A hydrophilic polytetrafluoroethylene membrane and a method for producing the same

Abstract

The application discloses a hydrophilic polytetrafluoroethylene membrane and a preparation method thereof. The hydrophilic polytetrafluoroethylene membrane comprises a PTFE base film and a hydrophilic layer attached to the PTFE base film; raw materials of the PTFE base film comprise polytetrafluoroethylene dispersion resin, maleic anhydride copolymer and extrusion aid in a mass percentage ratio of 1:0.05-0.2:0.2-0.4, the maleic anhydride copolymer is a copolymer of olefin or aromatic hydrocarbon and maleic anhydride; raw materials of the hydrophilic layer comprise polyethylene polyamine solution and polyethylene imine solution, and a water wetting angle of the hydrophilic polytetrafluoroethylene membrane is less than 50 degrees. In the filtration process of etching waste liquid and stripping liquid, the hydrophilic polytetrafluoroethylene membrane disclosed by the application is not prone to accumulate dirt, can maintain relatively stable transmembrane pressure and keep stable filtration effect.

Description

Technical Field

[0001] This application relates to the field of polytetrafluoroethylene (PTFE) membranes, and in particular to a hydrophilic PTFE membrane and its preparation method. Background Technology

[0002] Etching processes offer advantages such as high production efficiency, good selectivity, and low cost, making them an indispensable step in the microelectronics industry. With the rapid development of the microelectronics sector, technological products such as smart handheld devices, LCD screens, semiconductor devices, and integrated circuits are being mass-produced industrially, leading to the widespread application of etching processes. This has resulted in the generation of large quantities of etching waste liquid and increased consumption of stripping fluid. Etching waste liquid contains numerous harmful substances, including heavy metal ions, organic pollutants, and particulate matter; direct discharge would cause serious environmental pollution. Furthermore, the metal elements contained in etching waste liquid have significant recycling value. However, research on the collection of metal elements from etching waste liquid is scarce; often, the waste liquid is simply disposed of through simple harmless treatment, resulting in a waste of metal resources.

[0003] Polytetrafluoroethylene (PTFE) exhibits excellent resistance to strong acids and alkalis, and does not decompose even at high temperatures, thus demonstrating excellent stability. Microporous membranes made from PTFE are heat-resistant, chemically resistant, and possess extremely high filtration efficiency. They meet the stringent requirements for corrosion resistance and particle size control when filtering etching solutions, stripping solutions, and metal particles.

[0004] Chinese patent application CN113043620A uses a classic polytetrafluoroethylene (PTFE) film preparation process, modifying the parameters of biaxial stretching and heat setting to prepare a PTFE film with high air permeability. The operation process is simple. However, this film is prone to fouling and requires higher transmembrane pressure during filtration. Chinese patent application CN110038445A improves the hydrophilicity of a hydrophobic membrane by subjecting it to low-temperature, low-power plasma treatment, monomer grafting, and then atomic layer deposition. However, this method involves numerous steps in preparing a hydrophilic membrane, requiring multiple cyclic depositions, making the process complex and time-consuming. Summary of the Invention

[0005] The purpose of this application is to provide a hydrophilic polytetrafluoroethylene membrane and its preparation method, which imparts excellent hydrophilicity to the polytetrafluoroethylene membrane through a simpler process, reduces the adhesion of dirt in etching waste liquid to the membrane, and ensures filtration efficiency.

[0006] In a first aspect, this application provides a hydrophilic polytetrafluoroethylene membrane, comprising:

[0007] PTFE base film and hydrophilic layer attached to PTFE base film;

[0008] The raw materials of the PTFE base film include polytetrafluoroethylene dispersion resin, maleic anhydride copolymer and extrusion aid in a mass percentage of 1:0.05-0.2:0.2-0.4, wherein the maleic anhydride copolymer is a copolymer of olefin or aromatic hydrocarbon and maleic anhydride;

[0009] The raw material for the hydrophilic layer is a mixed solution containing polyethylene polyamine and polyethyleneimine;

[0010] The hydrophilic polytetrafluoroethylene membrane has a wetting angle of less than 50°.

[0011] Preferably, the concentration of polyethylene polyamine in the mixed solution is 0.1–0.5 mg / L, and the concentration of polyethyleneimine in the mixed solution is 0.1–0.5 mg / L.

[0012] Preferably, the polyethylene polyamine is selected from at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0013] This application improves the wetting effect of the aqueous solution in the etching waste liquid on the membrane by forming a hydrophilic layer on the PTFE base membrane, making it less likely for dirt to accumulate on the membrane surface, eliminating the need to increase the transmembrane pressure, and ensuring the filtration effect of the polytetrafluoroethylene membrane during long-term filtration.

[0014] Specifically, this application first incorporates maleic anhydride copolymer into the base membrane material, resulting in a PTFE base membrane surface containing a large number of carboxyl groups, forming crosslinking reaction sites. Polyethylene polyamine and polyethyleneimine undergo amidation reactions at these crosslinking reaction sites, forming hydrophilic crosslinking products and improving the hydrophilicity of the PTFE membrane. Polyethylene polyamine acts as a crosslinking agent, while the use of long-chain macromolecular polyethyleneimine forms a network structure, enabling the hydrophilic layer to firmly adhere to the PTFE membrane surface, thus improving the membrane's hydrophilicity and washability.

