CN115746404A - Surface-modified hexagonal boron nitride nanosheet, modification method thereof and epoxy composite material - Google Patents
Surface-modified hexagonal boron nitride nanosheet, modification method thereof and epoxy composite material Download PDFInfo
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Abstract
The invention relates to a surface modified hexagonal boron nitride nanosheet, a modification method thereof and an epoxy composite material, wherein the modification method comprises the following steps: (1) Adding hexagonal boron nitride powder into homogeneous aqueous solution of silane coupling agent containing epoxy group, carrying out ultrasonic dispersion to obtain hexagonal boron nitride dispersion liquid, and adjusting the pH value to 0-6; (2) Transferring the dispersion liquid obtained in the step (1) into a ball milling tank, carrying out ball milling for 1-48 h at 100-2000 rpm, carrying out vacuum filtration after ball milling, and drying powder obtained by filtration to obtain hexagonal boron nitride nanosheets with functionalized epoxy groups on the surface; (3) Adding the hexagonal boron nitride nanosheet obtained in the step (2) into a branched polyethyleneimine water solution, reacting for 1-48 h at 0-80 ℃ after ultrasonic dispersion, and then performing vacuum filtration and drying to obtain the surface-modified hexagonal boron nitride nanosheet. The surface modified hexagonal boron nitride nanosheet provided by the invention can be used for remarkably improving the heat conduction and mechanical properties of the epoxy composite material.
Description
Technical Field
The invention belongs to the field of nano composite materials, and particularly relates to a surface modified hexagonal boron nitride nanosheet, a modification method thereof and an epoxy composite material.
Background
With the development of modern power electronic devices toward miniaturization, high integration and high power density, the problem of thermal management of electronic components inside the device becomes more prominent. Electronic components with high integration density can generate a large amount of heat in a working state, so that the temperature of the components is rapidly increased, and finally, the performance and the service life of electronic equipment are seriously influenced. In order to lead out accumulated heat in time and ensure long-term stable operation of electronic components, it is necessary to fill heat conduction materials between the electronic components. Epoxy resins are thermosetting resins with good overall properties (mechanical strength, adhesive strength, insulating properties, chemical stability, etc.), and are widely used as encapsulating materials for electronic components. However, pure epoxy resins have a low thermal conductivity (about 0.2W/m · K), and cannot effectively diffuse heat from electronic components in a timely manner. Therefore, the development of the epoxy encapsulating material with high heat conduction and excellent comprehensive performance has important practical significance.
It is currently the most common practice to introduce highly thermally conductive fillers into an epoxy resin matrix to improve its thermal conductivity. As an inorganic filler with high thermal conductivity and excellent mechanical properties, hexagonal boron nitride (h-BN), especially stripped h-BN nanosheets, is widely used for manufacturing various high thermal conductive composite materials. It is noted that simply adding the h-BN filler roughly into the matrix usually results in uneven dispersion within the matrix, and a large number of interfacial voids exist between the filler and the matrix, which reduces the thermal conductivity of the composite material. The patent document with the publication number of CN110922719A discloses a high-thermal-conductivity boron nitride/epoxy resin composite material and a preparation method and application thereof, wherein h-BN nanoparticles are used as raw materials, ultrasonic stripping and silane coupling agent surface modification are sequentially carried out to obtain surface-modified h-BN nanosheets, and finally the surface-modified h-BN nanosheets are compounded with epoxy resin, so that the steps of the prepared surface-modified h-BN nanosheets are complicated, and the improvement of the interfacial compatibility between the h-BN nanosheets and the epoxy resin is limited. The patent document with publication number CN113969040A uses hyperbranched polyethylene polymer as a modifying molecule, and surface modification is performed on h-BN through non-covalent actions such as pi-pi, so as to effectively improve the dispersibility of h-BN nanoparticles and the interface compatibility of h-BN nanoparticles with an epoxy matrix, but the non-covalent actions make the binding force between the modifying molecule and h-BN weak, and the modifying molecule and the epoxy matrix cannot be chemically connected, so that the obtained epoxy composite material is still unsatisfactory in heat conductivity and mechanical properties.
