A polytetrafluoroethylene with both high wear resistance and low coefficient of friction and its preparation method

Abstract

This invention relates to a polytetrafluoroethylene (PTFE) exhibiting both high wear resistance and a low coefficient of friction, and its preparation method, belonging to the field of polymer materials technology. This invention utilizes a thiol coupling agent to modify the surface of halloysite nanotubes, grafting thiol groups onto the surface of the halloysite nanotubes. Simultaneously, an acyl chloride with a long-chain fluorocarbon, a side-chain tetrazolium, and a thioether structure is synthesized. The acyl chloride is then reacted with the modified halloysite nanotubes, bonding the organic acyl chloride to the surface of the halloysite nanotubes via thiocarboxylic acid ester chemical bonds. The long-chain fluorocarbon, side-chain tetrazolium, thioether, and thiocarboxylic acid ester organic groups synergistically work with the inorganic halloysite nanotubes to form functional structures with different hierarchical gradients. The long-chain fluorocarbon can improve the affinity between halloysite nanotubes and PTFE, the thioether and thiocarboxylic acid esters on the main chain can play a reinforcing and toughening role, and the tetrazolium groups on the side chain can play a rigid-flexible role, thereby improving the mechanical, tribological, and dielectric properties of the PTFE material.

Description

Technical Field

[0001] This invention relates to a polytetrafluoroethylene with both high wear resistance and low coefficient of friction, and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is an excellent self-lubricating material with a low coefficient of friction, good high and low temperature stability, and corrosion resistance, and has been widely used in various fields of industrial and agricultural production. However, pure PTFE has disadvantages such as high wear rate and poor load-bearing capacity, which limits its application range.

[0003] Currently, glass fiber, graphite, molybdenum disulfide, carbon fiber, and metal powder are commonly used to modify polytetrafluoroethylene (PTFE) to improve its wear resistance and reduce wear rate. However, the friction coefficient of composite materials prepared by using conventional fillers to modify PTFE tends to increase to some extent, leading to a decrease in the self-lubricating properties of PTFE. Therefore, there is an urgent need to develop a PTFE material that combines high wear resistance with a low friction coefficient. Summary of the Invention

[0004] The purpose of this invention is to provide a polytetrafluoroethylene and its preparation method to solve the problem that current polytetrafluoroethylene cannot simultaneously possess high wear resistance and low coefficient of friction.

[0005] This invention provides a method for preparing polytetrafluoroethylene (PTFE) with both high wear resistance and low coefficient of friction, comprising the following steps:

[0006] (1) Halloysite nanotubes with an average outer diameter of 30-40 nm, an average inner diameter of 10-15 nm, and an average length of 500-700 nm were mixed and reacted with 3-mercaptopropyltriethoxysilane at 110-115 °C to obtain modified halloysite nanotubes; then, the modified halloysite nanotubes and tetrazolium-modified fluorothioyl chloride compound were mixed and reacted in a solvent to obtain the first functional filler; the molar ratio of mercapto groups in the modified halloysite nanotubes to the molar ratio of tetrazolium-modified fluorothioyl chloride compound was 1:1.5-1.8; the mass ratio of halloysite nanotubes to 3-mercaptopropyltriethoxysilane was 5:5-6.

[0007] (2) Halloysite nanotubes with an average outer diameter of 60-70 nm, an average inner diameter of 20-30 nm, and an average length of 800-1000 nm were mixed and reacted with 3-mercaptopropyltriethoxysilane at 110-115 °C to obtain modified halloysite nanotubes; then, the modified halloysite nanotubes and tetrazolium-modified fluorothioyl chloride compound were mixed and reacted in a solvent to obtain a second functional filler; the molar ratio of mercapto groups in the modified halloysite nanotubes to the molar ratio of tetrazolium-modified fluorothioyl chloride compound was 1:1.5-1.8; the mass ratio of halloysite nanotubes to 3-mercaptopropyltriethoxysilane was 5:8-10;

[0008] (3) Mix polytetrafluoroethylene powder, the first functional filler, and the second functional filler in a mass ratio of 100:3~5:3~5, cold press and sinter to obtain a polytetrafluoroethylene composite material; the structure of the tetrazolium-modified fluorothionyl chloride compound in steps (1) and (2) is as follows:

[0009]

[0010] Wherein, R1 is methylene or ethylene; R2 is -S- or -SS-; and R3 is methylene or ethylene.

