Method for preparing high-aspect-ratio boron nitride nanotubes by paper pulp template method and application thereof

Abstract

The application relates to a method for preparing high-aspect-ratio boron nitride nanotubes by a paper pulp template method and application thereof, and the method comprises the following steps: preparing cellulose nanofilaments by taking paper pulp as raw material; placing a boron source, a nitrogen source and the cellulose nanofilaments in a vacuum autoclave, adjusting the pressure in the autoclave to 0.1-3 MPa, heating, and keeping the reaction for 0.5-2 hours; adjusting the pressure in the autoclave to 20-50 MPa, keeping the reaction for 2-18 hours, cooling, and preparing a boron nitride cellulose nanofilament mixture; placing the boron nitride cellulose nanofilament mixture in a high-temperature furnace for several hours to remove the cellulose nanofilaments in the mixture, obtaining boron nitride nanotube coarse powder; centrifuging, acid washing, water washing, drying, and obtaining boron nitride nanotubes.

Description

Technical Field

[0001] The present invention relates to the field of boron nitride nanotechnology, and in particular to a method for preparing high aspect ratio boron nitride nanotubes using a pulp template method and applications thereof. Background Art

[0002] Layered hexagonal boron nitride (h-BN) is commonly used in thermal interface materials, thermally conductive fillers, and other applications requiring efficient heat dissipation due to its high thermal conductivity and electrical insulation properties in packaging. Boron nitride nanotubes (BNNTs) have attracted considerable attention due to their unique physical and chemical properties. Their exceptional thermal stability and chemical inertness enable them to maintain stable performance even in extreme environments. Furthermore, BNNTs' excellent mechanical strength and wide-bandgap semiconductor properties hold great potential for broad applications in composite reinforcement, electronic and optoelectronic devices, thermal management, and biomedicine. Common methods for producing BNNTs include ball-milling CVD, template-based methods, and plasma-assisted methods. The plasma-assisted method can produce high-quality BNNTs in a short time, but the equipment is complex and the cost is high. The ball-milling CVD method combines the advantages of mechanical milling and chemical vapor deposition, making it suitable for large-scale production. However, the milling process can easily introduce impurities, and precise control of the nanotube size and morphology is difficult. The template method can precisely control the size and morphology of BNNTs, including diameter, length and wall thickness. Due to the guiding effect of the template, the BNNTs have high purity and low impurity content. This process has broad development and production potential.

[0003] The key steps in preparing boron nitride nanotubes by template methods are selecting the appropriate template material and preparing a high-quality template. Inappropriate templates can increase process complexity and cost. Using carbon nanotubes as templates can produce boron nitride nanotubes with excellent morphology and size. For example, Chinese invention patent application publication number CN102010611A provides a technical solution for preparing boron nitride nanotubes using carbon nanotubes as templates through methods such as chemical vapor deposition, and details the process parameters and steps involved in the preparation process. However, after forming boron nitride nanotubes on carbon nanotubes, it is difficult to effectively remove the template without leaving impurities and damaging the nanotube structure. The high covalent bond strength of carbon nanotubes makes it difficult to remove carbon atoms, resulting in carbon-doped boron nitride nanotubes. In addition, using carbon nanotubes as templates is expensive. Other porous templates, such as porous alumina, are difficult to prepare small-diameter boron nitride nanotubes. How to prepare high-purity and dimensionally stable boron nitride nanotubes and scale them up to industrial scale with good economic benefits still requires further research and development. Summary of the Invention

[0004] In view of this, a method for preparing high aspect ratio boron nitride nanotubes by a pulp template method and its application are provided, which have controllable size, high product purity, simple operation and practical application value.

[0005] A method for preparing high aspect ratio boron nitride nanotubes using a pulp template method comprises the following steps:

[0006] Preparation of cellulose nanofibrils using pulp as raw material;

[0007] A boron source and a nitrogen source are placed in a vacuum autoclave according to a predetermined reaction ratio, and cellulose nanofibrils are placed therein. The pressure in the autoclave is adjusted to 0.1-3 MPa by using a diluent gas, and the temperature is increased to 500-650°C at a predetermined heating rate. After the temperature is kept at this temperature for 0.5-2 hours, the pressure in the autoclave is adjusted to 20-50 MPa, and the temperature is kept at this temperature for 2-18 hours. After the reaction is completed, the mixture is cooled to obtain a boron nitride cellulose nanofibril mixture.

