PTFE / graphene composite material, and preparation method and application thereof

Abstract

The application discloses a PTFE / graphene composite material and a preparation method and application thereof, and relates to the technical field of composite materials. The preparation method of the PTFE / graphene composite material comprises the following steps: (1) placing graphene in a plasma device to obtain fluorinated graphene; (2) mixing PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid, and repeatedly performing alternating ultrasonic treatment and microwave treatment to obtain a mixed solution after uniform dispersion; (3) performing flow casting of the mixed solution in a direct current electric field to obtain a composite material blank; (4) freeze-drying the composite material blank; and (5) performing microwave pulse sintering of the freeze-dried blank in a mixed gas of nitrogen and tetrafluoromethane to obtain the PTFE / graphene composite material. The composite material has excellent wear resistance, electrical properties, thermal conductivity and mechanical properties, and can meet the stringent requirements of high-end fields on materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a PTFE / graphene composite material and a preparation method and application thereof. BACKGROUND

[0002] Polytetrafluoroethylene (PTFE) has excellent chemical stability, low friction coefficient and other characteristics, but its low strength, poor thermal conductivity and other shortcomings limit its application in high-end fields. The compounding of graphene and PTFE is an effective means to improve its performance, but the traditional compounding method has many problems. For example, the traditional acidification method seriously damages the structure of graphene, and mechanical mixing, solution blending and other methods are difficult to achieve uniform dispersion and effective compounding of graphene in PTFE, and cannot fully exert the synergistic advantages of the two. At the same time, the existing technology is difficult to balance the high lubricity, high strength and good thermal conductivity of the material in the preparation process, resulting in limited application in high-performance heat dissipation and other fields with high requirements for material performance. SUMMARY

[0003] The present application relates to the technical field of composite materials, in particular to a PTFE / graphene composite material and a preparation method and application thereof.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0005] In a first aspect, the present application also provides a preparation method of a PTFE / graphene composite material, comprising the following steps:

[0006] (1) Placing graphene in a plasma device, and introducing a mixed gas of argon (Ar) and fluorine (F2) for reaction to obtain fluorinated graphene; the volume ratio of argon and fluorine is (6-9):1;

[0007] (2) Mixing PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid according to a mass ratio of 100:5:(3-5), and repeatedly performing alternating ultrasonic treatment and microwave treatment to obtain a mixed solution after uniform dispersion;

[0008] (3) Casting the mixed solution in a direct current field to form a composite material blank;

[0009] (4) Freeze-drying the composite material blank;

[0010] (5) Microwave pulse sintering the freeze-dried blank in a mixed gas of nitrogen (N2) and tetrafluoromethane (CF4) to obtain the PTFE / graphene composite material.

[0011] The present application adopts low-temperature plasma fluorination technology to in-situ functionalize graphene, forms a 3-5 layer fluorinated layer, introduces C-F bonds on the surface of graphene, can enhance the interfacial compatibility with PTFE, and at the same time avoids the damage to the structure of graphene by traditional acidification method. Then a fluorine-containing ionic liquid is selected as a dispersion medium, and an alternating treatment is carried out by ultrasonic-microwave, and the cation in the fluorine-containing ionic liquid is electrostatically adsorbed on the fluorinated graphene, and the anion forms a hydrogen bond with the PTFE particles, so that the two-phase synergistic dispersion is realized. Then the mixed solution is flow-casted under a direct current electric field, and the fluorinated graphene is arranged in a direction by virtue of its conductivity, a vertical gradient structure is formed, and the anisotropic performance of the composite material is significantly improved. Then the composite material blank is subjected to freeze-drying treatment to remove water and volatile impurities in the blank, so that the blank is solidified and formed. Finally, the microwave sintering is adopted to obtain the composite material, and the N2 / CF4 mixed gas atmosphere is used to effectively inhibit the thermal decomposition of PTFE, and the sintering quality and performance of the material are improved.

[0012] It should be noted that the single-layer thickness of the fluorinated layer is 0.35 nm, and the total thickness of 3-5 layers is 1.05-1.75 nm.

[0013] Preferably, the graphene is treated at a power of 100-200 W for 5-10 min during the reaction in step (1).

[0014] Preferably, the number of layers of the graphene in step (1) is 1-5 layers.

[0015] If the number of layers of the graphene is too small, the mechanical enhancement effect will be reduced, and if the number of layers is too large, stacking will easily occur, which affects the dispersibility. The present application controls the number of layers of the graphene, which is beneficial to improve the dispersibility of the graphene and the mechanical performance of the composite material.

[0016] Preferably, the lateral size of the graphene in step (1) is 0.5-5 μm. The lateral size refers to the maximum size in the plane of the graphene sheet layer (measured by SEM).

