Hydrophilic boron nitride nanosheets, their preparation methods and applications

Abstract

This invention provides hydrophilic boron nitride nanosheets, their preparation method, and applications. The preparation method includes ball milling a first mixed slurry containing boron nitride raw material powder, catechols, and water to obtain hydrophilic boron nitride nanosheets. This invention uses water as a solvent and catechols as a modifier, combining liquid-phase ball milling to achieve the exfoliation and modification of boron nitride raw material powder in one step. It has advantages such as high efficiency, mild conditions, low cost, safety, environmental friendliness, simple process, and ease of operation. Simultaneously, it can improve the dispersibility and dispersion stability of the obtained hydrophilic boron nitride nanosheets in aqueous systems such as aqueous polymers and aqueous solutions, as well as their lateral dimensions. These hydrophilic boron nitride nanosheets can be used as high thermal conductivity fillers, for example, filling aqueous polymers to form thermally conductive composite materials, improving the thermal conductivity and other properties of the composite materials.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive composite materials, specifically to a hydrophilic boron nitride nanosheet, its preparation method, and its application. Background Technology

[0002] Boron nitride (BN) has advantages such as high thermal conductivity, good insulation, thermal stability and strong oxidation resistance, and has a wide range of applications. For example, it can be used as a high thermal conductivity filler to fill polymers to form thermally conductive composite materials.

[0003] Boron nitride powder itself is hydrophobic and lacks functional groups on its surface. It has poor dispersibility and stability in aqueous systems (such as aqueous polymers, aqueous solutions, etc.) and is prone to agglomeration and sedimentation, which limits its application. For example, when it is filled into aqueous polymers, it is easy to agglomerate and it is difficult to form a good thermal conduction path, resulting in poor thermal conductivity of thermally conductive composite materials, which seriously limits its application in the field of thermal management.

[0004] Exfoliation and surface modification of boron nitride are effective means to improve its hydrophilicity. For example, patent document CN102786815A discloses a method for surface modification of boron nitride powder, which uses boron nitride nanopowder as raw material and strong oxidants (ammonium persulfate, hydrogen peroxide, dilute nitric acid, etc.) as modifiers, and employs a hydrothermal preparation process to modify the surface of boron nitride to improve the thermal conductivity of boron nitride / polymer composites. Patent document CN109573965A discloses a method for preparing cyano-modified boron nitride nanosheet dispersion, which uses sodium hydroxide aqueous solution as solvent and prepares hydroxyl-modified boron nitride nanosheets by a hydrothermal method. To improve the water dispersion stability of hydroxyl-modified boron nitride (BNOH) nanosheet dispersions; Patent document CN110305559A discloses a corrosion-resistant thermally conductive coating and its preparation method, which uses hydrogen peroxide and carboxylic acid phthalocyanine to modify boron nitride sequentially, and uses the modified boron nitride and fluorinated graphene as a mixed filler to improve the compatibility of the filler with the coating; Patent document CN107324296A discloses a modification method for hexagonal boron nitride and hydroxyl-modified boron nitride, which disperses boron nitride pretreated with nitric acid in a mixed aqueous solution of formic acid and sulfuric acid to support the dispersion, and then irradiates the dispersion with gamma rays to obtain hydroxyl-modified boron nitride.

[0005] Although there are reports on the modification of boron nitride, these modification methods typically use chemicals such as strong acids, strong bases, and strong oxidants as modifiers. These methods suffer from drawbacks such as stringent modification conditions, high safety risks, environmental pollution, high costs, and complex processes, making it difficult to produce hydrophilic boron nitride on a large scale and limiting its industrial application. Furthermore, for hydrophilic boron nitride nanosheets, current methods also suffer from low yields (typically less than 20%) and small lateral dimensions (generally less than 1 μm). The small lateral dimensions of the hydrophilic boron nitride nanosheets, when incorporated into polymers, result in excessive filler-polymer matrix interfaces, leading to increased interfacial thermal resistance and unsatisfactory thermal conductivity in the composite material formed by the boron nitride nanosheets and polymer. Summary of the Invention

[0006] This invention provides a hydrophilic boron nitride nanosheet, its preparation method, and its application. It can produce hydrophilic boron nitride nanosheets with larger lateral dimensions and improve the yield of hydrophilic boron nitride nanosheets. It also has the advantages of mild conditions, safety and environmental protection, low cost, simple process, and easy operation, effectively overcoming the defects of the existing technology.