[0015] This application does not have any special requirements for the selection of polytetrafluoroethylene dispersion resin, and the extrusion aid is also a conventional lubricant.

[0016] Optionally, the number average molecular weight of the polytetrafluoroethylene dispersion resin is 1 million to 12 million.

[0017] Optionally, the number-average molecular weight of polyethyleneimine is 10,000 to 50,000;

[0018] Optionally, the extrusion aid is selected from at least one of lubricating oil, palm oil, naphthenic oil, white oil, aviation kerosene, defatted kerosene, and paraffin wax.

[0019] Optionally, the solvent of the mixed solution includes at least one of water, methanol, and ethanol.

[0020] Secondly, this application provides a method for preparing a hydrophilic polytetrafluoroethylene membrane, which includes the following steps:

[0021] Mixing: The raw materials for PTFE base film are mixed in a mixer and stirred evenly to obtain polytetrafluoroethylene material;

[0022] Preform pressing and calendering: pressing polytetrafluoroethylene material into cylindrical blanks, and calendering the cylindrical blanks into polytetrafluoroethylene tapes;

[0023] Stretching and heat setting: The polytetrafluoroethylene tape is stretched longitudinally, then stretched transversely, and then heat-set to prepare a PTFE base film.

[0024] Hydrophilic modification: The PTFE base film is placed in a mixed solution of polyethylene polyamine solution and polyethyleneimine solution, and a hydrophilic layer is formed by the reaction to obtain a hydrophilic polytetrafluoroethylene film.

[0025] Preferably, an acidic catalyst is added to the mixed solution, the reaction temperature is 30–70°C, and the reaction time is 5–20 hours;

[0026] And / or, the longitudinal stretching temperature is 180-250°C, and the longitudinal stretching speed is 1-2 m / min;

[0027] And / or, the transverse stretching temperature is 180–250°C, and the transverse stretching speed is 0.2–0.5 m / min;

[0028] And / or, the heat setting temperature is 400–450°C.

[0029] Preferably, the acidic catalyst is hydrochloric acid.

[0030] Preferably, the concentration of the acidic catalyst in the mixed solution is 0.1–0.2 mol / L.

[0031] Adding hydrochloric acid as a catalyst and raising the temperature appropriately can accelerate the cross-linking reaction rate and promote the formation of hydrophilic cross-linked networks.

[0032] Preferably, before the hydrophilic modification step, the PTFE base film is frozen at -150 to -100°C, then allowed to stand and heated to room temperature for calendering, and then hydrophilic modification is performed.

[0033] Preferably, the room temperature is 10–30°C.

[0034] Preferably, the freezing time is 10 to 30 minutes.

[0035] Preferably, the temperature during calendering is 100-150°C, the pressure of the pressure roller is 1-5 MPa, and the calendering speed is 1-3 m / min.

[0036] Current PTFE membrane fabrication processes produce membranes with pore sizes larger than 0.1 micrometers, making it difficult to effectively remove small organic molecules from etching waste and stripping solutions. This application introduces a low-temperature freezing process into the fabrication method, which causes the membrane to shrink, reducing the pore size. This allows the average pore size of the membrane to be controlled between 0.01 and 0.08 micrometers, resulting in an ultrafiltration membrane that significantly improves the filtration efficiency for small organic molecules.

[0037] It should be noted that this application performs calendering after freezing. This serves two purposes: firstly, it compacts and shapes the frozen film layer; secondly, the high-temperature, high-pressure calendering compensates for the loss of mechanical properties caused by freezing, ensuring the film's performance. Therefore, the calendering temperature and pressure selected in this application are higher than in conventional processes. It is important to note that if calendering is performed after stretching but before freezing, the film layer's shape will be fixed, causing the freezing process to fail and preventing effective reduction of the film pore size.

[0038] Preferably, the longitudinal stretching ratio is 2 to 4 times, and the transverse stretching ratio is 1 to 1.5 times.

[0039] In conventional manufacturing processes, the transverse stretching ratio is typically greater than the longitudinal stretching ratio, and both ratios are relatively large to improve the mechanical properties of the membrane. This is likely because polytetrafluoroethylene (PTFE) molecules have long, highly rigid, and compact chains, making it easy for these chains to align and conform during stretching. During transverse stretching, because the PTFE molecular chains are aligned parallel to the stretching direction, they can extend more easily along that direction, thus achieving a larger transverse stretching ratio.

[0040] However, a higher lateral stretching ratio than longitudinal stretching ratio prevents the membrane pores from shrinking during freeze-drying, thus hindering the production of ultrafiltration membranes with small pore sizes. This may be because, due to molecular chain orientation, lateral stretching more easily distorts and deforms the lattice of the PTFE membrane, making it difficult to recover through shrinkage.

[0041] Preferably, the maleic anhydride copolymer is an aromatic hydrocarbon-maleic anhydride copolymer; more preferably, it is a styrene-maleic anhydride copolymer.

