High-temperature-resistant low-permeability polytetrafluoroethylene pipe

Abstract

The application discloses a kind of high-temperature-resistant low-permeability polytetrafluoroethylene pipe, which is prepared by composite modified polytetrafluoroethylene composition, the composite modified polytetrafluoroethylene composition includes the following raw material components by weight parts: polytetrafluoroethylene 100 parts; modified boron nitride grafted carbon nanotube composite filler 3.5-8 parts; poly-p-hydroxybenzoic acid ester 12-23 parts; dipentaerythritol 1.7-4.5 parts.The application can effectively overcome the defects of poor thermal conductivity and insufficient high-temperature resistance of polytetrafluoroethylene by compounding and modifying the polytetrafluoroethylene base material. The prepared polytetrafluoroethylene pipe can better meet the application requirements of the heat exchanger pipe as a strong corrosive liquid. On the one hand, it can improve the application effect of polytetrafluoroethylene heat exchanger pipe, and on the other hand, it can provide more possibilities for widening the application scenarios.

Description

Technical Field

[0001] This invention relates to the field of polytetrafluoroethylene (PTFE) materials, and particularly to a high-temperature resistant, low-permeability PTFE pipe. Background Technology

[0002] Heat exchangers are indispensable equipment for heat exchange and transfer in chemical production processes. These heat exchangers often involve highly corrosive and oxidizing materials, therefore, the materials used to manufacture them must possess strong corrosion resistance. Conventional metals are clearly insufficient, while materials with corrosion resistance, such as graphite, ceramics, and glass, have drawbacks such as fragility, large size, and poor thermal conductivity.

[0003] Therefore, polytetrafluoroethylene (PTFE) heat exchangers were developed. These heat exchanger tubes are made of PTFE, which possesses extremely stable chemical properties, excellent corrosion resistance, and a smooth tube wall surface that is not prone to scaling, while also exhibiting moderate flexibility. These characteristics allow PTFE heat exchangers to replace metal heat exchangers for heat exchange with various highly corrosive media, such as strong acid and alkali solutions. However, PTFE has a low thermal conductivity, and compared to metals, its mechanical properties and high-temperature resistance are inferior. While using small-diameter, thin-walled tubes can compensate for some thermal conductivity issues, the compensation is limited. This affects the effectiveness of PTFE heat exchanger tubes as heat transfer components and limits their application scenarios, currently typically only suitable for lower pressure and lower temperature applications. Furthermore, heat exchanger tubes used with highly corrosive liquids place higher demands on the high-temperature resistance, corrosion resistance, and impermeability of PTFE. Patent CN114230835B discloses a low-permeability polytetrafluoroethylene (PTFE) tube and its preparation method. This method improves the density and thus permeability resistance of PTFE tubes by impregnating or spraying them with PFA emulsion. While it achieves some improvement in permeability resistance, it does not address the high-temperature resistance and thermal conductivity of the PTFE tubes, making it insufficient for applications requiring tubes for highly corrosive liquids.

[0004] Therefore, it is now necessary to improve existing technologies to provide more reliable solutions. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-temperature resistant and low-permeability polytetrafluoroethylene pipe, which addresses the shortcomings of the prior art.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a high-temperature resistant and low-permeability polytetrafluoroethylene (PTFE) pipe, which is prepared by a composite modified PTFE composition, wherein the composite modified PTFE composition comprises the following raw material components in parts by weight:

[0007] 100 parts of polytetrafluoroethylene;

[0008] 3.5-8 parts of modified boron nitride-grafted carbon nanotube composite filler;

[0009] 12-23 parts of poly(p-hydroxybenzoate);

[0010] Dipentaerythritol 1.7-4.5 parts.

[0011] Preferably, the modified boron nitride-grafted carbon nanotube composite filler is prepared by the following method:

[0012] S1. Preparation of borate carbon nanotubes;

[0013] S2. Preparation of boron nitride-grafted carbon nanotube composite filler: CNTs-BN by hydrothermal method;

[0014] S3. Grafting polymethyl methacrylate onto CNTs-BN yields a modified boron nitride-grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0015] Preferably, step S1 specifically includes:

[0016] S1-1. Preparation of oxidized modified carbon nanotubes: Take 0.75-3.0g of carbon nanotubes and add them to a mixed acid consisting of 50-150mL of 98wt% concentrated sulfuric acid and 15-50mL of 65wt% concentrated nitric acid. Sonicate at 50-70℃ for 0.5-2h, then stir and reflux at 70-95℃ for 2-8h, cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 80-100℃ for 3-12h to obtain oxidized modified carbon nanotubes.

[0017] S1-2. Take 0.25-1.0g of oxidized modified carbon nanotubes and add them to 50-200mL of methanol. Disperse them ultrasonically for 15-60min to obtain a carbon nanotube dispersion.

[0018] S1-3. Take 2.6-10.4g of 3-aminophenylboronic acid and add it to 75-300mL of methanol. Stir for 5-30min. Add the resulting mixture to the carbon nanotube dispersion, then add 2-8g of EDC hydrochloride. Sonicate and disperse for 10-30min. Then reflux at 70-80℃ for 3-8h. Cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 30-45℃ for 6-24h to obtain borate carbon nanotubes.

[0019] Preferably, step S2 specifically includes:

[0020] S2-1. Take 1-4g of the borate carbon nanotubes prepared in step S1 and add them to 25-100g of deionized water. Disperse them ultrasonically for 15-60min to obtain a borate carbon nanotube dispersion.

[0021] S2-2. Take 0.65-2.6g of sodium azide and add it to 12.5-50g of deionized water, then add 0.186-0.744g of white phosphorus powder, and then add boronized carbon nanotube dispersion. Stir for 10-40min. Transfer the resulting mixture to a stainless steel reactor, purge with nitrogen for 5-30min, seal the stainless steel reactor, and heat to 380-450℃ at a rate of 1-3℃ / min. React for 24-60h. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water until neutral, and vacuum dry at 70-90℃ for 3-12h to obtain boron nitride-grafted carbon nanotube composite filler: CNTs-BN.

[0022] Preferably, step S3 specifically includes:

[0023] Take 0.1-0.4g of CNTs-BN prepared in step S2 and add it to 100-400mL of methanol. Disperse it ultrasonically for 5-30min, then add 2.25-9.0g of methyl methacrylate. Purge with nitrogen gas for 30-90min while stirring, then add 0.035-0.14g of benzoyl peroxide. React at 50-60℃ for 2-8h, then add 0.02-0.08g of benzoyl peroxide, raise the temperature to 62-68℃, and continue the reaction for 1.5-6h. After the reaction is complete, wash the product with ethyl acetate and methanol in sequence, and dry it under vacuum at 40-55℃ for 6-24h to obtain the modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0024] Preferably, the modified boron nitride-grafted carbon nanotube composite filler is prepared by the following method:

[0025] S1. Preparation of borate carbon nanotubes:

[0026] S1-1. Preparation of oxidized modified carbon nanotubes: Take 1.5g of carbon nanotubes and add them to a mixed acid consisting of 75mL of 98wt% concentrated sulfuric acid and 25mL of 65wt% concentrated nitric acid. Sonicate at 60℃ for 1h, then stir and reflux at 80℃ for 4h. Cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 90℃ for 6h to obtain oxidized modified carbon nanotubes.

[0027] S1-2. Take 0.5g of oxidized modified carbon nanotubes and add them to 100mL of methanol. Disperse them by ultrasonication for 30min to obtain a carbon nanotube dispersion.

