Green preparation process of fusible polytetrafluoroethylene

Abstract

The invention discloses a green preparation process of fusible polytetrafluoroethylene, and relates to the field of fluorine-containing polymers. The specific process comprises the following steps: adding deoxidized high-purity water, perfluoro-n-propyl vinyl ether, ionic liquid and a chain transfer agent into a polymerization kettle with a stirrer and a temperature control system, controlling the oxygen content in the kettle, heating the polymerization kettle, introducing a tetrafluoroethylene monomer to a reaction pressure, adding an initiator, keeping the temperature and the pressure constant in the reaction process, and after the polymerization reaction is finished, cooling to room temperature to obtain the perfluoro-n-propyl vinyl ether. And washing the emulsion, and drying to obtain the fusible polytetrafluoroethylene resin. The method provides an ionic solution as an emulsifier and a stabilizer, the process route is green and environment-friendly, and the resin performance is stable and excellent.

Description

Technical Field

[0001] The invention relates to the field of fluorine-containing polymers, in particular to a green preparation process of fusible polytetrafluoroethylene. Background Art

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

[0003] PFA has a wide range of applications, including insulation layers of high-temperature wires and cables, chemical equipment, medical device parts, semiconductor industry, sealing materials, pump and valve bushings, and the manufacture of anti-corrosion equipment, 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 number: 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 a tetrafluoroethylene monomer to a reaction pressure not higher than 0.8 MPa, copolymerizing to obtain a fusible tetrafluoro polymer liquid, adding water to adjust the solid content in a post-treatment condensation process, and obtaining a fusible polytetrafluoroethylene resin through stirring condensation, filtering, washing, drying and fluorine gas treatment; the volume ratio of fluorine gas to nitrogen introduced in the fluorine gas treatment is 1:1 to 2:1, the fluorine gas treatment temperature is 100 to 120°C, the fluorine gas treatment time is 20 to 24 hours, and the fluorine gas treatment pressure is 0.05 to 0.1 MPa.

[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 closed, it is purged with tetrafluoroethylene (TFE), water, fluorocarbon solvent and perfluoroalkyl vinyl ether (PAVE) are sucked in, the mixture is heated to a polymerization reaction temperature (70-95°C), tetrafluoroethylene is introduced and the polymerization reaction pressure (1.7-2.4MPa) is maintained.

[0006] In the traditional PFA preparation process, PFOA is often used as an emulsifier to improve the dispersibility and processing properties of the polymer. The European Union has included PFOA, its salts and PFOA-related compounds in Annex I of the Persistent Organic Pollutants (POPs) Regulation, and this restriction has been effective since July 4, 2020. The "List of New Pollutants under Key Control (2023 Edition)" issued by the Ministry of Ecology and Environment of China also includes the control of PFOA and its related compounds. Therefore, the long-term development of fluoropolymers in the future must achieve green substitution of PFOA. Summary of the invention

[0007] The main purpose of the present invention is to provide a green preparation process of fusible polytetrafluoroethylene to overcome the shortcomings of the prior art.

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

[0009] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0010] The embodiment of the present invention provides a green preparation process of fusible polytetrafluoroethylene, and the operation steps are as follows:

[0011] Step 1: Add 60-80 parts of deoxygenated high-purity water in a polymerization kettle with an agitator and a temperature control system according to the weight ratio, start stirring, add 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, evacuate the polymerization kettle, replace with nitrogen until the oxygen content is qualified, and heat the polymerization kettle to the reaction temperature;

[0012] Step 2: Tetrafluoroethylene monomer is introduced into the polymerization kettle to the reaction pressure, and 0.1-1 parts of initiator are added to start the polymerization reaction. Tetrafluoroethylene monomer is continuously introduced during the reaction process to maintain the reaction pressure. The temperature control system maintains the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 15-20 parts, the polymerization reaction is terminated, and the emulsion is washed and dried to obtain a fusible polytetrafluoroethylene resin.

[0013] Further preferably, in step 1, the ionic liquid acts as an emulsifier and stabilizer in the present method system.

