Low-creep polytetrafluoroethylene composite material and preparation method thereof

Abstract

The invention discloses a low-creep polytetrafluoroethylene composite material and a preparation method thereof, the low-creep polytetrafluoroethylene composite material comprises the following raw materials by weight: 50-60 parts of polytetrafluoroethylene, 35-45 parts of perfluoroalkoxy resin, 15-25 parts of modified composite fiber, and 1-2 parts of a lubricant. Polytetrafluoroethylene and perfluoroalkoxy resin are blended according to a specific proportion to serve as a base material, a hot press molding process is matched, the core performance of the material is guaranteed, the molten perfluoroalkoxy resin can fully infiltrate and wrap the surface of the modified composite fiber under the driving of hot press pressure, and the performance of the composite fiber is improved. The composite material has the advantages that the composite material is high in mechanical strength, can form strong interface combination with PTFE (polytetrafluoroethylene) framework particles, can permeate and fill gaps of the PTFE framework particles, eliminates internal pores through a welding effect, and finally forms a highly-compact whole, so that the creep resistance of the composite material is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of polytetrafluoroethylene (PTFE) material technology, specifically relating to a low-creep PTFE composite material and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE), due to its unique perfluorinated carbon chain structure, possesses the best overall performance of any engineering plastic to date. It exhibits exceptional chemical stability, resisting corrosion from almost all chemical media except molten alkali metals and elemental fluorine under high temperature and pressure. Simultaneously, it boasts a wide operating temperature range (typically capable of long-term service between -196℃ and 260℃), and possesses the lowest coefficient of friction among plastics, along with excellent electrical insulation properties. This unique combination of properties makes PTFE widely used in critical fields such as chemical engineering, electronics, machinery, and aerospace as a sealant, lining, insulation layer, anti-stick coating, and self-lubricating bearing, making it an indispensable high-performance material in modern industry.

[0003] However, despite the significant performance advantages of PTFE, its highly linear and regular molecular structure, along with weak intermolecular forces, leads to an inherent and fatal weakness that limits its applications—a tendency to cold flow under load, i.e., extremely poor creep resistance. This means that pure PTFE products, under continuous stress, will undergo irreversible changes in shape and size over time, failing to meet the dimensional stability requirements of precision structural components and high-load conditions. To overcome this deficiency, the mainstream technical approach is physical modification through filler addition, i.e., adding various reinforcing fillers to the PTFE matrix, such as glass fiber, carbon fiber, graphite, molybdenum disulfide, or bronze powder. These fillers can improve the hardness and wear resistance of the composite material to a certain extent, and their rigidity can impede the flow of the polymer matrix, thereby improving the material's creep resistance.

[0004] Chinese patent application CN110655741A discloses a PTFE composite material modified with multi-component inorganic filler and its preparation method. The composite material comprises, by mass percentage: 10%-14% glass fiber, 5%-15% copper, and 1%-5% molybdenum disulfide, with the balance being polytetrafluoroethylene (PTFE). The preparation method includes the following steps: Step 1, treating copper powder, molybdenum disulfide powder, and glass fiber powder with a silane coupling agent and then drying them to obtain an activated inorganic filler material; Step 2, mixing the activated inorganic filler material with PTFE and pressing it into shape to obtain a PTFE-based composite material precursor; Step 3, sintering the PTFE-based composite material precursor at high temperature to obtain the PTFE composite material modified with multi-component inorganic filler. Chinese patent application CN108943779A discloses a method for preparing a polytetrafluoroethylene (PTFE) composite membrane material with a high filler content. The method involves high-speed mixing, cold pressing into a blank, sintering, turning into a film, and calendering post-treatment to prepare a PTFE composite membrane material with an inorganic filler content of up to 20 wt%. Furthermore, by designing the dispersion morphology of various functional inorganic fillers and controlling the preparation process, an inorganic filler / PTFE composite membrane material with controllable membrane structure and excellent mechanical, electrical, thermal conductivity, and wear resistance properties is prepared.

