Preparation and application of modified polytetrafluoroethylene composite material

Abstract

The application relates to the technical field of composite materials, and discloses preparation and application of a modified polytetrafluoroethylene composite material; the C-F groups in the fluorine-containing semi-aromatic polyamide molecular chain are extremely similar to the C-F groups in the polytetrafluoroethylene, and the two have good compatibility; in the friction process, the fluorine-containing semi-aromatic polyamide can effectively bear the friction load, plays the role of a physical crosslinking point, is closely combined with the polytetrafluoroethylene, the movement of the polytetrafluoroethylene segment is limited, the sliding between the wafer is hindered, the volume wear rate of the composite material is reduced, and the wear resistance is improved; the rigid polyamide particles act as rigid support points in the matrix and play the role of uniformly distributing the load, so that the modified polytetrafluoroethylene has good anti-creepproperty; meanwhile, the mechanical property is good, stress transmission is facilitated, a certain load can be borne, and the effect of reinforcement and toughening is achieved.

Description

Technical Field

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

[0002] Polytetrafluoroethylene (PTFE) is an engineering plastic with excellent comprehensive performance. Known as the "King of Plastics", it has unique properties such as excellent chemical corrosion resistance, thermal stability and non-stickiness. It is widely used in many fields such as aerospace, mechanical manufacturing, electronics and electrical engineering, and petrochemicals. However, as an engineering plastic, while PTFE has excellent performance, it also has some shortcomings such as wear resistance, poor high-temperature creep resistance, and the presence of voids within the molecules. Therefore, in order to improve the performance defects of PTFE and expand its application range, it must be appropriately modified.

[0003] Because the fluorine atoms in the PTFE molecular chain repel each other, the attraction between PTFE molecules is small. When subjected to external forces, PTFE molecules are easy to slip. In addition, its low hardness leads to large losses during friction, which limits its use in friction parts. Currently, inorganic reinforcing components such as glass fiber, carbon fiber, graphite, molybdenum disulfide, and non-ferrous metal powder are commonly used to fill and modify PTFE to improve its strength, wear resistance and dimensional stability. However, these fillers have poor compatibility with PTFE, which often increases the friction coefficient of the composite material and weakens it. The friction-reducing effect of polytetrafluoroethylene is weakened, thus restricting the widespread application of polytetrafluoroethylene composites. For example, publication number CN1304477C discloses a low-friction and highly wear-resistant polytetrafluoroethylene composite material and a preparation method thereof. Polytetrafluoroethylene is used as a self-lubricating material, and molybdenum disulfide and nano-alumina are added as modified fillers. The polytetrafluoroethylene composite material is obtained after high-speed mixing, molding, and sintering. Although the wear life of the prepared composite material is improved to a certain extent, the nano-alumina used in the material is difficult to disperse during industrial batch operations, and its feasibility is not strong.

[0004] The organic polymer filler has good compatibility and strong affinity with the polytetrafluoroethylene matrix, which can improve the creep resistance, compression and wear resistance of polytetrafluoroethylene. Polyamide is an engineering plastic containing repeated amide groups on the main chain of the molecule. It has excellent corrosion resistance, wear resistance and mechanical properties and is widely used in the field of wear-resistant materials such as gears and bearings. The present invention synthesizes a rigid fluorine-containing semi-aromatic polyamide with a similar structure to polytetrafluoroethylene, and improves the interface compatibility when blended with polytetrafluoroethylene, thereby enhancing the wear resistance, creep resistance and mechanical properties of the prepared composite material. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a preparation and application of a modified polytetrafluoroethylene composite material, thereby solving the problem of poor wear resistance of polytetrafluoroethylene.

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

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

[0008] (1) Under nitrogen atmosphere, 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, lithium chloride and N,N-dimethylacetamide were added to a reaction flask, stirred and dissolved, and then pyridine and succinyl chloride were added and stirred for reaction. After the reaction was completed, deionized water was added for precipitation, filtered, washed with acetone, and dried to obtain a fluorinated semi-aromatic polyamide.

[0009] (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 minutes, let it stand for 12-24 hours, spread it flat in a mold, and use a flat vulcanizer for cold pressing. Keep the pressure at 50-60 MPa for 30-50 minutes, demold and eject it, then add it into a vacuum carbon tube furnace for sintering, and cool it with the furnace to obtain a modified polytetrafluoroethylene composite material.

