Wave-absorbing heat-conducting composite material and preparation method thereof

Abstract

The embodiment of the application relates to the technical field of electromagnetic wave absorbing materials, and particularly discloses a wave-absorbing and heat-conducting composite material and a preparation method thereof, which comprises the following steps: S1, preparing a graphene oxide dispersion liquid with a preset concentration; S2, preparing a hexagonal boron nitride nanosheet dispersion liquid with a preset concentration; S3, preparing a mixed solution of graphene oxide and hexagonal boron nitride: taking a preset volume of the graphene oxide dispersion liquid in the step S1 and a preset volume of the hexagonal boron nitride nanosheet dispersion liquid in the step S2, mixing, magnetically stirring and ultrasonic treating to obtain a first mixed solution; S4, preparing a composite aerogel: taking a preset volume of the first mixed solution, adding an aqueous polyurethane prepolymer, stirring to obtain a second mixed solution, freezing the second mixed solution at a preset temperature for a preset time length, freeze-drying to obtain an aerogel, and heat-treating the dried aerogel in a reducing gas atmosphere to obtain an rGO / h-BN / PU composite aerogel. Through the above mode, the heat conduction and electromagnetic shielding capacity of the composite material can be improved.

Description

Technical Field

[0001] This application relates to the field of electromagnetic wave absorbing materials technology, and in particular to a wave-absorbing and thermally conductive composite material and its preparation method. Background Technology

[0002] With the rapid development of 5G communication, high-power electronic devices, and aerospace equipment, the miniaturization and high integration of these devices have led to a rapid accumulation of heat and increasingly prominent electromagnetic interference problems. The inventors of this application have discovered that polymer-based composite materials have attracted much attention due to their good processability and low density. However, traditional polymers (such as polyurethane and epoxy resin) have extremely low intrinsic thermal conductivity and limited electromagnetic shielding effectiveness, making it difficult to meet the heat dissipation and electromagnetic shielding compatibility requirements of high-power devices. Summary of the Invention

[0003] In view of the above problems, this application provides a microwave absorbing and thermally conductive composite material and its preparation method, which overcomes or at least partially solves the above problems.

[0004] According to one aspect of this application, a method for preparing a wave-absorbing and heat-conducting composite material is provided, comprising: S1, preparing a graphene oxide dispersion: taking a predetermined mass of graphene oxide and dispersing it in a predetermined volume of deionized water to obtain a graphene oxide dispersion of a predetermined concentration; S2, preparing a hexagonal boron nitride nanosheet dispersion: taking a predetermined mass of hexagonal boron nitride and adding it to a predetermined volume of organic solvent, and exfoliating to obtain a hexagonal boron nitride nanosheet dispersion of a predetermined concentration; S3, preparing a mixture of graphene oxide and hexagonal boron nitride: taking a predetermined volume of the graphene oxide dispersion from step S1 and a predetermined volume of the hexagonal boron nitride nanosheet dispersion from step S2 and mixing them, magnetically stirring and ultrasonically treating to obtain a first mixture; S4, preparing a composite aerogel: taking a predetermined volume of the first mixture, adding an aqueous polyurethane prepolymer, stirring to obtain a second mixture, freezing the second mixture at a predetermined temperature for a predetermined time, and then freeze-drying it to obtain an aerogel, and heat-treating the dried aerogel in a reducing gas atmosphere to obtain an rGO / h-BN / PU composite aerogel.

[0005] In an alternative approach, in step S1, the concentration of the graphene oxide dispersion is 4 mg / mL.

[0006] In an alternative embodiment, in step S2, the organic solvent is isopropanol, and the concentration of the hexagonal boron nitride nanosheet dispersion is 2 mg / mL.

[0007] In an alternative embodiment, in step S3, the volume ratio between the graphene oxide dispersion and the hexagonal boron nitride nanosheet dispersion is 2:1.

[0008] In an alternative embodiment, in step S3, the volume ratio between the graphene oxide dispersion and the hexagonal boron nitride nanosheet dispersion is 1:1.

[0009] In one alternative approach, in step S3, the mass ratio of graphene oxide to hexagonal boron nitride nanosheets is 4:1, or in step S3, the mass ratio of graphene oxide to hexagonal boron nitride nanosheets is 2:1.

