CN105731435A - High-strength flexible graphene composite heat conduction film and preparation method thereof - Google Patents

Abstract

The invention discloses a high-strength flexible graphene composite heat-conducting film and a preparation method thereof. The film is composed of macroscopic multilayer wrinkled graphene with microscopic scale wrinkles through physical crosslinking, and the sheets can slide, so it has extremely high flexible. Its graphene sheet structure is perfect, the sheet crystal area is extremely large and contains few defects, the structure is dense after high-pressure pressing, and it has ultra-high electrical and thermal conductivity. At the same time, the existence of the polymer composite can cross-link the graphene sheets and enhance the strength of the graphene film. This high-strength flexible graphene composite heat-conducting film has a strength of 100-300MP, can withstand repeated bending for more than 1000 times, an elongation at break of 6-16%, an electrical conductivity of 6000-8600S/cm, and a thermal conductivity of 1400? 1800W/mK, can be widely used in high-strength and designable thermal and conductive devices.

Description

A kind of high-strength flexible graphene composite heat-conducting film and preparation method thereof

technical field

The invention relates to a novel heat-conducting material and a preparation method thereof, in particular to an ultra-flexible high-heat-conduction graphene film and a preparation method thereof.

Background technique

In 2010, two professors Andre GeiM and Konstantin Novoselov from the University of Manchester won the Nobel Prize in Physics for their first successful separation of stable graphene, which set off a wave of research on graphene around the world. Graphene has excellent electrical properties (electron mobility up to 2×10 ⁵ cM ² /Vs at room temperature), outstanding thermal conductivity (5000W/(MK), extraordinary specific surface area (2630M ² /g), and its Young’s Modulus (1100GPa) and breaking strength (125GPa). The excellent electrical and thermal conductivity of graphene completely exceeds that of metals. At the same time, graphene has the advantages of high temperature resistance and corrosion resistance, and its good mechanical properties and low density make it more Potential to replace metals in the field of electrocaloric materials.

Graphene film assembled with graphene oxide or graphene nanosheets macroscopically is the main application form of nanoscale graphene, and the commonly used preparation methods are suction filtration method, scraping film method, spin coating method, spray coating method and dip coating method. Through further high-temperature treatment, the defects of graphene can be repaired, and the electrical conductivity and thermal conductivity of the graphene film can be effectively improved. It can be widely used in portable electronics with high heat dissipation requirements such as smartphones, smart portable hardware, tablet computers, and notebook computers. device.

However, at present, the size of graphene oxide used is insufficient and contains a lot of fragments, so that it has not been developed enough in thermal conductivity, and its thermal conductivity is limited to 1400W/mK, which cannot meet the needs of rapid technological development. Moreover, the lack of film structure design makes its flexibility unclear, which limits its application in flexible devices. More importantly, the strength of graphene heat conduction film is less than 80MP, which greatly limits its application.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a high-strength flexible graphene composite heat-conducting film and a preparation method thereof.

The purpose of the present invention is achieved through the following technical solutions: a high-strength flexible graphene composite heat-conducting film, the high-flexibility graphene film density is 1.8-2.0g/cm ³ Graphene sheets overlap each other through ππ conjugation. Among them, in the polymer composite graphene sheet, the polymer is compounded on the graphene sheet through ππ conjugation or chemical bonds.

Further, the heat conduction film contains a graphene structure composed of 1-4 layers of polymer composite graphene sheets. And the graphene sheet has very few defects, and its I _D /T _G <0.01.

A preparation method of ultra-flexible high thermal conductivity graphene film, comprising the steps of:

(1) 1 mass part of graphene oxide with an average size greater than 100um and 0.01-1 mass part of organic polymers are formulated into a graphene oxide aqueous solution with a concentration of 6-30 mg/mL, and 0.1-5% of the mass fraction is added to the solution. Auxiliary agent, the auxiliary agent is an inorganic salt degradable at 2500 °C or a small organic molecule degradable at 2500 °C; after ultrasonic dispersion, pour it on the mold plate and dry it into a graphene oxide film, and then use a reducing agent to restore;

(2) Heating the reduced graphene film to 500-800°C at a rate of 0.1-1°C/min in an inert gas atmosphere, and keeping it warm for 0.5-2h;

(3) Raise the temperature to 1000-1300°C at a rate of 1-3°C/min in an inert gas atmosphere, and keep it warm for 0.5-3h;

(4) Raise the temperature to 2500-3000° C. at a rate of 5-8° C./min in an inert gas atmosphere, keep it warm for 0.5-4 hours, and obtain a porous graphene film after cooling down naturally.

