Highly dispersed carbon nanotube reinforced PTFE composite and preparation method thereof

Abstract

The application relates to a high-dispersion carbon nanotube reinforced PTFE composite material and a preparation method thereof, relates to the technical field of polymer composites, and comprises PTFE powder, surface-modified carbon nanotubes and a composite dispersant; wherein the surface-modified carbon nanotubes are multi-walled carbon nanotubes modified by a fluorosilane coupling agent, and the composite dispersant is composed of polyethylene glycol octyl phenyl ether and potassium perfluorooctyl sulfonate. The application has the effects of realizing stable and uniform dispersion of carbon nanotubes in a PTFE matrix, enhancing interface bonding force, and not damaging the intrinsic properties of the carbon nanotubes.

Description

Technical Field

[0001] This application relates to the field of polymer composite materials technology, specifically to a highly dispersed carbon nanotube-reinforced PTFE composite material and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE), as a high-performance polymer material, possesses excellent chemical stability, high-temperature resistance (operating temperature range 200–260℃), low coefficient of friction, and excellent aging resistance, and is widely used in chemical, electronics, aerospace, and machinery industries. However, pure PTFE material has inherent defects: on the one hand, it is a typical insulating material with a volume resistivity as high as 10⁻⁶. 18 ~10 20 The Ω·cm of pure PTFE cannot meet the functional requirements of conductivity and electromagnetic shielding. On the other hand, the mechanical strength of pure PTFE is low, with a tensile strength of only 15-25 MPa and poor creep resistance. It is prone to deformation failure under long-term stress or dynamic working conditions, which limits its application in high-end functional components.

[0003] Carbon nanotubes, as a one-dimensional nanomaterial, possess extremely high specific surface area and excellent electrical conductivity (volume resistivity as low as 10⁻⁶). -4 With its excellent tensile strength (Ω·cm) and superior mechanical properties (tensile strength exceeding 100 GPa and elastic modulus reaching 1 TPa), PTFE is an ideal filler for improving the electrical conductivity and mechanical properties of polymer materials. Introducing carbon nanotubes into the PTFE matrix theoretically allows for the preparation of composite functional materials that combine the corrosion resistance and high-temperature resistance of PTFE with the electrical conductivity and reinforcing properties of carbon nanotubes, thus expanding the application range of PTFE.

[0004] However, the preparation of carbon nanotube / PTFE composites currently faces two major technical challenges: First, the strong van der Waals forces between carbon nanotube molecules make them prone to aggregation, making it difficult to achieve uniform dispersion in the PTFE matrix. This not only prevents them from fully exerting their reinforcing and conductive effects, but the aggregates also become internal defects, leading to a decline in the mechanical properties of the composite material. Second, the inert surface of carbon nanotubes results in poor interfacial compatibility with the PTFE matrix and weak interfacial bonding. Under external forces, interfacial delamination easily occurs, affecting the overall performance stability of the composite material. Therefore, developing a carbon nanotube-reinforced PTFE composite material and its preparation method that can achieve stable and uniform dispersion of carbon nanotubes in a PTFE matrix, enhance interfacial bonding, and not damage the intrinsic properties of carbon nanotubes, and that has a simple preparation process and is easy to industrialize, has important practical significance and application value. Summary of the Invention

[0005] This application provides a highly dispersed carbon nanotube-reinforced PTFE composite material and its preparation method, which achieves stable and uniform dispersion of carbon nanotubes in the PTFE matrix, enhances interfacial bonding, and does not damage the intrinsic properties of carbon nanotubes.

