Method for preparing high aspect ratio two-dimensional material based on frit-fragmentation exfoliation and applications thereof

Abstract

The application discloses a method for preparing high-area-ratio two-dimensional materials based on frit-fragmentation peeling and application, and the method comprises the following steps: 1) mixing: uniformly mixing powder of a crystal material with a layered stacking structure and powder of a thermoplastic material to form mixed powder; 2) fritting: after the mixed powder is heated and melted into a melt, the melt is cooled and solidified into a solid block; 3) fragmentation: the solid block is fragmented into powder particles by using a non-mechanical ball milling fragmentation mode, and a screen is arranged in the fragmentation process; and 4) circulation: the fragmented powder particles are subjected to the fritting-fragmentation process repeatedly by repeating steps 2) to 3), the number of repetitions is 5 to 50, and high-area-ratio two-dimensional material powder containing the thermoplastic material is obtained, and the high-area-ratio two-dimensional material powder is denoted as powder A. The application has high universality, can realize peeling for various layered stacking structures, and can obtain high-area-ratio ultrathin two-dimensional nanosheet materials.

Description

Technical Field

[0001] This invention relates to the technical field of functional two-dimensional ceramic nanosheets and polymer composite products with high thermal conductivity formed therefrom, specifically to a method and application for preparing two-dimensional materials with high aspect ratio based on fused mass-fragmentation exfoliation. Background Technology

[0002] In two-dimensional materials, such as graphene, hexagonal boron nitride nanosheets, Mxene, or few-layer / monolayer molybdenum sulfide nanosheets, the interactions between atoms or molecules within the two-dimensional plane are typically stronger than those in the interlayer direction. This strong in-plane bonding helps increase the in-plane phonon flux density, making in-plane heat conduction more efficient and endowing two-dimensional materials with high thermal conductivity. Typically, two-dimensional materials have relatively simple crystal structures, resulting in a more regular arrangement of atoms or molecules. This regularity helps reduce phonon scattering and vibrational obstruction, significantly promoting in-plane thermal conductivity.

[0003] Two-dimensional filled thermally conductive polymer composites offer the advantage of achieving high-efficiency heat transfer with low filler content, while maintaining the lightweight and processability of composite materials. Therefore, these composites are widely used in fields such as thermal packaging of electronic devices, high thermal conductivity substrates for integrated circuits, thermal interface bonding and encapsulation, heat pipes, thermal encapsulation for battery assembly, and high-temperature heat dissipation, improving equipment efficiency, extending device lifespan, and enhancing industrial economic benefits.

[0004] High aspect ratio ultrathin two-dimensional nanosheets exhibit a higher degree of two-dimensional regularity than low aspect ratio two-dimensional nanosheets, and their intrinsic properties are minimally affected by edge random states. Typically, high aspect ratio two-dimensional nanosheets have higher in-plane crystallinity, making the ordered transmission of lattice vibrations along longer planes more efficient, resulting in higher heat flow conduction efficiency over longer distances and reduced heat loss. Simultaneously, the ultrathin characteristic reduces the inefficient transmission of vibrations along interplanar planes and increases the efficiency of efficient transmission along planes, endowing high aspect ratio ultrathin two-dimensional nanosheets with outstanding directional heat transport capabilities.

[0005] Therefore, the development and application of high aspect ratio ultrathin two-dimensional materials to high thermal conductivity composite materials will make an important contribution to improving or enhancing the heat dissipation performance of my country's Industry 4.0 automation systems and future 5G / 6G high-density / high-performance communication base stations.

[0006] Currently, methods for exfoliating layered stacked crystals into two-dimensional nanosheets include micromechanical exfoliation, mechanical force-assisted liquid phase exfoliation, ion insertion-assisted liquid phase exfoliation, ion exchange-assisted liquid phase exfoliation, oxidation-assisted liquid phase exfoliation, and selective corrosion-assisted liquid phase exfoliation.

[0007] Micromechanical exfoliation uses adhesive tape to peel off layered structures. Although this method does not destroy the covalent bond state within the layers when obtaining two-dimensional crystalline materials with single or multiple layers, the yield and efficiency of this method are extremely low, and it cannot achieve large-scale industrial production.

[0008] Mechanical force / mechanical ball milling-assisted liquid phase exfoliation or mechanical force liquid phase assisted exfoliation after molten salt pretreatment, that is, relying on sonic mechanical force or mechanical shear force to peel off and disperse the layered crystal structure in the liquid phase. Although shear force assistance can increase the yield to a certain extent, the yield is still not high, usually less than 50%. After screening the exfoliated products produced in one go, a very small amount of exfoliated two-dimensional materials with high aspect ratio and ultrathin features can be obtained.

[0009] Liquid-phase assisted or shear-force assisted exfoliation involves the insertion of ions or molecules into the gaps between layered structures to form ion-intercalated compounds or intermediate intercalation states. This is followed by ultrasonic waves in the liquid phase or direct mechanical shearing to facilitate the exfoliation of the layered material. However, this method is primarily suitable for graphite and molybdenum disulfide, and is largely unsuitable for hexagonal boron nitride. While some literature reports protonation intercalation for hexagonal boron nitride, combined with subsequent ultrasonic exfoliation, the use of highly corrosive protonation solvents and the high chemical reactivity after protonation lead to increased in-plane defects in the exfoliated hexagonal boron nitride nanosheets, weakening their intrinsic properties. In normal environments, deprotonation easily occurs, and the exfoliated layers readily re-stack and thicken, causing exfoliation failure.

[0010] Ion exchange-assisted liquid-phase exfoliation utilizes ions with larger ionic radii to replace ions with relatively smaller ionic radii in layered crystals. After ion exchange, the interlayer spacing of the layered bulk is drastically increased, weakening the interlayer spacing and connections between adjacent layers. Then, with the assistance of mechanical vibration or ultrasound, it can be easily exfoliated into single-layer or few-layer nanosheets. However, this method is currently only applicable to layered perovskite structures of hydroxides or oxides, as well as polymers with layered structures, and is not suitable for exfoliating layered crystals without interlayer ions, such as hexagonal boron nitride, graphite, and transition metal sulfides.

[0011] Oxidation-assisted liquid-phase exfoliation utilizes strong oxidants to oxidize materials or form oxygen-containing functional groups between layers, thereby expanding the interlayer spacing. With the aid of ultrasound, these materials can be exfoliated into single-layer or few-layer nanosheets. This method is well-suited for the exfoliation of graphite. However, for materials with relatively stable chemical properties, the oxidation effect is not significant, resulting in almost no exfoliation effect. For example, the exfoliation effect of this method on hexagonal boron nitride is significantly poor, and a large number of defects are easily introduced into the crystal planes of the resulting two-dimensional layers, which has a significant impact on the thermal conductivity of the subsequent hexagonal boron nitride two-dimensional filler in the composite system.

[0012] Selective etching-assisted liquid-phase exfoliation uses strong corrosive agents to etch away the weakly bonded intermediate layer, yielding single-layer or multi-layer nanosheet materials. However, this method currently only works on Max phase materials, and is ineffective for exfoliating other types of layered crystalline materials.

[0013] Therefore, it is of particular importance to develop a new, efficient, universally applicable, and scalable method for exfoliating high aspect ratio ultrathin two-dimensional nanosheets. Summary of the Invention

[0014] The purpose of this invention is to provide a method and application for preparing high aspect ratio two-dimensional materials based on frit-fragmentation exfoliation. The method has high versatility and can exfoliate various layered stacked structures to obtain high aspect ratio ultrathin two-dimensional nanosheet materials.

[0015] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0016] In a first aspect, the present invention provides a method for preparing high aspect ratio two-dimensional materials based on frit-fragmentation exfoliation, the method comprising the following steps:

[0017] 1) Mixing: The powder of crystalline material with layered stacked structure and the powder of thermoplastic material are mixed uniformly in a weight ratio between 0.1 and 0.5 to form a mixed powder;

[0018] 2) Fused block: The mixed powder is heated to melt it into a melt, and then cooled to solidify it into a solid block;

[0019] 3) Crushing: The solid block is crushed into powder particles using a non-mechanical ball milling method. A screen is set up during the crushing process. The mesh size of the screen is determined according to the mesh size corresponding to 1.2 to 3 times the average particle size of the powder of the initial layered stacked crystal material.

[0020] 4) Cycling: Repeat steps 2)-3) to perform the melting-crushing process on the crushed powder particles. Repeat the process 5-50 times to obtain a powder of a two-dimensional material with a high aspect ratio containing thermoplastic material, denoted as powder A.

[0021] The process of obtaining powder A is referred to as the frit-fragmentation and exfoliation process of layered stacked crystal materials. The heating rate and cooling rate in the frit are both between 5℃ / min and 100℃ / min. The target melting temperature range for heating and cooling is 50-400℃. The heating and cooling rates and target melting temperatures in the same cycle can be the same or different. The heating and cooling rates and target melting temperatures in different cycles can be the same or different.

[0022] Powder A is a mixed powder containing high aspect ratio ultrathin two-dimensional nanosheet material and thermoplastic material powder.

[0023] The fragmentation method can be hammering, crushing, smashing, breaking, or tearing.

[0024] In multiple cyclic fragmentation processes: to protect the high aspect ratio two-dimensional material already formed in the previous fragmentation from becoming finer or smaller during the fragmentation process, while also avoiding the formation of too many large fragmented particles in the current fragmentation; and because the fragmentation force no longer applies to particles that reach a certain fineness in each fragmentation, it is necessary to fragment all materials as much as possible in a single fragmentation. Therefore, the statistical average particle size of the fragmented mixed powder must meet certain requirements, namely, it should be 1.2-3 times the statistical average particle size of the powder with a layered stacked crystalline structure, or all particles of the fragmented mixed powder should pass through a sieve with an average mesh size that is 1.2-3 times the statistical average particle size of the powder with a layered stacked crystalline structure.

[0025] Furthermore, the thermoplastic material components in powder A that are not layered materials are removed by dissolving and filtering with a heated solvent, or by high-temperature calcination.