[0014] Further preferably, the preparation method of the ionic liquid in step 1 is:

[0015] T1: Add 3-5.5 parts of perfluorohexylethylsulfonamidopropyl betaine, 0.0004-0.02 parts of lithium 2-aminoadipate, 0.5-1 parts of perfluoropolyether (meth)acrylate, 10-13 parts of DMF, and 0.2-0.5 parts of tetramethylguanidine to the reactor in parts by mass, and stir at 60-70° C. for 20-50 minutes;

[0016] T2: Add 0.2-0.6 parts of 1-allyl-3-methylimidazolium hexafluorophosphate, stir and react at 80-90° C. for 1-3 hours. After the reaction is completed, remove DMF by vacuum distillation to obtain an ionic liquid.

[0017] More preferably, in step 1, the chain transfer agent is selected from at least one of methane, ethane, propane and cyclohexane.

[0018] Further preferably, the oxygen content index in step 1 is not higher than 30 ppm.

[0019] More preferably, the reaction temperature in step 1 is 65-85°C.

[0020] More preferably, the reaction pressure in step 2 is 1.6-2.2 MPa.

[0021] More preferably, the initiator in step 2 is selected from at least one of azobisisobutyronitrile, isobutyryl peroxide, diisopropyl peroxydicarbonate and tert-butyl peroxyacetate.

[0022] Reaction mechanism:

[0023] The amino group of perfluorohexylethylsulfonamidopropyl betaine and 2-aminoadipate lithium reacts with the alkenyl group of perfluoropolyether (meth)acrylate and 1-allyl-3-methylimidazolium hexafluorophosphate to obtain a betaine ionic liquid emulsifier containing perfluoropolyether, hexafluorophosphate and lithium complex, which is used to replace the perfluorooctanoic acid emulsifier; the lithium ion can form a new lithium salt complex with the hexafluorophosphate ion in AMIM PF6. This ion exchange helps to adjust the hydrophilic-hydrophobic balance of the final emulsifier.

[0024] Technical effects:

[0025] 1. Improve emulsification performance:

[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 properties and helps stabilize the emulsion.

[0027] 2. Environmental friendliness:

[0028] Replace perfluorooctanoic acid-based emulsifiers to reduce the release of persistent organic pollutants (POPs) to the environment and organisms. DETAILED DESCRIPTION

[0029] In view of the deficiencies in the prior art, the inventor of this case, after long-term research and extensive practice, was able to propose the technical solution of the present invention. The technical solution, its implementation process and principle, etc. will be further explained as follows.

[0030] Example 1

[0031] A green preparation process for fusible polytetrafluoroethylene, the operating steps are:

[0032] Step 1: Add 60 kg of deoxygenated high-purity water to a polymerization kettle equipped with a stirrer and a 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, evacuate the polymerization kettle, replace with nitrogen until the oxygen content is qualified, and heat the polymerization kettle to the reaction temperature;

[0033] Step 2: Tetrafluoroethylene monomer is introduced into the polymerization kettle to the reaction pressure, and 0.1 kg of initiator is added to start the polymerization reaction. Tetrafluoroethylene monomer is continuously introduced during the reaction process to maintain the reaction pressure. The temperature control system maintains the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 15 kg, the polymerization reaction is terminated, and the emulsion is washed and dried to obtain a fusible polytetrafluoroethylene resin.

[0034] In the step 1, the ionic liquid acts as an emulsifier and stabilizer in the present method system.

[0035] The preparation method of the ionic liquid in step 1 is:

[0036] T1: Add 3 kg of perfluorohexylethylsulfonamidopropyl betaine, 0.0004 kg of lithium 2-aminoadipate, 0.5 kg of perfluoropolyether (meth)acrylate, 10 kg of DMF, and 0.2 kg of tetramethylguanidine into the reactor, and stir at 60° C. for 20 minutes;

[0037] T2: 0.2 kg of 1-allyl-3-methylimidazolium hexafluorophosphate was added, and the mixture was stirred at 80° C. for 1 hour. After the reaction was completed, DMF was removed by vacuum distillation to obtain an ionic liquid.

[0038] In the step 1, the chain transfer agent is selected from methane.

[0039] The oxygen content index in the step 1 is not higher than 30 ppm.

[0040] The reaction temperature in step 1 is 65°C.

[0041] The reaction pressure in step 2 is 1.6 MPa.

[0042] In the step 2, the initiator is selected from azobisisobutyronitrile.

