Graphene / epoxy resin heat conductive composite material and preparation method thereof

Abstract

The application provides a graphene / epoxy resin heat-conducting composite material and a preparation method thereof. The preparation method comprises the following steps: mixing a graphene nanosheet slurry and a nanocellulose slurry to obtain a graphene / nanofiber suspension; drying the graphene / nanofiber suspension by a freeze-drying orientation method to obtain graphene / nanofiber aerogel with vertically oriented graphene nanosheets; mixing the graphene / nanofiber aerogel with epoxy resin and a curing agent and curing to obtain the graphene / epoxy resin heat-conducting composite material. The graphene / epoxy resin heat-conducting composite material prepared by the preparation method has good heat-conducting performance, and the preparation process is simple.

Description

Technical Field

[0001] This application relates to the field of thermally conductive composite materials technology, and in particular to a graphene / epoxy resin thermally conductive composite material and its preparation method. Background Technology

[0002] Since the invention of the transistor, integrated circuits have followed Moore's Law in their development, becoming increasingly powerful, miniaturized, and integrated. The pursuit of high performance has greatly increased the power density of integrated circuits, which has created challenges for heat dissipation in electronic devices and has put Moore's Law to the test.

[0003] Thermal interface materials (TIMs) possess high thermal conductivity, effectively reducing the operating temperature of electronic devices and equipment, ensuring optimal operating efficiency and lifespan. Besides metallic and ceramic TIMs, thermally conductive polymer composites have attracted considerable attention due to their low density, corrosion resistance, and ease of processing. However, most polymer materials themselves have low thermal conductivity (below 0.5 W / (m·K)) and cannot be used alone.

[0004] Currently, it is commonly combined with various thermally conductive inorganic fillers, such as metals (Cu, Al, Ni, Ag), ceramics (BN, AlN), and carbon materials (graphene, carbon fiber, MXene, diamond), to improve the thermal conductivity of polymer materials. However, during the composite process, the viscosity of the composite material increases continuously with the increase of the thermally conductive filler content, which greatly affects the mechanical and processing properties of the material. In addition, due to the imbalance between the polymer and the filler ratio, excessive filler is difficult to form an ordered phonon transport pathway in the polymer material, and the resulting high interfacial thermal resistance also limits the enhancement of thermal conductivity.

[0005] Therefore, traditional technologies still need further improvement. Summary of the Invention

[0006] Based on this, this application provides a graphene / epoxy resin thermally conductive composite material with good thermal conductivity and a simple preparation process, and a method for preparing the same.

[0007] The technical solution proposed in this application is as follows: According to a first aspect of this application, a method for preparing a graphene / epoxy resin thermally conductive composite material is provided, comprising the following steps: Graphene nanosheet slurry and nanocellulose slurry are mixed to obtain graphene / nanofiber suspension; The graphene / nanofiber suspension was dried by freeze-drying orientation method to obtain graphene / nanofiber aerogel with vertically oriented graphene nanosheets. The graphene / nanofiber aerogel is mixed with epoxy resin and curing agent and then cured to obtain the graphene / epoxy resin thermally conductive composite material.

[0008] In some embodiments, drying the graphene / nanofiber suspension includes the following steps: placing the graphene / nanofiber suspension in a freeze-drying orientation molding mold and freeze-drying it at -70°C to -60°C for 48 to 72 hours.

[0009] In some embodiments, the freeze-drying orientation molding die includes a base and a die body, wherein the thermal conductivity of the base is greater than that of the die body.

[0010] In some embodiments, the base is made of one or more of brass, pure copper, and aluminum alloy.

[0011] In some embodiments, the material of the mold body includes one or more of polytetrafluoroethylene, polypropylene, and silicone.

[0012] In some embodiments, mixing the graphene nanosheet slurry with the nanocellulose slurry includes the following steps: stirring and mixing the graphene nanosheet slurry and the nanocellulose slurry at 80°C to 90°C for 3 to 4 hours.

[0013] In some embodiments, the mass-to-volume ratio of the graphene nanosheet slurry to the nanocellulose slurry is 5 mg to 40 mg: 1 mL.

[0014] In some embodiments, the mass-to-volume ratio of the graphene nanosheet slurry to the nanocellulose slurry is 10 mg to 20 mg: 1 mL.