[0026] The specific process of the heating solvent dissolution and filtration method is as follows: Powder A is dissolved in a solvent with a temperature range of 25-60℃. After washing and filtering to remove the thermoplastic material components, the remaining material is a powder of a high aspect ratio two-dimensional material obtained by exfoliation, denoted as nanosheet powder B; the solvent is a liquid that can dissolve the thermoplastic material components in the temperature range of 25-60℃.

[0027] The specific process of the high-temperature calcination method is as follows: Powder A is processed and removed by high-temperature decomposition within a temperature range of 350-900℃. After removal, the remaining material is the powder of high aspect ratio two-dimensional material obtained by exfoliation, which is denoted as nanosheet powder B.

[0028] The nanosheet powder B is a two-dimensional nanomaterial with a high aspect ratio and ultrathin characteristics.

[0029] Nanosheet powder B is a two-dimensional nanosheet structured nanomaterial with high thermal conductivity in-plane or along the two-dimensional plane.

[0030] When choosing a method to obtain nanosheet powder B, the properties of the thermoplastic and crystalline materials themselves must be considered. For example, graphite cannot be calcined at high temperatures and needs to be removed by heating, solvent dissolution, and filtration. When the thermoplastic material is rosin resin, the solvent is ethanol or petroleum ether. When the thermoplastic material is sugar, the solvent is water. When the thermoplastic material is terpene resin, the solvent is petroleum ether. The thermoplastic material removed by high-temperature calcination is at least one of polyethylene, polyvinyl acetate, polyethylene-vinyl acetate, polyamide, polyetheretherketone, or polyphenylene sulfide.

[0031] The solvent used to dissolve and clean thermoplastic materials, as well as the thermoplastic materials dissolved in the solvent after cleaning, are characterized by being recyclable and reusable. Specifically, the filtrate after filtering out the nanosheet powder B is separated by rotary evaporation in a temperature range of 45-80℃ using conventional rotary evaporator equipment. The solvent and thermoplastic materials obtained from the rotary evaporation separation are recovered. The recovered solvent can be reused in the process of removing thermoplastic materials by heating and solvent dissolution filtration. The recovered thermoplastic materials can be reused in the frit-fragmentation and exfoliation process of layered stacked crystal materials.

[0032] The crystalline material with a layered stacking structure includes at least one of highly crystalline micron-sized particles of hexagonal boron nitride, graphite, hexagonal molybdenum sulfide, or Max group materials, with a statistical average size ranging from 5 to 100 micrometers; the Max group materials include at least one of Ti3AlC2, Ti2AlC, Ti2AlN, V2AlC, Ti2GaC, Ti3GaC2, V3AlC2, Ti4AlN3, V4AlC3, or Nb4AlC3; the graphite includes, but is not limited to, flake graphite materials;

[0033] The thermoplastic material is a thermoplastic polymer material or a sugar that has a structure that can be melted into a melt when the temperature is raised and can be solidified into a block when the temperature is lowered; after the thermoplastic material is solidified, it has a hardness that can be crushed into powder within the room temperature range;

[0034] The thermoplastic polymer includes at least one of resins, hot melt adhesives, polyamides (PA), polyetheretherketones (PEEK), and polyphenylene sulfide (PPS), wherein the resin is at least one of rosin or terpene resins;

[0035] The hot melt adhesive includes at least one of polyethylene (PE), polyvinyl acetate (EVA), or polyethylene-vinyl acetate (PEVA);

[0036] The sugar is, but is not limited to, at least one of granulated sugar, brown sugar, glucose, or isomalto.

[0037] The preferred thermoplastic material is at least one of rosin resin, sugar, terpene resin or polyethylene-vinyl acetate.

[0038] The powder of the layered stacked crystal material is a crystal material that has undergone surface activation treatment, which can shorten the number of cycles in the frit-fragmentation process; the surface activation treatment does not cause changes in the internal lattice of the layered crystal material;

[0039] When the powder of the layered stacked crystal material is a highly crystalline micron-sized hexagonal boron nitride, the surface activation process is as follows: after uniformly mixing commercial hexagonal boron nitride powder and boron trioxide at a mass ratio of 6:1-1:6, it is calcined at a constant temperature in high-temperature air at a temperature range of 500-800℃ for 2-96 hours.

[0040] Alternatively, without adding boron trioxide, commercial hexagonal boron nitride powder can be directly calcined in high-temperature air at a temperature range of 800-900℃ for more than 72 hours.

[0041] The preferred method for surface oxidation treatment is to add boron trioxide, which can reduce the calcination temperature by at least 100°C, shorten the calcination time, and reduce the number of frit-fragmentation cycles.

[0042] Secondly, the present invention provides a high aspect ratio two-dimensional material, obtained by the method described above, wherein the high aspect ratio two-dimensional material is a two-dimensional nanosheet with a thickness at the nanometer level and an aspect ratio of not less than 1500.

[0043] Thirdly, the present invention provides applications of the above-mentioned high aspect ratio two-dimensional materials, which are used to prepare bulk polymer composite materials, polymer composite film materials, and interfacial adhesive composite materials. These materials are polymer composite materials with high thermal conductivity.

[0044] The first method: Powder A is directly prepared into bulk polymer composite materials, polymer composite film materials, or interfacial adhesive composite materials;

[0045] The process for preparing bulk polymer composite materials includes, but is not limited to, the following steps: (i) directly loading powder A into a compression molding die of a certain shape, and pressing powder A into shape within a pressure range of 1-100 MPa to obtain a bulk prototype before heat treatment; (ii) subjecting the bulk prototype to a heat treatment process of 0.5-50 hours at a temperature range of 50-300℃ to particle densification, and then cooling it to room temperature to obtain a bulk polymer composite material.

[0046] The heating and cooling rates are maintained within the range of 1℃ / min to 10℃ / min.

[0047] The process for preparing polymer composite film materials is as follows: (i) Powder A is added to an unpolymerized or uncured liquid polymer precursor and stirred for 0.5-72 hours in the temperature range of 0℃-100℃ to form a viscous and uniformly mixed slurry; (ii) The slurry is coated onto a substrate with a smooth surface by a doctor blade or centrifuged at high speed to form a film, and the substrate covered with the slurry film is desolvated and pre-cured in the temperature range of 25-100℃ for 1-48 hours, and then the desolvated and pre-cured cover film is removed from the substrate; (iii) The cover film removed from the substrate is subjected to a secondary reaction in the temperature range of 120-320℃ for 4-96 hours, and after cooling to room temperature, the polymer composite film material is obtained.

[0048] The process of preparing the interfacial adhesive composite material is as follows: (i) Powder A is dissolved in a solvent and rapidly stirred to dissolve and disperse it, resulting in a uniformly dispersed solvent dispersion of powder A; (ii) The original polymer adhesive components are dissolved or diluted to form a viscous polymer adhesive liquid with strong fluidity; (iii) The solvent dispersion of powder A is added to the polymer adhesive liquid, and the mixture is stirred uniformly for 2-96 hours within a temperature range of 60-150℃ to obtain a viscous mixed adhesive liquid, which is the liquid interfacial adhesive composite material formed by thermoplastic material, nanosheet powder B, polymer adhesive and solvent.

[0049] The second method is to directly use the nanosheet powder B as a filler in polymer composite materials with polymer as the matrix to obtain bulk polymer composite materials, polymer composite film materials or interfacial adhesive composite materials.

[0050] The filling amount of nanosheet powder B in the bulk polymer composite material is not higher than 35 wt.%, and the thermal conductivity of the bulk polymer composite material is not lower than 3 W•m. -1 K -1 The nanosheet powder B exhibits a relatively ordered orientation of its two-dimensional plane along the direction perpendicular to the bulk pressure compression molding direction. Its thermal conductivity exhibits anisotropic characteristics within the bulk polymer composite material, with the thermal conductivity value perpendicular to the molding pressure direction being higher than that parallel to the molding pressure direction.

[0051] The amount of nanosheet powder B in the polymer composite thin film material is not higher than 20 wt.%, and the thermal conductivity along the film plane is not lower than 14 W•m. -1 K -1The nanosheet structure of nanosheet powder B exhibits a highly ordered orientation of its two-dimensional planes along the plane of the film. The thermal conductivity along the plane of the film is much higher than that perpendicular to the plane. The thermal conductivity within the film is anisotropic, and the film has the characteristic of directional heat transfer along its plane.

[0052] The filler content of nanosheet powder B in the interfacial adhesive composite material is no higher than 30 wt.%, preferably between 1 wt.% and 30 wt.%, resulting in an interfacial adhesive composite material with high adhesion and high thermal conductivity. The preferred polymer material for the polymer composite film material is polyimide (PI).

[0053] In the preparation of interfacial adhesive composites, the solvent used to dissolve or disperse powder A and the solvent used to dissolve / dilute the polymer adhesive have similar compatibility characteristics, but are not limited to ethanol or glycerol.

[0054] The original polymer adhesive is any one of the non-toxic and pollution-free biomass adhesives; the raw material components of the biomass adhesive are mixed in the following weight ratios, but not limited to the following two: the weight ratio of epoxidized soybean oil: tannic acid: malic acid: ethanol is (8-10): (4-6): (3-5): (10-15) or the weight ratio of epoxidized soybean oil: tannic acid: glycerin is (8-10): (4-6): (10-20). The polymer adhesive after filling powder A also has the characteristic of improved adhesive performance.

[0055] The product obtained through the first method is equivalent to a polymer composite material with high thermal conductivity, consisting of nanosheet powder B filled with a thermoplastic material from powder A as the matrix. The thermal conductivity value of the material is used as an indicator to evaluate its thermal conductivity; the higher the thermal conductivity, the better the thermal conductivity. The product obtained through the second method is not limited to the type of thermoplastic material used in preparing nanosheet powder B.

