A high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film and its preparation method

Abstract

This invention belongs to the field of thermally conductive graphite materials, specifically relating to a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film and its preparation method. The graphite film of this invention is prepared by first obtaining a base film from modified polyarylene oxadiazole, followed by carbonization, graphitization, and cold pressing. The modified polyarylene oxadiazole is mainly prepared using terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes, and hydrazine salts as raw materials.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive graphite materials, specifically relating to a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film and its preparation method. Background Technology

[0002] In this era of rapid technological advancement, electronic devices are rapidly evolving towards higher performance, miniaturization, and multifunctionality. From mobile terminals such as smartphones and tablets to large-scale equipment like data centers and communication base stations, they all generate significant amounts of heat during operation. If this heat cannot be dissipated effectively and promptly, the performance of the devices will be severely affected, and their lifespan will be drastically shortened. Therefore, efficient thermal management technology has become a key factor in ensuring the stable operation of electronic devices, and graphite film, as an important material in the field of thermal management, has attracted considerable attention.

[0003] Currently, the main technologies used to prepare graphite films include the organic precursor method and the graphene oxide method. The organic precursor method typically uses polymers such as polyimide (PI) and polyarylene diazole (POD) as precursors, and prepares graphite films through preforming, carbonization, and high-temperature graphitization. This method can produce graphene thermally conductive films or fibers with high thermal conductivity, good crystallinity, and orientation, thus meeting some thermal management requirements to a certain extent. The graphene oxide method utilizes the thermal reduction properties of graphene oxide to prepare graphite films; its process is relatively simple and it also has applications in some fields.

[0004] However, both of these mainstream graphite film preparation technologies suffer from a critical drawback—low vertical thermal conductivity, typically below 3 W / (mK). This problem severely limits the application of graphite films in many fields with high requirements for vertical heat dissipation. In 5G communication base stations, with the continuous increase in signal transmission frequency, the heat generated by base station equipment increases dramatically. Because existing graphite films with low vertical thermal conductivity cannot quickly and effectively conduct heat away from heat-generating elements, the internal temperature of the equipment becomes too high, affecting the stability of signal transmission and the reliability of the equipment, increasing the risk of equipment failure. A similar dilemma exists in the CPU cooling modules of high-performance computers. CPUs generate a large amount of heat during high-speed operation. If the vertical thermal conductivity of the graphite film is poor, heat will accumulate on the surface of the CPU chip, causing the chip temperature to rise rapidly, reducing the CPU's operating speed, and potentially even causing serious problems such as system crashes. In the battery thermal management system of electric vehicles, the battery generates heat during charging and discharging, which needs to be vertically conducted to the heat dissipation components via a graphite film. However, existing graphite films with low vertical thermal conductivity cannot meet the requirements for rapid heat dissipation, potentially leading to excessively high battery temperatures, affecting the battery's charging and discharging efficiency and lifespan, and even posing safety hazards.

[0005] Currently, researchers have made numerous attempts to improve the vertical thermal conductivity of graphite films. However, most existing methods have limitations, often sacrificing the in-plane thermal conductivity of the graphite film while increasing vertical thermal conductivity. For example, when adding certain special fillers to improve vertical thermal conductivity, these fillers may disrupt the original in-plane crystal structure of the graphite film, leading to a decrease in in-plane thermal conductivity. This makes it difficult to find a balance between ensuring good vertical heat dissipation performance and maintaining high in-plane thermal conductivity in practical applications, greatly limiting the improvement of the overall performance of graphite films and their widespread application. Summary of the Invention

[0006] This invention obtains a modified poly(arylene oxadiazole) by carboxylating carbon nanotubes and then polymerizing them in situ with poly(arylene oxadiazole) (POD), thereby obtaining a graphite film based on aromatic heterocyclic polymer with high vertical thermal conductivity. This graphite film can balance both horizontal and vertical thermal conductivity.

[0007] The technical solution of the present invention:

[0008] The first technical problem to be solved by the present invention is to provide a graphite film based on aromatic heterocyclic polymer with high vertical thermal conductivity. The graphite film is prepared by first obtaining a base film from modified polyarylene oxadiazole, and then by carbonization, graphitization and cold pressing. The modified polyarylene oxadiazole is prepared by using terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt as the main raw materials.