[0005] However, this type of traditional filler modification technology has significant drawbacks: the lack of an effective interfacial bonding mechanism between the filler and the extremely inert PTFE matrix leads to insufficient interfacial bonding force between the filler and the matrix. Under long-term or alternating loads, this weak interface is prone to debonding and slippage, forming stress concentration points and failure sources. As a result, stress cannot be effectively transferred from the matrix to the reinforcing filler. Therefore, the effect of improving anti-creep performance is limited and unreliable, making it difficult to meet the application requirements under more stringent high-temperature and high-load conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a low-creep polytetrafluoroethylene composite material and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0009] 50-60 parts polytetrafluoroethylene, 35-45 parts perfluoroalkoxy resin, 10-15 parts modified composite fiber, and 1-2 parts lubricant.

[0010] Preferably, a low-creep polytetrafluoroethylene composite material comprises, by weight, the following raw materials:

[0011] 50-55 parts polytetrafluoroethylene, 35-40 parts perfluoroalkoxy resin, 12-15 parts modified composite fiber, and 1-2 parts lubricant.

[0012] In this invention, the polytetrafluoroethylene composite material uses a blend of polytetrafluoroethylene (PTFE) and perfluoroalkoxy resin (PFA) in a specific ratio as the matrix material, and is matched with a hot pressing process. This not only ensures the core performance of the material and cost control, but also allows PFA to melt into a low-viscosity fluid at the processing temperature, which can be used as a melt binder. Under the driving force of hot pressing pressure, the molten PFA can not only fully wet and coat the surface of the modified composite fiber to form a strong interfacial bond, but also penetrate and fill the gaps in the PTFE skeleton particles, eliminating internal pores through a "welding" effect, and finally forming a highly dense whole, thereby significantly improving the creep resistance of the composite material.

[0013] Preferably, the method for preparing the modified composite fiber includes the following steps:

[0014] S1. After pre-burning the carbon fiber, add it to concentrated nitric acid for impregnation treatment. After the treatment is completed, filter, wash and dry to obtain pre-treated carbon fiber.

[0015] S2. Add the pretreated carbon fiber from step S1 to a mixed solution of nickel nitrate and aluminum nitrate, stir evenly, add urea, and carry out a hydrothermal reaction. After the reaction is completed, let it stand, filter, wash, and dry to obtain composite fiber.

[0016] S3. Add the composite fiber from step S2 to an ethanol aqueous solution, then add vinyltriethoxysilane, stir and react. After the reaction is complete, filter, wash and dry to obtain organic composite fiber.

[0017] S4. Add the organic composite fiber from step S3 to DMF, then add perfluorooctyl ethyl acrylate and azobisisobutyronitrile, and carry out a constant temperature reaction. After the reaction is completed, filter, wash and dry to obtain the modified composite fiber.

[0018] Preferably, the pre-firing temperature in step S1 is 450-500℃ and the time is 1-2 hours; the impregnation treatment temperature is 70-80℃ and the time is 3-4 hours.

[0019] In this invention, carbon fiber is used as the skeleton material, which has extremely high strength and modulus, and is the basis for the final composite material to resist load and suppress creep. By pre-firing and acid treatment of carbon fiber, a large number of oxygen-containing functional groups are introduced on the surface of carbon fiber, which is beneficial to the subsequent reaction.

[0020] Preferably, in step S2, the concentration of nickel ions in the mixed solution is 0.3-0.5 mol / L, the concentration of aluminum ions is 0.15-0.25 mol / L, the material-to-liquid ratio of the pretreated carbon fiber, the mixed solution, and urea is 20-30 g: 900-1000 mL: 25-35 g, and the hydrothermal reaction temperature is 120-130℃ for 8-10 h.

[0021] In this invention, a nickel-aluminum layered bimetallic hydroxide is generated in situ on carbon fibers via a hydrothermal reaction. This layered structure, composed of countless nanosheets, greatly increases the specific surface area of ​​the fiber, providing a large number of active sites for subsequent functionalization. More importantly, it forms a physical anchoring effect on the carbon fiber matrix at the microscopic level, ensuring that the subsequently grafted organic functional layers (S3 and S4) can form an extremely stable bond with the carbon fiber skeleton. When the final composite material is subjected to stress, the stress from the PTFE / PFA matrix can be efficiently and completely transferred to the core load-bearing carbon fiber through the nickel-aluminum layered bimetallic hydroxide, thereby effectively inhibiting the creep deformation of the matrix and significantly improving the macroscopic creep resistance of the composite material.