[0006] Firstly, the highly dispersed carbon nanotube-reinforced PTFE composite material provided in this application adopts the following technical solution: A highly dispersed carbon nanotube-reinforced PTFE composite material is composed of the following components by mass percentage: 85-97% PTFE powder, 2-12% surface-modified carbon nanotubes, and 0.5-3% composite dispersant; The surface-modified carbon nanotubes are multi-walled carbon nanotubes modified with a fluorosilane coupling agent. These multi-walled carbon nanotubes have a diameter of 10–50 nm, a length of 5–20 μm, and a volume resistivity ≤10. -3 The fluorosilane coupling agent is perfluorooctyltriethoxysilane, and its dosage is 2-5% of the mass of the carbon nanotubes. The composite dispersant is composed of polyethylene glycol octylphenyl ether and potassium perfluorooctyl sulfonate in a mass ratio of 1.5 to 2.5:1.

[0007] By adopting the above technical solution, the amount of PTFE powder is 85-97%, which allows PTFE to serve as a continuous matrix phase, maintaining its chemical corrosion resistance, temperature resistance, and low friction properties.

[0008] The amount of surface-modified carbon nanotubes used is 2-12%. When it is less than 2%, it is difficult to form an effective conductive network and a reinforcing skeleton. When it is more than 12%, the dispersion difficulty increases and agglomerates are prone to occur, which become defects.

[0009] Among them, multi-walled carbon nanotubes have a diameter of 10–50 nm and a length of 5–20 μm. This size range gives the carbon nanotubes a high aspect ratio, which is beneficial for forming overlapping conductive pathways and transferring stress in the matrix with a low addition amount. Furthermore, the volume resistivity of multi-walled carbon nanotubes is ≤10 Ω·cm. -3 Ω·cm provides the basic conductivity for its use as a conductive filler.

[0010] Fluorosilane coupling agents contain perfluorocarbon chains, similar in structure to the PTFE matrix, which can improve the interfacial compatibility between carbon nanotubes and PTFE. Their siloxane end groups can react with the hydroxyl groups on the carbon nanotube surface to form chemical bonds. When the dosage is below 2%, the interfacial modification is insufficient; when it is above 5%, the free coupling agent may volatilize or decompose at high temperatures, producing pores.

[0011] The composite dispersant consists of polyethylene glycol octylphenyl ether and potassium perfluorooctyl sulfonate. Polyethylene glycol octylphenyl ether adsorbs onto the surface of carbon nanotubes, creating steric hindrance, while potassium perfluorooctyl sulfonate provides auxiliary dispersing. The combination of these two components reduces the tendency of carbon nanotubes to aggregate during mixing. When the total amount is below 0.5%, the dispersion effect is not significant; when it exceeds 3%, the dispersant decomposition residue may affect the material's density.

[0012] Optionally, the PTFE powder has an average particle size of 30–80 μm and a density of 2.10–2.15 g / cm³. 3 Purity ≥ 99.5%.

[0013] By adopting the above technical solution, PTFE powder particles and nanoscale carbon nanotubes within the particle size range of 30–80 μm achieve a suitable particle size match, which is beneficial for the adhesion and uniform mixing of carbon nanotubes on the powder surface. The density range corresponds to the conventional density range of PTFE resin, indicating that the raw material is a qualified resin that has not been excessively degraded. A purity of ≥99.5% can reduce the potential interference of low-molecular-weight impurities or inorganic residues on the interface and chemical corrosion resistance of the composite material.

[0014] Optionally, the volume resistivity of the composite material is 10. -2 ~10 6 Ω·cm, tensile strength is 35~45MPa.

[0015] By adopting the above technical solution, the degree of conductive network formation can be controlled by adjusting the carbon nanotube content. The lower limit corresponds to the formation of a relatively complete conductive network by carbon nanotubes, while the upper limit corresponds to the region where the conductive network is initially established, indicating that the material has departed from the intrinsic insulating state of PTFE. The tensile strength of 35–45 MPa is 40–80% higher than that of pure PTFE. This improvement stems from the improved dispersion and interfacial bonding of surface-modified carbon nanotubes in the matrix, allowing some of the load to be transferred to the carbon nanotubes. At the same time, the uniform dispersion of carbon nanotubes helps to reduce stress concentration.