[0009] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the modified polyarylene oxadiazole is prepared by the following method: terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes, and hydrazine salt are reacted at 80–90°C under the action of fuming sulfuric acid until the reaction solution becomes transparent; then the temperature is raised to 100–120°C and reacted for 2–5 hours; the reaction is terminated with benzoic acid; then the reaction is continued at 120–135°C for 0.5–1 hour, followed by vacuum degassing and drying. The modified polyarylene oxadiazole was prepared; wherein the molar ratio of isophthalic acid to terephthalic acid was 0.05–0.55:0.95–0.45; the mass ratio of azophthalic acid to the total mass of isophthalic acid and terephthalic acid was 0.01–0.10:1; the mass ratio of carboxyl-modified carbon nanotubes to the total mass of isophthalic acid and terephthalic acid was 0.001–0.01:1; and the molar addition of hydrazine salt to the total molar amount of isophthalic acid and terephthalic acid was 1.10–1.20:1.

[0010] Preferably, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the mass ratio of azophthalic acid to the total mass ratio of isophthalic acid and terephthalic acid is 0.05:1.

[0011] Furthermore, in the aforementioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the carboxyl-modified carbon nanotubes are obtained by surface carboxyl functionalization treatment of carbon nanotubes using a mixed solution of concentrated sulfuric acid and concentrated nitric acid. Preferably, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1. The mass-to-volume ratio of carbon nanotubes to the mixed acid is 1g:50-100mL (preferably 1g:50mL). The surface carboxyl functionalization treatment is performed by co-stirring at 60-100℃ (preferably 80℃) for 4-8 hours (preferably 6 hours). Preferably, the carbon nanotubes have a length of 10-30 μm.

[0012] Furthermore, in the aforementioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the carboxyl-modified carbon nanotubes are obtained by surface carboxyl functionalization treatment of carbon nanotubes with a mixed solution of concentrated sulfuric acid and concentrated nitric acid, removing impurities (by filtering with a Buchner funnel to obtain a solid), washing repeatedly until neutral, and holding at 60–80°C to constant weight (preferably for 8–12 hours) to obtain carboxyl-modified carbon nanotubes. When single-walled carbon nanotubes are used as the raw material, they are named SWCNT-COOH (carboxyl-modified single-walled carbon nanotubes); when multi-walled carbon nanotubes are used as the raw material, they are named MWCNT-COOH (carboxyl-modified multi-walled carbon nanotubes).

[0013] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the hydrazine salt is a hydrazine sulfate.

[0014] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the azophthalic acid is azophenyl-4,4'-dicarboxylic acid.

[0015] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the thickness of the graphite film is 30–100 μm.

[0016] Furthermore, in the aforementioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the density of the graphite film is 1.8–2.1 g / cm³. 3 .

[0017] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the horizontal thermal conductivity of the graphite film is 1300–1700 W / (mK).

[0018] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the vertical thermal conductivity of the graphite film is 3.5 to 12 W / (mK).

[0019] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the graphitization degree of the graphite film is 95-100%.

[0020] Furthermore, in the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, the lattice spacing of the graphite film is 0.335–0.350 nm.

[0021] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, comprising the following steps:

[0022] (1) Preparation of poly(arylene oxadiazole) stock solution: First, terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes, and hydrazine salt are reacted at 80–90°C under the action of fuming sulfuric acid until the reaction solution becomes transparent; then the temperature is raised to 100–120°C and reacted for 2–5 h; the reaction is terminated with benzoic acid; then the reaction is continued at 120–135°C for 0.5–1 h, and vacuum degassing and drying are performed to obtain the modified poly(arylene oxadiazole) stock solution; In this mixture, the molar ratio of isophthalic acid to terephthalic acid is 0.05–0.55: 0.95–0.45; the mass ratio of azophthalic acid to the total mass of isophthalic acid and terephthalic acid is 0.01–0.10:1; the mass ratio of carboxyl-modified carbon nanotubes to the total mass of isophthalic acid and terephthalic acid is 0.001–0.01:1; and the molar addition of hydrazine salt to the total molar amount of isophthalic acid and terephthalic acid is 1.10–1.20:1.