[0017] If the lateral size of the graphene is too small, the specific surface area will be too large, which will further increase the risk of agglomeration, and if the lateral size is too large, it will be difficult to achieve uniform distribution in the fluorine-containing ionic liquid dispersion system. Therefore, by controlling the size of the graphene, the dispersibility and enhancement effect of the graphene in the composite material are improved.

[0018] It should be noted that the single-layer thickness of the graphene before fluorination is 0.34 nm, and the C-F bond length increases to 0.38 nm after fluorination. However, the number of layers before and after fluorination does not change (verified by AFM), and the lateral size does not change significantly.

[0019] Preferably, the fluorine-containing ionic liquid in step (2) is [BMIM][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate) and / or [EMIM][Tf2N] (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide).

[0020] Preferably, nanodiamonds are further added to the fluorine-containing ionic liquid in step (2), and the mass of the nanodiamonds is 0.05-0.3% of the mass of the fluorine-containing ionic liquid, preferably 0.1%.

[0021] The present application facilitates reducing the viscosity of the system and further improving the dispersion effect of fluorinated graphene and PTFE by adding nanodiamonds as “molecular bearings” to the fluorine-containing ionic liquid. Moreover, if the content of nanodiamonds is too high, the interface bonding between PTFE and graphene will be weakened due to steric hindrance effect, resulting in a decrease in the tensile strength of the composite material. If the content of nanodiamonds is too low, the dispersion effect will be poor. Therefore, by controlling the content of nanodiamonds, the present application facilitates further improving the dispersibility between fluorinated graphene and PTFE.

[0022] Preferably, the average particle size of the nanodiamonds is 10-30 nm.

[0023] If the particle size of the nanodiamonds is too small, the nanodiamonds will easily agglomerate due to van der Waals force and cannot effectively serve as “molecular bearings” to reduce the viscosity of the system; if the particle size of the nanodiamonds is too large, the risk of sedimentation in the fluorine-containing ionic liquid dispersion system will increase, and the interface bonding between fluorinated graphene and PTFE may be damaged. Therefore, by controlling the particle size of the nanodiamonds, the present application facilitates improving the comprehensive performance of the composite material.

[0024] Preferably, the average molecular weight of the PTFE emulsion in step (2) is 1x10 6 ~5x10 6 g / mol. The detection standard for the molecular weight of the PTFE emulsion is ASTM D4441-20 (Determination of Molecular Weight of PTFE Emulsion by Inherent Viscosity).

[0025] If the molecular weight of PTFE is too low, the mechanical strength of the composite material will be insufficient; if the molecular weight of PTFE is too high, the viscosity of the emulsion will be large, and it will be difficult to uniformly mix the fluorinated graphene. Therefore, by controlling the molecular weight of PTFE, the present application can uniformly mix PTFE and fluorinated graphene, and facilitates improving the mechanical strength of the composite material.

[0026] Preferably, the viscosity of the PTFE emulsion at 25°C in step (2) is 200-400 mPa·s. The viscosity is measured by a Brookfield DV2T viscometer.

[0027] Preferably, the specific step of alternately performing ultrasonic treatment and microwave treatment in step (2) is: first ultrasonic treatment under the condition of a frequency of 40 kHz and a power of 500 W for 1 min, and then microwave irradiation under the condition of a frequency of 2.45 GHz and a power of 300 W for 10 s, which is one cycle and the cycle is repeated for 20-30 times.

[0028] The method of intermittent ultrasonic-microwave alternating treatment adopted in the application can avoid local overheating of PTFE, and further improve the uniformity of dispersion between PTFE and fluorinated graphene.

[0029] Preferably, the specific step of performing flow casting of the mixed solution in a direct current electric field in step (3) is: first maintaining in an X-axis electric field with a strength of 30 V / cm for 10 s, then maintaining in a Y-axis electric field with a strength of 50 V / cm for 10 s, and finally maintaining in a Z-axis electric field with a strength of 70 V / cm for 10 s, which is one cycle of X-axis electric field, Y-axis electric field and Z-axis electric field and the cycle is repeated until the end of the forming.

[0030] The application constructs a three-dimensional interlocking network by regulating the direction of the electric field (X / Y / Z-axis alternation), which is beneficial to further improve the anisotropic performance of the composite material.

[0031] Preferably, the specific step of freeze drying in step (4) is: first pre-freezing the composite material blank at-40~-30℃ for 3-4 h, and then drying at a temperature of-50℃ and a vacuum degree of 10 Pa for 12-24 h.

