Preparation and application of modified polytetrafluoroethylene composite material

Abstract

The invention relates to the technical field of composite materials, and discloses preparation and application of a modified polytetrafluoroethylene composite material, a C-F group in a fluorine-containing semi-aromatic polyamide molecular chain is extremely similar to a C-F group in polytetrafluoroethylene, and the fluorine-containing semi-aromatic polyamide molecular chain and the polytetrafluoroethylene have good compatibility; in the friction process, the fluorine-containing semi-aromatic polyamide can effectively bear friction load, plays a role of a physical crosslinking point and is tightly combined with the polytetrafluoroethylene, so that the movement of a polytetrafluoroethylene chain segment is limited, slippage between wafers is hindered, the volume wear rate of the composite material is reduced, and the wear resistance is improved; the rigid polyamide particles serve as rigid supporting points in a matrix and play a role in uniformly distributing loads, so that the modified polytetrafluoroethylene has good creep resistance; meanwhile, the mechanical property is good, stress transfer is facilitated, a certain load can be borne, and the reinforcing and toughening effects are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite materials, and specifically to the preparation and application of a modified polytetrafluoroethylene composite material. Background Art

[0002] Polytetrafluoroethylene is an engineering plastic with very excellent comprehensive properties, known as the "king of plastics", and has unique properties such as excellent chemical corrosion resistance, thermal stability and non-stickiness, and is widely used in many fields such as aerospace, machinery manufacturing, electronic and electrical, and petrochemical industries. However, as an engineering plastic, while polytetrafluoroethylene has excellent properties, it also has some deficiencies such as poor wear resistance, high-temperature creep resistance, and voids inside the molecules. Therefore, in order to improve the performance defects of polytetrafluoroethylene and expand its application range, it is necessary to appropriately modify it.

[0003] Due to the mutual repulsion of fluorine atoms in the polytetrafluoroethylene molecular chain, the intermolecular attraction of polytetrafluoroethylene is relatively small. Under the action of external force, the polytetrafluoroethylene molecules are prone to slip, and coupled with its low hardness, it causes large losses during the friction process, restricting its use on friction components. Currently, inorganic reinforcing components such as glass fiber, carbon fiber, graphite, molybdenum disulfide, and non-ferrous metal powders are commonly used to fill and modify polytetrafluoroethylene to improve its strength, wear resistance, and dimensional stability. However, the compatibility of these fillers with polytetrafluoroethylene is poor, often causing an increase in the friction coefficient of the composite material and weakening the anti-friction effect of polytetrafluoroethylene, thus restricting the wide application of polytetrafluoroethylene composite materials. For example, the patent with publication number CN1304477C discloses a low-friction and high-wear-resistant polytetrafluoroethylene composite material and its preparation method. Using polytetrafluoroethylene as a self-lubricating material, adding molybdenum disulfide and nano-aluminum oxide as modified fillers, and obtaining a polytetrafluoroethylene composite material after high-speed mixing, molding, and sintering. Although the wear life of the prepared composite material is improved to a certain extent, the nano-aluminum oxide used in the material has problems of difficult dispersion during industrial batch operation, and the feasibility is not strong.

[0004] The compatibility between organic polymer fillers and the polytetrafluoroethylene matrix is good, and the affinity is large, which can improve the anti-creep property, compression and wear resistance of polytetrafluoroethylene. Polyamide is an engineering plastic with repeating amide groups on the molecular main chain, and has excellent corrosion resistance, wear resistance and mechanical properties, and has a very wide application in the field of wear-resistant materials such as gears and bearings. In the present invention, a rigid fluorine-containing semi-aromatic polyamide with a structure similar to that of polytetrafluoroethylene is synthesized. When blended with polytetrafluoroethylene, the interfacial compatibility is improved, thereby enhancing the wear resistance, anti-creep property and mechanical properties of the prepared composite material. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies existing in the prior art, and provides a preparation method and application of a modified polytetrafluoroethylene composite material, which solves the problem of poor wear resistance of polytetrafluoroethylene.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a modified polytetrafluoroethylene composite material is carried out according to the following steps:

[0008] (1) Under a nitrogen atmosphere, 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl, lithium chloride and N,N-dimethylacetamide are added to a reaction flask. After stirring and dissolving, pyridine and succinyl chloride are added, and stirring reaction is carried out. After the reaction is completed, deionized water is added for precipitation, filtration, washing with acetone, and drying to obtain a fluorine-containing semi-aromatic polyamide.