[0056] This invention also includes the preparation of bulk or thermal interface composite materials directly using powder A and / or nanosheet powder B, or through other polymer composite methods, but not limited to the filling of thin film or other types of nanosheet powder B formed by powder A or nanosheet powder B through preparation processes and molding technologies such as compression molding, high-temperature casting molding, coating-heat treatment molding, etc. The preparation and synthesis methods involving the direct use of powder A and nanosheet powder B as filler components of polymer composite materials should fall within the scope of protection of this patent.

[0057] Compared with the prior art, the beneficial effects of the present invention are:

[0058] (1) The method of the present invention is applicable to a wide range of layered stacked crystal structure materials and can peel off two-dimensional materials with high aspect ratio, extremely thin thickness, high crystallinity and high integrity. It can produce two-dimensional materials with high aspect ratio and extremely thin properties in one go. After several melting-fragmentation cycles, the peeled products have relatively uniform high aspect ratio and extremely thin properties. When high aspect ratio and extremely thin high thermal conductivity filler are required, there is no need for multiple graded screening and selection of peeled products.

[0059] (2) The method of the present invention has the advantages of simple equipment and production line, safe process and easy control. The raw materials are recycled and reused during the stripping process, which significantly reduces energy waste and reduces preparation cost, and has the advantage of large-scale mass production.

[0060] (3) The process of preparing polymer composite materials by directly using the powder product of the present invention as a filler or raw material improves the preparation efficiency and performance of high thermal conductivity composite materials and has considerable economic benefits. Attached Figure Description

[0061] To more clearly illustrate the technical solutions and product types of this invention, we have provided a brief description of the accompanying drawings used in the embodiments. It should be emphasized that these accompanying drawings represent only a portion of the embodiments of this invention. For those skilled in the art, these drawings may be extended and derived into other similar and related examples without creative effort; such extensions would be considered an infringement of this invention.

[0062] Figure 1 This is a process flow diagram of one embodiment of the method of the present invention;

[0063] Figure 2 A schematic diagram illustrating the physical mechanism by which the frit-fragmentation process exfoliates layered crystalline materials into high aspect ratio ultrathin two-dimensional nanosheets;

[0064] Figure 3 The image is a scanning electron microscope (SEM) image of the commercial cosmetic-grade hexagonal boron nitride powder in Example 1 after surface oxidation treatment.

[0065] Figure 4 Comparison images of the original commercial cosmetic grade hexagonal boron nitride powder (a) used in Example 1 and the hexagonal boron nitride powder (b) after being stripped by a frit-crushing cycle;

[0066] Figure 5 To compare the X-ray powder diffraction (XRD) patterns of the original commercial cosmetic-grade hexagonal boron nitride powder in Example 1 and the hexagonal boron nitride powder after being exfoliated by a frit-crushing cycle;

[0067] Figure 6 High-resolution and low-resolution transmission electron microscopy (TEM) images of high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B obtained after 10 frit-fragmentation exfoliation processes in Example 1.

[0068] Figure 7 The images and line scan data of the thickness / planar dimensions of the high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B obtained after 10 frit-fragmentation exfoliation processes in Example 1 are obtained from atomic force microscopy.

[0069] Figure 8 The image shows a physical picture of a block-type polymer composite material obtained by directly pressing a mold and then heat-treating the powder A, which is a mixture of powder B containing high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets and thermoplastic component rosin, obtained by 10 frit-fragmentation peelings in Example 1.

[0070] Figure 9 The test data for the compressive mechanical properties of the bulk polymer composite material and the blank pure rosin bulk material in Example 1 are the compressive stress-strain curves.

[0071] Figure 10 The results of thermal conductivity tests on the three bulk materials are presented as follows: a high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B filled with B, a bulk polymer composite material filled with the same amount of raw commercial cosmetic grade hexagonal boron nitride that has not undergone frit-fragmentation and stripping as filler, and a blank pure rosin bulk material, using the same synthesis process as in Example 1.

[0072] Figure 11 The image shows a physical picture of a polymer composite film material of polyimide with nanosheet powder B as filler, synthesized in Example 1.

[0073] Figure 12 The comparison is presented as a comparison of the visible light transmittance test data of the polymer composite film material synthesized in Example 1 with that of a blank pure polyimide film.

[0074] Figure 13 The stress-strain curves of the mechanical property test results of the polymer composite film material synthesized in Example 1 are presented for comparison with those of the blank pure polyimide film.

[0075] Figure 14 The thermal conductivity test results of the polymer composite film material synthesized in Example 1 are compared with those of the blank pure polyimide film.

[0076] Figure 15The interfacial adhesive composite material formed by directly filling the powder A synthesized in Example 1 into the original polymer adhesive component was used to adhere a broken steel rod. The tensile fracture properties of the bonded steel rod, i.e., the tensile stress-strain curve, were tested to test its adhesive performance and compared with the adhesive performance of the blank pure polymer adhesive.

[0077] Figure 16 The interfacial adhesive composite material was formed by directly filling 5 wt.% powder A synthesized in Example 1 into the original polymer adhesive components, and the thermal conductivity value of the adhesive interface layer formed by its curing was tested and compared with the thermal conductivity value of the blank pure polymer adhesive.

[0078] Figure 17 Comparison of X-ray powder diffraction (XRD) spectra of Mxene two-dimensional nanosheet powder B after frit-fragmentation exfoliation and the original unexfoliated Max family ceramic powder in Example 6.

[0079] Figure 18 The X-ray powder diffraction (XRD) patterns of the flake graphite samples after flotation-fragmentation exfoliation and before exfoliation are compared after the layered material in Example 6 was replaced with flake graphite.

[0080] Figure 19 The image is a scanning electron microscope (SEM) image of graphite after frit-fragmentation exfoliation following the replacement of the layered material in Example 6 with flake graphite.

[0081] Figure 20 The image is a scanning electron microscope (SEM) image of a sample of hexagonal boron nitride crystal particles that were peeled into high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B after the frit-fragmentation cyclic peeling process in Example 11, in which rosin was replaced with sugar. Detailed Implementation

[0082] To better assist those skilled in the art in understanding this invention, we will further describe the details of the invention in detail and further analyze and clarify the method mechanism of the invention with practical examples. It should be emphasized that the following examples are only used to more clearly illustrate the invention and should not be construed as limiting the scope of protection of this invention in any way. Those skilled in the art can make various improvements and adjustments based on the content of this invention, and these improvements and adjustments should still be included within the scope of protection of this invention.

[0083] Unless otherwise defined, the technical terms used in this invention have the same meaning as commonly understood by those skilled in the art. All raw materials, reagents, instruments, equipment and some consumable materials used in this invention can be purchased from the market or prepared by existing methods.

[0084] This invention relates to a method and application for preparing high aspect ratio two-dimensional materials based on fused fragmentation exfoliation. The process flow for preparing high aspect ratio two-dimensional materials and their high thermal conductivity polymer composites using fused fragmentation exfoliation can be referred to [reference needed]. Figure 1 It includes the following steps:

[0085] (a) The frit-fragmentation and stripping process of layered stacked crystalline materials:

[0086] That is, the powder of a crystalline material with a layered stacked structure and the powder of a thermoplastic material are uniformly mixed to form a mixed powder;

[0087] The crystalline materials with layered stacking structures include, but are not limited to, powders of hexagonal boron nitride, graphite, or Max group ceramics;

[0088] The thermoplastic materials include, but are not limited to, powders of one or more of the following: rosin (resin), terpene resin, polyamide, polyetheretherketone, polyphenylene sulfide, hot melt adhesive polyethylene, hot melt adhesive polyvinyl acetate, or hot melt adhesive polyethylene-vinyl acetate.

[0089] Specifically, the mixed powder is heated at a rate between 5°C / min and 100°C / min to achieve a target melting temperature range of 50°C to 400°C.

[0090] When the thermoplastic material is rosin, the target melting temperature range is 80℃-160℃.

[0091] When the thermoplastic material is a terpene resin, the target melting temperature range is 100℃-220℃.

[0092] When the thermoplastic material is polyamide, the target melting temperature range is 140℃-320℃.

[0093] When the thermoplastic material is polyetheretherketone, the target melting temperature range is 350℃-400℃.

[0094] When the thermoplastic material is polyphenylene sulfide, the target melting temperature range is 290℃-350℃.

[0095] When the thermoplastic material is sugar, the target melting temperature range is 150℃-190℃.

[0096] When the thermoplastic material is a hot melt adhesive, the target melting temperature range is 50℃-150℃. That is, when it is polyethylene, the target melting temperature range is between 100℃-150℃, and when it is polyethyl acetate and polyethylene-ethyl acetate, the target melting temperature range is between 50℃-100℃.

[0097] When the proportion of layered crystalline materials is high (the weight ratio of layered materials to thermoplastic materials is between 0.3 and 0.5), the inorganic non-metallic layered crystalline particles restrict the fluidity of the melt, resulting in poor overall fluidity of the mixture in the molten state at the target melting temperature. The melting process usually requires a continuous melting time of up to 12-48 hours.

[0098] Among them, for rosin, sugar, terpene resin and hot melt adhesive thermoplastic materials or polyetheretherketone, which have good self-flowability in the molten state, the addition of layered crystal materials in a low proportion (their weight ratio to thermoplastic materials is between 0.1 and 0.3) can usually achieve a high melting process at the target melting temperature of 0.5-12 hours.

[0099] Considering the characteristics of easily forming a highly fluid melt in a short time and the advantages of a relatively moderate or low melting point, the preferred thermoplastic materials are rosin, sugar, terpene resin or polyethylene-vinyl acetate.

[0100] After the above-mentioned mixed powder is melted for 0.5-48 hours, a melt is formed. Then, the temperature is gradually reduced at a cooling rate between 5℃ / min and 100℃ / min. The melt is cooled and solidified into a solid block. The cooled solid block is then crushed into powder particles.

[0101] Then, the pulverized powder is melted into a melt under the same temperature rise conditions to reach the same target melting temperature, and then the melt is maintained for the same time. After that, it is cooled into a solid block under the same cooling conditions. Then, the cooled solid block is subjected to the same crushing process to form powder, and then powdered granules are obtained.