[0032] Preferably, two-stage microwave sintering is adopted in step (5), the first stage is sintering at a microwave frequency of 2.45±0.5 GHz and a temperature of 250-350℃ for 8-10 min, and the second stage is sintering at a microwave frequency of 5.8±0.2 GHz and a temperature of 350-380℃ for 5-10 min, and the duty cycle is 20-50%.

[0033] The application adopts two-stage microwave sintering, the first stage is to induce the interface dipole coupling between PTFE molecular chain and fluorinated graphene under low-frequency microwave, and then the second stage is to selectively heat the graphene interface under high-frequency pulse microwave to promote local melting and bonding, which is beneficial to improve the comprehensive performance of the composite material.

[0034] In the first stage: if the sintering temperature is too high, the excessive movement of PTFE molecular chains leads to thermal decomposition (toxic gases such as tetrafluoroethylene are generated), the material structure is destroyed, and the mechanical properties decrease sharply. If the sintering temperature is too low, the activity of PTFE molecular chains is insufficient, and effective dipole coupling cannot be formed with fluorinated graphene, the interface bonding is weak, and the thermal conductivity of the composite material decreases. If the microwave frequency is too low, the dipole coupling efficiency decreases, and if the microwave frequency is too high, it is easy to cause local overheating and decomposition of PTFE. If the sintering time is too short, the dipole coupling is insufficient, and the interface thermal resistance rises.

[0035] In the second stage: if the duty cycle is too large, the high-frequency microwave acts continuously for too long, local overheating leads to carbonization of the graphene interface or degradation of PTFE, the material brittleness increases, and the material wear rate increases. If the duty cycle is too small, the energy input is insufficient, the local fusion bonding of graphene and PTFE is insufficient, the interface bonding strength is low, and the tensile strength of the material decreases. If the frequency is too high, the graphene is selectively overheated and locally carbonized. If the sintering time is too short, the interface bonding rate decreases.

[0036] Therefore, by controlling the frequency, sintering temperature and sintering time and duty cycle in the first stage and the second stage, the comprehensive performance of the composite material can be further improved.

[0037] Preferably, the volume ratio of nitrogen and tetrafluoromethane in step (5) is (1-3): 1.

[0038] In a second aspect, the application provides a PTFE / graphene composite material prepared by the above method.

[0039] In a third aspect, the application also provides a PTFE / graphene composite material for use in aerospace seals, engine components, high-frequency electronic device heat dissipation films, aircraft components, automobile brake pads, and electronic packaging materials.

[0040] Specifically, the PTFE / graphene composite material has a low friction coefficient and wear rate, and when used in aerospace seals and engine components, it can greatly reduce the friction loss between components, reduce energy consumption, significantly prolong the service life of the components, reduce maintenance frequency, and improve the stability and reliability of equipment operation.

[0041] The PTFE / graphene composite material can efficiently conduct heat, and when used in high-frequency electronic device heat dissipation films, it can quickly dissipate the heat generated by electronic devices, avoid performance degradation or damage due to overheating, ensure stable operation of electronic devices, and prolong their service life.

[0042] The PTFE / graphene composite material has good electrical insulation, and can be applied to the field of electronic packaging materials and the like which require electrical insulation, thereby preventing safety problems caused by static electricity and the like.

[0043] The PTFE / graphene composite material has excellent mechanical properties, effectively breaks through the contradiction of 'high lubrication-low strength' of traditional PTFE composite materials, and can withstand greater mechanical stress, and is suitable for application scenarios such as aircraft structural parts and automobile brake pads which have high strength requirements.

[0044] Compared with the prior art, the PTFE / graphene composite material has the following beneficial effects:

[0045] (1) The graphene is in-situ functionalized by using low-temperature plasma fluorination technology, 3-5 layers of fluorinated layers are formed on the surface of the graphene, and C-F bonds are introduced to enhance the interfacial compatibility with PTFE, compared with the traditional acidification method, the damage to the structure of the graphene is avoided, and a foundation is laid for subsequent effective compounding.

[0046] (2) The fluorine-containing ionic liquid is selected as a dispersion medium, and the ultrasonic-microwave alternating treatment is used, the electrostatic adsorption of the cation and the fluorinated graphene and the hydrogen bond formed by the anion and the PTFE particles realize the synergistic dispersion of the two phases.

[0047] (3) The casting forming is carried out under a direct current electric field, the fluorinated graphene is directionally arranged to form a vertical gradient structure by using the conductivity of the fluorinated graphene, and a three-dimensional interlocking network is constructed by adjusting the electric field direction (X / Y / Z axis alternation), which significantly improves the anisotropic performance of the composite material, and this unique forming method is different from the traditional forming process.