[0009] (2) Polytetrafluoroethylene and the fluorine-containing semi-aromatic polyamide are added to a high-speed mixer, and mixed at a rotation speed of 1800 - 2200 r / min for 5 - 10 min, then left standing for 12 - 24 h, spread out in a mold, cold-pressed and formed by a flat vulcanizing machine, kept under pressure at 50 - 60 MPa for 30 - 50 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering, and cooled with the furnace to obtain a modified polytetrafluoroethylene composite material.

[0010] Preferably, in step (1), the proportional relationship of 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl, lithium chloride, pyridine and succinyl chloride is 1 mol : (2 - 2.5) mol : (1.1 - 1.2) mol : (1.05 - 1.1) mol.

[0011] Preferably, in step (1), the reaction temperature is 0 - 5 °C and the reaction time is 5 - 12 h.

[0012] Preferably, in step (2), the proportional relationship of polytetrafluoroethylene and the fluorine-containing semi-aromatic polyamide is 100 g : (5 - 25) g.

[0013] Preferably, in step (2), the heating rate during sintering is 50 - 65 °C / min, the sintering temperature is 350 - 400 °C, the sintering time is 3 - 5 h, the cooling rate is 40 - 55 °C / min, and heat preservation is carried out at 280 - 320 °C for 20 - 40 min during the cooling process.

[0014] Preferably, the preparation method of 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl in step (1) is carried out according to the following steps:

[0015] S1. Under a nitrogen atmosphere, add 3,3'-dinitro-4,4'-dihydroxybiphenyl, triethylamine, and dichloromethane to a reaction flask. After stirring evenly in an ice-water bath, add pentafluoropropionyl chloride, and stir at 20 - 35 °C for 2 - 5 h. Concentrate under reduced pressure, purify by column chromatography, and dry to obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl.

[0016] S2. Under a nitrogen atmosphere, add 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and ethanol to a reaction flask. After stirring evenly, add ammonium chloride, iron powder, and deionized water, and stir for reaction. After the reaction is completed, cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl.

[0017] Preferably, in step S1, the molar ratio of 3,3'-dinitro-4,4'-dihydroxybiphenyl, triethylamine, and pentafluoropropionyl chloride is 1 mol : (2.1 - 3) mol : (2.05 - 2.2) mol.

[0018] Preferably, in step S2, the molar ratio of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl, ammonium chloride, and iron powder is 1 mol : (4 - 8) mol : (5 - 10) mol.

[0019] Preferably, in step S2, the reaction temperature is 50 - 65 °C, and the reaction time is 3 - 8 h.

[0020] Adopting the above technical solution, the beneficial effects of the present invention are as follows:

[0021] In the present invention, first, 3,3'-dinitro-4,4'-dihydroxybiphenyl and pentafluoropropionyl chloride undergo an esterification reaction under the action of triethylamine to obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl. Then, in a reduction system of iron powder and ammonium chloride, a nitro reduction reaction occurs to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl. Then, it undergoes a polymerization reaction with succinyl chloride to obtain a fluorine-containing semi-aromatic polyamide. Finally, it is mixed, pressed, and sintered with polytetrafluoroethylene at high speed to obtain a modified polytetrafluoroethylene composite material.

[0022] Polyamide is a type of heat-resistant polymer material with a very stable aromatic structural unit, featuring outstanding thermal stability and high-temperature resistance. The semi-aromatic polyamide molecular chain contains both benzene rings and aliphatic chain segments, possessing properties such as high strength, high heat resistance, and low water absorption that are superior to those of aliphatic polyamides, as well as better molding and processing properties than aromatic polyamides. In the fluorinated semi-aromatic polyamide molecular chain prepared by the present invention, the C-F group in the fluorinated group is extremely similar to the C-F group in polytetrafluoroethylene. During the mixing process, based on the principle of similar compatibility, there is better compatibility between the two. During the friction process, the polyamide effectively bears the friction load, acting as a physical cross-linking point, which can prevent the molecular chain from moving easily and tightly binds with polytetrafluoroethylene to form a relatively complete integrated structure. This reduces the movement space of the polytetrafluoroethylene chain segments, restricts the movement of the molecular chain, hinders the slip between the wafers, and the wear resistance of the polyamide particles is superior to that of the polytetrafluoroethylene matrix. During the friction process, it will gradually accumulate in the wear scar interface area, resulting in a gradual decrease in the volume wear rate of the composite material and an improvement in the wear resistance.