[0042] Among maleic anhydride copolymers, aromatic hydrocarbon-maleic anhydride copolymers exhibit superior resistance to freezing treatment due to their benzene ring structure. Therefore, using aromatic hydrocarbon-maleic anhydride copolymers as carboxyl modification components is beneficial for compensating for the reduction in the mechanical strength of the base film caused by low-temperature freezing.

[0043] Preferably, the average pore size of the PTFE base film is 0.01 micrometers to 0.08 micrometers.

[0044] Preferably, in the hydrophilic modification step, after the hydrophilic layer is formed by the reaction, the membrane is immersed in an alkaline solution, and after immersion, a hydrophilic polytetrafluoroethylene membrane is obtained.

[0045] Preferably, the alkaline solution is a 0.1-0.2 mol / L NaOH solution.

[0046] Preferably, the soaking time in the alkaline solution is 1 to 2 hours.

[0047] During immersion in an alkaline solution, the polystyrene-maleic anhydride copolymer in the base film will hydrolyze to form hydrophilic sodium carboxylate groups, thereby improving the hydrophilicity of the polytetrafluoroethylene film and helping to reduce the adhesion and accumulation of dirt.

[0048] In summary, this application has the following beneficial effects:

[0049] 1. This application uses a blend of maleic anhydride copolymer and polytetrafluoroethylene resin as the raw material for PTFE membrane. The prepared PTFE base membrane contains a large number of carboxyl groups on its surface, effectively improving the problems of high surface tension and poor affinity for hydrophilic substances in PTFE membrane. This ensures that polyethylene polyamine and polyethyleneimine react and crosslink at the carboxyl reaction sites to form a strong hydrophilic layer, thereby improving the hydrophilicity of the PTFE membrane and reducing the probability of fouling accumulation on the membrane surface.

[0050] 2. This application introduces a low-temperature freezing process into the preparation method of PTFE membrane, which causes the PTFE base membrane to shrink under low temperature, reducing the membrane pore size to within 0.01 micrometers to 0.08 micrometers, thus significantly improving the separation and filtration effect of small organic molecules.

[0051] 3. In conjunction with the freezing process, this application employs a high-temperature and high-pressure calendering process, special stretching parameters, and a styrene-maleic anhydride copolymer, which effectively ensures the small pore size characteristics and good mechanical strength of the PTFE membrane. Attached Figure Description

[0052] Figure 1 This is a static water contact angle diagram of the hydrophilic polytetrafluoroethylene membrane in Example 1 of this application.

[0053] Figure 2 This is a SEM image showing the microstructure of the hydrophilic polytetrafluoroethylene membrane in Example 1 of this application.

[0054] Figure 3 This is a pore size distribution diagram of the hydrophilic polytetrafluoroethylene membrane in Example 1 of this application.

[0055] Figure 4 This is a static water contact angle diagram of the hydrophilic polytetrafluoroethylene membrane in Example 4 of this application.

[0056] Figure 5This is a static water contact angle diagram of the polytetrafluoroethylene membrane at 0s in Comparative Example 4 of this application.

[0057] Figure 6 This is a self-made dead-end filtration system used for water filtration rate testing in this application.

[0058] Explanation of reference numerals in the attached figures:

[0059] 1. Storage tank; 2. Pressure pump; 3. Flow meter; 4. Pressure gauge; 5. Membrane module; 6. Collection bottle; 7. Electronic balance. Detailed Implementation

[0060] Example

[0061] In the examples, the raw materials selected were: DuPont Teflon 601A PTFE dispersion resin, MSDS-30 styrene-maleic anhydride copolymer, ZeMac E60 ethylene-maleic anhydride copolymer, aviation kerosene as the extrusion aid, and polyethyleneimine with a molecular weight of 20,000.

[0062] Example 1

[0063] A hydrophilic polytetrafluoroethylene membrane is prepared according to the following method:

[0064] a) Mixing: Polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are mixed in a mixer. The amounts of polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are 100 kg, 20 kg and 40 kg respectively. After stirring evenly, polytetrafluoroethylene material is obtained.

[0065] b) Pressing and calendering: The polytetrafluoroethylene material is pressed into a cylindrical blank on a pressing machine, the cylindrical blank is extruded through a pusher, and the blank is pressed into a polytetrafluoroethylene tape through a calender.

[0066] c) Stretching and Heat Setting: The polytetrafluoroethylene (PTFE) tape is longitudinally stretched at 250°C at a speed of 2 m / min, resulting in a stretching ratio of 4 times. Then, it is transversely stretched at 180°C at a speed of 0.2 m / min, resulting in a stretching ratio of 1.5 times. Finally, it is heat-set in a high-temperature sintering furnace at 400°C to prepare the PTFE base film.

[0067] d) Low-temperature freezing treatment: Freeze the PTFE base film at -100℃ for 30 minutes, remove it and place it at room temperature to allow the base film to warm up to room temperature, thus obtaining the frozen base film.

[0068] e) Calendering: The frozen base membrane is calendered at 150°C at a calendering speed of 3 m / min and a roller pressure of 1 MPa to obtain a PTFE ultrafiltration membrane.