[0016] Secondly, this application provides a method for preparing a highly dispersed carbon nanotube-reinforced PTFE composite material, comprising the following steps: S1. Surface modification of carbon nanotubes: Perfluorooctyltriethoxysilane was added to anhydrous ethanol and stirred to prepare a modification solution, wherein the mass concentration of perfluorooctyltriethoxysilane in the modification solution was 1% to 3%; multi-walled carbon nanotubes were added to the modification solution, with a mass-to-volume ratio of carbon nanotubes to modification solution of 1 g: 50 to 80 mL, and ultrasonically dispersed for 40 to 60 min, and then stirred and reacted in a constant temperature water bath at 50 to 60 °C for 3 to 5 h; after the reaction was completed, the mixture was centrifuged, washed with anhydrous ethanol, vacuum dried at 80 to 100 °C for 6 to 8 h, and ground through a 300-mesh sieve to obtain surface-modified carbon nanotubes; S2. Preparation of premixed material: Weigh PTFE powder, surface-modified carbon nanotubes obtained in step S1 and composite dispersant according to mass fraction. Dissolve the composite dispersant in anhydrous ethanol to obtain a dispersant solution. Spray the dispersant solution onto the surface of PTFE powder and stir for 10-15 min. Then add surface-modified carbon nanotubes and place the mixture in a planetary ball mill for ball milling. The ball-to-material ratio is 9-11:1, the rotation speed is 200-300 r / min, and the ball milling time is 2-3 h to obtain the premixed material. S3. Cold pressing: The premixed material is poured into a stainless steel mold with a release agent applied to the inner wall, and then subjected to a pressing at room temperature at 200-300 kg / cm². 2 The pressure is maintained for 40-60 minutes to produce a preform. S4. Sintering and Shaping: The preform is placed in a high-temperature sintering furnace and sintered in stages under an inert gas atmosphere according to the following procedure: First stage: Raise the temperature from room temperature to 280-300℃ at a rate of 80-100℃ / h and hold for 30-40 minutes. Second stage: Continue to heat to 340-360℃, heating rate 50-60℃ / h, hold for 40-50min; Third stage: Continue to heat to 375-385℃, heating rate 30-40℃ / h, hold for 90-120min; Cooling stage: Cool to 320-330℃ at a rate of 40-50℃ / h, hold for 30-40 minutes, and then cool naturally to room temperature to obtain highly dispersed carbon nanotube reinforced PTFE composite material.

[0017] By adopting the above technical solution, step S1 involves dissolving perfluorooctyltriethoxysilane in anhydrous ethanol to prepare a modified solution with a mass concentration of 1–3%. This concentration range ensures uniform dispersion of the coupling agent in the solvent, facilitating contact and reaction with carbon nanotubes. The mass-to-volume ratio of carbon nanotubes to the modified solution is 1 g: 50–80 mL, providing ample space for ultrasonic dispersion and coupling agent adsorption. Ultrasonic dispersion for 40–60 min aids in the dissociation of carbon nanotube aggregates. A water bath reaction at 50–60 °C for 3–5 h accelerates the reaction rate between the coupling agent and the surface of the carbon nanotubes.

[0018] Step S2 involves spraying the dispersant solution onto the PTFE powder and stirring for 10–15 minutes to allow the dispersant to adhere to the powder surface. The ball milling mixing parameters ensure that the carbon nanotubes and PTFE powder are mixed uniformly under mechanical force.

[0019] Step S3 involves cold pressing at a pressure of 200–300 kg / cm² and holding the pressure for 40–60 minutes, which compacts the powder into a dense green body.

[0020] In step S4, during segmented sintering, the first stage involves holding at 280–300℃ for 30–40 min to remove residual ethanol and some low-volatile components. The second stage involves holding at 340–360℃ for 40–50 min at a slower heating rate, allowing PTFE to begin melting and facilitating further distribution of carbon nanotubes with the melt flow. The third stage involves holding at 375–385℃ for 90–120 min to ensure complete melting of PTFE, enabling full contact between the modified carbon nanotubes and the matrix. The cooling stage involves lowering the temperature at 40–50℃ / h to 320–330℃, holding, and then allowing natural cooling to control the cooling rate and reduce internal stress and deformation of the product. The continuous introduction of inert gas throughout the process prevents high-temperature oxidation of the carbon nanotubes.