[0023] When the fluorinated semi-aromatic polyamide is blended with polytetrafluoroethylene, they have good compatibility, there is no obvious interface between the two, and they are firmly bonded. When subjected to external forces, it is not easy for slippage and detachment to occur at the interface between the two. At the same time, the rigid polyamide particles act as rigid support points in the polytetrafluoroethylene matrix, playing a role in evenly distributing the load, reducing the compression deformation of the blend, and greatly improving the compression resistance, making the modified polytetrafluoroethylene have good anti-creep performance. The fluorinated semi-aromatic polyamide itself has rigidity and good mechanical properties, and also contains a molecular structure similar to that of polytetrafluoroethylene, making the polyamide have good dispersibility in the matrix, capable of forming bonds with polytetrafluoroethylene, enhancing the interfacial adhesion between the particles and the matrix, facilitating stress transfer, and being able to bear external loads to a certain extent, having the effect of enhancing and toughening. Detailed implementation methods

[0024] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further elaborates on the present invention in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] 4,4'-Dihydroxybiphenyl, with a CAS number of 92-88-6.

[0026] Pentafluoropropionyl chloride, with a CAS number of 422-59-3.

[0027] Succinyl chloride, with a CAS number of 543-20-4.

[0028] Preparation of 3,3'-dinitro-4,4'-dihydroxybiphenyl: Add 12.2 g of 4,4'-dihydroxybiphenyl and 250 mL of acetone to a three-necked flask equipped with a condenser and a dropping funnel. After stirring and dissolving at 60 °C, add 11.9 g of a nitric acid solution with a mass fraction of 65%. Then react at 60 °C for 6 h, filter, wash with acetone, and dry to obtain 3,3'-dinitro-4,4'-dihydroxybiphenyl (the structural formula is ).

[0029] Example 1

[0030] (1) Under a nitrogen atmosphere, add 50 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 140 mmol of triethylamine, and 1250 mL of dichloromethane to a reaction flask. After stirring evenly in an ice-water bath, add 105 mmol of pentafluoropropionyl chloride and stir at 25 °C for 4 h. Concentrate under reduced pressure, and use ethyl acetate and petroleum ether (volume ratio 1:2) as the eluent for purification by column chromatography. After drying, obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl. The preparation process is as follows:

[0031]

[0032] (2) Under a nitrogen atmosphere, add 35 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and 420 mL of ethanol to a reaction flask. After stirring evenly, add 210 mmol of ammonium chloride, 280 mmol of iron powder, and 140 mL of deionized water, and react at 55 °C for 6 h. Cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl. The preparation process is as follows:

[0033]

[0034] (3) Under a nitrogen atmosphere, add 20 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, 48 mmol of lithium chloride, and 170 mL of N,N-dimethylacetamide to a reaction flask. After stirring and dissolving, add 23 mmol of pyridine and 21.6 mmol of succinyl chloride, and react at 2 °C for 10 h. Add deionized water to precipitate, filter, wash with acetone, and dry to obtain a fluorinated semi-aromatic polyamide. The principle of the preparation process is as follows:

[0035]

[0036] (4) Add 100 g of polytetrafluoroethylene and 5 g of fluorine-containing semi-aromatic polyamide into a high-speed mixer, mix at a rotation speed of 2000 r / min for 8 min, let it stand for 16 h, lay it flat in a mold, and cold press it into shape with a flat vulcanizing machine. Keep the pressure at 55 MPa for 45 min, demold and eject, then add it into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 60 °C / min, the sintering temperature is 360 °C, the sintering time is 4 h, the cooling rate is 45 °C / min, keep the temperature at 300 °C for 30 min during the cooling process, and cool with the furnace to obtain the modified polytetrafluoroethylene composite material.

[0037] Example 2

[0038] (1) Under a nitrogen atmosphere, add 30 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 63 mmol of triethylamine and 600 mL of dichloromethane into a reaction flask. After stirring evenly in an ice-water bath, add 61.5 mmol of pentafluoropropionyl chloride, stir at 35 °C for 2 h, concentrate under reduced pressure, and purify by column chromatography using ethyl acetate and petroleum ether (volume ratio 1:2) as the eluent. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl is obtained.

