h at a speed of 150r / min to obtain aramid nanofiber / boron nitride hydrogel. Pour the aramid nanofiber / boron nitride hydrogel into a Buchner funnel, use suction filtration, and clean it with ethanol and deionized water for 3 times respectively to make the PH of the hydrogel neutral. The volume of the cleaned aramid nanofiber / boron nitride hydrogel is 80ml.

[0106] Transfer the cleaned aramid nanofiber / boron nitride hydrogel to a directional freezing mold, place it on the surface of a specific device filled with liquid nitrogen for 30min, and perform directional freezing from bottom to top. Transfer the aramid nanofiber / boron nitride hydrogel after directional freezing of liquid nitrogen to a vacuum freeze dryer for processing for 24h to obtain boron nitride / aramid nanofiber aerogel.

[0107] The content of boron nitride nanobelt powder in the boron nitride / aramid nanofiber aerogel is 50% of the total amount of the boron nitride / aramid nanofiber aerogel.

[0108] Test results show that the thermal conductivity value is 41.5mW / m·k, the density is 19.354mg / cm 3 , and the mechanical properties are stable.

[0109] Example 4:

[0110] Take 0.4838g melamine, 0.4762g boric acid, and add them into 48mL of t-butyl alcohol / distilled water co-solvent in turn, wherein the ratio of t-butyl alcohol to distilled water is 7:5, to obtain a melamine diborate solution with a concentration of 20mg / mL. Transfer it to a vacuum freeze dryer for 24h to obtain melamine diborate aerogel.

[0111] Transfer the melamine diborate aerogel to a tube furnace, heat to 1100℃ in an ammonia / nitrogen environment for 3h high-temperature heat treatment to obtain boron nitride nanobelt powder.

[0112] Take 0.23g short aramid fiber, wash it with ethanol, and then dry the washed short aramid fiber in an oven, with a drying temperature of 60℃ and a drying time of 1h.

[0113] Dissolve 0.345g potassium hydroxide in 2ml deionized water, add 0.537g boron nitride nanobelt powder and 0.23g washed and dried short aramid fiber to it, and then add 50ml dimethyl sulfoxide to it, stir at room temperature and normal pressure for 4h at a speed of 150r / min to obtain a dark red solution.

[0114] Add 150ml deionized water to the dark red solution, stir thoroughly for 4h at a speed of 150r / min to obtain aramid nanofiber / boron nitride hydrogel. Pour the aramid nanofiber / boron nitride hydrogel into a Buchner funnel, use suction filtration, and wash it with ethanol and deionized water for 3 times respectively to make the hydrogel neutral, and the volume of the washed aramid nanofiber / boron nitride hydrogel is 80ml.

[0115] Transfer the washed aramid nanofiber / boron nitride hydrogel to a directional freezing mold, place it on the surface of a specific device filled with liquid nitrogen for 30min, and directional freeze from bottom to top. Transfer the aramid nanofiber / boron nitride hydrogel after liquid nitrogen directional freezing to a vacuum freeze dryer for 24h to obtain boron nitride / aramid nanofiber aerogel.

[0116] The content of boron nitride nanobelt powder in the boron nitride / aramid nanofiber aerogel is 70% of the total amount of boron nitride / aramid nanofiber aerogel.

[0117] The test results show that the thermal conductivity value is 45.2mW / m·k, the density is 23.837mg / cm 3 , and the mechanical properties are stable.

[0118] With the increase of the content of boron nitride aerogel, the density of the boron nitride / aramid nanofiber aerogel slightly increases but is still lightweight, the thermal conductivity of the boron nitride / aramid nanofiber aerogel gradually increases but still has good thermal insulation performance. The content of boron nitride aerogel added in the implementation case 4 is the most, and the mechanical elasticity is also the best.

Claims

1. A method for preparing a boron nitride / aramid nanofiber aerogel, characterized by, The method comprises the following steps: The short-cut aramid fiber and boron nitride nanobelt powder are dispersed in an organic solvent to react, and aramid nanofiber / boron nitride hydrogel is obtained; The aramid nanofiber / boron nitride hydrogel is subjected to downward liquid nitrogen directional freezing and freeze-drying treatment to obtain boron nitride / aramid nanofiber aerogel. The short-cut aramid fiber is washed and dried, and then the dried short-cut aramid fiber, boron nitride nanobelt powder, alkali and deionized water are dissolved in an organic solvent to obtain a dark red solution; Deionized water is added to the dark red solution and stirred to obtain initial aramid nanofiber / boron nitride hydrogel; The initial aramid nanofiber / boron nitride hydrogel is subjected to suction filtration treatment to obtain aramid nanofiber / boron nitride hydrogel; the mass ratio of the short-cut aramid fiber to the alkali is 2:3-5:7; the volume ratio of the deionized water to the organic solvent is 1:25-3:100; the solid-liquid ratio of the use amount of the short-cut aramid fiber to the organic solvent is (0.2-1) g:(50-600) ml; and the mass of the boron nitride nanobelt powder is 10%-70% of the total mass of the boron nitride / aramid nanofiber aerogel.

2. The method for preparing a boron nitride / aramid nanofiber aerogel according to claim 1, characterized in that, The length of the short-cut aramid fiber is 3-15 mm, and the diameter is 0.2-0.25 mm.

3. The method for preparing a boron nitride / aramid nanofiber aerogel according to claim 1, characterized in that, The preparation method of the boron nitride nanobelt powder comprises the following steps: Melamine and boric acid are dissolved in a cosolvent to obtain a melamine diborate solution; The melamine diborate solution is subjected to freeze-drying treatment to obtain melamine diborate aerogel; The melamine diborate aerogel is pyrolyzed under a high-temperature atmosphere to obtain boron nitride nanobelt powder.

4. A boron nitride / aramid nanofiber aerogel, characterized by, The boron nitride / aramid nanofiber aerogel is prepared by the preparation method in any one of claims 1-3.

5. The boron nitride / aramid nanofiber aerogel of claim 4, wherein, The boron nitride / aramid nanofiber aerogel is a three-dimensional lamellar porous network.

6. The boron nitride / aramid nanofiber aerogel of claim 4, wherein, The density of the boron nitride / aramid nanofiber aerogel is 5-80 mg / mL.

7. The boron nitride / aramid nanofiber aerogel of claim 4, wherein the boron nitride / aramid nanofiber aerogel has a density of 0.1 g / cm3 or less. The porosity of the boron nitride / aramid nanofiber aerogel is 1-97%. The porosity of the boron nitride / aramid nanofiber aerogel is 1-97%.

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