[0023] (2) Preparation of wet poly(arylexadiazole) (POD) membrane: The obtained POD stock solution was scraped through a wet membrane preparation device and the aqueous wet POD membrane was obtained after solvent replacement;

[0024] (3) The obtained wet poly(aryloxadiazole) (POD) membrane is then used to prepare a dry POD membrane;

[0025] (4) Finally, the dry POD film is subjected to carbonization and graphitization treatment and cold pressing treatment to obtain the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film.

[0026] Furthermore, in the above-mentioned method for preparing aromatic heterocyclic polymer-based graphite films with high vertical thermal conductivity, in step (1), the molar ratio of excess benzoic acid to hydrazine salt is 1:1.

[0027] Furthermore, in the above-mentioned method for preparing aromatic heterocyclic polymer-based graphite films with high vertical thermal conductivity, in step (1), the sulfur trioxide content in the fuming sulfuric acid is 20-40 wt%, preferably 25 wt%.

[0028] Furthermore, in the above-mentioned method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (2), the method for preparing a wet POD film from the obtained POD stock solution is as follows: the obtained POD stock solution is spread on a substrate at 60-120 °C, and a wet film preparation device is used to scrape the film to obtain a wet film; then the substrate is placed in a 30-60 wt% sulfuric acid aqueous solution for solvent replacement, and after washing with water, a water-containing wet POD film is obtained.

[0029] Furthermore, in the above-mentioned method for preparing aromatic heterocyclic polymer-based graphite films with high vertical thermal conductivity, in step (3), the wet POD film is annealed at 60-120°C for 10-60 minutes to obtain a dry POD film.

[0030] Furthermore, in the above-mentioned method for preparing aromatic heterocyclic polymer-based graphite films with high vertical thermal conductivity, in step (4), the carbonization temperature is 1200-1500℃ and the graphitization temperature is 2600-3000℃.

[0031] Preferably, in the above-mentioned method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (4), the carbonization process is as follows: under the protection of an inert gas, the dry POD film is gradually heated from room temperature to 400-500°C at a heating rate of 2-5°C / min, and held for 0.5-2h. Then, the heating rate is reduced to 0.5-2°C / min (preferably 1°C / min) and the temperature is increased to 500-600°C, and held for 0.5-2h. Then, the heating rate is increased to 2-5°C / min (preferably 2.5°C / min) and the temperature is increased to 1200-1500°C (preferably 1400°C) and held for 0.5-5h.

[0032] Preferably, in the above-mentioned method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film, in step (4), the graphitization process is as follows: heating to 2200-2300°C at a heating rate of 3-10°C / min, holding for 0.5-2h, then reducing the heating rate to 0.5-2°C / min and heating to 2400-2500°C, holding for 0.5-2h; then increasing the heating rate to 3-10°C / min and heating to 2600-3000°C and holding for 0.5-2h, followed by natural cooling to room temperature.

[0033] Furthermore, in the above-mentioned method for preparing aromatic heterocyclic polymer-based graphite films with high vertical thermal conductivity, the cold pressing process in step (4) is as follows: first, the air inside the film is discharged, then it is pressed for 1 to 2 hours under a pressure of 50 to 150 MPa, and then pressed for 5 to 10 hours under a pressure of 250 to 300 MPa.

[0034] The beneficial effects of this invention are:

[0035] This invention involves carboxylating carbon nanotubes and then polymerizing them in situ with poly(arylene oxadiazole) (POD) to obtain modified POD, thereby yielding a high-vertical-thermal-conductivity aromatic heterocyclic polymer-based graphite film. This graphite film achieves good balance between horizontal and vertical thermal conductivity. The graphite film of this invention has a thickness ranging from 30 to 100 μm and a density of 1.8 to 2.1 g / cm³. 3 The horizontal thermal conductivity is 1300–1700 W / (mK), and the vertical thermal conductivity is 3.5–12 W / (mK), which significantly improves the overall performance of graphite film. Attached Figure Description

[0036] Figure 1 Transmission electron microscopy (TEM) morphology image (a), elemental analysis diagram (b), and TEM morphology image (c) of the graphite film sample used in the embodiments of the present invention.