[0039] (2) Under a nitrogen atmosphere, add 15 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl and 150 mL of ethanol into a reaction flask. After stirring evenly, add 60 mmol of ammonium chloride, 75 mmol of iron powder and 45 mL of deionized water, react at 65 °C for 3 h, cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl.

[0040] (3) Under a nitrogen atmosphere, add 10 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl, 20 mmol of lithium chloride and 50 mL of N,N-dimethylacetamide into a reaction flask. After stirring and dissolving, add 11 mmol of pyridine and 10.5 mmol of succinyl chloride, react at 5 °C for 5 h, add deionized water to precipitate, filter, wash with acetone, and dry to obtain the fluorine-containing semi-aromatic polyamide.

[0041] (4) Add 100 g of polytetrafluoroethylene and 10 g of fluorine-containing semi-aromatic polyamide into a high-speed mixer, mix at a rotation speed of 2200 r / min for 5 min, let stand for 12 h, lay it flat in a mold, and cold press and form it with a flat vulcanizing machine. Keep the pressure at 60 MPa for 30 min, demold and eject, then add it into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 65 °C / min, the sintering temperature is 400 °C, the sintering time is 3 h, the cooling rate is 55 °C / min, keep the temperature at 320 °C for 20 min during the cooling process, and cool with the furnace to obtain the modified polytetrafluoroethylene composite material.

[0042] Example 3

[0043] (1) Under a nitrogen atmosphere, add 18 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 54 mmol of triethylamine and 540 mL of dichloromethane into a reaction flask. After stirring evenly in an ice-water bath, add 39.6 mmol of pentafluoropropionyl chloride, stir at 20 °C for 5 h, concentrate under reduced pressure, and purify by column chromatography using ethyl acetate and petroleum ether (volume ratio 1:2) as the eluent. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl is obtained.

[0044] (2) Under a nitrogen atmosphere, add 12 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl and 180 mL of ethanol into a reaction flask. After stirring evenly, add 96 mmol of ammonium chloride, 120 mmol of iron powder and 60 mL of deionized water, react at 50 °C for 8 h, cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl.

[0045] (3) Under a nitrogen atmosphere, add 5 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl, 12.5 mmol of lithium chloride and 50 mL of N,N-dimethylacetamide into a reaction flask. After stirring and dissolving, add 6 mmol of pyridine and 5.5 mmol of succinyl chloride, react at 0 °C for 12 h, add deionized water to precipitate, filter, wash with acetone, and dry to obtain the fluorine-containing semi-aromatic polyamide.

[0046] (4) Add 100 g of polytetrafluoroethylene and 15 g of fluorine-containing semi-aromatic polyamide into a high-speed mixer, mix at a rotation speed of 1800 r / min for 10 min, let stand for 24 h, lay flat in a mold, and cold press and form with a flat vulcanizing machine. Keep the pressure at 50 MPa for 50 min, demold and eject, then add it into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 50 °C / min, the sintering temperature is 350 °C, the sintering time is 5 h, the cooling rate is 40 °C / min, keep the temperature at 280 °C for 40 min during the cooling process, and cool with the furnace to obtain the modified polytetrafluoroethylene composite material.

[0047] Example 4

[0048] (1) Under a nitrogen atmosphere, add 40 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 100 mmol of triethylamine and 1040 mL of dichloromethane into a reaction flask. After stirring evenly in an ice-water bath, add 86 mmol of pentafluoropropionyl chloride, stir at 30 °C for 3 h, concentrate under reduced pressure, and purify by column chromatography using ethyl acetate and petroleum ether (volume ratio 1:2) as the eluent. After drying, obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl.

[0049] (2) Under a nitrogen atmosphere, add 25 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl and 350 mL of ethanol into a reaction flask. After stirring evenly, add 175 mmol of ammonium chloride, 225 mmol of iron powder and 75 mL of deionized water, react at 55 °C for 6 h, cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl.

[0050] (3) Under a nitrogen atmosphere, add 15 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl, 33 mmol of lithium chloride and 120 mL of N,N-dimethylacetamide into a reaction flask. After stirring and dissolving, add 17.4 mmol of pyridine and 15.9 mmol of succinyl chloride, react at 0 °C for 8 h, add deionized water to precipitate, filter, wash with acetone, and dry to obtain the fluorine-containing semi-aromatic polyamide.