[0022] Preferably, in step S3, the mass ratio of the composite fiber to vinyltriethoxysilane is 30-40:4-5, the mass fraction of ethanol in the aqueous ethanol solution is 70-80%, the temperature of the stirring reaction is 65-75°C, and the time is 4-6 hours.

[0023] In this invention, carbon-carbon double bond active functional groups are introduced into the composite fiber by reacting vinyltriethoxysilane with the composite fiber, which is beneficial to the subsequent reaction.

[0024] Preferably, in step S4, the mass ratio of the organic composite fiber, perfluorooctyl ethyl acrylate, and azobisisobutyronitrile is 30-40:10-14:0.1-0.2, and the isothermal reaction is carried out at a temperature of 70-80°C for 5-8 hours.

[0025] In this invention, perfluorooctyl ethyl acrylate is introduced into the composite fiber through a free radical reaction. Its chemical structure is highly similar to that of the PFA / PTFE matrix. On the one hand, this greatly improves the physical compatibility between the fiber and the matrix. On the other hand, the long-chain perfluoroalkyl chain it contains will deeply and physically interpenetrate and entangle with the molten PFA matrix molecular chain during hot pressing. The resulting interfacial bonding strength is far superior to that of simple physical contact or chemical bonds, thereby significantly improving the creep resistance of the composite material.

[0026] Preferably, the lubricant is either graphite or boron nitride.

[0027] This invention also protects a method for preparing a low-creep polytetrafluoroethylene composite material as described above, comprising the following steps:

[0028] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and lubricant are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. Under pressure, it is cooled to room temperature and demolded to obtain the final product.

[0029] Preferably, the hot pressing temperature is 360-390℃, the pressure is 10-15MPa, and the time is 40-60min.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The low creep polytetrafluoroethylene composite material provided by the present invention uses polytetrafluoroethylene (PTFE) and perfluoroalkoxy resin (PFA) blended in a specific ratio as matrix material and matched with hot pressing molding process. This not only ensures the core performance and cost control of the material, but also allows PFA to melt into a low viscosity fluid at the processing temperature, which can be used as a melt adhesive. Under the drive of hot pressing pressure, the molten PFA can not only fully wet and wrap the surface of the modified composite fiber to form a strong interfacial bond, but also penetrate and fill the gaps in the PTFE skeleton particles. Through the "welding" action, the internal pores are eliminated, and finally a highly dense whole is formed, thereby significantly improving the creep resistance of the composite material.

[0032] (2) The low creep polytetrafluoroethylene composite material provided by the present invention incorporates modified composite fibers. The modified composite fibers are made by using carbon fibers with multi-step surface functionalization (in-situ growth of LDH, silane coupling, and free radical grafting polymerization) as the core reinforcement. The carbon fibers are then combined with polytetrafluoroethylene / perfluoroalkoxy resin (PTFE / PFA) blend matrix by hot pressing. During the hot pressing process, the PFA melt phase effectively wets the fiber surface and "welds" the PTFE matrix particles, forming a dense composite structure with optimized interface. This structure effectively inhibits the slippage and movement of polymer chains under load and high temperature, giving the composite material extremely excellent creep resistance, higher mechanical modulus and dimensional stability. At the same time, it retains the inherent high and low temperature resistance and chemical corrosion resistance of the fluoropolymer matrix, significantly broadening its application potential as a load-bearing structural component under harsh working conditions.

[0033] (3) The low-creep polytetrafluoroethylene composite material provided by this invention grows Ni-Al double hydroxide (LDH) nanosheets with a layered structure in situ on the surface of carbon fibers. Compared with traditional surface oxidation or simple deposition, the inorganic nanosheet layer prepared by this method not only greatly increases the specific surface area and roughness of the fiber, providing a large number of active sites for subsequent functionalization, but more importantly, it forms a physical "anchoring" structure, which greatly enhances the bonding strength between the subsequent perfluorooctyl ethyl acrylate layer and the carbon fiber body, laying the foundation for the final realization of efficient stress transfer. It has a solid structural foundation; at the same time, it innovatively adopts a free radical graft polymerization method to introduce long-chain perfluorooctyl ethyl acrylate on the fiber surface. Its chemical structure is highly similar to that of the PFA / PTFE matrix. On the one hand, it can greatly improve the physical compatibility between the fiber and the matrix; on the other hand, the long-chain perfluoroalkyl chain it contains will deeply and physically interpenetrate and entangle with the molten PFA matrix molecular chains during hot pressing. The interfacial bonding strength formed is far beyond that of simple physical contact or chemical bonds, thus significantly improving the creep resistance of the composite material. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0035] Unless otherwise specified, all chemical reagents and materials in this invention are purchased from the market or synthesized from raw materials purchased from the market.