[0007] In one aspect, the present invention provides a method for preparing hydrophilic boron nitride nanosheets, comprising: ball milling a first mixed slurry containing boron nitride raw material powder, catechols, and water to obtain hydrophilic boron nitride nanosheets.

[0008] According to one embodiment of the present invention, the catechins include one or more of tannic acid, gallic acid, dopamine, caffeic acid, and catecholamines.

[0009] According to one embodiment of the present invention, the boron nitride raw material powder includes hexagonal boron nitride, and / or the particle size of the boron nitride raw material powder is 10-30 μm.

[0010] According to one embodiment of the present invention, the mass ratio of the boron nitride raw material powder to the catechins is 15:1 to 1:15.

[0011] According to one embodiment of the present invention, the first mixed slurry is ultrasonicated for 1 to 2 hours and then subjected to the ball milling treatment.

[0012] According to one embodiment of the present invention, the ball milling process includes: adding ball milling beads with a diameter of 1-10 mm to the first mixed slurry for ball milling, wherein the mass ratio of the ball milling beads to the boron nitride raw material powder is 200:1 to 50:1.

[0013] According to one embodiment of the present invention, the ball milling process is carried out at room temperature.

[0014] According to one embodiment of the present invention, the ball milling process takes 3-36 hours.

[0015] In another aspect, the present invention provides a hydrophilic boron nitride nanosheet, which is prepared according to the above-described method for preparing hydrophilic boron nitride nanosheets.

[0016] In another aspect, the present invention provides a thermally conductive composite material comprising the hydrophilic boron nitride nanosheets as described above, and an aqueous polymer composited with the hydrophilic boron nitride nanosheets.

[0017] According to one embodiment of the present invention, the waterborne polymer includes one or more of waterborne polyurethane, waterborne epoxy resin, polyvinyl alcohol, and waterborne acrylic resin.

[0018] According to one embodiment of the present invention, the mass ratio of the hydrophilic boron nitride nanosheets to the aqueous polymer is 1:1 to 1:20.

[0019] According to one embodiment of the present invention, the thermally conductive composite material further includes a curing agent.

[0020] In another aspect, the present invention provides a method for preparing the above-mentioned thermally conductive composite material, comprising: mixing the hydrophilic boron nitride nanosheets with the aqueous polymer and then performing a curing treatment to obtain the thermally conductive composite material.

[0021] According to one embodiment of the present invention, the process of mixing the hydrophilic boron nitride nanosheets with the aqueous polymer and then performing a curing treatment includes: mixing the hydrophilic boron nitride nanosheets, the aqueous polymer and the curing agent, performing a degassing treatment, and then performing the curing treatment.

[0022] According to one embodiment of the present invention, the curing conditions are: curing temperature of 20-120°C and curing time of 4-24 hours.

[0023] In this invention, catechins are used as modifiers and water as solvent. Boron nitride raw material powder is exfoliated and modified by liquid-phase ball milling. Catechins can be adsorbed onto the surface of boron nitride nanosheets through π-π interactions and other forces, making the surface rich in hydrophilic groups such as hydroxyl groups. This improves the hydrophilicity of the prepared hydrophilic boron nitride nanosheets, thereby improving their dispersibility and stability in aqueous systems such as aqueous polymers and aqueous solutions, and avoiding phenomena such as agglomeration and sedimentation of hydrophilic boron nitride nanosheets.

