Fluorine-containing surfactant and application thereof in preparation of polytetrafluoroethylene

Abstract

The invention discloses a fluorine-containing surfactant. The structure of the fluorine-containing surfactant is shown as follows: AOO2SC2F4O-(CF( CF3) CF2-O-) n-CF (CF3) COOA, wherein n is 2-8, and A is one of H < + >, Li < + >, K < + >, Na < + > and NH4 < + >. The fluorine-containing surfactant has a bifunctional structure, can improve the dispersing capacity of a polytetrafluoroethylene polymerization system and improve the reaction stability, and the structure has the characteristic of easy biodegradation and has small influence on the environment. The invention also discloses a preparation method of the fluorine-containing surfactant, the fluorine-containing surfactant can be prepared only by a one-step neutralization method, the preparation conditions are mild and controllable, and the process is environment-friendly. The invention also discloses a method for preparing polytetrafluoroethylene solid powder by using the fluorine-containing polymer. According to the method, the polytetrafluoroethylene solid powder with the solid content gt can be prepared; the polymerization reaction stability of the polytetrafluoroethylene solid powder is still relatively good when the content is 29.8%.

Description

Technical Field

[0001] The invention relates to the field of fluorine-containing polymers, in particular to a fluorine-containing surfactant and application thereof in the preparation of polytetrafluoroethylene. Background Art

[0002] Perfluorosulfonate (PFOS) and perfluorooctanoate (PFOA) are the most commonly used fluorinated surfactants and are important additives in the production process of fluorinated polymers. However, they are difficult to degrade and are a type of fluorinated surfactant with limited use. Therefore, the development of new environmentally friendly surfactants is a major issue that needs to be urgently addressed in the field of fluorinated polymers.

[0003] Currently, the main research directions for replacing PFOA are new fluorinated surfactants and fluorinated-free surfactants. US20090436280 discloses the use of a mixture of fluoropolyether acids or salts with a molecular weight of 800 to 2500 for the aqueous dispersion polymerization of fluorinated polymers.

[0004] Publication No. CN115466343A discloses a polyether diacid or its salt surfactant and its application; the general structural formula of the polyether diacid or its salt surfactant is as follows:

[0005] XL-(O-CH2CHZ) a -(O-CR1R2CR3R4) b -OLX;

[0006] Wherein, Z represents H or CH3; L represents C1-C5 alkylene; X represents -COOM or -SO3M, and M represents H + NH4 + Or Na + ; R1 to R4 independently represent H atoms, F atoms, non-fluorinated alkyl or alkoxy groups, partially fluorinated alkyl or alkoxy groups, and fully fluorinated alkyl or alkoxy groups; a and b independently represent positive integers of 0 to 10. The polyether diacid or its salt surfactant can significantly reduce the surface tension of the polymerization system, improve the stability of the fluorinated polymer aqueous dispersion, and significantly reduce the amount of fluorinated surfactant used.

[0007] Publication No. CN117645682A discloses a fusible polytetrafluoroethylene resin and a preparation method thereof, the method comprising 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 solution, 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 product obtained by the fusible polytetrafluoroethylene resin preparation process adopted by the present invention has a transparent appearance, the product fluorine ion precipitation is less than 10ppm, the metal ion precipitation is less than 1ppm, and the high-purity field requirements are met, but the solid content of the polytetrafluoroethylene resin finally obtained is only controlled at 5% to 15%.

[0008] From the perspective of research and production technology in recent years, most of the existing types of fluorinated surfactants that meet the PFOA / PFOS restriction requirements have problems such as low reaction selectivity, low yield, difficult purification, and environmentally unfriendly production processes. Therefore, it is necessary to develop more fluorinated surfactants with new structures to solve environmental problems. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a fluorine-containing surfactant, which has a bifunctional structure, can improve the dispersion ability of the polytetrafluoroethylene polymerization system, improve the stability of the reaction, and the structure has the characteristics of easy biodegradability and little impact on the environment.

[0010] A fluorinated surfactant, the structure of which is shown below:

[0011] AOO2SC2F4O-(CF(CF3)CF2-O-) n -CF(CF3)COOA;

[0012] Where n = 2 to 8, A is H + , Li + , K + 、Na + NH4 + One of them.