[0021] Optionally, in step S1, the stirring is magnetic stirring, and the stirring time is 15-25 minutes; the washing with anhydrous ethanol is performed 3-4 times.

[0022] By employing the above technical solution, magnetic stirring allows the coupling agent to fully dissolve in ethanol, and the stirring time is sufficient to form a uniform modified liquid. Multiple washes with anhydrous ethanol essentially remove unreacted free coupling agent from the carbon nanotube surface, reducing the generation of volatiles during high-temperature sintering.

[0023] Optionally, in step S2, the grinding media used in the ball milling mixture is agate balls.

[0024] By adopting the above technical solution, the agate ball has high hardness, good wear resistance, and stable chemical properties. During the ball milling process, the introduction of metal impurities can be reduced, thus avoiding affecting the purity of the composite material.

[0025] Optionally, in step S3, the release agent is a polytetrafluoroethylene release agent.

[0026] By adopting the above technical solution, the polytetrafluoroethylene release agent is made of the same material as the blank. Coating it on the inner wall of the mold is beneficial for the complete demolding of the blank after cold pressing. Moreover, the release agent transferred in small amounts to the surface of the blank can be compatible with the matrix in subsequent sintering.

[0027] Optionally, in step S4, the inert gas is nitrogen or argon, and the gas flow rate is 0.5 to 1 L / min.

[0028] By employing the above technical solution, nitrogen or argon gas can be used as a protective atmosphere to replace oxygen in the furnace, reducing the degree of oxidation of carbon nanotubes at high temperatures. A gas flow rate of 0.5–1 L / min can maintain the renewal of the atmosphere inside the furnace while avoiding temperature fluctuations caused by excessive flow rate.

[0029] In summary, this application includes at least one of the following beneficial technical effects: 1. Surface modification of carbon nanotubes was performed using perfluorooctyltriethoxysilane. The perfluorocarbon segments in this coupling agent molecule have a chemical structure similar to that of PTFE molecular chains, which can improve the interfacial compatibility between carbon nanotubes and the PTFE matrix, reduce interfacial tension, and thus reduce the tendency of carbon nanotubes to aggregate in the matrix. Its siloxane end groups can react with the hydroxyl groups on the carbon nanotube surface to form chemical bonds, transforming the carbon nanotube surface from inert to a surface state that can interact strongly with the matrix. Compared with strong acid oxidation modification, this modification method does not destroy the carbon nanotube wall structure, and the intrinsic conductivity and mechanical strength of carbon nanotubes are preserved, allowing the composite material to achieve improved conductivity and mechanical strength with a lower carbon nanotube addition amount. 2. A composite dispersant composed of polyethylene glycol octylphenyl ether and potassium perfluorooctyl sulfonate is used. The polyoxyethylene segments of polyethylene glycol octylphenyl ether can be adsorbed onto the surface of carbon nanotubes, weakening the van der Waals attraction between carbon nanotubes through steric hindrance. The fluorinated alkyl segments of potassium perfluorooctyl sulfonate are compatible with PTFE, and its ionic groups can provide auxiliary electrostatic repulsion. The combined use of these two dispersants reduces the agglomeration of carbon nanotubes in PTFE powder during the premixing stage, promoting uniform adhesion of carbon nanotubes to the matrix. Compared with single dispersants, this composite dispersant achieves similar dispersion effects at a lower total addition amount, reducing the potential impact of dispersant decomposition residues on material density during high-temperature sintering. 3. A segmented heating and sintering process is adopted. The first stage involves holding at 280–300℃, at which point the PTFE has not yet melted, allowing residual ethanol and some low-molecular-weight components to escape from the interparticle gaps, reducing porosity formation in the subsequent melting stage. The second stage involves heating at a slower rate to 340–360℃ and holding, allowing the PTFE to gradually melt and the melt viscosity to decrease slowly, which is beneficial for the further distribution of carbon nanotubes as they flow with the melt. The third stage involves heating to 375–385℃ and holding for a sufficient amount of time, ensuring complete melting of the PTFE to form a continuous matrix, and ensuring full contact between the modified carbon nanotubes and the matrix. The cooling stage involves controlling the cooling rate and holding at 320–330℃, which reduces internal stress and dimensional deformation caused by uneven cooling. Inert gas is introduced throughout the process to reduce the oxidation of carbon nanotubes at high temperatures. Compared with existing conventional uniform heating, this segmented temperature control program is beneficial for improving the density, conductive network uniformity, and dimensional stability of the composite material. Detailed Implementation