[0028] S1-3. Take 5.2g of 3-aminophenylboronic acid and add it to 150mL of methanol. Stir for 10min. Add the resulting mixture to the carbon nanotube dispersion and then add 4g of EDC hydrochloride. Disperse by ultrasonication for 15min. Then reflux at 75℃ for 6h. Cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 40℃ for 12h to obtain borate carbon nanotubes.

[0029] S2. Hydrothermal preparation of boron nitride-grafted carbon nanotube composite fillers:

[0030] S2-1. Take 2g of the borate carbon nanotubes prepared in step S1 and add them to 50g of deionized water. Disperse them by ultrasonication for 30min to obtain a borate carbon nanotube dispersion.

[0031] S2-2. Take 1.30g of sodium azide and add it to 25g of deionized water, then add 0.372g of white phosphorus powder, and then add boronized carbon nanotube dispersion. Stir for 20min, transfer the resulting mixture to a stainless steel reactor, purge with nitrogen for 15min, seal the stainless steel reactor, and heat to 420℃ at a rate of 2℃ / min. React for 48h. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water until neutral, and vacuum dry at 80℃ for 6h to obtain boron nitride grafted carbon nanotube composite filler: CNTs-BN.

[0032] S3. Grafting polymethyl methacrylate onto CNTs-BN yields a modified boron nitride-grafted carbon nanotube composite filler:

[0033] 0.2 g of CNTs-BN prepared in step S2 was added to 200 mL of methanol and ultrasonically dispersed for 15 min. Then, 4.5 g of methyl methacrylate was added, and nitrogen gas was purged under stirring for 45 min. Then, 0.07 g of benzoyl peroxide was added, and the reaction was carried out at 55 °C for 4 h. Then, 0.04 g of benzoyl peroxide was added, the temperature was raised to 65 °C, and the reaction was continued for 3 h. After the reaction was completed, the product was washed with ethyl acetate and methanol in sequence, and vacuum dried at 50 °C for 12 h to obtain the modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0034] Preferably, the composite modified polytetrafluoroethylene composition comprises the following raw material components in parts by weight:

[0035] 100 parts of polytetrafluoroethylene;

[0036] 6.5 parts of modified boron nitride-grafted carbon nanotube composite filler;

[0037] 18 parts of poly(p-hydroxybenzoate);

[0038] Dipentaerythritol 3.6 parts.

[0039] Preferably, the preparation method of the high-temperature resistant and low-permeability polytetrafluoroethylene pipe includes the following steps:

[0040] 1) Mix polytetrafluoroethylene and modified boron nitride-grafted carbon nanotube composite filler, ball mill under nitrogen protection for 1-4 hours, control the ball-to-material ratio at 5:1-9:1, and the ball milling speed at 200-500 rpm. Mix the ball milling product with poly(p-hydroxybenzoate) and dipentaerythritol, and stir at 140-155℃ and 180-400 rpm for 0.5-2 hours to obtain a composite modified polytetrafluoroethylene composition.

[0041] 2) Add the composite modified polytetrafluoroethylene composition into the mold, pressurize it at 30-70 MPa for 1-4 hours, then heat it to 360-375℃ at a heating rate of 40-70℃ / h, hold it at that temperature for 4-8 hours, and then cool it down to room temperature at a cooling rate of 15-30℃ / h. Remove it from the mold to obtain the high-temperature resistant and low-permeability polytetrafluoroethylene pipe.

[0042] Preferably, the preparation method of the high-temperature resistant and low-permeability polytetrafluoroethylene pipe includes the following steps:

[0043] 1) Mix polytetrafluoroethylene and modified boron nitride grafted carbon nanotube composite filler, ball mill under nitrogen protection for 2 hours, control the ball-to-material ratio at 8:1, and the ball milling speed at 400 rpm. Mix the ball milling product with poly(p-hydroxybenzoate) and dipentaerythritol, and stir at 160℃ and 350 rpm for 1 hour to obtain a composite modified polytetrafluoroethylene composition.

[0044] 2) The composite modified polytetrafluoroethylene composition is added into the mold, pressure is maintained at 50 MPa for 2 hours, then heated to 365°C at a heating rate of 60°C / h, held at that temperature for 6 hours, and then cooled to room temperature at a cooling rate of 20°C / h. The product is then removed from the mold to obtain the high-temperature resistant and low-permeability polytetrafluoroethylene pipe.

[0045] The beneficial effects of this invention are:

[0046] This invention provides a high-temperature resistant and low-permeability polytetrafluoroethylene (PTFE) pipe. By compounding and modifying the PTFE material, the defects of PTFE, such as poor thermal conductivity and insufficient high-temperature resistance, can be effectively overcome. The prepared PTFE pipe can better meet the application requirements of heat exchanger tubes used for highly corrosive liquids. On the one hand, it can improve the application effect of PTFE heat exchanger tubes, and on the other hand, it can provide more possibilities for expanding its application scenarios.

[0047] In this invention, the addition of poly(p-hydroxybenzoate) to the polytetrafluoroethylene system can improve the thermal conductivity and high-temperature resistance of the prepared polytetrafluoroethylene pipe, and further enhance its resistance to organic solvent corrosion.

[0048] The modified boron nitride-grafted carbon nanotube composite filler PMMA@CNTs-BN prepared in this invention is obtained by first synthesizing boron nitride grains in situ on borate carbon nanotubes via a hydrothermal method using a coupled reaction mechanism, and then grafting polymethyl methacrylate onto the carbon nanotubes based on an in-situ precipitation polymerization reaction. The carbon nanotubes in PMMA@CNTs-BN significantly enhance the mechanical strength, high-temperature resistance, and thermal conductivity of polytetrafluoroethylene (PTFE) materials. The boron nitride grains on them can improve the high-temperature corrosion resistance of PTFE materials and fill the gaps between the substrates, enhancing the density of the substrate and thus improving the permeability resistance of the PTFE tubing. Furthermore, the carbon nanotubes can also reduce permeability by increasing the crystallinity of PTFE. The grafted polymer polymethyl methacrylate can significantly improve the compatibility of boron nitride-grafted carbon nanotube composite filler in polytetrafluoroethylene (PTFE) systems, enabling uniform dispersion. This simultaneously solves the defects of easy agglomeration and poor dispersion of carbon nanotubes and boron nitride in PTFE. The carbon nanotube-loaded boron nitride structure, combined with the grafting of polymethyl methacrylate onto the carbon nanotubes, can also overcome the problem that boron nitride is not easy to surface modify to improve its dispersion ability in polymers. Attached Figure Description

[0049] Figure 1 The infrared absorption spectra of borate carbon nanotubes (CNTs) and modified boron nitride grafted carbon nanotube composite filler (PMMA@CNTs-BN) prepared in Example 1 are shown.

[0050] Figure 2 The XRD pattern of the boron nitride-grafted carbon nanotube composite filler CNTs-BN prepared in Example 1;

[0051] Figure 3 The results of room temperature and high temperature tensile strength tests on polytetrafluoroethylene pipes prepared in the examples and comparative examples;

[0052] Figure 4 The permeability coefficient test results of polytetrafluoroethylene pipes prepared in the examples and comparative examples at room temperature and high temperature;

[0053] Figure 5 The thermal conductivity test results are shown for the polytetrafluoroethylene pipes prepared in the examples and comparative examples. Detailed Implementation

[0054] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0055] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0056] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0057] This invention provides a high-temperature resistant, low-permeability polytetrafluoroethylene (PTFE) pipe, which is prepared by a composite modified PTFE composition. The composite modified PTFE composition comprises the following raw material components in parts by weight:

[0058] 100 parts of polytetrafluoroethylene;

[0059] 3.5-8 parts of modified boron nitride-grafted carbon nanotube composite filler;

[0060] 12-23 parts of poly(p-hydroxybenzoate);

[0061] Dipentaerythritol 1.7-4.5 parts.

