Low creep polytetrafluoroethylene composite and method of making same

Abstract

The application discloses a low-creep polytetrafluoroethylene composite material and a preparation method thereof, and comprises the following raw materials in parts by weight: polytetrafluoroethylene 50-60 parts, perfluoroalkoxy resin 35-45 parts, modified composite fiber 15-25 parts and lubricant 1-2 parts. The polytetrafluoroethylene and the perfluoroalkoxy resin are blended in a specific ratio to serve as a base material, and a hot-pressing process is matched, so that the core performance of the material is ensured, under the driving of the hot-pressing pressure, the molten perfluoroalkoxy resin can fully infiltrate and wrap the surface of the modified composite fiber, form a strong interface combination with the modified composite fiber, can also penetrate and fill into the gaps of PTFE skeleton particles, eliminate internal pores through a 'welding' effect, and finally form a highly dense whole, so that the anti-creep performance of the composite material is significantly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polytetrafluoroethylene materials, and particularly relates to a low-creep polytetrafluoroethylene composite material and a preparation method thereof. BACKGROUND

[0002] Polytetrafluoroethylene (PTFE) has the most excellent comprehensive performance among all engineering plastics to date due to its unique perfluorinated carbon chain structure. It has extremely excellent chemical stability and can resist the corrosion of almost all chemical media except molten alkali metals, high-temperature and high-pressure elemental fluorine. At the same time, it has a wide working temperature range (usually can serve for a long time between -196℃ and 260℃), and has the lowest friction coefficient and excellent electrical insulation performance among plastics. These unique combinations of properties make polytetrafluoroethylene widely used as seals, liners, insulation layers, anti-sticking coatings and self-lubricating bearings in key fields such as chemical industry, electronics, machinery, aerospace, etc., and it is an indispensable high-performance material in modern industry.

[0003] However, although the performance advantages of polytetrafluoroethylene are significant, its high linearity, regularity and weak intermolecular force also lead to a fatal weakness that limits its application, that is, it is prone to cold flow under load, that is, it has very poor creep resistance. This means that pure polytetrafluoroethylene products will change their shape and size irreversibly over time when subjected to continuous stress, which cannot meet the dimensional stability requirements of precision structural parts and high-load working conditions. In order to overcome this defect, the current mainstream technical means is physical filling modification, that is, adding various reinforcing fillers such as glass fibers, carbon fibers, graphite, molybdenum disulfide or bronze powder to the PTFE matrix. These fillers can improve the hardness and wear resistance of the composite material to some extent, and through their own rigidity, they can hinder the flow of the polymer matrix to some extent, thereby improving the anti-creep property of the material.

[0004] Chinese patent application CN110655741A discloses a kind of multi-element inorganic material filling modified PTFE composite material and its preparation method, according to mass percentage, including the following components: 10%-14% glass fiber, 5%-15% copper and 1%-5% molybdenum disulfide, the rest is polytetrafluoroethylene. Preparation method, including the following steps: step 1, after copper powder, molybdenum disulfide powder and glass fiber powder are treated by silane coupling agent, dry, obtain activated inorganic filling material;Step 2, activated inorganic filling material is mixed with PTFE, and is pressed into shape, to obtain PTFE-based composite material precursor;Step 3, PTFE-based composite material precursor is sintered at high temperature, to obtain multi-element inorganic material filling modified PTFE composite material. Chinese patent application CN108943779A discloses a kind of preparation method of high filler filling amount polytetrafluoroethylene composite film material, by high speed mixing, cold pressing into blank, sintering forming, turning into film, calendering post-processing method preparation a kind of inorganic filler filling amount reaches 20wt% above polytetrafluoroethylene composite film material, and by the design and preparation process of a variety of different functional inorganic filler dispersion form is prepared film structure controllable, mechanical property, electric conductivity, thermal conductivity and wear resistance performance excellent inorganic filler / polytetrafluoroethylene composite film material.