[0030] Example 1 A highly dispersed carbon nanotube-reinforced PTFE composite material is composed of the following components by mass percentage: 92% PTFE powder, 6% surface-modified carbon nanotubes, and 2% composite dispersant; The PTFE powder has an average particle size of 50 μm, a density of 2.13 g / cm³, and a purity of 99.8%. The method for preparing this highly dispersed carbon nanotube-reinforced PTFE composite material includes the following steps: S1. Add FAS-13 to anhydrous ethanol and stir magnetically for 20 min to prepare a modified solution with a mass concentration of 2%; add multi-walled carbon nanotubes to the modified solution at a ratio of 1g:60mL, disperse ultrasonically for 50 min, and stir in a water bath at 55℃ for 4 h; after centrifugation, wash 4 times with anhydrous ethanol, vacuum dry at 90℃ for 7 h, and grind through a 300-mesh sieve to obtain surface-modified carbon nanotubes. The multi-walled carbon nanotubes have a diameter of 20–30 nm, a length of 8–15 μm, and a volume resistivity of ≤10. -3 Ω·cm; the amount of fluorosilane coupling agent FAS-13 is 3% of the mass of carbon nanotubes; S2. Weigh each component according to the ratio, dissolve the composite dispersant in a small amount of anhydrous ethanol and spray it onto the surface of PTFE powder, stir for 12 min; add surface-modified carbon nanotubes, place in a planetary ball mill with agate balls as the medium, ball-to-material ratio of 10:1, rotation speed of 250 r / min, and ball mill for 2.5 h to obtain the premixed material; The composite dispersant is composed of Triton X-100 and potassium perfluorooctanesulfonate mixed in a mass ratio of 2:1. S3. The premixed material is poured into a stainless steel mold coated with polytetrafluoroethylene release agent, and a pressure of 250 kg / cm² is applied at room temperature and held for 50 min to obtain the preform. S4. Place the preform into a sintering furnace, purge with nitrogen (flow rate 0.8 L / min), and heat in stages: room temperature → 290℃ (90℃ / h, hold for 35 min) → 350℃ (55℃ / h, hold for 45 min) → 380℃ (35℃ / h, hold for 100 min); cool down to 325℃ at 45℃ / h, hold for 35 min, and allow to cool naturally to room temperature to obtain the composite material.

[0031] Example 2 A highly dispersed carbon nanotube reinforced PTFE composite material, which differs from Example 1 in that it is composed of the following components by mass percentage: 88% PTFE powder, 10% surface-modified carbon nanotubes, and 2% composite dispersant.

[0032] Example 3 A highly dispersed carbon nanotube reinforced PTFE composite material, which differs from Example 1 in that it is composed of the following components by mass percentage: 95% PTFE powder, 3% surface-modified carbon nanotubes, and 2% composite dispersant.

[0033] Example 4 A highly dispersed carbon nanotube-reinforced PTFE composite material differs from Example 1 in that, in step S1, the amount of fluorosilane coupling agent FAS-13 is adjusted to 4.5% of the carbon nanotube mass.