[0024] Therefore, the hydrophilic boron nitride nanosheets of the present invention have good hydrophilicity and can be used as high thermal conductivity fillers. For example, they can be filled into aqueous polymers to form thermally conductive composite materials, which can improve the interaction sites between the nanosheets and the aqueous polymers, enhance the interfacial compatibility / compatibility between the two, facilitate the formation of good thermal conductivity pathways, and thus improve the thermal conductivity and other properties of the thermally conductive composite materials. They can be applied to electronic packaging (e.g., as microelectronic packaging materials) and other fields.

[0025] Furthermore, the present invention can also increase the lateral size of hydrophilic boron nitride nanosheets and reduce the interface (i.e., filler-matrix interface) between hydrophilic boron nitride nanosheets and aqueous polymers in thermally conductive composite materials, thereby reducing interfacial thermal resistance and improving the thermal conductivity and other properties of thermally conductive composite materials.

[0026] Furthermore, this invention can improve the yield of hydrophilic boron nitride nanosheets. It achieves the exfoliation and modification of boron nitride raw material powder in one step through mechanical ball milling / liquid phase ball milling, thus obtaining hydrophilic boron nitride nanosheets. The preparation efficiency is high, and the solvent used in the preparation process is water. The modifier is a natural, environmentally friendly, inexpensive, efficient, and highly absorbent / adhesive catechol, avoiding the use of toxic / harmful / corrosive chemicals such as strong acids, strong alkalis, and strong oxidants. The process is mild, low-cost, green, and pollution-free, making it safer, more environmentally friendly, and more economical. It also has advantages such as a simple process flow and ease of operation, enabling mass production (large-scale production), which is of great significance for practical industrial applications. Attached Figure Description

[0027] Figure 1 Here is a SEM image of the hydrophilic boron nitride nanosheets f-BNNS prepared in Example 1;

[0028] Figure 2 The infrared spectrum of the hydrophilic boron nitride nanosheets f-BNNS prepared in Example 1;

[0029] Figure 3 The images show the state of f-BNNS aqueous dispersion and BN aqueous dispersion after standing for one week.

[0030] Figure 4 A schematic diagram of the water contact angles of f-BNNS and BN ( Figure 4 (a) is a schematic diagram of the water contact angle of BN; Figure 4 (b) is a schematic diagram of the water contact angle of f-BNNS;

[0031] Figure 5 The graph shows the change in thermal conductivity with filler content (the horizontal axis represents filler content, and the vertical axis represents thermal conductivity). Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] With the development of technology, electronic components are evolving towards higher frequencies, thinner profiles, higher power outputs, and greater integration. This leads to the rapid accumulation of heat within these components, significantly impacting the stability, reliability, and lifespan of electronic products. Therefore, there is an urgent need to utilize high thermal conductivity materials for thermal management.

[0034] Thermally conductive polymer composites are characterized by their light weight, easy processing, and low manufacturing cost, making them widely used microelectronic packaging materials in thermal conductive fields such as 5G communication equipment, electronic packaging, and energy transmission. However, the thermal conductivity of polymers is usually very low (0.1-0.5 W / mK), so it is necessary to add fillers with high thermal conductivity (such as graphene, carbon nanotubes, aluminum nitride, boron nitride (BN), etc.) to improve the thermal conductivity of the polymer substrate.

[0035] BN is a two-dimensional sheet material composed of alternating boron and nitrogen atoms, similar in structure to graphene, and is therefore also known as "white graphene". Compared with graphene, BN has advantages such as high thermal conductivity, good insulation, thermal stability and strong oxidation resistance. It not only conducts heat well, but also effectively avoids risks such as short circuits in electronic devices, thus having unique advantages in thermal management applications of electronic devices.

[0036] However, boron nitride powder itself is hydrophobic and lacks functional groups on its surface. It has poor dispersibility and stability in aqueous systems (such as aqueous polymers, aqueous solutions, etc.) and is prone to agglomeration and sedimentation, which limits its application. For example, when it is filled into aqueous polymers, it is easy to agglomerate and it is difficult to form a good thermal conduction path, resulting in poor thermal conductivity of thermally conductive composite materials, which seriously limits its application in the field of thermal management.