Disclosure of Invention
Based on the defects and shortcomings in the prior art, the invention provides a surface modified hexagonal boron nitride nanosheet, a modification method thereof and an epoxy composite material. The method aims to obtain the surface-modified h-BN nanosheet through simple steps, improve the dispersibility of h-BN, ensure that the surface of the modified h-BN nanosheet has rich active groups, can simultaneously perform interfacial chemical reaction with epoxy molecules and a curing agent, improve the compatibility of a filler-matrix interface and finally improve the heat conductivity and mechanical properties of the epoxy composite material.
In order to achieve the purpose, the invention adopts the following technical scheme:
the modification method of the surface modified hexagonal boron nitride nanosheet comprises the following steps:
(1) Adding hexagonal boron nitride powder into homogeneous aqueous solution of silane coupling agent containing epoxy group, carrying out ultrasonic dispersion to obtain hexagonal boron nitride dispersion liquid, and adjusting the pH value to 0-6;
(2) Transferring the dispersion liquid obtained in the step (1) into a ball milling tank, carrying out ball milling for 1-48 h at 100-2000 rpm, carrying out vacuum filtration after ball milling, and drying powder obtained by filtration to obtain hexagonal boron nitride nanosheets with functionalized epoxy groups on the surface;
(3) And (3) adding the hexagonal boron nitride nanosheet obtained in the step (2) into a branched polyethyleneimine water solution, reacting for 1-48 h at 0-80 ℃ after ultrasonic dispersion, and then performing vacuum filtration and drying to obtain the surface modified hexagonal boron nitride nanosheet.
Preferably, in the step (1), the silane coupling agent containing an epoxy group is selected from KH560, and the homogeneous aqueous solution is a water/ethanol mixed solution.
Preferably, in the step (1), the dispersion concentration of the hexagonal boron nitride powder in the water/ethanol mixed solution is 0.5 to 50 mg/mL -1 (ii) a The mass fraction of KH560 in the water/ethanol mixed solution is 0.01-30 wt%; the volume ratio of the water/ethanol mixed solution is 1/(0.1-10).
As a preferable scheme, in the step (1), the time length of ultrasonic dispersion is 5-120 min; the pH of the hexagonal boron nitride dispersion was adjusted by an acid solution.
Preferably, the acid solution is at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, oxalic acid and citric acid;
the molar concentration of the acid solution is 0.01-10 mol.L -1 。
Preferably, in the step (2), the drying temperature is 30-150 ℃, and the drying time is 1-48 h.
Preferably, the molecular weight of the branched polyethyleneimine is 200 to 100000, and the concentration of the branched polyethyleneimine aqueous solution is 0.01 to 30wt%.
The invention also provides a surface modified hexagonal boron nitride nanosheet modified by the modification method in any one of the above aspects.
The invention also provides an epoxy composite material, and the preparation process comprises the following steps:
(1) Adding the surface modified hexagonal boron nitride nanosheet of claim 8 into ethanol, and ultrasonically dispersing for 5-120 min to obtain a concentration of 0.5-50 mg-mL -1 The nanosheet dispersion of (a);
(2) Stirring and mixing the nanosheet dispersion liquid, epoxy resin and a curing agent uniformly, and then carrying out reduced pressure distillation to remove ethanol completely to obtain a mixed liquid;
(3) And (3) uniformly stirring and mixing the mixed solution and the accelerant at normal temperature, standing and defoaming in vacuum, pouring the mixed solution onto a mold after bubbles are removed, and curing to obtain the epoxy composite material.
Wherein, E-51 epoxy resin is adopted as a matrix, methyl hexahydrophthalic anhydride (MHHPA) is adopted as a curing agent, 2,4, 6-tri (dimethylaminomethyl) phenol (DMP-30) is adopted as an accelerating agent, and the mass ratio of the epoxy resin to the methyl hexahydrophthalic anhydride (MHHPA) is E-51: MHHPA: DMP-30=100: (70-100) and (0.1-2); the curing temperature is 80-180 ℃, and the curing time is 1-24 h.