[0048] (4) The two-stage microwave sintering is adopted, the interface dipole coupling is induced by low-frequency microwave in the first stage, the graphene interface is selectively heated by high-frequency pulse microwave in the second stage to promote local melting bonding, and the thermal decomposition of PTFE is inhibited in the N2 / CF4 mixed gas atmosphere, and this innovative sintering process improves the sintering quality and performance of the material. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a preparation flowchart of the PTFE / graphene composite material. DETAILED DESCRIPTION

[0050] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific embodiments, but the protection scope and implementation mode of the present application are not limited thereto.

[0051] The materials, reagents, etc. used in the following examples are commercially available reagents and materials, unless otherwise specified.

[0052] Graphene: Graphenea SA, Model: AQ-01.

[0053] Low temperature plasma equipment: Diener Electronic Pico series.

[0054] [BMIM][PF6]: Sigma-Aldrich, Catalog No.: 90178-100ML.

[0055] Cast molding equipment: Customized equipment, manufacturer: Shanghai Precision Instrument Factory.

[0056] Freeze-drying equipment: Labconco 12L.

[0057] Microwave sintering furnace: ThermWave GmbH, Germany, Model: MultiFreq 6000 (double frequency microwave pulse function).

[0058] The sources of the above-mentioned substances and equipment are used in the examples and comparative examples of the present application.

[0059] Example 1

[0060] A preparation method of a PTFE / graphene composite material, comprising the following steps:

[0061] (1) The graphene is washed, dried, and impurities are removed to improve the purity of the graphene. Then the pretreated graphene is placed in a low temperature plasma equipment, and a mixed gas of argon and fluorine gas (the volume ratio of argon and fluorine gas is 9:1) is introduced for reaction. The graphene is treated at a power of 150W for 5min to obtain fluorinated graphene.

[0062] (2) PTFE emulsion, fluorinated graphene, and fluorine-containing ionic liquid [BMIM][PF6] are added to a dispersion container in a mass ratio of 100:5:3, and 0.1% of nano-diamond (average particle size of 20 nanometers) is added to the fluorine-containing ionic liquid. The average molecular weight of the PTFE emulsion is 1x10 6 g / mol, and the viscosity at 25°C is 300 mPa·s; the source of the PTFE emulsion is Chemours™ DISP206;

[0063] Then ultrasonic is applied at a frequency of 40kHz and a power of 500W for 1min, followed by microwave irradiation at a frequency of 2.45GHz and a power of 300W for 10s, which is one cycle and is repeated for 30 cycles. After uniform dispersion, a mixed solution is obtained.

[0064] (3) Transfer the mixed solution into the casting forming equipment, maintain in the X-axis electric field with the intensity of 30 V / cm for 10 s, then maintain in the Y-axis electric field with the intensity of 50 V / cm for 10 s, and finally maintain in the Z-axis electric field with the intensity of 70 V / cm for 10 s, taking the X-axis electric field, the Y-axis electric field and the Z-axis electric field as one cycle and repeating until the forming is completed, to obtain the composite blank after forming.

[0065] (4) Put the composite blank into the freeze-drying equipment, pre-freeze the composite blank at -40℃ for 4 h, and then dry at -50℃ and under the vacuum degree of 10 Pa for 24 h, to remove the water and volatile impurities in the blank and preliminarily solidify the blank.

[0066] (5) Put the freeze-dried blank into the microwave sintering furnace, first sinter at 300℃ for 10 min under the low-frequency microwave of 2.45 GHz to induce the interface dipole coupling between the PTFE molecular chain and the fluorinated graphene; then switch to the high-frequency pulse microwave of 5.8 GHz, sinter at 380℃ for 5 min with the duty cycle of 30%, to promote the local melting bonding. The sintering process is carried out in the atmosphere of N2 / CF4 mixed gas (pressure of 0.5 MPa) with the volume ratio of N2 to CF4 being 1:1. The PTFE / graphene composite material is obtained after sintering.

[0067] Example 2

[0068] A preparation method of a PTFE / graphene composite material, comprising the following steps:

[0069] (1) Wash and dry the graphene to remove impurities and improve the purity of the graphene; then put the pretreated graphene into the low-temperature plasma equipment, and introduce the mixed gas of argon and fluorine gas (volume ratio of argon to fluorine gas being 9:1) to react, treat the graphene at a power of 150 W for 7 min to obtain fluorinated graphene.