[0015] In some embodiments, the mass ratio of the epoxy resin to the curing agent is (50~100):(40~80).

[0016] In some embodiments, the solid content of the graphene nanosheet slurry is 5wt% to 10wt%.

[0017] In some embodiments, the graphene nanosheet slurry is mixed with the nanocellulose slurry by magnetic stirring.

[0018] In some embodiments, the curing method is vacuum impregnation curing, the vacuum degree of vacuum impregnation curing is -0.08MPa to -0.09MPa, the temperature of vacuum impregnation curing is 60℃ to 65℃, and the time of vacuum impregnation curing is 4h to 5h.

[0019] According to a second aspect of this application, a graphene / epoxy resin thermally conductive composite material is provided, which is prepared by the method for preparing the graphene / epoxy resin thermally conductive composite material of the first aspect of this application.

[0020] Compared with traditional technologies, this application has at least the following beneficial effects: The preparation method of this application involves mixing cellulose nanofibers and graphene nanosheets and then preparing graphene / nanofiber aerogels via freeze-drying orientation. Cellulose nanofibers are bridged onto two-dimensional graphene nanosheets, and the graphene nanosheets are vertically oriented and orderly arranged within the aerogel. These vertically oriented graphene nanosheets are uniformly distributed on the cellulose nanofiber framework, constructing an anisotropic three-dimensional thermally conductive network structure, which significantly improves the thermal conductivity of the composite material. Furthermore, this preparation method is simple and low-cost. Attached Figure Description

[0021] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 The images are scanning electron microscope (SEM) images of the graphene / epoxy resin thermally conductive composite materials and graphene / nanofiber aerogels of Examples 1-4 of this application. Detailed Implementation

[0022] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0023] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this document; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2~10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0024] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0027] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0028] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used herein are commercially available or can be prepared by existing methods.

[0030] One embodiment of this application provides a method for preparing a graphene / epoxy resin thermally conductive composite material, the method comprising the following steps S100 to S300: Step S100: Mix graphene nanosheet slurry with nanocellulose slurry to obtain graphene / nanofiber suspension.

[0031] Step S200: The graphene / nanofiber suspension is dried by freeze-drying orientation method to obtain graphene / nanofiber aerogel with vertically oriented graphene nanosheets.

[0032] Step S300: Mix graphene / nanofiber aerogel with epoxy resin and curing agent and cure to obtain graphene / epoxy resin thermally conductive composite material.

[0033] The method for preparing the graphene / epoxy resin thermally conductive composite material described above in this application involves first mixing graphene nanosheet slurry with nanocellulose slurry to prepare a graphene / nanofiber suspension, then drying the graphene / nanofiber suspension by a freeze-drying orientation method to obtain a graphene / nanofiber aerogel with vertically oriented graphene nanosheets; then mixing the graphene / nanofiber aerogel with epoxy resin and a curing agent and curing to obtain the graphene / epoxy resin thermally conductive composite material.

[0034] This application employs a freeze-drying orientation method to prepare graphene / nanofiber aerogels by mixing nanocellulose and graphene nanosheets. Nanocellulose is bridged onto two-dimensional graphene nanosheets, and the graphene nanosheets are vertically oriented and orderly arranged within the aerogel. These vertically oriented graphene nanosheets are uniformly distributed on the nanocellulose framework, constructing an anisotropic three-dimensional thermally conductive network structure, which significantly improves the thermal conductivity of the composite material. Furthermore, this preparation method is simple and low-cost.

[0035] In some embodiments, drying the graphene / nanofiber suspension includes the following steps: placing the graphene / nanofiber suspension in a freeze-drying orientation molding mold and freeze-drying it at -70°C to -60°C for 48 to 72 hours.

[0036] After placing the graphene / nanofiber suspension in a freeze-drying orientation molding mold, the water gradually freezes from a liquid state into ice crystals during the freeze-drying process. By controlling the freeze-drying temperature and time within the aforementioned range, it is beneficial to allow the ice crystals to grow continuously from the base of the freeze-drying orientation molding mold in a direction perpendicular to the base, forming a vertical ice crystal template. The graphene nanosheets are pushed by the growing ice crystals to align along the ice crystal growth direction and wrap around the ice crystals. After the ice crystals sublimate, the graphene nanosheets retain the vertical alignment structure, thereby forming a vertically oriented aerogel.