[0069] f) Hydrophilic modification: The PTFE ultrafiltration membrane was placed in a mixed solution containing diethylenetriamine and polyethyleneimine, with hydrochloric acid added as a catalyst. The concentrations of both diethylenetriamine and polyethyleneimine in the mixed solution were 0.5 mg / L, and the hydrochloric acid concentration was 0.1 mol / L. The reaction was carried out at 70°C for 5 hours, allowing the polyethylenetriamine and polyethyleneimine to undergo cross-linking at the carboxyl sites on the membrane surface. After the cross-linking reaction, the PTFE ultrafiltration membrane was immersed in 0.1 mol / L NaOH solution for 2 hours to obtain a hydrophilic polytetrafluoroethylene membrane.

[0070] The processed hydrophilic polytetrafluoroethylene (PTFE) membrane has an average pore size of 0.08 micrometers and a thickness of 60 micrometers. The 0s static water contact angle diagram of this hydrophilic PTFE membrane is shown below. Figure 1 As shown, the microstructure is as follows Figure 2 As shown, the aperture distribution is as follows Figure 3 As shown.

[0071] Example 2

[0072] A hydrophilic polytetrafluoroethylene membrane is prepared according to the following method:

[0073] a) Mixing: Polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are mixed in a mixer. The amounts of polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are 100 kg, 5 kg and 20 kg respectively. After stirring evenly, polytetrafluoroethylene material is obtained.

[0074] b) Pressing and calendering: The polytetrafluoroethylene material is pressed into a cylindrical blank on a pressing machine, the cylindrical blank is extruded through a pusher, and the blank is pressed into a polytetrafluoroethylene tape through a calender.

[0075] c) Stretching and Heat Setting: The polytetrafluoroethylene (PTFE) tape is longitudinally stretched at 180°C at a speed of 1 m / min, with a stretching ratio of 2. Then, it is transversely stretched at 250°C at a speed of 0.5 m / min, with a stretching ratio of 1. Finally, it is heat-set in a high-temperature sintering furnace at 450°C to prepare the PTFE base film.

[0076] d) Low-temperature freezing treatment: Freeze the PTFE base film at -150℃ for 10 minutes, remove it and place it at room temperature to allow the base film to warm up to room temperature, thus obtaining the frozen base film.

[0077] e) Calendering: The frozen base membrane is calendered at 100°C at a calendering speed of 1 meter / minute and a roller pressure of 5 MPa to obtain a PTFE ultrafiltration membrane.

[0078] f) Hydrophilic modification: The PTFE ultrafiltration membrane was placed in a mixed solution containing diethylenetriamine and polyethyleneimine, with hydrochloric acid added as a catalyst. The concentrations of both diethylenetriamine and polyethyleneimine in the mixed solution were 0.1 mg / L, and the hydrochloric acid concentration was 0.2 mol / L. The reaction was carried out at 30°C for 20 hours, allowing the polyethylenetriamine and polyethyleneimine to undergo cross-linking at the carboxyl sites on the membrane surface. After the cross-linking reaction, the PTFE ultrafiltration membrane was immersed in a 0.1 mol / L NaOH solution for 1 hour to obtain a hydrophilic polytetrafluoroethylene membrane.

[0079] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.01 micrometers and a thickness of 10 micrometers.

[0080] Example 3

[0081] A hydrophilic polytetrafluoroethylene membrane is prepared according to the following method:

[0082] a) Mixing: Polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are mixed in a mixer. The amounts of polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are 100 kg, 8 kg and 30 kg respectively. After stirring evenly, polytetrafluoroethylene material is obtained.

[0083] b) Pressing and calendering: The polytetrafluoroethylene material is pressed into a cylindrical blank on a pressing machine, the cylindrical blank is extruded through a pusher, and the blank is pressed into a polytetrafluoroethylene tape through a calender.

[0084] c) Stretching and Heat Setting: The polytetrafluoroethylene (PTFE) vinyl tape was longitudinally stretched at 210°C at a speed of 1.3 m / min, resulting in a stretching ratio of 3.2 times. Then, it was transversely stretched at 200°C at a speed of 0.3 m / min, also resulting in a stretching ratio of 1.2 times. Finally, it was heat-set in a high-temperature sintering furnace at 420°C to prepare the PTFE base film.

[0085] d) Low-temperature freezing treatment: Freeze the PTFE base film at -120℃ for 25 minutes, remove it and place it at room temperature to allow the base film to warm up to room temperature, thus obtaining the frozen base film.

[0086] e) Calendering: The frozen base membrane is calendered at 120°C at a calendering speed of 1.5 m / min and a roller pressure of 2 MPa to obtain a PTFE ultrafiltration membrane.

[0087] f) Hydrophilic modification: The PTFE ultrafiltration membrane was placed in a mixed solution containing diethylenetriamine and polyethyleneimine, with hydrochloric acid added as a catalyst. The concentrations of both diethylenetriamine and polyethyleneimine in the mixed solution were 0.2 mg / L, and the hydrochloric acid concentration was 0.15 mol / L. The reaction was carried out at 45°C for 15 hours, allowing the polyethylenetriamine and polyethyleneimine to undergo cross-linking at the carboxyl sites on the membrane surface. After the cross-linking reaction, the PTFE ultrafiltration membrane was immersed in 0.1 mol / L NaOH solution for 1 hour to obtain a hydrophilic polytetrafluoroethylene membrane.