(5) Press the graphene film under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film.

Further, the inorganic salt degradable at 2500°C is selected from ammonium bicarbonate, urea, thiourea, and azodicarbonamide; the small organic molecule degradable at 2500°C is selected from glycerin, polyethylene glycol 200, polyethylene glycol 400; organic polymers are mainly composed of hyperbranched polyglycidyl ether, hyperbranched copoly(ester-amine), hyperbranched polysulfone amine, hyperbranched polysiloxysilane, cellulose, hydroxymethyl fiber Sodium sodium, silk protein, sodium alginate, chitosan, gelatin, agar, urea-melamine, polyimide, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene, polypropylene , polybutylene, styrene resin, polyoxymethylene, polyamide, polycarbonate, polymethyl methacrylate, polyphenylene sulfide, polyphenylene ether, modified polyphenylene ether, polysulfone, polyether One or more of sulfone, polyketone, polyether ketone, polyether ether ketone, polyarylate and polyether nitrile are mixed according to any ratio.

Further, the reducing agent includes hydrazine hydrate, amines, ascorbic acid, and hydrogen iodide; since hydrazine hydrate will expand the membrane material during the reduction process, hydrazine hydrate is preferred.

Further, the pressure of the pressing process is 50-200MP, and the time is 6-300h.

Further, the graphene oxide with an average size greater than 100um in the step 1 is obtained by the following method:

(1) After diluting the reaction solution of the graphite oxide sheet obtained by the Modified-Hummer method, filter at 140 mesh sieves to obtain a filter product;

(2) After mixing the filtered product obtained in step 1 with ice water according to the volume ratio of 1:10, let it stand for 2 hours, and add hydrogen peroxide (H ₂ O ₂ mass fraction is 30%) dropwise until the color of the mixed solution changes. Change again (that is, the potassium permanganate in the mixed solution has been completely removed);

(3) Add concentrated hydrochloric acid (concentration is 12mol/L) dropwise in the mixed solution after step 2 treatment, until the flocculent graphite oxide disappears, then filter out the graphite oxide wafer with 140 mesh screens;

(4) Place the graphite oxide wafer obtained in step 3 in a shaker, 20 to 80 rpm, shake and wash, so that the graphite oxide wafer is peeled off, and a large piece of graphene oxide without fragments is obtained, the average size is greater than 87um, and the distribution coefficient Between 0.2-0.5.

Further, the Modified-Hummer method in step 1 is specifically: at -10°C, fully dissolve potassium permanganate in concentrated sulfuric acid with a mass fraction of 98%, add graphite, and stir at 60 rpm for 2 hours Stop stirring, react at low temperature (-10-20°C) for 6-48h, and obtain a wide-distributed graphite oxide flake reaction solution; the mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid is: 1g: 2-4g : 30-40ml, the particle size of graphite is greater than 150μm.

Further, the mesh screen is an acid-resistant mesh screen such as titanium alloy.

Further, in the step 1, the reaction solution of the graphite oxide sheet is diluted with a diluent such as concentrated sulfuric acid, and the volume of the diluent is 1-10 times the volume of the reaction solution.

The beneficial effect of the present invention is that: the present invention perfectly repairs graphene defects by forming a film of super large graphene oxide and annealing it at high temperature, and minimizes edge defects to form a perfect large conjugate structure, its conjugated size even extends to the entire graphene, which ensures the smooth flow of the graphene heat conduction path; further through the three-step independent heating process, the functional groups on the surface of the graphene are gradually detached, and the entrapped graphene sheets The auxiliary agent (pore-forming agent) decomposes slowly, and both are released step by step in the form of gas. At the same time, the graphitization process unfolds successively to form graphene micro-airbags; The deformation of the membrane is memorized, giving it ultrahigh flexibility. Under the condition of nitrogen protection, the polymers compounded on graphene gradually remove their functional groups, and graphitization evolves with the graphene graphitization, forming crosslinks in the form of conjugated structures or chemical bonds between layers, Greatly enhanced the strength of the graphene film.