[0008] The boron nitride cellulose nanofibril mixture is placed in a high-temperature furnace and heated to 300-700°C, and kept at this temperature for 2-12 hours to remove the cellulose nanofibrils in the mixture, thereby obtaining a coarse boron nitride nanotube powder;

[0009] The obtained coarse powder of boron nitride nanotubes is centrifugally acid-washed for multiple times, centrifugally water-washed for multiple times, and dried to obtain boron nitride nanotubes.

[0010] Preferably, the predetermined reaction ratio is a molar ratio of boron to nitrogen of 1:1 to 1:3.

[0011] Preferably, the boron source is one or a mixture of two or more of boron powder, sodium borohydride, ammonium borohydride, ammonium fluoroborate, boric acid, and boron oxide.

[0012] Preferably, the nitrogen source is one or a mixture of two or more of melamine, dicyandiamide, cyanamide, ammonium fluoroborate, ammonium chloride, and ammonia.

[0013] Preferably, the mass ratio of the added amount of the cellulose nanofibrils to the sum of the mass of the nitrogen source and the boron source is 1:10 to 10:10.

[0014] Preferably, the diluent gas is one of nitrogen, ammonia, argon, and helium, or a mixture of two or more thereof.

[0015] In some specific embodiments, the preparation of cellulose nanofibrils using pulp as raw material comprises the following steps:

[0016] a) dispersing 5 to 20 parts by weight of the absolute dry pulp in 30 to 70 parts of a 5 to 15% sodium hydroxide aqueous solution, using 3 mm zirconium oxide beads as a ball milling medium, placing the mixture in a ball mill at a speed of 200 to 260 rpm for 0.5 to 2 hours, and then ball milling at a speed of 350 to 450 rpm for 0.5 to 2 hours, sieving the beads, filtering, washing with water to remove the alkali, and obtaining pretreated microfibrillated cellulose;

[0017] b) The pretreated microfibrillated cellulose is dispersed in deionized water to form a 0.5-4 wt% slurry, and the cellulose nanofibrils are obtained by high-pressure homogenization at 20-150 MPa for 5-30 times.

[0018] Preferably, the autoclave is pre-evacuated to 50-1000 Pa, and after the boron source, nitrogen source, and cellulose nanofibrils are placed, the pressure in the autoclave is adjusted to 1-3 MPa with a diluent gas, and the temperature is raised to 500-650°C at a heating rate of 2-10°C / min. The high-temperature furnace is preferably a muffle furnace, and the boron nitride cellulose nanofibril mixture is placed in the muffle furnace and heated to 300-700°C in an air atmosphere. The temperature is maintained for 2-12 hours to remove the cellulose nanofibrils from the mixture, thereby obtaining a coarse boron nitride nanotube powder.

[0019] Specifically, the obtained coarse boron nitride nanotube powder is centrifugally acid-washed with HCl solution for 1 to 5 times, centrifugally washed with water for 1 to 5 times, and dried in an oven at 50 to 100° C. to obtain boron nitride nanotubes.

[0020] Furthermore, the above-mentioned method for preparing high aspect ratio boron nitride nanotubes by the pulp template method is applied to prepare thermal interface materials or thermal conductive fillers.

[0021] The above-mentioned method for preparing high aspect ratio boron nitride nanotubes by pulp template method and its application have at least the following beneficial effects:

[0022] 1. This method uses low-cost pulp as a raw material to produce cellulose nanofibrils, which serve as a template for preparing boron nitride nanotubes. Cellulose is a low-cost material that is easy to obtain and process, making it more suitable for large-scale production applications than carbon nanotubes.

[0023] 2. Preparation processes using carbon nanotubes as templates often suffer from issues such as excessive carbon residue or carbon doping within the boron nitride nanotube structure. Cellulose has good oxidizability and a low thermal oxidative decomposition temperature, making it a good template agent. Relatively mild conditions can be used to achieve good template removal.