[0037] Exfoliation and surface modification of boron nitride are effective means to improve its hydrophilicity. However, current modification methods typically use chemicals such as strong acids, strong bases, and strong oxidants as modifiers, which have drawbacks such as stringent modification conditions, high safety risks, environmental pollution, high costs, and complex processes. These methods make it difficult to prepare hydrophilic boron nitride on a large scale, limiting its industrial application. In particular, for hydrophilic boron nitride nanosheets, there are also drawbacks such as low yield (usually less than 20%) and small lateral size (generally less than 1 μm). The small lateral size of hydrophilic boron nitride nanosheets leads to excessive filler-polymer matrix interfaces when they are filled into polymers, resulting in increased interfacial thermal resistance and unsatisfactory thermal conductivity of the composite material formed by boron nitride nanosheets and polymers.

[0038] In view of the above problems, embodiments of the present invention provide a method for preparing hydrophilic boron nitride nanosheets, comprising: ball milling a first mixed slurry containing boron nitride raw material powder, catechols, and water to obtain hydrophilic boron nitride nanosheets.

[0039] In the above preparation process, water is used as a solvent and catechols are used as modifiers. The boron nitride raw material powder is exfoliated and modified in one step by liquid-phase ball milling. This method has advantages such as high efficiency, mild conditions, low cost, safety, environmental protection, simple process, and easy operation. At the same time, the surface of boron nitride nanosheets is modified with catechols to improve their hydrophilicity. This can improve the dispersibility and dispersion stability of the prepared hydrophilic boron nitride nanosheets in aqueous systems such as aqueous polymers and aqueous solutions. It can be used as a high thermal conductivity filler, for example, by filling it into aqueous polymers (i.e., hydrophilic boron nitride nanosheets and aqueous polymers are combined) to form thermally conductive composite materials, thereby improving the dispersibility and compatibility of hydrophilic boron nitride nanosheets and aqueous polymers, and thus improving the thermal conductivity and other properties of thermally conductive composite materials.

[0040] Furthermore, by controlling the lateral dimensions and yield of hydrophilic boron nitride nanosheets through liquid-phase ball milling, boron nitride nanosheets with high yield, large lateral dimensions, and good hydrophilicity are obtained. When these hydrophilic boron nitride nanosheets are combined with aqueous polymers to form thermally conductive composite materials, the interface between the hydrophilic boron nitride nanosheets and the aqueous polymer in the thermally conductive composite material can be reduced, the interfacial thermal resistance can be lowered, and the thermal conductivity and other properties of the thermally conductive composite material can be improved.

[0041] Through the above preparation process, the boron nitride raw material powder is simultaneously exfoliated and modified to obtain thin-layer hydrophilic boron nitride nanosheets. Generally, the thickness of the obtained hydrophilic boron nitride nanosheets can be 1-10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm or any combination thereof.

[0042] Specifically, in the above preparation process, the boron nitride raw material powder used may include hexagonal boron nitride (BN), which is generally a white powder with a relative density of about 2.25.

[0043] In some specific embodiments, the particle size of the boron nitride raw material powder can be 10-30 μm, for example, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm or any combination thereof.

[0044] In the above preparation process, catechins are used as modifiers, specifically adsorbed onto the surface of boron nitride nanosheets through π-π interactions, thereby giving the prepared hydrophilic boron nitride nanosheets good hydrophilicity. In some specific embodiments, catechins may include one or more of tannic acid, gallic acid, dopamine, caffeic acid, and catecholamines.

[0045] Generally, the mass ratio of boron nitride raw material powder to catechins can be 15:1 to 1:15, 15:1, 14:2, 13:3, 12:4, 11:5, 10:6, 9:7, 8:8, 7:9, 6:10, 5:11, 4:12, 3:13, 2:14, 1:15, or any combination thereof.

