Preparation method of a perfluorinated hollow fiber porous membrane

Abstract

The present invention discloses a method for preparing a perfluorinated hollow fiber porous membrane, comprising the following steps: 1) uniformly mixing perfluoroethylene-propylene resin, polyvinylidene fluoride resin, water-soluble latent solvent, inorganic pore-forming agent, and additive to obtain a mixed powder for film casting; 2) melt-extruding the mixed powder, cooling it in a coagulation bath, then performing extraction, stretching, heat setting, secondary coating, water washing, and winding. This method is simple and effective, generates less three wastes during the film-making process, the water-soluble latent solvent is easy to extract and recycle, the prepared perfluorinated hollow fiber porous membrane has small pore size, excellent product performance, and uniform pore size distribution.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, specifically relates to hollow porous membranes, and more specifically relates to small-aperture perfluorinated hollow fiber porous membranes. Background Art

[0002] As a new separation technology, membrane separation technology has currently been widely applied in fields such as chemical engineering, energy, medicine, and water treatment. With the continuous expansion of the membrane application field, newer and higher requirements are put forward for membrane materials: it is required that the membrane has high selectivity and permeability, and at the same time has high enough mechanical strength, chemical corrosion resistance, and thermal stability.

[0003] At the present stage, polyvinylidene fluoride (PVDF), as an excellent membrane material, is widely used in the preparation of industrial microfiltration membranes and ultrafiltration membranes. However, with the explosive growth of new energy vehicles, PVDF, as a binder for battery materials, has seen a sharp increase in demand. The market has seen a situation where prices have doubled and supply falls short of demand, making it impossible for most membrane enterprises to purchase raw materials. Therefore, there is an urgent need to find a membrane material that can comprehensively replace PVDF in terms of various properties.

[0004] Fluorinated ethylene propylene (FEP) is a typical perfluoropolymer with a completely fluorinated structure, which is copolymerized from tetrafluoroethylene (TFE) and hexafluoropropylene (HFP). Compared with the regular molecular structure of polytetrafluoroethylene (PTFE), the introduction of trifluoromethyl (CF3) on the side chain of the FEP macromolecule destroys its original regularity, reduces the crystallinity of FEP, and endows FEP with good melt processing performance. At the same time, because FEP has similar chemical stability, high and low temperature resistance, anti-aging ability, and excellent mechanical properties to PTFE, it can be used as an excellent membrane material in membrane separation systems under harsh conditions and has strong competitive advantages.

[0005] As a film-forming material with excellent properties, perfluoropolymers have also attracted more and more attention from researchers in recent years. Chinese Patent CN101884878B discloses a method for preparing a perfluoropolymer hollow fiber porous membrane, which is to forcibly mix perfluoropolymer, polymer additive, composite pore-forming agent and organic low-molecular liquid in proportion, then inject it into a twin-screw extruder for melt spinning, and finally obtain the perfluoropolymer hollow fiber porous membrane through conventional post-treatment. The organic low-molecular liquid added is selected from one of dioctyl phthalate or dibutyl phthalate, or a mixture of dioctyl phthalate and dibutyl phthalate in any proportion as the plasticizer therein to make the perfluoropolymer have good meltability. Patent CN109351209A also discloses a method for preparing a poly(ethylene-co-tetrafluoroethylene) hollow fiber porous membrane, which is to uniformly mix FEP, pore-forming agent, plasticizer and auxiliary additive in proportion and then granulate, and then extrude, stretch, heat-set, extract the pore-forming agent, and wash with water to finally obtain a poly(ethylene-co-tetrafluoroethylene) hollow fiber membrane with a multi-pore structure of tensile pores, dissolution pores and interfacial pores. The plasticizer used therein is at least one of dibutyl phthalate, diethyl phthalate or dioctyl phthalate. Japanese Patent JP2899903B2 discloses a polyvinylidene fluoride porous membrane and a manufacturing method thereof, in which a phthalate-based substance is used as an organic additive, and at the same time, hydrophobic nano-silica is added to obtain a polyvinylidene fluoride porous membrane with a narrower pore size distribution and a three-dimensional network structure. Chinese Patent CN104941464A discloses a catalytic hollow fiber membrane and a preparation method thereof, in which the composite pore-forming agent used includes a soluble pore-forming agent and an insoluble pore-forming agent. The soluble pore-forming agent includes one of lithium chloride, calcium chloride, sodium chloride and potassium chloride, etc., and the insoluble pore-forming agent is one of silica and calcium carbonate or a mixture in any proportion. The organic low-molecular liquid still uses phthalate-based substances. In the above four patents, phthalate-based substances are used as plasticizers for resins. Such plasticizers need to be extracted from the membrane with substances such as ethanol, chloroform or n-hexane in subsequent post-treatment to form pores in the membrane. These solvents are highly dangerous, polluting, and not easy to recycle, posing greater safety risks and environmental hazards.