As a preferable scheme, the content of the surface modified hexagonal boron nitride nanosheet in the epoxy composite material is 1-40 wt%.
Compared with the prior art, the invention has the beneficial effects that:
the surface modified hexagonal boron nitride nanosheet is a hexagonal boron nitride nanosheet with functionalized epoxy groups on the surface, which is directly obtained in one step by dispersing hexagonal boron nitride nanoparticles in a homogeneous aqueous solution of a silane coupling agent containing epoxy groups through wet ball milling; and further obtaining BPEI modified hexagonal boron nitride through the reaction of amino and epoxy.
The surface-modified hexagonal boron nitride nanosheet prepared by the modification method is high in yield and uniform in size, has rich amino groups on the surface, can be well dispersed in an epoxy matrix, and generates good interface compatibility between a filler/the matrix; and can generate covalent bonding with the epoxy group of the epoxy molecular chain, improve the crosslinking degree and enhance the heat conduction and mechanical properties of the epoxy composite material.
The modification method has the advantages of simple process, low cost, environmental friendliness and suitability for large-scale production, and can be widely used for enhancing the heat conduction and mechanical properties of various thermosetting and thermoplastic polymers.
Drawings
FIG. 1 is an SEM photograph of the nano-powder involved in example 1 of the present invention. Wherein A is original BN powder (denoted as BN); b is BN nano-sheet (named BNNS) obtained by ball milling; panel C shows BN nanoplates (denoted KH 560-BNNS) obtained by ball milling using a solution containing KH560; graph D shows BPEI surface-modified BN nanoplate (denoted as BPEI-KH 560-BNNS);
FIG. 2 is an FTIR spectrum of the relevant nanopowder involved in example 1 of the present invention. Wherein a is BN; b is BNNS; c is KH560-BNNS; d is BPEI-KH560-BNNS; e is KH560; and f is BPEI.
Figure 3 is a TGA trace of the relevant nanopowder involved in example 1 of the present invention. Wherein a is BN; b is BNNS; c is KH560-BNNS; d is BPEI-KH560-BNNS.
Detailed Description
The technical solution of the present invention is further explained by the following specific examples.
Example 1:
the preparation method of the surface modified BN nano sheet comprises the following steps:
1) 2g of BN powder was added to 120mL of a water/ethanol mixed solution containing 1wt% KH560 (water: ethanol =1 = 4), ultrasonically dispersed for 30min, and passed through 8mol · L -1 Adjusting the pH value of the BN dispersion to 4 by using a hydrochloric acid solution; then transferring the BN dispersion liquid into a tungsten carbide ball milling tank, and adding 30 tungsten carbide grinding balls; ball milling is carried out for 24 hours at the rotating speed of 600 rpm;
2) After the ball milling is finished, carrying out vacuum filtration on the solution; drying the powder obtained by suction filtration at 80 ℃ for 12 hours to obtain surface epoxy group functionalized BN nano-sheets;
3) Adding the epoxy group functionalized BN nano-sheets obtained in the step 2) into an aqueous solution containing 1wt% of BPEI, and carrying out ultrasonic dispersion for 30min; and then reacting for 12h at 50 ℃, and obtaining the surface modified BN nano-sheet through vacuum filtration and drying.
The preparation method of the epoxy composite material of the embodiment comprises the following steps:
4) Adding the surface modified BN nano sheet into ethanol, and performing ultrasonic dispersion for 30min to obtain the surface modified BN nano sheet with the concentration of 10 mg/mL -1 BN nanosheet dispersion of (1);
5) Stirring and mixing the BN dispersion liquid with E-51 epoxy resin and MHHPA for 2h, and then carrying out reduced pressure distillation at the temperature of 60 ℃ for 12h to remove ethanol solvent;
6) Stirring and mixing the solution obtained in the step 5) and DMP-30 for 0.5h at normal temperature, standing and defoaming for 1h under vacuum, pouring the mixed solution onto a mold after bubbles are removed, and curing for 4h at 120 ℃ to obtain the surface modified BN nanosheet/epoxy composite material.