[0010] Preferably, in step (1), the ratio 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, the reaction temperature in step (1) is 0-5°C and the reaction time is 5-12h.

[0012] Preferably, in step (2), the ratio of polytetrafluoroethylene to fluorinated semi-aromatic polyamide is 100 g:(5-25) g.

[0013] Preferably, the heating rate during sintering in step (2) 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.

[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 hours. 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 the reaction flask, stir evenly, then add ammonium chloride, iron powder and deionized water, stir and 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'-bis(pentafluoropropionate)biphenyl.

[0017] Preferably, in 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.

[0018] Preferably, in step S2, the 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, the reaction temperature in step S2 is 50-65° C., and the reaction time is 3-8 h.

[0020] By adopting the above technical solution, the beneficial effects of the present invention are:

[0021] The invention firstly causes esterification reaction of 3,3'-dinitro-4,4'-dihydroxybiphenyl and pentafluoropropionyl chloride under the action of triethylamine to obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl, then causes nitro reduction reaction in a reduction system of iron powder and ammonium chloride to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, then causes polymerization reaction with succinyl chloride to obtain fluorine-containing semi-aromatic polyamide, and finally, the modified polytetrafluoroethylene composite material is obtained by high-speed mixing, pressing and sintering with polytetrafluoroethylene.

[0022] Polyamide is a type of heat-resistant polymer material with very stable aromatic structural units, which has outstanding thermal stability and high temperature resistance. The semi-aromatic polyamide molecular chain contains both benzene rings and aliphatic chain segments, and has properties such as high strength, high heat resistance, and low water absorption that are superior to aliphatic polyamides, as well as molding and processing properties that are superior to aromatic polyamides. The CF group in the fluorine-containing group of the fluorine-containing semi-aromatic polyamide molecular chain prepared by the present invention is very similar to the CF group in polytetrafluoroethylene. During the mixing process, according to the principle of like dissolves like, the two have better compatibility. During the friction process, the polyamide effectively bears the friction load and acts as a physical cross-linking point, which can make the molecular chain difficult to move and is tightly combined with polytetrafluoroethylene to form a relatively complete integrated structure, thereby reducing the activity space of the polytetrafluoroethylene chain segment, restricting the movement of the molecular chain, and hindering the slippage between the wafers. The wear resistance of the polyamide particles is better than that of the polytetrafluoroethylene matrix. During the friction process, the polyamide particles will gradually enrich in the wear scar interface area, so that the volume wear rate of the composite material is gradually reduced and the wear resistance is improved.

[0023] Fluorinated semi-aromatic polyamide and polytetrafluoroethylene have good compatibility when blended, with no obvious interface between the two and strong bonding. When subjected to external forces, the interface between the two is not prone to slippage or detachment. 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, so that the modified polytetrafluoroethylene has good creep resistance. Fluorinated semi-aromatic polyamide itself has rigidity and good mechanical properties, and contains a molecular structure similar to that of polytetrafluoroethylene, which makes the polyamide well dispersed in the matrix and can form bonds with polytetrafluoroethylene, thereby 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 strengthening and toughening. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] 4,4'-Dihydroxybiphenyl, CAS number is 92-88-6.

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

[0027] Succinyl chloride, CAS number is 543-20-4.

[0028] Preparation of 3,3'-dinitro-4,4'-dihydroxybiphenyl: 12.2 g of 4,4'-dihydroxybiphenyl and 250 mL of acetone were added to a three-necked flask equipped with a condenser and an addition funnel. After stirring and dissolving at 60°C, 11.9 g of a 65% nitric acid solution was added dropwise. The mixture was then reacted at 60°C for 6 h, filtered, washed with acetone, and dried to obtain 3,3'-dinitro-4,4'-dihydroxybiphenyl (structural formula: ).