[0005] However, such traditional filling modification technology has significant defects: lack of effective interface bonding mechanism between filler and extremely inert PTFE matrix, resulting in insufficient interface bonding force between filler and matrix, under long-term or alternating load, the weak interface is prone to debonding, slipping, forming stress concentration point and damage source, resulting in stress cannot be effectively transmitted from matrix to reinforcing filler, therefore the improvement effect on anti creep performance is limited and unreliable, difficult to meet the application requirements under more severe high temperature and high load working conditions. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a low creep polytetrafluoroethylene composite material and a preparation method thereof.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

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

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

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

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

[0012] In the present application, the polytetrafluoroethylene composite material uses polytetrafluoroethylene (PTFE) and perfluoroalkoxy resin (PFA) as the base material by blending in a specific ratio, and matches the hot pressing process, which not only ensures the core performance and cost control of the material, and the PFA melts into a low viscosity fluid at the processing temperature, which can be used as a molten adhesive, under the driving of the hot pressing pressure, the molten PFA not only fully infiltrates and wraps the surface of the modified composite fiber to form a strong interfacial bond, but also penetrates and fills into the gap of the PTFE skeleton particles, eliminates internal pores through "welding" effect, and finally forms a highly dense whole, thereby significantly improving the creep resistance of the composite material.

[0013] Preferably, the preparation method of the modified composite fiber comprises the following steps:

[0014] S1, the carbon fiber is pre-burned and then added into concentrated nitric acid for immersion treatment, and after the treatment is completed, the carbon fiber is filtered, washed and dried to obtain pretreated carbon fiber;

[0015] S2, the pretreated carbon fiber in step S1 is added into a mixed solution of nickel nitrate and aluminum nitrate, and after being uniformly stirred, urea is added for hydrothermal reaction, and after the reaction is completed, the mixture is left to stand, filtered, washed and dried to obtain composite fiber;

[0016] S3, the composite fiber in step S2 is added into an ethanol aqueous solution, and then vinyltriethoxysilane is added for stirring reaction, and after the reaction is completed, the mixture is filtered, washed and dried to obtain organicized composite fiber;

[0017] S4, the organicized composite fiber in step S3 is added into DMF, and then perfluorooctyl ethyl acrylate and azobisisobutyronitrile are added for constant temperature reaction, and after the reaction is completed, the mixture is filtered, washed and dried to obtain modified composite fiber.

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

[0019] In the present application, 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 inhibit creep. By pre-burning and acid treatment of the carbon fiber, a large number of oxygen-containing functional groups are introduced on the surface of the carbon fiber, which is beneficial to the subsequent reaction.

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

[0021] In the present application, the nickel-aluminum layered double hydroxide is generated in situ on the carbon fiber through a hydrothermal reaction. The layered structure composed of numerous 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 at the microscopic level, ensuring that the subsequently grafted organic functional layer (S3 and S4) can form an extremely stable combination with the carbon fiber skeleton. When the final composite material is stressed, the stress from the PTFE / PFA matrix can be efficiently and completely transmitted to the core load-bearing carbon fiber through the nickel-aluminum layered double hydroxide, thereby effectively inhibiting the creep deformation of the matrix and significantly improving the macroscopic anti-creep performance 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 ethanol aqueous solution is 70-80%, the stirring reaction temperature is 65-75℃, and the time is 4-6 h.

[0023] In the present application, the carbon-carbon double bond active functional group is introduced onto the composite fiber by reacting vinyltriethoxysilane with the composite fiber, which is beneficial for subsequent reactions.

[0024] Preferably, in step S4, the mass ratio of the organic composite fiber to perfluorooctyl ethyl acrylate to azobisisobutyronitrile is 30-40:10-14:0.1-0.2, the constant temperature reaction temperature is 70-80℃, and the time is 5-8 h.

[0025] In the present application, perfluorooctyl ethyl acrylate is introduced onto the composite fiber through a free radical reaction. Its chemical structure is highly similar to that of the PFA / PTFE matrix, which greatly improves the physical compatibility between the fiber and the matrix. On the other hand, the long-chain perfluoroalkyl chain contained in it can deeply and physically interpenetrate and entangle with the molecular chains of the molten PFA matrix during hot pressing, forming an interface with a bonding strength far superior to simple physical contact or chemical bonds, thereby significantly improving the anti-creep performance of the composite material.