[0034] Comparative Example 1 A highly dispersed carbon nanotube-reinforced PTFE composite material differs from Example 1 in that the carbon nanotubes are not modified with fluorosilane coupling agents, but are directly replaced with an equal amount of original multi-walled carbon nanotubes.

[0035] Comparative Example 2 A highly dispersed carbon nanotube-reinforced PTFE composite material differs from Example 1 in that the carbon nanotubes are placed in a mixed acid of concentrated sulfuric acid / concentrated nitric acid (volume ratio 3:1), ultrasonically treated at 60°C for 4 hours, filtered and washed until neutral, and dried to obtain carboxylated carbon nanotubes, which replace fluorosilane-modified carbon nanotubes in an equal amount.

[0036] Comparative Example 3 A highly dispersed carbon nanotube-reinforced PTFE composite material differs from Example 1 in that no composite dispersant is added during the preparation process.

[0037] Comparative Example 4 A highly dispersed carbon nanotube reinforced PTFE composite material, which differs from Example 1 in that the composite dispersant is replaced with an equal mass of Triton X-100.

[0038] Comparative Example 5 A highly dispersed carbon nanotube-reinforced PTFE composite material differs from Example 1 in that the composite dispersant is replaced with an equal mass of potassium perfluorooctyl sulfonate.

[0039] Comparative Example 6 A highly dispersed carbon nanotube-reinforced PTFE composite material differs from Example 1 in that the mass ratio of Triton X-100 to potassium perfluorooctyl sulfonate in the composite dispersant is 5:1.

[0040] Comparative Example 7 A highly dispersed carbon nanotube-reinforced PTFE composite material, which differs from Example 1 in that the amount of fluorosilane coupling agent FAS-13 is adjusted to 1% of the mass of the carbon nanotubes.

[0041] Comparative Example 8 A highly dispersed carbon nanotube-reinforced PTFE composite material, which differs from Example 1 in that the amount of fluorosilane coupling agent FAS-13 is adjusted to 6% of the mass of carbon nanotubes.

[0042] Comparative Example 9 A highly dispersed carbon nanotube reinforced PTFE composite material differs from Example 1 in that, in step S4, segmented heating is not used; instead, the preform is directly heated to 380°C at a uniform rate of 60°C / h, held at that temperature for 120 min, and then cooled to room temperature at a uniform rate of 60°C / h.

[0043] Comparative Example 10 A highly dispersed carbon nanotube reinforced PTFE composite material differs from Example 1 in that nitrogen or argon gas is not introduced during the sintering process, but the sintering is carried out in an air atmosphere.

[0044] Comparative Example 11 A highly dispersed carbon nanotube-reinforced PTFE composite material, differing from Example 1 in that the cold pressing pressure in step S3 is 150 kg / cm². 2 .

[0045] Comparative Example 12 A highly dispersed carbon nanotube reinforced PTFE composite material, which differs from Example 1 in that the ball milling time in step S1 is changed to 1 hour.

[0046] Detection example Volume resistivity: Tested according to GB / T 1551-2021 "Method for Determination of Resistivity of Single Crystal Silicon"; Tensile strength and elongation at break: Tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics"; The specific test results are shown in Table 1.

[0047] Table 1

[0048] The performance test data from Example 1 and Comparative Example 1 show that Comparative Example 1, without modification of the carbon nanotubes with a fluorosilane coupling agent, exhibits a volume resistivity seven orders of magnitude higher than that of Example 1, and significantly reduced tensile strength and elongation at break. The performance test data from Example 1 and Comparative Example 2 show that Comparative Example 2, modified with strong acid oxidation, exhibits a volume resistivity two orders of magnitude higher than that of Example 1, a slight decrease in tensile strength, and a particularly significant decrease in elongation at break. These comparisons demonstrate that fluorosilane coupling agent modification is superior to both the unmodified and strong acid oxidation modification methods in improving conductivity and maintaining mechanical toughness.