[0102] The above completes one frit-fragmentation cycle, which is two frit-fragmentation processes. After several frit-fragmentation cycles, the resulting fragmented mixed powder is labeled as powder A, which is a powder of a high aspect ratio two-dimensional material containing thermoplastic material. It is a powder composed of a two-dimensional nanosheet structure nanomaterial with high aspect ratio and ultrathin characteristics and thermoplastic material.

[0103] The surface activation and functionalization of graphite and Max group layered materials involved in this invention are easier to achieve compared to hexagonal boron nitride layered structures. During heating, the edges of graphite stacks readily form bonds with thermoplastic materials. The relatively weak interlayer bonding of Max ceramic powders makes their surfaces or interlayer edges easily activated or functionalized by active groups. However, due to its inherent high-temperature inertness, high chemical and physical inertness, and high resistance to oxidation and corrosion, the surface of highly crystalline hexagonal boron nitride crystal particles is difficult to activate or functionalize with active groups.

[0104] In this invention, the hexagonal boron nitride crystal powder that needs to be melted and broken is oxidized in order to activate some active groups or bond-breaking active sites on the edges or exposed surfaces of these highly crystalline hexagonal boron nitride particles.

[0105] The oxidation process for highly crystalline hexagonal boron nitride micron particles can be achieved by activating the inert surface or edges of hexagonal boron nitride through various methods, but is not limited to the following oxidation activation schemes:

[0106] Hexagonal boron nitride powder and boron trioxide powder are thoroughly mixed at a mass ratio of 6:1 and then calcined in a muffle furnace at 500-800℃ for 48-96 hours.

[0107] When the mass ratio is 1:1, it is calcined in a muffle furnace at 500-800℃ for 24-48 hours;

[0108] When the mass ratio is 1:6, it is calcined in a muffle furnace at 500-800℃ for 2-24 hours;

[0109] Alternatively, the hexagonal boron nitride powder can be directly calcined in a high-temperature muffle furnace at a temperature range of 800-900℃ for no less than 72 hours.

[0110] The excellent melting fluidity of high-temperature boron trioxide promotes a tight adhesion of the high-temperature interface, and its oxidative corrosion effect on the exposed surface and edges of hexagonal boron nitride is better than that of direct calcination in air by hexagonal boron nitride powder alone. Therefore, the preferred solution is an oxidation treatment scheme of calcination in a muffle furnace at 500-800℃ for 24-48 hours with a mass ratio of 1:1.

[0111] Oxidation treatment activates the surface of hexagonal boron nitride to produce abundant hydroxyl and amino groups, but does not introduce defects into the internal planes of the hexagonal boron nitride, nor does it affect the crystallinity of its internal layers (from...). Figure 3 and Figure 4 In the comparison, it can be seen that the basic morphology is consistent with that of the untreated material, except that its surface is slightly roughened. Oxidation treatment is beneficial for the strong bonding between thermoplastic material molecules and the surface of hexagonal boron nitride during the melting process. These strong bonds can tear or peel off the stacked layers of hexagonal boron nitride as the thermoplastic material blocks break apart during the fragmentation process, thereby achieving the peeling effect of hexagonal boron nitride layered material. Analogous to this fragmentation tearing or peeling effect when applied to graphite and Max group layered structure materials, the same peeling effect is achieved.

[0112] The physical mechanism by which this invention utilizes a frit-fragmentation process to effectively peel off layered crystalline materials with high aspect ratio and ultrathin features is as follows:

[0113] (i) Polymers in the molten or melted state are in a high-energy state, and there is the formation of broken bonds or rearrangement between polymer molecules, which increases the activity of polymer molecules and makes them more likely to react chemically with other active molecules, groups or surfaces to form strong bonds; in addition, polymers in the molten state have better adhesion and wettability, which promotes their easy access to other active groups or active surfaces in the melt, making it easier to form strong interactions and exhibiting strong adhesion to the surfaces of other filler phases;

[0114] (ii) The molten mass formed by cooling is a polymer mixture consisting of thermoplastic material molecules tightly adhering to layered material crystal particles, with the layered crystal particles encapsulated within the polymer. When this mixture is broken (see...). Figure 2 Because the stress levels formed or borne by atoms and molecules within the plane of a layered material or a single layer far exceed the stress levels of the breaking force supported by its interlayer interaction forces, when the breaking force is perpendicular to the stacking direction of the layered material plane, these breaking forces will be relaxed and decomposed, and will not develop into stress that tears the layered stacked layers. However, because thermoplastic material molecules form relatively strong bonds with the surface or edges of layered crystal particles, when the breaking force develops along the stacking direction of the layered material, the stacked structure of the layered crystals will be torn or peeled apart by polymer fragmentation caused by the breaking force. In this way, the peeled part of the layered material is left in the cracked block. The cracked fragments are further crushed. When a certain level of fragmentation particle size is reached, it can be ensured that the peeled two-dimensional thin layer still has a high planar dimension. At the same time, by controlling the number of peelings, the layered material can be gradually peeled off to achieve ultra-thin characteristics. In this way, the layered material is effectively peeled off with a high aspect ratio.

[0115] In this invention, based on the above-mentioned physical mechanism of peeling, the best peeling effect can be achieved in terms of energy saving. It can both protect the high aspect ratio two-dimensional material formed in the previous fragmentation from being refined or becoming smaller during the fragmentation process, and at the same time avoid the formation of too many large fragmentation particles in this fragmentation process. These large fragmentation particles contain layered materials that have not participated in the fragmentation and tearing, resulting in poor fragmentation and tearing effect.

[0116] Therefore, based on the above two technical requirements, the crushed particles need to meet certain standards. The standard is that the small particles of the mixture crushed each time must all pass through a mesh screen with a mesh size corresponding to 1.2 to 3 times the average particle size of the powder with the initial layered stacked crystalline material. After meeting this requirement, the layered crystalline material can be peeled off into high aspect ratio ultrathin two-dimensional nanosheet material after 5 to 50 cycles of frit-crushing.

[0117] The fragmentation method used in this invention employs industrially available fragmentation equipment that utilizes hammering, crushing, beating, breaking, or tearing techniques. Ball milling should be strictly avoided. This is because ball milling causes excessive shear stress to occur on the already successfully peeled, high-aspect-ratio ultrathin two-dimensional layers of the layered structure. This relatively large shear stress directly fragments the unpeeled layered material, and may even fragment the already successfully peeled high-aspect-ratio ultrathin two-dimensional material, resulting in an indistinct high-aspect-ratio ultrathin characteristic in the final peeled two-dimensional material.

[0118] The high aspect ratio two-dimensional material obtained by this invention still possesses high crystallinity characteristics similar to the original layered crystals. Therefore, the layered stacked crystal particles corresponding to the highly crystalline two-dimensional nanosheet powder B mentioned in this invention are commercially available materials with high crystallinity and an average particle size distribution in the range of approximately 5-100 micrometers, including highly crystalline hexagonal boron nitride particle powder (…). Figure 4 Figure (a) and Figure 5 ), flake-like highly crystalline graphite ( Figure 18 XRD can illustrate the properties of highly crystalline graphite and highly crystalline Max group Ti3AlC2 materials ( Figure 17 ).

[0119] (b) This step is to remove the thermoplastic material components from powder A:

[0120] That is, the powder A produced in step (a) is dissolved in a temperature range of 25-60°C using a suitable solvent reagent. These solvent reagents have the ability to completely dissolve the thermoplastic material in powder A, but do not have the ability to dissolve any layered crystal structure material or its exfoliated two-dimensional nanosheet material.

[0121] After complete dissolution, the solvent was repeatedly washed through filtration to obtain undissolved, high-purity, high-aspect-ratio, ultrathin two-dimensional material after frit-fragmentation exfoliation. This two-dimensional material is nanosheet powder B obtained by exfoliating layered crystal structure material under frit-fragmentation assisted by thermoplastic materials (see [link]). Figure 4 Chinese (b) map Figure 6 , Figure 7 , Figure 19 and Figure 20 );

[0122] When the thermoplastic material is rosin (resin), the preferred solvent is, but not limited to, any one of ethanol or petroleum ether or any combination thereof in any proportion, which can be dissolved at 25-60°C; when the thermoplastic material is sugar, the preferred solvent is, but not limited to, water, which can be dissolved at 25°C; when the thermoplastic material is terpene resin, the preferred solvent is, but not limited to, petroleum ether, which can be dissolved at 25-50°C; therefore, suitable solvents are, but not limited to, water, ethanol or petroleum ether.

[0123] The solvents and their corresponding thermoplastic materials described above can all be recycled and reused in the frit-shredding process and the dissolution and removal process of thermoplastic materials.

[0124] That is, the solution after filtering out the two-dimensional material nanosheet powder B is put into the rotary evaporation flask of the rotary evaporator for rotary evaporation separation. After the rotary evaporation is completed, the material remaining in the rotary evaporation flask is thermoplastic material, while the solvent reagent that dissolved the corresponding thermoplastic material is recovered in the waste liquid collection bottle.

[0125] In the case of sugar as a thermoplastic material, the rotary evaporation temperature range for separating the water solvent and sugar is 70℃-80℃; the rotary evaporation temperature range for dissolving rosin in ethanol is 50℃-60℃; and the rotary evaporation temperature range for dissolving terpene resin in petroleum ether is 45℃-50℃.

[0126] The recovered solvents, water, ethanol, or petroleum ether, can be reused in the dissolution and removal process of thermoplastic sugar, rosin, or terpene resin in the fused-fragmented powder. The recovered thermoplastic sugar, rosin, or terpene resin can also be reused in the fused-fragmentation stripping process of layered stacked crystal materials.

[0127] When the thermoplastic material is polyethylene, polyvinyl acetate, polyethylene-vinyl acetate, polyamide, polyetheretherketone, or polyphenylene sulfide, and no solvent type that can dissolve these thermoplastic materials has been developed, the high-temperature chemical stability of layered crystalline materials and the high-temperature decomposition characteristics of these thermoplastic materials are used to carry out the removal process of these thermoplastic materials.