During the formation of micro-airbags, the most stable functional groups on the surface of graphene also fall off, and the gas expands at high temperature, resulting in a graphene structure composed of 1-4 layers of graphene sheets; graphene few-layer structure The successful introduction of the material has greatly improved the electrical and thermal conductivity of the material. The combination of ultra-high thermal conductivity and flexibility makes this thermally conductive film have extremely wide application potential in high-frequency flexible electronic devices.

Description of drawings

Figure 1 shows graphite oxide crystals before filtration (left), and graphite oxide crystals after filtration (right).

Figure 2 shows graphene oxide before filtration (left) and graphene oxide after filtration (right).

Figure 3 is graphene oxide obtained by reaction at 50 degrees.

Figure 4 shows the size distribution of graphene oxide obtained by reaction at 50 degrees (left), and the size distribution of graphene oxide obtained by reaction at 20 degrees (right).

Figure 5 is a cross-sectional view of a graphene film.

Figure 6 is a scanning electron microscope picture of the surface and interior of the graphene film.

Fig. 7 is a schematic diagram of the relationship between the elongation at break and the strength of the graphene film.

detailed description

The present invention forms a film by using super large sheets of graphene oxide, in which graphene sheets with an average size of plane orientation greater than 100 μm play an important role in the process of forming the graphene film of the present invention. Before the graphite oxide crystals are washed with water, the present invention uses a mesh screen The method of separation is to separate the fragments. And use more than 10 times the volume of ice water to dilute, so that the wafer will not be damaged by the heat of dissolution of sulfuric acid. Further use of a shaker to shake and wash, so that the graphene oxide sheet avoids mechanical crushing when it is peeled off. Further, the present invention also prepares graphene sheets by low temperature conditions. At low temperatures, potassium permanganate has relatively weak oxidizing properties, and its self-decomposition produces oxygen at a relatively slow rate, so the fragmentation effect of gas on graphite oxide crystals is very weak. This allows large sheets of graphene oxide to be preserved. Moreover, there is no vigorous stirring and ultrasonic process in the reaction process and the cleaning process, so the sheet is basically not broken. Combining the above points, we obtained a super-large piece of non-fragmented graphene oxide, with an average size greater than 87um, a distribution coefficient between 0.2-0.5, and a fragment content of less than 1%. Moreover, the graphene sheet has very few defects, and its I _D /T _G <0.01.

The present invention will be further described below in conjunction with the accompanying drawings and embodiments. This embodiment is only used to further illustrate the present invention, and should not be understood as limiting the protection scope of the present invention. Those skilled in the art make some non-essential changes and adjustments according to the content of the above invention, which all belong to the protection scope of the present invention .

Example 1: Preparation of Graphene Oxide without Fragmentary Super Large Sheets

Example 1-1

(1) Slowly add potassium permanganate into the rapidly stirring concentrated sulfuric acid at -10°C. After fully dissolving, add graphite, stir slowly at 60 rpm for 2 hours, then stop stirring. React 6h, obtain the graphite oxide crystal of wide distribution respectively; As shown in Figure 1, all there are more fragments in the graphite oxide wafer that obtains under two kinds of temperatures, this makes its corresponding graphene oxide have a lot of fragments equally (Fig. 2).

(2) The reaction solution obtained in step 1 is diluted with concentrated sulfuric acid (the dilution factor can be any multiple, and the present embodiment is diluted about 10 times), and the graphite oxide crystals are filtered out with a titanium alloy mesh sieve with a 150um aperture (140 mesh) (Reaction solution recovery), and slowly poured into rapidly stirred ice water with respect to 10 times the volume of the filtered product, let stand for 2h, slowly added H ₂ O ₂ , to remove excess potassium permanganate in the reaction, add an appropriate amount of hydrochloric acid Until the flocculent graphite oxide disappears, the graphite oxide wafer is filtered out with a titanium alloy mesh sieve (140 mesh); the shaking table is slowly oscillated and washed to obtain super large pieces of graphene oxide without fragments (the average size is 87um, and the distribution coefficient is 0.5). The mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid is: 1g:2g:40ml, and the particle size of graphite is 200um.

As shown in Figure 3, the graphite oxide wafer separated after the reaction at a high temperature of 50 degrees is separated and the graphene oxide obtained after washing has a lot of fragments; The size distribution of graphene oxide is more uniform and concentrated, and the fragment content is very small.