[0036] The polytetrafluoroethylene is designated as 3M Dyneon PTFE TF 9201Z; the perfluoroalkoxy resin is designated as Chemours PFA 350; and the carbon fiber has a length of 3-5 mm and a diameter of 5-7 μm.

[0037] Example 1

[0038] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0039] 55 parts polytetrafluoroethylene, 40 parts perfluoroalkoxy resin, 13 parts modified composite fiber, and 1.5 parts boron nitride.

[0040] The method for preparing the modified composite fiber includes the following steps:

[0041] S1. The carbon fiber was pre-calcined at 480℃ for 1.5h, cooled, and then added to concentrated nitric acid with a mass concentration of 68% and impregnated at 75℃ for 3.5h. After the treatment was completed, it was filtered, washed, and dried to obtain pretreated carbon fiber.

[0042] S2. Add 25g of pretreated carbon fiber from step S1 to a mixed solution of nickel nitrate and aluminum nitrate (nickel ion concentration is 0.4mol / L, aluminum ion concentration is 0.2mol / L), stir evenly, add 30g of urea, and hydrothermally react at 125℃ for 9h. After the reaction is complete, let stand for 12h, filter, wash and dry to obtain composite fiber.

[0043] S3. Add 35g of composite fiber from step S2 to 800mL of ethanol aqueous solution (ethanol mass fraction is 75%), then add 4.5g of vinyltriethoxysilane, stir and react at 70℃ for 5h, filter, wash and dry after the reaction is completed to obtain organic composite fiber.

[0044] S4. Add 35g of organic composite fiber from step S3 to 900mL of DMF, then add 12g of perfluorooctyl ethyl acrylate and 0.15g of azobisisobutyronitrile, and react at 75℃ for 7h. After the reaction is complete, filter, wash and dry to obtain modified composite fiber.

[0045] A method for preparing a low-creep polytetrafluoroethylene composite material includes the following steps:

[0046] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. The hot-pressing temperature is 380℃, the pressure is 13MPa, and the time is 50min. Under the pressure, the mixture is cooled to room temperature and demolded to obtain the final product.

[0047] Example 2

[0048] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0049] 50 parts polytetrafluoroethylene, 35 parts perfluoroalkoxy resin, 10 parts modified composite fiber, and 1 part boron nitride.

[0050] The method for preparing the modified composite fiber includes the following steps:

[0051] S1. The carbon fiber was pre-calcined at 450℃ for 2 hours, cooled, and then added to concentrated nitric acid with a mass concentration of 68%. It was then impregnated at 70℃ for 4 hours. After the treatment was completed, it was filtered, washed, and dried to obtain pretreated carbon fiber.

[0052] S2. Add 20g of pretreated carbon fiber from step S1 to a 900mL mixed solution of nickel nitrate and aluminum nitrate (nickel ion concentration is 0.3mol / L, aluminum ion concentration is 0.15mol / L), stir evenly, add 25g of urea, and hydrothermally react at 120℃ for 10h. After the reaction is complete, let stand for 12h, filter, wash, and dry to obtain composite fiber.

[0053] S3. Add 30g of composite fiber from step S2 to 800mL of ethanol aqueous solution (ethanol mass fraction is 70%), then add 4g of vinyltriethoxysilane, stir and react at 65℃ for 6h, filter, wash and dry after the reaction is completed to obtain organic composite fiber.

[0054] S4. Add 30g of organic composite fiber from step S3 to 900mL of DMF, then add 10g of perfluorooctyl ethyl acrylate and 0.1g of azobisisobutyronitrile, and react at 70℃ for 8h. After the reaction is complete, filter, wash and dry to obtain modified composite fiber.