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

[0027] The application also protects a preparation method of the low-creep polytetrafluoroethylene composite material, comprising the following steps:

[0028] The polytetrafluoroethylene, the perfluoroalkoxy resin, the modified composite fiber and the lubricant are uniformly mixed to obtain a mixed powder, the mixed powder is placed in a preheated mold, hot-pressing is performed, the pressure is maintained until the mold is cooled to room temperature, and the low-creep polytetrafluoroethylene composite material is obtained after demolding.

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

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

[0031] (1) The low-creep polytetrafluoroethylene composite material provided by the application adopts polytetrafluoroethylene (PTFE) and perfluoroalkoxy resin (PFA) as a base material, and matches a hot-pressing process, so that the core performance of the material is guaranteed and the cost is controlled, and the PFA is melted into a low-viscosity fluid at a processing temperature, can be used as a molten adhesive, and can fully infiltrate and wrap the surface of the modified composite fiber under the driving of the hot-pressing pressure, form a strong interfacial bond with the modified composite fiber, penetrate and fill into the gap of the PTFE skeleton particles, eliminate internal pores through a welding effect, and finally form a highly dense whole, so that the anti-creep performance of the composite material is significantly improved.

[0032] (2) The low-creep polytetrafluoroethylene composite material provided by the application adds the modified composite fiber, adopts a multi-step surface functionalization (in-situ growth of LDH, silane coupling, and free radical graft polymerization) of carbon fiber as a core reinforcing body, and composites the carbon fiber and a polytetrafluoroethylene / perfluoroalkoxy resin (PTFE / PFA) blended base material through hot-pressing, so that the PFA melt phase effectively infiltrates the surface of the fiber and welds the PTFE base particles during the hot-pressing process, forms a dense and interfacially synergistically optimized composite structure, effectively inhibits the sliding and movement of polymer chains under load and high temperature, gives the composite material extremely excellent anti-creep performance, higher mechanical modulus and dimensional stability, and retains the inherent high and low temperature resistance, chemical corrosion resistance and other properties of the fluoropolymer base, and significantly widens the application potential of the fluoropolymer base as a load-bearing structural part under severe working conditions.

[0033] (3) The low-creep polytetrafluoroethylene composite provided by the application grows Ni-Al double hydroxide (LDH) nanosheets with a layered structure on the surface of the carbon fiber in situ, 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, a physical "anchoring" structure is formed, greatly enhancing the binding firmness between the subsequent perfluorooctyl ethyl acrylate layer and the carbon fiber body, laying a solid structural foundation for the final realization of efficient stress transfer; at the same time, the free radical graft polymerization method is innovatively used to introduce perfluorooctyl ethyl acrylate containing long chains on the fiber surface, which has a highly similar chemical structure to the PFA / PTFE matrix, which can greatly improve the physical compatibility between the fiber and the matrix on the one hand; on the other hand, the long-chain perfluoroalkyl chain contained therein will physically interpenetrate and entangle with the molten PFA matrix molecular chain during hot pressing, forming an interface bonding strength far beyond that of simple physical contact or chemical bonds, thereby significantly improving the creep resistance of the composite. DETAILED DESCRIPTION

[0034] The technical solutions of the application will be described clearly and completely below in combination with the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0035] Unless otherwise specified, the chemical reagents and materials in the application are purchased through market channels or synthesized from raw materials purchased through market channels.

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

[0037] Embodiment 1

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

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

[0040] The preparation method of the modified composite fiber comprises the following steps:

[0041] S1, carbon fibers are pre-burned at 480℃ for 1.5h, after cooling, 68% concentrated nitric acid is added, and the mixture is immersed at 75℃ for 3.5h, after treatment, filtration, washing and drying, pretreated carbon fibers are obtained;

[0042] S2, 25g of pretreated carbon fibers in step S1 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), after stirring, 30g of urea is added, and the mixture is hydrothermally reacted at 125℃ for 9h, after reaction, the mixture is left to stand for 12h, and then filtered, washed and dried to obtain composite fibers;

[0043] S3, 35g of composite fibers in step S2 is added to 800mL of an ethanol aqueous solution (the mass fraction of ethanol is 75%), then 4.5g of vinyltriethoxysilane is added, and the mixture is stirred and reacted at 70℃ for 5h, after reaction, the mixture is filtered, washed and dried to obtain organic composite fibers;

[0044] S4, 35g of organic composite fibers in step S3 is added to 900mL of DMF, then 12g of perfluoroalkyl ethyl acrylate and 0.15g of azobisisobutyronitrile are added, and the mixture is reacted at 75℃ for 7h, after reaction, the mixture is filtered, washed and dried to obtain modified composite fibers.