[0013] The fluorinated surfactant used in the present invention has a bifunctional structure, one end of which is a sulfonic acid group, which improves the water solubility of the fluorinated surfactant, improves the dispersibility of the polytetrafluoroethylene polymerization system, and improves the stability of the reaction; the other end is a carboxylic acid group, which can significantly reduce the surface tension of the polytetrafluoroethylene polymerization system. Because it has the characteristic of being easily biodegradable, it can solve the problem that the existing fluorinated surfactants are not environmentally friendly.

[0014] The present invention also provides a method for preparing the fluorinated surfactant, the preparation conditions are mild and controllable, and the process is environmentally friendly.

[0015] A method for preparing a fluorinated surfactant comprises the following steps: reacting a fluorinated polyether monomer with AOH to obtain a fluorinated surfactant, wherein the structural formula of the fluorinated polyether monomer is as shown in formula (1):

[0016]

[0017] Formula (1)

[0018] Among them, n=2~8.

[0019] In the present invention, the synthesis of the fluorinated polyether monomer refers to the preparation of the intermediate pure product of step 1) in the preparation method in patent CN202210499054.1. After tetrafluorosulfone and hexafluoropropylene oxide undergo an isomerization / addition reaction, the obtained fluorinated polyether monomer has a double-end difference in acyl fluoride end groups, i.e., a carbonyl fluoride end group and a sulfonyl fluoride end group. This fluorinated polyether monomer has a structure with hexafluoropropoxy repeating segments, which has obvious degradable advantages compared to long-chain fluoroalkyl groups. The fluorinated polyether monomer is obtained by reacting with AOH to obtain the above-mentioned fluorinated surfactant. To synthesize fluorinated surfactant active agents with different n numbers, it is only necessary to replace the raw materials with fluorinated polyether monomer raw materials with different n numbers. The preparation conditions are mild and controllable, and the process is environmentally friendly.

[0020] Preferably, the AOH is one of H2O, LiOH, KOH, NaOH, and NH4OH.

[0021] The present invention also provides a method for preparing polytetrafluoroethylene using the fluorine-containing polymer. The method can prepare polytetrafluoroethylene solid powder having good polymerization reaction stability when the solid content is greater than 29.8%.

[0022] A method for preparing polytetrafluoroethylene with a high solid content comprises the following steps:

[0023] (1) adding an aqueous reaction medium, the above-mentioned fluorinated surfactant and an auxiliary agent into a reaction kettle under vacuum and oxygen-free conditions to obtain a mixed solution;

[0024] (2) heating the mixed solution obtained in step (1) and stirring it, introducing tetrafluoroethylene monomer and then adding an initiator, and continuing to add tetrafluoroethylene monomer until the reaction pressure is reached, and obtaining a polytetrafluoroethylene emulsion after a polymerization reaction;

[0025] (3) The polytetrafluoroethylene emulsion obtained in step (2) is coagulated, washed and dehydrated to obtain polytetrafluoroethylene.

[0026] Polytetrafluoroethylene is insoluble in water, and tetrafluoroethylene monomer gas diffuses into the aqueous solution, and begins to polymerize under the action of an initiator to form polytetrafluoroethylene particles, which are precipitated from the aqueous reaction medium under the action of a fluorinated surfactant to form a polytetrafluoroethylene emulsion. In the present invention, by controlling the parameters of the polymerization process, a polytetrafluoroethylene emulsion with a solid content of 29.8% to 35% can be obtained, and the particle morphology of the obtained polytetrafluoroethylene emulsion is relatively uniform, and no demulsification occurs during the polymerization process, and no obvious floccules are present.

[0027] Preferably, in step (1), the anaerobic condition is an oxygen content less than 20 ppm.

[0028] Preferably, in step (1), the aqueous reaction medium is deionized water.

[0029] In the present invention, the provided fluorinated surfactant containing a terminal bifunctional structure is used as an emulsifier in the polymerization reaction system, and the emulsifier can reduce the surface tension in the polymerization reaction system, making the components in the polymerization reaction system more soluble in each other. Preferably, the amount of the fluorinated surfactant added is 0.01% to 5% by weight of the aqueous reaction medium.

[0030] Preferably, in step (1), the auxiliary agent is a stabilizing auxiliary agent and a chain transfer agent.

[0031] More preferably, the stabilizing agent is one of paraffin, silicone oil and fluorocarbon compounds.

[0032] More preferably, the stabilizing agent is perfluoropolyether, and the addition amount of the perfluoropolyether is 0.1% to 12% of the weight of the aqueous reaction medium.