[0046] In the above preparation process, the first mixed slurry can be premixed by first ultrasonic treatment. Specifically, the first mixed slurry can be ultrasonicated for 1 to 2 hours (i.e., the first ultrasonic treatment time is 1 to 2 hours) and then ball milled. The first ultrasonic treatment time is, for example, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min or any combination thereof, which is beneficial to the uniformity of the first mixed slurry and improves the performance of the prepared hydrophilic boron nitride nanosheets.

[0047] In practice, boron nitride raw material powder can be mixed with catechins (for example, boron nitride raw material powder can be added to catechins), and the resulting mixture can be added to water (or boron nitride raw material powder and catechins can be added to water). Then, a first ultrasonic treatment is performed to obtain a uniform first mixed slurry; then, ball milling beads are added to it for liquid phase ball milling.

[0048] Specifically, the first mixed slurry can be ball-milled using grinding balls. The ball-milling process can include adding grinding balls to the first mixed slurry for ball milling. The grinding balls can be spherical and have a diameter of 1-10 mm, such as 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any combination thereof.

[0049] In addition, the mass ratio of the grinding balls to the boron nitride raw material powder can be 200:1 to 50:1, for example, 200:1, 180:1, 150:1, 120:1, 100:1, 80:1, 50:1 or any combination thereof.

[0050] Generally, the yield and transverse size of hydrophilic boron nitride nanosheets can be controlled by adjusting the ball milling time. In some preferred embodiments, the ball milling time can be 3-36 hours, for example, 3 hours, 5 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, 25 hours, 28 hours, 30 hours, 32 hours, 35 hours, 36 hours or any combination thereof, which is convenient for improving both the transverse size and the yield of hydrophilic boron nitride nanosheets.

[0051] In the above preparation process, ball milling can be carried out at room temperature (20-30℃), which is more gentle and can efficiently produce hydrophilic boron nitride nanosheets with larger lateral dimensions and improve their yield.

[0052] In the above preparation process, after ball milling, a dispersion containing hydrophilic boron nitride nanosheets is obtained. The dispersion is then filtered (e.g., by vacuum filtration), and the resulting solid product is dried to obtain hydrophilic boron nitride nanosheets, which are generally in powder form, i.e., hydrophilic boron nitride nanosheet powder.

[0053] The hydrophilic boron nitride nanosheets provided in this embodiment of the invention are prepared according to the above-described method for preparing hydrophilic boron nitride nanosheets. As mentioned above, their surface is coated with catechols, thereby possessing hydrophilic groups such as hydroxyl groups, and exhibiting good hydrophilicity. Studies have shown that their water contact angle can generally be less than 40°.

[0054] Furthermore, the thickness of the aforementioned hydrophilic boron nitride nanosheets can be 1-10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any combination thereof.

[0055] In addition, the aforementioned hydrophilic boron nitride nanosheets have a large lateral size, with an average lateral size that can be greater than 3 μm.

[0056] The lateral dimension refers to the cross-sectional dimension of the hydrophilic boron nitride nanosheet perpendicular to its thickness direction, that is, the cross-sectional dimension of the hydrophilic boron nitride nanosheet is greater than 3 μm, and the cross-section of the hydrophilic boron nitride nanosheet is perpendicular to its thickness direction.

[0057] The aforementioned hydrophilic boron nitride nanosheets can be used as thermally conductive fillers to be combined with aqueous polymers to form thermally conductive composite materials with good thermal conductivity and other properties.

[0058] The thermally conductive composite material (i.e., hydrophilic boron nitride nanosheet-polymer composite material) provided in this invention includes the aforementioned hydrophilic boron nitride nanosheets and an aqueous polymer composited with the hydrophilic boron nitride nanosheets. As described above, based on the good hydrophilicity and large lateral size of the hydrophilic boron nitride nanosheets, their dispersibility in the aqueous polymer can be improved, their compatibility with the aqueous polymer can be enhanced, the hydrophilic boron nitride nanosheets can be uniformly dispersed in the aqueous polymer, tightly bonded to the aqueous polymer, and their interfacial impedance with the aqueous polymer can be reduced, thereby improving the thermal conductivity and other properties of the thermally conductive composite material. This thermally conductive composite material has good and broad application prospects in thermal management, such as being used as a microelectronic packaging material.