[0051] (4) Add 100 g of polytetrafluoroethylene and 20 g of fluorine-containing semi-aromatic polyamide into a high-speed mixer, mix at a rotation speed of 2100 r / min for 9 min, let stand for 20 h, lay them flat in a mold, and cold press them into shape using a flat vulcanizer. Keep the pressure at 60 MPa for 40 min, demold and eject, then add them into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 60 °C / min, the sintering temperature is 360 °C, the sintering time is 3 h, the cooling rate is 50 °C / min, keep the temperature at 310 °C for 25 min during the cooling process, and cool with the furnace to obtain the modified polytetrafluoroethylene composite material.

[0052] Example 5

[0053] (1) Under a nitrogen atmosphere, add 12 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 32.4 mmol of triethylamine, and 300 mL of dichloromethane into a reaction flask. After stirring evenly in an ice-water bath, add 24.6 mmol of pentafluoropropionyl chloride, stir at 35 °C for 4 h, concentrate under reduced pressure, and purify by column chromatography using ethyl acetate and petroleum ether (volume ratio 1:2) as the eluent. After drying, obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl.

[0054] (2) Under a nitrogen atmosphere, add 6 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate) biphenyl and 66 mL of ethanol into a reaction flask. After stirring evenly, add 42 mmol of ammonium chloride, 48 mmol of iron powder, and 30 mL of deionized water, react at 55 °C for 6 h, cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl.

[0055] (3) Under a nitrogen atmosphere, add 3 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate) biphenyl, 7.2 mmol of lithium chloride, and 24 mL of N,N-dimethylacetamide into a reaction flask. After stirring and dissolving, add 3.6 mmol of pyridine and 3.3 mmol of succinyl chloride, react at 0 °C for 9 h, add deionized water to precipitate, filter, wash with acetone, and dry to obtain the fluorine-containing semi-aromatic polyamide.

[0056] (4) Add 100 g of polytetrafluoroethylene and 25 g of fluorine-containing semi-aromatic polyamide into a high-speed mixer, mix at a rotation speed of 2000 r / min for 10 min, let stand for 16 h, lay flat in a mold, and cold press and form using a flat vulcanizing machine. Keep the pressure at 60 MPa for 50 min, demold and eject, then add it into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 55 °C / min, the sintering temperature is 400 °C, the sintering time is 3 h, the cooling rate is 40 °C / min, keep the temperature at 310 °C for 35 min during the cooling process, and cool with the furnace to obtain the modified polytetrafluoroethylene composite material.

[0057] Comparative Example 1

[0058] Add 100 g of polytetrafluoroethylene into a high-speed mixer, mix at a rotation speed of 2000 r / min for 8 min, let stand for 16 h, lay flat in a mold, and cold press and form using a flat vulcanizing machine. Keep the pressure at 55 MPa for 45 min, demold and eject, then add it into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 60 °C / min, the sintering temperature is 360 °C, the sintering time is 4 h, the cooling rate is 45 °C / min, keep the temperature at 300 °C for 30 min during the cooling process, and cool with the furnace to obtain the polytetrafluoroethylene material.

[0059] Comparative Example 2

[0060] (1) Under a nitrogen atmosphere, add 20 mmol of 4,4'-diaminodiphenyl (structural formula is )), 48 mmol of lithium chloride and 170 mL of N,N-dimethylacetamide into a reaction flask. After stirring and dissolving, add 23 mmol of pyridine and 21.6 mmol of succinyl chloride, react at 2 °C for 10 h, add deionized water for precipitation, filter, wash with acetone, and dry to obtain the semi-aromatic polyamide.

[0061] (2) Add 100 g of polytetrafluoroethylene and 5 g of semi-aromatic polyamide into a high-speed mixer, mix at a rotation speed of 2000 r / min for 8 min, let stand for 16 h, lay flat in a mold, and cold press and form using a flat vulcanizing machine. Keep the pressure at 55 MPa for 45 min, demold and eject, then add it into a vacuum carbon tube furnace for sintering. The heating rate during sintering is 60 °C / min, the sintering temperature is 360 °C, the sintering time is 4 h, the cooling rate is 45 °C / min, keep the temperature at 300 °C for 30 min during the cooling process, and cool with the furnace to obtain the modified polytetrafluoroethylene composite material.

[0062] Friction and wear performance test: The test is carried out with reference to Standard GB / T 3960-2016, the rotation speed is 200 r / min, the load is 200 N, the test time is 2 h, and the specimen size is 30 mm × 5 mm × 10 mm.