[0011] Preferably, the preparation method of the tetrazolium-modified fluorothionyl chloride compound is as follows:

[0012] (1) Glycidyl ether hexafluorononyl ether, thiodicarboxylic acid, tetrabutylammonium bromide and organic solvent are mixed and reacted at 85-90°C to obtain a fluorothiocarboxylic acid compound; the thiodicarboxylic acid is 3,3′-dithiodipropionic acid or thionyl diacetic acid; the molar ratio of glycidyl ether hexafluorononyl ether and thiodicarboxylic acid is 1:1;

[0013] (2) A fluorothiocarboxylic acid compound, 1H-tetrazole-1-acetyl chloride and a solvent are mixed and reacted at 0-5°C to obtain a tetrazolium-modified fluorothiocarboxylic acid compound; the molar ratio of hydroxyl groups in the 1H-tetrazole-1-acetyl chloride and the fluorothiocarboxylic acid compound is 1:1.

[0014] (3) The tetrazolium-modified fluorothiocarboxylic acid compound, oxalyl and solvent are mixed and reacted at 58-62°C to obtain a tetrazolium-modified fluorothiocarboxylic acid chloride compound; the molar ratio of carboxyl group and oxalyl chloride in the tetrazolium-modified fluorothiocarboxylic acid compound is 1:4.2-4.5.

[0015] Preferably, the organic solvent in step (1) of the method for preparing the tetrazolium-modified fluorothioyl chloride compound is composed of dichloromethane, acetone and ethanol in a mass ratio of 0.5:1:1.

[0016] Preferably, in step (1) of the method for preparing the tetrazolium-modified fluorothioyl chloride compound, the mass of the organic solvent is 120-150% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid; the mass of tetrabutylammonium bromide is 2-3% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid; and the mixing reaction time is 4-5 h.

[0017] Preferably, in step (2) of the method for preparing tetrazolium-modified fluorothioyl chloride compound, the mixing reaction time is 6-8 h.

[0018] Preferably, in step (3) of the method for preparing tetrazolium-modified fluorothioyl chloride compound, the mixing reaction time is 18-22 h.

[0019] Preferably, the average particle size of the polytetrafluoroethylene powder is 30-35 μm.

[0020] Preferably, the cold pressing pressure is 40-45 MPa, the time is 15-20 min, and the pressurization rate is 0.1-0.15 MPa / s.

[0021] Preferably, the sintering temperature is 375–380°C and the time is 3–3.5 h.

[0022] A method for preparing polytetrafluoroethylene (PTFE) with both high wear resistance and low coefficient of friction, as described above, yields PTFE with both high wear resistance and low coefficient of friction.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) This invention utilizes a mercapto coupling agent to modify the surface of halloysite nanotubes, grafting mercapto groups onto the surface of halloysite nanotubes, and simultaneously synthesizing acyl chlorides with long-chain fluorocarbon, side-chain tetrazolium, and thioether structures. The acyl chlorides are then reacted with the modified halloysite nanotubes, and the organic acyl chlorides are bonded to the surface of the halloysite nanotubes via thiocarboxylic acid ester chemical bonds. The organic groups of long-chain fluorocarbon, side-chain tetrazolium, thioether, and thiocarboxylic acid ester work synergistically with the inorganic halloysite nanotubes to form functional structures with different hierarchical gradients. Long-chain fluorocarbon can improve the affinity between halloysite nanotubes and polytetrafluoroethylene (PTFE), while the thioether and thiocarboxylic acid esters on the main chain can play a role in strengthening and toughening, and the tetrazolium groups on the side chain can play a role in rigidity-flexibility enhancement, thereby improving the mechanical properties, tribological properties, and dielectric properties of PTFE materials.

[0025] (2) The present invention uses a small first functional filler and a large second functional filler to modify polytetrafluoroethylene. Since the small first functional filler and the large second functional filler can form a denser and more compact aggregate, and can also form a ladder structure with distinct high and low levels, thereby making up for the defects of polytetrafluoroethylene and improving the mechanical properties, friction and wear properties and dielectric properties of the material.