[0037] The freeze-drying orientation process conditions described above facilitate the formation of uniformly distributed, vertically oriented graphene nanosheets in graphene / nanofiber aerogels, thereby improving the thermal conductivity of graphene / epoxy resin thermally conductive composites.

[0038] In some embodiments, the freeze-drying orientation molding die includes a base and a die body, wherein the thermal conductivity of the base is greater than that of the die body. The die body has an inner cavity for containing the graphene / nanofiber suspension; the base supports the die body and is in contact with the cold source components of the freeze dryer. Because the thermal conductivity of the base is greater than that of the die body, the cold energy from the cold source can be rapidly and uniformly transferred to the graphene / nanofiber suspension in the die body through the base, achieving directional freezing of the graphene nanosheets.

[0039] In some embodiments, the base material includes one or more of brass, pure copper, and aluminum alloy; the mold body material includes one or more of polytetrafluoroethylene, polypropylene, and silicone. The aforementioned base material has a high thermal conductivity, which is much greater than that of the aforementioned mold body material, which is beneficial for achieving directional freezing of graphene nanosheets to form a vertically oriented graphene / nanofiber aerogel.

[0040] In some specific examples, the base of the freeze-drying orientation molding die is a brass base, and the die body is a polytetrafluoroethylene (PTFE) die. The significant difference in thermal conductivity between brass and PTFE is beneficial for the directional freezing of graphene nanosheets.

[0041] In some embodiments, the graphene nanosheet slurry is mixed with the nanocellulose slurry, including the following steps: stirring the graphene nanosheet slurry and the nanocellulose slurry at 80°C to 90°C for 3 to 4 hours. By mixing the graphene nanosheet slurry and the nanocellulose slurry under the above temperature and time conditions, the nanocellulose at this temperature has a suitable viscosity, which is more conducive to the uniform mixing of the graphene nanosheet slurry and the nanocellulose, and to the uniform orientation of the graphene nanosheets in the aerogel.

[0042] In some embodiments, the mass-to-volume ratio of graphene nanosheet slurry to nanocellulose slurry is 5 mg to 40 mg: 1 mL. By controlling the content of nanocellulose slurry and graphene nanosheet slurry, the concentration, density, and viscosity of the graphene / nanofiber suspension can be controlled. The concentration, density, and viscosity of the graphene / nanofiber suspension, in turn, affect the uniformity of distribution and orientation of graphene nanosheets and nanocellulose in the graphene / nanofiber aerogel, influencing the construction of the three-dimensional thermally conductive network structure and thus the thermal conductivity of the composite material. Controlling the mass-to-volume ratio of graphene nanosheets and nanocellulose slurry within the above-mentioned range is beneficial for achieving good thermal conductivity in the graphene / epoxy resin thermally conductive composite material.

[0043] Understandably, the mass-to-volume ratio of graphene nanosheet slurry to nanocellulose slurry can be 5 mg:1 mL, 10 mg:1 mL, 15 mg:1 mL, 20 mg:1 mL, 25 mg:1 mL, 30 mg:1 mL, 35 mg:1 mL, 40 mg:1 mL, or any ratio within the range formed by any two of the above ratios.

[0044] In some embodiments, the mass-to-volume ratio of graphene nanosheet slurry to nanocellulose slurry is 10 mg to 20 mg: 1 mL. Further controlling the mass-to-volume ratio of graphene nanosheet slurry to nanocellulose slurry within this range effectively improves the thermal conductivity of the graphene / epoxy resin thermally conductive composite material while making the composite material easier to prepare.

[0045] In some embodiments, the solid content of the graphene nanosheet slurry is 5wt%~10wt%, and the solid content of the nanocellulose slurry is 1.09wt%. The graphene nanosheet slurry and the nanocellulose slurry are mixed by magnetic stirring. Compared with mechanical stirring, magnetic stirring can avoid the damage to the materials caused by the blades of an electric mixer.

[0046] In some embodiments, the mass ratio of epoxy resin to curing agent is (50~100):(40~80). In some specific examples, the epoxy resin used is GCC135 epoxy resin; the curing agent used is Q120 methyltetrahydrophthalic anhydride curing agent; the ratio of epoxy resin to curing agent is 40g of curing agent for every 50g of epoxy resin.

