Polytetrafluoroethylene composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of friction sealing materials, and discloses a polytetrafluoroethylene composite material as well as a preparation method and application thereof. The polytetrafluoroethylene composite material is prepared from the following components in parts by mass: 80 to 100 parts of polytetrafluoroethylene; 5 to 20 parts of wollastonite fiber; and 1 to 7 parts of stannous sulfide-phosphate. According to the polytetrafluoroethylene composite material provided by the invention, polytetrafluoroethylene is used for providing basic performance, wollastonite fiber is used for enhancing mechanical strength, stannous sulfide-phosphate is used for ensuring lubricity, and a durable and stable friction interface is formed through the synergistic effect of polytetrafluoroethylene, wollastonite fiber and stannous sulfide-phosphate, so that the material has excellent comprehensive performance; under the conditions of high pressure of 35 MPa, wide temperature range of-55 DEG C to 135 DEG C and high-speed reciprocating motion of 3 m / s, the lubricating oil shows extremely low friction coefficient and excellent stability, keeps extremely small leakage rate, and is suitable for an aviation reciprocating hydraulic sealing system.

Description

Technical Field

[0001] This invention relates to the field of friction sealing materials technology, and in particular to a polytetrafluoroethylene composite material, its preparation method, and its application. Background Technology

[0002] As the aviation industry gradually moves towards high performance, lightweight design, and energy conservation and environmental protection, aviation hydraulic systems are also developing towards high power density, rapid response, and low noise. Currently, the working pressure of aviation hydraulic systems has increased from the traditional 28MPa to 35MPa, using No. 15 aviation hydraulic oil as the medium, operating at temperatures ranging from -55℃ to 135℃, and with instantaneous speeds reaching up to 3m / s. This presents challenges to seals under extreme conditions (extrusion under high temperature and pressure, leakage at low temperatures, and high-speed movement), including frictional heat generation and severe wear. Traditional rubber elastomers exhibit various problems when operating under wide temperature ranges (-55℃ to 135℃), high pressures (35MPa), and high speeds (3m / s). For example, nitrile rubber (NBR) is prone to extrusion deformation under high temperature and pressure, resulting in a high coefficient of friction and seal failure; fluororubber (FKM) experiences decreased elasticity at low temperatures, leading to leakage; and fluorosilicone rubber (FVMQ) has low mechanical strength and cannot withstand high pressure and high-speed friction. Polytetrafluoroethylene (PTFE) has become an ideal matrix material for high-pressure sealing due to its advantages such as low coefficient of friction, chemical corrosion resistance, and wide temperature range adaptability. However, pure PTFE has problems such as poor wear resistance and low mechanical strength, and needs to be modified by fiber reinforcement and solid lubricants.

[0003] CN 117209930 A discloses a high-heat-resistant, low-friction wollastonite fiber-modified polytetrafluoroethylene (PTFE) lubricating material and its preparation method. Using PTFE resin as the polymer matrix and wollastonite fiber as the main reinforcing filler, combined with a small amount of lubricating filler as a modifying component, the material is prepared through mechanical blending, pre-pressing, sintering, turning, and stretching / setting processes with parameter control. This ensures the composite material's performance and dimensional precision. In particular, the stretching / setting process promotes the directional alignment of needle-like wollastonite fibers, solving the problem of excessively high friction coefficients caused by the short, brittle, and poorly flexible nature of wollastonite fibers. The resulting composite material exhibits good mechanical strength, tribological properties, thermal conductivity, and dimensional stability, making it suitable for manufacturing precision lubrication components in high-tech fields such as aerospace and marine engineering. However, this patent only addresses dry friction (such as mechanical sliding parts in oil-free environments) and does not cover performance research under oil lubrication (such as aviation hydraulic oil). Furthermore, the material's maximum withstand temperature is 130℃, lower than the 135℃ required by aviation hydraulic systems, which may lead to performance degradation under high-temperature conditions.

[0004] CN 118834486 A discloses a polytetrafluoroethylene (PTFE) composite material, its preparation method, and its applications. By adding a specific amount of dispersed PTFE, a network structure is formed in the composite material with suspension-processed PTFE as the matrix. Further addition of surface-fluorinated carbon fibers, fluorinated graphene, and wollastonite significantly improves the elongation at break and radiation resistance of the PTFE composite material. However, this patent only addresses PTFE solid lubricating materials under high-energy radiation environments and does not involve research on friction and wear properties.