[0049] The performance test data from Examples 1 and Comparative Examples 3, 4, 5, and 6 show that, in Comparative Example 3 without any dispersant, the volume resistivity increased by approximately five orders of magnitude compared to Example 1, and the tensile strength also decreased. In Comparative Example 4 using only Triton X-100 or in Comparative Example 5 using only potassium perfluorooctanesulfonate, the volume resistivity increased by two to three orders of magnitude compared to Example 1, and the mechanical properties were slightly lower than in Example 1. In Comparative Example 6, when the dispersant ratio deviated from 2:1, the elongation at break decreased. These comparisons indicate that using a composite dispersant at a 2:1 ratio can effectively reduce the agglomeration of carbon nanotubes, and is superior to using a single dispersant or an improperly proportioned solution in terms of conductivity, mechanical strength, and toughness retention.

[0050] The performance test data from Examples 1 and Comparative Examples 7 and 8 show that when the coupling agent dosage in Comparative Example 7 is less than 2%, the volume resistivity increases by about two orders of magnitude compared to Example 1, and the tensile strength decreases. In Comparative Example 8, when the coupling agent dosage is higher than 5%, the volume resistivity changes less, but the elongation at break decreases. These comparisons indicate that a coupling agent dosage within the range of 2-5% can balance interfacial modification and material density. Too low a dosage results in insufficient modification, while too high a dosage may affect toughness due to the decomposition of free coupling agent.

[0051] The performance test data from Examples 1, 2, and 3 show that as the carbon nanotube content increases from 3% to 6% and then to 10%, the volume resistivity of the composite material increases from 10... 4 The level gradually decreased to 10 -2 The tensile strength gradually increased from 36 MPa to 44 MPa, while the elongation at break gradually decreased from 287% to 231%. This trend indicates that adjusting the carbon nanotube content within the range of 2% to 12% can achieve flexible control of conductivity and mechanical properties. Increasing the carbon nanotube content makes the conductive network more perfect, but it is accompanied by a slight decrease in matrix continuity and a downward trend in elongation at break.

[0052] The performance test data from Examples 1 and Comparative Examples 9 and 10 show that, when Comparative Example 9 was sintered at a conventional uniform rate, its volume resistivity increased by about two orders of magnitude compared to Example 1, while its tensile strength and elongation at break both decreased. When Comparative Example 10 was sintered in an air atmosphere, its volume resistivity increased by nearly six orders of magnitude compared to Example 1, and its tensile strength and elongation at break decreased even more significantly. These comparisons indicate that a segmented heating program is beneficial for the full escape of volatile components and the uniform distribution of carbon nanotubes, while inert gas protection can effectively suppress the high-temperature oxidation of carbon nanotubes. Both play an important role in maintaining the electrical conductivity and mechanical properties of the composite material.

[0053] The performance test data from Example 1 and Comparative Examples 11 and 12 show that when the cold pressing pressure of Comparative Example 11 is below the lower limit, the compaction of the green body is insufficient, and the volume resistivity increases and the elongation at break decreases after sintering. When the ball milling time of Comparative Example 12 is below the lower limit, the mixing uniformity of carbon nanotubes and PTFE powder is insufficient, the volume resistivity increases, and the tensile strength also decreases. The above comparisons indicate that a cold pressing pressure of 200–300 kg / cm² is optimal. 2 A range of 2 to 3 hours for ball milling time is necessary to ensure the compactness of the green body and the uniformity of mixing.

[0054] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A highly dispersed carbon nanotube-reinforced PTFE composite material, characterized in that, It is composed of the following components by weight percentage: 85-97% PTFE powder, 2-12% surface-modified carbon nanotubes, and 0.5-3% composite dispersant; The surface-modified carbon nanotubes are multi-walled carbon nanotubes modified with a fluorosilane coupling agent. These multi-walled carbon nanotubes have a diameter of 10–50 nm, a length of 5–20 μm, and a volume resistivity ≤10. -3 The fluorosilane coupling agent is perfluorooctyltriethoxysilane, and its dosage is 2-5% of the mass of the carbon nanotubes. The composite dispersant is composed of polyethylene glycol octylphenyl ether and potassium perfluorooctyl sulfonate in a mass ratio of 1.5 to 2.5:

1.