[0047] In some embodiments, the curing method is vacuum impregnation curing, with a vacuum level of -0.08 MPa to -0.09 MPa, a temperature of 60°C to 65°C, and a curing time of 4 to 5 hours. By mixing graphene / nanofiber aerogel with epoxy resin and a curing agent, and then performing vacuum impregnation curing under the above conditions, it is beneficial to ensure that the epoxy resin is fully impregnated into the graphene / nanofiber aerogel and cured, thus forming a graphene / epoxy resin thermally conductive composite material with good thermal conductivity.

[0048] One embodiment of this application provides a graphene / epoxy resin thermally conductive composite material, which is prepared by the method described above. This graphene / epoxy resin thermally conductive composite material contains nanocellulose, graphene nanosheets, and epoxy resin, with the nanocellulose and graphene nanosheets forming a three-dimensional thermally conductive network structure, and the graphene nanosheets arranged in a vertical orientation. This graphene / epoxy resin thermally conductive composite material exhibits excellent thermal conductivity.

[0049] The present application will be further described below with reference to specific embodiments and comparative examples, but should not be construed as limiting the scope of protection of the present application.

[0050] The graphene nanosheet slurry (GNPs) used in all examples and comparative examples had a solids content of 5 wt% and was dissolved in water. The nanocellulose (NFC) slurry had a solids content of 1.09 wt%, was dissolved in water, had a carboxyl group content of 2.4 mmol / g, a cellulose length of 400 nm to 1000 nm, and a cellulose diameter of 5 nm to 10 nm. The epoxy resin used was GCC135 epoxy resin, which is transparent at room temperature. The curing agent used was methyltetrahydrophthalic anhydride (Q120).

[0051] Example 1: A method for preparing a graphene / epoxy resin (V-GA / EP) thermally conductive composite material, comprising the following steps: (1) Preparation of graphene / nanofiber (GNPs / NFC) suspension A graphene nanosheet slurry and a nanocellulose slurry were mixed using a magnetic stirrer at a ratio of 5 mg graphene nanosheet slurry to 1 mL nanocellulose slurry. The temperature was controlled at 80°C and the stirring time was 3 h to obtain a graphene / nanofiber (GNPs / NFC) suspension.

[0052] (2) Preparation of graphene / nanofiber aerogel (V-GA) by freeze-drying of GNPs / NFC suspension The prepared graphene / nanofiber (GNPs / NFC) suspension was poured into a prepared mold, which was a polytetrafluoroethylene (PTFE) mold with a brass base. The graphene / nanofiber suspension in the PTFE mold with the brass base was freeze-dried into a graphene / nanofiber aerogel using a freeze dryer. The freeze dryer temperature was set to -60℃ and the time was set to 48 hours. After ice crystals continuously grew from the brass base and completely sublimated, the mold was removed, and the prepared graphene / nanofiber aerogel was taken out. It was named V-GA-5 based on the amount of graphene nanosheets added.

[0053] (3) Preparation of graphene / epoxy resin thermally conductive composite material The freeze-dried graphene / nanofiber aerogel was copolymerized with a resin system via liquid-phase vacuum impregnation. The resin system consisted of epoxy resin and a curing agent. GCC135 epoxy resin was used, and methyltetrahydrophthalic anhydride (Q120) was used as the curing agent. The ratio of epoxy resin to curing agent was 40g of curing agent per 50g of epoxy resin. The vacuum impregnation temperature was set at 60℃, and the impregnation time was 4 hours. After 4 hours, the aerogel was promptly removed to ensure complete impregnation and simultaneous curing of the resin system, resulting in a graphene / epoxy resin thermally conductive composite material. Based on the amount of graphene nanosheets added, it was named V-GA / EP-5.

[0054] Example 2: This embodiment is basically the same as Embodiment 1, except that in step (1), the graphene nanosheet slurry and the nanocellulose slurry are mixed at a ratio of 10 mg graphene nanosheet slurry to 1 mL nanocellulose slurry; the prepared graphene / nanofiber aerogel is named V-GA-10. The final prepared graphene / epoxy resin thermally conductive composite material is named V-GA / EP-10 according to the amount of graphene nanosheets added.