[0005] CN 116120684 A discloses a wear-resistant composite material, its preparation method, and its application. By introducing mineral fibers and halloysite nanotubes into polytetrafluoroethylene (PTFE), the temperature resistance of the wear-resistant composite material is improved through the combined action of PTFE, mineral fibers, and halloysite nanotubes. This allows the wear-resistant composite material to adapt to working conditions over a wide temperature range. The resulting wear-resistant composite material exhibits excellent sealing performance from room temperature to high temperature (150°C). CN 111303568 A discloses a sealing composite material for hydraulic cylinders. After mixing PTFE with fluorinated graphene, mineral fibers, and antimony trioxide, the resulting sealing composite material for hydraulic cylinders exhibits extremely low friction coefficient, excellent thermal stability, corrosion resistance, self-lubricating properties, high temperature resistance, and superior friction resistance when used to prepare hydraulic cylinder seals. This further improves the performance of the seals under harsh working conditions in hydraulic cylinders. CN 114456525 A discloses a polytetrafluoroethylene (PTFE) seal for hydraulic cylinders and its preparation method. By combining modified PTFE, wollastonite, molybdenum disulfide, vinyl bis-stearamide, and nano-zinc oxide, the friction coefficient of the product is significantly reduced, solving the problems of poor conformability and oil leakage associated with conventional materials, resulting in only a small amount of lubricating oil film. However, all of the above patents use GB / T 3960 as the test standard to measure the dynamic friction coefficient of the samples and bench tests to determine the service life or leakage of the seals. They do not examine the friction coefficient under oil lubrication or the sealing performance under high temperature (135℃) and high pressure (35MPa) conditions. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a polytetrafluoroethylene composite material.

[0007] The second objective of this invention is to provide a method for preparing this polytetrafluoroethylene composite material.

[0008] The third objective of this invention is to provide a sealing element.

[0009] The fourth objective of this invention is to provide applications of polytetrafluoroethylene composite materials or seals.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A first aspect of the present invention provides a polytetrafluoroethylene composite material, comprising the following components by weight:

[0012] 80-100 parts of polytetrafluoroethylene;

[0013] 5-20 parts of wollastonite fiber;

[0014] 1-7 parts of stannous sulfide-phosphate.

[0015] In some embodiments of the present invention, the polytetrafluoroethylene composite material comprises the following components by weight:

[0016] 80-90 parts of polytetrafluoroethylene;

[0017] 10-20 parts of wollastonite fiber;

[0018] 1-5 parts of stannous sulfide-phosphate.

[0019] In some preferred embodiments of the present invention, the polytetrafluoroethylene composite material comprises the following components in parts by weight:

[0020] 80-85 parts of polytetrafluoroethylene;

[0021] 13-18 parts of wollastonite fiber;

[0022] 2-4 parts of stannous sulfide-phosphate.

[0023] In some embodiments of the present invention, the particle size D50 of the polytetrafluoroethylene is 180 μm.

[0024] Specifically, the present invention uses polytetrafluoroethylene with a particle size D50 of 180 μm as the matrix, which can overcome the problems of low efficiency, high energy consumption and high time cost in the subsequent air jet pulverization process caused by excessively large raw material particle size, and can also avoid the problem of excessively large particle specific surface area after air jet pulverization caused by excessively small raw material particle size, which leads to excessively thick lubricating film and increased leakage due to adsorption of aviation hydraulic oil.

[0025] In some embodiments of the present invention, the length of the wollastonite fiber is 35-70 μm; the diameter D50 = 7 μm.

[0026] Specifically, this invention uses wollastonite fibers with a length of 35-70μm as filler. This specification of wollastonite fibers can be fully dispersed without causing dust due to being too short or fiber agglomeration due to being too long. The diameter of the wollastonite fibers is limited to D50 = 7μm. When the fibers are cold-pressed, they form an ideal stacked structure with polytetrafluoroethylene particles, ensuring the stability of the entire process of mixing-forming-sintering, and achieving synergistic optimization of high strength, low friction, and wear resistance.

[0027] In some embodiments of the present invention, the stannous sulfide-phosphate has a particle size of D50 = 2 μm, D90 = 7 μm, and a density of 3.0-3.5 g / cm³. 3 .

[0028] Specifically, this invention uses stannous sulfide-phosphate as a solid lubricant, and specifically limits its density to 3.0-3.5 g / cm³. 3 This ensures that the density matches that of PTFE and wollastonite fibers, guaranteeing coordinated deformation of each component during cold pressing and preventing delamination of the billet due to density differences.