Example 1-2

Slowly add potassium permanganate into the rapidly stirring concentrated sulfuric acid at -10°C. After fully dissolving, add graphite, stir slowly at 60 rpm for 2 hours, stop stirring, and react at low temperature (0°C,) for 48 hours. Obtain the reaction solution; the reaction solution is diluted with concentrated sulfuric acid with a mass fraction of more than 98% and dilute sulfuric acid with a mass fraction of 10% respectively, and then the graphite oxide crystals are filtered out with a titanium alloy mesh sieve with a 150um aperture (recovery of the reaction solution), And slowly pour into rapidly stirred ice water 10 times the volume of the filtered product, let it stand for 2 hours, slowly add H ₂ O ₂ to remove excess potassium permanganate in the reaction, add an appropriate amount of hydrochloric acid until the flocculent graphite oxide disappears , and then filter the graphite oxide wafer with a titanium alloy mesh sieve; slowly shake and wash the shaker to obtain the reaction product. The mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid is: 1:4g:30ml; the particle size of graphite is 500um.

Diluted with concentrated sulfuric acid, the reaction obtained non-fragmented super large graphene oxide (average size is 98um, distribution coefficient at 0.4), and diluted with dilute sulfuric acid, the obtained product contains a large number of fragments, and the size distribution coefficient exceeds 100%. This is due to the large amount of heat released during the dilution process of dilute sulfuric acid, which destroys the graphite oxide crystals.

Example 1-3

Slowly add potassium permanganate into the rapidly stirring concentrated sulfuric acid at -10°C. After fully dissolving, add graphite, stir slowly at 60 rpm for 2 hours, stop stirring, and react at low temperature (20°C) for 28 hours to obtain Widely distributed graphite oxide crystals; dilute the reaction solution with concentrated sulfuric acid and filter the graphite oxide crystals with a titanium alloy mesh screen with a pore size of 150um (recovery of the reaction solution), and slowly pour them into rapidly stirring 5 times the volume of the filtered product, 8 times the volume and 10 times the volume of ice water, let it stand for 2 hours, slowly add H ₂ O ₂ to remove excess potassium permanganate in the reaction, add an appropriate amount of hydrochloric acid until the flocculent graphite oxide disappears, and then use a titanium alloy mesh screen The graphite oxide wafers were filtered out; the shaker was shaken and washed slowly to obtain the reaction product; the mass volume ratio of graphite, potassium permanganate and concentrated sulfuric acid was 1:5g:34ml, and the particle size of graphite was 2mm.

The experimental results show that 5 times the volume and 8 times the volume of ice water cannot obtain graphene sheets with uniform size, and only 10 times the volume can obtain the super-large graphene oxide without fragments (the average size is 92um, and the distribution coefficient is 0.2 ). It can be seen that if the amount of ice water is too low, the heat of mixing will be released intensively and the crystal structure will be destroyed.

Embodiment 2: Using the non-fragmented super large sheet of graphene oxide prepared in embodiment 1 to prepare an ultra-flexible and highly thermally conductive graphene film.

Prepare 1 mass part of graphene oxide with an average size greater than 100um and 1 mass part of silk protein into a graphene oxide aqueous solution with a concentration of 30mg/mL, add 5% urea in the solution, and pour it on the mold plate after ultrasonic dispersion Dry the graphene oxide film, and then reduce it with hydrogen iodide reducing agent; the reduced graphene film is first gradually heated up to 500°C in an inert gas atmosphere, and kept for 0.5h; gradually heated to 1000°C in an inert gas atmosphere, Keep warm for 0.5h; gradually raise the temperature to 3000°C in an inert gas atmosphere, keep warm for 0.5h, and then naturally cool down to obtain a porous graphene film. The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film.

The heating rate at 500°C is 1°C/min, at 1000°C it is 3°C/min, and below 3000°C it is 8°C/min.

The pressure of the pressing process is 200MP, and the time is 300h.

The density of the obtained film is 1.8g/cm ³ , it can withstand more than 900 times of repeated bending, the elongation at break is 14%, the strength is 210MP, the electrical conductivity is 6000S/cm, and the thermal conductivity is 1400W/mK.

Fig. 5 is a cross-sectional view of the graphene film before pressing. It can be seen from the figure that the graphene film is assembled and cross-linked layer by layer, which lays the foundation for high strength.