[0063]

[0064]

[0065] Polytetrafluoroethylene is a self-lubricating material with weak intermolecular attractive forces and easy slippage between molecular chains, resulting in poor wear resistance. As can be seen from the test results in the above table, as the content of fluorinated semi-aromatic polyamide increases, the friction coefficient and volume wear rate of the modified polytetrafluoroethylene composite material both show a downward trend. Among them, the decrease in the volume wear rate is very significant. Comparative example 1 is pure polytetrafluoroethylene, and its volume wear rate is 1.35×10 -3 mm 3 / (N·m). The volume wear rate of Example 4 is only 2.96×10 -6 mm 3 / (N·m). This is because fluorinated semi-aromatic polyamide has a high modulus and strong rigidity, and the C-F groups in its fluorine-containing groups of molecular chains are very similar to the C-F groups in polytetrafluoroethylene. Therefore, during the mixing process, according to the principle of similar compatibility, there is better compatibility between the two. During the friction process, polyamide effectively bears the friction load. Appropriate addition will reduce the movement space of polytetrafluoroethylene chain segments, limit the movement of molecular chains, and hinder the slippage between wafers. The wear resistance of polyamide particles is better than that of the matrix. During the friction process, polyamide will gradually accumulate in the wear scar interface area, bear the main external load, and at the same time, rigid aromatic polyamide particles can effectively limit the slippage between polytetrafluoroethylene molecular chains, making the volume wear rate of the composite material gradually decrease and the wear resistance improved.

[0066] Comparative example 1 is pure polytetrafluoroethylene, which has a high volume wear rate and poor wear resistance. Comparative example 2 is a composite material of semi-aromatic polyamide and polytetrafluoroethylene, which has a certain effect of improving wear resistance, but does not contain a structure similar to polytetrafluoroethylene, resulting in poor compatibility during the blending process of the composite material and its wear resistance being inferior to that of the examples.

[0067] Compressive creep performance: The prepared composite material is made into a test sample with dimensions of 10mm×12mm×12mm. The test temperature is 25°C and 150°C, the test pressure is 10MPa, and the test time is 48h.

[0068]

[0069] Compressive creep refers to the irreversible plastic deformation of a material over time under a constant temperature and a constant stress below the yield limit of the material. The magnitude of the instantaneous deformation after applying an external load reflects the level of the compressive modulus of the material. The smaller the deformation amount, the higher the compressive modulus of the material. The compressive creep test value of the present invention is the difference between the total deformation 48 hours after the external force is applied and the instantaneous deformation within 10 seconds after the application.

[0070] As can be seen from the test results in the above table, as the content of the fluorinated semi-aromatic polyamide increases, the compressive creep value of the modified polytetrafluoroethylene composite material decreases. The minimum compressive creep at 25°C reaches 2.16%, and the minimum compressive creep value at 150°C is 10.89%. This indicates that the addition of the fluorinated semi-aromatic polyamide effectively improves the creep performance of the composite material. This is because the fluorinated semi-aromatic polyamide has good compatibility when blended with polytetrafluoroethylene, there is no obvious interface between the two, and the bonding is firm. When subjected to an external force, slippage and detachment are not likely to occur at the interface between the two. At the same time, the rigid polyamide particles restrict the movement of the polytetrafluoroethylene chain segments, and large-area slippage of banded crystals is not easily generated. And an appropriate amount of polyamide particles act as rigid support points in the matrix, playing a role in evenly distributing the load. Eventually, the compressive deformation of the blend decreases, and the compressive resistance is greatly improved, thereby enabling the modified polytetrafluoroethylene to have good anti-creep performance.

[0071] Hardness test: The Brinell hardness of the composite material was measured using a Brinell hardness tester, and the average value was obtained by measuring three times.

[0072] Hardness (HB) Example 1 15.2 Example 2 17.6 Example 3 18.0 Example 4 20.7 Example 5 16.4 Comparative Example 1 8.9 Comparative Example 2 13.6

[0073] As can be seen from the test results in the above table, as the content of the fluorinated semi-aromatic polyamide increases, the hardness of the modified polytetrafluoroethylene composite material is effectively improved. This is because the fluorinated semi-aromatic polyamide itself has rigidity and good mechanical properties, and also contains a molecular structure similar to that of polytetrafluoroethylene, making the polyamide have good dispersibility in the matrix. Therefore, it can be fully adsorbed and bonded with the polytetrafluoroethylene matrix, thereby enhancing the interfacial adhesion between the particles and the matrix, facilitating stress transfer. Thus, the composite material can bear a certain load, playing a role in enhancing toughness and increasing the hardness of the composite material.