[0062] The preparation method of this high-temperature resistant, low-permeability polytetrafluoroethylene pipe includes the following steps:

[0063] 1) Mix polytetrafluoroethylene and modified boron nitride-grafted carbon nanotube composite filler, ball mill under nitrogen protection for 1-4 hours, control the ball-to-material ratio at 5:1-9:1, and the ball milling speed at 200-500 rpm. Mix the ball milling product with poly(p-hydroxybenzoate) and dipentaerythritol, and stir at 140-155℃ and 180-400 rpm for 0.5-2 hours to obtain a composite modified polytetrafluoroethylene composition.

[0064] 2) Add the composite modified polytetrafluoroethylene composition into the mold, pressurize it at 30-70 MPa for 1-4 hours, then heat it to 360-375℃ at a heating rate of 40-70℃ / h, hold it at that temperature for 4-8 hours, and then cool it down to room temperature at a cooling rate of 15-30℃ / h. Remove it from the mold to obtain the high-temperature resistant and low-permeability polytetrafluoroethylene pipe.

[0065] The appropriate mold is selected based on the required pipe size and shape.

[0066] In this invention, the modified boron nitride-grafted carbon nanotube composite filler is prepared by the following method:

[0067] S1. Preparation of borate carbon nanotubes:

[0068] S1-1. Preparation of oxidized modified carbon nanotubes: Take 0.75-3.0g of carbon nanotubes and add them to a mixed acid consisting of 50-150mL of 98wt% concentrated sulfuric acid and 15-50mL of 65wt% concentrated nitric acid. Sonicate at 50-70℃ for 0.5-2h, then stir and reflux at 70-95℃ for 2-8h, cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 80-100℃ for 3-12h to obtain oxidized modified carbon nanotubes.

[0069] S1-2. Take 0.25-1.0g of oxidized modified carbon nanotubes and add them to 50-200mL of methanol. Disperse them ultrasonically for 15-60min to obtain a carbon nanotube dispersion.

[0070] S1-3. Take 2.6-10.4g of 3-aminophenylboronic acid and add it to 75-300mL of methanol. Stir for 5-30min. Add the resulting mixture to the carbon nanotube dispersion, and then add 2-8g of EDC hydrochloride (1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride). Disperse by ultrasonication for 10-30min, then reflux at 70-80℃ for 3-8h. Cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 30-45℃ for 6-24h to obtain borate carbon nanotubes.

[0071] S2. Hydrothermal preparation of boron nitride-grafted carbon nanotube composite fillers:

[0072] S2-1. Take 1-4g of the borate carbon nanotubes prepared in step S1 and add them to 25-100g of deionized water. Disperse them ultrasonically for 15-60min to obtain a borate carbon nanotube dispersion.

[0073] S2-2. Take 0.65-2.6g of sodium azide and add it to 12.5-50g of deionized water, then add 0.186-0.744g of white phosphorus powder, and then add boronized carbon nanotube dispersion. Stir for 10-40min. Transfer the resulting mixture to a stainless steel reactor, purge with nitrogen for 5-30min, seal the stainless steel reactor, and heat to 380-450℃ at a rate of 1-3℃ / min. React for 24-60h. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water until neutral, and vacuum dry at 70-90℃ for 3-12h to obtain boron nitride-grafted carbon nanotube composite filler: CNTs-BN.

[0074] S3. Grafting polymethyl methacrylate onto CNTs-BN yields a modified boron nitride-grafted carbon nanotube composite filler:

[0075] Take 0.1-0.4g of CNTs-BN prepared in step S2 and add it to 100-400mL of methanol. Disperse it ultrasonically for 5-30min, then add 2.25-9.0g of methyl methacrylate. Purge with nitrogen gas for 30-90min while stirring, then add 0.035-0.14g of benzoyl peroxide. React at 50-60℃ for 2-8h, then add 0.02-0.08g of benzoyl peroxide, raise the temperature to 62-68℃, and continue the reaction for 1.5-6h. After the reaction is complete, wash the product with ethyl acetate and methanol in sequence, and dry it under vacuum at 40-55℃ for 6-24h to obtain the modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0076] Polytetrafluoroethylene (PTFE) heat exchangers use PTFE tubes as heat transfer components. PTFE is chemically stable, possesses excellent corrosion resistance, and has a smooth tube wall surface that is not prone to scaling, while also exhibiting moderate flexibility. These characteristics allow PTFE heat exchangers to replace metal heat exchangers for heat exchange with various highly corrosive media, such as strong acid and alkali solutions. However, PTFE has a low thermal conductivity, and compared to metals, its mechanical properties and high-temperature resistance are inferior. While using small-diameter, thin-walled tubes can compensate for some thermal conductivity issues, the compensation is limited. This affects the effectiveness of PTFE heat exchanger tubes as heat transfer components and limits their application scenarios, currently typically only suitable for lower pressure and lower temperature applications. This invention, through compound modification of PTFE materials, effectively overcomes these shortcomings. On the one hand, it improves the application performance of PTFE heat exchanger tubes; on the other hand, it provides more possibilities for broadening their application scenarios.

[0077] Poly(p-hydroxybenzoate) has excellent high-temperature resistance and organic solvent resistance, and its thermal conductivity is significantly better than that of polytetrafluoroethylene (PTFE), with a thermal conductivity coefficient approximately 3 to 5 times that of PTFE (Zhang Zaili, Zeng Zimin, Li Jia, et al. High-temperature resistant and low-wear polyphenylene ester modified polytetrafluoroethylene [J]. New Chemical Materials, 2002, 30(8):5.DOI:10.3969 / j.issn.1006-3536.2002.08.001.). In this invention, its compounding into the PTFE system can improve the thermal conductivity and high-temperature resistance of the prepared PTFE pipes, and further enhance their resistance to organic solvent corrosion.

[0078] The modified boron nitride-grafted carbon nanotube composite filler prepared in this invention, PMMA@CNTs-BN, is obtained by first synthesizing boron nitride grains in situ on borate carbon nanotubes via a hydrothermal method using a coupled reaction mechanism, and then grafting polymethyl methacrylate onto the carbon nanotubes based on an in-situ precipitation polymerization reaction. Carbon nanotubes significantly enhance the mechanical strength, high-temperature resistance, and thermal conductivity of polytetrafluoroethylene (PTFE) materials. The boron nitride grains on the nanotubes improve the high-temperature corrosion resistance of PTFE materials and fill the gaps between the substrates, enhancing the substrate's density and thus improving the PTFE tubing's permeability resistance. Furthermore, carbon nanotubes can reduce permeability by increasing the crystallinity of PTFE. Finally, the grafted polymer polymethyl methacrylate (PMMA) significantly improves the compatibility of boron nitride-grafted carbon nanotube composite filler in the polytetrafluoroethylene (PTFE) system, enabling uniform dispersion. This simultaneously addresses the shortcomings of carbon nanotubes and boron nitride in PTFE, such as easy agglomeration and poor dispersion. The structure of carbon nanotubes loaded with boron nitride, combined with PMMA grafting onto the carbon nanotubes, also overcomes the difficulty of surface modification to improve the dispersion ability of boron nitride in polymers. The synthesis mechanism and its reinforcing and modifying mechanism on PTFE are described in detail below to facilitate understanding of the invention.