[0010] In an alternative approach, in step S4, a preset volume of the first mixture is taken, and a template agent and an aqueous polyurethane prepolymer are added, and the mixture is stirred to obtain a second mixture.

[0011] In an alternative embodiment, in step S4, polyethylene glycol is used as the template agent, and the average molecular weight of polyethylene glycol is 2000 g / mol.

[0012] In an alternative embodiment, in step S4, the solid content of the aqueous polyurethane prepolymer is 40%, and the reducing gas is argon.

[0013] According to another aspect of this application, a wave-absorbing and thermally conductive composite material is provided, which is prepared using the wave-absorbing and thermally conductive composite material preparation method described above.

[0014] The beneficial effects of this application embodiment are as follows: Unlike the prior art, this application embodiment provides a method for preparing a wave-absorbing and thermally conductive composite material, including: S1, preparing a graphene oxide dispersion: dispersing a predetermined mass of graphene oxide in a predetermined volume of deionized water to obtain a graphene oxide dispersion of a predetermined concentration; S2, preparing a hexagonal boron nitride nanosheet dispersion: adding a predetermined mass of hexagonal boron nitride to a predetermined volume of organic solvent and peeling to obtain a hexagonal boron nitride nanosheet dispersion of a predetermined concentration; S3, preparing a mixture of graphene oxide and hexagonal boron nitride... Mixing liquid: Take a preset volume of graphene oxide dispersion from step S1 and a preset volume of hexagonal boron nitride nanosheet dispersion from step S2, mix them, and then magnetically stir and sonicate to obtain a first mixture; S4, Prepare composite aerogel: Take a preset volume of the first mixture, add waterborne polyurethane prepolymer, stir to obtain a second mixture, freeze the second mixture at a preset temperature for a preset time, and then freeze-dry to obtain an aerogel. Heat-treat the dried aerogel in a reducing gas atmosphere to obtain rGO / h-BN / PU composite aerogel. The microwave absorbing and thermally conductive composite material prepared by this method exhibits the following advantages: the high conductivity of graphene (rGO) generates dielectric loss for electromagnetic waves, while the phonon matching characteristics of hexagonal boron nitride (h-BN) synergistically enhance in-plane and vertical thermal conduction. The interface between graphene and hexagonal boron nitride, along with the porous structure of the aerogel, enhances multiple reflections and interface polarization loss. This results in both efficient thermal conduction and excellent electromagnetic shielding, while maintaining low density and flexibility, providing a novel lightweight solution for integrated thermal management and electromagnetic compatibility in fields such as 5G electronics and aerospace. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0016] Figure 1 This is a schematic flowchart of the preparation method of the wave-absorbing and thermally conductive composite material according to the embodiments of this application. Detailed Implementation

[0017] To facilitate understanding of this application, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected" to another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this specification are for illustrative purposes only.

[0018] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0019] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0020] In the process of developing this application, the applicant discovered that aerogels, as three-dimensional porous materials, possess ultra-low density, high porosity, and compressibility, making them an ideal matrix for constructing lightweight thermally conductive / shielding composite materials. Polyurethane (PU) aerogels not only retain the low density and high specific surface area characteristics of ordinary aerogels but also exhibit excellent flexibility and mechanical resilience, showing great potential in wearable electronics, flexible heat dissipation films, and other fields. However, pure PU aerogels have extremely poor thermal and electrical conductivity, necessitating modification with functional fillers. Graphene possesses an extremely high thermal conductivity (approximately 5000 W·m). -1 ·K -1 Two-dimensional graphene sheets, with their excellent electrical conductivity, are ideal fillers for constructing thermally / electrically conductive networks. However, they tend to stack in-plane orientation within aerogels, resulting in limited improvement in vertical thermal conductivity. Furthermore, high filler content can lead to agglomeration, impairing mechanical properties.

[0021] To address the aforementioned technical problems, this application provides a method for preparing a microwave absorbing and thermally conductive composite material, comprising the following steps: S1. Preparation of graphene oxide dispersion: Take a preset mass of graphene oxide and disperse it in a preset volume of deionized water to obtain a graphene oxide dispersion of a preset concentration.

[0022] In some embodiments, GO is prepared using a modified Hummers method.