[0059] Specifically, the mass ratio of hydrophilic boron nitride nanosheets to aqueous polymers can be 1:1 to 1:20, for example, 1:1, 1:3, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20 or any combination thereof, which is beneficial for further optimizing the thermal conductivity and other properties of the thermally conductive composite material.

[0060] Specifically, the aforementioned waterborne polymers (or water-soluble polymers) may include one or more of waterborne polyurethane, waterborne epoxy resin, polyvinyl alcohol, and waterborne acrylic resin, but are not limited thereto.

[0061] Generally, the above-mentioned thermally conductive composite material may also include a curing agent, which is used to cure the water-based polymer and hydrophilic boron nitride after mixing to form a thermally conductive composite material, thereby further improving the performance of the thermally conductive composite material.

[0062] Specifically, in the above-mentioned thermally conductive composite material, the mass content of the curing agent can be 10 to 25 wt%, for example, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 22 wt%, 25 wt%, or any combination thereof.

[0063] The preparation method of the above-mentioned thermally conductive composite material provided in the embodiments of the present invention includes: mixing hydrophilic boron nitride nanosheets with an aqueous polymer and then performing a curing treatment to obtain the thermally conductive composite material.

[0064] Specifically, the mass ratio of hydrophilic boron nitride nanosheets to aqueous polymers can be 1:1 to 1:20, for example, 1:1, 1:3, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18, 1:20 or any combination thereof.

[0065] In some embodiments, the mass content of hydrophilic boron nitride nanosheets in the thermally conductive composite material can be 5 to 50 wt%, for example, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, or any combination thereof.

[0066] Under normal circumstances, the above-mentioned curing treatment can be carried out under the action of a curing agent. For example, hydrophilic boron nitride nanosheets, water-based polymers and curing agents can be mixed and then cured.

[0067] For example, the curing agent used may include amine and / or acid anhydride curing agents, which may be conventional curing agents in the art and are not particularly limited thereto.

[0068] In addition, the amount of curing agent added can meet the following requirements: the mass of the curing agent is 10 to 25 wt% of the sum of the mass of the hydrophilic boron nitride nanosheets, the aqueous polymer and the curing agent, for example, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 22 wt%, 25 wt% or any combination thereof.

[0069] Furthermore, after mixing hydrophilic boron nitride nanosheets, aqueous polymers, and curing agents, the mixture can be degassed before curing, which helps to further improve the thermal conductivity and other properties of the resulting thermally conductive composite material.

[0070] In practice, hydrophilic boron nitride nanosheets can be mixed with an aqueous polymer to form a second mixed slurry. For example, hydrophilic boron nitride nanosheets can be added to an aqueous polymer and mixed by ultrasonic stirring (i.e., stirring is carried out simultaneously during ultrasonication) for 0.5 h to 1.5 h to better disperse the hydrophilic boron nitride nanosheets in the aqueous polymer and obtain a second mixed slurry. Then, a curing agent is added to the second mixed slurry, and then degassing and curing treatments are carried out in sequence to obtain a thermally conductive composite material.

[0071] Alternatively, hydrophilic boron nitride nanosheets, aqueous polymers, and curing agents can be mixed and subjected to ultrasonic stirring, for example, ultrasonic stirring for 0.5h to 1.5h, to make the components more uniformly dispersed and mixed. Then, degassing and curing treatments are performed sequentially (i.e., degassing treatment followed by curing treatment) to obtain a thermally conductive composite material.

[0072] Specifically, the curing conditions can be: a curing temperature of 20–120°C, such as 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, or any combination thereof; and a curing time of 4–24 hours, such as 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 18 hours, 20 hours, 22 hours, 24 hours, or any combination thereof. In practice, for example, heat curing can be used.