[0043] Example 2

[0044] A green preparation process for fusible polytetrafluoroethylene, the operating steps are:

[0045] Step 1: 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, evacuate the polymerization kettle, replace with nitrogen until the oxygen content is qualified, and heat the polymerization kettle to the reaction temperature;

[0046] Step 2: Tetrafluoroethylene monomer is introduced into the polymerization kettle to the reaction pressure, and 0.4 kg of initiator is added to start the polymerization reaction. Tetrafluoroethylene monomer is continuously introduced during the reaction process to maintain the reaction pressure. The temperature control system maintains the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 16.5 kg, the polymerization reaction is terminated, and the emulsion is washed and dried to obtain a fusible polytetrafluoroethylene resin.

[0047] In the step 1, the ionic liquid acts as an emulsifier and stabilizer in the present method system.

[0048] The preparation method of the ionic liquid in step 1 is:

[0049] T1: Add 4.5 kg of perfluorohexylethylsulfonamidopropyl betaine, 0.005 kg of lithium 2-aminoadipate, 0.65 kg of perfluoropolyether (meth)acrylate, 11 kg of DMF, and 0.3 kg of tetramethylguanidine into the reactor, and stir at 65° C. for 30 minutes;

[0050] T2: 0.35 kg of 1-allyl-3-methylimidazolium hexafluorophosphate was added, and the mixture was stirred at 85° C. for 2 hours. After the reaction was completed, DMF was removed by vacuum distillation to obtain an ionic liquid.

[0051] In the step 1, the chain transfer agent is selected from ethane.

[0052] The oxygen content index in the step 1 is not higher than 30 ppm.

[0053] The reaction temperature in step 1 is 75°C.

[0054] The reaction pressure in the step 2 is 1.8 MPa.

[0055] In the step 2, the initiator is selected from isobutyryl peroxide.

[0056] Example 3

[0057] A green preparation process for fusible polytetrafluoroethylene, the operating steps are:

[0058] Step 1: Add 70 kg of deoxygenated high-purity water to a polymerization kettle equipped with a stirrer and a temperature control system, start stirring, add 1.2 kg of perfluoro-n-propyl vinyl ether, 0.9 kg of ionic liquid and 0.08 kg of chain transfer agent, evacuate the polymerization kettle, replace with nitrogen until the oxygen content is qualified, and heat the polymerization kettle to the reaction temperature;

[0059] Step 2: Tetrafluoroethylene monomer is introduced into the polymerization kettle to the reaction pressure, and 0.75 kg of initiator is added to start the polymerization reaction. Tetrafluoroethylene monomer is continuously introduced during the reaction process to maintain the reaction pressure. The temperature control system maintains the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 18 kg, the polymerization reaction is terminated, and the emulsion is washed and dried to obtain a fusible polytetrafluoroethylene resin.

[0060] In the step 1, the ionic liquid acts as an emulsifier and stabilizer in the present method system.

[0061] The preparation method of the ionic liquid in step 1 is:

[0062] T1: Add 5 kg of perfluorohexylethylsulfonamidopropyl betaine, 0.01 kg of lithium 2-aminoadipate, 0.85 kg of perfluoropolyether (meth)acrylate, 12 kg of DMF, and 0.4 kg of tetramethylguanidine into the reactor, and stir at 65° C. for 40 minutes;

[0063] T2: 0.5 kg of 1-allyl-3-methylimidazolium hexafluorophosphate was added, and the mixture was stirred at 85° C. for 2 hours. After the reaction was completed, DMF was removed by vacuum distillation to obtain an ionic liquid.

[0064] In the step 1, the chain transfer agent is selected from propane.

[0065] The oxygen content index in the step 1 is not higher than 30 ppm.

[0066] The reaction temperature in step 1 is 75°C.

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

[0068] In the step 2, the initiator is selected from diisopropyl peroxydicarbonate.