[0070] (2) Add PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid [BMIM][PF6] according to the mass ratio of 100:5:4 into a dispersion container, and add 0.1% of nano diamond (average particle size of 20 nanometers) into the fluorine-containing ionic liquid; the average molecular weight of the PTFE emulsion is 5×10 6 g / mol, and the viscosity at 25℃ is 200 mPa·s; the source of the PTFE emulsion is Daikin™ Polyflon™ D-210C;

[0071] Then ultrasonic for 1 min under the condition of 40 kHz frequency and 500 W power, followed by microwave irradiation for 10 s under the condition of 2.45 GHz frequency and 300 W power, as a cycle and repeat the cycle for 30 times; after uniform dispersion, a mixed solution is obtained.

[0072] (3) The mixed solution is transferred to a casting forming device, first maintained for 10 s in an X-axis electric field with a strength of 30 V / cm, then maintained for 10 s in a Y-axis electric field with a strength of 50 V / cm, and finally maintained for 10 s in a Z-axis electric field with a strength of 70 V / cm, as a cycle of X-axis electric field, Y-axis electric field and Z-axis electric field and repeated until the forming is completed, and a composite material blank is obtained after forming.

[0073] (4) The composite material blank is placed in a freeze-drying device, first pre-frozen for 4 h at -40℃, and then dried for 24 h under the condition of -50℃ temperature and 10 Pa vacuum degree, to remove the water and volatile impurities in the blank, and to preliminarily solidify the blank.

[0074] (5) The freeze-dried blank is placed in a microwave sintering furnace, first sintered for 10 min at 250℃ under 2.45 GHz low-frequency microwave to induce the interface dipole coupling between PTFE molecular chain and fluorinated graphene; then switched to 5.8 GHz high-frequency pulse microwave in the second stage, sintered for 5 min at 380℃, with a duty cycle of 20%, to promote local melting and bonding. The sintering process is carried out in a N2 / CF4 mixed gas (pressure 0.5 MPa) atmosphere, with a volume ratio of N2 to CF4 being 1:1. The PTFE / graphene composite material is obtained after sintering.

[0075] Example 3

[0076] A preparation method of a PTFE / graphene composite material, comprising the following steps:

[0077] (1) The graphene is washed, dried, and impurities are removed to improve the purity of the graphene; then the pretreated graphene is placed in a low-temperature plasma device, and a mixed gas of argon and fluorine gas (volume ratio of argon to fluorine gas is 9:1) is introduced for reaction, and the graphene is treated at a power of 150 W for 10 min to obtain fluorinated graphene.

[0078] (2) PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid [BMIM][PF6] are added to a dispersion container in a mass ratio of 100:5:5, and 0.1% of nano diamond (average particle size of 20 nanometers) is added to the fluorine-containing ionic liquid, and the average molecular weight of the PTFE emulsion is 3.5×10 6g / mol, viscosity at 25℃ is 350 mPa·s; the source of PTFE emulsion: 3M™ Dyneon™ TF-5035;

[0079] Then ultrasonic for 1 min under the condition of frequency 40 kHz, power 500 W, followed by microwave irradiation for 10 s under the condition of frequency 2.45 GHz, power 300 W, which is a cycle and repeats 30 cycles; after uniform dispersion, a mixed solution is obtained.

[0080] (3) The mixed solution is transferred to a casting forming device, first maintained for 10 s in the X-axis electric field with intensity 30 V / cm, then maintained for 10 s in the Y-axis electric field with intensity 50 V / cm, and finally maintained for 10 s in the Z-axis electric field with intensity 70 V / cm, which is a cycle of X-axis electric field, Y-axis electric field and Z-axis electric field and repeats until the forming is completed, and a composite material blank is obtained after forming.

[0081] (4) The composite material blank is placed in a freeze-drying device, first pre-frozen at -40℃ for 4 h, and then dried at a temperature of -50℃ and a vacuum degree of 10 Pa for 24 h, to remove water and volatile impurities in the blank and preliminarily solidify the blank.

[0082] (5) The freeze-dried blank is placed in a microwave sintering furnace, first sintered at 350℃ for 10 min under 2.45 GHz low-frequency microwave to induce the interface dipole coupling between PTFE molecular chain and fluorinated graphene; then switched to 5.8 GHz high-frequency pulse microwave in the second stage, sintered at 380℃ for 5 min, duty cycle is 50%, to promote local melting bonding. The sintering process is carried out in N2 / CF4 mixed gas (pressure is 0.5 MPa) atmosphere, the volume ratio of N2 and CF4 is 1:1. The PTFE / graphene composite material is obtained after sintering.

[0083] Example 4

[0084] A preparation method of a PTFE / graphene composite material, which is different from example 1 in that the viscosity of PTFE emulsion at 25℃ in step (2) is 150 mPa·s.

[0085] Example 5

[0086] A preparation method of a PTFE / graphene composite material, which is different from example 1 in that the viscosity of PTFE emulsion at 25℃ in step (2) is 450 mPa·s.