[0029] A second aspect of the present invention provides a method for preparing the polytetrafluoroethylene composite material described in the first aspect of the present invention, comprising the following steps:

[0030] S1. Pulverize polytetrafluoroethylene with airflow to D50 = 25μm, then freeze;

[0031] S2. Mix the frozen polytetrafluoroethylene with the remaining components to obtain the blank;

[0032] S3. The blank is cold-pressed and then sintered to obtain the polytetrafluoroethylene composite material.

[0033] In some embodiments of the present invention, the airflow pulverization time is 1-2 minutes.

[0034] In some embodiments of the present invention, the freezing temperature is 12-15°C and the freezing time is 12-24 hours.

[0035] In some embodiments of the present invention, the mixing speed is 1500-2000 r / min and the mixing time is 1-2 min.

[0036] In some embodiments of the present invention, the cold pressing speed is 0.5-1 mm / s, the cold pressing pressure is 40-50 MPa, and the holding time is 5-10 min.

[0037] In some preferred embodiments of the present invention, the cold pressing speed is 0.8-1 mm / s, the cold pressing pressure is 40-45 MPa, and the holding time is 8-10 min.

[0038] In some embodiments of the present invention, the cold pressing process further includes a static pressing operation for 20-24 hours.

[0039] In some embodiments of the present invention, the sintering temperature is 360-380℃ / min and the time is 2-4h.

[0040] In some preferred embodiments of the present invention, the sintering temperature is 360-370℃ / min and the time is 2-3h.

[0041] In some embodiments of the present invention, the sintering heating rate is 10-30°C / min.

[0042] In some preferred embodiments of the present invention, the sintering heating rate is 10-15 °C / min.

[0043] In some embodiments of the present invention, the cooling rate after sintering is 10-30°C / min.

[0044] In some preferred embodiments of the present invention, the cooling rate after sintering is 25-30°C / min.

[0045] Specifically, this invention performs air jet milling on polytetrafluoroethylene (PTFE). Compared with commercially available PTFE powder with a D50 of 25 μm, the PTFE particles generate a fresh surface due to mechanical force during the air jet milling process. This results in higher chemical activity and easier formation of a tight bond with wollastonite fibers and stannous sulfide-phosphate, thereby improving the interfacial strength of the composite material. Furthermore, commercially available PTFE powder is prone to agglomeration during long-term storage and requires secondary processing, while in-situ milling followed by direct freezing can preserve particle dispersibility.

[0046] A third aspect of the present invention provides a sealing element comprising the polytetrafluoroethylene composite material described in the first aspect of the present invention.

[0047] The fourth aspect of the present invention provides the application of the polytetrafluoroethylene composite material described in the first aspect of the present invention, or the seal described in the third aspect, in an aerospace reciprocating hydraulic sealing system.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] 1) The polytetrafluoroethylene composite material provided by this invention utilizes polytetrafluoroethylene to provide basic properties, wollastonite fiber to enhance mechanical strength, and stannous sulfide-phosphate to ensure lubricity. The three work synergistically to form a durable and stable friction interface, giving the material excellent comprehensive performance. Under conditions of 35MPa high pressure, a wide temperature range of -55℃ to 135℃, and high-speed reciprocating motion of 3m / s, it exhibits an extremely low coefficient of friction (minimum 0.063) and excellent stability (fluctuation ±0.001), while maintaining a very small leakage (minimum 12g), making it suitable for aerospace reciprocating hydraulic sealing systems.

[0050] 2) The method for preparing polytetrafluoroethylene composite material provided by the present invention effectively avoids the agglomeration of fine powder by combining airflow pulverization with low-temperature freezing treatment, thereby improving the material density. Combined with precisely controlled mixing, cold pressing and programmed sintering processes, the stability and repeatability of product performance are ensured. This method not only has controllable process parameters and is suitable for industrial production, but also gives full play to the synergistic effect of each component, so that the material can obtain the best comprehensive performance. Detailed Implementation

[0051] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0052] Note: Unless otherwise specified, "parts" in the following examples and comparative examples refer to "parts by mass".

[0053] Example 1

[0054] This embodiment prepares a polytetrafluoroethylene composite material, and the steps are as follows:

[0055] S11. Polytetrafluoroethylene with a particle size of D50 = 180 μm is subjected to air jet milling for 1 min to obtain polytetrafluoroethylene powder with a D50 = 25 μm, and then placed in a freezer at 12-15℃ for 12-24 h.