[0024] 3. The use of a high-pressure reactor for staged pressurization avoids the problem of excessively high reaction pressure in the initial stage of the reaction, which leads to difficulty in decomposition and vaporization of the reactants. After the boron nitrogen compound precursor is basically generated, the high reaction pressure is conducive to the formation of boron nitride, and the overall reaction temperature can be lowered to below 700°C, which is energy-saving and environmentally friendly.

[0025] 4. High-quality and high-purity thin-walled boron nitride nanotubes can be obtained by autoclave reaction without adding catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The present invention provides a method for preparing high aspect ratio boron nitride nanotubes by a pulp template method.

[0027] Figure 2 This is an SEM image of a boron nitride nanotube product obtained by the method for preparing high aspect ratio boron nitride nanotubes using the pulp template method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0029] The present invention provides a method for preparing high aspect ratio boron nitride nanotubes by pulp template method, such as Figure 1 As shown, the following steps are included:

[0030] Step S10, preparing cellulose nanofibrils using pulp as raw material;

[0031] Step S20: Place a boron source and a nitrogen source in a predetermined reaction ratio in a vacuum autoclave, add cellulose nanofibrils, adjust the pressure in the autoclave to 0.1-3 MPa using a diluent gas, heat the autoclave to 500-650° C. at a predetermined heating rate, and maintain the reaction for 0.5-2 hours. Then, adjust the pressure in the autoclave to 20-50 MPa, maintain the reaction for 2-18 hours, and cool the autoclave after the reaction is complete to obtain a boron nitride cellulose nanofibril mixture.

[0032] Step S30, placing the boron nitride cellulose nanofibril mixture in a high-temperature furnace and heating it to 300-700° C., keeping the temperature for 2-12 hours to remove the cellulose nanofibrils in the mixture, and obtaining a coarse boron nitride nanotube powder;

[0033] Step S40: centrifugally acid-washing the obtained coarse boron nitride nanotube powder for multiple times, centrifugally washing it with water for multiple times, and drying it to obtain boron nitride nanotubes.

[0034] In step S10, the pulp is preferably wood pulp, etc., and the prepared cellulose nanofibrils are sufficiently dried to be free of water. In some specific embodiments, the preparation of cellulose nanofibrils using pulp as raw material includes the following steps:

[0035] a) dispersing 5 to 20 parts by weight of the absolute dry pulp in 30 to 70 parts of a 5 to 15% sodium hydroxide aqueous solution, using 3 mm zirconium oxide beads as a ball milling medium, placing the mixture in a ball mill at a speed of 200 to 260 rpm for 0.5 to 2 hours, and then ball milling at a speed of 350 to 450 rpm for 0.5 to 2 hours, sieving the beads, filtering, washing with water to remove the alkali, and obtaining pretreated microfibrillated cellulose;

[0036] b) The pretreated microfibrillated cellulose is dispersed in deionized water to form a 0.5-4 wt% slurry, and the cellulose nanofibrils are homogenized 5-30 times at 20-150 MPa using a high-pressure homogenizer. The resulting cellulose nanofibrils are then fully dried for later use.

[0037] In step S20, the predetermined reaction ratio is preferably a molar ratio of boron to nitrogen of 1:1 to 1:3. Preferably, the boron source is a mixture of one or more of boron powder, sodium borohydride, ammonium borohydride, ammonium fluoroborate, boric acid, and boron oxide. The nitrogen source is preferably a mixture of one or more of melamine, dicyandiamide, cyanamide, ammonium fluoroborate, ammonium chloride, and ammonia. Preferably, the mass ratio of the amount of cellulose nanofibrils added to the mass sum of the nitrogen source and the boron source is 1:10 to 10:10. The diluent gas is preferably a mixture of one or more of nitrogen, ammonia, argon, and helium.

[0038] Preferably, the autoclave is pre-evacuated to 50-1000 Pa, and after the boron source, nitrogen source, and cellulose nanofibrils are placed, the pressure in the autoclave is adjusted to 1-3 MPa with a diluent gas, and the temperature is raised to 500-650°C at a heating rate of 2-10°C / min. The high-temperature furnace is preferably a muffle furnace, and the boron nitride cellulose nanofibril mixture is placed in the muffle furnace and heated to 300-700°C in an air atmosphere. The temperature is maintained for 2-12 hours to remove the cellulose nanofibrils from the mixture, thereby obtaining a coarse boron nitride nanotube powder.