[0128] Because graphite has poor temperature resistance and high oxidizing activity at high temperatures, graphite will be oxidized at high temperatures during the process of these thermoplastic components being removed by high-temperature combustion or high-temperature decomposition, resulting in the burning or loss of its two-dimensional material graphene products.

[0129] Therefore, the method of high-temperature decomposition or oxidative burnout of thermoplastic materials cannot efficiently separate the graphite exfoliation two-dimensional material assisted by the above thermoplastic materials in the melt-fragmentation exfoliation process.

[0130] Therefore, in the technology suitable for obtaining high aspect ratio ultrathin two-dimensional materials through the thermal decomposition or burnout mechanism of thermoplastic materials in high temperature air, layered crystal materials only include hexagonal boron nitride crystal particle powder and Max group crystal powder materials mentioned in this invention.

[0131] In the case where the thermoplastic material is selected from the above-mentioned hot melt adhesive polymers polyethylene, polyvinyl acetate, or polyethylene-vinyl acetate, the powder A obtained in step (a) is directly loaded into a muffle furnace in an air environment and subjected to thermal decomposition or oxidation burn-off reaction within a temperature range of 350℃-600℃. After the reaction is complete, the remaining product is high aspect ratio ultrathin two-dimensional nanosheet powder B that has undergone frit-fragmentation peeling. In the case where the thermoplastic material is selected from the above-mentioned polymers polyamide, polyetheretherketone, or polyphenylene sulfide, thermal decomposition or oxidation burn-off reaction is carried out within a temperature range of 600℃-800℃. After the reaction is complete, the remaining product is high aspect ratio ultrathin two-dimensional nanosheet powder B that has undergone frit-fragmentation peeling.

[0132] In this invention, the high aspect ratio ultrathin two-dimensional hexagonal boron nitride nanosheet powder B has ultra-high thermal conductivity characteristics in its two-dimensional plane or along its two-dimensional plane direction.

[0133] (c) This step involves using powder A from step (a) directly as a filler for polymer composites with a polymer matrix to synthesize polymer composites with high thermal conductivity.

[0134] These high thermal conductivity polymer composite materials include several preparation methods mentioned in this invention, but are not limited to the specific preparation methods of bulk polymer composite materials, polymer composite film materials and interfacial adhesive composite materials described in this invention.

[0135] Preparation of bulk polymer composite materials:

[0136] The powder A obtained in step (a), which contains high aspect ratio ultrathin two-dimensional material and thermoplastic material, is directly loaded into a compression molding mold of a certain shape. The powder A is compressed and molded within a pressure range of 1-100 MPa to obtain a block prototype before heat treatment. After the block prototype is kept at a target melting temperature range of 50-300℃ for 0.5-50 hours to achieve particle densification, it is cooled to room temperature to obtain a block polymer composite material with high thermal conductivity, which is filled with nanosheet powder B and uses the thermoplastic material in powder A as the matrix.

[0137] The heating and cooling rates during the heat treatment process are maintained within the range of 1℃ / min to 10℃ / min; and the thermal conductivity of the obtained bulk polymer composite material is not less than 3 W•m when the filling amount of nanosheet powder B is not higher than 35 wt.%. -1 K -1 ;

[0138] In this preparation method, hexagonal boron nitride and graphite, which have high thermal conductivity, are used as layered crystal materials in step (a). Therefore, the nanosheet powder B in powder A is composed of hexagonal boron nitride nanosheets or graphene two-dimensional materials that have been successfully exfoliated and have high aspect ratio and ultrathin thickness.

[0139] In the polymer composites synthesized by this method, the planes of high aspect ratio ultrathin two-dimensional materials (e.g., the planes of hexagonal boron nitride nanosheets as two-dimensional fillers) exhibit an orientational alignment along the direction perpendicular to the pressure, resulting in anisotropic thermal conductivity characteristics in both the parallel and perpendicular directions to the pressure (see references and views). Figure 10 , Figure 14 and Figure 16 ).

[0140] Preparation of polymer composite thin film materials:

[0141] The powder A obtained in step (a) is directly used as filler to fill the unpolymerized or uncured liquid polymer precursor. The mixture is stirred for 0.5-72 hours within a temperature range of 0℃-100℃ to form a viscous, uniformly mixed slurry. This slurry is then coated onto a substrate with a smooth surface using a doctor blade or centrifuged at high speed. The substrate covered with the slurry film is then desolvated and pre-cured at a temperature range of 25-100℃ for 1-48 hours. The desolvated and pre-cured film is then removed from the substrate. The removed film undergoes a secondary reaction in a suitable atmosphere within a temperature range of 120-320℃ for 4-96 hours. After cooling to room temperature, a polymer composite film material of a three-phase system of thermoplastic material / B / polymer filled with nanosheet powder B is obtained. Figure 11 ).

[0142] In the preparation method of the film composite obtained by directly synthesizing powder A using the powder A obtained in this invention, the powder A is characterized by requiring that it be prepared using a melt-crush process assisted by thermoplastic materials such as rosin, sugar, or terpene resin, excluding thermoplastic materials such as polyethylene, polyvinyl acetate, polyethylene-vinyl acetate, polyamide, polyetheretherketone, or polyphenylene sulfide. This is because these thermoplastic materials do not have good soluble solvents to dissolve and disperse them in the unpolymerized or uncured liquid polymer precursor during the film preparation process.

[0143] However, by directly filling the nanosheet powder B obtained in step (b) into an unpolymerized or uncured liquid polymer precursor, while keeping the rest of the film preparation process unchanged, a polymer composite film material of B / polymer two-phase system filled with nanosheet powder B can be obtained, which also exhibits good film properties, similar to the case of directly filling powder A (see [reference]). Figures 11-14 );

[0144] Figure 11 The nanosheet powder B in powder A used in the thin film product is a hexagonal boron nitride two-dimensional nanosheet filler with high aspect ratio and ultrathin thickness that has been successfully exfoliated by frit-fragmentation. The preferred polymer material for the polymer composite thin film material is polyimide (PI).

[0145] In this invention, the internal structural features of the film are similar to those of the bulk polymer composite material filled with nanosheet powder B. That is, within the polymer composite film material, the high aspect ratio ultrathin two-dimensional nanosheet powder B undergoes a highly ordered orientation along the plane of the film. This results in anisotropy of heat transfer within the composite material, with the thermal conductivity in the orientation direction of the nanosheet powder B being significantly higher than that in the direction where the nanosheet powder B is not significantly oriented.

[0146] In this invention, the polymer composite film material prepared, with a nanosheet powder B filling amount not exceeding 20 wt.%, exhibits a high thermal conductivity along the film plane, not less than 14 W•m. -1 K -1 ( Figure 14 ).

[0147] Preparation of interfacial adhesive composite materials:

[0148] Powder A is rapidly dissolved in a soluble solvent by stirring, and after complete dissolution, a uniformly dispersed mixed liquid filler is obtained. The interface adhesive composite material components are dissolved or diluted in a suitable solvent to form a highly fluid viscous liquid. The solvent dispersion of powder A is added to the polymer adhesive liquid, and after uniform stirring at a temperature range of 60-150℃ for 2-96 hours, a viscous mixed adhesive liquid is obtained, resulting in a liquid composite adhesive interface material with thermoplastic material / B / polymer adhesive as the main components, formed by thermoplastic material, nanosheet powder B, polymer adhesive, and solvent.

[0149] Similarly, because solvents are used to dissolve and form a uniformly dispersed mixed liquid filler, the characteristic of powder A used in the preparation of this type of interfacial adhesive composite material is that it requires powder A to be prepared by a melt-crush process assisted by thermoplastic materials such as rosin, sugar, or terpene resin, excluding these thermoplastic materials such as polyethylene, polyvinyl acetate, polyethylene-vinyl acetate, polyamide, polyetheretherketone, or polyphenylene sulfide that do not have good solvent solubility properties.

[0150] In this invention, in the preparation of the interfacial adhesive composite material, the solvent used to dissolve and disperse powder A has similar compatibility characteristics with the solvent used to dissolve / dilute the interfacial adhesive composite material: the solvent is, but is not limited to, ethanol or glycerol;

[0151] The interface adhesive composite material is, but is not limited to, any kind of biomass adhesive: preferably a non-toxic and pollution-free biomass adhesive, and the raw material components of the biomass adhesive are mixed in the following mass ratios, but are not limited to, the following two methods: either the weight ratio of epoxidized soybean oil: tannic acid: malic acid: ethanol is (8-10): (4-6): (3-5): (10-15) or the weight ratio of epoxidized soybean oil: tannic acid: glycerin is (8-10): (4-6): (10-20);

[0152] In this invention, when the filler content of nanosheet powder B in the interfacial adhesive composite material is not higher than 30 wt.% after filling with powder A, the adhesive performance of the interfacial adhesive composite material shows an improved trend. Figure 15 The image shows a tensile strain-stress orientation diagram obtained from a tensile test of steel rods bonded with the prepared adhesive polymer, illustrating a significant improvement in adhesion. The adhesive polymer also shows a clear trend towards improved interfacial thermal conductivity (see [reference]). Figure 16 After filling with 5 wt.% powder A, the thermal conductivity of the interfacial adhesive layer of the interfacial adhesive composite material increased by approximately 2.5 times.

[0153] In terms of improving the thermal conductivity of interfacial adhesive composites, the trend of thermal conductivity improvement is similar when the amount of nanosheet powder B directly filled is equal to the amount of powder B filled after powder A is filled.

[0154] Example 1:

[0155] The oxidation process of hexagonal boron nitride is as follows: 1000g of commercially available, highly crystalline cosmetic-grade hexagonal boron nitride crystal powder with an average particle size range of 20 micrometers is uniformly mixed with 1000g of boron trioxide in a mixer to obtain a mixture. The mixture is then placed in a stainless steel cylinder and heat-treated in a muffle furnace at 500℃ for 48 hours. After naturally cooling to room temperature, the mixture is removed and washed in hot water at least 5 times to remove the boron trioxide components. The remaining hexagonal boron nitride powder with an oxidized surface is then dried in an oven to obtain a powder of hexagonal boron nitride crystals with an oxidized surface. Figure 3 The image shown is a SEM image obtained after the above surface oxidation treatment, compared with the original commercial cosmetic-grade hexagonal boron nitride powder (compared to...). Figure 4As can be seen from the SEM image in (a), the size and thickness of the hexagonal boron nitride particles did not change significantly after oxidation, but the surface underwent slight roughening, which indirectly confirms the edge activation effect of surface oxidation.