[0033] In the present invention, perfluoropolyether is selected as a stabilizing agent to improve the thermal stability of the polymerization reaction system and reduce the generation of coagulation. However, when the amount of the stabilizing agent added is too much, the difficulty of post-processing will increase, and the stabilizing agent will remain in the polytetrafluoroethylene, affecting the quality of the product.

[0034] More preferably, the chain transfer agent is an alcohol or an alkane with a carbon number ≤ 3, and the added amount of the chain transfer agent is 0.005% to 5% of the weight of the aqueous phase reaction medium.

[0035] In the present invention, the polymerization reaction speed increases with the increase of the polymerization reaction temperature, but when the polymerization reaction temperature is too high, the polymerization reaction is difficult to control, and when the temperature is too low, the polymerization reaction is difficult to proceed. On the other hand, the reaction speed will also increase with the increase of the polymerization reaction pressure, but if the polymerization reaction pressure is too high, the equipment requirements are high and the investment cost is increased; if the polymerization reaction pressure is too low, the solubility of tetrafluoroethylene in water is low and the reaction speed is slow. The stirring speed will affect the particle size of polytetrafluoroethylene in the emulsion, and the particle size will decrease with the increase of the stirring speed. Preferably, the polymerization reaction temperature is 50-100°C, the reaction pressure is 0.5-6.0MPa, and the stirring speed is 300-800r / min.

[0036] Further preferably, the amount of the fluorinated surfactant added is 0.01% to 5% by weight of the aqueous reaction medium, the amount of the perfluoropolyether added is 2% to 10% by weight of the aqueous reaction medium, and the stirring speed of the polymerization reaction is 500 to 700 r / min.

[0037] When the addition amount of fluorinated surfactant and perfluoropolyether and the stirring speed of the polymerization reaction are within the above ranges, the emulsion stability is good during the preparation of the polytetrafluoroethylene emulsion, no demulsification occurs, and no obvious flocculants are generated. In the prepared polytetrafluoroethylene emulsion, the primary particle size of polytetrafluoroethylene is 200-230nm, and the solid content can be as high as 34%.

[0038] Preferably, in step (2), the initiator is an inorganic peroxide initiator, such as ammonium persulfate, potassium persulfate, etc.; the amount of the initiator added is 0.0003% to 10% of the weight of the aqueous reaction medium.

[0039] The amount of initiator added has an impact on the stability of the polymerization reaction. When the amount of initiator added is controlled within the above range of the aqueous phase reaction system, the stability of the polymer reaction system can be maintained while ensuring that the particle size is also small.

[0040] Preferably, in the polytetrafluoroethylene emulsion, the primary particle size of polytetrafluoroethylene is 200-230 nm, and the solid content is 29.8%-35%.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention provides a fluorinated surfactant having a sulfonic acid group and a carboxylic acid group at the end, which can solve the environmental pollution pressure of the existing perfluorooctanoic acid-based fluorinated surfactants due to its biodegradable properties. At the same time, the fluorinated surfactant can reduce the surface tension in the polymerization reaction system and improve the stability of the polymerization reaction system.

[0043] (2) The fluorinated surfactant provided by the present invention can be used as an emulsifier in the preparation process of polytetrafluoroethylene, which can reduce the surface tension in the polymerization reaction system, make the components in the polymerization reaction system more soluble in each other, and prevent demulsification during the polymerization reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the infrared spectrum of the fluorinated surfactant prepared in Example 1.

[0045] Figure 2 The following is the nuclear magnetic resonance fluorine spectrum of the fluorine-containing surfactant prepared in Example 1. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited to the following examples.

[0047] The raw materials used in the present invention are all commercially available.

[0048] Example 1: Preparation of fluorinated surfactant

[0049] The synthesis of the fluorinated polyether monomer refers to the preparation of the intermediate pure product in step 1) of the preparation method in patent CN202210499054.1. After tetrafluorosulfone and hexafluoropropylene oxide undergo an isomerization / addition reaction, the obtained fluorinated polyether monomer has two different acyl fluoride end groups, namely, carbonyl fluoride end groups and sulfonyl fluoride end groups. The fluorinated polyether monomer is reacted with AOH to obtain the above-mentioned fluorinated surfactant, and the specific steps are as follows.

