Green process for the preparation of a fusible polytetrafluoroethylene

Abstract

The application discloses a green preparation process of fusible polytetrafluoroethylene and relates to the field of fluorine-containing polymers. The specific process is as follows: deoxygenated high-purity water, perfluoropropyl vinyl ether, an ionic liquid and a chain transfer agent are added into a polymerization kettle with an agitator and a temperature control system, the oxygen content in the kettle is controlled, the polymerization kettle is heated, tetrafluoroethylene monomers are introduced until the reaction pressure is reached, an initiator is added, the temperature and pressure are kept constant during the reaction, and after the polymerization reaction is completed, the emulsion is washed and dried to obtain fusible polytetrafluoroethylene resin. The method proposes an ionic solution as an emulsifier and a stabilizer, the process route is green and environment-friendly, and the resin has stable and excellent performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fluoropolymers, in particular a green process for the preparation of a fusible polytetrafluoroethylene. BACKGROUND

[0002] Fusible polytetrafluoroethylene (PFA), also known as Polyfluoroalkoxy or perfluoroalkoxy, is a fluoropolymer with excellent properties. PFA is a copolymer of tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PPVE). It retains many of the excellent properties of polytetrafluoroethylene (PTFE), such as exceptional chemical resistance, high temperature resistance, low dielectric constant, non-flammability, weather resistance, low coefficient of friction, non-stick and self-lubricating. At the same time, PFA, due to its thermoplasticity, can be processed by conventional thermoplastic processing methods such as injection molding, extrusion, compression molding, etc., which makes the design and manufacture of PFA products more flexible.

[0003] The application field of PFA is very wide, including the insulation layer of high temperature wire and cable, chemical equipment, medical device parts, semiconductor industry, sealing material, pump valve bushing and anticorrosion equipment manufacturing, etc. These properties of PFA make it an ideal material choice under extreme chemical environments and requirements.

[0004] A fusible polytetrafluoroethylene resin and a preparation method thereof (Patent Application No. CN202311539107.9) The method comprises adding an aqueous reaction medium, a fluorine-containing surfactant, a buffer, an initiator and a perfluoroalkyl vinyl ether into a reaction kettle, introducing tetrafluoroethylene monomer to a reaction pressure, the reaction pressure is not higher than 0.8 MPa, copolymerization reaction to obtain a fusible tetrafluoro polymer liquid, adding water to adjust the solid content during the post-treatment condensation process, stirring and condensing, filtering, washing, drying and fluorine gas treatment to obtain a fusible polytetrafluoroethylene resin; the volume ratio of fluorine gas to nitrogen gas introduced in the fluorine gas treatment is 1:1 to 2:1, the fluorine gas treatment temperature is 100-120℃, the fluorine gas treatment time is 20-24h, and the fluorine gas treatment pressure is 0.05-0.1MPa.

[0005] Aqueous process for making improved tetrafluoroethylene / fluoroalkylperfluorovinyl ether copolymers (patent application number: US3635926DA) discloses a copolymerization reaction of tetrafluoroethylene and perfluoroalkyl vinyl ether in an aqueous medium containing a small amount of fluorocarbon solvent. The typical polymerization reaction is as follows: an initiator (ammonium persulfate) and a surfactant (ammonium perfluorooctanoate) are added to a stainless steel container. After the container is sealed, it is purged with tetrafluoroethylene (TFE) to draw in water, fluorocarbon solvent and perfluoroalkyl vinyl ether (PAVE). The mixture is heated to the polymerization reaction temperature (70-95°C), tetrafluoroethylene is introduced and the polymerization reaction pressure is maintained (1.7-2.4 MPa).

[0006] In traditional PFA preparation processes, PFOA is often used as an emulsifier to improve polymer dispersibility and processing properties. The European Union has included PFOA, its salts, and PFOA-related compounds in Annex I of its Persistent Organic Pollutants (POPs) Regulation, which came into effect on July 4, 2020. China's Ministry of Ecology and Environment's "List of Key Controlled New Pollutants (2023 Edition)" also includes controls on PFOA and its related compounds. Therefore, for the long-term development of fluoropolymers, the green substitution of PFOA is essential. Summary of the Invention

[0007] The main objective of this invention is to provide a green preparation process for meltable polytetrafluoroethylene to overcome the shortcomings of the prior art.