[0037] Figure 2 Raman data (a) and corresponding I values ​​of the carbonized films at 1400°C in Examples 1-10 and Comparative Example 1 of the present invention D / I G Data analysis diagram (c), Raman data of the graphitized film at 3000℃ (b) and corresponding I 2D / I G Data analysis chart (d).

[0038] Figure 3 XRD data (a) and corresponding d) of graphite films at 3000℃ in Examples 1-10 and Comparative Example 1 of the present invention 002 and L c Data analysis chart (b). Detailed Implementation

[0039] This invention proposes a method for improving the vertical thermal conductivity of poly(aromatic oxadiazole) (POD)-based graphite films using carboxyl-modified carbon nanotubes. The graphite film is prepared by first obtaining a base film from modified poly(aromatic oxadiazole), followed by carbonization, graphitization, and cold pressing. The structural diagram of the modified poly(aromatic oxadiazole) is shown below:

[0040] .

[0041] This method includes the following key steps:

[0042] 1) Preparation of POD polymer stock solution: The solution mixing copolymerization method is adopted, using fuming sulfuric acid as solvent and dehydrating agent to promote the polymerization and cyclization reaction of monomers; in this process, carboxyl-modified carbon nanotubes are added to the reaction system as reactants to ensure that they are uniformly dispersed during the polymerization process.

[0043] 2) Preparation and drying of wet POD film: The obtained POD stock solution is spread evenly on a substrate (such as a glass plate) at 60-120 °C. A wet film preparation device is used to scrape the film. By adjusting the slit width of the wet film preparation device, wet films of different thicknesses can be prepared. Subsequently, the substrate is placed in a 30-60 wt% (preferably 50 wt%) sulfuric acid aqueous solution for solvent replacement for 10-30 minutes. At this time, the solvent of the wet film changes from concentrated sulfuric acid to water and gradually separates from the glass plate. Then, it is transferred to deionized water for 10-30 minutes to remove surface sulfuric acid. Finally, it is transferred to flowing deionized water for rinsing for more than 12 hours to remove residual sulfuric acid, thus obtaining a water-containing wet POD film.

[0044] 3) Then, the wet POD membrane is fixed with nails and dried to obtain a dry POD membrane of carboxyl-modified carbon nanotubes.

[0045] 4) Carbonization-graphitization and cold pressing: The POD dry film undergoes carbonization-graphitization treatment, in which carbon nanotubes act as the vertical phase in the film. Through in-situ polymerization, the pores and defects caused by the different shrinkage during the carbonization process of the substrate can be effectively improved. During the graphitization process, it does not interfere with the growth of graphite sheets and acts as a vertical phase thermal conduction path between the layers, thereby improving the vertical thermal conductivity of the graphite film. Then, the graphitized film is subjected to a step-by-step cold pressing treatment to improve its density and performance: the air inside the film is removed under low pressure using a roller press, then pressed under 50-150 MPa pressure for 1-2 hours using a cold press, and finally pressed under 250-300 MPa pressure for 5-10 hours to obtain a flexible and dense graphite film. For example, the graphite film is first placed between two smooth release papers to ensure the smoothness of the graphite film surface after calendering and separation from the pressing surface. The air inside the film is first removed by using a roller press at low pressure, then pressed for 1 hour at 100 MPa pressure by a cold press, and finally pressed for 5 hours at 300 MPa pressure to obtain a flexible and dense graphite film.

[0046] This invention achieves in-situ polymerization of carbon nanotubes and POD by carboxylating carbon nanotubes and combining the strong dispersing and dehydrating effects of the polyarylene dioxadiazole (POD) polymerization system. This fundamentally solves the problem of difficult dispersion of carbon nanotubes and simultaneously mitigates the destruction of graphite crystal orientation caused by the difference in heterogeneous shrinkage rates during carbonization. The strong solubility and dispersing ability of the polyarylene dioxadiazole system and the dehydrating effect of fuming sulfuric acid significantly reduce defects and vacancies caused by the difference in shrinkage rates during the carbonization of carbon materials and organic precursors, laying a key foundation for the preparation of high-performance graphite films.