Figure 6 is a scanning electron microscope picture of the graphene film surface. It can be seen from the picture that there are many folds on the surface and inside, which lay the foundation for the flexibility of the graphene membrane.

Figure 7 shows the elongation at break and strength of the graphene film. From the figure, the elongation at break of the graphene film we prepared reached 14%, and the strength was as high as 210MP; while the elongation at break of the graphene film containing 20% fragments was only about 6%, and the strength was less than 100MP. After repeated folding in half, the electrical conductivity does not change much, indicating that its flexibility is very good, and after repeated calendering, its performance can be restored to its original state, which indicates that the graphene film we prepared is a real macroscopic assembly of graphene.

Comparative Example 1: As in Example 1, the amount of silk protein is changed to 2 parts by mass, and the obtained film has a density of 1.6 g/cm ³ , can withstand repeated bending for more than 100 times, and has an elongation at break of 6%. The strength is 60MP, the conductivity is 2500S/cm, and the thermal conductivity is 600W/mK.

Comparative Example 2: As in Example 1, the reduced graphene oxide film is directly heated at 100 degrees per minute to 3000 degrees, and the obtained film has a density of 1.63 g/cm ³ , which can withstand repeated bending for more than 400 times without breaking. The elongation is 5%, the strength is 90MP, the electrical conductivity is 4000S/cm, and the thermal conductivity is 700W/mK.

Comparative example 3: As shown in the above example 1, the raw material of the graphene oxide used is changed, and the graphene oxide with a fragment content of about 20% is used. The density of the prepared film was 1.63g/cm ³ , and the film was damaged after repeated bending for 240°, the elongation at break was 6%, the strength was 84MP, the electrical conductivity was 2400S/cm, and the thermal conductivity was 800W/mK.

Embodiment 3: Using the non-fragmented super large sheet of graphene oxide prepared in embodiment 1 to prepare an ultra-flexible and highly thermally conductive graphene film.

1 part by mass of graphene oxide with an average size greater than 100um and 0.01 part by mass of hyperbranched polyglycidyl ether were formulated into an aqueous solution of graphene oxide with a concentration of 6 mg/mL, and 0.1 mass fraction of ammonium bicarbonate was added to the solution, and after ultrasonic dispersion Pour it on the mold plate and dry it into a graphene oxide film, and then reduce it with hydrazine hydrate reducing agent; the reduced graphene film is firstly heated up to 700°C in an inert gas atmosphere, and kept for 2 hours; it is gradually heated up to 1100°C, keep warm for 3 hours; gradually raise the temperature to 3000°C in an inert gas atmosphere, keep warm for 4 hours, and then get a porous graphene film after natural cooling. The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film.

The heating rate at 700°C is 0.2°C/min, at 1100°C it is 1°C/min, and below 3000°C it is 5°C/min.

The pressure of the pressing process is 200MP, and the time is 100h.

The density of the obtained film is 2.0g/cm ³ , it can withstand repeated bending for more than 1000 times, the elongation at break is 16%, the strength is 100MP, the electrical conductivity is 8600S/cm, and the thermal conductivity is 1800W/mK.

Embodiment 4: Using the non-fragmented super large sheet of graphene oxide prepared in embodiment 1 to prepare an ultra-flexible and highly thermally conductive graphene film.

Prepare 1 part by mass of graphene oxide with an average size greater than 100um and 0.1 part by mass of polyphenylene sulfide to prepare a graphene oxide aqueous solution with a concentration of 16 mg/mL, add 1% glycerol in the solution, and pour it on the mold plate after ultrasonic dispersion Dry the graphene oxide film on the surface, and then reduce it with anticorrosion; the reduced graphene film is heat-treated according to the heat treatment methods shown in Table 1-Table 3, and the porous graphene film can be obtained after natural cooling. The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film. The pressure of the pressing process is 50MP, and the time is 6h.

Table 1: The heating conditions of the first step

Table 2: Second step heating conditions

Table 3: The third step heating conditions

It can be seen from Table 1 to Table 3 that the performance of this material is mainly determined by three aspects. One is the repair of the graphene oxide sheet structure inside the material, that is, the loss of functional groups and the repair of the carbon conjugated structure at high temperature. Second, the continuity of the three-dimensional orientation structure inside the material, that is, the connectivity of the internal lamellar structure. Third, the formation of micro-air pockets can ensure the flexibility of the material and the existence of the graphene sheet structure. All three work together to increase the performance of graphene membranes.