[0055] Example 3:

[0056] This embodiment is basically the same as Embodiment 1, except that: in step (1), the graphene nanosheet slurry and the nanocellulose slurry are mixed at a ratio of 20 mg graphene nanosheet slurry to 1 mL nanocellulose slurry; the prepared graphene / nanofiber aerogel is named V-GA-20. The final prepared graphene / epoxy resin thermally conductive composite material is named V-GA / EP-20 according to the amount of graphene nanosheets added.

[0057] Experiment Example 4: This embodiment is basically the same as Embodiment 1, except that in step (1), the graphene nanosheet slurry and the nanocellulose slurry are mixed at a ratio of 30 mg graphene nanosheet slurry to 1 mL nanocellulose slurry; the prepared graphene / nanofiber aerogel is named V-GA-30. The final prepared graphene / epoxy resin thermally conductive composite material is named V-GA / EP-30 according to the amount of nanocellulose added.

[0058] Example 5:

[0059] This embodiment is basically the same as Embodiment 1, except that in step (1), the graphene nanosheet slurry and the nanocellulose slurry are mixed at a ratio of 40 mg graphene nanosheet slurry to 1 mL nanocellulose slurry; the prepared graphene / nanofiber aerogel is named V-GA-40. The final prepared graphene / epoxy resin thermally conductive composite material is named V-GA / EP-40 according to the amount of graphene nanosheets added.

[0060] Comparative Example 1: Comparative Example 1 is basically the same as Example 1, except that in step (2), the graphene / nanofiber suspension is not freeze-dried in a directional manner using the lyophilization orientation method; instead, the graphene / nanofiber suspension is directly frozen into solid ice, and then sublimated into water vapor in a vacuum environment to form an aerogel; the prepared graphene / nanofiber aerogel is named GA-5. That is, the graphene / nanofiber suspension is freeze-dried in a non-directional manner. The final graphene / epoxy resin thermally conductive composite material is named GA / EP-5.

[0061] The thermal diffusivity of the graphene / epoxy resin thermally conductive composite materials in the above embodiments and comparative examples was measured using a laser flash thermal analyzer, and the result was calculated according to λ=α×C. p The formula ×ρ is used to calculate the thermal conductivity λ of pure epoxy resin and its composite materials in various embodiments and comparative examples. In the formula, α is the thermal diffusivity, and C... p ρ is the specific heat capacity at constant pressure, and ρ is the density. The test results are shown in Table 1. In Table 1, " / " indicates that it does not exist.

[0062] Table 1 Graphene nanosheet slurry / nanocellulose slurry ratio (mg:mL) / 5 10 20 30 40 5 Graphene Orientation / Vertical orientation Vertical orientation Vertical orientation Vertical orientation Vertical orientation non-directional <![CDATA[Thermal diffusivity (mm 2 / s)]]> 0.16 0.24 0.41 0.62 0.81 1.03 0.21 Thermal conductivity (W / (mK)) 0.20 0.36 0.59 0.82 1.38 1.95 0.32 .

[0063] As shown in Table 1, the graphene / epoxy resin thermally conductive composite materials prepared in each embodiment of this application exhibit high thermal diffusivity and thermal conductivity, demonstrating excellent thermal conductivity. In Examples 4 and 5, although the thermal diffusivity and thermal conductivity of the composite material improved with increasing proportions of graphene nanosheet slurry and nanocellulose slurry, the severe aggregation of graphene nanosheets made the composite material preparation difficult. In Examples 2 and 3, the moderate content of graphene nanosheets not only effectively improved the thermal conductivity of the composite material but also made it easier to prepare. In Comparative Example 1, the graphene nanosheets were non-oriented, resulting in a thermally conductive composite material with lower thermal conductivity than those in the other embodiments.

[0064] Figure 1 These are scanning electron microscope (SEM) images of graphene / nanofiber aerogel (V-GA) composites and graphene / epoxy resin (V-GA / EP) thermally conductive composites at different concentrations. These images visually demonstrate the microstructure of the composites.