[0073] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0074] In the following embodiments, material characterization and thermal conductivity testing are performed:

[0075] (1) The microstructure of hydrophilic boron nitride powder was characterized by electron microscopy (SEM);

[0076] (2) The angle between the water droplet and the plane when the deionized water droplet falls on the raw boron nitride powder and hydrophilic boron nitride powder sample tablets is measured by a contact angle meter to test the hydrophilicity of the raw boron nitride and hydrophilic boron nitride nanosheets.

[0077] (3) The aqueous dispersion of boron nitride powder and hydrophilic boron nitride nanosheet powder was left to stand for one week to verify the dispersion stability of hydrophilic boron nitride nanosheets.

[0078] (4) The thermal conductivity of the hydrophilic boron nitride nanosheet / epoxy resin composite material and the raw boron nitride / epoxy resin composite material was tested.

[0079] Example 1

[0080] Boron nitride raw material powder (BN) and tannic acid (TA) are added to deionized water at a mass ratio of 1:1 and mixed. The mixture is then sonicated for 1-2 hours to ensure uniform mixing, thus obtaining the first mixed slurry.

[0081] After adding ball milling beads to the first mixed slurry, liquid-phase ball milling was performed for 6 hours to obtain a dispersion containing hydrophilic boron nitride nanosheets. After filtering and drying the dispersion, hydrophilic boron nitride nanosheets (powder) was obtained, denoted as f-BNNS. The yield (the ratio of the mass of hydrophilic boron nitride nanosheet powder f-BNNS to the mass of boron nitride raw material powder BN) was measured to be 60%.

[0082] f-BNNS was analyzed using electron microscopy (SEM), and its microstructure was measured (SEM image). See attached image. Figure 1 As can be seen, hydrophilic boron nitride nanosheets have been successfully exfoliated, which have a large average lateral size (greater than 3 μm).

[0083] In addition, BN, tannic acid (TA), and f-BNNS were characterized by infrared spectroscopy, and the results are shown in [Figure number missing]. Figure 2 Further analysis shows that f-BNNS contains hydroxyl groups, indicating that tannic acid is adsorbed on the surface of the exfoliated boron nitride nanosheets, thus the modification was successful. This demonstrates that the above preparation process not only achieved the exfoliation of boron nitride raw materials to form thin-layer boron nitride nanosheets, but also modified the exfoliated thin-layer boron nitride nanosheets to contain hydrophilic groups (hydroxyl groups) on their surface, resulting in f-BNNS with large lateral dimensions and good hydrophilicity.

[0084] In addition, f-BNNS was dispersed in water to obtain a high-concentration (50 mg / mL) f-BNNS aqueous dispersion. After standing for one week, its state was as follows. Figure 3 As shown (see) Figure 3 f-BNNS in (in);

[0085] Separately, boron nitride powder (BN) was dispersed in water to prepare a high-concentration (50 mg / mL) BN aqueous dispersion. After standing for one week, its state was as follows. Figure 3 As shown (see) Figure 3 (BN in the middle).

[0086] from Figure 3 As can be seen, BN in the BN aqueous dispersion settles (BN settles almost completely at the bottom of the reagent bottle containing the aqueous dispersion), while the prepared f-BNNS aqueous dispersion exhibits uniform and good dispersibility and stability compared to BN, further demonstrating that f-BNNS has good hydrophilicity and long-term dispersion stability in water.

[0087] In addition, the water contact angle of f-BNNS (i.e., the angle between the water droplet and the tablet surface (plane) when a deionized water droplet falls on the f-BNNS powder sample tablet) and the water contact angle of BN (i.e., the angle between the water droplet and the tablet surface (plane) when a deionized water droplet falls on the BN powder sample tablet) were measured using a contact angle meter to test their hydrophilicity. The results are shown in […]. Figure 4 ( Figure 4 (a) is a schematic diagram of the water contact angle of BN; Figure 4 (b) is a schematic diagram of the water contact angle of f-BNNS. It can be seen that the water contact angle of BN is 77°. After the above preparation process and peeling modification, the water contact angle of the f-BNNS is 35°, which further shows that the hydrophilicity of f-BNNS is significantly improved.