[0026] (3) This invention utilizes halloysite nanotubes with tetrazolium side chains grafted on their surface to modify polytetrafluoroethylene. The tetrazolium group located on the side chain has greater rigidity and can rotate, thus possessing a certain degree of toughness. The tetrazolium heterocycle and the hydrophobic fluorocarbon long chain at the end of the molecular chain can cooperate with each other to improve strength and tribological properties. In addition, the mercaptocarboxylic acid ester group generated after the reaction of thiol and acyl chloride in the modified halloysite nanotube has good hydrophobicity and can rotate freely, which is beneficial to improving dielectric constant and tribological properties. Attached Figure Description

[0027] Figure 1 The image shows the proton NMR spectrum of the tetrazolium-modified fluorothioyl chloride compound prepared in Example 1 of this invention. Detailed Implementation

[0028] The following examples are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the present invention.

[0029] Example 1

[0030] The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction in this embodiment includes the following steps:

[0031] (1) Glycidyl ether hexafluorononyl ether, 3,3′-dithiodipropionic acid and organic solvent (the organic solvent is composed of dichloromethane, acetone and ethanol in a mass ratio of 0.5:1:1) are added to a reaction vessel. The molar ratio of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid is 1:1. The mass of the organic solvent is 120% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid. Then tetrabutylammonium bromide is added. The mass of tetrabutylammonium bromide is 2% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid. After stirring evenly, the temperature is raised to 85°C and stirred under reflux for 4 hours. After cooling to room temperature, the reaction product is rotary evaporated to remove the solvent and obtain a fluorothiocarboxylic acid compound with the structure shown in Formula 1.

[0032]

[0033] (2) Add the fluorothiocarboxylic acid compound and acetone in a mass ratio of 10:30 to the reaction vessel and stir until homogeneous. Then, under stirring conditions at 0°C, add a dichloromethane solution of 1H-tetrazole-1-acetyl chloride (mass fraction of 10%, molar ratio of hydroxyl groups in 1H-tetrazole-1-acetyl chloride and fluorothiocarboxylic acid compound of 1:1) dropwise to the reaction vessel. After the dropwise addition is complete, add the acid-binding agent triethylamine and continue stirring for 6 hours. Filter and rotary evaporate the filtrate to obtain the tetrazolium-modified fluorothiocarboxylic acid compound, the structure of which is shown in Formula 2.

[0034]

[0035] (3) Tetraazole-modified fluorothiocarboxylic acid compound, toluene, and oxalyl chloride (the molar ratio of carboxyl group to oxalyl chloride in the tetraazole-modified fluorothiocarboxylic acid compound is 1:4.2, and the mass ratio of tetraazole-modified fluorothiocarboxylic acid compound to toluene is 1:7) were added to a reaction vessel, stirred evenly, heated to 58°C, and stirred under reflux for 18 h. Then, the solvent and unreacted oxalyl chloride were removed by vacuum distillation of the reaction system to obtain the tetraazole-modified fluorothiocarboxylic acid chloride compound, the structure of which is shown in Formula 3, and the hydrogen NMR spectrum is shown in Formula 3. Figure 1 As shown.

[0036]

[0037] (4) Add 5g halloysite nanotubes (average outer diameter of 30nm, average inner diameter of 10nm, and average length of 500nm) and 100mL toluene to a reaction vessel, and then add 5g of 3-mercaptopropyltriethoxysilane (structure shown in Formula 4). Heat the material in the reaction vessel to 110℃, stir and reflux for 8h, filter, wash the filtered solid with toluene and ethanol respectively, and dry to obtain modified halloysite nanotubes.

[0038]

[0039] (5) The modified halloysite nanotubes obtained in step (4) are dispersed in dichloromethane to obtain a modified halloysite nanotube dispersion with a mass fraction of 15%. Then, under stirring conditions, a dichloromethane solution of tetrazolium-modified sulfofluoride chloride compound with a mass fraction of 8% is added dropwise to the modified halloysite nanotube dispersion (the molar ratio of the mercapto group in the modified halloysite nanotube to the molar amount of the tetrazolium-modified sulfofluoride chloride compound is 1:1.5). After the addition is completed, the mixture is stirred for 4 hours, filtered, and the filter cake is washed with dichloromethane to remove unreacted tetrazolium-modified sulfofluoride chloride compound. After drying, the first functional filler is obtained, and its structural schematic diagram is shown in Formula 5.

[0040]

[0041] (6) Add 5g halloysite nanotubes (average outer diameter of 60nm, average inner diameter of 20nm, and average length of 800nm) and 100mL toluene to a reaction vessel, then add 8g of 3-mercaptopropyltriethoxysilane, heat the material in the reaction vessel to 110℃, stir and reflux for 8h, filter, wash the filtered solid with toluene and ethanol respectively, and dry to obtain modified halloysite nanotubes.

