Polytetrafluoroethylene sealing material and preparation method thereof

Abstract

The present invention provides a polytetrafluoroethylene sealing material and a preparation method thereof, and belongs to the technical field of sealing materials, the polytetrafluoroethylene sealing material comprises the following components by weight: 100 parts of polytetrafluoroethylene and 10-40 parts of a filler, and the filler comprises boron nitride and a polyvinylidene fluoride coating layer coating the surface of boron nitride. The boron nitride filler with the surface coated with polyvinylidene fluoride is introduced into a polytetrafluoroethylene matrix, so that the comprehensive performance of the sealing material is remarkably improved. The wear resistance is greatly enhanced by boron nitride through a pinning effect, and a constructed high-thermal-conductivity network can effectively export friction heat, so that the interface temperature is lower than the glass transition point of polytetrafluoroethylene to maintain rigidity; meanwhile, the polyvinylidene fluoride coating layer realizes covalent crosslinking through dehydrofluorination reaction with polytetrafluoroethylene, so that the mechanical strength and the interface bonding force of the material are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of sealing material technology, specifically relating to a polytetrafluoroethylene sealing material and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE), with its extremely low coefficient of friction, excellent thermal stability, good self-lubricating properties, and outstanding chemical inertness, has become an important engineering plastic. It is widely used in sealing components in industrial equipment (such as pumps, valves, and compressors), automobiles (such as engines and transmissions), and aerospace and chemical industries, playing a crucial role in ensuring the normal operation and safety of equipment. However, PTFE's inherent non-adhesive properties and poor wear resistance limit its application under certain operating conditions.

[0003] To overcome these shortcomings, existing technologies often employ inorganic materials (such as graphite, molybdenum disulfide, carbon powder, and graphene) to modify polytetrafluoroethylene (PTFE), aiming to improve its mechanical properties, wear resistance, and processing performance, thereby expanding its application range. While such modifications can improve the wear resistance of PTFE to some extent, they often lead to an increase in the coefficient of friction. More importantly, due to the poor interfacial compatibility between the PTFE vinyl body and the inorganic fillers, interfacial defects are easily formed within the composite material, resulting in a decline in the overall mechanical properties of the composite. Summary of the Invention

[0004] In view of the above situation and to overcome the defects of the prior art, the purpose of this invention is to provide a polytetrafluoroethylene sealing material and its preparation method, so as to at least partially solve the problems mentioned in the background art.

[0005] The technical solution adopted in this invention is as follows: The first aspect of the present invention provides a polytetrafluoroethylene sealing material, comprising the following components in parts by weight: 100 parts of polytetrafluoroethylene and 10-40 parts of filler, wherein the filler comprises boron nitride and a polyvinylidene fluoride coating layer on the surface of the boron nitride.

[0006] In some embodiments of the present invention, the boron nitride is hexagonal boron nitride with a particle size between 50-100 nm.

[0007] In some embodiments of the present invention, the thickness of the polyvinylidene fluoride coating is between 5-10 nm.

[0008] A second aspect of this invention provides a method for preparing a polytetrafluoroethylene (PTFE) sealing material, comprising the following steps: The filler was added to an organic solvent, stirred until homogeneous, and then subjected to ultrasonic treatment to obtain a dispersion. Add polytetrafluoroethylene to the dispersion, stir until homogeneous, then add ammonia water, and stir the mixture at 50-55℃ for 10-15 hours to obtain polytetrafluoroethylene sealing material.

[0009] In some embodiments of the present invention, the concentration of the ammonia water is 25-28 wt%, and the mass ratio of polytetrafluoroethylene to ammonia water is 4:(1-1.5).

[0010] In some embodiments of the present invention, the method for preparing the filler includes the following steps: Boron nitride was dispersed in a sodium hydroxide solution and stirred at 80-95°C for 4-8 hours to obtain hydroxylated boron nitride. Hydroxylated boron nitride was added to toluene and ultrasonically dispersed for 10-20 min. Then, 3-chloropropyltriethoxysilane was added under a nitrogen atmosphere and reacted at 80-85 °C for 8-12 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Silanized boron nitride was dispersed in ethanol, and potassium ethyl xanthate was added under a nitrogen atmosphere. The reaction was carried out at 80-90℃ for 10-15 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Xanthate-oxidized boron nitride was added to dimethyl carbonate, an initiator was added, and the mixture was sonicated for 20-30 minutes. Vinylidene fluoride was introduced under vacuum, and the mixture was reacted at 60-65°C for 10-15 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the filler.