[0087] Example 6

[0088] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (5), the first stage is sintered at 200℃ for 10min under 2.45GHz low frequency microwave.

[0089] Example 7

[0090] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (5), the first stage is sintered at 400℃ for 10min under 2.45GHz low frequency microwave.

[0091] Example 8

[0092] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (5), the second stage is switched to 5.8GHz high frequency pulse microwave, sintered at 380℃ for 5min, and the duty cycle is 10%.

[0093] Example 9

[0094] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (5), the second stage is switched to 5.8GHz high frequency pulse microwave, sintered at 380℃ for 5min, and the duty cycle is 60%.

[0095] Example 10

[0096] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (5), the freeze-dried green body is placed in a microwave sintering furnace, and sintered at 300℃ for 10min under 2.45GHz low frequency microwave.

[0097] Example 11

[0098] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (5), the freeze-dried green body is placed in a microwave sintering furnace, and sintered at 380℃ for 5min under 5.8GHz high frequency pulse microwave, and the duty cycle is 30%.

[0099] Comparative example 1

[0100] A preparation method of a PTFE / graphene composite material, a traditional mechanical mixing method is adopted, that is, graphene and PTFE emulsion with a mass ratio of 5:100 are directly mixed by mechanical stirring, the stirring speed is 2000rpm / 30min (Cowles paddle dispersion); then hot-pressed at 350℃, 20MPa for 30min, and a PTFE / graphene composite material is obtained.

[0101] Comparative example 2

[0102] A preparation method of a PTFE / graphene composite material, which adopts a traditional solution blending method, i.e. 5 g of graphene is dispersed in 100 mL of N,N-dimethylformamide (DMF), then mixed with 100 g of a PTFE emulsion, and then the solvent is evaporated at 80°C for 2 h, and finally the PTFE / graphene composite material is obtained by hot pressing at 350°C and 20 MPa for 30 min.

[0103] Comparative Example 3

[0104] A preparation method of a PTFE / graphene composite material, which is different from Example 1 in that step (1) is not performed, i.e. the graphene is not subjected to fluorination treatment.

[0105] Comparative Example 4

[0106] A preparation method of a PTFE / graphene composite material, which is different from Example 1 in that no fluorine-containing ionic liquid is added for dispersion in step (2), and the PTFE / graphene composite material is prepared by conventional stirring dispersion through a high-speed homogenizer (speed of 10000 rpm / 10 min).

[0107] Comparative Example 5

[0108] A preparation method of a PTFE / graphene composite material, which is different from Example 1 in that step (3) is not performed, i.e. the PTFE / graphene composite material is prepared by using an ordinary molding method instead of the electric field self-assembly technology, and the molding pressure is 10 MPa and the pressure holding time at room temperature is 10 min.

[0109] Comparative Example 6

[0110] A preparation method of a PTFE / graphene composite material, which is different from Example 1 in that the volume ratio of argon gas to fluorine gas is 5:1 in step (1).

[0111] Comparative Example 7

[0112] A preparation method of a PTFE / graphene composite material, which is different from Example 1 in that the volume ratio of argon gas to fluorine gas is 10:1 in step (1).

[0113] Comparative Example 8

[0114] A preparation method of a PTFE / graphene composite material, which is different from Example 1 in that the mass ratio of PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid is 100:5:1 in step (2).

[0115] Comparative Example 9

[0116] A preparation method of a PTFE / graphene composite material, different from example 1 is that in step (2), the mass ratio of PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid is 100:5:7.

[0117] Performance detection

[0118] 1. The fluorinated layer thickness of fluorinated graphene is measured by atomic force microscope (AFM), and the F / C ratio is analyzed by X-ray photoelectron spectroscopy (XPS).

[0119] 2. Friction coefficient: tested according to ASTM D1894-24.

[0120] 3. Wear rate: tested according to ASTM G99-17, load is 20 N, rotation speed is 200 rpm, counter electrode is GCr15 steel ball, and time is 60 min.

[0121] 4. Thermal conductivity: tested according to ASTM D5470-17(2024).

[0122] 5. Tensile strength: tested according to ASTM D638-22.

[0123] 6. Volume resistivity: tested according to ASTM D257-14, electrode spacing is 2 mm, and voltage is 500 V DC.

[0124] The above detection results are shown in Table 1.

[0125] Table 1

[0126]

[0127] It can be obtained from the comparison of examples 4-5 and example 1 that if the viscosity of the PTFE emulsion is too low, the emulsion stability is poor, and phase separation occurs in the dispersion process; if the viscosity of the PTFE emulsion is too high, the flowability is poor, and the directional arrangement effect of the electro-field casting is affected. Therefore, by controlling the viscosity of the PTFE emulsion to be 200-400 mPa·s, the comprehensive performance of the composite material is improved.