[0156] (a) 30g of commercially available, highly crystalline cosmetic-grade hexagonal boron nitride crystal powder with an average particle size range of 20 micrometers, which has undergone surface oxidation treatment, and 100g of rosin powder are mixed in a mortar to form a uniformly mixed powder. The mixed powder is then placed into a covered stainless steel cylinder, and the covered stainless steel cylinder containing the mixed powder is placed into a muffle furnace or oven or other heating equipment with controllable heating and constant temperature holding capabilities for melting. The heating rate is controlled at 20℃ / min until the target melting temperature is reached. After being heated to 140℃ and held at that temperature for 10 hours, the temperature was lowered to room temperature at a rate of 20℃ / min. The molten block containing hexagonal boron nitride and rosin was then removed from the stainless steel cylinder and pulverized on a commercial pendulum pulverizer equipped with a 325-mesh filter to obtain powder. The powder product then underwent the same molten block and further pulverization process described above. After 10 cycles of molten block-pulverization, powder A was obtained, which is a pulverized mixed powder containing high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet material and thermoplastic polymer material rosin.

[0157] (b) The fragmented mixed powder obtained above is added to 500 mL of anhydrous ethanol and stirred and dissolved at room temperature. After complete dissolution, the filtrate in the mixture is filtered by vacuum filtration. The filter residue is dissolved and washed again in ethanol. After washing 3-5 times, the filter residue is dried in a freeze dryer or air to obtain high-purity, high-crystallinity, high-area-ratio ultrathin hexagonal boron nitride two-dimensional nanosheet material.

[0158] After comparison with original commercial cosmetic-grade hexagonal boron nitride nanosheets ( Figure 4 (Comparison images) clearly show that after 10 frit-fragmentation exfoliation processes, the hexagonal boron nitride crystal particles were successfully exfoliated into thinner hexagonal boron nitride two-dimensional nanosheets;

[0159] Analysis of the XRD test results of the two showed that the original thickness of the hexagonal boron nitride particles was significantly reduced, and the data values ​​of the (002) crystal plane diffraction peak in the XRD were used as the basis (see Figure 5 According to the Scherrer formula, the average thickness of the obtained hexagonal boron nitride two-dimensional nanosheets is 3 nm, which is approximately equivalent to a stack of 10 layers of hexagonal boron nitride (002) planar layers in two-dimensional nanosheets. Compared with the original commercial cosmetic grade hexagonal boron nitride particles with an average thickness of about 1 μm, the thickness value of the obtained hexagonal boron nitride two-dimensional nanosheets is about 3‰ of the thickness value of the original hexagonal boron nitride particles.

[0160] Statistical analysis of the planar dimensions of the exfoliated hexagonal boron nitride two-dimensional nanosheets revealed that their basic distribution is 1-10 μm (similar to...). Figure 6 The thickness and planar dimensions, Figure 6 The characteristics of the transmission electron microscopy (TEM) images represent the basic features of the exfoliated hexagonal boron nitride nanosheets, based on statistical data from optical electron microscopy (OEM) and atomic force microscopy (AFM) images (see [link to OEM image).) Figure 7 With an average planar dimension of about 5 μm, the resulting two-dimensional hexagonal boron nitride material has an aspect ratio of about 1700, exhibiting high aspect ratio and ultrathin characteristics.

[0161] It is worth noting here that the filtrate, i.e., the ethanol + rosin mixture containing dissolved rosin, can be used to recover ethanol and rosin by rotary evaporation at 50°C.

[0162] (c) Using powder A, which contains high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet material and thermoplastic rosin polymer material in step (a), as a raw material or filler to prepare a high thermal conductivity polymer composite material;

[0163] Preparation of bulk polymer composite materials:

[0164] A suitable amount of powder A is directly loaded into a stainless steel round / square column mold. After pressing for 10 minutes under a pressure of 20 MPa, the sample is removed from the mold to obtain a hard and dense block formed by these powders. After being kept in an oven at 50°C for 50 hours, a block polymer composite material with rosin as the matrix and filled with high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets is obtained, which is the high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet / rosin polymer block polymer composite material.

[0165] Using molding dies of different shapes, physical examples of bulk polymer composite materials with different bulk shapes can be prepared, such as... Figure 8 As shown.

[0166] Based on the results of mechanical tests (see...) Figure 9 Analysis shows that the bulk polymer composite material made by pressure molding and heat treatment using powder A directly as raw material has higher mechanical properties than the pure rosin bulk material prepared by using blank rosin as powder raw material through the same pressure molding and heat treatment process. The mechanical strength is increased by more than 2 times and the compression modulus is increased by about 3 times, showing the mechanical property advantages of filling or directly using fused-fragmented mixed powder to prepare bulk composite structures.

[0167] Based on this excellent, dense, and mechanically strong bulk polymer composite material, the presence of hexagonal boron nitride nanosheets with high in-plane thermal conductivity within its interior results in superior thermal conductivity. For example... Figure 10 As shown, its thermal conductivity is significantly higher than that of unpeeled commercial hexagonal boron nitride-filled bulk materials, and its thermal conductivity is much higher than that of blank rosin polymer matrix blocks. Notably, the thermal conductivity exhibits anisotropic characteristics in different directions of the bulk composite structure; specifically, the thermal conductivity along the molding pressure direction changes with temperature by approximately 1.5 W·m after filling with 30 wt.% high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets. -1 K -1 In the direction perpendicular to the magnetic field, the same amount of hexagonal boron nitride two-dimensional nanosheets can increase the thermal conductivity to 2.1 times that in the parallel direction, with thermal conductivity values ​​not lower than 3.0 W•m. -1 K -1 This is due to the high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets that are regularly oriented along the direction perpendicular to the pressure molding direction within the bulk polymer composite material. These arrangements promote the anisotropy of thermal conductivity and result in thermal conductivity values ​​that are significantly higher than those of bulk polymer composite materials filled with unpeeled hexagonal boron nitride.

[0168] Preparation of polymer composite thin film materials:

[0169] 10g of mixed powder A was directly dissolved in a three-necked flask in an ice bath. The flask contained a mixed solution of 10g of polyamic acid dissolved in 50ml of N,N-dimethylacetamide and 50ml of ethanol. After vigorous stirring for 12 hours, a uniform viscous slurry with rosin / hexagonal boron nitride two-dimensional nanosheets / polyamic acid as the main components was obtained. The viscous slurry was then coated onto a glass substrate with a smooth surface using a doctor blade. The glass substrate coated with the slurry layer was then kept at a constant temperature of 8°C in an oven. After vacuum drying at 0℃ for 20 minutes, the glass substrate was cooled and removed, and the coated film was taken off. The film was then directly thermally imidized to 160℃ (heating rate of 5℃ / min) in a nitrogen environment (nitrogen flow rate not higher than 50 ml / min) and held for 2 hours. Finally, it was held at 310℃ for 2 hours and then naturally cooled to room temperature to obtain a polymer composite film material of rosin / hexagonal boron nitride high aspect ratio two-dimensional nanosheets / polyimide (PI) filled with hexagonal boron nitride two-dimensional nanosheet powder B.

[0170] It is worth noting that by directly replacing powder A with nanosheet powder B and performing the above operations, a polymer composite film material of polyimide (PI) filled with hexagonal boron nitride two-dimensional nanosheet powder B can be obtained (e.g., Figure 11As shown in the figure, the properties of the physical sample are similar to those of the sample directly filled with powder A. However, when rosin is added, the viscosity and adhesion of the resulting slurry are better than those of the sample directly filled with nanosheet powder B.

[0171] Combining tests of the thin film in the visible light range with actual light transmittance properties (see...) Figure 11 This can be visualized and demonstrated through test data that the visible light transmittance of the polyimide polymer composite film material filled with 15 wt.% of this high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B is approximately half that of the pure polyimide film in the 600-800 nm range, and the visible light transmittance is approximately 40%. Figure 12 As shown, its performance is similar to that of filler powder A.

[0172] In terms of mechanical properties (such as Figure 13 As shown, the tensile strength of the polyimide polymer composite film material filled with 15 wt.% of the high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B is more than twice that of the unfilled blank polyimide film, but its tensile elastic modulus is 4.4 times that of the unfilled blank polyimide film. Its tested tensile elastic modulus can reach 2.2 GPa. When powder A is filled, the mechanical properties are slightly higher than those when nanosheet powder B is directly filled. Therefore, the mechanical properties of the polyimide composite film obtained by directly filling powder A are better.

[0173] In terms of thermal conductivity (e.g.) Figure 14 As shown), the in-plane thermal conductivity of the polyimide polymer composite film material filled with 15 wt.% of this high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B is at least 14 W·m. -1 K -1 Its thermal conductivity is more than 120 times higher than that of the unfilled blank polyimide film, and its in-plane thermal conductivity is more than 100 times higher than that in the direction perpendicular to the film plane. This fully demonstrates the effect of filling with this high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets on improving the thermal conductivity of the film and the directional heat transfer characteristics caused by their orientation. Compared with the case of directly filling powder A, although the final thermal conductivity of directly filling 15 wt.% powder A is slightly lower than that of directly filling 15 wt.% nanosheet powder B, this is because the rosin component in powder A occupies a part of the filling amount, making the actual thermally conductive filling component in the polymer composite film material less than 15 wt.%. Therefore, the influence of the filling amount on the thermal conductivity is weakened to some extent. However, the polymer composite film material obtained by directly filling powder A exhibits superior mechanical and optical properties (see Figure 11 , Figure 12 and Figure 13 ).