[0011] In some embodiments of the present invention, the concentration of the sodium hydroxide solution is 1-3 mol / L, and the amount of boron nitride added to the sodium hydroxide solution is 20-30 g / L.

[0012] In some embodiments of the present invention, the mass ratio of the hydroxylated boron nitride to 3-chloropropyltriethoxysilane is 3:(5-8).

[0013] In some embodiments of the present invention, the mass ratio of the silanized boron nitride to potassium ethyl xanthate is 5:(2-4).

[0014] In some embodiments of the present invention, the mass ratio of xanthate-oxidized boron nitride to vinylidene fluoride is 1:(2-3).

[0015] The beneficial effects achieved by this invention are as follows: This invention significantly improves the overall performance of sealing materials by introducing boron nitride filler with a surface coating of polyvinylidene fluoride (PVDF) into the polytetrafluoroethylene (PTFE) matrix. Boron nitride greatly enhances wear resistance through a pinning effect, and its highly thermally conductive network effectively dissipates frictional heat, keeping the interface temperature below the glass transition point of PTFE to maintain rigidity. Simultaneously, the PVDF coating layer achieves covalent cross-linking through a defluorination reaction with PTFE, significantly improving the material's mechanical strength and interfacial bonding. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] In view of the shortcomings of the prior art mentioned in the background, the first aspect of the present invention provides a polytetrafluoroethylene sealing material, comprising the following components in parts by weight: 100 parts of polytetrafluoroethylene and 10-40 parts of filler. Polytetrafluoroethylene, as a highly crystalline polymer, has advantages such as resistance to high and low temperatures, resistance to chemical corrosion, and low coefficient of friction, and is particularly suitable for manufacturing sealing materials.

[0020] The filler comprises boron nitride and a polyvinylidene fluoride (PVDF) coating on the surface of the boron nitride. Boron nitride, as a rigid filler dispersed within the PTFE matrix, can significantly improve the wear resistance of PTFE by hindering the slippage of PTFE molecular chains through a pinning effect. Simultaneously, the high thermal conductivity network of boron nitride rapidly dissipates heat, keeping the interface temperature below the glass transition point of PTFE, thus maintaining the rigidity of the PTFE sealing material. Furthermore, the PVDF coating on the surface of the boron nitride can undergo a dehydrofluorination reaction with PTFE, achieving covalent cross-linking between the filler and PTFE, thereby improving the mechanical properties of the PTFE sealing material.

[0021] In summary, this invention significantly improves the overall performance of sealing materials by introducing boron nitride fillers with a surface coating of polyvinylidene fluoride (PVDF) into the polytetrafluoroethylene (PTFE) matrix. Boron nitride greatly enhances wear resistance through a pinning effect, and its high thermal conductivity network effectively dissipates frictional heat, keeping the interface temperature below the glass transition point of PTFE to maintain rigidity. Simultaneously, the PVDF coating layer achieves covalent cross-linking through a defluorination reaction with PTFE, significantly improving the material's mechanical strength and interfacial bonding.

[0022] In some embodiments, boron nitride is hexagonal boron nitride with a particle size between 50-100 nm. Hexagonal boron nitride has a layered structure, with weak van der Waals forces binding the layers, giving it graphite-like self-lubricating properties. This significantly reduces the coefficient of friction of polytetrafluoroethylene (PTFE), thereby further enhancing PTFE's wear resistance. By controlling the particle size of hexagonal boron nitride within a suitable range, its surface activity can be improved, promoting the bonding between hexagonal boron nitride and the polymer matrix.

[0023] In some embodiments, the thickness of the polyvinylidene fluoride (PVDF) coating is between 5 and 10 nm. A thicker PVDF coating results in higher thermal stability, while a thinner coating provides better dispersibility. By controlling the thickness of the PVDF coating to 5-10 nm, the filler can exhibit both good thermal stability and good dispersibility.