[0128] It can be obtained from the comparison of Examples 6-7 and Example 1 respectively that, in step (5), if the sintering temperature in the first stage is too high, the excessive movement of PTFE molecular chains leads to thermal decomposition (generation of toxic gases such as tetrafluoroethylene), the material structure is destroyed, and the mechanical properties and thermal conductivity coefficient are reduced, and the wear rate is increased. If the sintering temperature is too low, the activity of PTFE molecular chains is insufficient, and effective dipole coupling cannot be formed with fluorinated graphene, the interface bonding is weak, and the mechanical properties and thermal conductivity coefficient of the composite material are reduced, and the wear rate is increased. Therefore, by controlling the temperature of the first stage sintering to be 250-350℃, the mechanical properties, thermal conductivity and wear resistance of the composite material are improved.

[0129] It can be obtained from the comparison of Examples 8-9 and Example 1 respectively that, in step (5), if the duty cycle in the second stage is too large, the continuous action time of high-frequency microwave is too long, local overheating leads to carbonization of the graphene interface or degradation of PTFE, the material brittleness increases, and the wear rate of the material increases. If the duty cycle is too small, the energy input is insufficient, the local fusion bonding of graphene and PTFE is insufficient, the interface bonding strength is low, the tensile strength of the material is reduced, and the wear rate is increased. Therefore, by controlling the duty cycle in the second stage to be 20-50%, the wear resistance and mechanical properties of the composite material are improved.

[0130] It can be obtained from the comparison of Examples 10-11 and Example 1 respectively that, in Example 10, only low-frequency microwave is used for sintering, and local fusion bonding cannot be achieved, and the thermal conductivity and mechanical properties of the composite material are limited. In Example 11, high-frequency microwave is directly used, which can lead to rapid melting of PTFE but insufficient interface dipole coupling, and the bonding force between graphene and PTFE is weak, and the composite material is prone to delamination. It can be seen that, by using two-stage microwave sintering, the friction coefficient of the composite material is lower than that of single-stage microwave sintering, and the tensile strength of the composite material is higher than that of single-stage microwave sintering. Therefore, by using two-stage microwave sintering, the wear resistance and mechanical properties of the composite material are improved.

[0131] It can be obtained from the comparison of Comparative Example 1 and Example 1 that, in Comparative Example 1, the traditional mechanical mixing method is used, and the friction coefficient and wear rate of the composite material are higher than those of Example 1, and the thermal conductivity coefficient and tensile strength are lower than those of Example 1, indicating that the traditional mechanical mixing method cannot improve the comprehensive performance of the composite material.

[0132] It can be obtained from the comparison of Comparative Example 2 and Example 1 that, in Comparative Example 2, the traditional solution blending method is used, and the friction coefficient and wear rate of the composite material are higher than those of Example 1, and the thermal conductivity coefficient and tensile strength are lower than those of Example 1, indicating that the composite material prepared by the traditional solution blending method cannot meet the requirements of high-end fields for the comprehensive performance of the material.

[0133] It can be seen from the comparison of Comparative Examples 3-5 with Example 1 that, in Comparative Example 3, the graphene is not subjected to fluorination treatment, in Comparative Example 4, the fluorine-containing ionic liquid is not added for dispersion, and in Comparative Example 5, the electric field self-assembly technology is not used for forming, but only a conventional stirring dispersion method and a general forming method are used to prepare the composite material, the friction coefficient of the composite material is higher than that of Example 1, and the thermal conductivity and tensile strength are lower than those of Example 1, which indicates that the fluorination treatment of the graphene or the lack of the fluorine-containing ionic liquid for directional dispersion or the lack of the gradient structure formed by the electric field self-assembly cannot effectively improve the comprehensive performance of the composite material.

[0134] It can be seen from the comparison of Comparative Examples 6-7 with Example 1 that, if the volume ratio of argon and fluorine is too large (excessive Ar), the concentration of F2 is insufficient, the thickness of the fluorination layer on the surface of the graphene is insufficient (<3 layers), the density of the C-F bond is low, the interface compatibility is limitedly improved, and the wear resistance, thermal conductivity and mechanical properties of the composite material are affected. If the volume ratio of argon and fluorine is too small (excessive F2), excessive fluorination will destroy the sp 2 hybrid structure of the graphene, the electrical conductivity of the material is reduced, and excessive fluorination will increase the thickness of the fluorination layer (>5 layers), thereby increasing the interface stress and reducing the mechanical strength, wear resistance and thermal conductivity of the composite material. Therefore, by controlling the volume ratio of argon and fluorine to be (6-9):1, the comprehensive performance of the composite material can be improved.