[0050] In a 0.5L autoclave, add 90g of ethylene glycol dimethyl ether and 18g of KF, start stirring, cool to 0°C, then slowly drop 180g (1mol) of tetrafluorosulfone, control the internal temperature at 0-10°C, continue stirring for 0.5h after the addition is complete, then add 0.09g of dimethylethylenediamine. After the addition is complete, cool to -25°C, slowly introduce 282.2g (1.7mol) of hexafluoropropylene oxide at normal pressure, the reaction is complete, stop stirring, stand and separate, continue to use the upper solvent, purify the lower intermediate by distillation, and obtain 390g of fluorine-containing ether structure active monomer (n=2). The fluorinated ether structure active monomer (n=2) was slowly added dropwise to the ammonia water, and the internal temperature was controlled at 0-10°C. After the addition was completed, stirring was continued. The amount of ammonia water was 180g (5.14mol). The reaction progress was monitored by infrared. The reaction was terminated after the acyl fluoride peak disappeared to obtain a fluorinated surfactant with the structural formula of NH4OO2SC2F4O-(CF(CF3)CF2-O-)2-CF(CF3)COONH4. Its infrared spectrum is as follows Figure 1 As shown, SO stretching vibration (947 cm -1 )、SO2 stretching vibration (1231cm-1 )、-COO- antisymmetric stretching vibration (1650cm -1 ) and NH stretching vibration (3275cm -1 ), its NMR fluorine spectrum is as follows Figure 2 shown.

[0051] Example 2: Preparation of polytetrafluoroethylene

[0052] (1) A 25 L sealed reactor with a stirrer was evacuated and replaced with high-purity nitrogen until the oxygen content in the reactor was less than 20 ppm. 14 kg of deionized water and 280 g of a perfluoropolyether stabilizer (purchased from Zhejiang Chuangfu High-Tech New Materials Co., Ltd., brand JHT-230), 14 g of NH4OO2SC2F4O-(CF(CF3)CF2-O-)2-CF(CF3)COONH4 prepared in Example 1 and 140 g of methanol were added to the reactor to obtain a mixed solution;

[0053] (2) heating the mixed solution obtained in step (1) to 70° C., stirring at a speed of 300 r / min, introducing tetrafluoroethylene monomer into the reactor, adding 0.06 g of ammonium persulfate when the pressure reaches 2 MPa, and continuously adding tetrafluoroethylene monomer during the reaction to ensure that the reaction pressure is 2 MPa and the reaction temperature is 80° C. After reacting for 2 hours, stopping adding tetrafluoroethylene monomer and terminating the reaction to obtain a polytetrafluoroethylene emulsion;

[0054] (3) Recovering tetrafluoroethylene monomer, coagulating, washing and drying the polytetrafluoroethylene emulsion obtained in step (2) to obtain polytetrafluoroethylene.

[0055] Example 3: Preparation of polytetrafluoroethylene

[0056] (1) A 25 L sealed reactor with a stirrer was evacuated and replaced with high-purity nitrogen until the oxygen content in the reactor was less than 20 ppm. 14 kg of deionized water and 300 g of a perfluoropolyether stabilizer (purchased from Zhejiang Chuangfu High-Tech New Materials Co., Ltd., brand JHT-230), 10 g of NH4OO2SC2F4O-(CF(CF3)CF2-O-)2-CF(CF3)COONH4 and 200 g of methanol were added to the reactor to obtain a mixed solution;

[0057] (2) heating the mixed solution obtained in step (1) to 70° C., stirring at a speed of 450 r / min, introducing tetrafluoroethylene monomer into the reactor, adding 0.07 g of ammonium persulfate when the pressure reaches 2 MPa, and continuously adding tetrafluoroethylene monomer during the reaction to ensure that the reaction pressure is 3.0 MPa and the reaction temperature is 80° C. After reacting for 2 hours, stopping adding tetrafluoroethylene monomer and terminating the reaction to obtain a polytetrafluoroethylene emulsion;

[0058] (3) Recovering tetrafluoroethylene monomer, coagulating, washing and drying the polytetrafluoroethylene emulsion obtained in step (2) to obtain polytetrafluoroethylene.