[0024] A second aspect of this invention provides a method for preparing a polytetrafluoroethylene (PTFE) sealing material, comprising the following steps: The filler was added to an organic solvent, stirred until homogeneous, and then subjected to ultrasonic treatment to obtain a dispersion. Add polytetrafluoroethylene to the dispersion, stir until homogeneous, then add ammonia water, and stir the mixture at 50-55℃ for 10-15 hours to obtain polytetrafluoroethylene sealing material.

[0025] In an alkaline ammonia environment, polytetrafluoroethylene (PTFE) can undergo a dehydrofluorination reaction with polyvinylidene fluoride (PVDF) on the filler surface to form a covalent cross-linked network, allowing the filler to be tightly embedded in PTFE and improving the mechanical properties of the PTFE sealing material.

[0026] In some embodiments, the concentration of ammonia is 25-28 wt%, and the mass ratio of polytetrafluoroethylene (PTFE) to ammonia is 4:(1-1.5). Controlling the ammonia concentration within a suitable range helps to accelerate the defluorination reaction, allowing the reaction to proceed more completely and thus forming a complete covalently cross-linked network. Setting the mass ratio of PTFE to ammonia to 3:(1-1.5) allows for sufficient cross-linking of PTFE with the polyvinylidene fluoride (PVDF) on the filler surface.

[0027] In some embodiments, the method for preparing the filler includes the following steps: Boron nitride was dispersed in a sodium hydroxide solution and stirred at 80-95°C for 4-8 hours to obtain hydroxylated boron nitride. Hydroxylated boron nitride was added to toluene and ultrasonically dispersed for 10-20 min. Then, 3-chloropropyltriethoxysilane was added under a nitrogen atmosphere and reacted at 80-85 °C for 8-12 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Silanized boron nitride was dispersed in ethanol, and potassium ethyl xanthate was added under a nitrogen atmosphere. The reaction was carried out at 80-90℃ for 10-15 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Xanthate-oxidized boron nitride was added to dimethyl carbonate, an initiator was added, and the mixture was sonicated for 20-30 minutes. Vinylidene fluoride was introduced under vacuum, and the mixture was reacted at 60-65°C for 10-15 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain the filler.

[0028] Treatment of boron nitride with sodium hydroxide solution increases the number of active hydroxyl groups on its surface, providing sites for subsequent reactions. Next, 3-chloropropyltriethoxysilane is used to condense the hydroxyl groups on the surface of hydroxylated boron nitride, introducing chloropropyl groups. Then, the chloropropyl groups react with potassium ethyl xanthate to covalently attach xanthate groups to the boron nitride surface. Finally, under the action of an initiator (e.g., tert-butyl peroxypentanoate) and with dimethyl carbonate as a solvent, the polymerization of vinylidene fluoride monomer is carried out at 60-65°C. During polymerization, free radicals generated from the initiator are rapidly captured by the xanthate groups on the boron nitride surface, forming dormant species that then initiate controlled chain growth of the vinylidene fluoride monomer on the boron nitride surface, forming a chemically bonded polyvinylidene fluoride layer.

[0029] In some embodiments, the concentration of the sodium hydroxide solution is 1-3 mol / L, and the amount of boron nitride added to the sodium hydroxide solution is 20-30 g / L. Controlling the concentration of the sodium hydroxide solution within a suitable range facilitates the complete hydroxylation of boron nitride, allowing the reaction to proceed more completely. Lower amounts of boron nitride added to the sodium hydroxide solution result in lower reaction efficiency, while higher amounts lead to uneven dispersion of boron nitride. Therefore, the amount of boron nitride added to the sodium hydroxide solution needs to be set to 20-30 g / L.

[0030] In some embodiments, the mass ratio of hydroxylated boron nitride to 3-chloropropyltriethoxysilane is 3:(5-8). Since hydroxylated boron nitride has a high specific surface area, setting the mass ratio of hydroxylated boron nitride to 3-chloropropyltriethoxysilane to 3:(5-8) satisfies the coverage requirement.

[0031] In some embodiments, the mass ratio of boron silanized nitride to potassium ethyl xanthate is 5:(2-4). By setting the mass ratio of boron silanized nitride to potassium ethyl xanthate to 5:(2-4), xanthate groups can be sufficiently grafted.