[0042] (7) The modified halloysite nanotubes obtained in step (6) are dispersed in dichloromethane to obtain a modified halloysite nanotube dispersion with a mass fraction of 15%. Then, under stirring conditions, a dichloromethane solution of tetrazolium-modified sulfofluoride chloride compound with a mass fraction of 8% is added dropwise to the modified halloysite nanotube dispersion (the molar ratio of the mercapto group in the modified halloysite nanotube to the molar amount of the tetrazolium-modified sulfofluoride chloride compound is 1:1.5). After the addition is completed, the mixture is stirred for 4 hours, filtered, and the filter cake is washed with dichloromethane to remove unreacted tetrazolium-modified sulfofluoride chloride compound. After drying, the second functional filler is obtained.

[0043] (8) Mix polytetrafluoroethylene powder (average particle size of 30 μm), first functional filler and second functional filler in a mass ratio of 100:3:5 evenly, add to the mold, and then place in a press for cold pressing. The cold pressing pressure is 40 MPa, the time is 15 min, and the pressurization rate is 0.1 MPa / s. Then demold and take out the blank. Then place the blank in a nitrogen-protected sintering furnace for sintering. The sintering temperature is 375℃ and the time is 3 h. After sintering, cool to room temperature with the furnace to obtain polytetrafluoroethylene composite material.

[0044] Example 2

[0045] The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction in this embodiment includes the following steps:

[0046] (1) Glycidyl ether hexafluorononyl ether, 3,3′-dithiodipropionic acid and organic solvent (the organic solvent is composed of dichloromethane, acetone and ethanol in a mass ratio of 0.5:1:1) were added to a reaction vessel. The molar ratio of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid was 1:1, and the mass of the organic solvent was 130% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid. Then tetrabutylammonium bromide was added, and the mass of tetrabutylammonium bromide was 2.5% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid. After stirring evenly, the temperature was raised to 87°C and the mixture was stirred and refluxed for 4.5 h. After cooling to room temperature, the reaction product was rotary evaporated to remove the solvent, and a fluorothiocarboxylic acid compound was obtained, the structure of which is shown in Formula 1.

[0047]

[0048] (2) A fluorothiocarboxylic acid compound and acetone with a mass ratio of 10:35 were added to a reaction vessel and stirred until homogeneous. Then, under stirring conditions at 2°C, a dichloromethane solution of 1H-tetrazole-1-acetyl chloride (mass fraction of 12%, molar ratio of hydroxyl groups in 1H-tetrazole-1-acetyl chloride and fluorothiocarboxylic acid compound of 1:1) was added dropwise to the reaction vessel. After the dropwise addition was completed, triethylamine, an acid-binding agent, was added and the reaction was stirred for 7 hours. The mixture was filtered and the filtrate was rotary evaporated to obtain a tetrazolium-modified fluorothiocarboxylic acid compound with the structure shown in Formula 2.

[0049]

[0050] (3) Tetrazazole-modified fluorothiocarboxylic acid compound, toluene and oxalyl chloride (the molar ratio of carboxyl group to oxalyl chloride in tetrazazole-modified fluorothiocarboxylic acid compound is 1:4.3, and the mass ratio of tetrazazole-modified fluorothiocarboxylic acid compound to toluene is 1:7.5) are added to a reaction vessel, stirred evenly, heated to 60°C, and stirred under reflux for 20 h. Then, the solvent and unreacted oxalyl chloride are removed by vacuum distillation of the reaction system to obtain tetrazazole-modified fluorothiocarboxylic acid chloride compound, the structure of which is shown in Formula 3.

[0051]

[0052] (4) Add 5g halloysite nanotubes (average outer diameter of 35nm, average inner diameter of 12nm, and average length of 600nm) and 100mL toluene to a reaction vessel, and then add 5.5g of 3-mercaptopropyltriethoxysilane (structure shown in Formula 4). Heat the material in the reaction vessel to 112℃, stir and reflux for 9h, filter, wash the filtered solid with toluene and ethanol respectively, and dry to obtain modified halloysite nanotubes.