[0079] Synthesis mechanism

[0080] (1) First, a rich number of carboxyl functional groups are introduced on the surface of carbon nanotubes by strong acid oxidation. Then, the amino group on 3-aminophenylboronic acid reacts with the carboxyl group to fix the boric acid group on the carbon nanotubes in a covalent manner, thus obtaining borated carbon nanotubes.

[0081] (2) Then, using the coupling effect, boron nitride crystals were synthesized in situ on borate carbon nanotubes via a hydrothermal method: borate carbon nanotubes were mixed with sodium azide and white phosphorus, and a hydrothermal reaction was carried out under high temperature and high pressure. The borate groups on the borate carbon nanotubes reacted with sodium azide in the presence of white phosphorus, and boron nitride microcrystals were generated in situ on the carbon nanotubes. The main reaction processes involved are as follows:

[0082] NaN3→Na+N2+N * ;

[0083] Na + H₂O → NaOH + H₂ * ;

[0084] BO2 - +P(H * → B * +PO4 3- ;

[0085] B * +N *→BN.

[0086] Where, N * H * B * Each represents a corresponding atom.

[0087] The above reaction principle is based on the following reference: Yu Meiyan, Xu Hongyan, Cui Deliang, et al. Coupling effect in hydrothermal synthesis of boron nitride [C] / / Progress in Nanomaterials and Technological Applications - Proceedings of the Third National Conference on Nanomaterials and Technological Applications (Volume 1). 2003. DOI:ConferenceArticle / 5aa57fabc095d72220dc7d1a.

[0088] The active nitrogen atoms (N) produced by the decomposition of sodium azide at high temperature * If there is not enough time to react with the active boron atoms (B * When combined, it will combine with active nitrogen atoms to form N2, which leads to a decrease in BN synthesis efficiency. However, in this invention, the boric acid groups are uniformly distributed on the surface of carbon nanotubes, which has better dispersion uniformity. Moreover, active nitrogen atoms are easily adsorbed onto carbon nanotubes and efficiently combine with the active boron atoms generated on them, thereby effectively improving the BN generation efficiency.

[0089] (3) Finally, polymethyl methacrylate (PMMA) grafting is achieved through in-situ precipitation polymerization of PMMA monomers on carbon nanotubes. The main mechanism is as follows:

[0090] In the poor solvent of methyl methacrylate, after the reaction is initiated, oligomers soluble in the solvent are first formed. As the polymer free radical chains grow, their solubility in the poor solvent decreases, and they are adsorbed onto the surface of carbon nanotubes. Once the polymer free radical chains reach a critical chain length in the poor solvent, the active polymer free radicals of the critical chain length can be adsorbed onto the carbon nanotubes and react chemically with the residual active sites thereon. The polymer chains intertwine and interpenetrate on the carbon nanotubes, forming a coating graft. (Guo Guiquan. Polymer-Modified Carbon Nanotubes and Their Applications in Catalysis and Biology [D]. Fudan University, 2007. DOI:10.7666 / d.y1171123.)

[0091] Enhancement mechanism

[0092] The thermal conductivity of polytetrafluoroethylene (PTFE) ranges from 0.167 to 0.35 W / (m·K), while that of carbon nanotubes reaches approximately 3000-3500 W / (m·K), and that of boron nitride is approximately 250-300 W / (m·K). Adding carbon nanotubes and boron nitride to PTFE composites can significantly improve the thermal conductivity of PTFE.

[0093] Meanwhile, carbon nanotubes also have excellent mechanical strength and high temperature resistance. When carbon nanotubes are uniformly dispersed in polytetrafluoroethylene (PTFE), they can form a network structure, which can significantly improve the thermal conductivity, high temperature resistance and mechanical strength of the substrate. Furthermore, carbon nanotubes can reduce the permeability of PTFE tubing by increasing the crystallinity of PTFE.

[0094] In-situ grafted boron nitride microcrystals onto carbon nanotubes can serve as connecting nodes in the network structure, providing rigid support points and thus further improving mechanical and thermal properties. Uniformly dispersed boron nitride microcrystals can also enhance the high-temperature resistance and corrosion resistance of the substrate. Furthermore, due to their nanoscale characteristics, boron nitride microcrystals can fill gaps in the substrate and enhance its density, thereby improving the permeability resistance of PTFE tubing. The mechanical tensile effect of boron nitride microcrystals on carbon nanotubes can reduce their curling.

[0095] Grafting modification of polymethyl methacrylate (PMMA) onto carbon nanotubes can significantly improve the compatibility of boron nitride-grafted carbon nanotube composite fillers in polytetrafluoroethylene (PTFE) systems, enabling uniform dispersion. The construction of a carbon nanotube-boron nitride microcrystalline composite system, coupled with PMMA grafting modification, can simultaneously address the defects of easy agglomeration and poor dispersion of carbon nanotubes and boron nitride in PTFE, and overcome the problem of difficulty in surface modification of boron nitride to improve its dispersion ability in polymers. Ultimately, carbon nanotubes and boron nitride can fully exert their respective performance-enhancing effects on PTFE materials, achieving a synergistic reinforcement effect and significantly improving the high-temperature resistance, corrosion resistance, impermeability, and mechanical strength of PTFE tubing.

[0096] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0097] Polytetrafluoroethylene (PTFE), powder, particle size 0.4μm, specific gravity 2.2 g / cm³, melting point 325~335℃, Guangzhou Songbai Chemical Co., Ltd.

[0098] Poly(p-hydroxybenzoate), Shanghai Guangshi Plastics Co., Ltd.;

[0099] Dipentaerythritol, Nantong Runfeng Petrochemical Co., Ltd.;

[0100] Multi-walled carbon nanotubes (all carbon nanotubes mentioned in the following examples and comparative examples are multi-walled carbon nanotubes), 100 nm in diameter, 5 μm in average length, Suzhou Kaifa New Material Technology Co., Ltd.

[0101] Cubic boron nitride, hexagonal boron nitride, 2μm, Suzhou Kaifa New Materials Technology Co., Ltd.;

[0102] 3-Aminophenylboronic acid, Brand: Kramar, Shanghai Ziyi Reagent Factory;

[0103] Methyl methacrylate, Jiangsu Wenru Technology Chemical Co., Ltd.;

[0104] Benzoyl peroxide, Suzhou Senfida Chemical Co., Ltd.

[0105] Example 1

[0106] A high-temperature resistant, low-permeability polytetrafluoroethylene (PTFE) pipe is prepared by a composite modified PTFE composition, wherein the composite modified PTFE composition comprises the following raw material components in parts by weight:

[0107] 100 parts of polytetrafluoroethylene;

[0108] 6.5 parts of modified boron nitride-grafted carbon nanotube composite filler;

[0109] 18 parts of poly(p-hydroxybenzoate);

[0110] Dipentaerythritol 3.6 parts.

[0111] The preparation method of this high-temperature resistant, low-permeability polytetrafluoroethylene pipe includes the following steps:

[0112] 1) Mix polytetrafluoroethylene and modified boron nitride grafted carbon nanotube composite filler, ball mill under nitrogen protection for 2 hours, control the ball-to-material ratio at 8:1, and the ball milling speed at 400 rpm. Mix the ball milling product with poly(p-hydroxybenzoate) and dipentaerythritol, and stir at 160℃ and 350 rpm for 1 hour to obtain a composite modified polytetrafluoroethylene composition.