[0045] A preparation method of a low-creep polytetrafluoroethylene composite material, comprising the following steps:

[0046] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fibers and boron nitride are uniformly mixed to obtain a mixed powder, and the mixed powder is placed in a preheated mold for hot pressing, the hot pressing temperature is 380℃, the pressure is 13MPa, the time is 50min, and the pressure is maintained until the temperature drops to room temperature, and then the mold is demolded to obtain the low-creep polytetrafluoroethylene composite material.

[0047] Example 2

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

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

[0050] The preparation method of the modified composite fibers, comprising the following steps:

[0051] S1, carbon fibers are pre-burned at 450℃ for 2h, after cooling, 68% concentrated nitric acid is added, and the mixture is immersed at 70℃ for 4h, after treatment, filtration, washing and drying, pretreated carbon fibers are obtained;

[0052] S2, 20 g of the pretreated carbon fiber in step S1 is added into 900 mL of a mixed solution of nickel nitrate and aluminum nitrate (the concentration of nickel ions is 0.3 mol / L, and the concentration of aluminum ions is 0.15 mol / L), 25 g of urea is added after stirring uniformly, hydrothermal reaction is carried out at 120℃ for 10 h, after reaction is completed, standing is carried out for 12 h, filtration, washing and drying are carried out, and the composite fiber is obtained;

[0053] S3, 30 g of the composite fiber in step S2 is added into 800 mL of an ethanol aqueous solution (the mass fraction of ethanol is 70%), then 4 g of vinyl triethoxysilane is added, stirring reaction is carried out at 65℃ for 6 h, after reaction is completed, filtration, washing and drying are carried out, and the organic composite fiber is obtained;

[0054] S4, 30 g of the organic composite fiber in step S3 is added into 900 mL of DMF, then 10 g of perfluoroalkyl ethyl acrylate and 0.1 g of azobisisobutyronitrile are added, constant-temperature reaction is carried out at 70℃ for 8 h, after reaction is completed, filtration, washing and drying are carried out, and the modified composite fiber is obtained.

[0055] A preparation method of a low-creep polytetrafluoroethylene composite material, comprising the following steps:

[0056] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are uniformly mixed to obtain a mixed powder, and the mixed powder is placed in a preheated mold to perform hot pressing forming, the temperature of hot pressing is 380℃, the pressure is 13 MPa, the time is 50 min, and the pressure is kept to drop to room temperature, and the modified composite fiber is obtained after demolding.

[0057] Example 3

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

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

[0060] The preparation method of the modified composite fiber comprises the following steps:

[0061] S1, carbon fiber is pre-burned at 500℃ for 1 h, and after cooling, the carbon fiber is immersed in concentrated nitric acid with a mass concentration of 68% at 80℃ for 3 h, after treatment, filtration, washing and drying are carried out, and pretreated carbon fiber is obtained;

[0062] S2, 30 g of the pretreated carbon fiber in step S1 is added into 1000 mL of a mixed solution of nickel nitrate and aluminum nitrate (the concentration of nickel ions is 0.5 mol / L, and the concentration of aluminum ions is 0.25 mol / L), 35 g of urea is added after stirring uniformly, hydrothermal reaction is carried out at 130℃ for 8 h, after reaction is completed, standing is carried out for 12 h, filtration, washing and drying are carried out, and the composite fiber is obtained;

[0063] S3, 40 g of the composite fiber in step S2 is added into 800 mL of an ethanol aqueous solution (the mass fraction of ethanol is 80%), then 5 g of vinyl triethoxysilane is added, and the reaction is stirred at 75°C for 4 h. After the reaction is completed, filtration, washing, and drying are performed to obtain the organic composite fiber;

[0064] S4, 40 g of the organic composite fiber in step S3 is added into 900 mL of DMF, then 14 g of perfluorooctyl ethyl acrylate and 0.2 g of azobisisobutyronitrile are added, and the reaction is performed at 80°C for 5 h. After the reaction is completed, filtration, washing, and drying are performed to obtain the modified composite fiber.