[0069] Example 4

[0070] A green preparation process for fusible polytetrafluoroethylene, the operating steps are:

[0071] Step 1: Add 80 kg of deoxygenated high-purity water to a polymerization kettle equipped with a stirrer and a temperature control system, start stirring, add 1.3 kg of perfluoro-n-propyl vinyl ether, 1.2 kg of ionic liquid and 0.1 kg of chain transfer agent, evacuate the polymerization kettle, replace with nitrogen until the oxygen content is qualified, and heat the polymerization kettle to the reaction temperature;

[0072] Step 2: Tetrafluoroethylene monomer is introduced into the polymerization kettle to the reaction pressure, 1 kg of initiator is added, and the polymerization reaction begins. Tetrafluoroethylene monomer is continuously introduced during the reaction process to maintain the reaction pressure. The temperature control system maintains the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 20 kg, the polymerization reaction is terminated, and the emulsion is washed and dried to obtain a fusible polytetrafluoroethylene resin.

[0073] In the step 1, the ionic liquid acts as an emulsifier and stabilizer in the present method system.

[0074] The preparation method of the ionic liquid in step 1 is:

[0075] T1: Add 5.5 kg of perfluorohexylethylsulfonamidopropyl betaine, 0.02 kg of lithium 2-aminoadipate, 1 kg of perfluoropolyether (meth)acrylate, 13 kg of DMF, and 0.5 kg of tetramethylguanidine into the reactor, and stir at 70° C. for 50 minutes;

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

[0077] In the step 1, the chain transfer agent is selected from propane.

[0078] The oxygen content index in the step 1 is not higher than 30 ppm.

[0079] The reaction temperature in step 1 is 85°C.

[0080] The reaction pressure in step 2 is 2.2 MPa.

[0081] In the step 2, the initiator is selected from tert-butyl peroxyacetate.

[0082] Example test:

[0083] The performance of the fusible polytetrafluoroethylene resin prepared in the example was tested. Its melting point was tested according to the ASTM D4591 test standard, its melt index was tested according to the ASTM D3307 test standard, and metal ion precipitation was tested by ICP-OES.

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

[0085]

[0086]

[0087] The specific implementation scheme of the present invention prepares fusible polytetrafluoroethylene, proposes an ion solution as an emulsifier and stabilizer, the process route is green and environmentally friendly, and the resin has stable and excellent performance.

[0088] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A green preparation process for fusible polytetrafluoroethylene, the operating steps of which are: Step 1: Add 60-80 parts of deoxygenated high-purity water in a polymerization kettle with an agitator and a temperature control system according to the weight ratio, start stirring, add 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, evacuate the polymerization kettle, replace with nitrogen until the oxygen content is qualified, and heat the polymerization kettle to the reaction temperature; Step 2: Tetrafluoroethylene monomer is introduced into the polymerization kettle to the reaction pressure, and 0.1-1 parts of initiator are added to start the polymerization reaction. Tetrafluoroethylene monomer is continuously introduced during the reaction process to maintain the reaction pressure. The temperature control system maintains the reaction temperature stable. When the amount of tetrafluoroethylene added reaches 15-20 parts, the polymerization reaction is terminated, and the emulsion is washed and dried to obtain a fusible polytetrafluoroethylene resin.

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

3. The green preparation process of fusible polytetrafluoroethylene according to claim 1, characterized in that: The preparation method of the ionic liquid in step 1 is: T1: Add 3-5.5 parts of perfluorohexylethylsulfonamidopropyl betaine, 0.0004-0.02 parts of lithium 2-aminoadipate, 0.5-1 parts of perfluoropolyether (meth)acrylate, 10-13 parts of DMF, and 0.2-0.5 parts of tetramethylguanidine to the reactor in parts by mass, and stir at 60-70° C. for 20-50 minutes; T2: Add 0.2-0.6 parts of 1-allyl-3-methylimidazolium hexafluorophosphate, stir and react at 80-90° C. for 1-3 hours. After the reaction is completed, remove DMF by vacuum distillation to obtain an ionic liquid.

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

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

6. The green preparation process of fusible polytetrafluoroethylene according to claim 1, characterized in that: The reaction temperature in step 1 is 65-85°C.

7. The green preparation process of fusible polytetrafluoroethylene according to claim 1, characterized in that: The reaction pressure in step 2 is 1.6-2.2 MPa.

8. The green preparation process of fusible polytetrafluoroethylene according to claim 1, characterized in that: In the step 2, the initiator is selected from at least one of azobisisobutyronitrile, isobutyryl peroxide, diisopropyl peroxydicarbonate and tert-butyl peroxyacetate.

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