[0039] Specifically, the obtained coarse boron nitride nanotube powder is centrifugally acid-washed with HCl solution for 1 to 5 times, centrifugally washed with water for 1 to 5 times, and dried in an oven at 50 to 100° C. to obtain boron nitride nanotubes.

[0040] like Figure 2 As shown in Figure 1, the SEM image of the prepared boron nitride nanotube product. Figure 2 From the SEM image, we can see that the length-diameter ratio of boron nitride nanotubes is relatively high and the tube diameter is relatively uniform, mainly distributed between 10 and 30 nm; they can be well used in thermal interface materials or thermal conductive fillers, or other products that require efficient heat dissipation.

[0041] The following uses multiple examples to illustrate various aspects of the method for preparing high aspect ratio boron nitride nanotubes using the pulp template method and the performance of the obtained products.

[0042] Example 1

[0043] 60 g of dry bleached softwood kraft pulp was dispersed in 340 ml of 6 wt% sodium hydroxide aqueous solution and allowed to stand for 30 min. 3 mm zirconium oxide beads were used as ball milling media and the mixture was placed in a ball mill at 250 rpm for 1 hour, then at 350 rpm for 1 hour. After the beads were sieved, they were filtered and washed with water three times to remove the alkali to obtain pretreated microfibrillated cellulose.

[0044] The pretreated microfibrillated cellulose was dispersed in ionized water to form a 2 wt% suspension, which was then homogenized 10 times at 80 MPa using a high-pressure homogenizer to obtain cellulose nanofibrils.

[0045] 8.49 g of sodium borohydride, 12 g of ammonium chloride and 1.5 g of cellulose nanofibrils were placed in a stainless steel autoclave, and the autoclave was evacuated to 100 Pa. The pressure in the autoclave was then adjusted to 1 MPa by injecting a mixture of nitrogen and argon in a volume ratio of 2:1. The autoclave was heated to 600 ° C at a heating rate of 7 ° C / min, and the reaction was kept warm for 0.5 hours. The pressure in the autoclave was adjusted to 25 MPa and the reaction was kept warm for 8 hours. After the reaction, the reactor was kept in a low oxygen atmosphere and cooled to room temperature to obtain a boron nitride cellulose nanofibril mixture.

[0046] The boron nitride cellulose nanofibril mixture was placed in a muffle furnace and heated to 450° C. at 4° C. / min in an air atmosphere, and kept warm for 5 hours to remove the cellulose nanofibrils in the mixture, thereby obtaining coarse boron nitride nanotube powder.

[0047] The obtained coarse boron nitride nanotube powder was acid-washed three times with HCl solution by centrifugation, washed three times with water by centrifugation, and dried in an oven at 80° C. to obtain the boron nitride nanotube product.

[0048] Example 2

[0049] 60 g of dry bleached softwood kraft pulp was dispersed in 340 ml of 6 wt% sodium hydroxide aqueous solution and allowed to stand for 30 min. 3 mm zirconium oxide beads were used as ball milling media and the mixture was placed in a ball mill at 250 rpm for 1 hour, then at 350 rpm for 1 hour. After the beads were sieved, they were filtered and washed with water three times to remove the alkali to obtain pretreated microfibrillated cellulose.

[0050] The pretreated microfibrillated cellulose was dispersed in ionized water to form a 2 wt% suspension, which was then homogenized 10 times at 80 MPa using a high-pressure homogenizer to obtain cellulose nanofibrils.

[0051] 13.86 g of boric acid, 12 g of ammonium chloride and 1.5 g of cellulose nanofibrils were placed in a stainless steel autoclave, and the autoclave was evacuated to 100 Pa. Then, a mixed gas of nitrogen and ammonia in a volume ratio of 2:1 was injected to adjust the pressure in the autoclave to 1 MPa. The autoclave was heated to 600 ° C at a heating rate of 7 ° C / min. After the reaction was kept warm for 0.5 hours, the pressure in the autoclave was adjusted to 25 MPa, and the reaction was kept warm for 10 hours. After the reaction, the reactor was kept in a low oxygen atmosphere and cooled to room temperature to obtain a boron nitride cellulose nanofibril mixture.