[0055] A method for preparing a low-creep polytetrafluoroethylene composite material includes the following steps:

[0056] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. The hot-pressing temperature is 380℃, the pressure is 13MPa, and the time is 50min. Under the pressure, the mixture is cooled to room temperature and demolded to obtain the final product.

[0057] Example 3

[0058] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0059] 60 parts polytetrafluoroethylene, 45 parts perfluoroalkoxy resin, 15 parts modified composite fiber, and 2 parts boron nitride.

[0060] The method for preparing the modified composite fiber includes the following steps:

[0061] S1. The carbon fiber is pre-calcined at 500℃ for 1 hour, cooled and then added to concentrated nitric acid with a mass concentration of 68%, and impregnated at 80℃ for 3 hours. After the treatment is completed, it is filtered, washed and dried to obtain pretreated carbon fiber.

[0062] S2. Add 30g of pretreated carbon fiber from step S1 to 1000mL of a mixed solution of nickel nitrate and aluminum nitrate (nickel ion concentration is 0.5mol / L, aluminum ion concentration is 0.25mol / L), stir evenly, add 35g of urea, and hydrothermally react at 130℃ for 8h. After the reaction is complete, let stand for 12h, filter, wash, and dry to obtain composite fiber.

[0063] S3. Add 40g of composite fiber from step S2 to 800mL of ethanol aqueous solution (ethanol mass fraction is 80%), then add 5g of vinyltriethoxysilane, stir and react at 75℃ for 4h, filter, wash and dry after the reaction is completed to obtain organic composite fiber.

[0064] S4. Add 40g of organic composite fiber from step S3 to 900mL of DMF, then add 14g of perfluorooctyl ethyl acrylate and 0.2g of azobisisobutyronitrile, and react at 80℃ for 5h. After the reaction is complete, filter, wash and dry to obtain modified composite fiber.

[0065] A method for preparing a low-creep polytetrafluoroethylene composite material includes the following steps:

[0066] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. The hot-pressing temperature is 380℃, the pressure is 13MPa, and the time is 50min. Under the pressure, the mixture is cooled to room temperature and demolded to obtain the final product.

[0067] Comparative Example 1

[0068] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0069] 55 parts polytetrafluoroethylene, 40 parts perfluoroalkoxy resin, 13 parts modified composite fiber, and 1.5 parts boron nitride.

[0070] The method for preparing the modified composite fiber includes the following steps:

[0071] S1. The carbon fiber was pre-calcined at 480℃ for 1.5h, cooled, and then added to concentrated nitric acid with a mass concentration of 68% and impregnated at 75℃ for 3.5h. After the treatment was completed, it was filtered, washed, and dried to obtain pretreated carbon fiber.

[0072] S2. Add 25g of pretreated carbon fiber from step S1 to a mixed solution of nickel nitrate and aluminum nitrate (nickel ion concentration is 0.4mol / L, aluminum ion concentration is 0.2mol / L), stir evenly, add 30g of urea, and hydrothermally react at 125℃ for 9h. After the reaction is complete, let stand for 12h, filter, wash and dry to obtain composite fiber.

[0073] S3. Add 35g of composite fiber from step S2 to 800mL of ethanol aqueous solution (ethanol mass fraction is 75%), then add 4.5g of vinyltriethoxysilane, stir and react at 70℃ for 5h, filter, wash and dry after the reaction is completed to obtain modified composite fiber.

[0074] A method for preparing a low-creep polytetrafluoroethylene composite material includes the following steps:

[0075] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. The hot-pressing temperature is 380℃, the pressure is 13MPa, and the time is 50min. Under the pressure, the mixture is cooled to room temperature and demolded to obtain the final product.

[0076] Compared to Example 1, the modified composite fibers in this comparative example did not introduce perfluorooctyl ethyl acrylate.

[0077] Comparative Example 2

[0078] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0079] 55 parts polytetrafluoroethylene, 40 parts perfluoroalkoxy resin, 13 parts modified composite fiber, and 1.5 parts boron nitride.