[0113] 2) The composite modified polytetrafluoroethylene composition is added into the mold, pressure is maintained at 50 MPa for 2 hours, then heated to 365°C at a heating rate of 60°C / h, held at that temperature for 6 hours, and then cooled to room temperature at a cooling rate of 20°C / h. The product is then removed from the mold to obtain the high-temperature resistant and low-permeability polytetrafluoroethylene pipe.

[0114] The modified boron nitride-grafted carbon nanotube composite filler was prepared by the following method:

[0115] S1. Preparation of borate carbon nanotubes:

[0116] S1-1. Preparation of oxidized modified carbon nanotubes: Take 1.5g of carbon nanotubes and add them to a mixed acid consisting of 75mL of 98wt% concentrated sulfuric acid and 25mL of 65wt% concentrated nitric acid. Sonicate at 60℃ for 1h, then stir and reflux at 80℃ for 4h. Cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 90℃ for 6h to obtain oxidized modified carbon nanotubes.

[0117] S1-2. Take 0.5g of oxidized modified carbon nanotubes and add them to 100mL of methanol. Disperse them by ultrasonication for 30min to obtain a carbon nanotube dispersion.

[0118] S1-3. Take 5.2g of 3-aminophenylboronic acid and add it to 150mL of methanol. Stir for 10min. Add the resulting mixture to the carbon nanotube dispersion and then add 4g of EDC hydrochloride. Disperse by ultrasonication for 15min. Then reflux at 75℃ for 6h, cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 40℃ for 12h to obtain borate carbon nanotubes (CNTs).

[0119] S2. Hydrothermal preparation of boron nitride-grafted carbon nanotube composite fillers:

[0120] S2-1. Take 2g of the borate carbon nanotubes prepared in step S1 and add them to 50g of deionized water. Disperse them by ultrasonication for 30min to obtain a borate carbon nanotube dispersion.

[0121] S2-2. Take 1.30g of sodium azide and add it to 25g of deionized water, then add 0.372g of white phosphorus powder, and then add boronized carbon nanotube dispersion. Stir for 20min, transfer the resulting mixture to a stainless steel reactor, purge with nitrogen for 15min, seal the stainless steel reactor, and heat to 420℃ at a rate of 2℃ / min. React for 48h. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water until neutral, and vacuum dry at 80℃ for 6h to obtain boron nitride grafted carbon nanotube composite filler: CNTs-BN.

[0122] S3. Grafting polymethyl methacrylate onto CNTs-BN yields a modified boron nitride-grafted carbon nanotube composite filler:

[0123] 0.2 g of CNTs-BN prepared in step S2 was added to 200 mL of methanol and ultrasonically dispersed for 15 min. Then, 4.5 g of methyl methacrylate was added, and nitrogen gas was purged under stirring for 45 min. Then, 0.07 g of benzoyl peroxide was added, and the reaction was carried out at 55 °C for 4 h. Then, 0.04 g of benzoyl peroxide was added, the temperature was raised to 65 °C, and the reaction was continued for 3 h. After the reaction was completed, the product was washed with ethyl acetate and methanol in sequence, and vacuum dried at 50 °C for 12 h to obtain the modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0124] Example 2

[0125] A high-temperature resistant, low-permeability polytetrafluoroethylene (PTFE) pipe is prepared by a composite modified PTFE composition, wherein the composite modified PTFE composition comprises the following raw material components in parts by weight:

[0126] 100 parts of polytetrafluoroethylene;

[0127] Six parts of modified boron nitride-grafted carbon nanotube composite filler;

[0128] 18.5 parts of poly(p-hydroxybenzoate);

[0129] Dipentaerythritol 3.6 parts.

[0130] The preparation method of this high-temperature resistant, low-permeability polytetrafluoroethylene pipe includes the following steps:

[0131] 1) Mix polytetrafluoroethylene and modified boron nitride grafted carbon nanotube composite filler, ball mill under nitrogen protection for 2 hours, control the ball-to-material ratio at 8:1, and the ball milling speed at 400 rpm. Mix the ball milling product with poly(p-hydroxybenzoate) and dipentaerythritol, and stir at 160℃ and 350 rpm for 1 hour to obtain a composite modified polytetrafluoroethylene composition.

[0132] 2) The composite modified polytetrafluoroethylene composition is added into the mold, pressure is maintained at 50 MPa for 2 hours, then heated to 365°C at a heating rate of 60°C / h, held at that temperature for 6 hours, and then cooled to room temperature at a cooling rate of 20°C / h. The product is then removed from the mold to obtain the high-temperature resistant and low-permeability polytetrafluoroethylene pipe.

[0133] The modified boron nitride-grafted carbon nanotube composite filler was prepared by the following method:

[0134] S1. Preparation of borate carbon nanotubes:

[0135] S1-1. Preparation of oxidized modified carbon nanotubes: Take 1.5g of carbon nanotubes and add them to a mixed acid consisting of 75mL of 98wt% concentrated sulfuric acid and 25mL of 65wt% concentrated nitric acid. Sonicate at 60℃ for 1h, then stir and reflux at 80℃ for 4h. Cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 90℃ for 6h to obtain oxidized modified carbon nanotubes.

[0136] S1-2. Take 0.5g of oxidized modified carbon nanotubes and add them to 100mL of methanol. Disperse them by ultrasonication for 30min to obtain a carbon nanotube dispersion.

[0137] S1-3. Take 5.2g of 3-aminophenylboronic acid and add it to 150mL of methanol. Stir for 10min. Add the resulting mixture to the carbon nanotube dispersion and then add 4g of EDC hydrochloride. Disperse by ultrasonication for 15min. Then reflux at 75℃ for 6h, cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 40℃ for 12h to obtain borate carbon nanotubes (CNTs).

[0138] S2. Hydrothermal preparation of boron nitride-grafted carbon nanotube composite fillers:

[0139] S2-1. Take 2g of the borate carbon nanotubes prepared in step S1 and add them to 50g of deionized water. Disperse them by ultrasonication for 30min to obtain a borate carbon nanotube dispersion.

[0140] S2-2. Take 1.30g of sodium azide and add it to 25g of deionized water, then add 0.372g of white phosphorus powder, and then add boronized carbon nanotube dispersion. Stir for 20min, transfer the resulting mixture to a stainless steel reactor, purge with nitrogen for 15min, seal the stainless steel reactor, and heat to 420℃ at a rate of 2℃ / min. React for 48h. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water until neutral, and vacuum dry at 80℃ for 6h to obtain boron nitride grafted carbon nanotube composite filler: CNTs-BN.

[0141] S3. Grafting polymethyl methacrylate onto CNTs-BN yields a modified boron nitride-grafted carbon nanotube composite filler:

[0142] 0.2 g of CNTs-BN prepared in step S2 was added to 200 mL of methanol and ultrasonically dispersed for 15 min. Then, 4.5 g of methyl methacrylate was added, and nitrogen gas was purged under stirring for 45 min. Then, 0.07 g of benzoyl peroxide was added, and the reaction was carried out at 55 °C for 4 h. Then, 0.04 g of benzoyl peroxide was added, the temperature was raised to 65 °C, and the reaction was continued for 3 h. After the reaction was completed, the product was washed with ethyl acetate and methanol in sequence, and vacuum dried at 50 °C for 12 h to obtain the modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0143] Example 3

[0144] A high-temperature resistant, low-permeability polytetrafluoroethylene (PTFE) pipe is prepared by a composite modified PTFE composition, wherein the composite modified PTFE composition comprises the following raw material components in parts by weight:

[0145] 100 parts of polytetrafluoroethylene;

[0146] 6.2 parts of modified boron nitride-grafted carbon nanotube composite filler;

[0147] 19 parts of poly(p-hydroxybenzoate);

[0148] 4 parts of dipentaerythritol.