[0029] Example 1

[0030] (1) Under nitrogen atmosphere, 50 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 140 mmol of triethylamine and 1250 mL of dichloromethane were added to a reaction flask. After stirring evenly in an ice-water bath, 105 mmol of pentafluoropropionyl chloride was added. The mixture was stirred at 25°C for 4 h, concentrated under reduced pressure, and purified by column chromatography using ethyl acetate and petroleum ether (volume ratio of 1:2) as eluents. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl was obtained. The preparation process is as follows:

[0031]

[0032] (2) Under nitrogen atmosphere, 35 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and 420 mL of ethanol were added to the reaction flask, stirred evenly, and then 210 mmol of ammonium chloride, 280 mmol of iron powder and 140 mL of deionized water were added. The mixture was reacted at 55°C for 6 h, cooled to room temperature, filtered, washed with ethyl acetate, and the filtrate was concentrated, diluted with ethyl acetate, washed with saturated sodium chloride, and dried to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl. The preparation process is as follows:

[0033]

[0034] (3) Under nitrogen atmosphere, 20 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, 48 mmol of lithium chloride and 170 mL of N,N-dimethylacetamide were added to the reaction flask. After stirring and dissolving, 23 mmol of pyridine and 21.6 mmol of succinyl chloride were added. The mixture was reacted at 2°C for 10 h. Deionized water was added for precipitation, filtered, washed with acetone, and dried to obtain fluorinated semi-aromatic polyamide. The preparation process principle is as follows:

[0035]

[0036] (4) 100 g of polytetrafluoroethylene and 5 g of fluorinated semi-aromatic polyamide were added to a high-speed mixer, mixed at a speed of 2000 r / min for 8 min, allowed to stand for 16 h, spread flat in a mold, and cold-pressed using a flat vulcanizer. The pressure was maintained at 55 MPa for 45 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 60 ° C / min, the sintering temperature was 360 ° C, the sintering time was 4 h, the cooling rate was 45 ° C / min, and the temperature was maintained at 300 ° C for 30 min during the cooling process. The modified polytetrafluoroethylene composite material was obtained by cooling with the furnace.

[0037] Example 2

[0038] (1) Under nitrogen atmosphere, 30 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 63 mmol of triethylamine and 600 mL of dichloromethane were added to a reaction flask. After stirring evenly in an ice-water bath, 61.5 mmol of pentafluoropropionyl chloride was added. The mixture was stirred at 35°C for 2 h, concentrated under reduced pressure, and purified by column chromatography using ethyl acetate and petroleum ether (volume ratio of 1:2) as eluents. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl was obtained.

[0039] (2) Under nitrogen atmosphere, 15 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and 150 mL of ethanol were added to the reaction flask, and after stirring evenly, 60 mmol of ammonium chloride, 75 mmol of iron powder and 45 mL of deionized water were added. The mixture was reacted at 65°C for 3 h, cooled to room temperature, filtered, washed with ethyl acetate, and the filtrate was concentrated, diluted with ethyl acetate, washed with saturated sodium chloride, and dried to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl.

[0040] (3) Under nitrogen atmosphere, 10 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, 20 mmol of lithium chloride, and 50 mL of N,N-dimethylacetamide were added to a reaction flask. After stirring and dissolving, 11 mmol of pyridine and 10.5 mmol of succinyl chloride were added. The mixture was reacted at 5°C for 5 h. Deionized water was added for precipitation, the mixture was filtered, washed with acetone, and dried to obtain a fluorinated semi-aromatic polyamide.

[0041] (4) 100 g of polytetrafluoroethylene and 10 g of fluorinated semi-aromatic polyamide were added to a high-speed mixer, mixed at a speed of 2200 r / min for 5 min, allowed to stand for 12 h, spread flat in a mold, and cold-pressed using a flat vulcanizer. The pressure was maintained at 60 MPa for 30 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 65 ° C / min, the sintering temperature was 400 ° C, the sintering time was 3 h, the cooling rate was 55 ° C / min, and the temperature was maintained at 320 ° C for 20 min during the cooling process. The modified polytetrafluoroethylene composite material was obtained by cooling with the furnace.

[0042] Example 3

[0043] (1) Under nitrogen atmosphere, 18 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 54 mmol of triethylamine and 540 mL of dichloromethane were added to a reaction flask. After stirring evenly in an ice-water bath, 39.6 mmol of pentafluoropropionyl chloride was added. The mixture was stirred at 20°C for 5 h, concentrated under reduced pressure, and purified by column chromatography using ethyl acetate and petroleum ether (volume ratio of 1:2) as eluents. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl was obtained.