[0023] In some embodiments, the concentration of the graphene oxide dispersion is 4 mg / mL.

[0024] In some embodiments, the specific implementation of preparing the graphene oxide dispersion can be as follows: GO is prepared by using the modified Hummers method, and 0.2g of GO is ultrasonically dispersed in 50mL of deionized water to obtain a 4 mg / mL graphene oxide (GO) dispersion.

[0025] S2. Preparation of hexagonal boron nitride nanosheet dispersion: Take a preset mass of hexagonal boron nitride and add it to a preset volume of organic solvent, and peel it to obtain a hexagonal boron nitride nanosheet dispersion of preset concentration.

[0026] In some embodiments, the organic solvent is isopropanol.

[0027] In some embodiments, the concentration of the hexagonal boron nitride nanosheet dispersion obtained by exfoliation is 2 mg / mL.

[0028] In some embodiments, the specific implementation of preparing the hexagonal boron nitride nanosheet dispersion can be as follows: take 0.1 g of hexagonal boron nitride (particle size of 5 μm) and add it to 50 mL of isopropanol, and ultrasonically exfoliate for 6 h (ultrasonic power of 300 W) to obtain an exfoliated hexagonal boron nitride (h-BN) nanosheet dispersion with a concentration of 2 mg / mL.

[0029] S3. Preparation of a mixture of graphene oxide and hexagonal boron nitride: Take a preset volume of graphene oxide dispersion from step S1 and a preset volume of hexagonal boron nitride nanosheet dispersion from step S2, mix them, and then magnetically stir and sonicate to obtain the first mixture.

[0030] In some embodiments, in step S3, the volume ratio between the graphene oxide dispersion and the hexagonal boron nitride nanosheet dispersion is 2:1.

[0031] In some embodiments, in step S3, the volume ratio between the graphene oxide dispersion and the hexagonal boron nitride nanosheet dispersion is 1:1.

[0032] In some embodiments, in step S3, the mass ratio of graphene oxide to hexagonal boron nitride nanosheets is 4:1.

[0033] In some embodiments, in step S3, the mass ratio of graphene oxide to hexagonal boron nitride nanosheets is 2:1.

[0034] In some embodiments, the specific implementation of preparing the mixture of graphene oxide and hexagonal boron nitride can be as follows: take a GO dispersion with a concentration of 4 mg / mL and an h-BN nanosheet dispersion with a concentration of 2 mg / mL and mix them at a volume ratio of 2:1 (GO:h-BN mass ratio of 4:1), stir magnetically for 1 h, and sonicate for 30 min to obtain the first mixture.

[0035] In some embodiments, the specific implementation of preparing the mixture of graphene oxide and hexagonal boron nitride can be as follows: take a GO dispersion with a concentration of 4 mg / mL and an h-BN nanosheet dispersion with a concentration of 2 mg / mL and mix them at a volume ratio of 1:1 (GO:h-BN mass ratio of 2:1), stir magnetically for 1 h, and sonicate for 30 min to obtain the first mixture.

[0036] S4. Preparation of composite aerogel: Take a preset volume of the first mixture, add waterborne polyurethane prepolymer, stir to obtain a second mixture, freeze the second mixture at a preset temperature for a preset time, and then freeze-dry to obtain an aerogel. Heat-treat the dried aerogel in a reducing gas atmosphere to obtain rGO / h-BN / PU composite aerogel.

[0037] In some embodiments, in step S4, a preset volume of the first mixture is taken, and a template agent and an aqueous polyurethane prepolymer are added, and the mixture is stirred to obtain a second mixture.

[0038] In some embodiments, in step S4, polyethylene glycol is used as the template agent.

[0039] In some embodiments, the average molecular weight of polyethylene glycol is 2000 g / mol.

[0040] In some embodiments, in step S4, the solid content of the waterborne polyurethane prepolymer is 40%.

[0041] In some embodiments, the reducing gas is argon.

[0042] In some embodiments, the specific implementation of preparing composite aerogel may be as follows: take 10 mL of the first mixture, add 1.0 g of waterborne polyurethane prepolymer (solid content of 40%), stir rapidly for 2 min to obtain the second mixture, pour the second mixture into a mold, freeze the second mixture at -20℃ for 12 h, and then freeze-dry for 48 h to obtain the aerogel, and heat-treat the dried aerogel at 800℃ for 2 h under Ar atmosphere to reduce GO to graphene (rGO) to obtain rGO / h-BN / PU composite aerogel.