[0149] The preparation method of this high-temperature resistant, low-permeability polytetrafluoroethylene pipe includes the following steps:

[0150] 1) Mix polytetrafluoroethylene and modified boron nitride grafted carbon nanotube composite filler, ball mill under nitrogen protection for 2 hours, control the ball-to-material ratio at 8:1, and the ball milling speed at 400 rpm. Mix the ball milling product with poly(p-hydroxybenzoate) and dipentaerythritol, and stir at 160℃ and 350 rpm for 1 hour to obtain a composite modified polytetrafluoroethylene composition.

[0151] 2) The composite modified polytetrafluoroethylene composition is added into the mold and pressure is maintained at 50 MPa for 2 hours. Then, it is heated to 370°C at a heating rate of 55°C / h and held at that temperature for 6.5 hours. Then, it is cooled to room temperature at a cooling rate of 20°C / h and removed from the mold to obtain the high-temperature resistant and low-permeability polytetrafluoroethylene pipe.

[0152] The modified boron nitride-grafted carbon nanotube composite filler was prepared by the following method:

[0153] S1. Preparation of borate carbon nanotubes:

[0154] S1-1. Preparation of oxidized modified carbon nanotubes: Take 1.5g of carbon nanotubes and add them to a mixed acid consisting of 75mL of 98wt% concentrated sulfuric acid and 25mL of 65wt% concentrated nitric acid. Sonicate at 60℃ for 1h, then stir and reflux at 80℃ for 4h. Cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 90℃ for 6h to obtain oxidized modified carbon nanotubes.

[0155] S1-2. Take 0.5g of oxidized modified carbon nanotubes and add them to 100mL of methanol. Disperse them by ultrasonication for 30min to obtain a carbon nanotube dispersion.

[0156] S1-3. Take 5.2g of 3-aminophenylboronic acid and add it to 150mL of methanol. Stir for 10min. Add the resulting mixture to the carbon nanotube dispersion and then add 4g of EDC hydrochloride. Disperse by ultrasonication for 15min. Then reflux at 75℃ for 6h, cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 40℃ for 12h to obtain borate carbon nanotubes (CNTs).

[0157] S2. Hydrothermal preparation of boron nitride-grafted carbon nanotube composite fillers:

[0158] S2-1. Take 2g of the borate carbon nanotubes prepared in step S1 and add them to 50g of deionized water. Disperse them by ultrasonication for 30min to obtain a borate carbon nanotube dispersion.

[0159] S2-2. Take 1.30g of sodium azide and add it to 25g of deionized water, then add 0.372g of white phosphorus powder, and then add boronized carbon nanotube dispersion. Stir for 20min, transfer the resulting mixture to a stainless steel reactor, purge with nitrogen for 15min, seal the stainless steel reactor, and heat to 420℃ at a rate of 2℃ / min. React for 48h. After the reaction is completed, cool to room temperature, filter, wash the solid product with deionized water until neutral, and vacuum dry at 80℃ for 6h to obtain boron nitride grafted carbon nanotube composite filler: CNTs-BN.

[0160] S3. Grafting polymethyl methacrylate onto CNTs-BN yields a modified boron nitride-grafted carbon nanotube composite filler:

[0161] 0.2 g of CNTs-BN prepared in step S2 was added to 200 mL of methanol and ultrasonically dispersed for 15 min. Then, 4.5 g of methyl methacrylate was added, and nitrogen gas was purged under stirring for 45 min. Then, 0.07 g of benzoyl peroxide was added, and the reaction was carried out at 55 °C for 4 h. Then, 0.04 g of benzoyl peroxide was added, the temperature was raised to 65 °C, and the reaction was continued for 3 h. After the reaction was completed, the product was washed with ethyl acetate and methanol in sequence, and vacuum dried at 50 °C for 12 h to obtain the modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

[0162] Comparative Example 1

[0163] This example is essentially the same as Example 1, except that in this example, the composite modified polytetrafluoroethylene composition comprises the following raw material components in parts by weight:

[0164] 100 parts of polytetrafluoroethylene;

[0165] 18 parts of poly(p-hydroxybenzoate);

[0166] Dipentaerythritol 3.6 parts.

[0167] Comparative Example 2

[0168] This example is essentially the same as Example 1, except that in this example, the composite modified polytetrafluoroethylene composition comprises the following raw material components in parts by weight:

[0169] 100 parts of polytetrafluoroethylene;

[0170] 18 parts of poly(p-hydroxybenzoate);

[0171] 4.9 parts of carbon nanotubes;

[0172] 1.6 parts of boron nitride;

[0173] Dipentaerythritol 3.6 parts.

[0174] Boron nitride is a mixture of cubic boron nitride and hexagonal boron nitride, with a mass ratio of cubic boron nitride to hexagonal boron nitride of 2:1.

[0175] Comparative Example 3

[0176] This example is essentially the same as Example 1, except that in this example, the composite modified polytetrafluoroethylene composition comprises the following raw material components in parts by weight:

[0177] 100 parts of polytetrafluoroethylene;

[0178] 6.5 parts of boron nitride-grafted carbon nanotube composite filler;

[0179] 18 parts of poly(p-hydroxybenzoate);

[0180] Dipentaerythritol 3.6 parts.

[0181] The preparation method of the boron nitride-grafted carbon nanotube composite filler is the same as that in Example 1.

[0182] Comparative Example 4

[0183] This example is essentially the same as Example 1, except that in this example, the composite modified polytetrafluoroethylene composition comprises the following raw material components in parts by weight:

[0184] 100 parts of polytetrafluoroethylene;

[0185] 6.5 parts of modified carbon nanotube composite filler;

[0186] 18 parts of poly(p-hydroxybenzoate);

[0187] Dipentaerythritol 3.6 parts.

[0188] The modified carbon nanotube composite filler is prepared by the following method:

[0189] S1. Preparation of borate carbon nanotubes:

[0190] S1-1. Preparation of oxidized modified carbon nanotubes: Take 1.5g of carbon nanotubes and add them to a mixed acid consisting of 75mL of 98wt% concentrated sulfuric acid and 25mL of 65wt% concentrated nitric acid. Sonicate at 60℃ for 1h, then stir and reflux at 80℃ for 4h. Cool to room temperature, filter, wash with deionized water until neutral, and vacuum dry at 90℃ for 6h to obtain oxidized modified carbon nanotubes.

[0191] S1-2. Take 0.5g of oxidized modified carbon nanotubes and add them to 100mL of methanol. Disperse them by ultrasonication for 30min to obtain a carbon nanotube dispersion.

[0192] S1-3. Take 5.2g of 3-aminophenylboronic acid and add it to 150mL of methanol. Stir for 10min. Add the resulting mixture to the carbon nanotube dispersion and then add 4g of EDC hydrochloride. Disperse by ultrasonication for 15min. Then reflux at 75℃ for 6h, cool to room temperature, filter, wash the solid product with deionized water, and vacuum dry at 40℃ for 12h to obtain borate carbon nanotubes (CNTs).