[0065] A preparation method of a low-creep polytetrafluoroethylene composite material, comprising the following steps:

[0066] The polytetrafluoroethylene, the perfluoroalkoxy resin, the modified composite fiber, and the boron nitride are uniformly mixed to obtain a mixed powder, and the mixed powder is placed in a preheated mold to perform hot pressing molding. The temperature of the hot pressing is 380°C, the pressure is 13 MPa, and the time is 50 min. The pressure is maintained until the temperature drops to room temperature. After demolding, the low-creep polytetrafluoroethylene composite material is obtained.

[0067] Comparative Example 1

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

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

[0070] A preparation method of the modified composite fiber, comprising the following steps:

[0071] S1, carbon fiber is pre-burned at 480°C for 1.5 h, and then is immersed in concentrated nitric acid with a mass concentration of 68% at 75°C for 3.5 h. After the treatment is completed, filtration, washing, and drying are performed to obtain the pretreated carbon fiber.

[0072] S2, 25 g of the pretreated carbon fiber in step S1 is added into 950 mL of a mixed solution of nickel nitrate and aluminum nitrate (the concentration of nickel ions is 0.4 mol / L, and the concentration of aluminum ions is 0.2 mol / L). After being uniformly stirred, 30 g of urea is added, and the hydrothermal reaction is performed at 125°C for 9 h. After the reaction is completed, the solution is left to stand for 12 h. Then, filtration, washing, and drying are performed to obtain the composite fiber.

[0073] S3, 35 g of the composite fiber in step S2 is added into 800 mL of an ethanol aqueous solution (the mass fraction of ethanol is 75%), then 4.5 g of vinyl triethoxysilane is added, and the reaction is stirred at 70°C for 5 h. After the reaction is completed, filtration, washing, and drying are performed to obtain the modified composite fiber.

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

[0075] The polytetrafluoroethylene, the perfluoroalkoxy resin, the modified composite fiber and the boron nitride are uniformly mixed to obtain a mixed powder, which is placed in a preheated mold to perform hot pressing, the temperature of the hot pressing is 380℃, the pressure is 13MPa, the time is 50min, and the temperature is lowered to room temperature under the state of maintaining the pressure, and the low-creep polytetrafluoroethylene composite material is obtained after demolding.

[0076] Compared with Example 1, the modified composite fiber in the present comparative example does not introduce perfluoroalkyl ethyl acrylate.

[0077] Comparative Example 2

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

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

[0080] A method for preparing the modified composite fiber, comprising the following steps:

[0081] S1, carbon fibers are pre-burned at 480℃ for 1.5h, and after cooling, they are added into concentrated nitric acid with a mass concentration of 68%, and then immersed at 75℃ for 3.5h, and after the treatment is completed, the carbon fibers are filtered, washed and dried to obtain pretreated carbon fibers;

[0082] S2, 25g of the pretreated carbon fibers in step S1 are added into 800mL of an ethanol aqueous solution (the mass fraction of ethanol is 75%), and then 4.5g of vinyl triethoxysilane is added, and then stirred and reacted at 70℃ for 5h, and after the reaction is completed, the carbon fibers are filtered, washed and dried to obtain organicized composite fibers;

[0083] S3, 35g of the organicized composite fibers in step S2 are added into 900mL of DMF, and then 12g of perfluoroalkyl ethyl acrylate and 0.15g of azobisisobutyronitrile are added, and then reacted at 75℃ for 7h, and after the reaction is completed, the composite fibers are filtered, washed and dried to obtain modified composite fibers.

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

[0085] The polytetrafluoroethylene, the perfluoroalkoxy resin, the modified composite fiber and the boron nitride are uniformly mixed to obtain a mixed powder, which is placed in a preheated mold to perform hot pressing, the temperature of the hot pressing is 380℃, the pressure is 13MPa, the time is 50min, and the temperature is lowered to room temperature under the state of maintaining the pressure, and the low-creep polytetrafluoroethylene composite material is obtained after demolding.