[0008] Another object of the present invention is to provide a fusible polytetrafluoroethylene prepared by the above method.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] This invention provides a green preparation process for meltable polytetrafluoroethylene, the operation steps of which are as follows:

[0011] Step 1: According to the mass proportions, add 60-80 parts of deoxygenated high-purity water to the polymerization reactor equipped with a stirrer and temperature control system, start stirring, add 0.8-1.3 parts of perfluoropropyl vinyl ether, 0.5-1.2 parts of ionic liquid and 0.02-0.1 parts of chain transfer agent, evacuate the polymerization reactor, replace with nitrogen until the oxygen content is qualified, and heat the polymerization reactor to the reaction temperature;

[0012] Step two: polymeric kettle into tetrafluoroethylene monomer to the reaction pressure, the addition of 0.1-1 parts of initiator, the polymerization reaction begins, the reaction process continues to add tetrafluoroethylene monomer to maintain the reaction pressure, temperature control system to maintain the reaction temperature stable, when the tetrafluoroethylene make-up amount reaches 15-20 parts, end the polymerization reaction, emulsion washing, drying to get fusible polytetrafluoroethylene resin.

[0013] Further preferably, the ionic liquid in step one acts as an emulsifier and stabilizer in the present method system.

[0014] Further preferably, the preparation method of the ionic liquid in step one is:

[0015] T1: according to mass fraction, 3-5.5 parts of perfluorohexyl ethyl sulfonamide propyl betaine, 0.0004-0.02 parts of lithium 2-aminoadipate, 0.5-1 parts of perfluoropolyether (methyl) acrylate, 10-13 parts of DMF, 0.2-0.5 parts of tetramethyl guanidine, stirring at 60-70℃ for 20-50 minutes;

[0016] T2: add 0.2-0.6 parts of 1-allyl-3-methyl imidazole hexafluorophosphate, stirring at 80-90℃ for 1-3 hours, after the reaction is completed, remove DMF by vacuum distillation to obtain ionic liquid.

[0017] Further preferably, the chain transfer agent in step one is selected from at least one of methane, ethane, propane and cyclohexane.

[0018] Further preferably, the oxygen content index in step one is not higher than 30 ppm.

[0019] Further preferably, the reaction temperature in step one is 65-85℃.

[0020] Further preferably, the reaction pressure in step two is 1.6-2.2 MPa.

[0021] Further preferably, the initiator in step two is selected from at least one of azobisisobutyronitrile, isobutyryl peroxide, diisopropyl peroxydicarbonate and tert-butyl peroxyacetate.

[0022] Reaction mechanism:

[0023] The amino group of perfluorohexyl ethyl sulfonamide propyl betaine, lithium 2-aminoadipate and the alkenyl group of perfluoropolyether (methyl) acrylate, 1-allyl-3-methyl imidazole hexafluorophosphate undergo addition reaction to obtain betaine ionic liquid emulsifier containing perfluoropolyether, hexafluorophosphate and lithium complex, which is used to replace perfluorooctanoic acid-based emulsifier; lithium ions can form a new lithium salt complex with hexafluorophosphate ions in AMIM PF6. This ion exchange helps to adjust the hydrophilic-hydrophobic balance of the final emulsifier.

[0024] Technical effects:

[0025] 1. Improved emulsifying properties:

[0026] The introduction of perfluoropolyether segments increases the hydrophobicity of the emulsifier, making it more suitable for use in non-aqueous systems, while the presence of hexafluorophosphate enhances the ionic character, helping to stabilize the emulsion.

[0027] 2. Environmental friendliness:

[0028] Replacing perfluorooctanoic acid-based emulsifiers reduces the emission of persistent organic pollutants (POPs) to the environment and living organisms. DETAILED DESCRIPTION

[0029] In view of the deficiencies in the prior art, the present inventors have developed a green preparation process for fusible polytetrafluoroethylene through long-term research and extensive practice. The technical solution will be further explained below, along with its implementation process and principles.