[0059] Example 4: Preparation of polytetrafluoroethylene

[0060] (1) A 25 L sealed reactor with a stirrer was evacuated and replaced with high-purity nitrogen until the oxygen content in the reactor was less than 20 ppm. 14 kg of deionized water and 300 g of a perfluoropolyether stabilizer (purchased from Zhejiang Chuangfu High-Tech New Materials Co., Ltd., brand JHT-230), 10 g of NH4OO2SC2F4O-(CF(CF3)CF2-O-)2-CF(CF3)COONH4 and 300 g of methanol were added to the reactor to obtain a mixed solution;

[0061] (2) heating the mixed solution obtained in step (1) to 70° C., stirring at a speed of 600 r / min, introducing tetrafluoroethylene monomer into the reactor, adding 0.05 g of ammonium persulfate when the pressure reaches 2.5 MPa, and continuously adding tetrafluoroethylene monomer during the reaction to ensure that the reaction pressure is 3.0 MPa and the reaction temperature is 85° C. After reacting for 2.5 hours, stopping adding tetrafluoroethylene monomer and terminating the reaction to obtain a polytetrafluoroethylene emulsion;

[0062] (3) Recovering tetrafluoroethylene monomer, coagulating, washing and drying the polytetrafluoroethylene emulsion obtained in step (2) to obtain polytetrafluoroethylene.

[0063] Example 5: Preparation of polytetrafluoroethylene

[0064] (1) A 50 L sealed reactor with a stirrer was evacuated and replaced with high-purity nitrogen until the oxygen content in the reactor was less than 20 ppm. 20 kg of deionized water and 500 g of a perfluoropolyether stabilizer (purchased from Zhejiang Chuangfu High-Tech New Materials Co., Ltd., brand JHT-230), 12 g of NH4OO2SC2F4O-(CF(CF3)CF2-O-)2-CF(CF3)COONH4 and 200 g of methanol were added to the reactor to obtain a mixed solution;

[0065] (2) heating the mixed solution obtained in step (1) to 70° C., stirring at a speed of 700 r / min, introducing tetrafluoroethylene monomer into the reactor, adding 0.07 g of ammonium persulfate when the pressure reaches 2.0 MPa, and continuously adding tetrafluoroethylene monomer during the reaction to ensure that the reaction pressure is 2.0 MPa and the reaction temperature is 80° C. After reacting for 2.5 hours, stopping adding tetrafluoroethylene monomer, terminating the reaction, and obtaining a polytetrafluoroethylene emulsion;

[0066] (3) Recovering tetrafluoroethylene monomer, coagulating, washing and drying the polytetrafluoroethylene emulsion obtained in step (2) to obtain polytetrafluoroethylene.

[0067] Comparative Example 1: Preparation of polytetrafluoroethylene

[0068] (1) A 50 L closed reactor with a stirrer was evacuated and replaced with high-purity nitrogen until the oxygen content in the reactor was less than 20 ppm. 20 kg of deionized water and 500 g of a perfluoropolyether stabilizer (purchased from Zhejiang Chuangfu High-Tech New Materials Co., Ltd., brand JHT-230), 8 g of NH4OOC-CH2CH2-(O-CH2CH2)3-O-CH2CH2-COONH4, 2 g of CF3-OCF(CF3)-CF2-O-CH2CH2COONH4 and 200 g of methanol were added to the reactor to obtain a mixed solution;

[0069] (2) heating the mixed solution obtained in step (1) to 70° C., stirring at a speed of 700 r / min, introducing tetrafluoroethylene monomer into the reactor, adding 0.07 g of ammonium persulfate when the pressure reaches 2.0 MPa, and continuously adding tetrafluoroethylene monomer during the reaction to ensure that the reaction pressure is 2.0 MPa and the reaction temperature is 80° C. After reacting for 2.5 hours, stopping adding tetrafluoroethylene monomer, terminating the reaction, and obtaining a polytetrafluoroethylene emulsion;

[0070] (3) Recovering tetrafluoroethylene monomer, coagulating, washing and drying the polytetrafluoroethylene emulsion obtained in step (2) to obtain polytetrafluoroethylene.

[0071] Performance Analysis

[0072] 1. Primary particle size test

[0073] The polytetrafluoroethylene solid powder obtained in Examples 2 to 5 and the aqueous dispersion of polytetrafluoroethylene obtained in Comparative Examples 1 and 2 were diluted to a dispersion containing 1.0% polytetrafluoroethylene, and measured using dynamic light scattering at 25°C, a solvent (water) with a refractive index of 1.3328, a solvent (water) viscosity of 0.8878 mPa·S, and a cumulative total of 70 times. The results are shown in Table 1.

[0074] 2. Solid content test

[0075] The polytetrafluoroethylene solid powder obtained in Examples 2 to 5 and the polytetrafluoroethylene aqueous dispersion obtained in Comparative Examples 1 and 2 were equally divided into weighed samples. After evaporation and drying, the weight of the dry solid was weighed. The results are shown in Table 2.