[0088] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.06 micrometers, a thickness of 40 micrometers, and a water filtration rate of 40 kg / m²·h (filtration pressure of 1 MPa).

[0089] Example 4

[0090] A hydrophilic polytetrafluoroethylene membrane is prepared according to the following method:

[0091] a) Mixing: Polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are mixed in a mixer. The amounts of polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are 100 kg, 15 kg and 25 kg respectively. After stirring evenly, polytetrafluoroethylene material is obtained.

[0092] b) Pressing and calendering: The polytetrafluoroethylene material is pressed into a cylindrical blank on a pressing machine, the cylindrical blank is extruded through a pusher, and the blank is pressed into a polytetrafluoroethylene tape through a calender.

[0093] c) Stretching and Heat Setting: The polytetrafluoroethylene (PTFE) vinyl tape was longitudinally stretched at 235°C at a speed of 1.7 m / min, resulting in a stretching ratio of 2.5 times. Then, it was transversely stretched at 230°C at a speed of 0.4 m / min, resulting in a stretching ratio of 1.4 times. Finally, it was heat-set in a high-temperature sintering furnace at 440°C to prepare the PTFE base film.

[0094] d) Low-temperature freezing treatment: Freeze the PTFE base film at -140℃ for 15 minutes, remove it and place it at room temperature to allow the base film to warm up to room temperature, thus obtaining the frozen base film.

[0095] e) Calendering: The frozen base membrane is calendered at 140°C at a calendering speed of 2.5 m / min and a roller pressure of 4 MPa to obtain a PTFE ultrafiltration membrane.

[0096] f) Hydrophilic modification: The PTFE ultrafiltration membrane was placed in a mixed solution containing diethylenetriamine and polyethyleneimine, with hydrochloric acid added as a catalyst. The concentrations of both diethylenetriamine and polyethyleneimine in the mixed solution were 0.4 mg / L, and the hydrochloric acid concentration was 0.2 mol / L. The reaction was carried out at 60°C for 5 hours, allowing the polyethylenetriamine and polyethyleneimine to undergo a cross-linking reaction at the carboxyl sites on the membrane surface. After the cross-linking reaction, the PTFE ultrafiltration membrane was immersed in 0.1 mol / L NaOH solution for 1.8 hours to obtain a hydrophilic polytetrafluoroethylene membrane.

[0097] The processed hydrophilic polytetrafluoroethylene (PTFE) membrane has an average pore size of 0.02 micrometers and a thickness of 20 micrometers; the 0s static water contact angle diagram of this hydrophilic PTFE membrane is shown below. Figure 4 As shown.

[0098] Example 5

[0099] A hydrophilic polytetrafluoroethylene membrane is prepared according to the following method:

[0100] a) Mixing: Polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are mixed in a mixer. The amounts of polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are 100 kg, 20 kg and 40 kg respectively. After stirring evenly, polytetrafluoroethylene material is obtained.

[0101] b) Pressing and calendering: The polytetrafluoroethylene material is pressed into a cylindrical blank on a pressing machine, the cylindrical blank is extruded through a pusher, and the blank is pressed into a polytetrafluoroethylene tape through a calender.

[0102] c) Stretching and Heat Setting: The polytetrafluoroethylene (PTFE) tape is longitudinally stretched at 250°C at a speed of 2 m / min, resulting in a stretching ratio of 4 times. Then, it is transversely stretched at 180°C at a speed of 0.2 m / min, resulting in a stretching ratio of 1.5 times. Finally, it is heat-set in a high-temperature sintering furnace at 400°C to prepare the PTFE base film.

[0103] d) Calendering: The PTFE base membrane is calendered at 150°C at a calendering speed of 3 m / min and a roller pressure of 1 MPa to obtain the PTFE ultrafiltration membrane.

[0104] e) Hydrophilic modification: The PTFE ultrafiltration membrane was placed in a mixed solution containing diethylenetriamine and polyethyleneimine, with hydrochloric acid added as a catalyst. The concentrations of both diethylenetriamine and polyethyleneimine in the mixed solution were 0.5 mg / L, and the hydrochloric acid concentration was 0.1 mol / L. The reaction was carried out at 70°C for 5 hours, allowing the polyethylenetriamine and polyethyleneimine to undergo cross-linking at the carboxyl sites on the membrane surface. After the cross-linking reaction, the PTFE ultrafiltration membrane was immersed in 0.1 mol / L NaOH solution for 2 hours to obtain a hydrophilic polytetrafluoroethylene membrane.

[0105] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.25 micrometers and a thickness of 60 micrometers.

[0106] Example 6

[0107] A hydrophilic polytetrafluoroethylene membrane is prepared according to the following method:

[0108] a) Mixing: Polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are mixed in a mixer. The amounts of polytetrafluoroethylene dispersion resin, styrene-maleic anhydride copolymer and extrusion aid are 100 kg, 20 kg and 40 kg respectively. After stirring evenly, polytetrafluoroethylene material is obtained.