[0053]

[0054] (5) The modified halloysite nanotubes obtained in step (4) are dispersed in dichloromethane to obtain a modified halloysite nanotube dispersion with a mass fraction of 17%. Then, under stirring conditions, a dichloromethane solution of tetrazolium-modified sulfofluoride chloride compound with a mass fraction of 9% is added dropwise to the modified halloysite nanotube dispersion (the molar ratio of the mercapto group in the modified halloysite nanotube to the molar amount of the tetrazolium-modified sulfofluoride chloride compound is 1:1.6). After the addition is completed, the mixture is stirred for 5 hours, filtered, and the filter cake is washed with dichloromethane to remove unreacted tetrazolium-modified sulfofluoride chloride compound. After drying, the first functional filler is obtained, and its structural schematic diagram is shown in Formula 5.

[0055]

[0056] (6) Add 5g halloysite nanotubes (average outer diameter of 65nm, average inner diameter of 25nm, and average length of 900nm) and 100mL toluene to a reaction vessel, then add 7.5g of 3-mercaptopropyltriethoxysilane, heat the material in the reaction vessel to 112℃, stir and reflux for 9h, filter, wash the filtered solid with toluene and ethanol respectively, and dry to obtain modified halloysite nanotubes.

[0057] (7) The modified halloysite nanotubes obtained in step (6) are dispersed in dichloromethane to obtain a modified halloysite nanotube dispersion with a mass fraction of 18%. Then, under stirring conditions, a dichloromethane solution of tetrazolium-modified sulfofluoride chloride compound with a mass fraction of 9% is added dropwise to the modified halloysite nanotube dispersion (the molar ratio of the mercapto group in the modified halloysite nanotube to the molar amount of the tetrazolium-modified sulfofluoride chloride compound is 1:1.7). After the addition is completed, the mixture is stirred for 5 hours, filtered, and the filter cake is washed with dichloromethane to remove unreacted tetrazolium-modified sulfofluoride chloride compound. After drying, the second functional filler is obtained.

[0058] (8) Mix polytetrafluoroethylene powder (average particle size of 32 μm), first functional filler and second functional filler in a mass ratio of 100:4:4 evenly, add to the mold, and then place in a press for cold pressing. The cold pressing pressure is 43 MPa, the time is 18 min, and the pressurization rate is 0.12 MPa / s. Then demold and take out the blank. Then place the blank in a nitrogen-protected sintering furnace for sintering. The sintering temperature is 378℃ and the time is 3.2 h. After sintering, cool to room temperature with the furnace to obtain polytetrafluoroethylene composite material.

[0059] Example 3

[0060] The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction in this embodiment includes the following steps:

[0061] (1) Glycidyl ether hexafluorononyl ether, 3,3′-dithiodipropionic acid and organic solvent (the organic solvent is composed of dichloromethane, acetone and ethanol in a mass ratio of 0.5:1:1) are added to a reaction vessel. The molar ratio of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid is 1:1. The mass of the organic solvent is 150% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid. Then tetrabutylammonium bromide is added. The mass of tetrabutylammonium bromide is 3% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid. After stirring evenly, the temperature is raised to 90°C and stirred under reflux for 5 hours. After cooling to room temperature, the reaction product is rotary evaporated to remove the solvent and obtain a fluorothiocarboxylic acid compound with the structure shown in Formula 1.

[0062]

[0063] (2) Add the fluorothiocarboxylic acid compound and acetone in a mass ratio of 10:40 to the reaction vessel and stir until homogeneous. Then, under stirring conditions at 5°C, add a dichloromethane solution of 1H-tetrazole-1-acetyl chloride (mass fraction of 15%, molar ratio of hydroxyl groups in 1H-tetrazole-1-acetyl chloride and fluorothiocarboxylic acid compound of 1:1) dropwise to the reaction vessel. After the dropwise addition is complete, add the acid-binding agent triethylamine and continue stirring for 8 hours. Filter and rotary evaporate the filtrate to obtain the tetrazolium-modified fluorothiocarboxylic acid compound, the structure of which is shown in Formula 2.

[0064]

[0065] (3) Tetrazazole-modified fluorothiocarboxylic acid compound, toluene and oxalyl chloride (the molar ratio of carboxyl group to oxalyl chloride in tetrazazole-modified fluorothiocarboxylic acid compound is 1:4.5, and the mass ratio of tetrazazole-modified fluorothiocarboxylic acid compound to toluene is 1:8) are added to a reaction vessel, stirred evenly, heated to 62°C, and stirred under reflux for 22 h. Then, the solvent and unreacted oxalyl chloride are removed by vacuum distillation of the reaction system to obtain tetrazazole-modified fluorothiocarboxylic acid chloride compound, the structure of which is shown in Formula 3.