[0043] In some embodiments, the specific implementation of preparing composite aerogel can be as follows: Take 10 mL of the first mixture, add 0.5 g of polyethylene glycol (PEG, average molecular weight 2000 g / mol) as a template agent, stir to dissolve, then add 1.0 g of waterborne polyurethane prepolymer (solid content of 40%), stir rapidly for 2 min to obtain the second mixture, pour the second mixture into a mold, freeze the second mixture at -20℃ for 12 h, then freeze dry for 48 h to obtain the aerogel, heat treat the dried aerogel at 800℃ for 2 h under Ar atmosphere to reduce GO to graphene (rGO) to obtain rGO / h-BN / PU composite aerogel.

[0044] In this embodiment of the application, a method for preparing a wave-absorbing and thermally conductive composite material is provided, comprising: S1, preparing a graphene oxide dispersion: taking a preset mass of graphene oxide and dispersing it in a preset volume of deionized water to obtain a graphene oxide dispersion of a preset concentration; S2, preparing a hexagonal boron nitride nanosheet dispersion: taking a preset mass of hexagonal boron nitride and adding it to a preset volume of organic solvent, and peeling it to obtain a hexagonal boron nitride nanosheet dispersion of a preset concentration; S3, preparing a mixture of graphene oxide and hexagonal boron nitride: taking a preset volume of the graphene oxide dispersion from step S1 and a preset volume of the hexagonal boron nitride nanosheet dispersion from step S2 and mixing them, magnetically stirring and ultrasonically treating to obtain a first mixture; S4, preparing a composite aerogel: taking a preset volume of the first mixture, adding a template agent and an aqueous polyurethane prepolymer, stirring to obtain a second mixture, freezing the second mixture at a preset temperature for a preset time, and then freeze-drying it to obtain an aerogel, and heat-treating the dried aerogel in a reducing gas atmosphere to obtain an rGO / h-BN / PU composite aerogel. The microwave absorbing and thermally conductive composite material prepared by this method exhibits the following advantages: the high conductivity of graphene (rGO) generates dielectric loss for electromagnetic waves, while the phonon matching characteristics of hexagonal boron nitride (h-BN) synergistically enhance in-plane and vertical thermal conduction. The interface between graphene and hexagonal boron nitride, along with the porous structure of the aerogel, enhances multiple reflections and interface polarization loss. This results in both efficient thermal conduction and excellent electromagnetic shielding, while maintaining low density and flexibility, providing a novel lightweight solution for integrated thermal management and electromagnetic compatibility in fields such as 5G electronics and aerospace.

[0045] This application also provides an embodiment of a microwave absorbing and thermally conductive composite material, which is prepared using the microwave absorbing and thermally conductive composite material preparation method described above.

[0046] To facilitate readers' understanding of the inventive concept of the embodiments of the present invention, the technical effects of using the embodiments of the present invention are demonstrated below.

[0047] Example 1 <Preparation of graphene oxide dispersion> GO was prepared using a modified Hummers method. 0.2 g of GO was ultrasonically dispersed in 50 mL of deionized water to obtain a 4 mg / mL graphene oxide (GO) dispersion.

[0048] <Preparation of Hexagonal Boron Nitride Nanosheet Dispersion> 0.1 g of hexagonal boron nitride (particle size 5 μm) was added to 50 mL of isopropanol and ultrasonically exfoliated for 6 h (ultrasonic power 300 W) to obtain a dispersion of exfoliated hexagonal boron nitride (h-BN) nanosheets with a concentration of 2 mg / mL.

[0049] <Preparation of a mixture of graphene oxide and hexagonal boron nitride> A GO dispersion with a concentration of 4 mg / mL and an h-BN nanosheet dispersion with a concentration of 2 mg / mL were mixed at a volume ratio of 2:1 (GO:h-BN mass ratio of 4:1), magnetically stirred for 1 h, and sonicated for 30 min to obtain the first mixture.