[0109] b) Pressing and calendering: The polytetrafluoroethylene material is pressed into a cylindrical blank on a pressing machine, the cylindrical blank is extruded through a pusher, and the blank is pressed into a polytetrafluoroethylene tape through a calender.

[0110] c) Stretching and Heat Setting: The polytetrafluoroethylene (PTFE) tape is longitudinally stretched at 250°C at a speed of 2 m / min, resulting in a stretching ratio of 4 times. Then, it is transversely stretched at 180°C at a speed of 0.2 m / min, resulting in a stretching ratio of 1.5 times. Finally, it is heat-set in a high-temperature sintering furnace at 400°C to prepare the PTFE base film.

[0111] d) Low-temperature freezing treatment: Freeze the PTFE base film at -100℃ for 30 minutes, remove it and place it at room temperature to allow the base film to warm up to room temperature, thus obtaining the frozen base film.

[0112] e) Hydrophilic modification: The frozen base membrane was placed in a mixed solution containing diethylenetriamine and polyethyleneimine, with hydrochloric acid added as a catalyst. The concentrations of both diethylenetriamine and polyethyleneimine in the mixed solution were 0.5 mg / L, and the hydrochloric acid concentration was 0.1 mol / L. The reaction was carried out at 70°C for 5 hours to induce a crosslinking reaction. After the crosslinking reaction, the PTFE ultrafiltration membrane was immersed in 0.1 mol / L NaOH solution for 2 hours to obtain a hydrophilic polytetrafluoroethylene membrane.

[0113] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.08 micrometers and a thickness of 100 micrometers.

[0114] Example 7

[0115] A hydrophilic polytetrafluoroethylene film differs from Example 1 in that the calendering temperature is different, specifically 80°C.

[0116] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.09 micrometers and a thickness of 85 micrometers.

[0117] Example 8

[0118] A hydrophilic polytetrafluoroethylene membrane differs from Example 1 in that, in the stretching and heat-setting steps, the transverse stretching speed is 2 m / min and the transverse stretching ratio is 4 times; the longitudinal stretching speed is 0.2 m / min and the longitudinal stretching ratio is 1.5 times.

[0119] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.45 micrometers and a thickness of 60 micrometers.

[0120] Example 9

[0121] A hydrophilic polytetrafluoroethylene membrane differs from Example 1 in that an equal amount of ethylene-maleic anhydride copolymer is used instead of styrene-maleic anhydride copolymer.

[0122] The hydrophilic polytetrafluoroethylene membrane obtained by the process has an average pore size of 0.08 micrometers and a thickness of 60 micrometers.

[0123] Comparative Example

[0124] Comparative Example 1, a polytetrafluoroethylene membrane, differs from Example 1 in that an equal amount of polytetrafluoroethylene dispersion resin is used instead of the styrene-maleic anhydride copolymer in the mixing step.

[0125] The processed polytetrafluoroethylene membrane has an average pore size of 0.08 micrometers and a thickness of 60 micrometers.

[0126] Comparative Example 2, a polytetrafluoroethylene membrane, differs from Example 1 in that, in the hydrophilic modification step, an equal amount of polyethyleneimine is used instead of polyethyleneimine.

[0127] The processed polytetrafluoroethylene membrane has an average pore size of 0.08 micrometers and a thickness of 60 micrometers.

[0128] Comparative Example 3, a polytetrafluoroethylene membrane, differs from Example 1 in that, in the hydrophilic modification step, an equal amount of polyethyleneimine is used to replace polyethylene polyamine.

[0129] The processed polytetrafluoroethylene membrane has an average pore size of 0.08 micrometers and a thickness of 60 micrometers.

[0130] Comparative Example 4 is a polytetrafluoroethylene membrane, which differs from Example 1 in that it does not undergo a hydrophilic modification step and the polytetrafluoroethylene membrane is obtained after the freeze treatment.

[0131] The processed polytetrafluoroethylene (PTFE) membrane has an average pore size of 0.08 micrometers and a thickness of 60 micrometers. The 0s static water contact angle diagram of this hydrophilic PTFE membrane is shown below. Figure 6 As shown.

[0132] Performance testing

[0133] 1. Wetting angle test

[0134] The water wetting angle of the polytetrafluoroethylene film in this application was tested according to the method in GB / T 14216-2008 "Determination of wetting tension of plastic films and sheets".

[0135] 2. Membrane pore size test

[0136] The pore size distribution of different polytetrafluoroethylene membranes was tested using a pore size analyzer (PMIPorometer, iPore-1100A, USA).

[0137] 3. Water filtration speed test

[0138] Using a self-made dead-end filtration system (such as...) Figure 6 The water filtration rate of the polytetrafluoroethylene membrane before and after modification was tested (as shown). The test pressure was 1 MPa and the test time was 10 minutes.