[0047] This invention constructs a composite bidirectional structure of carbon nanotubes and graphene: during the graphitization process, carbon nanotubes mainly exist between graphite microcrystals, which does not affect the continuous growth and stacking of graphene sheets, and can also serve as a vertical phase thermal conduction pathway, forming a synergistic effect with the horizontal thermal conduction pathway of graphene sheets, thus achieving a balance between horizontal and vertical thermal conductivity.

[0048] The graphite film of this invention exhibits significantly improved performance: vertical thermal conductivity is increased by 300%, while the decrease in horizontal thermal conductivity is less than 10%; at a thickness of 45 μm, the horizontal thermal conductivity reaches 1564 W / (mK), and the vertical thermal conductivity reaches 7.0 W / (mK). The overall product density is 1.8–2.1 g / cm³. 3 This invention effectively overcomes the current technical deficiency in improving the vertical thermal conductivity of thermally conductive graphite films, and solves the problem of excessively low vertical thermal conductivity in graphite films prepared from organic polymer precursors. The graphite film of this invention can be widely used in fields such as electronics manufacturing, energy storage, and aerospace, enabling uniform distribution and rapid heat dissipation from heat-generating devices, significantly improving equipment thermal management efficiency, and providing a better option for the application of thermal management systems in different scenarios.

[0049] The embodiments will further illustrate the above implementation scheme. It should be emphasized that these embodiments are only used to illustrate the process and effects of the present invention and do not limit the scope of application of the present invention. Unless otherwise specified, the conditions, reagents, or equipment used in the experiments follow industry standards or manufacturer-recommended specifications.

[0050] In this embodiment of the invention, all raw materials are directly purchased industrial-grade raw materials.

[0051] Examples 1-5

[0052] 1) Synthesis of the stock solution: First, the raw materials were mixed according to the proportions shown in Table 1 and dissolved at 85℃ for 0.5 hours. After all the solids were dissolved, the temperature was raised to 90℃ and reacted for 1 hour, and then further raised to 120℃ and reacted for 3 hours. After the reaction was completed, the reaction was terminated with benzoic acid (the amount of which was equal to the molar amount of excess hydrazine sulfate), and the reaction was continued at 120℃ for 0.5 hours. Then, a vacuum degassing treatment was performed for 12 hours to obtain the POD stock solution. Among them, the carboxyl-modified carbon nanotubes were subjected to surface carboxyl functionalization treatment in a mixed solution of concentrated sulfuric acid and concentrated nitric acid (3:1). After removing impurities, the carbon nanotubes were washed multiple times until neutral and kept at 60℃ for 10 hours to obtain carboxyl-modified carbon nanotubes, which were named MWCNT-COOH (carboxyl-modified multi-walled carbon nanotubes). The carbon nanotubes were selected with a length of 10-30 μm.

[0053] Table 1. Proportioning of each raw material (can be scaled up proportionally according to usage).

[0054] raw material mass or volume terephthalic acid 20 g isophthalic acid 5 g Azobenzene-4,4'-dicarboxylic acid 1.25 g Carboxyl-modified multi-walled carbon nanotubes 0.025 / 0.0625 / 0.125 / 0.1875 / 0.25 g hydrazine sulfate 20.56 g concentrated sulfuric acid 80 mL Fuming sulfuric acid (50%) 70 mL benzoic acid 0.9189 g

[0055] 2) Wet film formation: The POD stock solution is processed by a wet film preparation device. The specific operation is as follows: POD stock solution is spread on a glass plate at 80 ℃, and the film is scraped using a wet film preparation device with a 750 μm slit. After the film is separated from the glass plate by 50 wt% sulfuric acid solution for 20 minutes, it is rinsed with deionized water for more than 12 hours to remove residual sulfuric acid and obtain the POD wet film.

[0056] 3) Preparation of dry film: The POD wet film is fixed around the perimeter using a needle plate and dried in an oven at 100°C to obtain POD dry film.