2. The highly dispersed carbon nanotube-reinforced PTFE composite material according to claim 1, characterized in that, The PTFE powder has an average particle size of 30–80 μm and a density of 2.10–2.15 g / cm³. 3 Purity ≥ 99.5%.

3. The highly dispersed carbon nanotube-reinforced PTFE composite material according to claim 1, characterized in that, The volume resistivity of the composite material is 10. -2 ~10 6 Ω·cm, tensile strength is 35~45MPa.

4. A method for preparing a highly dispersed carbon nanotube-reinforced PTFE composite material according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Surface modification of carbon nanotubes: Perfluorooctyltriethoxysilane was added to anhydrous ethanol and stirred to prepare a modification solution, wherein the mass concentration of perfluorooctyltriethoxysilane in the modification solution was 1% to 3%; multi-walled carbon nanotubes were added to the modification solution, with a mass-to-volume ratio of carbon nanotubes to modification solution of 1 g: 50 to 80 mL, and ultrasonically dispersed for 40 to 60 min, and then stirred and reacted in a constant temperature water bath at 50 to 60 °C for 3 to 5 h; after the reaction was completed, the mixture was centrifuged, washed with anhydrous ethanol, vacuum dried at 80 to 100 °C for 6 to 8 h, and ground through a 300-mesh sieve to obtain surface-modified carbon nanotubes; S2. Preparation of premixed material: Weigh PTFE powder, surface-modified carbon nanotubes obtained in step S1 and composite dispersant according to mass fraction. Dissolve the composite dispersant in anhydrous ethanol to obtain a dispersant solution. Spray the dispersant solution onto the surface of PTFE powder and stir for 10-15 min. Then add surface-modified carbon nanotubes and place the mixture in a planetary ball mill for ball milling. The ball-to-material ratio is 9-11:1, the rotation speed is 200-300 r / min, and the ball milling time is 2-3 h to obtain the premixed material. S3. Cold pressing: The premixed material is poured into a stainless steel mold with a release agent applied to the inner wall, and then subjected to a pressing at room temperature at 200-300 kg / cm². 2 The pressure is maintained for 40-60 minutes to produce a preform. S4. Sintering and Shaping: The preform is placed in a high-temperature sintering furnace and sintered in stages under an inert gas atmosphere according to the following procedure: First stage: Raise the temperature from room temperature to 280-300℃ at a rate of 80-100℃ / h and hold for 30-40 minutes. Second stage: Continue to heat to 340-360℃, heating rate 50-60℃ / h, hold for 40-50min; Third stage: Continue to heat to 375-385℃, heating rate 30-40℃ / h, hold for 90-120min; Cooling stage: Cool to 320-330℃ at a rate of 40-50℃ / h, hold for 30-40 minutes, and then cool naturally to room temperature to obtain highly dispersed carbon nanotube reinforced PTFE composite material.

5. The highly dispersed carbon nanotube-reinforced PTFE composite material according to claim 1, characterized in that, In step S1, the stirring is magnetic stirring, and the stirring time is 15-25 minutes; the washing with anhydrous ethanol is performed 3-4 times.

6. The highly dispersed carbon nanotube-reinforced PTFE composite material according to claim 1, characterized in that, In step S2, the grinding media used in the ball milling mixture is agate balls.

7. The highly dispersed carbon nanotube-reinforced PTFE composite material according to claim 1, characterized in that, In step S3, the release agent is a polytetrafluoroethylene release agent.

8. The highly dispersed carbon nanotube-reinforced PTFE composite material according to claim 1, characterized in that, In step S4, the inert gas is nitrogen or argon, and the gas flow rate is 0.5 to 1 L / min.

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