[0139] 4. Bovine serum albumin retention rate test

[0140] Prepare a 1 g / L bovine serum albumin raw material solution using a self-made dead-end filtration system (e.g., Figure 5 (As shown) The bovine serum albumin (BSA) rejection rate of the polytetrafluoroethylene (PTFE) membrane before and after modification was tested. Specifically, the BSA raw material solution was stored in the storage tank 1, and the BSA raw material solution was pumped into the membrane module 5 with the PTFE membrane fixed by the pressure pump 2. The test pressure was 1 MPa. The filtrate from the permeate filtration membrane was collected through the collection bottle 6, and the collection time was 10 minutes. The concentration of BSA in the raw material solution and the filtrate was tested separately, and the BSA rejection rate was calculated according to the following formula.

[0141] R = (C f -C p ) / C f 100%

[0142] Among them, C f : Concentration of bovine serum albumin in the feed solution, in grams per liter; C p : Concentration of bovine serum albumin in the filtrate, in grams per liter.

[0143] Bovine serum albumin (BSA) concentration was determined using a UV-Vis spectrophotometer-standard curve method. The procedure was as follows: 0.5 g of BSA was accurately weighed, dissolved in phosphate buffer (pH = 7.4), and added to a 100 mL volumetric flask to prepare a 5 g / L BSA solution. The standard solution was then accurately pipetted into a 25 mL volumetric flask and diluted with the phosphate buffer to obtain 0.1, 0.3, 0.5, 0.7, and 0.9 g / L BSA standard solutions, as well as a blank phosphate buffer (pH = 7.4) solution. The absorbance was measured at 280 nm using a TU-1950 UV-Vis spectrophotometer. The standard curve and equation for BSA were obtained: y = 0.2658x - 0.0279, with a linear fit of 99.98%.

[0144] 5. Stain resistance test

[0145] The stain resistance test used bovine serum albumin (BSA) as a simulated pollutant. A polytetrafluoroethylene (PTFE) membrane was immersed in a 5 g / L BSA solution for 8 hours, and the absorbance of the remaining BSA solution was measured using a UV-Vis spectrophotometer. The amount of BSA adsorbed per unit membrane area was calculated based on the decrease in concentration, using the following formula.

[0146]

[0147] In the formula, Г represents the adsorption capacity of bovine serum albumin, in g / m³. 2 C0 is the concentration of bovine serum albumin before membrane immersion, g / L; C is the concentration of bovine serum albumin after membrane immersion for a period of time, g / L; V is the volume of the solution, L; A is the effective area of ​​the polytetrafluoroethylene membrane, m². 2 .

[0148] Table 1. Basic Performance Test Results

[0149]

[0150] 6. Mechanical property test

[0151] The tensile properties of the polytetrafluoroethylene film in this application were tested according to the method in GB / T 1040.3-2006 "Determination of tensile properties of plastics". The test sample was 20 mm wide and 100 mm long, with a clamping distance of 50 mm and a tensile speed of 100 mm / min. Each group of samples was tested five times, and the average value was taken.

[0152] Table 2. Mechanical Performance Test Results

[0153]

[0154] Analysis of experimental results:

[0155] The above experiments characterized the filtration performance of polytetrafluoroethylene (PTFE) membranes for small organic molecules by the rejection rate of bovine serum albumin (BSAL), and characterized the fouling resistance of PTFE membranes by the amount of BSAL adsorbed on the membrane surface.

[0156] (1) As can be seen from Examples 1-9 and Comparative Examples 1-4 and Table 1, this application introduces carboxylic acid groups into the PTFE base membrane in advance, and then uses a mixed solution of polyethylene polyamine solution and polyethyleneimine solution to hydrophilically modify the base membrane, thereby obtaining a polytetrafluoroethylene membrane with excellent hydrophilicity and improving the stability of the filtration performance of the polytetrafluoroethylene membrane.

[0157] Specifically, referring to Example 1 and Comparative Example 1, and Table 1, it can be seen that for PTFE base membranes, if maleic anhydride copolymer is not used in the raw materials, carboxylic acid groups cannot be introduced into the obtained PTFE base membrane. This results in the mixed solution failing to effectively wet the PTFE base membrane, thus preventing cross-linking and the formation of an effective hydrophilic layer. Consequently, the resulting polytetrafluoroethylene membrane exhibits poor stain resistance. Furthermore, referring to Example 1 and Comparative Examples 2-3, and Table 1, it can be seen that the absence of either polyethylene polyamine or polyethyleneimine in the hydrophilic modification solution significantly affects the hydrophilic properties of the obtained polytetrafluoroethylene membrane.

[0158] It should be noted that, because the wetting angle of the polytetrafluoroethylene membrane obtained in Comparative Example 4 is much higher than 90°, the aqueous solution cannot effectively wet it, and its water flux will be zero. Similarly, in the bovine serum albumin rejection test, the raw material solution cannot permeate the polytetrafluoroethylene membrane and produce filtrate, making it impossible to measure the rejection rate.