[0074] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, or improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a modified polytetrafluoroethylene composite material, characterized in that: The preparation method is carried out according to the following steps: (1) Under a nitrogen atmosphere, 3,3'-diamino-4,4'-di(pentafluoropropionate)biphenyl, lithium chloride and N,N-dimethylacetamide are added to a reaction flask, stirred and dissolved, pyridine and succinyl chloride are added, stirred and reacted, after the reaction is completed, deionized water is added for precipitation, filtered, washed with acetone, and dried to obtain a fluorinated semi-aromatic polyamide; (2) Add polytetrafluoroethylene and fluorine-containing semi-aromatic polyamide into a high-speed mixer, mix at a speed of 1800-2200 r / min for 5-10 min, let stand for 12-24 h, spread flat in a mold, and cold-press molded using a flat vulcanizer. Maintain the pressure at 50-60 MPa for 30-50 min, demold and eject, then add into a vacuum carbon tube furnace for sintering, and cool with the furnace to obtain a modified polytetrafluoroethylene composite material.

2. The method for preparing the modified polytetrafluoroethylene composite material according to claim 1, characterized in that: In the step (1), the ratio of 3,3'-diamino-4,4'-di(pentafluoropropionate)biphenyl, lithium chloride, pyridine and succinyl chloride is 1 mol:(2-2.5) mol:(1.1-1.2) mol:(1.05-1.1) mol.

3. The method for preparing the modified polytetrafluoroethylene composite material according to claim 1, characterized in that: In the step (1), the reaction temperature is 0-5°C and the reaction time is 5-12h.

4. The method for preparing the modified polytetrafluoroethylene composite material according to claim 1, characterized in that: In the step (2), the ratio of polytetrafluoroethylene to fluorine-containing semi-aromatic polyamide is 100 g:(5-25) g.

5. The method for preparing the modified polytetrafluoroethylene composite material according to claim 1, characterized in that: In the step (2), the heating rate during sintering is 50-65°C / min, the sintering temperature is 350-400°C, the sintering time is 3-5h, the cooling rate is 40-55°C / min, and the temperature is kept at 280-320°C for 20-40min during the cooling process.

6. The method for preparing the modified polytetrafluoroethylene composite material according to claim 1, characterized in that: The preparation method of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl in step (1) is carried out according to the following steps: S1. Under a nitrogen atmosphere, add 3,3'-dinitro-4,4'-dihydroxybiphenyl, triethylamine and dichloromethane to a reaction flask, stir evenly in an ice-water bath, add pentafluoropropionyl chloride, stir at 20-35°C for 2-5h, concentrate under reduced pressure, purify by column chromatography, and dry to obtain 3,3'-dinitro-4,4'-di(pentafluoropropionate)biphenyl; S2. Under a nitrogen atmosphere, add 3,3'-dinitro-4,4'-di(pentafluoropropionate)biphenyl and ethanol to a reaction flask, stir evenly, then add ammonium chloride, iron powder and deionized water, stir to react. After the reaction is completed, cool to room temperature, filter, wash with ethyl acetate, concentrate the filtrate, dilute with ethyl acetate, wash with saturated sodium chloride, and dry to obtain 3,3'-diamino-4,4'-di(pentafluoropropionate)biphenyl.

7. The method for preparing the modified polytetrafluoroethylene composite material according to claim 6, characterized in that: In the step S1, the ratio of 3,3'-dinitro-4,4'-dihydroxybiphenyl, triethylamine and pentafluoropropionyl chloride is 1 mol:(2.1-3) mol:(2.05-2.2) mol.

8. The method for preparing the modified polytetrafluoroethylene composite material according to claim 6, characterized in that: In the step S2, the ratio of 3,3'-dinitro-4,4'-di(pentafluoropropionate)biphenyl, ammonium chloride and iron powder is 1 mol:(4-8) mol:(5-10) mol.

9. The method for preparing the modified polytetrafluoroethylene composite material according to claim 6, characterized in that: In step S2, the reaction temperature is 50-65° C. and the reaction time is 3-8 h.

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