[0080] The method for preparing the modified composite fiber includes the following steps:

[0081] S1. The carbon fiber was pre-calcined at 480℃ for 1.5h, cooled, and then added to concentrated nitric acid with a mass concentration of 68% and impregnated at 75℃ for 3.5h. After the treatment was completed, it was filtered, washed, and dried to obtain pretreated carbon fiber.

[0082] S2. Add 25g of pretreated carbon fiber from step S1 to 800mL of ethanol aqueous solution (ethanol mass fraction is 75%), then add 4.5g of vinyltriethoxysilane, stir and react at 70℃ for 5h, filter, wash and dry after the reaction is completed to obtain organic composite fiber.

[0083] S3. Add 35g of organic composite fiber from step S2 to 900mL of DMF, then add 12g of perfluorooctyl ethyl acrylate and 0.15g of azobisisobutyronitrile, and react at 75℃ for 7h. After the reaction is complete, filter, wash and dry to obtain modified composite fiber.

[0084] A method for preparing a low-creep polytetrafluoroethylene composite material includes the following steps:

[0085] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. The hot-pressing temperature is 380℃, the pressure is 13MPa, and the time is 50min. Under the pressure, the mixture is cooled to room temperature and demolded to obtain the final product.

[0086] Compared to Example 1, the modified composite fibers in this comparative example did not introduce nickel-aluminum layered bimetallic hydroxide.

[0087] Comparative Example 3

[0088] A low-creep polytetrafluoroethylene composite material, comprising the following raw materials by weight:

[0089] 55 parts polytetrafluoroethylene, 40 parts perfluoroalkoxy resin, 13 parts modified composite fiber, and 1.5 parts boron nitride.

[0090] The method for preparing the modified composite fiber includes the following steps:

[0091] S1. The carbon fiber was pre-calcined at 480℃ for 1.5h, cooled, and then added to concentrated nitric acid with a mass concentration of 68% and impregnated at 75℃ for 3.5h. After the treatment was completed, it was filtered, washed, and dried to obtain pretreated carbon fiber.

[0092] S2. Mix 25g of pretreated carbon fiber, 10g of nickel-aluminum layered bimetallic hydroxide and 12g of perfluorooctyl ethyl acrylate from step S1 evenly to obtain modified composite fiber.

[0093] The preparation method of the nickel-aluminum layered bimetallic hydroxide is as follows: 30g of urea is added to 950mL of a mixed solution of nickel nitrate and aluminum nitrate (the concentration of nickel ions is 0.4mol / L and the concentration of aluminum ions is 0.2mol / L), and the mixture is subjected to hydrothermal reaction at 125℃ for 9h. After the reaction is completed, the mixture is allowed to stand for 12h, filtered, washed, and dried to obtain the final product.

[0094] A method for preparing a low-creep polytetrafluoroethylene composite material includes the following steps:

[0095] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. The hot-pressing temperature is 380℃, the pressure is 13MPa, and the time is 50min. Under the pressure, the mixture is cooled to room temperature and demolded to obtain the final product.

[0096] Compared to Example 1, the modified composite fiber in this comparative example was obtained by physical blending of pretreated carbon fiber, nickel-aluminum layered bimetallic hydroxide and perfluorooctyl ethyl acrylate.

[0097] The low-creep polytetrafluoroethylene composites prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. Tensile strength and elongation at break were tested according to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molding and extruding plastics" using a 180mm × 10mm × 4mm specimen at a tensile speed of 10mm / min. Creep rate was tested according to GB / T 11546.1-2008 "Determination of creep properties of plastics - Part 1: Tensile creep" using a 120 × 10 × 4mm specimen at a temperature of 150℃, a stress of 20MPa, and a test time of 100h. Volumetric wear rate was tested according to GB / T 3960-2016 "Plastics - Test method for sliding friction and wear" at a temperature of 25℃. The grinding disc material was quenched GCr15 bearing steel with a surface roughness Ra = The thickness was 0.2 μm, the applied normal load was 10 N, the rotation speed was 200 r / min, and the total sliding distance was 1000 m; the test results are shown in Table 1 below:

[0098] Table 1

[0099] Tensile strength (MPa) Elongation at break (%) Creep rate (%) <![CDATA[Volume wear rate (×10 -6 mm 3 / N·m)]]> Example 1 39.6 231 3.5 8.7 Example 2 38.1 215 3.9 8.4 Example 3 39.2 223 3.6 8.9 Comparative Example 1 32.3 164 7.1 21.6 Comparative Example 2 31.7 182 7.8 19.3 Comparative Example 3 30.4 197 9.2 26.7

[0100] As can be seen from Table 1 above, the low-creep polytetrafluoroethylene composite material prepared by this invention has good mechanical properties, as well as low creep rate and volumetric wear rate, which broadens the application scenarios of polytetrafluoroethylene materials under harsh working conditions.