[0056] S21. Mix 84 parts of polytetrafluoroethylene powder, 15 parts of wollastonite fiber (length 35-70 μm, diameter D50 = 7 μm), and 1 part of stannous sulfide-phosphate (D50 = 2 μm, D90 = 7 μm, density 3.2 g / cm³). 3 The mixture is mixed in a high-speed mixer at a rotation speed of 2000 r / min for 1 min to obtain a billet.

[0057] S31. The blank is cold-pressed in a mold at room temperature at a cold pressing speed of 1 mm / s, a final cold pressing pressure of 40 MPa, and a holding time of 10 min. The blank is then removed from the mold and left to stand for 24 h to form. The formed blank is then sintered in a sintering furnace at a heating rate of 10℃ / h, a holding temperature of 360℃, a holding time of 2 h, and a cooling rate of 30℃ / h to obtain a polytetrafluoroethylene composite material.

[0058] Example 2

[0059] This embodiment prepares a polytetrafluoroethylene composite material, and the steps are as follows:

[0060] S11. Polytetrafluoroethylene with a particle size of D50 = 180 μm is subjected to air jet milling for 1 min to obtain polytetrafluoroethylene powder with a D50 = 25 μm, and then placed in a freezer at 12-15℃ for 12-24 h.

[0061] S21. Mix 82 parts of polytetrafluoroethylene powder, 15 parts of wollastonite fiber (length 35-70 μm, diameter D50 = 7 μm), and 3 parts of stannous sulfide-phosphate (D50 = 2 μm, D90 = 7 μm, density 3.2 g / cm³). 3 The mixture is mixed in a high-speed mixer at a rotation speed of 2000 r / min for 1 min to obtain a billet.

[0062] S31. The blank is cold-pressed in a mold at room temperature at a cold pressing speed of 1 mm / s, a final cold pressing pressure of 40 MPa, and a holding time of 10 min. The blank is then removed from the mold and left to stand for 24 h to form. The formed blank is then sintered in a sintering furnace at a heating rate of 10℃ / h, a holding temperature of 360℃, a holding time of 2 h, and a cooling rate of 30℃ / h to obtain a polytetrafluoroethylene composite material.

[0063] Example 3

[0064] This embodiment prepares a polytetrafluoroethylene composite material, and the steps are as follows:

[0065] S11. Polytetrafluoroethylene with a particle size of D50 = 180 μm is subjected to air jet milling for 1 min to obtain polytetrafluoroethylene powder with a D50 = 25 μm, and then placed in a freezer at 12-15℃ for 12-24 h.

[0066] S21. Mix 80 parts of polytetrafluoroethylene powder, 15 parts of wollastonite fiber (length 35-70 μm, diameter D50 = 7 μm), and 5 parts of stannous sulfide-phosphate (D50 = 2 μm, D90 = 7 μm, density 3.2 g / cm³). 3The mixture is mixed in a high-speed mixer at a rotation speed of 2000 r / min for 1 min to obtain a billet.

[0067] S31. The blank is cold-pressed in a mold at room temperature at a cold pressing speed of 1 mm / s, a final cold pressing pressure of 40 MPa, and a holding time of 10 min. The blank is then removed from the mold and left to stand for 24 h to form. The formed blank is then sintered in a sintering furnace at a heating rate of 10℃ / h, a holding temperature of 360℃, a holding time of 2 h, and a cooling rate of 30℃ / h to obtain a polytetrafluoroethylene composite material.

[0068] Comparative Example 1

[0069] This comparative example prepares a polytetrafluoroethylene composite material, and the steps are as follows:

[0070] S11. Polytetrafluoroethylene with a particle size of D50 = 180 μm is subjected to air jet milling for 1 min to obtain polytetrafluoroethylene powder with a D50 = 25 μm, and then placed in a freezer at 12-15℃ for 12-24 h.

[0071] S21. Mix 85 parts of polytetrafluoroethylene powder with 15 parts of wollastonite fiber (length 35-70μm, diameter D50=7μm) in a high-speed mixer at a rotation speed of 2000r / min for 1min to obtain a billet.