Wherein the mass fraction of the surface modified BN nanosheet in the epoxy composite material is 15wt%; e-51 mhhpa.
The epoxy composite of this example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
The preparation of surface-modified BN nanosheets (i.e., BPEI-KH 560-BNNS) is the first step in the preparation of epoxy nanocomposites. As shown in fig. 1A, BN exhibits an irregular morphology and a tightly stacked layered structure. After ball milling, a distinct nanosheet structure was observed, as shown in fig. 1B, primarily due to the shear forces during ball milling which stripped the stacked nanosheets. Fig. 1C shows that the addition of KH560 does not have a significant effect on the structure of the BN nanosheets obtained by ball milling. Also, fig. 1D shows that post-modification with BPEI also does not significantly affect the structure of BN nanosheets.
To determine the chemical structure of the surface-modified BN nanoplates, infrared spectra were recorded. As shown in FIG. 2, KH560-BNNS was 2933cm in comparison to BN and BNNS -1 And 1091cm -1 Two new absorption bands appear, which are respectively attributed to the stretching vibration of C-H and Si-O bonds in KH560 molecules. Whereas for BPEI-KH560-BNNS, except 2933cm -1 And 1091cm -1 The two absorption bands are at 1460cm -1 A new absorption band is shown, which is attributed to the stretching vibration of C-N bond in BPEI molecule, which indicates that BPEI molecule realizes surface modification to KH560-BNNS.
To determine the thermal stability of the surface-modified BN nanoplates, thermogravimetric analysis was performed. As shown in FIG. 3, the weight loss of BN over the entire temperature range (30-800 ℃) was only 0.27%, whereas the weight loss of BNNS was estimated to be 2.85%, mainly due to the removal of-OH and adsorbed water molecules on the surface of BNNS. After being modified by KH560, the weight loss ratio of KH560-BNNS is 4.99%. When KH560-BNNS is further modified by BPEI, the weight loss rate of BPEI-KH560-BNNS reaches 9.43%, mainly because the surface KH560 and BPEI molecules are thermally decomposed at high temperature.
Comparative example 1:
this comparative example differs from example 1 in that:
in the step 1), ball milling is carried out in a water/ethanol mixed solution without KH560;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 2:
this comparative example differs from example 1 in that:
in the step 1), ball milling is carried out in a water/ethanol mixed solution without KH560 to obtain BN nanosheets;
in step 2), the BN nanosheets are added to a water/ethanol mixed solution containing 1wt% kh560 (water: ethanol = 1) -1 Adjusting the pH value of the BN dispersion liquid to 4 by using a hydrochloric acid solution, and stirring and reacting for 24 hours to obtain a functionalized BN nanosheet;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 3:
this comparative example differs from example 1 in that:
adding BN powder into a water/ethanol mixed solution containing KH560 during the step 1) and mechanically stirring;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 4:
this comparative example differs from example 1 in that:
in the step 1), KH560 in the water/ethanol mixed solution is replaced by KH550, and the KH550 has no epoxy group;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 5:
this comparative example differs from example 1 in that:
in the step 3), adding the surface epoxy group functionalized BN nanosheet into a BPEI solution, and stirring and mixing for 12 hours at room temperature;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 6:
this comparative example differs from example 1 in that:
in the step 3), the Branched Polyethyleneimine (BPEI) in the solution is replaced by Linear Polyethyleneimine (LPEI) with the same molecular weight, and the LPEI has no amino side chain;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 7:
the comparative example differs from example 1 in that:
commercial BN nanopowder was used instead of the surface modified BN nanosheets of example 1;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 8:
this comparative example differs from example 1 in that:
commercial BN nanosheets were used in place of the surface-modified BN nanosheets of example 1;
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
Comparative example 9:
this comparative example differs from example 1 in that:
omitting the step (3), and replacing the surface modified BN nanosheet in example 1 with a surface epoxy group functionalized BN nanosheet (namely KH560 modified BN nanosheet);
the other steps and process conditions were the same as in example 1.