As can be seen from Table 1, comparing A1, B1, C1, D1, and E1, the temperature of A1 is too low to remove most of the easily degradable functional groups, resulting in the rapid generation of a large amount of gas in the second high-temperature process. Split layer structure; E1 temperature is too high, gas is generated too fast, and the internal structure of the material will be torn in large quantities, both of which will make the material performance worse. Only at B1, C1, and D1 temperatures, the functional groups will be removed slowly and completely to ensure the performance of the material. Comparing C1, F1, G1, and H1, the heating rate of F1 is too low, and the gas release is too slow, which cannot form through holes inside the material, which is not conducive to the formation of micro-air pockets in the subsequent heating process; the heating process of H1 is too fast, and the gas release Too fast will tear the internal structure of the material, which is not conducive to the formation of transmission channels. Only at the heating rate of CG can both the formation of micro-air pockets and the integrity of the channel be guaranteed. Comparing C1, I1, J1, K1, L1, and M1, the holding time of I1 is too short, which cannot guarantee the degradation of most functional groups; the holding time of M1 is too long, which will absorb the tar in the furnace, which is not conducive to the improvement of performance. C1, J1, K1, and L1 just avoid the above two.

It can be seen from Table 2 that, comparing A2, B2, C2, D2, and E2, the heating rate of A2 is too low to form a tiny void structure, so that the film cannot form micro-air pockets, which seriously affects the electromagnetic shielding performance. If the heating rate of E2 is too high, the interlayer structure of graphene will be torn, making the linkability of graphene film worse, and the heat conduction and electromagnetic shielding performance will be worse. Only at the heating rates of B2, C2, and D2 can it be possible to ensure both the micro-airbag structure and the continuity inside the graphene membrane. Comparing C2, I2, J2, K2, L2, and M2, the holding time of I2 is too short, and the stable functional groups cannot be fully detached; the holding time of M2 is too long, the graphene film is easy to absorb tar, which is not conducive to the improvement of film performance; while C2, J2, Under the conditions of K2 and M2, it can not only ensure the sufficient shedding of stable functional groups, but also avoid the trouble of tar.

As can be seen from Table 3, comparing A3, B3, C3, D3, and E, the heating rate of A3 is too low, and the most stable functional group falls off too slowly, which is not enough to support the formation of microairbags in the process of forming microairbags; E3 heating process Too fast, gas release and high temperature expansion are too fast, easily destroying the formation of micro air pockets. Only in the case of B3, C3, and D3, the micro-air pockets can be formed stably, and the structure on the graphene can be slowly repaired. Comparing C3, F3, G3, H3, and I3, the end temperature of F3 is too low, and the repair of graphene structure is not perfect, so various performances are poor; the end temperature of I3 is too high, graphene will be vaporized; C3, G3, H3 Only at a high temperature can the repair of the graphene structure be guaranteed without being vaporized. Comparing C3, J3, K3, L3, and M3, the holding time of J3 is too low, the graphene structure cannot be fully repaired, and the holding time of M3 is too long, which will also cause the tar in the furnace to be adsorbed and affect the performance of the membrane.

Example 5: Using the non-fragmented super large sheet of graphene oxide prepared in Example 1 to prepare an ultra-flexible and highly thermally conductive graphene film.

1 part by mass of graphene oxide with an average size greater than 100um and 0.5 parts by mass of polyether nitrile are formulated into a graphene oxide aqueous solution with a concentration of 16 mg/mL, and 4% azodicarbonamide is added to the solution, and after ultrasonic dispersion Pour it on the mold plate and dry it into a graphene oxide film, and then reduce it with ascorbic acid; the reduced graphene film is first gradually heated up to 500°C in an inert gas atmosphere, and kept for 2 hours; gradually heated up to 1000°C in an inert gas atmosphere, Keep warm for 0.5h; gradually raise the temperature to 2500°C in an inert gas atmosphere, keep warm for 4h, and get a porous graphene film after cooling down naturally. The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film.

The heating rate at 500°C is 0.1°C/min, at 1000°C it is 1°C/min, and below 2500°C it is 7°C/min.

The pressure of the pressing process is 50MP, and the time is 120h.