[0174] Preparation of interfacial adhesive composite materials:

[0175] 1g of powder A was dissolved in 5ml of ethanol to form a rosin-filled mixture of rosin and ethanol, which is uniformly dispersed in high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets. Biomass adhesive (composed of 10g epoxidized soybean oil, 6g tannic acid and 5g malic acid) was dissolved in 10g of ethanol at room temperature and stirred until a uniform, transparent, viscous liquid was obtained, resulting in a viscous polymer adhesive liquid. The filler mixture and the viscous polymer adhesive liquid were combined and stirred at 60℃ for 96 hours to obtain a viscous mixed liquid. This liquid is a liquid composite material of interfacial adhesive composite material formed by rosin, high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets, biomass adhesive and ethanol.

[0176] The bonding performance (bond strength) of the interfacial adhesive composite material filled with 5 wt.% powder A is 1.5 times that of the unfilled blank polymer adhesive (e.g., ...). Figure 15 As shown in the figure, after filling with only 5 wt.% powder, its bonding strength to steel material can reach about 30 MPa, while the bonding strength test value of the blank original polymer adhesive is about 20 MPa.

[0177] After filling with 5 wt.% powder A, the calculated high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets ranged from 0.5 to 1.5 wt.%. Such a low filling amount of hexagonal boron nitride two-dimensional nanosheets can induce the binder to form a high-heat-transfer interfacial adhesive layer. The average measured thermal conductivity of this thermal interface material is as low as 0.42 W•m. -1 K -1 Furthermore, its thermal conductivity at a high temperature of 130℃ can be stably maintained at 0.75 W•m. -1 K -1 The thermal conductivity values ​​of the cured thermal interface layer formed by the original polymer adhesive are approximately 2.8 times and 3.5 times, respectively (e.g., ...). Figure 16 As shown), this significantly enhances the adhesion properties of the polymer adhesive (see Figure 1). Figure 15 (and its thermal conductivity after forming a thermal interface structure).

[0178] Example 2:

[0179] The oxidation process in Example 1 was modified as shown in the table below:

[0180]

[0181] The remaining steps (a), (b), and (c) are exactly the same as those in Example 1. The resulting powder A and nanosheet powder B are the same as those in Example 1, and the properties of the prepared composite material are similar to those in Example 1, with similar mechanical property enhancement and significantly improved thermal conductivity.

[0182] Example 3:

[0183] By changing the amount of hexagonal boron nitride used in the oxidation treatment in Examples 1 and 2 to 10g, 20g, 40g, and 50g, respectively, and changing the heating rate and cooling rate to 5, 40, 80, and 100℃ / min, respectively, it is worth noting that when the amount of hexagonal boron nitride used in the oxidation treatment is 40g or 50g, the target melting temperature is adjusted to 150 and 160℃, respectively, and the holding time is adjusted to 24 and 48 hours, respectively. When the amount of hexagonal boron nitride used in the oxidation treatment is 10g or 20g, the target melting temperature is adjusted to 80℃ and 120℃, respectively, and the holding time is adjusted to 0.5-12 hours, respectively. Keeping other steps consistent with those in Examples 1 and 2, the resulting powder A and nanosheet powder B are the same as those in Examples 1 and 2, and the properties of the prepared composite material are similar to those in Examples 1 and 2, with similar enhanced mechanical properties and significantly improved thermal conductivity.

[0184] Example 4:

[0185] When the number of frit fragmentation times in Examples 1, 2, and 3 was adjusted to 5, 20, and 50 times, respectively, while keeping other steps unchanged, the mechanical and thermal conductivity properties of powder A obtained after 5 fragmentation times were weaker than those obtained after 10 fragmentation times when preparing subsequent composite materials. However, these properties were still much better than those of the blank backing sample. As the number of fragmentation times increased, reaching 20 and then 50 times, the mechanical properties of the resulting composite material showed slight enhancement fluctuations. However, the further increase in thermal conductivity was not significant. This may be because the high aspect ratio ultrathin feature inevitably led to the gradual reduction of the fragmentation particles due to the increased number of fragmentation times. Smaller two-dimensional particles created more heterogeneous interfaces in the composite system, which negatively affected the thermal conductivity. Moreover, the tendency of particle orientation was gradually weakened as the number of frit fragmentation times increased to 20 and 50 times, which also weakened the trend of anisotropic thermal conductivity. In summary, the mechanical and thermal conductivity properties of the synthesized composite material change with the increase of the number of melt-crush cycles, but the overall trend is similar to that in Examples 1, 2 and 3.

[0186] Example 5:

[0187] The ethanol dissolution environment in Examples 1, 2, 3 and 4 was adjusted to 40°C and 60°C, respectively, while the other steps remained unchanged, to obtain the same high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet powder B as in Examples 1, 2, 3 and 4. However, changing the rotary evaporation temperature for recovering ethanol and rosin to 60°C also allowed for the separation and recovery of ethanol and rosin.

[0188] Examples 6-17:

[0189] After replacing the thermoplastic material and layered stacked crystal material in step (a) of steps 1, 2, 3, 4, and 5 in the embodiments, and the dissolving and cleaning solvent in step (b), with the thermoplastic material and solvent material listed in the table below, and adjusting some parameters in the table, see the following table example:

[0190]

[0191]

[0192] The operation process and specific parameters of the remaining steps remain unchanged. The recovered rosin, sugar and terpene resin, as well as the recovered solvents petroleum ether, ethanol and water mentioned in the examples can be reused in the fused-crushing cycle process.

[0193] The obtained nanosheet powder B has the same properties as the nanosheet powder B in Examples 1, 2, 3, 4 and 5. Among them, the high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheet structure exfoliated in Example 11 can be visualized by SEM image photographs (see Figure 20 The images in the figure clearly illustrate that by replacing rosin with sugar and using the same steps, commercial hexagonal boron nitride highly crystalline particle powder can be effectively exfoliated through a frit-crushing process to prepare ultrathin hexagonal boron nitride two-dimensional nanosheet materials with a high aspect ratio. The high thermal conductivity polymer composite material prepared using powder A has similar properties to those in Examples 1, 2, 3, 4 and 5.

[0194] Example 18:

[0195] In step (c) of Examples 1-17, the proportions of each component in the original polymer adhesive, the filling amount of powder A, the stirring time, and the stirring temperature in the preparation of powder A directly filled with the original polymer adhesive were adjusted. The specific adjustment values ​​are shown in the table below:

[0196]

[0197] With the remaining steps and specific parameters remaining unchanged, the original polymer adhesive prepared with the modified parameters in this embodiment, after being filled with powder A, exhibits similar thermal conductivity and mechanical properties to the interfacial adhesive composite materials in Examples 1, 2, 3, 4, and 5.

[0198] Example 19:

[0199] The thermoplastic material in step (a) of Examples 1-18 and some parameters of it in the frit-fragmentation process, as well as the corresponding parameters of the thermoplastic material in the cleaning process in subsequent step (b), are replaced with the parameters in the table below:

[0200]

[0201] The remaining steps and specific parameters remain unchanged, and the obtained nanosheet powder B has the same high aspect ratio and ultrathin characteristics as the nanosheet powder B in Examples 1, 2, 3, 4 and 5. Thus, an ultrathin hexagonal boron nitride two-dimensional nanosheet material with a high aspect ratio is prepared. The high thermal conductivity bulk polymer composite material prepared directly from powder A raw material in this example through pressure molding and heat treatment has similar properties to those in Examples 1, 2, 3, 4 and 5. The difference is that no additional thermoplastic component was filled when preparing the film and interface adhesive composite material, but the effect on improving thermal conductivity is significant.

[0202] Example 20:

[0203] The layered crystal material in step (a) of Examples 1-19 is replaced with the following: For each case, the mesh size of the crushing sieve changes as shown in the table below when the screen of the crushing equipment is changed.

[0204]

[0205] The operation process and specific parameters of the remaining steps remain unchanged, and the layered crystals are still hexagonal boron nitride. The resulting powder A and nanosheet powder B are the same as those in Examples 1, 2, 3, 4 and 5. The properties of the prepared composite materials are similar to those in Examples 1, 2, 3, 4 and 5, with similar results and similar properties of enhanced mechanical properties and significantly improved thermal conductivity.

[0206] If the layered crystals are Max group Ti3AlC2, then after cleaning, powder A can yield Mxene two-dimensional nanosheets with high aspect ratio and ultrathin characteristics, such as... Figure 17As shown, the XRD pattern after several melting-fragmentation cycles shows a significant enhancement in the intensity of the main diffraction peak of the layered structure. The significant weakening and disappearance of other Miller index peaks that do not characterize the layered stacking demonstrate the effectiveness of exfoliating Max into Mxene two-dimensional material. At the same time, the high crystallinity after melting-fragmentation indicates that the exfoliated Mxene two-dimensional material still has high crystallinity characteristics, demonstrating the ultrathin two-dimensional characteristics with a high aspect ratio.

[0207] Similarly, if the layered crystals are flake graphite, then powder A, after washing, can yield graphene with a high aspect ratio and ultrathin characteristics, such as... Figure 18 As shown, the (002) diffraction peak in the XRD pattern after several melting-fragmentation cycles showed a significant leftward shift and a significantly increased full width at half maximum (FWHM). This indicates that the presence of thin-film graphite is a typical characteristic of highly crystalline graphene with a high aspect ratio. Figure 19 The SEM images also show that the frit-fragmentation process is very similar to the exfoliation effect on large-particle-size graphite and the high aspect ratio ultrathin hexagonal boron nitride two-dimensional nanosheets obtained by exfoliation.

[0208] According to the present invention, the function of powder A obtained in step (a) is not limited to its direct use as a filler in the preparation of bulk, thin film, and adhesive polymer composites. It also includes using powder A directly as a filler to prepare thin film or other types of nanosheet powder B-filled polymer composites through other polymer compounding methods, including but not limited to compression molding, high-temperature casting molding, coating-heat treatment molding, and other preparation processes and molding technologies. In these steps, the direct use of powder A as a product for use as a filler component in polymer composites is considered to be within the scope of protection of this patent.