The epoxy composite of this comparative example was cast into a standard sample to test the thermal conductivity and mechanical properties of the composite.
The epoxy composite materials of example 1 and comparative examples 1 to 9 and the pure epoxy materials were subjected to thermal conductivity, tensile strength and impact strength tests, and the specific test results are shown in table 1.
TABLE 1 thermal conductivity, tensile strength and impact strength of the samples of examples and comparative examples
| Sample name | Thermal conductivity coefficient (W/m. K) | Tensile Strength (MPa) | Impact Strength (kJ/m) 2 ) |
| Pure epoxy | 0.21 | 48.3 | 9.2 |
| Example 1 | 1.14 | 95.1 | 24.5 |
| Comparative example 1 | 0.49 | 59.6 | 13.1 |
| Comparative example 2 | 0.68 | 71.9 | 17.7 |
| Comparative example 3 | 0.45 | 53.3 | 12.2 |
| Comparative example 4 | 0.56 | 63.8 | 15.9 |
| Comparative example 5 | 0.79 | 82.7 | 18.6 |
| Comparative example 6 | 0.72 | 72.4 | 17.3 |
| Comparative example 7 | 0.41 | 50.2 | 11.5 |
| Comparative example 8 | 0.54 | 57.6 | 13.3 |
| Comparative example 9 | 0.61 | 62.7 | 16.4 |
In comparative example 1, BPEI produced a non-covalent modification of BN nanoplates. The comparison result with the embodiment 1 shows that the BPEI covalently modified BN nanosheet has better heat conduction and mechanical promotion effects than the BPEI non-covalently modified BN nanosheet;
in comparative example 2, epoxy-functionalized BN nanosheets were stepwise modified using KH 560. The comparison result with the embodiment 1 shows that the epoxy group functionalized BN nano sheet obtained by BPEI modification and one-step ball milling has better heat conduction and mechanical promotion effects than the epoxy group functionalized BN nano sheet obtained by BPEI modification and step modification;
in comparative example 3, BN was not ball milled and a nanosheet structure could not be obtained. The comparison result with the embodiment 1 shows that the BPEI surface modified BN nanosheet has better heat conduction and mechanical improvement effects than the BPEI surface modified BN powder;
in comparative example 4, using KH550 instead of KH560, the resulting amino-functionalized BN nanosheets were unable to further covalently link to BPEI. The comparison result with the embodiment 1 shows that the BPEI surface modified BN nanosheet has better heat conduction and mechanical improvement effects than the KH550 modified BN nanosheet;
in comparative example 5, BPEI reacted less with epoxy BN nanosheets at room temperature. The comparison result with the embodiment 1 shows that the BPEI surface modified BN nano-sheet prepared at a certain temperature has better heat conduction and mechanical promotion effects than the BPEI surface modified BN nano-sheet prepared at normal temperature;
in comparative example 6, the number of amino groups on the linear polyethyleneimine LPEI surface-modified BN nanoplatelets was small, so that the degree of crosslinking with the epoxy matrix was low. The comparison result with the embodiment 1 shows that the BPEI surface modified BN nano-sheet has better heat conduction and mechanical promotion effects than the LPEI surface modified BN nano-sheet;
the comparison results of comparative examples 7, 8 and 9 with example 1 show that, under the same addition ratio, the BPEI surface-modified BN nanosheets have better heat conduction and mechanical improvement effects than commercial BN powder, BN nanosheets and KH 560-modified BN nanosheets.
The chemical modification principle of the surface modified BN is as follows:
1. under the action of shearing force in the ball milling process, the BN powder is stripped into BN nanosheets; meanwhile, hydroxyl on the surface of the BN nanosheet reacts with the hydrolyzed KH560 to obtain an epoxy functionalized BN nanosheet, so that a connection point is provided for further modification of BPEI;
2. carrying out ring-opening reaction on the BPEI containing rich amino and an epoxy group of the epoxy functionalized BN nanosheet to obtain the BPEI surface modified BN nanosheet; after BPEI surface modification, the surface of the BN nanosheet contains rich amino groups, and the amino groups can react with an epoxy group in an epoxy resin matrix and an anhydride group in an anhydride curing agent simultaneously to generate firm chemical connection and improve the dispersibility and the interface compatibility of the BN nanosheet.