[0065] Figure 1 Images (a-d) are Z-direction (out-of-plane orientation) SEM images of V-GA-5 (Example 1), V-GA-10 (Example 2), V-GA-20 (Example 3), and V-GA-30 (Example 4), respectively. The images show that the aerogels prepared by the freeze-drying orientation method exhibit extremely high orientation in the vertical direction. With increasing graphene nanosheet concentration, the graphene nanosheets adhere more compactly to the nanocellulose framework, and the pore size of the aerogel decreases. For the same aerogel volume, smaller pore sizes result in more thermally conductive pathways and better thermal conductivity.

[0066] V-GA / EP composite material was prepared by impregnating aerogel in epoxy resin under vacuum, allowing the epoxy resin to fill the pores in the aerogel, and then curing it at high temperature. Figure 1 (e~h) are Z-direction SEM images of V-GA / EP-5, V-GA / EP-10, V-GA / EP-20, and V-GA / EP-30, respectively. The vertically oriented graphene three-dimensional network can become a thermally conductive pathway in the composite material to improve the thermal conductivity of the polymer. At the same time, the originally loose physical structure of V-GA is also reinforced by curing epoxy resin.

[0067] Figure 1The images (i~l) are SEM images of V-GA-5, V-GA-10, V-GA-20 and V-GA-30 in the XY direction (in-plane). It can be seen from the images that, due to the excellent thermal conductivity of graphene nanosheets, the pore size of the aerogel decreases as the concentration of graphene nanosheets in the suspension increases.

[0068] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A method for preparing a graphene / epoxy resin thermally conductive composite material, characterized in that, Includes the following steps: Graphene nanosheet slurry and nanocellulose slurry are mixed to obtain graphene / nanofiber suspension; The graphene nanosheet slurry has a solid content of 5wt%~10wt%, and the nanocellulose slurry has a solid content of 1.09wt%. The graphene / nanofiber suspension was dried by freeze-drying orientation method to obtain graphene / nanofiber aerogel with vertically oriented graphene nanosheets. The graphene / nanofiber aerogel is mixed with epoxy resin and curing agent and then cured to obtain the graphene / epoxy resin thermally conductive composite material. The drying of the graphene / nanofiber suspension by freeze-drying orientation method includes the following steps: The graphene / nanofiber suspension is placed in a freeze-drying orientation molding mold and freeze-dried at -70℃ to -60℃ for 48h to 72h. The freeze-drying orientation molding mold includes a base and a mold body, and the thermal conductivity of the base is greater than that of the mold body. The mass-volume ratio of the graphene nanosheet slurry to the nanocellulose slurry is 5mg to 40mg: 1mL. The mass ratio of the epoxy resin to the curing agent is (50 to 100): (40 to 80).

2. The method for preparing the graphene / epoxy resin thermally conductive composite material according to claim 1, characterized in that, The base is made of one or more of the following materials: brass, pure copper, and aluminum alloy.

3. The method for preparing the graphene / epoxy resin thermally conductive composite material according to claim 1, characterized in that, The mold body is made of one or more of polytetrafluoroethylene, polypropylene, and silicone.

4. The method for preparing the graphene / epoxy resin thermally conductive composite material according to any one of claims 1 to 3, characterized in that, The process of mixing graphene nanosheet slurry and nanocellulose slurry includes the following steps: stirring and mixing the graphene nanosheet slurry and the nanocellulose slurry at 80℃~90℃ for 3h~4h.

5. The method for preparing the graphene / epoxy resin thermally conductive composite material according to any one of claims 1 to 3, characterized in that, The mass-to-volume ratio of the graphene nanosheet slurry to the nanocellulose slurry is 10 mg to 20 mg: 1 mL.

6. The method for preparing the graphene / epoxy resin thermally conductive composite material according to any one of claims 1 to 3, characterized in that, The graphene nanosheet slurry and the nanocellulose slurry are mixed by magnetic stirring.

7. The method for preparing the graphene / epoxy resin thermally conductive composite material according to any one of claims 1 to 3, characterized in that, The curing method is vacuum impregnation curing, with a vacuum degree of -0.08MPa to -0.09MPa, a vacuum temperature of 60℃ to 65℃, and a vacuum impregnation curing time of 4h to 5h.

8. A graphene / epoxy resin thermally conductive composite material, characterized in that, The graphene / epoxy resin thermally conductive composite material was prepared by any one of claims 1 to 7.

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