[0050] <Preparation of Composite Aerogels> Take 10 mL of the first mixture, add 0.5 g of polyethylene glycol (PEG, average molecular weight 2000 g / mol) as a template agent, stir to dissolve, then add 1.0 g of waterborne polyurethane prepolymer (solid content 40%), stir rapidly for 2 min to obtain the second mixture, pour the second mixture into a mold, freeze the second mixture at -20℃ for 12 h, and then freeze dry for 48 h to obtain an aerogel. Heat treat the dried aerogel at 800℃ for 2 h under Ar atmosphere to reduce GO to graphene (rGO) to obtain rGO / h-BN / PU composite aerogel.

[0051] Performance Testing The density and thermal conductivity of the aerogel were measured, and the shielding performance of the electromagnetic shielding material in the X-band (8.2~12.4GHz) was tested using a vector network analyzer to obtain the shielding effectiveness and absorption loss ratio.

[0052] Example 2 <Preparation of graphene oxide dispersion> GO was prepared using a modified Hummers method. 0.2 g of GO was ultrasonically dispersed in 50 mL of deionized water to obtain a 4 mg / mL graphene oxide (GO) dispersion.

[0053] <Preparation of Hexagonal Boron Nitride Nanosheet Dispersion> 0.1 g of hexagonal boron nitride (particle size 5 μm) was added to 50 mL of isopropanol and ultrasonically exfoliated for 6 h (ultrasonic power 300 W) to obtain a dispersion of exfoliated hexagonal boron nitride (h-BN) nanosheets with a concentration of 2 mg / mL.

[0054] <Preparation of a mixture of graphene oxide and hexagonal boron nitride> Take a GO dispersion with a concentration of 4 mg / mL and an h-BN nanosheet dispersion with a concentration of 2 mg / mL and mix them at a mass ratio of 2:1 (GO is 0.2 g and h-BN is 0.1 g). Stir magnetically for 1 h and sonicate for 30 min to obtain the first mixture.

[0055] <Preparation of Composite Aerogels> Take 10 mL of the first mixture, add 1.0 g of aqueous polyurethane prepolymer (solid content 40%), stir rapidly for 2 min to obtain the second mixture, pour the second mixture into a mold, freeze the second mixture at -20℃ for 12 h, and then freeze-dry for 48 h to obtain an aerogel. Heat-treat the dried aerogel at 800℃ for 2 h under Ar atmosphere to reduce GO to graphene (rGO), obtaining rGO / h-BN / PU composite aerogel. (No template agent is added in step S4 of Example 2) Performance Testing Same as Example 1.

[0056] Comparative Example 1 <Preparation of graphene oxide dispersion> Same as Example 1.

[0057] In Comparative Example 1, h-BN was not added.

[0058] <Preparation of Composite Aerogels> Same as Example 2 (without h-BN, without template agent, otherwise identical) Performance Testing Same as Example 1.

[0059] The test results for Example 1 are as follows: The composite aerogel in Example 1 has a density of 28 mg / cm³ and a thermal conductivity of 1.8 W·m. -1 ·K -1 (In-plane) In the 8.2-12.4 GHz band, the total shielding effectiveness is 32.6 dB, the absorption loss accounts for 68%, and the springback rate is >85% after 50% compression.

[0060] The overall shielding effectiveness was 32.6 dB, indicating that the composite aerogel in Example 1 possesses excellent shielding performance. The absorption loss ratio was 68%, indicating that the composite aerogel in Example 1 primarily relies on the material's internal conversion of electromagnetic wave energy into heat energy for shielding, rather than reflection causing secondary pollution. The density was 28 mg / cm³, indicating that the composite aerogel in Example 1 has a low density, making it suitable for weight-sensitive applications. The thermal conductivity of the composite aerogel was 1.8 W·m. -1·K -1 (In-plane) indicates that the composite aerogel has good thermal conductivity. A 50% compression recovery rate of >85% indicates that the composite aerogel has excellent flexibility and fatigue resistance in its internal structure.

[0061] The test results for Example 2 are as follows: The composite aerogel in Example 2 has a density of 32 mg / cm³ and a thermal conductivity of 1.5 W·m. -1 ·K -1 (In-plane) In the 8.2-12.4GHz band, the total shielding effectiveness is 35.2dB, and the absorption loss accounts for 72%.