[0052] The boron nitride cellulose nanofibril mixture was placed in a muffle furnace and heated to 450° C. at 4° C. / min in an air atmosphere, and kept warm for 5 hours to remove the cellulose nanofibrils in the mixture, thereby obtaining coarse boron nitride nanotube powder.

[0053] The obtained coarse boron nitride nanotube powder was acid-washed three times with HCl solution by centrifugation, washed three times with water by centrifugation, and dried in an oven at 80° C. to obtain the boron nitride nanotube product.

[0054] Example 3

[0055] 60 g of dry bleached softwood kraft pulp was dispersed in 340 ml of 6 wt% sodium hydroxide aqueous solution and allowed to stand for 30 min. 3 mm zirconium oxide beads were used as ball milling media and the mixture was placed in a ball mill at 250 rpm for 1 hour, then at 350 rpm for 1 hour. After the beads were sieved, they were filtered and washed with water three times to remove the alkali to obtain pretreated microfibrillated cellulose.

[0056] The pretreated microfibrillated cellulose was dispersed in ionized water to form a 2 wt% suspension, which was then homogenized 10 times at 80 MPa using a high-pressure homogenizer to obtain cellulose nanofibrils.

[0057] 13.86 g of boric acid, 28.29 g of melamine and 1.5 g of cellulose nanofibrils were placed in a stainless steel autoclave, and the autoclave was evacuated to 100 Pa. Then, a mixed gas of nitrogen and argon with a volume ratio of 2:1 was injected to adjust the pressure in the autoclave to 1 MPa. The autoclave was heated to 600 ° C at a heating rate of 7 ° C / min. After the reaction was kept warm for 0.5 hours, the pressure in the autoclave was adjusted to 25 MPa, and the reaction was kept warm for 8 hours. After the reaction, the reactor was kept in a low oxygen atmosphere and cooled to room temperature to obtain a boron nitride cellulose nanofibril mixture.

[0058] The boron nitride cellulose nanofibril mixture was placed in a muffle furnace and heated to 450° C. at 4° C. / min in an air atmosphere, and kept warm for 5 hours to remove the cellulose nanofibrils in the mixture, thereby obtaining coarse boron nitride nanotube powder.

[0059] The obtained coarse boron nitride nanotube powder was acid-washed three times with HCl solution by centrifugation, washed three times with water by centrifugation, and dried in an oven at 80° C. to obtain the boron nitride nanotube product.

[0060] Example 4

[0061] 60 g of dry bleached softwood kraft pulp was dispersed in 340 ml of 6 wt% sodium hydroxide aqueous solution and allowed to stand for 30 min. 3 mm zirconium oxide beads were used as ball milling media and the mixture was placed in a ball mill at 250 rpm for 1 hour, then at 350 rpm for 1 hour. After the beads were sieved, they were filtered and washed with water three times to remove the alkali to obtain pretreated microfibrillated cellulose.

[0062] The pretreated microfibrillated cellulose was dispersed in ionized water to form a 2 wt% suspension, which was then homogenized 10 times at 80 MPa using a high-pressure homogenizer to obtain cellulose nanofibrils.

[0063] 15.61 g of boron oxide, 28.29 g of melamine and 1.5 g of cellulose nanofibrils were placed in a stainless steel autoclave, and the autoclave was evacuated to 100 Pa. Then, a mixed gas of nitrogen and argon with a volume ratio of 2:1 was injected to adjust the pressure in the autoclave to 1 MPa. The autoclave was heated to 600 ° C at a heating rate of 7 ° C / min. After the reaction was kept warm for 0.5 hours, the pressure in the autoclave was adjusted to 25 MPa, and the reaction was kept warm for 6 hours. After the reaction, the reactor was kept in a low oxygen atmosphere and cooled to room temperature to obtain a boron nitride cellulose nanofibril mixture.

[0064] The boron nitride cellulose nanofibril mixture was placed in a muffle furnace and heated to 450° C. at 4° C. / min in an air atmosphere, and kept warm for 5 hours to remove the cellulose nanofibrils in the mixture, thereby obtaining coarse boron nitride nanotube powder.

[0065] The obtained coarse boron nitride nanotube powder was acid-washed three times with HCl solution by centrifugation, washed three times with water by centrifugation, and dried in an oven at 80° C. to obtain boron nitride nanotubes.