[0044] (2) Under nitrogen atmosphere, 12 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and 180 mL of ethanol were added to the reaction flask, and after stirring evenly, 96 mmol of ammonium chloride, 120 mmol of iron powder and 60 mL of deionized water were added. The mixture was reacted at 50°C for 8 h, cooled to room temperature, filtered, washed with ethyl acetate, and the filtrate was concentrated, diluted with ethyl acetate, washed with saturated sodium chloride, and dried to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl.

[0045] (3) Under nitrogen atmosphere, 5 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, 12.5 mmol of lithium chloride, and 50 mL of N,N-dimethylacetamide were added to the reaction flask. After stirring and dissolving, 6 mmol of pyridine and 5.5 mmol of succinyl chloride were added. The mixture was reacted at 0°C for 12 h. Deionized water was added for precipitation, the mixture was filtered, washed with acetone, and dried to obtain a fluorinated semi-aromatic polyamide.

[0046] (4) 100 g of polytetrafluoroethylene and 15 g of fluorinated semi-aromatic polyamide were added to a high-speed mixer, mixed at a speed of 1800 r / min for 10 min, allowed to stand for 24 h, spread flat in a mold, and cold-pressed using a flat vulcanizer. The mixture was maintained at a pressure of 50 MPa for 50 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 50 ° C / min, the sintering temperature was 350 ° C, the sintering time was 5 h, the cooling rate was 40 ° C / min, and the mixture was kept at 280 ° C for 40 min during the cooling process. The mixture was cooled with the furnace to obtain a modified polytetrafluoroethylene composite material.

[0047] Example 4

[0048] (1) Under nitrogen atmosphere, 40 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 100 mmol of triethylamine and 1040 mL of dichloromethane were added to a reaction flask. After stirring evenly in an ice-water bath, 86 mmol of pentafluoropropionyl chloride was added. The mixture was stirred at 30°C for 3 h, concentrated under reduced pressure, and purified by column chromatography using ethyl acetate and petroleum ether (volume ratio of 1:2) as eluents. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl was obtained.

[0049] (2) Under nitrogen atmosphere, 25 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and 350 mL of ethanol were added to the reaction flask, and after stirring evenly, 175 mmol of ammonium chloride, 225 mmol of iron powder and 75 mL of deionized water were added. The mixture was reacted at 55 °C for 6 h, cooled to room temperature, filtered, washed with ethyl acetate, and the filtrate was concentrated, diluted with ethyl acetate, washed with saturated sodium chloride, and dried to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl.

[0050] (3) Under nitrogen atmosphere, 15 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, 33 mmol of lithium chloride, and 120 mL of N,N-dimethylacetamide were added to a reaction flask. After stirring and dissolving, 17.4 mmol of pyridine and 15.9 mmol of succinyl chloride were added. The mixture was reacted at 0°C for 8 h. Deionized water was added for precipitation, the mixture was filtered, washed with acetone, and dried to obtain a fluorinated semi-aromatic polyamide.

[0051] (4) 100 g of polytetrafluoroethylene and 20 g of fluorinated semi-aromatic polyamide were added to a high-speed mixer, mixed at a speed of 2100 r / min for 9 min, allowed to stand for 20 h, spread flat in a mold, and cold-pressed using a flat vulcanizer. The mixture was kept at a pressure of 60 MPa for 40 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 60 ° C / min, the sintering temperature was 360 ° C, the sintering time was 3 h, the cooling rate was 50 ° C / min, and the temperature was kept at 310 ° C for 25 min during the cooling process. The mixture was cooled with the furnace to obtain a modified polytetrafluoroethylene composite material.

[0052] Example 5

[0053] (1) Under nitrogen atmosphere, 12 mmol of 3,3'-dinitro-4,4'-dihydroxybiphenyl, 32.4 mmol of triethylamine and 300 mL of dichloromethane were added to a reaction flask. After stirring evenly in an ice-water bath, 24.6 mmol of pentafluoropropionyl chloride was added. The mixture was stirred at 35°C for 4 h, concentrated under reduced pressure, and purified by column chromatography using ethyl acetate and petroleum ether (volume ratio of 1:2) as eluents. After drying, 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl was obtained.