[0066]

[0067] (4) Add 5g halloysite nanotubes (average outer diameter of 40nm, average inner diameter of 15nm, and average length of 700nm) and 100mL toluene to a reaction vessel, and then add 6g of 3-mercaptopropyltriethoxysilane (structure shown in Formula 4). Heat the material in the reaction vessel to 115℃, stir and reflux for 10h, filter, wash the filtered solid with toluene and ethanol respectively, and dry to obtain modified halloysite nanotubes.

[0068]

[0069] (5) The modified halloysite nanotubes obtained in step (4) are dispersed in dichloromethane to obtain a modified halloysite nanotube dispersion with a mass fraction of 20%. Then, under stirring conditions, a dichloromethane solution of tetrazolium-modified sulfofluoride chloride compound with a mass fraction of 10% is added dropwise to the modified halloysite nanotube dispersion (the molar ratio of the mercapto group in the modified halloysite nanotube to the molar amount of the tetrazolium-modified sulfofluoride chloride compound is 1:1.8). After the addition is completed, the mixture is stirred for 6 hours, filtered, and the filter cake is washed with dichloromethane to remove unreacted tetrazolium-modified sulfofluoride chloride compound. After drying, the first functional filler is obtained, and its structural schematic diagram is shown in Formula 5.

[0070]

[0071] (6) Add 5g halloysite nanotubes (average outer diameter of 70nm, average inner diameter of 30nm, and average length of 1000nm) and 100mL toluene to a reaction vessel, then add 10g of 3-mercaptopropyltriethoxysilane, heat the material in the reaction vessel to 115℃, stir and reflux for 10h, filter, wash the filtered solid with toluene and ethanol respectively, and dry to obtain modified halloysite nanotubes.

[0072] (7) The modified halloysite nanotubes obtained in step (6) are dispersed in dichloromethane to obtain a modified halloysite nanotube dispersion with a mass fraction of 20%. Then, under stirring conditions, a dichloromethane solution of tetrazolium-modified sulfofluoride chloride compound with a mass fraction of 10% is added dropwise to the modified halloysite nanotube dispersion (the molar ratio of the mercapto group in the modified halloysite nanotube to the molar amount of the tetrazolium-modified sulfofluoride chloride compound is 1:1.8). After the addition is completed, the mixture is stirred for 6 hours, filtered, and the filter cake is washed with dichloromethane to remove unreacted tetrazolium-modified sulfofluoride chloride compound. After drying, the second functional filler is obtained.

[0073] (8) Mix polytetrafluoroethylene powder (average particle size of 35 μm), first functional filler and second functional filler in a mass ratio of 100:5:3 evenly, add to the mold, and then place in a press for cold pressing. The cold pressing pressure is 45 MPa, the time is 20 min, and the pressurization rate is 0.12 MPa / s. Then demold and take out the blank. Then place the blank in a nitrogen-protected sintering furnace for sintering. The sintering temperature is 380℃ and the time is 3.5 h. After sintering, cool to room temperature with the furnace to obtain polytetrafluoroethylene composite material.

[0074] Example 4

[0075] The difference between the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this embodiment and the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in Example 1 is that in step (1) of the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this embodiment, 3,3′-dithiodipropionic acid is replaced with thionyl diacetic acid.

[0076] Comparative Example 1

[0077] The difference between the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example and the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in Example 1 is that in step (2) of the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example, 1H-tetrazole-1-acetyl chloride is replaced with phenylacetyl chloride.

[0078] Comparative Example 2

[0079] The difference between the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example and the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in Example 1 is that in step (4) of the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example, 3-mercaptopropyltriethoxysilane is replaced with 3-aminopropyltriethoxysilane.

[0080] Comparative Example 3

[0081] The difference between the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example and the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in Example 1 is that in step (6) of the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example, 3-mercaptopropyltriethoxysilane is replaced with 3-aminopropyltriethoxysilane.

[0082] Comparative Example 4

[0083] The difference between the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example and the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in Example 1 is that the amount of the first functional filler in step (8) of the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example is 0, and the mass ratio of polytetrafluoroethylene powder and the second functional filler is 100:8.