[0159] Bovine serum albumin raw material solution is also ineffective

[0160] (2) As can be seen from Examples 1 and 5-7, and Tables 1 and 2, this application employs a low-temperature (-150-100℃) freezing treatment of the PTFE base membrane before the hydrophilic freezing process, combined with a high-temperature and high-pressure calendering process. This effectively reduces the pore size of the PTFE membrane, improving its filtration performance for small organic molecules while ensuring the membrane layer retains certain mechanical properties. Example 5 shows that when the freezing process is not performed, the pore size of the membrane will be greater than 0.1 micrometers, significantly reducing its filtration performance for small organic molecules. Example 6 shows that when the calendering process is not performed under high-temperature and high-pressure conditions after freezing, the mechanical properties of the membrane layer will decrease. This may be because the freezing treatment effectively shrinks the pores of the PTFE base membrane, and the calendering process fixes the pore morphology, while simultaneously increasing the density of the membrane structure and improving its mechanical properties.

[0161] (3) As can be seen from Examples 1 and 8 and Tables 1 and 2, when the transverse stretching ratio is higher than the longitudinal stretching ratio, the pore size of the polytetrafluoroethylene membrane prepared by freeze treatment cannot be effectively reduced, and the filtration performance for small organic molecules is significantly reduced. The reason may be that the process of transverse stretching ratio being higher than longitudinal stretching ratio is usually the condition for preparing large-pore polytetrafluoroethylene membranes. However, for the ultrafiltration membrane (average pore size less than 0.1 micrometers) prepared in this application, a high transverse stretching ratio will cause the lattice structure of the PTFE base membrane to be distorted and deformed, making it difficult to shrink by freeze-thaw recovery, thus affecting the final pore size.

[0162] (4) As can be seen from Examples 1 and 9 and Tables 1 and 2, compared with polyolefin-maleic anhydride copolymer, the use of styrene-maleic anhydride copolymer for carboxyl grafting of PTFE base film in this application not only promotes the improvement of hydrophilicity but also helps to improve the mechanical strength of the resulting polytetrafluoroethylene film. This may be because the styrene-maleic anhydride copolymer molecular chain has a benzene ring structure, which, when dispersed in polytetrafluoroethylene resin, helps to improve the low-temperature resistance of the PTFE base film and reduces the loss of mechanical properties after freezing treatment.

[0163] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A hydrophilic polytetrafluoroethylene membrane, characterized in that, include: PTFE base film and hydrophilic layer attached to PTFE base film; The raw materials for the PTFE base film include a mixture of polytetrafluoroethylene dispersion resin, maleic anhydride copolymer and extrusion aid in a mass percentage ratio of 1:0.05-0.2:0.2-0.4, wherein the maleic anhydride copolymer is a copolymer of olefin or aromatic hydrocarbon with maleic anhydride; The raw material for the hydrophilic layer is a mixed solution containing polyethylene polyamine and polyethyleneimine; The hydrophilic polytetrafluoroethylene membrane has a wetting angle of less than 50°.

2. The hydrophilic polytetrafluoroethylene membrane according to claim 1, characterized in that, The concentration of polyethylene polyamine in the mixed solution is 0.1–0.5 mg / L, and the concentration of polyethyleneimine is 0.1–0.5 mg / L.

3. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to any one of claims 1 to 2, characterized in that, Includes the following steps: Mixing: The raw materials for PTFE base film are mixed in a mixer and stirred evenly to obtain polytetrafluoroethylene material; Preform pressing and calendering: pressing polytetrafluoroethylene material into cylindrical blanks, and calendering the cylindrical blanks into polytetrafluoroethylene tapes; Stretching and heat setting: The polytetrafluoroethylene tape is stretched longitudinally, then stretched transversely, and then heat-set to prepare a PTFE base film. Hydrophilic modification: The PTFE base film is placed in a mixed solution of polyethylene polyamine solution and polyethyleneimine solution, and a hydrophilic layer is formed by the reaction to obtain a hydrophilic polytetrafluoroethylene film.

4. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 3, characterized in that, In the hydrophilic modification step, an acidic catalyst is added to the mixed solution, the reaction temperature is 30-70℃, and the reaction time is 5-20 hours. And / or, the longitudinal stretching temperature is 180-250°C, and the longitudinal stretching speed is 1-2 m / min; And / or, the transverse stretching temperature is 180–250°C, and the transverse stretching speed is 0.2–0.5 m / min; And / or, the heat setting temperature is 400–450°C.

5. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 3, characterized in that, Before the hydrophilic modification step, the PTFE base film is frozen at -150 to -100°C. After freezing, it is allowed to stand and then heated to room temperature for calendering before hydrophilic modification.

6. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 5, characterized in that, After freezing, the calendering temperature is 100-150℃, the pressure of the pressure roller is 1-5MPa, and the calendering speed is 1-3 meters / minute.

7. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 5, characterized in that, The longitudinal stretching ratio is 2 to 4 times, and the transverse stretching ratio is 1 to 1.5 times.

8. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 5, characterized in that, The maleic anhydride copolymer is selected from styrene-maleic anhydride copolymer.

9. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 5, characterized in that, The average pore size of the PTFE base film after freeze treatment is 0.01 μm to 0.08 μm.

10. The method for preparing the hydrophilic polytetrafluoroethylene membrane according to claim 3, characterized in that, In the hydrophilic modification step, after the hydrophilic layer is formed by the reaction, the membrane is immersed in an alkaline solution. After immersion, a hydrophilic polytetrafluoroethylene membrane is obtained.

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