[0062] The overall shielding effectiveness was 35.2 dB, indicating that the composite aerogel in Example 2 has excellent shielding performance. The absorption loss ratio was 72%, indicating that the composite aerogel in Example 2 primarily relies on the material's internal structure to convert electromagnetic wave energy into heat energy for shielding, rather than reflecting it and causing secondary pollution. The density was 32 mg / cm³, indicating that the composite aerogel in Example 2 has a low density, making it suitable for applications where weight is a concern. The thermal conductivity of the composite aerogel was 1.5 W·m⁻¹·K⁻¹ (in-plane), indicating that the composite aerogel still has good thermal conductivity. It can be seen that in Example 2, due to the increased h-BN ratio, the thermal conductivity decreased slightly, but the shielding effectiveness improved.

[0063] The test results for Comparative Example 1 are as follows: The aerogel in Comparative Example 1 has a density of 25 mg / cm³ and a thermal conductivity of 0.9 W·m. -1 ·K -1 Within the 8.2-12.4 GHz band, the total shielding effectiveness was 28.4 dB, with an absorption loss ratio of 52%. It is evident that the shielding effectiveness in Comparative Example 1 is lower than that in Examples 1 and 2. The in-plane thermal conductivity of the aerogel in Comparative Example 1 is significantly reduced. The 52% absorption loss ratio of the aerogel in Comparative Example 1 indicates that the aerogel in Comparative Example 1, as a "reflector," primarily functions as a reflector.

[0064] In summary, the comparison shows that in Examples 1 and 2, the addition of h-BN improved the thermal conductivity (due to the synergistic effect of graphene and h-BN thermal bridge) and increased the shielding absorption loss (due to enhanced interface polarization).

[0065] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing a wave-absorbing and thermally conductive composite material, characterized in that, include: S1. Preparation of graphene oxide dispersion: Take a preset mass of graphene oxide and disperse it in a preset volume of deionized water to obtain a graphene oxide dispersion of a preset concentration. S2. Preparation of hexagonal boron nitride nanosheet dispersion: Take a preset mass of hexagonal boron nitride and add it to a preset volume of organic solvent, and peel it to obtain a hexagonal boron nitride nanosheet dispersion of preset concentration. S3. Preparation of a mixture of graphene oxide and hexagonal boron nitride: Take a preset volume of graphene oxide dispersion from step S1 and a preset volume of hexagonal boron nitride nanosheet dispersion from step S2, mix them, and then stir magnetically and sonicate to obtain the first mixture. S4. Preparation of composite aerogel: Take a preset volume of the first mixture, add waterborne polyurethane prepolymer, stir to obtain a second mixture, freeze the second mixture at a preset temperature for a preset time, and then freeze-dry to obtain an aerogel. Heat-treat the dried aerogel in a reducing gas atmosphere to obtain rGO / h-BN / PU composite aerogel.

2. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S1, the concentration of the graphene oxide dispersion is 4 mg / mL.

3. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S2, the organic solvent is isopropanol, and the concentration of the hexagonal boron nitride nanosheet dispersion is 2 mg / mL.

4. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S3, the volume ratio between the graphene oxide dispersion and the hexagonal boron nitride nanosheet dispersion is 2:

1.

5. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S3, the volume ratio between the graphene oxide dispersion and the hexagonal boron nitride nanosheet dispersion is 1:

1.

6. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S3, the mass ratio of graphene oxide to hexagonal boron nitride nanosheets is 4:1; or, in step S3, the mass ratio of graphene oxide to hexagonal boron nitride nanosheets is 2:

1.

7. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S4, a preset volume of the first mixture is taken, and a template agent and an aqueous polyurethane prepolymer are added. The mixture is then stirred to obtain a second mixture.

8. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 7, characterized in that, In step S4, polyethylene glycol is used as the template agent, and the average molecular weight of polyethylene glycol is 2000 g / mol.

9. The method for preparing the microwave absorbing and thermally conductive composite material according to claim 1, characterized in that, In step S4, the solid content of the waterborne polyurethane prepolymer is 40%, and the reducing gas is argon.

10. A wave-absorbing and thermally conductive composite material, characterized in that, The microwave absorbing and thermally conductive composite material is prepared using the method for preparing microwave absorbing and thermally conductive composite materials as described in any one of claims 1-9.

Images