[0072] S31. The blank is cold-pressed in a mold at room temperature at a cold pressing speed of 1 mm / s, a final cold pressing pressure of 40 MPa, and a holding time of 10 min. The blank is then removed from the mold and left to stand for 24 h to form. The formed blank is then sintered in a sintering furnace at a heating rate of 10℃ / h, a holding temperature of 360℃, a holding time of 2 h, and a cooling rate of 30℃ / h to obtain a polytetrafluoroethylene composite material.

[0073] Comparative Example 2

[0074] This comparative example prepares a polytetrafluoroethylene composite material, and the steps are as follows:

[0075] S21. Mix 85 parts of polytetrafluoroethylene powder with a particle size D50 = 180 μm and 15 parts of wollastonite fiber (length 35-70 μm, diameter D50 = 7 μm) in a high-speed mixer at a rotation speed of 2000 r / min for 1 min to obtain a billet.

[0076] S31. The blank is cold-pressed in a mold at room temperature at a cold pressing speed of 1 mm / s, a final cold pressing pressure of 40 MPa, and a holding time of 10 min. The blank is then removed from the mold and left to stand for 24 h to form. The formed blank is then sintered in a sintering furnace at a heating rate of 10℃ / h, a holding temperature of 360℃, a holding time of 2 h, and a cooling rate of 30℃ / h to obtain a polytetrafluoroethylene composite material.

[0077] Comparative Example 3

[0078] This comparative example prepares a polytetrafluoroethylene composite material, and the steps are as follows:

[0079] S11. Polytetrafluoroethylene with a particle size of D50 = 180 μm is subjected to air jet milling for 1 min to obtain polytetrafluoroethylene powder with a D50 = 25 μm.

[0080] S21. Mix 85 parts of polytetrafluoroethylene powder with 15 parts of wollastonite fiber (length 35-70μm, diameter D50=7μm) in a high-speed mixer at a rotation speed of 2000r / min for 1min to obtain a billet.

[0081] S31. The blank is cold-pressed in a mold at room temperature at a cold pressing speed of 1 mm / s, a final cold pressing pressure of 40 MPa, and a holding time of 10 min. The blank is then removed from the mold and left to stand for 24 h to form. The formed blank is then sintered in a sintering furnace at a heating rate of 10℃ / h, a holding temperature of 360℃, a holding time of 2 h, and a cooling rate of 30℃ / h to obtain a polytetrafluoroethylene composite material.

[0082] Application examples

[0083] The polytetrafluoroethylene composite materials prepared in Examples 1-3 and Comparative Examples 1-3 were machined on a lathe to obtain friction and wear test specimens of 40mm×40mm×6mm and sealing products of VL type with specifications of 45×53×8.5.

[0084] 1. In the corresponding use case of aviation hydraulic oil No. 15, the friction coefficient of the friction and wear test specimens prepared by the polytetrafluoroethylene composite material in Examples 1-3 and Comparative Examples 1-3 was tested for 8 hours. The reciprocating friction test machine was used, with the wear pair being Φ8 GCr15 steel balls, the load being 35MPa, and the reciprocating speed being 0.5m / s.

[0085] Table 1 shows the test results of the friction coefficient of the friction and wear samples in the application examples.

[0086] 1h 2h 3h 4h 5h 6h 7h 8h Example 1 0.067 0.069 0.068 0.070 0.068 0.071 0.072 0.070 Example 2 0.063 0.064 0.063 0.065 0.064 0.064 0.063 0.064 Example 3 0.068 0.070 0.071 0.069 0.072 0.070 0.071 0.072 Comparative Example 1 0.075 0.075 0.080 0.083 0.080 0.082 0.085 0.083 Comparative Example 2 0.075 0.092 0.095 0.080 0.095 0.088 0.095 0.083 Comparative Example 3 0.073 0.088 0.090 0.088 0.082 0.090 0.085 0.082