[0088] Experimental examples and comparative examples

[0089] In the following experimental examples 1-6, thermally conductive composite materials were prepared according to the following process: f-BNNS, water-based polymer, and curing agent were mixed, ultrasonically stirred for 1 hour, degassed, and then heated and cured (i.e., cured) to obtain thermally conductive composite materials (denoted as f-BNNS / EP).

[0090] The difference between Comparative Examples 1-6 and Experimental Examples 1-6 is that BN is used instead of f-BNNS.

[0091] The differences between Experimental Examples 1-6 and Comparative Examples 1-6 are shown in Table 1. Except for the differences shown in Table 1, the other conditions are the same.

[0092] Table 1

[0093]

[0094] The thermal conductivity of the thermally conductive composite materials in each experimental example and comparative example was tested, and the results are shown in the figure. Figure 5 (The curves showing the change in thermal conductivity with filler (f-BNNS) content based on the test results of Experimental Examples 1-6 and the curves showing the change in thermal conductivity with filler (f-BNNS) content based on the test results of Comparative Examples 1-6) show that the thermal conductivity of the experimental thermal conductive composite material is significantly improved compared to the thermal conductive composite material of the comparative examples.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a hydrophilic boron nitride nanosheet, characterized by, The preparation method comprises the following steps: The first mixed slurry containing boron nitride raw material powder, catechol, and water is subjected to ball milling treatment to obtain hydrophilic boron nitride nanosheets, wherein the average lateral size of the hydrophilic boron nitride nanosheets is greater than 3 μm. The first mixed slurry is subjected to ultrasonic treatment for 1-2 h before the ball milling treatment. The ball milling treatment comprises adding ball milling beads with a diameter of 1-10 mm to the first mixed slurry for ball milling, wherein the mass ratio of the ball milling beads to the boron nitride raw material powder is 200:1-50:1, the ball milling treatment is performed for 3-36 h, and the ball milling treatment is performed at a temperature of 20-30 ℃.

2. The method of claim 1, wherein the hydrophilic boron nitride nanosheets are prepared by the method comprising: The catechol comprises one or more of tannic acid, gallic acid, dopamine, caffeic acid, and catecholamine. ​ 3. The method for preparing hydrophilic boron nitride nanosheets according to claim 1, characterized in that, The boron nitride raw material powder comprises hexagonal boron nitride, and / or the particle size of the boron nitride raw material powder is 10-30 μm.

4. The method for preparing hydrophilic boron nitride nanosheets according to any one of claims 1-3, characterized in that, The mass ratio of the boron nitride raw material powder to the catechol is 15:1-1:

15.

5. A hydrophilic boron nitride nanoplate, characterized by, The hydrophilic boron nitride nanosheets are prepared by the preparation method according to any one of claims 1-4.

6. A thermally conductive composite material, characterized by, The hydrophilic boron nitride nanosheets according to claim 5 are compounded with an aqueous polymer.

7. The thermally conductive composite material according to claim 6, wherein, The aqueous polymer comprises one or more of an aqueous polyurethane, an aqueous epoxy resin, polyvinyl alcohol, and an aqueous acrylic resin; And / or, the mass ratio of the hydrophilic boron nitride nanosheets to the aqueous polymer is 1:1-1:20; And / or, the thermally conductive composite material further comprises a curing agent.

8. A method of producing the thermally conductive composite material according to claim 6 or 7, characterized by, The preparation method comprises the following steps: The hydrophilic boron nitride nanosheets are mixed with the aqueous polymer and then subjected to curing treatment to obtain the thermally conductive composite material.

9. The preparation method of the thermally conductive composite material according to claim 8, wherein, The process of mixing the hydrophilic boron nitride nanosheets with the aqueous polymer and then subjecting to curing treatment comprises mixing the hydrophilic boron nitride nanosheets, the aqueous polymer, and a curing agent, performing defoaming treatment, and then subjecting to the curing treatment. And / or, the curing treatment is at a curing temperature of 20-120 o C for 4-24 hours.

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