[0030] Example 1

[0031] A green preparation process for fusible polytetrafluoroethylene, the operation steps are as follows:

[0032] Step one: Add 60 kg of deoxygenated high-purity water to a polymerization kettle equipped with a stirrer and temperature control system, start stirring, add 0.8 kg of perfluoro-n-propyl vinyl ether, 0.5 kg of ionic liquid, and 0.02 kg of chain transfer agent, vacuum the polymerization kettle, replace it with nitrogen to the qualified oxygen content, and heat the polymerization kettle to the reaction temperature;

[0033] Step two: Introduce tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure, add 0.1 kg of initiator, start the polymerization reaction, continuously introduce tetrafluoroethylene monomer during the reaction process to maintain the reaction pressure, and the temperature control system maintains the reaction temperature stable. When the tetrafluoroethylene make-up amount reaches 15 kg, the polymerization reaction is completed, and the emulsion is washed and dried to obtain fusible polytetrafluoroethylene resin.

[0034] The ionic liquid in step one acts as an emulsifier and stabilizer in the method system.

[0035] The preparation method of the ionic liquid in step one is as follows:

[0036] T1: Add 3 kg of perfluoro-hexyl ethyl sulfonamide propyl betaine, 0.0004 kg of lithium 2-aminoadipate, 0.5 kg of perfluoropolyether (methyl) acrylate, 10 kg of DMF, and 0.2 kg of tetramethylguanidine to the reactor, stir at 60°C for 20 minutes;

[0037] T2: Add 0.2 kg of 1-allyl-3-methylimidazolium hexafluorophosphate, stir at 80°C for 1 hour, and then remove the DMF by vacuum distillation to obtain the ionic liquid.

[0038] The chain transfer agent in step one is selected from methane.

[0039] The oxygen content in step one is not higher than 30 ppm.

[0040] The reaction temperature in step one is 65°C.

[0041] The reaction pressure in step two is 1.6 MPa.

[0042] The initiator in step two is selected from azobisisobutyronitrile.

[0043] Example 2

[0044] A green process for preparing a fusible polytetrafluoroethylene, the operation steps of which are as follows:

[0045] Step one: add 70 kg of deoxygenated high-purity water to a polymerization kettle equipped with a stirrer and a temperature control system, start stirring, add 1 kg of perfluoro-n-propyl vinyl ether, 0.7 kg of ionic liquid, and 0.05 kg of chain transfer agent, vacuum the polymerization kettle, replace it with nitrogen to an acceptable oxygen content, and heat the polymerization kettle to the reaction temperature.

[0046] Step two: introduce tetrafluoroethylene monomer into the polymerization kettle to maintain the reaction pressure, add 0.4 kg of initiator, start the polymerization reaction, continuously introduce tetrafluoroethylene monomer during the reaction to maintain the reaction pressure, and use the temperature control system to maintain the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 16.5 kg, the polymerization reaction is completed, the emulsion is washed and dried to obtain fusible polytetrafluoroethylene resin.

[0047] The ionic liquid in step one acts as an emulsifier and stabilizer in the method system.

[0048] The preparation method of the ionic liquid in step one is as follows:

[0049] T1: add 4.5 kg of perfluoroalkyl ethyl sulfonamide propyl betaine, 0.005 kg of lithium 2-aminoadipate, 0.65 kg of perfluoropolyether (methyl) acrylate, 11 kg of DMF, and 0.3 kg of tetramethylguanidine to the reactor, stir at 65°C for 30 minutes;

[0050] T2: add 0.35 kg of 1-allyl-3-methylimidazolium hexafluorophosphate, stir at 85°C for 2 hours, and then remove the DMF by vacuum distillation to obtain the ionic liquid.

[0051] The chain transfer agent in step one is selected from ethane.

[0052] The oxygen content index in step one is not higher than 30 ppm.

[0053] The reaction temperature in step one is 75℃.