[0084] Comparative Example 5

[0085] The difference between the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example and the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in Example 1 is that the amount of the second functional filler in step (8) of the preparation method of polytetrafluoroethylene with high wear resistance and low friction coefficient in this comparative example is 0, and the mass ratio of polytetrafluoroethylene powder to the first functional filler is 100:8.

[0086] Example of effect

[0087] To evaluate the comprehensive properties of the polytetrafluoroethylene (PTFE) prepared in each embodiment and comparative example, the Shore hardness, tensile strength, elongation at break, flexural strength, compressive strength, coefficient of friction, wear mark width, and dielectric constant of PTFE were tested. Shore hardness was obtained using a Shore hardness tester; tensile strength and elongation at break were tested according to the methods specified in standard GB / T1040-92; flexural strength was tested according to the methods specified in standard GB / T9341-2000; and compressive strength was tested according to the methods specified in standard GB / T1041-92. The coefficient of friction was tested according to the methods specified in standard GB3960-83, and the wear mark width was determined by observation using a polarizing microscope. The dielectric constant was determined by testing double-sided gold-sprayed PTFE using a broadband dielectric impedance relaxation spectrometer at a frequency of 1 MHz. The Shore hardness, tensile strength, elongation at break, flexural strength, compressive strength, coefficient of friction, wear mark width, and dielectric constant of the PTFE prepared in each embodiment and comparative example are shown in Table 1.

[0088] Table 1. Shore hardness, tensile strength, elongation at break, flexural strength, compressive strength, coefficient of friction, wear track width, and dielectric constant of polytetrafluoroethylene prepared in each example and comparative example.

[0089]

[0090] As shown in Table 1, compared with pure PTFE material, the hardness, tensile strength, elongation at break, flexural strength, compressive strength and dielectric constant of the polytetrafluoroethylene composite materials prepared in Examples 1-4 are significantly improved to varying degrees, while the coefficient of friction and wear track width are significantly reduced. This indicates that the polytetrafluoroethylene material of the present invention has the advantages of both high wear resistance and low coefficient of friction.

[0091] As shown in Example 1 and Comparative Example 1, replacing 1H-tetrazole-1-acetyl chloride with phenylacetyl chloride resulted in a decrease in the hardness, tensile strength, elongation at break, flexural strength, compressive strength, and dielectric constant of the prepared polytetrafluoroethylene composite material. Conversely, the wear track width and coefficient of friction increased, with the coefficient of friction exceeding that of pure PTFE material. Therefore, it was impossible to simultaneously achieve both high wear resistance and a low coefficient of friction. This phenomenon may be due to the high rigidity of the tetrazolium group located in the side chain, its rotatable position, and its inherent toughness. The tetrazolium heterocycle and the hydrophobic fluorocarbon chain at the molecular chain end can work together to improve strength and tribological properties.

[0092] As shown in Example 1 and Comparative Examples 2-3, replacing 3-mercaptopropyltriethoxysilane used in the preparation of the first or second filler with 3-aminopropyltriethoxysilane increased the wear track width and friction coefficient of the polytetrafluoroethylene composite material, and the friction coefficient was greater than that of pure PTFE material, while the dielectric constant decreased. These phenomena may be due to the good hydrophobicity of the thiol carboxylic acid ester groups generated after the reaction of thiol groups and acyl chlorides in the modified halloysite nanotubes, which allows for free rotation and thus improves the dielectric constant and tribological properties.

[0093] As shown in Example 1 and Comparative Examples 4-5, the mechanical strength of polytetrafluoroethylene (PTFE) composites prepared using either a smaller first functional filler or a larger second functional filler alone is reduced, while the coefficient of friction, wear track width, and dielectric constant increase. These phenomena may be because the smaller first functional filler and the larger second functional filler can form denser and more compact aggregates, and simultaneously create a hierarchical structure with distinct high and low layers, thereby compensating for the defects of PTFE and improving the material's mechanical properties, tribological properties, and dielectric properties.