[0057] 4) Carbonization and graphitization of POD dry film, and cold pressing treatment:

[0058] Carbonization treatment: carried out in a graphite furnace; under argon protection at a rate of 5 L / min, first heat to 400 °C at a rate of 2.5 °C / min, hold for 0.5 hours, then adjust the heating rate to 1 °C / min to 600 °C, hold for 0.5 hours; then adjust the heating rate to 2.5 °C / min to 1400 °C and hold for 1 hour;

[0059] Graphitization treatment: First, heat to 2200 ℃ at a rate of 5 ℃ / min and hold for 0.5 hours. Then, adjust the heating rate to 1 ℃ / min to 2500 ℃ and hold for 0.5 hours. Next, adjust the heating rate to 5 ℃ / min to 3000 ℃ and hold for 1 hour. Then, allow it to cool naturally to room temperature to obtain the initial graphite film.

[0060] Cold pressing: First, place the graphite film between two smooth release papers to ensure the smoothness of the graphite film surface after calendering and separation from the pressing surface. First, use a roller press at low pressure to remove the air inside the film, then use a cold press at 100 MPa pressure for 1 hour, and finally press at 300 MPa pressure for 5 hours to obtain a flexible and dense graphite film.

[0061] The obtained graphite films were named according to the amount of multi-walled carbon nanotubes added, namely Example 1-MWCNT0.1 (i.e., carboxyl-modified multi-walled carbon nanotubes account for 0.1 wt% of the total mass of terephthalic acid and isophthalic acid), Example 2-MWCNT0.25, Example 3-MWCNT0.5, Example 4-MWCNT0.75, and Example 5-MWCNT1.0. The thickness of the final prepared graphite film was 45 μm.

[0062] Examples 6-10

[0063] The preparation method was the same as in Example 1, except that multi-walled carbon nanotubes were replaced with single-walled carbon nanotubes. The resulting graphite films were named according to the amount of single-walled carbon nanotubes added, namely Example 6-SWCNT0.1 (i.e., carboxyl-modified single-walled carbon nanotubes accounted for 0.1 wt% of the total mass of terephthalic acid and isophthalic acid), Example 7-SWCNT0.25, Example 8-SWCNT0.5, Example 9-SWCNT0.75, and Example 10-SWCNT1.0.

[0064] Comparative Example 1

[0065] The preparation method is the same as in Example 1, except that carbon nanotubes were not added during the preparation process; the graphite film is referred to as origin.

[0066] Comparative Example 2

[0067] The preparation method is the same as in Example 3, except that the multi-walled carbon nanotubes added during the preparation process are not carboxylated.

[0068] Comparative Example 3

[0069] The preparation method is the same as in Example 8, except that the single-walled carbon nanotubes added during the preparation process are not carboxylated.

[0070] Comparative Example 4

[0071] The preparation method is the same as in Example 3, except that the carboxyl-modified multi-walled carbon nanotubes are replaced with graphene oxide during the preparation process.

[0072] Performance testing and results:

[0073] Thermal conductivity testing: The thermal diffusivity of the graphite film was tested using Netzsch LFA 467. The test temperature was set at room temperature (25°C). The test sample was a circular disc with a diameter of 2.5 cm, and graphite was sprayed on both sides of the sample during the test. The test results of the thermal conductivity of the graphite films obtained in the examples and comparative examples are shown in Table 2.

[0074] Table 2 Performance Comparison of Graphite Films

[0075] Serial Number <![CDATA[Density (g·cm -3 )]]> <![CDATA[Horizontal thermal conductivity (W·m -1 ·K -1 )]]> <![CDATA[Vertical thermal conductivity (W·m -1 ·K -1 )]]> Comparative Example 1 2.08 1675.7 2.21 Example 1 2.06 1602.6 4.17 Example 2 2.04 1537.9 5.91 Example 3 2.01 1458.9 7.78 Example 4 1.95 1337.8 8.93 Example 5 1.9 1173.9 12.26 Comparative Example 2 1.87 1205.5 4.71 Example 6 2.04 1646.9 3.77 Example 7 2.01 1621.7 4.62 Example 8 1.95 1564.3 7.05 Example 9 1.85 1460.1 8.43 Example 10 1.77 1357.3 9.89 Comparative Example 3 1.82 1348.5 4.12 Comparative Example 4 1.88 1377.5 2.74