[0209] By combining the layered crystalline structure materials mentioned in this invention with thermoplastic materials not mentioned in this invention, or by combining the thermoplastic materials mentioned in this invention with layered crystalline structure materials not mentioned in this invention, and employing the basic route and principle of the exfoliation technique of this invention, two-dimensional materials of hexagonal boron nitride and other two-dimensional materials of layered crystalline structure have been synthesized, along with corresponding product types. These innovative products, including the application techniques and methods of using this hexagonal boron nitride two-dimensional nanosheet material or other two-dimensional materials in other related fields, are all within the protection scope of this invention.

[0210] Without altering the basic principles, basic routes, or basic raw materials of this invention, non-inventive technologies and processes have been developed, such as replacing, simplifying, substituting, modifying, improving, altering, or adding experimental steps and raw materials, to synthesize hexagonal boron nitride two-dimensional nanosheets or other two-dimensional materials and their composite materials used directly as fillers, by substituting, simplifying, replacing, modifying, improving, altering, or adding experimental steps and raw materials. These derivative technologies are also considered to infringe upon this invention.

[0211] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing high aspect ratio two-dimensional materials based on frit-fragmentation exfoliation, characterized in that, The method includes the following steps: 1) Mixing: The powder of crystalline material with layered stacked structure and the powder of thermoplastic material are mixed uniformly in a weight ratio between 0.1 and 0.5 to form a mixed powder; The crystalline material with a layered stacking structure includes at least one of hexagonal boron nitride, graphite, hexagonal molybdenum sulfide, or highly crystalline micron-sized particles of Max group materials; 2) Fused block: The mixed powder is heated to melt it into a melt and then cooled to solidify it into a block of solid material; 3) Crushing: The solid block is crushed into powder particles using a non-mechanical ball milling method. A screen is set up during the crushing process. The mesh size of the screen is determined according to the mesh size corresponding to 1.2 to 3 times the average particle size of the powder of the initial layered stacked crystal material. 4) Cycling: Repeat steps 2)-3) to perform the melting-crushing process on the crushed powder particles. Repeat the process 5-50 times to obtain a powder containing thermoplastic material with a high aspect ratio two-dimensional material, denoted as powder A.

2. The method according to claim 1, characterized in that, The non-layered thermoplastic material components in powder A are removed by dissolving and filtering with a heated solvent, or by high-temperature calcination. The specific process of the heating solvent dissolution and filtration method is as follows: Powder A is dissolved in a solvent with a temperature range of 25-60℃. After washing and filtering to remove the thermoplastic material components, the remaining material is a powder of a high aspect ratio two-dimensional material obtained by exfoliation, denoted as nanosheet powder B; the solvent is a liquid that can dissolve the thermoplastic material components in the temperature range of 25-60℃. The specific process of the high-temperature calcination method is as follows: Powder A is processed and removed by high-temperature decomposition in the temperature range of 350-900℃. After removal, the remaining material is the powder of high aspect ratio two-dimensional material obtained by peeling, which is denoted as nanosheet powder B. The nanosheet powder B is a two-dimensional nanomaterial with a high aspect ratio and ultrathin characteristics.

3. The method according to claim 2, characterized in that, The solvent includes at least one of water, ethanol, or petroleum ether: when the thermoplastic material is rosin resin, the solvent is ethanol or petroleum ether; when the thermoplastic material is sugar, the solvent is water; when the thermoplastic material is terpene resin, the solvent is petroleum ether. The thermoplastic material removed by high-temperature calcination is at least one of polyethylene, polyvinyl acetate, polyethylene-vinyl acetate, polyamide, polyetheretherketone, or polyphenylene sulfide. In this process, the solvent used in the heating solvent dissolution and filtration method and its corresponding thermoplastic material can both be recycled. The corresponding thermoplastic material is reused for the stripping of powder of crystalline material with layered stacked structure, and the solvent is reused in the dissolution and removal process of thermoplastic material.

4. The method according to claim 1, characterized in that, The crushing method is a crushing method such as hammering, crushing, breaking, or tearing; the statistical average particle size of the crushed mixed powder must meet certain requirements, that is, it must be 1.2-3 times the statistical average particle size of the powder material with layered stacked structure, or all particles of the crushed mixed powder must pass through a screen with an average mesh size that is 1.2-3 times the statistical average particle size of the powder material with layered stacked structure.

5. The method according to claim 1, characterized in that, The statistical average size range of the crystal material is 5-100 micrometers; the Max group material includes at least one of Ti3AlC2, Ti2AlC, Ti2AlN, V2AlC, Ti2GaC, Ti3GaC2, V3AlC2, Ti4AlN3, V4AlC3 or Nb4AlC3; The thermoplastic material is a thermoplastic polymer material or a sugar that can be melted into a melt when the temperature is raised and can be solidified into a block structure when the temperature is lowered; after the thermoplastic material is solidified, it has a hardness that can be crushed into powder within the room temperature range; The thermoplastic polymer includes at least one of resins, hot melt adhesives, polyamides, polyetheretherketones, and polyphenylene sulfides, wherein the resin is at least one of rosin or terpene resins; The hot melt adhesive includes at least one of polyethylene, polyvinyl acetate, or polyethylene-vinyl acetate. The sugars include at least one of granulated sugar, brown sugar, glucose, or isomalto.

6. The method according to claim 1, characterized in that, The thermoplastic material is at least one of rosin resin, sugar, terpene resin or polyethylene-vinyl acetate.

7. The method according to claim 1, characterized in that, The heating and cooling rates in the molten block are both between 5°C / min and 100°C / min, and the target melting temperature range for heating and cooling is 50-400°C. The heating and cooling rates and the target melting temperature are different in the same cycle and in different cycles.

8. The method according to any one of claims 1-7, characterized in that, The powder of the layered stacked crystal material is a crystal material that has undergone surface activation treatment, which can shorten the number of cycles in the frit-fragmentation process; the surface activation treatment does not cause changes in the internal lattice of the layered crystal material; When the powder of the layered stacked crystal material is a highly crystalline micron-sized hexagonal boron nitride, the surface activation process is as follows: after uniformly mixing commercial hexagonal boron nitride powder and boron trioxide at a mass ratio of 6:1-1:6, it is calcined at a constant temperature in high-temperature air at a temperature range of 500-800℃ for 2-96 hours. Alternatively, without adding boron trioxide, commercial hexagonal boron nitride powder can be directly calcined in high-temperature air at a temperature range of 800-900℃ for more than 72 hours.

9. A two-dimensional material with a high aspect ratio, characterized in that, The high aspect ratio two-dimensional material is obtained by using the method described in any one of claims 1-8. The high aspect ratio two-dimensional material is a two-dimensional nanosheet with a thickness at the nanometer level and an aspect ratio of not less than 1500.

10. An application of a high aspect ratio two-dimensional material obtained by the method of any one of claims 1-8 or the high aspect ratio two-dimensional material of claim 9, characterized in that, The high aspect ratio two-dimensional material is used to prepare bulk polymer composite materials, polymer composite film materials, and interfacial adhesive composite materials.

11. The application according to claim 10, characterized in that, Powder A can be directly prepared into bulk polymer composite materials, polymer composite film materials, or interface adhesive composite materials. The process of preparing bulk polymer composite materials is as follows: (i) Powder A is directly loaded into a compression molding mold of a certain shape, and the powder A is compressed and molded within a pressure range of 1-100 MPa to obtain a bulk prototype before heat treatment; (ii) The bulk prototype is subjected to a particle densification process of heat treatment at a temperature range of 50-300℃ for 0.5-50 hours, and then cooled to room temperature to obtain a bulk polymer composite material. The process for preparing polymer composite film materials is as follows: (i) Powder A is added to an unpolymerized or uncured liquid polymer precursor and stirred for 0.5-72 hours in the temperature range of 0℃-100℃ to form a viscous and uniformly mixed slurry; (ii) The slurry is coated onto a substrate with a smooth surface by a doctor blade or centrifugation at high speed, and the substrate covered with the slurry film is desolvated and pre-cured in the temperature range of 25-100℃ for 1-48 hours, and then the desolvated and pre-cured cover film is removed from the substrate; (iii) The cover film removed from the substrate is subjected to a secondary reaction in the temperature range of 120-320℃ for 4-96 hours, and after cooling to room temperature, the polymer composite film material is obtained. The process of preparing the interfacial adhesive composite material is as follows: (i) Powder A is rapidly stirred, dissolved, and dispersed in a solvent to obtain a uniformly dispersed solvent dispersion of powder A; (ii) The original polymer adhesive components are dissolved or diluted to form a viscous polymer adhesive liquid with strong fluidity; (iii) The solvent dispersion of powder A is added to the polymer adhesive liquid, and the mixture is stirred uniformly for 2-96 hours in a temperature range of 60-150℃ to obtain a viscous mixed adhesive liquid, which is the liquid interfacial adhesive composite material formed by thermoplastic material, nanosheet powder B, polymer adhesive, and solvent. Alternatively, the nanosheet powder B described in claim 2 can be directly used as a filler for polymer composite materials with polymer as the matrix to obtain bulk polymer composite materials, polymer composite film materials, or interfacial adhesive composite materials. The filling amount of nanosheet powder B in the bulk polymer composite material is not higher than 35 wt.%, and the thermal conductivity of the bulk polymer composite material is not lower than 3 W•m. -1 K -1 Thermal conductivity exhibits anisotropic characteristics in bulk polymer composites, with values ​​perpendicular to the molding pressure direction being higher than those parallel to it. In polymer composite thin film materials, the filling amount of nanosheet powder B is no higher than 20 wt.%, and the thermal conductivity along the film plane is no less than 14 W•m. -1 K -1 The thermal conductivity along the plane of the thin film is much higher than that perpendicular to the plane, indicating that the thermal conductivity within the thin film is anisotropic and that the thin film exhibits directional heat transfer along its plane. The filling amount of nanosheet powder B in the interfacial adhesive composite material is not higher than 30 wt.%.

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