[0054] The reaction pressure in step two is 1.8 MPa.

[0055] The initiator in step two is selected from isobutyryl peroxide.

[0056] Example 3

[0057] A green preparation process of fusible polytetrafluoroethylene, the operation steps of which are as follows:

[0058] Step one: 70 kg of deoxygenated high-purity water is added to a polymerization kettle with an agitator and a temperature control system, the agitator is turned on, 1.2 kg of perfluoro-n-propyl vinyl ether, 0.9 kg of ionic liquid and 0.08 kg of chain transfer agent are added, the polymerization kettle is vacuumed and replaced by nitrogen until the oxygen content is qualified, and the polymerization kettle is heated to the reaction temperature;

[0059] Step two: the polymerization kettle is connected with tetrafluoroethylene monomer to maintain the reaction pressure, 0.75 kg of initiator is added, the polymerization reaction starts, tetrafluoroethylene monomer is continuously added during the reaction to maintain the reaction pressure, and the temperature control system maintains the reaction temperature stable; when the amount of tetrafluoroethylene added reaches 18 kg, the polymerization reaction is ended, and the emulsion is washed and dried to obtain fusible polytetrafluoroethylene resin.

[0060] The ionic liquid in step one acts as an emulsifier and stabilizer in the method system.

[0061] The preparation method of the ionic liquid in step one is as follows:

[0062] T1: 5 kg of perfluoro-hexyl ethyl sulfonamide propyl betaine, 0.01 kg of lithium 2-aminoadipate, 0.85 kg of perfluoropolyether (methyl) acrylate, 12 kg of DMF, and 0.4 kg of tetramethyl guanidine are added to a reactor, and stirred at 65℃ for 40 minutes;

[0063] T2: 0.5 kg of 1-allyl-3-methyl imidazole hexafluorophosphate is further added, and stirred at 85℃ for 2 hours; after the reaction is completed, the DMF is removed by vacuum distillation to obtain the ionic liquid.

[0064] The chain transfer agent in step one is selected from propane.

[0065] The oxygen content index in step one is not higher than 30 ppm.

[0066] The reaction temperature in step one is 75℃.

[0067] The reaction pressure in step two is 2 MPa.

[0068] The initiator in the step two is selected from diisopropyl peroxydicarbonate.

[0069] Example 4

[0070] A green preparation process of fusible polytetrafluoroethylene, the operation steps of which are as follows:

[0071] Step one: 80 kg of deoxygenated high-purity water is added to a polymerization kettle with an agitator and a temperature control system, the agitator is turned on, 1.3 kg of n-propyl vinyl ether, 1.2 kg of ionic liquid and 0.1 kg of chain transfer agent are added, the polymerization kettle is vacuumed and replaced by nitrogen until the oxygen content is qualified, and the polymerization kettle is heated to the reaction temperature;

[0072] Step two: tetrafluoroethylene monomer is introduced into the polymerization kettle to maintain the reaction pressure, 1 kg of initiator is added, the polymerization reaction starts, tetrafluoroethylene monomer is continuously introduced during the reaction to maintain the reaction pressure, and the temperature control system is used to maintain the reaction temperature stable; when the amount of tetrafluoroethylene added reaches 20 kg, the polymerization reaction is ended, and the emulsion is washed and dried to obtain fusible polytetrafluoroethylene resin.

[0073] The ionic liquid in the step one acts as an emulsifier and a stabilizer in the method system.

[0074] The preparation method of the ionic liquid in the step one is as follows:

[0075] T1: 5.5 kg of perfluorohexylethyl sulfonamide propyl betaine, 0.02 kg of lithium 2-aminoadipate, 1 kg of perfluoropolyether (methyl) acrylate, 13 kg of DMF, and 0.5 kg of tetramethylguanidine are added to a reactor, and stirred at 70°C for 50 minutes;

[0076] T2: 0.6 kg of 1-allyl-3-methylimidazolium hexafluorophosphate is further added, and stirred at 90°C for 3 hours; after the reaction is completed, the DMF is removed by vacuum distillation to obtain the ionic liquid.