[0076] As can be seen from the thermal conductivity data in Table 1, the introduction of untreated carbon nanotubes (Comparative Examples 2 and 3) leads to a more severe shrinkage mismatch during the carbonization process, causing a sharp decrease in horizontal thermal conductivity and little improvement in vertical thermal conductivity. This effect is significantly reduced after carboxylation treatment. Furthermore, in Example 8, the use of carboxyl-modified single-walled carbon nanotubes resulted in the final graphite film maintaining a horizontal thermal conductivity above 1560 W·m. -1 ·K -1At the same time, the vertical thermal conductivity was increased to 7 W·m -1 ·K -1 The above demonstrates the excellent effects of this invention. In contrast, introducing other carbon-based fillers, such as graphene oxide (Comparative Example 4), results in a significant decrease in horizontal thermal conductivity without effectively improving vertical thermal conductivity.

[0077] Depend on Figure 1 a, Figure 1 b、 Figure 1 Morphological and elemental analysis revealed that the carbon nanotubes underwent successful surface carboxylation, which facilitates their dispersion and participation in the polymerization reaction within the POD polymerization system. After graphitization, effective connections were observed between the graphene sheets, constructing vertical thermal conduction pathways.

[0078] Depend on Figure 2 a, Figure 2 b. Raman data graph and Figure 2 c. Figure 2 d of I D / I G Data analysis shows that the addition of carboxyl-modified carbon nanotubes affected the growth quality of graphite crystallites during the carbonization process. This is mainly due to the mismatch in shrinkage between the matrix and the carbon nanotubes. However, this effect can be mitigated during the graphitization process if it is controlled and weakened. Figure 2 As can be seen from b, the defect peaks all disappear after graphitization, indicating that this technology can effectively reduce the defects introduced by carbon nanotubes. Furthermore, through I... 2D / I G The comparison shows that as the amount of carbon nanotubes introduced increases, I 2D / I G The rate of increase will continue, which means that the average number of stacked graphite sheets is decreasing. This is mainly because most carbon nanotubes are located between the layers, and this effect is greater for multi-walled carbon nanotubes than for single-walled carbon nanotubes.

[0079] Depend on Figure 3 a XRD data chart and Figure 3 b of d 002 and L c Further data analysis shows that the intercalation effect after introducing carbon nanotubes is due to the fact that most of the carbon nanotubes are inserted into the graphene sheets, which leads to an increase in interlayer spacing and a decrease in average stacking thickness. Moreover, the intercalation effect of multi-walled carbon nanotubes is greater than that of single-walled carbon nanotubes.

[0080] In summary, this invention addresses the technical bottlenecks of low vertical thermal conductivity in existing graphite films and the tendency for introducing fillers to reduce horizontal thermal conductivity. It employs an in-situ polymerization process of carboxylated carbon nanotubes and poly(arylexadiazole) (POD). By modifying the carbon nanotubes with carboxylation and polymerizing them with POD, the problems of interfacial incompatibility between carbon-based materials and organic matrices, and the mismatch in heterogeneous shrinkage during high-temperature carbonization are effectively solved. Experimental results show that this invention significantly improves vertical thermal conductivity while maintaining high horizontal thermal conductivity in graphite films, greatly enhancing the overall thermal conductivity of graphite films compared to traditional techniques. This invention provides a novel solution for the preparation of high-performance thermal management materials and has broad application prospects in fields such as electronics manufacturing, energy storage, and aerospace.

Claims

1. A graphite film based on aromatic heterocyclic polymers with high vertical thermal conductivity, characterized in that: The graphite film is prepared by first obtaining a base film from modified polyarylene oxadiazole, and then obtaining it through carbonization, graphitization, and cold pressing. The modified polyarylene oxadiazole is prepared using the following method: terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes, and hydrazine salt are reacted at 80–90°C in the presence of fuming sulfuric acid until the reaction solution becomes transparent; then the temperature is raised to 100–120°C and reacted for 2–5 hours; the reaction is terminated with benzoic acid; and the reaction is continued at 120–135°C for 0.5–1 hour, followed by vacuum desulfurization. The modified polyarylene oxadiazole was prepared by foaming and drying treatment; wherein, the molar ratio of isophthalic acid to terephthalic acid was 0.05-0.55:0.95-0.45; the mass ratio of azophthalic acid to the total mass of isophthalic acid and terephthalic acid was 0.01-0.10:1; the mass ratio of carboxyl-modified carbon nanotubes to the total mass of isophthalic acid and terephthalic acid was 0.001-0.01:1; and the molar addition of hydrazine salt to the total molar amount of isophthalic acid and terephthalic acid was 1.10-1.20:

1.