[0101] The above description is a further detailed explanation of the present invention in conjunction with specific implementation examples. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the protection scope of the present invention.

[0102] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-creep polytetrafluoroethylene composite material, characterized in that, By weight, it includes the following ingredients: 50-60 parts polytetrafluoroethylene, 35-45 parts perfluoroalkoxy resin, 10-15 parts modified composite fiber, and 1-2 parts lubricant.

2. The low-creep polytetrafluoroethylene composite material according to claim 1, characterized in that, By weight, it includes the following ingredients: 50-55 parts polytetrafluoroethylene, 35-40 parts perfluoroalkoxy resin, 12-15 parts modified composite fiber, and 1-2 parts lubricant.

3. The low-creep polytetrafluoroethylene composite material according to claim 1, characterized in that, The method for preparing the modified composite fiber includes the following steps: S1. After pre-burning the carbon fiber, add it to concentrated nitric acid for impregnation treatment. After the treatment is completed, pre-treated carbon fiber is obtained. S2. Add the pretreated carbon fiber to a mixed solution of nickel nitrate and aluminum nitrate, stir evenly, add urea, and carry out a hydrothermal reaction. After the reaction is completed, let it stand, filter, wash, and dry to obtain composite fiber. S3. Add the composite fiber to an ethanol aqueous solution, then add vinyltriethoxysilane, stir and react. After the reaction is complete, organic composite fiber is obtained. S4. Add the organic composite fiber to DMF, then add perfluorooctyl ethyl acrylate and azobisisobutyronitrile, and carry out a constant temperature reaction. After the reaction is completed, the modified composite fiber is obtained.

4. The low-creep polytetrafluoroethylene composite material according to claim 3, characterized in that, In step S1, the pre-firing temperature is 450-500℃ and the time is 1-2 hours; the impregnation treatment temperature is 70-80℃ and the time is 3-4 hours.

5. The low-creep polytetrafluoroethylene composite material according to claim 3, characterized in that, In step S2, the concentration of nickel ions in the mixed solution is 0.3-0.5 mol / L, and the concentration of aluminum ions is 0.15-0.25 mol / L. The ratio of the pretreated carbon fiber, the mixed solution, and urea is 20-30 g: 900-1000 mL: 25-35 g. The hydrothermal reaction temperature is 120-130℃, and the time is 8-10 h.

6. The low-creep polytetrafluoroethylene composite material according to claim 3, characterized in that, In step S3, the mass ratio of the composite fiber to vinyltriethoxysilane is 30-40:4-5, the mass fraction of ethanol in the aqueous ethanol solution is 70-80%, the temperature of the stirring reaction is 65-75℃, and the time is 4-6h.

7. The low-creep polytetrafluoroethylene composite material according to claim 3, characterized in that, In step S4, the mass ratio of the organic composite fiber, perfluorooctyl ethyl acrylate, and azobisisobutyronitrile is 30-40:10-14:0.1-0.2, and the isothermal reaction is carried out at a temperature of 70-80℃ for 5-8 hours.

8. The low-creep polytetrafluoroethylene composite material according to claim 1, characterized in that, The lubricant is either graphite or boron nitride.

9. A method for preparing a low-creep polytetrafluoroethylene composite material as described in any one of claims 1-8, characterized in that, Includes the following steps: Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and lubricant are mixed evenly, and the resulting mixed powder is placed in a preheated mold and hot-pressed. Under pressure, it is cooled to room temperature and demolded to obtain the final product.

10. The preparation method according to claim 9, characterized in that, The hot pressing temperature is 360-390℃, the pressure is 10-15MPa, and the time is 40-60min.