[0032] In some embodiments, the mass ratio of xanthate-oxidized boron nitride to vinylidene fluoride is 1:(2-3). By setting the mass ratio of xanthate-oxidized boron nitride to vinylidene fluoride to 1:(2-3), the polyvinylidene fluoride can be fully coated with boron nitride.

[0033] The present invention will be further described below by way of specific embodiments.

[0034] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods already existing in the art; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0035] Example 1: Boron nitride was dispersed in a 1 mol / L sodium hydroxide solution at an addition rate of 20 g / L, and stirred at 80 °C for 4 hours to obtain hydroxylated boron nitride. Hydroxylated boron nitride was added to toluene and ultrasonically dispersed for 10 min. Then, 3-chloropropyltriethoxysilane was added under a nitrogen atmosphere. The mass ratio of hydroxylated boron nitride to 3-chloropropyltriethoxysilane was 3:5. The reaction was carried out at 80 °C for 8 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Silanized boron nitride was dispersed in ethanol, and potassium ethyl xanthate was added under a nitrogen atmosphere. The mass ratio of silanized boron nitride to potassium ethyl xanthate was 5:2. The reaction was carried out at 80°C for 10 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Xanthate-oxidized boron nitride was added to dimethyl carbonate, along with the initiator tert-butyl peroxypentanoate. The mixture was ultrasonically treated for 20 minutes, and then vinylidene fluoride was introduced under vacuum. The mass ratio of xanthate-oxidized boron nitride to vinylidene fluoride was 1:2. The reaction was carried out at 60°C for 10 hours. After the reaction was completed, the filler was obtained by centrifugation, washing, and drying.

[0036] According to the weight ratio, 10 parts of filler were added to 150 parts of acetone, stirred evenly, and then ultrasonically treated to obtain a dispersion. Add 100 parts of polytetrafluoroethylene to the dispersion and stir until homogeneous. Then add 25 parts of 25wt% ammonia water and stir at 50°C for 10 hours to obtain polytetrafluoroethylene sealing material.

[0037] Example 2: Boron nitride was dispersed in a 3 mol / L sodium hydroxide solution at an addition rate of 30 g / L, and stirred at 95 °C for 8 hours to obtain hydroxylated boron nitride. Hydroxylated boron nitride was added to toluene and ultrasonically dispersed for 20 min. Then, 3-chloropropyltriethoxysilane was added under a nitrogen atmosphere. The mass ratio of hydroxylated boron nitride to 3-chloropropyltriethoxysilane was 3:8. The reaction was carried out at 85 °C for 12 h. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Silanized boron nitride was dispersed in ethanol, and potassium ethyl xanthate was added under a nitrogen atmosphere. The mass ratio of silanized boron nitride to potassium ethyl xanthate was 5:4. The reaction was carried out at 90°C for 15 minutes. After the reaction was completed, the boron nitride was obtained by centrifugation, washing and drying. Xanthate-oxidized boron nitride was added to dimethyl carbonate, along with the initiator tert-butyl peroxypentanoate. The mixture was ultrasonically treated for 30 minutes, and then vinylidene fluoride was introduced under vacuum. The mass ratio of xanthate-oxidized boron nitride to vinylidene fluoride was 1:3. The reaction was carried out at 65°C for 15 hours. After the reaction was completed, the filler was obtained by centrifugation, washing, and drying.

[0038] According to the weight ratio, 40 parts of filler were added to 250 parts of acetone, stirred evenly, and then ultrasonically treated to obtain a dispersion. 100 parts of polytetrafluoroethylene were added to the dispersion and stirred until homogeneous. Then, 37.5 parts of 28wt% ammonia water were added and stirred at 55°C for 15 hours to obtain polytetrafluoroethylene sealing material.

[0039] Example 3: Consistent with Example 1, except that the amount of filler added to the polytetrafluoroethylene sealing material is changed to 20 parts.

[0040] Example 4: Consistent with Example 1, except that the amount of filler added to the polytetrafluoroethylene sealing material is changed to 30 parts.

[0041] Comparative Example 1: It uses pure polytetrafluoroethylene and does not contain any fillers.

[0042] Comparative Example 2: Consistent with Example 1, except that boron nitride is used instead of filler.