2. The high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 1, characterized in that: The carboxyl-modified carbon nanotubes are obtained by surface carboxyl functionalization treatment of carbon nanotubes using a mixed solution of concentrated sulfuric acid and concentrated nitric acid.

3. A high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 1 or 2, characterized in that: The thickness of the graphite film is 30–100 μm; or, The density of the graphite film is 1.8–2.1 g / cm³; or, The horizontal thermal conductivity of the graphite film is 1300–1700 W / (mK); or, The graphite film has a vertical thermal conductivity of 3.5–12 W / (mK); or, The graphite film has a graphitization degree of 95-100%; or, The lattice spacing of the graphite film is 0.335–0.350 nm.

4. A method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to any one of claims 1-3, characterized in that: Includes the following steps: (1) Preparation of POD stock solution: First, terephthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt are reacted at 80-90℃ under the action of fuming sulfuric acid until the reaction solution becomes transparent; then the temperature is raised to 100-120℃ and reacted for 2-5 hours; the reaction is terminated with benzoic acid; then the reaction is continued at 120-135℃ for 0.5-1 hour, and vacuum degassing and drying are performed to obtain the modified polyarylene oxadiazole stock solution; wherein, isophthalic acid, isophthalic acid, azophthalic acid, carboxyl-modified carbon nanotubes and hydrazine salt are reacted at 80-90℃ ... The molar ratio of phthalic acid to terephthalic acid is 0.05–0.55:0.95–0.45; the mass ratio of azophthalic acid to the total mass of isophthalic acid and terephthalic acid is 0.01–0.10:1; the mass ratio of carboxyl-modified carbon nanotubes to the total mass of isophthalic acid and terephthalic acid is 0.001–0.01:1; and the molar addition of hydrazine salt to the total molar amount of isophthalic acid and terephthalic acid is 1.10–1.20:

1. (2) Preparation of POD membrane: The obtained POD stock solution is scraped through a wet membrane preparation device and the solvent is replaced to obtain a water-containing wet POD membrane; (3) The obtained wet POD membrane is then processed into a dry POD membrane; (4) Finally, the dry POD film is subjected to carbonization and graphitization treatment and cold pressing treatment to obtain the high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film.

5. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 4, characterized in that: In step (2), the method for preparing a wet POD film from the obtained POD stock solution is as follows: the obtained POD stock solution is spread on a substrate at 60-120 °C, and a wet film preparation device is used to scrape the film to obtain a wet film; then the substrate is placed in a 30-60 wt% sulfuric acid aqueous solution for solvent replacement, and after washing with water, a water-containing wet POD film is obtained.

6. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 4, characterized in that: In step (3), the wet POD membrane is annealed at 60-120°C for 10-60 minutes to obtain the dry POD membrane.

7. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 4, characterized in that: In step (4), the carbonization temperature is 1200-1500℃ and the graphitization temperature is 2600-3000℃.

8. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 4, characterized in that: In step (4), the carbonization process is as follows: under the protection of inert gas, the dry POD film is gradually heated from room temperature to 400-500°C at a heating rate of 2-5°C / min and held for 0.5-2h. Then the heating rate is reduced to 0.5-2°C / min and the temperature is increased to 500-600°C and held for 0.5-2h. Then the heating rate is increased to 2-5°C / min and the temperature is increased to 1200-1500°C and held for 0.5-5h.

9. The method for preparing a high vertical thermal conductivity aromatic heterocyclic polymer-based graphite film according to claim 4, characterized in that: In step (4), the graphitization process is as follows: heating to 2200-2300℃ at a heating rate of 3-10℃ / min, holding for 0.5h-2h, then reducing the heating rate to 0.5-2℃ / min to 2400-2500℃, holding for 0.5h-2h; then increasing the heating rate to 3-10℃ / min to 2600-3000℃ and holding for 0.5h-2h, followed by natural cooling to room temperature.

Images