Claims

1. A method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction, characterized in that, Includes the following steps: (1) Halloysite nanotubes with an average outer diameter of 30-40 nm, an average inner diameter of 10-15 nm, and an average length of 500-700 nm were mixed and reacted with 3-mercaptopropyltriethoxysilane at 110-115 °C to obtain modified halloysite nanotubes; then, the modified halloysite nanotubes and tetrazolium-modified fluorothioyl chloride compound were mixed and reacted in a solvent to obtain the first functional filler; the molar ratio of mercapto groups in the modified halloysite nanotubes to the molar ratio of tetrazolium-modified fluorothioyl chloride compound was 1:1.5-1.8; the mass ratio of halloysite nanotubes to 3-mercaptopropyltriethoxysilane was 5:5-6. (2) Halloysite nanotubes with an average outer diameter of 60-70 nm, an average inner diameter of 20-30 nm, and an average length of 800-1000 nm were mixed and reacted with 3-mercaptopropyltriethoxysilane at 110-115 °C to obtain modified halloysite nanotubes; then, the modified halloysite nanotubes and tetrazolium-modified fluorothioyl chloride compound were mixed and reacted in a solvent to obtain a second functional filler; the molar ratio of mercapto groups in the modified halloysite nanotubes to the molar ratio of tetrazolium-modified fluorothioyl chloride compound was 1:1.5-1.8; the mass ratio of halloysite nanotubes to 3-mercaptopropyltriethoxysilane was 5:8-10; (3) Mix polytetrafluoroethylene powder, the first functional filler, and the second functional filler in a mass ratio of 100:3~5:3~5, cold press and sinter to obtain a polytetrafluoroethylene composite material; the structure of the tetrazolium-modified fluorothionyl chloride compound in steps (1) and (2) is as follows: ， When R3 is -SS-, R1 is -CH2-CH2- and R2 is -CH2-CH2-; when R3 is -S-, R1 is -CH2- and R2 is -CH2-.

2. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 1, characterized in that, The preparation method of the tetrazolium-modified fluorothionyl chloride compound is as follows: (1) Glycidyl ether hexafluorononyl ether, thiodicarboxylic acid, tetrabutylammonium bromide and organic solvent are mixed and reacted at 85-90°C to obtain a fluorothiocarboxylic acid compound; the thiodicarboxylic acid is 3,3′-dithiodipropionic acid or thionyl diacetic acid; the molar ratio of glycidyl ether hexafluorononyl ether and thiodicarboxylic acid is 1:1; (2) A fluorothiocarboxylic acid compound, 1H-tetrazole-1-acetyl chloride and a solvent are mixed and reacted at 0-5°C to obtain a tetrazolium-modified fluorothiocarboxylic acid compound; the molar ratio of hydroxyl groups in the 1H-tetrazole-1-acetyl chloride and the fluorothiocarboxylic acid compound is 1:

1. (3) The tetrazolium-modified fluorothiocarboxylic acid compound, oxalyl and solvent are mixed and reacted at 58-62°C to obtain a tetrazolium-modified fluorothiocarboxylic acid chloride compound; the molar ratio of carboxyl group and oxalyl chloride in the tetrazolium-modified fluorothiocarboxylic acid compound is 1:4.2-4.

5.

3. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 2, characterized in that, In step (1) of the preparation method of tetrazolium-modified fluorothioyl chloride compound, the organic solvent is composed of dichloromethane, acetone and ethanol in a mass ratio of 0.5:1:

1.

4. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 2, characterized in that, In step (1) of the preparation method of tetrazolium-modified fluorothioyl chloride compound, the mass of the organic solvent is 120-150% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid; the mass of tetrabutylammonium bromide is 2-3% of the sum of the masses of glycidyl ether hexafluorononyl ether and 3,3′-dithiodipropionic acid; and the mixing reaction time is 4-5 h.

5. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 2, characterized in that, In step (2) of the preparation method of tetrazolium-modified fluorothioyl chloride compound, the mixing reaction time is 6-8 h.

6. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 2, characterized in that, In step (3) of the preparation method of tetrazolium-modified fluorothioyl chloride compound, the mixing reaction time is 18-22 h.

7. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 1, characterized in that, The average particle size of the polytetrafluoroethylene powder is 30–35 μm.

8. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 1, characterized in that, The cold pressing process involves a pressure of 40–45 MPa, a time of 15–20 min, and a pressurization rate of 0.1–0.15 MPa / s.

9. The method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in claim 1, characterized in that, The sintering temperature is 375–380°C, and the time is 3–3.5 h.

10. A polytetrafluoroethylene prepared by a method for preparing polytetrafluoroethylene with both high wear resistance and low coefficient of friction as described in any one of claims 1 to 9.

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