[0087] Table 1 shows the friction coefficient test results of the friction and wear samples in the application examples. As can be seen from Table 1, in Comparative Example 1, the PTFE composite material did not contain stannous sulfide-phosphate, and compared with Examples 1-3, the friction coefficient and fluctuation of the prepared friction and wear samples increased. In Comparative Example 2, no stannous sulfide-phosphate was added, and the PTFE was not pulverized or frozen; compared with Comparative Example 1, the friction coefficient and fluctuation further increased. In Comparative Example 3, no stannous sulfide-phosphate was added, and the PTFE was not frozen; the friction coefficient and fluctuation were between those of Comparative Example 1 and Comparative Example 2. The friction and wear samples prepared using the PTFE composite materials in Examples 1-3 all had a friction coefficient less than 0.07 within 1-8 hours. 5. The relatively small fluctuations indicate that the airflow pulverization and freezing steps of polytetrafluoroethylene (PTFE), as well as the addition of stannous sulfide-phosphate as a solid lubricant, are key to ensuring the material's performance. Stannous sulfide-phosphate forms a uniform and strongly adherent transfer film on the metal surface, effectively reducing frictional heat generation. Through the rigid support of wollastonite fibers and the shear slip of the lubricant, the dynamic balance of the friction interface is maintained. The wear resistance of the friction and wear test specimen prepared from the PTFE composite material in Example 2 is even better, indicating that the amount of stannous sulfide-phosphate added needs to be controlled within a reasonable range. When the amount of wollastonite fibers is 15 wt% and the amount of stannous sulfide-phosphate is 3 wt%, the material performance is optimal.

[0088] 2. Leakage tests were conducted on the sealing products made of polytetrafluoroethylene composite materials used in Examples 1-3 and Comparative Examples 1-3 in the corresponding use cases. A reciprocating seal simulation bench was used, with No. 15 aviation hydraulic oil as the lubricating medium, and the piston rod diameter was 45mm with chrome plating. First, the reciprocating speed was 0.3m / s, and the reciprocating stroke was 200mm, for 2000 cycles of break-in. Then, the reciprocating speed was 3m / s, and the reciprocating stroke was 200mm, for 2000 cycles. Finally, the reciprocating speed was 0.3m / s, for 200,000 cycles.

[0089] Table 2 shows the leakage rates of sealing products in application examples at 35 MPa, -55℃ / 135℃, and No. 15 aviation hydraulic oil.

[0090]

[0091] Table 2 shows the leakage of the sealing products in the application examples under conditions of 35 MPa, -55℃ / 135℃, and No. 15 aviation hydraulic oil. As can be seen from Table 2, the leakage of the sealing products made of PTFE composite material in Examples 1-3 under extreme conditions of No. 15 aviation hydraulic oil, a wide temperature range (-55℃ to 135℃), high pressure (35 MPa), and high speed (3 m / s) is much lower than that in Comparative Examples 1-3. The leakage at 135℃ can be as low as 12 g. In Comparative Example 2, without the addition of stannous sulfide-phosphate and without PTFE being pulverized and frozen, the leakage increased significantly. This indicates that by reducing the particle size of the PTFE powder through airflow pulverization and using freezing to prevent the agglomeration of fine PTFE powder, the elastic modulus, hardness, and strength of the PTFE material are improved, ensuring the sealing components' ability to withstand pressure and tension under high pressure and a wide temperature range.

Claims

1. A polytetrafluoroethylene composite material, characterized in that, By weight, it includes the following components: 80-100 parts of polytetrafluoroethylene; 5-20 parts of wollastonite fiber; 1-7 parts of stannous sulfide-phosphate.

2. The polytetrafluoroethylene composite material according to claim 1, characterized in that, The particle size of the polytetrafluoroethylene is D50 = 180 μm.

3. The polytetrafluoroethylene composite material according to claim 1, characterized in that, The wollastonite fibers have a length of 35-70 μm and a diameter D50 of 7 μm.

4. The polytetrafluoroethylene composite material according to claim 1, characterized in that, The particle size of the stannous sulfide-phosphate D50 = 2μm; D90 = 7μm; density is 3.0-3.5g / cm³ 3 .

5. The method for preparing the polytetrafluoroethylene composite material according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Pulverize polytetrafluoroethylene with airflow to D50 = 25μm, then freeze; S2. Mix the frozen polytetrafluoroethylene with the remaining components to obtain the blank; S3. The blank is cold-pressed and then sintered to obtain the polytetrafluoroethylene composite material.

6. The preparation method according to claim 5, characterized in that, The freezing temperature is 12-15℃, and the freezing time is 12-24h.

7. The preparation method according to claim 5, characterized in that, The cold pressing speed is 0.5-1 mm / s, the cold pressing pressure is 40-50 MPa, and the holding time is 5-10 min.

8. The preparation method according to claim 5, characterized in that, The sintering temperature is 360-380℃ / min, and the time is 2-4h.

9. A sealing element, characterized in that, Including the polytetrafluoroethylene composite material according to any one of claims 1-4.

10. The application of the polytetrafluoroethylene composite material according to any one of claims 1-4, or the seal according to claim 9, in an aerospace reciprocating hydraulic sealing system.

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