[0135] It can be seen from the comparison of Comparative Examples 8-9 with Example 1 that, when the mass ratio of the PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid is 100:5:1, the fluorinated graphene will appear agglomeration, and the PTFE particles are not uniformly dispersed. When the mass ratio is 100:5:7, the viscosity of the system is greatly increased, the dispersion effect is decreased, and some agglomerates are present. It can be seen that, by controlling the mass ratio of the PTFE emulsion: fluorinated graphene: ionic liquid to be 100:5:(3-5), the ionic liquid concentration can ensure good dispersion effect and make the composite material obtain the best comprehensive performance.

[0136] In summary, the PTFE / graphene composite material prepared by the plasma fluorination method, the fluorine-containing ionic liquid as the dispersion system, the forming process of the electric field gradient self-assembly and the double-frequency microwave pulse sintering has excellent wear resistance, thermal conductivity, electrical insulation, mechanical properties, and can effectively meet the stringent requirements of high-end fields on material performance.

[0137] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for preparing a PTFE / graphene composite material, characterized by, The method comprises the following steps: (1) placing graphene in a plasma device, introducing a mixed gas of argon and fluorine for reaction to obtain fluorinated graphene; the volume ratio of the argon and fluorine is (6-9):1; (2) mixing PTFE emulsion, fluorinated graphene and fluorine-containing ionic liquid according to a mass ratio of 100:5:(3-5), and repeatedly performing alternating ultrasonic treatment and microwave treatment to obtain a mixed solution after uniform dispersion; (3) performing flow casting of the mixed solution in a direct current electric field to obtain a composite blank after molding; (4) performing freeze drying on the composite blank; (5) performing microwave pulse sintering on the freeze-dried blank in a mixed gas of nitrogen and tetrafluoromethane to obtain the PTFE / graphene composite material after sintering; In step (2), the viscosity of the PTFE emulsion at 25°C is 200-400 mPa·s; In step (3), the specific steps of performing flow casting of the mixed solution in a direct current electric field are as follows: first maintaining for 10 s in an X-axis electric field with a strength of 30 V / cm, then maintaining for 10 s in a Y-axis electric field with a strength of 50 V / cm, and finally maintaining for 10 s in a Z-axis electric field with a strength of 70 V / cm, taking the X-axis electric field, the Y-axis electric field and the Z-axis electric field as one cycle and repeating the cycle until the molding is completed; In step (4), the specific steps of freeze drying are as follows: first pre-freezing the composite blank at -40~-30°C for 3-4 h, and then drying at a temperature of -50°C and a vacuum degree of 10 Pa for 12-24 h; In step (5), two-stage microwave sintering is adopted, the first stage is sintering at a microwave frequency of 2.45±0.5 GHz and a temperature of 250-350°C for 8-10 min, and the second stage is sintering at a microwave frequency of 5.8±0.2 GHz and a temperature of 350-380°C for 5-10 min, and the duty cycle is 20-50%.

2. The method for preparing the PTFE / graphene composite material as described in claim 1, characterized in that, In step (1), the graphene is treated at a power of 100-200 W for 5-10 min during the reaction.

3. The method for preparing the PTFE / graphene composite material as described in claim 1, characterized in that, In step (2), the fluorine-containing ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate and / or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imidazolium salt.

4. The method for preparing the PTFE / graphene composite material as described in claim 1, characterized in that, The average molecular weight of the PTFE emulsion in the step (2) is 1 x 10 6 g / mol. 6 g / mol.

5. The method for preparing the PTFE / graphene composite material as described in claim 1, characterized in that, In step (2), nano diamond is further added to the fluorine-containing ionic liquid, and the mass of the nano diamond is 0.05-0.3% of the mass of the fluorine-containing ionic liquid.

6. The method for preparing the PTFE / graphene composite material as described in claim 1, characterized in that, In step (2), the specific steps of performing alternating ultrasonic treatment and microwave treatment are as follows: first ultrasonic treatment at a frequency of 40 kHz and a power of 500 W for 1 min, and then microwave irradiation at a frequency of 2.45 GHz and a power of 300 W for 10 s, taking one cycle and repeating the cycle for 20-30 times.

7. A PTFE / graphene composite material prepared by the preparation method of any one of claims 1-6.

8. Application of the PTFE / graphene composite material of claim 7 in aerospace seals, engine components, high-frequency electronic device heat dissipation films, aircraft components, automobile brake pads and electronic packaging materials.

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