[0193] S2. Grafting polymethyl methacrylate onto CNTs yields modified carbon nanotube composite fillers:

[0194] 0.2 g of CNTs prepared in step S2 was added to 200 mL of methanol and ultrasonically dispersed for 15 min. Then, 4.5 g of methyl methacrylate was added, and nitrogen gas was purged under stirring for 45 min. Then, 0.07 g of benzoyl peroxide was added, and the mixture was reacted at 55 °C for 4 h. Then, 0.04 g of benzoyl peroxide was added, the temperature was raised to 65 °C, and the reaction was continued for 3 h. After the reaction was completed, the product was washed with ethyl acetate and methanol in sequence, and vacuum dried at 50 °C for 12 h to obtain the modified carbon nanotube composite filler: PMMA@CNTs.

[0195] I. Performance Characterization

[0196] 1. Reference Figure 1 The image shows the infrared absorption spectra of boronized carbon nanotubes (CNTs) and modified boron nitride-grafted carbon nanotube composite filler (PMMA@CNTs-BN) prepared in Example 1. According to the CNTs spectrum, the appearance of characteristic peaks such as BO and Benzene (benzene ring) indicates the successful modification of carbon nanotubes with 3-aminophenylboronic acid. In the PMMA@CNTs-BN spectrum, the peak at 1700 cm⁻¹... -1 2950cm -1 The newly added peaks in the vicinity originate from C=O and CH functional groups, respectively, indicating the successful grafting of polymethyl methacrylate; while the newly added peak at 1085 cm⁻¹... -1 The nearby peak is a characteristic absorption peak of cBN, at 1390 cm⁻¹. -1 and 788cm -1 The nearby peaks are characteristic absorption peaks of hBN (Li Kai, Lian Gang, Jiang Haihui, et al. Influence of the type of reactants in the hydrothermal synthesis of boron nitride [J]. Functional Materials, 2007, 038(010):1678-1681.), which indicates the successful grafting of boron nitride and includes two crystal forms: cubic boron nitride cBN and hexagonal boron nitride hBN.

[0197] 2. Reference Figure 2The image shows the XRD pattern of the boron nitride-grafted carbon nanotube composite filler CNTs-BN prepared in Example 1. It can be further seen that the boron nitride crystal forms synthesized in situ include cubic boron nitride (cBN) and hexagonal boron nitride (hBN).

[0198] II. Performance Testing

[0199] 1. Tensile property test

[0200] The tests were conducted in accordance with the standards GB / T1040.1-2018 "Determination of Tensile Properties of Plastics" and QB / T4877-2015 "Polytetrafluoroethylene Pipes".

[0201] 2. Thermal conductivity

[0202] A thermal conductivity meter was used, referring to the standard: GB / T1029-2015 Determination of thermal conductivity of non-metallic solid materials.

[0203] 3. Permeability coefficient

[0204] The test was conducted according to the method provided in patent CN114230835B, "A Low-Permeability Polytetrafluoroethylene Tube and Its Preparation Method," as follows:

[0205] (1) Seal the front end of the polytetrafluoroethylene pipe (diameter 12 mm, length 200 mm, wall thickness 2 mm) prepared in the examples and comparative examples, then inject 45% sulfuric acid, and then seal the end.

[0206] (2) Immerse the polytetrafluoroethylene pipe completely in a container filled with deionized water, control the pure water temperature at 25°C, and seal the container.

[0207] (3) After 10 days, sample the pure water in the container and test the concentration of sulfate ions. Calculate the permeability coefficient using the following formula:

[0208] Permeability coefficient k = (sulfate ion permeation amount μg) ÷ (permeability area cm²) 2 ) ÷ (number of days elapsed) × (thickness of the pipe in cm);

[0209] The sulfate ion permeation rate is calculated by the concentration of sulfate ions in deionized water and the volume of water, and the permeation area is the surface area of ​​the polytetrafluoroethylene pipe.

[0210] 4. High temperature resistance test

[0211] 4-1. High-temperature tensile strength

[0212] After the polytetrafluoroethylene pipe sample was kept at 200℃ for 2 hours, its tensile strength was measured according to the method in section 1.

[0213] 4-2. High-temperature permeability coefficient

[0214] Following the permeability test method in section 3, the temperature of the deionized water was controlled at 90°C, and the container was periodically replenished with 90°C deionized water to reach the initial volume. Then, the permeability coefficient at 90°C was tested using the same method.

[0215] Test results are shown in Tables 1 and 2. Figures 3-5 :

[0216] Table 1. Room temperature performance test results

[0217] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength / MPa 54.6 53.7 54.3 28.5 35.4 43.9 48.1 Thermal conductivity, W / (m·K) 5.8 5.5 5.6 0.9 2.1 3.4 3.7 <![CDATA[Permeability coefficient, (μg·cm) / (cm 2 ·day)]]> 0.012 0.016 0.014 0.075 0.051 0.027 0.033

[0218] Table 2 High Temperature Performance Test Results

[0219] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Keep warm at 200℃ for 2 hours Tensile strength / MPa 51.2 50.1 50.9 10.3 28.3 39.2 40.7 Control the pure water temperature to 90℃ <![CDATA[Permeability coefficient (μg·cm) / (cm 2 ·day)]]> 0.017 0.024 0.020 0.093 0.078 0.039 0.049

[0220] The test results show that the polytetrafluoroethylene pipes prepared in Examples 1-3 have high tensile strength, excellent thermal conductivity, impermeability, corrosion resistance, and good high-temperature resistance; they can be used as heat exchange pipes for heat transfer of high-temperature corrosive liquids.

[0221] In Comparative Example 1, the absence of modified boron nitride-grafted carbon nanotube composite filler resulted in a significant decrease in its overall performance. In Comparative Example 2, the combination of carbon nanotubes and boron nitride was used instead of the modified boron nitride-grafted carbon nanotube composite filler, but this failed to solve the problem of poor dispersion of carbon nanotubes and boron nitride, leading to a significant decrease in all properties. In Comparative Example 3, the modified boron nitride-grafted carbon nanotube composite filler was not coated with polymethyl methacrylate, which affected its dispersibility and caused a certain degree of decrease in overall performance. In Comparative Example 4, the modified carbon nanotube composite filler did not contain boron nitride, resulting in a decrease in its high-temperature resistance and impermeability.