[0086] The modified composite fiber in the present comparative example does not introduce nickel-aluminum layered double hydroxide compared with example 1.

[0087] Comparative example 3

[0088] A low-creep polytetrafluoroethylene composite material comprises the following raw materials in parts by weight:

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

[0090] The preparation method of the modified composite fiber comprises the following steps:

[0091] S1, carbon fiber is pre-burned at 480℃ for 1.5h, after cooling, 68% mass concentration of concentrated nitric acid is added, and immersed at 75℃ for 3.5h, after treatment, filtration, washing and drying, pretreated carbon fiber is obtained;

[0092] S2, 25g of pretreated carbon fiber, 10g of nickel-aluminum layered double hydroxide and 12g of perfluoroalkyl ethyl propenoate in step S1 are uniformly mixed to obtain a modified composite fiber.

[0093] The preparation method of the nickel-aluminum layered double hydroxide is as follows: 30g of urea is added to 950mL of 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 hydrothermal reaction is carried out at 125℃ for 9h, after reaction, standing for 12h, filtration, washing and drying are carried out, and the nickel-aluminum layered double hydroxide is obtained.

[0094] A preparation method of a low-creep polytetrafluoroethylene composite material comprises the following steps:

[0095] Polytetrafluoroethylene, perfluoroalkoxy resin, modified composite fiber and boron nitride are uniformly mixed, the obtained mixed powder is placed in a preheated mold, and hot pressing is carried out, the temperature of hot pressing is 380℃, the pressure is 13MPa, the time is 50min, and the pressure is maintained to room temperature, and after demolding, the low-creep polytetrafluoroethylene composite material is obtained.

[0096] The modified composite fiber in the present comparative example is obtained by physical blending of pretreated carbon fiber, nickel-aluminum layered double hydroxide and perfluoroalkyl ethyl propenoate compared with example 1.

[0097] The low-creep polytetrafluoroethylene composite materials prepared from Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, wherein the tensile strength and elongation at break were tested according to the standard test GB / T 1040.2-2022 "Determination of the tensile properties of plastics - Part 2: test conditions for moulded and extruded plastics", the sample size was 180mm x 10mm x 4mm, and the tensile speed was 10mm / min; the creep rate was tested according to the standard GB / T 11546.1-2008 "Determination of the creep properties of plastics - Part 1: tensile creep", the sample size was 120x10x4mm, the test temperature was 150℃, the stress was 20MPa, and the time was 100h; the volume wear rate was tested according to the standard GB / T 3960-2016 "Plastics - Method of sliding friction and wear testing", the test temperature was 25℃, the counter-plate material was quenched GCr15 bearing steel with a surface roughness Ra = 0.2μm, the applied normal load was 10N, the rotation speed was 200r / min, and the total sliding distance was 1000m; and the test results are shown in Table 1 below:

[0098] Table 1

[0099] Tensile strength (MPa) Elongation at break (%) Creep rate (%) Volume wear rate (x 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 the present application has good mechanical properties, and also has low creep rate and volume wear rate, thereby widening the application scenarios of polytetrafluoroethylene materials under severe working conditions.

[0101] The above content is a further detailed description of the present application in combination with specific implementation examples, and cannot be considered as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, any modification, equivalent replacement and improvement made without departing from the concept and principle of the present application should be considered as falling within the protection scope of the present application.

[0102] It is easy for those skilled in the art to understand that the above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

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. 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.

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, 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.

4. The low-creep polytetrafluoroethylene composite material according to claim 1, 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.

5. The low-creep polytetrafluoroethylene composite material according to claim 1, 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.

6. The low-creep polytetrafluoroethylene composite material according to claim 1, 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.

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

8. A method for preparing a low-creep polytetrafluoroethylene composite material as described in any one of claims 1-7, 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.

9. The preparation method according to claim 8, characterized in that, The hot pressing temperature is 360-390℃, the pressure is 10-15MPa, and the time is 40-60min.