[0054] (2) Under nitrogen atmosphere, 6 mmol of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and 66 mL of ethanol were added to the reaction flask, stirred evenly, and then 42 mmol of ammonium chloride, 48 mmol of iron powder and 30 mL of deionized water were added. The mixture was reacted at 55 °C for 6 h, cooled to room temperature, filtered, washed with ethyl acetate, and the filtrate was concentrated, diluted with ethyl acetate, washed with saturated sodium chloride, and dried to obtain 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl.

[0055] (3) Under nitrogen atmosphere, 3 mmol of 3,3'-diamino-4,4'-bis(pentafluoropropionate)biphenyl, 7.2 mmol of lithium chloride, and 24 mL of N,N-dimethylacetamide were added to a reaction flask. After stirring and dissolving, 3.6 mmol of pyridine and 3.3 mmol of succinyl chloride were added. The mixture was reacted at 0°C for 9 h. Deionized water was added for precipitation, the mixture was filtered, washed with acetone, and dried to obtain a fluorinated semi-aromatic polyamide.

[0056] (4) 100 g of polytetrafluoroethylene and 25 g of fluorinated semi-aromatic polyamide were added to a high-speed mixer, mixed at a speed of 2000 r / min for 10 min, allowed to stand for 16 h, spread flat in a mold, and cold-pressed using a flat vulcanizer. The pressure was maintained at 60 MPa for 50 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 55 ° C / min, the sintering temperature was 400 ° C, the sintering time was 3 h, the cooling rate was 40 ° C / min, and the temperature was maintained at 310 ° C for 35 min during the cooling process. The modified polytetrafluoroethylene composite material was obtained by cooling with the furnace.

[0057] Comparative Example 1

[0058] 100g of polytetrafluoroethylene was added to a high-speed mixer, mixed at a speed of 2000r / min for 8 minutes, allowed to stand for 16 hours, spread flat in a mold, and cold-pressed using a flat vulcanizer. The pressure was maintained at 55MPa for 45 minutes, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 60℃ / min, the sintering temperature was 360℃, the sintering time was 4 hours, the cooling rate was 45℃ / min, and the temperature was kept at 300℃ for 30 minutes during the cooling process. The polytetrafluoroethylene material was cooled with the furnace to obtain.

[0059] Comparative Example 2

[0060] (1) Under nitrogen atmosphere, 20 mmol of 4,4'-diaminodiphenyl (structural formula: ), 48mmol lithium chloride and 170mL N,N-dimethylacetamide, after stirring to dissolve, add 23mmol pyridine and 21.6mmol succinyl chloride, react at 2℃ for 10h, add deionized water to precipitate, filter, wash with acetone, and dry to obtain semi-aromatic polyamide.

[0061] (2) 100 g of polytetrafluoroethylene and 5 g of semi-aromatic polyamide were added to a high-speed mixer, mixed at a speed of 2000 r / min for 8 min, allowed to stand for 16 h, spread flat in a mold, and cold-pressed using a flat vulcanizer. The pressure was maintained at 55 MPa for 45 min, demolded and ejected, and then added to a vacuum carbon tube furnace for sintering. The heating rate during sintering was 60 ° C / min, the sintering temperature was 360 ° C, the sintering time was 4 h, the cooling rate was 45 ° C / min, and the temperature was maintained at 300 ° C for 30 min during the cooling process. The modified polytetrafluoroethylene composite material was obtained by cooling with the furnace.

[0062] Friction and wear performance test: The test was conducted in accordance with the standard GB / T 3960-2016, with a rotation speed of 200 r / min, a load of 200 N, a test time of 2 h, and a sample size of 30 mm × 5 mm × 10 mm.