[0222] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A high temperature resistant, low permeability polytetrafluoroethylene tubing, characterized by, It is prepared by a composite modified polytetrafluoroethylene composition, which comprises the following raw material components by weight parts: Polytetrafluoroethylene 100 parts; Modified boron nitride grafted carbon nanotube composite filler 3.5-8 parts; Poly-p-hydroxybenzoic acid ester 12-23 parts; Dipentaerythritol 1.7-4.5 parts; The modified boron nitride grafted carbon nanotube composite filler is prepared by the following method: S1, preparation of borated carbon nanotubes: S1-1, preparation of oxidatively modified carbon nanotubes: take 0.75-3.0 g of carbon nanotubes and add them to a mixed acid composed of 50-150 mL of concentrated sulfuric acid with a concentration of 98 wt% and 15-50 mL of concentrated nitric acid with a concentration of 65 wt%, ultrasonic at 50-70℃ for 0.5-2h, then stir and reflux at 70-95℃ for 2-8h, cool to room temperature, filter, wash with deionized water until neutral, vacuum dry at 80-100℃ for 3-12h to obtain oxidatively modified carbon nanotubes; S1-2, take 0.25-1.0 g of oxidatively modified carbon nanotubes and add them to 50-200 mL of methanol, ultrasonic dispersion for 15-60 min to obtain a carbon nanotube dispersion; S1-3, take 2.6-10.4 g of 3-aminobenzoic acid and add it to 75-300 mL of methanol, stir for 5-30 min, add the obtained mixture to the carbon nanotube dispersion, then add 2-8 g of EDC hydrochloride, ultrasonic dispersion for 10-30 min, then reflux at 70-80℃ for 3-8h, cool to room temperature, filter, wash the solid product with deionized water, vacuum dry at 30-45℃ for 6-24h to obtain borated carbon nanotubes; S2, preparation of boron nitride grafted carbon nanotube composite filler by hydrothermal method: S2-1, take 1-4 g of borated carbon nanotubes prepared in step S1 and add them to 25-100 g of deionized water, ultrasonic dispersion for 15-60 min to obtain a borated carbon nanotube dispersion; S2-2, take 0.65-2.6 g of sodium azide and add it to 12.5-50 g of deionized water, then add 0.186-0.744 g of white phosphorus powder, then add the borated carbon nanotube dispersion, stir for 10-40 min, transfer the obtained mixture to a stainless steel reaction kettle, introduce nitrogen for 5-30 min, seal the stainless steel reaction kettle, heat to 380-450℃ at a rate of 1-3℃ / min, react for 24-60h, after the reaction is completed, cool to room temperature, suction filter, wash the solid product with deionized water until neutral, vacuum dry at 70-90℃ for 3-12h to obtain boron nitride grafted carbon nanotube composite filler: CNTs-BN; S3, 0.1-0.4 g of the CNTs-BN prepared in step S2 is added into 100-400 mL of methanol, and ultrasonic dispersion is performed for 5-30 min, then 2.25-9.0 g of methyl methacrylate is added, nitrogen is passed under stirring for 30-90 min, 0.035-0.14 g of benzoyl peroxide is added, reaction is performed at 50-60 ℃ for 2-8 h, then 0.02-0.08 g of benzoyl peroxide is added, the temperature is increased to 62-68 ℃, and reaction is continued for 1.5-6 h; after the reaction is completed, the product is washed with ethyl acetate and methanol in sequence, and vacuum drying is performed at 40-55 ℃ for 6-24 h, to obtain a modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

2. The high temperature resistant low permeation polytetrafluoroethylene pipe according to claim 1, characterized by, The modified boron nitride grafted carbon nanotube composite filler is prepared by the following method: S1, boronated carbon nanotubes are prepared: S1-1, oxidized modified carbon nanotubes are prepared: 1.5 g of carbon nanotubes is added into a mixed acid composed of 75 mL of concentrated sulfuric acid with a concentration of 98 wt% and 25 mL of concentrated nitric acid with a concentration of 65 wt%, ultrasonic dispersion is performed at 60 ℃ for 1 h, then stirring reflux is performed at 80 ℃ for 4 h, after cooling to room temperature, filtration is performed, washing with deionized water is performed until neutral, and vacuum drying is performed at 90 ℃ for 6 h, to obtain oxidized modified carbon nanotubes; S1-2, 0.5 g of the oxidized modified carbon nanotubes is added into 100 mL of methanol, and ultrasonic dispersion is performed for 30 min, to obtain a carbon nanotube dispersion; S1-3, 5.2 g of 3-aminobenzoic acid is added into 150 mL of methanol, stirring is performed for 10 min, the obtained mixture is added into the carbon nanotube dispersion, 4 g of EDC hydrochloride is added, ultrasonic dispersion is performed for 15 min, then reflux is performed at 75 ℃ for 6 h, after cooling to room temperature, filtration is performed, the solid product is washed with deionized water, and vacuum drying is performed at 40 ℃ for 12 h, to obtain boronated carbon nanotubes; S2, boron nitride grafted carbon nanotube composite fillers are prepared by a hydrothermal method: S2-1, 2 g of the boronated carbon nanotubes prepared in step S1 is added into 50 g of deionized water, and ultrasonic dispersion is performed for 30 min, to obtain a boronated carbon nanotube dispersion; S2-2, 1.30 g of sodium azide is added into 25 g of deionized water, then 0.372 g of white phosphorus powder is added, the boronated carbon nanotube dispersion is added, stirring is performed for 20 min, the obtained mixture is transferred into a stainless steel reaction kettle, nitrogen is passed in for 15 min, the stainless steel reaction kettle is sealed, the temperature is increased to 420 ℃ at a rate of 2 ℃ / min, reaction is performed for 48 h, after the reaction is completed, the temperature is cooled to room temperature, suction filtration is performed, the solid product is washed with deionized water until neutral, and vacuum drying is performed at 80 ℃ for 6 h, to obtain a boron nitride grafted carbon nanotube composite filler: CNTs-BN; S3, poly methyl methacrylate is grafted on the CNTs-BN, to obtain a modified boron nitride grafted carbon nanotube composite filler: Take 0.2 g of CNTs-BN prepared in step S2 into 200 mL of methanol, ultrasonic dispersion for 15 min, then add 4.5 g of methyl methacrylate, stir under nitrogen for 45 min, then add 0.07 g of benzoyl peroxide, react at 55℃ for 4 h, then add 0.04 g of benzoyl peroxide, heat to 65℃, continue to react for 3 h; after the reaction is completed, the product is washed with ethyl acetate and methanol in turn, and vacuum dried at 50℃ for 12 h to obtain a modified boron nitride grafted carbon nanotube composite filler: PMMA@CNTs-BN.

3. The high temperature resistant low permeation polytetrafluoroethylene pipe according to claim 1, wherein, The composite modified polytetrafluoroethylene composition comprises the following raw material components by weight parts: Polytetrafluoroethylene 100 parts; Modified boron nitride grafted carbon nanotube composite filler 6.5 parts; Poly-p-hydroxybenzoic acid ester 18 parts; Dipentaerythritol 3.6 parts.

4. The high temperature resistant, low permeation polytetrafluoroethylene tubing of claim 1, wherein, The preparation method comprises the following steps: 1) Mix polytetrafluoroethylene and modified boron nitride grafted carbon nanotube composite filler, ball mill under nitrogen protection for 1-4 h, control the ball to material ratio to be 5:1-9:1, the ball milling speed is 200-500 rpm, mix the obtained ball milling product with poly-p-hydroxybenzoic acid ester and dipentaerythritol, stir at 140-155℃ and 180-400 rpm for 0.5-2 h to obtain a composite modified polytetrafluoroethylene composition; 2) Put the composite modified polytetrafluoroethylene composition into a mold, press for 1-4 h under 30-70 Mpa, then heat to 360-375℃ at a heating rate of 40-70℃ / h, keep for 4-8 h, then reduce to room temperature at a cooling rate of 15-30℃ / h, take out from the mold to obtain the high-temperature-resistant low-permeability polytetrafluoroethylene pipe.

5. The high temperature resistant, low permeation polytetrafluoroethylene tubing of claim 4, wherein, The preparation method comprises the following steps: 1) Mix polytetrafluoroethylene and modified boron nitride grafted carbon nanotube composite filler, ball mill under nitrogen protection for 2 h, control the ball to material ratio to be 8:1, the ball milling speed is 400 rpm, mix the obtained ball milling product with poly-p-hydroxybenzoic acid ester and dipentaerythritol, stir at 160℃ and 350 rpm for 1 h to obtain a composite modified polytetrafluoroethylene composition; 2) Put the composite modified polytetrafluoroethylene composition into a mold, press for 2 h under 50 Mpa, then heat to 365℃ at a heating rate of 60℃ / h, keep for 6 h, then reduce to room temperature at a cooling rate of 20℃ / h, take out from the mold to obtain the high-temperature-resistant low-permeability polytetrafluoroethylene pipe.

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