[0066] Examples 1 to 4 can produce boron nitride nanotube products with relatively good morphology. The products are smooth and cylindrical, with most tubes having an average diameter of 10 to 30 nm, a length generally greater than 50 μm, and an aspect ratio greater than 1500. Figure 2 .

[0067] Comparative Example

[0068] Essentially all implementation methods and technical steps were consistent with Example 1, with the difference being that the nanofiber preparation step was skipped, and the boron nitride formation reaction proceeded directly without a template. Observation revealed that the product was essentially a multi-layered, block-like stack, with some boron nitride nanosheets covering the block-like product, and essentially no tubular product was produced.

[0069] It should be noted that the present invention is not limited to the above-mentioned embodiments. Based on the creative spirit of the present invention, those skilled in the art can also make other changes. These changes made based on the creative spirit of the present invention should be included in the scope of protection required by the present invention.

Claims

1. A method for preparing high aspect ratio boron nitride nanotubes using a pulp template method, characterized in that: The following steps are involved: Preparation of cellulose nanofibrils using pulp as raw material; A boron source and a nitrogen source are placed in a vacuum autoclave according to a predetermined reaction ratio, and cellulose nanofibrils are placed therein. The pressure in the autoclave is adjusted to 0.1-3 MPa by using a diluent gas, and the temperature is increased to 500-650°C at a predetermined heating rate. After the temperature is kept at this temperature for 0.5-2 hours, the pressure in the autoclave is adjusted to 20-50 MPa, and the temperature is kept at this temperature for 2-18 hours. After the reaction is completed, the mixture is cooled to obtain a boron nitride cellulose nanofibril mixture. The boron nitride cellulose nanofibril mixture is placed in a high-temperature furnace and heated to 300-700°C, and kept at this temperature for 2-12 hours to remove the cellulose nanofibrils in the mixture, thereby obtaining a coarse boron nitride nanotube powder; The obtained coarse powder of boron nitride nanotubes is centrifugally acid-washed for multiple times, centrifugally water-washed for multiple times, and dried to obtain boron nitride nanotubes.

2. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The predetermined reaction ratio is a molar ratio of boron to nitrogen of 1:1 to 1:

3.

3. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The boron source is one or a mixture of two or more of boron powder, sodium borohydride, ammonium borohydride, ammonium fluoroborate, boric acid, and boron oxide.

4. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The nitrogen source is one or a mixture of two or more of melamine, dicyandiamide, cyanamide, ammonium fluoroborate, ammonium chloride and ammonia.

5. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The mass ratio of the added amount of the cellulose nanofibrils to the sum of the mass of the nitrogen source and the boron source is 1:10 to 10:

10.

6. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The diluent gas is one of nitrogen, ammonia, argon, and helium, or a mixture of two or more thereof.

7. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The preparation of cellulose nanofibrils using pulp as raw material comprises the following steps: a) dispersing 5-20 parts by weight of the absolute dry pulp in 30-70 parts of a 5-15% sodium hydroxide aqueous solution, using 3 mm zirconium oxide beads as a ball milling medium, placing the mixture in a ball mill at 200-260 rpm for 0.5-2 hours, and then at 350-450 rpm for 0.5-2 hours, sieving the beads, filtering, washing with water to remove the alkali, and obtaining pretreated microfibrillated cellulose; b) The pretreated microfibrillated cellulose is dispersed in deionized water to form a 0.5-4 wt% slurry, and the cellulose nanofibrils are obtained by high-pressure homogenization at 20-150 MPa for 5-30 times.

8. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The autoclave is pre-evacuated to 50~1000Pa, and after the boron source, nitrogen source, and cellulose nanofibrils are placed, the pressure in the autoclave is adjusted to 1~3MPa by diluting the gas, and the temperature is raised to 500~650℃ at a heating rate of 2~10℃ / min.

9. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to claim 1, characterized in that: The obtained coarse boron nitride nanotube powder is centrifugally acid-washed with HCl solution for 1 to 5 times, centrifugally washed with water for 1 to 5 times, and dried in an oven at 50 to 100° C. to obtain boron nitride nanotubes.

10. The method for preparing high aspect ratio boron nitride nanotubes by pulp template method according to any one of claims 1 to 9 is used for preparing thermal interface materials or thermal conductive fillers.

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