[0043] Tests were conducted on Examples 1-4 and Comparative Examples 1 and 2. The specific test contents are as follows: Tensile test: The tensile strength and elongation at break of the specimens were determined on an electronic universal testing machine according to HG / T2902-1997. The tensile speed was 10 mm / min. 3-5 specimens were tested for each formulation, and the tensile strength and elongation at break of each specimen were recorded. The average value of the test results was taken. The test results are shown in Table 1.

[0044] Wear test: Wear tests were conducted on an M-2000 friction and wear testing machine according to GB / T3960-1983. Dry grinding was performed at a speed of 200 r / min, a load of 200 N, and a wear time of 120 min. The wear amount was calculated based on the mass of the sample before and after wear, and the friction coefficient was calculated based on the friction torque recorded during the wear process. The test results are shown in Table 1.

[0045] Table 1

[0046] Referring to the test results in Table 1, although the tensile strength of Comparative Example 2 was improved compared to Comparative Example 1, it decreased significantly compared to Example 1. This indicates that using boron nitride with a polyvinylidene fluoride coating as a filler can improve the tensile properties of polytetrafluoroethylene (PTFE). Meanwhile, the wear amount of Comparative Example 2 was slightly increased compared to Example 1, indicating that using boron nitride with a polyvinylidene fluoride coating as a filler can also enhance the wear resistance of PTFE.

[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0048] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A polytetrafluoroethylene sealing material, characterized by, The polytetrafluoroethylene sealing material comprises the following components in parts by weight: 100 parts of polytetrafluoroethylene and 10-40 parts of a filler, wherein the filler comprises boron nitride and a polyvinylidene fluoride coating layer coated on the surface of the boron nitride.

2. The polytetrafluoroethylene sealing material according to claim 1, wherein The boron nitride is hexagonal boron nitride with a particle size of 50-100 nm.

3. The polytetrafluoroethylene sealing material according to claim 1, wherein The thickness of the polyvinylidene fluoride coating layer is 5-10 nm.

4. A process for the production of a polytetrafluoroethylene sealing material according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: The filler is added into an organic solvent and stirred uniformly, and then ultrasonic treatment is performed to obtain a dispersion liquid; Polytetrafluoroethylene is added into the dispersion liquid and stirred uniformly, and then ammonia is added, and stirring reaction is performed at 50-55 ℃ for 10-15 h to obtain the polytetrafluoroethylene sealing material.

5. The preparation method according to claim 4, characterized in that, The concentration of the ammonia is 25-28 wt%, and the mass ratio of the polytetrafluoroethylene to the ammonia is 4:(1-1.5).

6. The preparation method according to claim 4, characterized in that, The preparation method of the filler comprises the following steps: The boron nitride is dispersed in a sodium hydroxide solution, and stirring reaction is performed at 80-95 ℃ for 4-8 h to obtain hydroxylated boron nitride; The hydroxylated boron nitride is added into toluene and ultrasonic dispersed for 10-20 min, and then 3-chloropropyl triethoxysilane is added under a nitrogen atmosphere, and reaction is performed at 80-85 ℃ for 8-12 h, and then centrifugation, washing and drying are performed to obtain silanized boron nitride; The silanized boron nitride is dispersed in ethanol, and potassium ethyl xanthate is added under a nitrogen atmosphere, and reaction is performed at 80-90 ℃ for 10-15 h, and then centrifugation, washing and drying are performed to obtain xanthate esterified boron nitride; The xanthate esterified boron nitride is added into dimethyl carbonate, an initiator is added, ultrasonic treatment is performed for 20-30 min, and vinylidene fluoride is introduced under vacuum, and reaction is performed at 60-65 ℃ for 10-15 h, and then centrifugation, washing and drying are performed to obtain the filler.

7. The preparation method according to claim 6, characterized in that, The concentration of the sodium hydroxide solution is 1-3 mol / L, and the boron nitride is added into the sodium hydroxide solution in an amount of 20-30 g / L.

8. The preparation method according to claim 6, characterized in that, The mass ratio of the hydroxylated boron nitride to the 3-chloropropyl triethoxysilane is 3:(5-8).

9. The preparation method according to claim 6, characterized in that, The mass ratio of the silanized boron nitride to the potassium ethyl xanthate is 5:(2-4).

10. The method of claim 6, wherein, The mass ratio of the xanthate esterified boron nitride to the vinylidene fluoride is 1:(2-3).

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