The obtained film has a density of 1.84g/cm ³ , can withstand repeated bending for more than 1200 times, has an elongation at break of 9%, a strength of 300MP, an electrical conductivity of 6500S/cm, and a thermal conductivity of 1500W/mK.

Embodiment 6: Using the non-fragmented super large sheet of graphene oxide prepared in embodiment 1 to prepare an ultra-flexible and highly thermally conductive graphene film.

1 mass part of graphene oxide with an average size larger than 100um and 0.08 mass part of polyether ether ketone were prepared into a graphene oxide aqueous solution with a concentration of 6 mg/mL, 0.05 mass part of polyethylene glycol 200 was added to the solution, and after ultrasonic dispersion, pour Dry the graphene oxide film on the mold plate, and then reduce it with hydrogen iodide; the reduced graphene film is firstly heated up to 800°C in an inert gas atmosphere, and kept for 2 hours; it is gradually heated up to 1300°C in an inert gas atmosphere , keep warm for 3h; gradually raise the temperature to 3000°C in an inert gas atmosphere, keep warm for 0.5h, and then naturally cool down to get a porous graphene film. The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film.

The heating rate at 800°C is 0.6°C/min, at 1300°C is 1.3°C/min, and below 3000°C, the heating rate is 6.2°C/min.

The pressure of the pressing process is 150MP, and the time is 210h.

The density of the obtained film is 1.94g/cm ³ , it can withstand more than 890 times of repeated bending, the elongation at break is 15%, the strength is 173MP, the electrical conductivity is 7500S/cm, and the thermal conductivity is 1460W/mK.

Example 7: Using the non-fragmented super large sheet of graphene oxide prepared in Example 1 to prepare an ultra-flexible and highly thermally conductive graphene film.

1 mass part of graphene oxide with an average size larger than 100um and 0.2 mass part of poly(trimethylene terephthalate) were formulated into a graphene oxide aqueous solution with a concentration of 6-30 mg/mL, and 0.02 mass parts of polyethylene glycol 400 was added to the solution. , after ultrasonic dispersion, pour it on the mold plate and dry it to form a graphene oxide film, and then reduce it with hydrazine hydrate; the reduced graphene film is first gradually heated up to 600°C in an inert gas atmosphere, and kept for 1 hour; gradually in an inert gas atmosphere Raise the temperature to 1100°C and keep it warm for 2 hours; gradually raise the temperature to 2700°C in an inert gas atmosphere, keep it warm for 1 hour, and then naturally cool down to get a porous graphene film. The graphene film is pressed under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film.

The heating rate at 600°C is 0.1°C/min, at 1100°C it is 2.1°C/min, and below 2700°C it is 6.8°C/min.

The pressure of the pressing process is 220MP, and the time is 300h.

The obtained film has a density of 1.89g/cm ³ , can withstand repeated bending for more than 1200 times, has an elongation at break of 9%, a strength of 250MP, an electrical conductivity of 6100S/cm, and a thermal conductivity of 1430W/mK.

Claims (10)