[0077] The chain transfer agent in the step one is selected from propane.

[0078] The oxygen content index in the step one is not higher than 30 ppm.

[0079] The reaction temperature in the step one is 85°C.

[0080] The reaction pressure in the step two is 2.2 MPa.

[0081] The initiator in the step two is selected from tert-butyl peroxyacetate.

[0082] Example test:

[0083] The meltability polytetrafluoroethylene resin prepared by the embodiment is subjected to performance test, the melting point thereof is tested according to the test standard of ASTM D4591, the melt index thereof is tested according to the test standard of ASTM D3307, and the metal ion precipitation is tested by ICP-OES.

[0084] The test results of the above embodiment are as follows:

[0085]

[0086]

[0087] The meltability polytetrafluoroethylene prepared by the specific embodiment in the application proposes an ionic solution as an emulsifier and a stabilizer, the process route is green and environmentally friendly, and the resin performance is stable and excellent.

[0088] It should be understood that the above embodiment is only for illustrating the technical concept and characteristics of the application, and its purpose is to enable those skilled in the art to understand the content of the application and implement it, and it cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and principle of the application shall be covered within the protection scope of the application.

Claims

1. A green process for the preparation of fusible polytetrafluoroethylene, the operating steps of which are: Step one: according to the mass fraction, 60-80 parts of deoxygenated high-purity water is added to a polymerization kettle with an agitator and a temperature control system, the agitator is turned on, 0.8-1.3 parts of perfluoro-n-propyl vinyl ether, 0.5-1.2 parts of ionic liquid and 0.02-0.1 parts of chain transfer agent are added, the polymerization kettle is vacuumed, replaced by nitrogen to the qualified oxygen content, and the polymerization kettle is heated to the reaction temperature; Step two: the polymerization kettle is connected to the four fluorine ethylene monomer to maintain the reaction pressure, 0.1-1 parts of initiator is added, the polymerization reaction starts, the four fluorine ethylene monomer is continuously added to maintain the reaction pressure during the reaction process, the temperature control system maintains the reaction temperature stable, when the four fluorine ethylene supplement reaches 15-20 parts, the polymerization reaction is ended, the emulsion is washed and dried to obtain fusible polytetrafluoroethylene resin; The preparation method of the ionic liquid in step one is: T1: according to the mass fraction, 3-5.5 parts of perfluoro-hexyl ethyl sulfonamide propyl betaine, 0.0004-0.02 parts of lithium 2-aminoadipate, 0.5-1 parts of perfluoropolyether (methyl) acrylate, 10-13 parts of DMF, 0.2-0.5 parts of tetramethyl guanidine are added to the reactor, and stirred at 60-70℃ for 20-50 minutes; T2: 0.2-0.6 parts of 1-allyl-3-methyl imidazole hexafluorophosphate is added, stirred at 80-90℃ for 1-3 hours, after the reaction is completed, the DMF is removed by vacuum distillation to obtain the ionic liquid.

2. A green process for the preparation of a fusible polytetrafluoroethylene according to claim 1, characterized in that: The ionic liquid in step one acts as an emulsifier and stabilizer in the method system.

3. A green process for the preparation of a fusible polytetrafluoroethylene according to claim 1, characterized in that: The chain transfer agent in step one is selected from at least one of methane, ethane, propane and cyclohexane.

4. A green process for the preparation of a fusible polytetrafluoroethylene according to claim 1, characterized in that: The oxygen content index in step one is not higher than 30 ppm.

5. A green process for the preparation of a fusible polytetrafluoroethylene according to claim 1, characterized in that: The reaction temperature in step one is 65-85℃.

6. A green process for the preparation of a fusible polytetrafluoroethylene according to claim 1, characterized in that: The reaction pressure in step two is 1.6-2.2 MPa.

7. A green process for the preparation of a fusible polytetrafluoroethylene according to claim 1, characterized in that: The initiator in step two is selected from at least one of azobis isobutyronitrile, isobutyryl peroxide, diisopropyl peroxydicarbonate and tert-butyl peroxyacetate.

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