[0063]

[0064]

[0065] As a self-lubricating material, polytetrafluoroethylene has little mutual attraction between its molecules and is easy to slip between molecular chains, resulting in poor wear resistance. As can be seen from the test structure in the above table, with the increase of the content of fluorinated semi-aromatic polyamide, the friction coefficient and volume wear rate of the modified polytetrafluoroethylene composite material both show a downward trend, among which the decrease in 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), which is because the modulus of fluorinated semi-aromatic polyamide is high and the rigidity is strong. The CF group in the fluorinated group of its molecular chain is very similar to the CF group in polytetrafluoroethylene. Therefore, during the mixing process, according to the principle of like dissolves like, the two have better compatibility; during the friction process, polyamide effectively bears the friction load. The appropriate addition will reduce the activity space of the polytetrafluoroethylene chain segment, restrict the movement of the molecular chain, and hinder the slip between the wafers. The wear resistance of polyamide particles is better than that of the matrix. During the friction process, polyamide will gradually enrich in the wear scar interface area, bearing the main external load. At the same time, the rigid aromatic polyamide particles can effectively limit the slip between the polytetrafluoroethylene molecular chains, so that the volume wear rate of the composite material is gradually reduced and the wear resistance is 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, which makes the composite material less compatible during the blending process, resulting in its wear resistance being inferior to that of the embodiment.

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

[0068]

[0069] Compression creep refers to the irreversible plastic deformation of a material over time under a constant temperature and a constant stress below the material's yield point. The magnitude of the instantaneous deformation after the application of an external load reflects the material's compression modulus. The smaller the deformation, the higher the material's compression modulus. The compression creep test value of the present invention is the difference between the total deformation 48 hours after external force loading and the instantaneous deformation within 10 seconds after loading.

[0070] The test results in the above table show that with the increase of the content of fluorinated semi-aromatic polyamide, 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 a high temperature of 150°C is 10.89%, indicating that the addition of fluorinated semi-aromatic polyamide effectively improves the creep properties of the composite material. This is because the fluorinated semi-aromatic polyamide and polytetrafluoroethylene have good compatibility when blended, there is no obvious interface between the two, and the bond is strong. When subjected to external force, the interface between the two is not easy to slip or detach. At the same time, the rigid polyamide particles limit the movement of the polytetrafluoroethylene chain segments, making it difficult to produce large-area slip of the ribbon crystals. In addition, the appropriate amount of polyamide particles acts as rigid support points in the matrix, playing a role in evenly distributing the load. Ultimately, the compression deformation of the blend is reduced, and the compression resistance is greatly improved, thereby making the modified polytetrafluoroethylene have good creep resistance.

[0071] Hardness test: The Brinell hardness of the composite material was measured using a Brinell hardness tester, and the average value was calculated 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] From the test results in the above table, it can be seen that with the increase of the content of fluorinated semi-aromatic polyamide, 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. It also has a molecular structure similar to that of polytetrafluoroethylene, which makes the polyamide have good dispersion 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, which is beneficial to stress transfer. Therefore, the composite material can bear a certain load, has the effect of strengthening toughness and improving the hardness of the composite material.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection 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'-bis(pentafluoropropionate)biphenyl, lithium chloride, and N,N-dimethylacetamide were added to a reaction flask, stirred and dissolved, and then pyridine and succinyl chloride were added and stirred for reaction. After the reaction was completed, deionized water was 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 minutes, let it stand for 12-24 hours, spread it flat in a mold, and use a flat vulcanizer for cold pressing. Keep the pressure at 50-60 MPa for 30-50 minutes, demold and eject it, then add it into a vacuum carbon tube furnace for sintering, and cool it with the furnace to obtain a modified polytetrafluoroethylene composite material.

2. The method for preparing a modified polytetrafluoroethylene composite material according to claim 1, wherein: In the step (1), the ratio 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.

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

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

5. The method for preparing a modified polytetrafluoroethylene composite material according to claim 1, wherein: 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 a modified polytetrafluoroethylene composite material according to claim 1, wherein: 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, then add pentafluoropropionyl chloride, stir at 20-35°C for 2-5 hours, concentrate under reduced pressure, purify by column chromatography, and dry to obtain 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl; S2. Under a nitrogen atmosphere, add 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl and ethanol to the reaction flask, stir evenly, then add ammonium chloride, iron powder and deionized water, stir and 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'-bis(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 a modified polytetrafluoroethylene composite material according to claim 6, wherein: In the step S2, the ratio of 3,3'-dinitro-4,4'-bis(pentafluoropropionate)biphenyl, ammonium chloride, and iron powder is 1 mol: (4-8) mol: (5-10) mol.

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

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