1. A high-strength flexible graphene composite heat-conducting film, characterized in that, the high-flexibility graphene film density is 1.8-2.0g/cm ³ , and the average size of the planar orientation is greater than 100 μm polymer composite graphene sheet through ππ co- The yokes overlap each other. Among them, in the polymer composite graphene sheet, the polymer is compounded on the graphene sheet through ππ conjugation or chemical bonds. 2. The high-strength flexible graphene composite heat-conducting film according to claim 1, wherein the heat-conducting film comprises a graphene structure composed of 1-4 layers of polymer composite graphene sheets. And the graphene sheet has very few defects, and its I _D /T _G <0.01. 3. a preparation method of ultra-flexible high thermal conductivity graphene film, is characterized in that, comprises the steps: (1) 1 mass part of graphene oxide with an average size greater than 100um and 0.01-1 mass part of organic polymers are formulated into a graphene oxide aqueous solution with a concentration of 6-30 mg/mL, and 0.1-5% of the mass fraction is added to the solution. auxiliary agent (that is, the mass fraction of the auxiliary agent in the solution is 0.1-5%), the auxiliary agent is an inorganic salt degradable at 2500 °C or a small organic molecule degradable at 2500 °C; after ultrasonic dispersion, pour Dry the graphene oxide film on the mold plate, and then reduce it with a reducing agent; (2) Heating the reduced graphene film to 500-800°C at a rate of 0.1-1°C/min in an inert gas atmosphere, and keeping it warm for 0.5-2h; (3) Raise the temperature to 1000-1300°C at a rate of 1-3°C/min in an inert gas atmosphere, and keep it warm for 0.5-3h; (4) Raise the temperature to 2500-3000° C. at a rate of 5-8° C./min in an inert gas atmosphere, keep it warm for 0.5-4 hours, and obtain a porous graphene film after cooling down naturally. (5) Press the graphene film under high pressure to obtain an ultra-flexible and highly thermally conductive graphene film. 4. the preparation method of a kind of ultra-flexible high thermal conductivity graphene film as claimed in claim 3, is characterized in that, described inorganic salt degradable at 2500 ℃ is selected from ammonium bicarbonate, urea, thiourea, bismuth Nitrogen diformamide; degradable organic small molecules at 2500°C are selected from glycerin, polyethylene glycol 200, polyethylene glycol 400; organic polymers are mainly composed of hyperbranched polyglycidyl ether, hyperbranched copoly(ester-amine ), hyperbranched polysulfoneamine, hyperbranched polysiloxysilane, cellulose, sodium hydroxymethylcellulose, silk protein, sodium alginate, chitosan, gelatin, agar, urea-melamine, polyimide, Polybutylene terephthalate, Polypropylene terephthalate, Polyethylene, Polypropylene, Polybutylene, Styrenic resins, Polyoxymethylene, Polyamide, Polycarbonate, Polymethacrylic acid One or more of methyl ester, polyphenylene sulfide, polyphenylene ether, modified polyphenylene ether, polysulfone, polyethersulfone, polyketone, polyetherketone, polyetheretherketone, polyarylate, polyethernitrile are mixed in any ratio. 5. the preparation method of a kind of ultra-flexible high thermal conductivity graphene film as claimed in claim 3 is characterized in that, described reducing agent comprises hydrazine hydrate, amines, ascorbic acid, hydrogen iodide; It will make the membrane material swell, and hydrazine hydrate is preferred. 6. The preparation method of a kind of ultraflexible high thermal conductivity graphene film as claimed in claim 3, is characterized in that, described pressing process pressure is 50-200MP, and time is 6-300h. 7. the preparation method of a kind of ultra-flexible high thermal conductivity graphene film as claimed in claim 3, is characterized in that, in described step 1, the graphene oxide that average size is greater than 100um obtains by following method: (1) After diluting the reaction solution of the graphite oxide sheet obtained by the Modified-Hummer method, filter at 140 mesh sieves to obtain a filter product; (2) After mixing the filtered product obtained in step 1 with ice water according to the volume ratio of 1:10, let it stand for 2 hours, and add hydrogen peroxide (H ₂ O ₂ mass fraction is 30%) dropwise until the color of the mixed solution changes. Change again (that is, the potassium permanganate in the mixed solution has been completely removed); (3) Add concentrated hydrochloric acid (concentration is 12mol/L) dropwise in the mixed solution after step 2 treatment, until the flocculent graphite oxide disappears, then filter out the graphite oxide wafer with 140 mesh screens; (4) Place the graphite oxide wafer obtained in step 3 in a shaker, 20 to 80 rpm, shake and wash, so that the graphite oxide wafer is peeled off, and a large piece of graphene oxide without fragments is obtained, the average size is greater than 87um, and the distribution coefficient Between 0.2-0.5. 8. The method according to claim 7, characterized in that, the Modified-Hummer method in the step 1 is specifically: at -10°C, fully dissolving potassium permanganate in concentrated sulfuric acid with a mass fraction of 98% , add graphite, stir at 60 rev/min for 2h, stop stirring, and react at low temperature (-10-20°C) for 6-48h to obtain a wide-distributed graphite oxide flake reaction solution; the graphite, potassium permanganate and The mass volume ratio of concentrated sulfuric acid is: 1g: 2-4g: 30-40ml, and the particle size of graphite is greater than 150μm. 9. The method according to claim 7, characterized in that, the mesh screen is an acid-resistant mesh screen such as titanium alloy. 10. The method according to claim 7, characterized in that, in the step 1, the reaction liquid of the graphite oxide sheet is diluted by diluents such as concentrated sulfuric acid, and the volume of the diluent is 1-10 times the volume of the reaction liquid.