In the above examples and their alternatives, the process parameters related to each raw material and modification method can be determined within the limited range according to the actual application requirements.
In view of numerous embodiments of the present invention, all components, component contents, and process parameters can be determined in corresponding ranges according to application requirements, and experimental data of each embodiment is huge and numerous, and is not suitable for being enumerated and explained herein one by one, but contents required to be verified and final conclusions obtained in each embodiment are close to each other.
The foregoing has outlined rather broadly the preferred embodiments and principles of the present invention and it will be appreciated that those skilled in the art may devise variations of the present invention that are within the spirit and scope of the appended claims.
Claims (10)
1. The method for modifying the surface modified hexagonal boron nitride nanosheet is characterized by comprising the following steps:
(1) Adding hexagonal boron nitride powder into a homogeneous aqueous solution of a silane coupling agent containing an epoxy group, performing ultrasonic dispersion to obtain a hexagonal boron nitride dispersion liquid, and adjusting the pH value to 0-6;
(2) Transferring the dispersion liquid obtained in the step (1) into a ball milling tank, carrying out ball milling for 1-48 h at 100-2000 rpm, carrying out vacuum filtration after ball milling, and drying the powder obtained by filtration to obtain a hexagonal boron nitride nanosheet with an epoxy group functionalized surface;
(3) And (3) adding the hexagonal boron nitride nanosheet obtained in the step (2) into a branched polyethyleneimine water solution, reacting for 1-48 h at 0-80 ℃ after ultrasonic dispersion, and then performing vacuum filtration and drying to obtain the surface modified hexagonal boron nitride nanosheet.
2. The modification method according to claim 1, wherein in the step (1), the silane coupling agent containing an epoxy group is KH560, and the homogeneous aqueous solution is a water/ethanol mixed solution.
3. The modification method according to claim 2, wherein in the step (1), the dispersion concentration of the hexagonal boron nitride powder in the water/ethanol mixed solution is 0.5 to 50 mg-mL -1 (ii) a The mass fraction of the KH560 in the water/ethanol mixed solution is 0.01-30 wt%; the volume ratio of the water/ethanol mixed solution is 1/(0.1-10).
4. The modification method according to claim 1, wherein in the step (1), the ultrasonic dispersion time is 5 to 120min; the pH of the hexagonal boron nitride dispersion was adjusted by an acid solution.
5. The modification method according to claim 4, wherein the acid solution is at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, oxalic acid, acetic acid, oxalic acid, and citric acid;
the molar concentration of the acid liquor is 0.01-10 mol.L -1 。
6. The modification method according to claim 1, wherein in the step (2), the drying temperature is 30 to 150 ℃ and the drying time is 1 to 48 hours.
7. The modification method according to claim 1, wherein the branched polyethyleneimine has a molecular weight of 200 to 100000 and a concentration of the aqueous branched polyethyleneimine solution is 0.01 to 30wt%.
8. Surface-modified hexagonal boron nitride nanosheets modified by the modification method as defined in any one of claims 1 to 7.
9. The preparation process of the epoxy composite material includes the following steps:
(1) Adding the surface-modified hexagonal boron nitride nanosheet of claim 8 to ethanol, and ultrasonically dispersing for 5-120 min to obtain a concentration of 0.5-50 mg-mL -1 The nanosheet dispersion of (a);
(2) Uniformly stirring and mixing the nanosheet dispersion liquid, epoxy resin and a curing agent, and then distilling under reduced pressure to remove ethanol completely to obtain a mixed liquid;
(3) And (3) uniformly stirring and mixing the mixed solution and the accelerant at normal temperature, standing and defoaming in vacuum, pouring the mixed solution onto a mold after bubbles are removed, and curing to obtain the epoxy composite material.
10. The epoxy composite of claim 9, wherein the surface-modified hexagonal boron nitride nanosheets comprise 1 to 40wt% of the epoxy composite.
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