[0076] Table 1: Performance test results of Examples 2 to 5 and Comparative Examples 1 and 2

[0077] Example Primary particle size (nm) Solid content (%) Aggregation Example 2 230 29.8 No demulsification, no obvious coagulation Example 3 210 29.9 No demulsification, no obvious coagulation Example 4 200 34.8 No demulsification, no obvious coagulation Example 5 210 34.9 No demulsification, no obvious coagulation Comparative Example 1 260 29.5 No demulsification, no obvious coagulation

[0078] As shown in Table 1, the primary particle size of Examples 2 to 5 is 200 to 230 nm, the solid content is 29.8% to 35%, the emulsion stability is good during the polymerization reaction, no demulsification phenomenon is found, and no obvious floccules are found. The particle size of the polytetrafluoroethylene emulsion in Comparative Example 1 is 260 nm, the solid content is 29.5%, and its particle size is too large, which affects the stability of the emulsion. Compared with Comparative Example 1, the embodiments only use a single fluorinated surfactant to obtain a polytetrafluoroethylene emulsion with high solid content and high stability, which has better effect, lower cost, and is more conducive to later industrial scale-up.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fluorinated surfactant, characterized in that The structure is as follows: AOO2SC2F4O-(CF(CF3)CF2-O-) n -CF(CF3)COOA; Where n = 2 to 8, A is H + , Li + , K + 、Na + NH4 + One of them.

2. The method for preparing a fluorinated surfactant according to claim 1, characterized in that: The following steps are involved: The fluorinated polyether monomer is reacted with AOH to obtain a fluorinated surfactant, wherein the structural formula of the fluorinated polyether monomer is as shown in formula (1): Among them, n=2~8.

3. The method for preparing a fluorinated surfactant according to claim 2, characterized in that: The AOH is one of H2O, LiOH, KOH, NaOH and NH4OH.

4. A method for preparing polytetrafluoroethylene with a high solid content, comprising the following steps: (1) adding an aqueous reaction medium, the fluorinated surfactant according to claim 1 and an auxiliary agent into a reaction kettle under vacuum and oxygen-free conditions to obtain a mixed solution; (2) heating the mixed solution obtained in step (1) and stirring it, introducing tetrafluoroethylene monomer and then adding an initiator, and continuing to add tetrafluoroethylene monomer until the reaction pressure is reached, and obtaining a polytetrafluoroethylene emulsion after a polymerization reaction; (3) The polytetrafluoroethylene emulsion obtained in step (2) is coagulated, washed and dehydrated to obtain polytetrafluoroethylene.

5. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In step (1), the anaerobic condition is that the oxygen content is less than 20 ppm.

6. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In step (1), the aqueous phase reaction medium is deionized water.

7. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In step (1), the amount of the fluorinated surfactant added is 0.01% to 5% by weight of the aqueous reaction medium.

8. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In step (1), the auxiliary agents are stabilizing agents and chain transfer agents.

9. The method for preparing polytetrafluoroethylene with high solid content according to claim 8, characterized in that: The stabilizing aid is one of paraffin, silicone oil and fluorocarbon compounds.

10. The method for preparing polytetrafluoroethylene with high solid content according to claim 9, characterized in that: The stabilizing aid is perfluoropolyether, and the addition amount of the perfluoropolyether is 0.1% to 12% of the weight of the aqueous reaction medium.

11. The method for preparing polytetrafluoroethylene with high solid content according to claim 8, characterized in that: The chain transfer agent is alcohol or alkane with carbon number ≤ 3, and the added amount of the chain transfer agent is 0.005% to 5% of the weight of the aqueous phase reaction medium.

12. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In step (2), the polymerization reaction temperature is 50-100° C., the reaction pressure is 0.5-6.0 MPa, and the stirring speed is 300-800 r / min.

13. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In step (2), the initiator is an inorganic peroxide initiator, and the added amount of the initiator is 0.0003% to 10% of the weight of the aqueous reaction medium.

14. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: The amount of the fluorinated surfactant added is 0.01% to 5% of the weight of the aqueous reaction medium. The amount of the perfluoropolyether added is 2% to 10% of the weight of the aqueous reaction medium. The stirring speed of the polymerization reaction is 500 to 700 r / min.

15. The method for preparing polytetrafluoroethylene with high solid content according to claim 4, characterized in that: In the polytetrafluoroethylene emulsion, the primary particle size of polytetrafluoroethylene is 200-230nm and the solid content is 29.8%-35%.

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