[0006] US Patent US20090283469A1 discloses a method for preparing a polyvinylidene fluoride hollow fiber microporous membrane. It uses water-soluble latent solvents such as ethylene glycol monoethyl ether acetate and propylene glycol monomethyl ether acetate, which are dissolved together with polyvinylidene fluoride resin at high temperature to obtain a spinning dope. By using the dry-wet method, it is introduced into a cooling bath composed of water or a mixture of water and water-soluble latent solvents. The cross-sectional main layer uses the thermally induced phase separation method, and the outer surface uses the nonsolvent-induced phase separation method to form the membrane. The porosity of the cross-sectional main layer of the prepared membrane is larger than the porosity of the outer surface openings, and the cross-section of the membrane forms a discontinuous change structure with a fine structure of a dense surface layer and a rough structure of the main layer. This patent uses water-soluble latent solvents to optimize the process, which can reduce the use of high-risk extraction agents in post-treatment. However, the system used is single, and the preparation process is prone to problems such as uneven mixing, aggregation of latent solvents, and a wide membrane pore size distribution.

[0007] Chinese Patent CN102580573B discloses a method for preparing a perfluoropolymer hollow fiber membrane. The process used is as follows: First, a perfluoropolymer, polystyrene, a polymer additive, and a composite pore-forming agent are mixed evenly. Then, the obtained mixture is mixed evenly with the organic liquid. At a temperature of 300 - 350 °C, melt spinning is carried out using a twin-screw extruder, extruded through a hollow spinneret assembly, soaked in water for 48 hours and then dried. Then, the dried hollow fiber membrane is sulfonated, and finally, after being washed with deionized water and dried, a hydrophilic perfluoropolymer hollow fiber membrane is obtained. The process of the sulfonation treatment is as follows: Using concentrated sulfuric acid as a solvent and a sulfonating agent, the mass of concentrated sulfuric acid is 5 - 10 times the mass of the sulfonated hollow fiber membrane, the sulfonation reaction temperature is 50 - 80 °C, and the sulfonation reaction time is 5 - 10 hours. This patent sulfonates the membrane to improve the hydrophilicity of the FEP membrane. This treatment process is complex, highly polluting, and has a long reaction time. The pore size range of the polyperfluoroethylene-propylene hollow fiber membrane prepared by the above patent is about 0.5 μm, which severely limits its application fields and scope.

[0008] Chinese Patent CN102166484A discloses a method for preparing a hydrophilic polyvinylidene fluoride composite membrane. In its process, an amphiphilic copolymer is added to increase the compatibility between polyvinylidene fluoride and the matrix PET braided tube. However, the product is easily affected by the processing characteristics of the braided tube, such as unevenness and burrs, resulting in a high product defect rate. Chinese Patent CN1128176A discloses a method for preparing a wet polyvinylidene fluoride porous membrane. It uses the complementary performance and synergistic effect of a polymer pore-forming agent, a surfactant, and a nonsolvent to prepare a porous membrane with a pore size of 0.05 - 0.22 μm, a flux of 100 - 1500 LMH, and a porosity of 80 - 90%. This patent prepares a homogeneous hollow fiber membrane. In order to meet the self-supporting strength requirements of the membrane, the resin solid content used is relatively high, resulting in a high application cost. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of a perfluorinated hollow fiber porous membrane. This method is simple and effective, produces less three wastes during the membrane preparation process, the latent solvent is easy to extract and recycle, and after secondary coating, the prepared perfluorinated hollow fiber porous membrane has excellent product performance, small pore size, uniform pore size distribution, and high retention accuracy.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] A preparation method of a perfluorinated hollow fiber porous membrane, comprising the following steps:

[0012] 1) Mix perfluoroethylene-propylene resin, polyvinylidene fluoride resin, water-soluble latent solvent, inorganic pore-forming agent, and additive evenly to obtain a mixed powder for casting the membrane;

[0013] 2) Melt-extrude the mixed powder, cool it in a coagulation bath, then extract, stretch, heat-set, perform secondary coating, wash with water, and wind up.

[0014] In step 1) of the present invention, the raw materials comprise the following components:

[0015]

[0016] In the present invention, the perfluoroethylene-propylene resin is a powdery resin, and its melt index needs to be greater than 10 g / 10 min. If the melt index is too small, it will be difficult to melt completely in the extruder, which will affect the mechanical strength of the final formed membrane.

[0017] Preferably, the perfluoroethylene-propylene resin described in the present invention comprises DS605 of Shandong Huaxia Shenzhou New Materials Co., Ltd. or FR460 of Shanghai 3F New Materials Co., Ltd.

[0018] In the present invention, the polyvinylidene fluoride resin is a polyvinylidene fluoride homopolymer or copolymer with a weight-average molecular weight of 200,000 to 700,000. The addition of the polyvinylidene fluoride resin can, on the one hand, improve the processing performance of the perfluoroethylene-propylene resin during the melting process, and on the other hand, during the solidification process after adding the latent solvent, as the latent solvent migrates to the membrane surface, and during the subsequent coating process, since the polyvinylidene fluoride can dissolve in the solvent of the coating solution, the coating interface is more firm, reducing the delamination problem caused by the compatibility of the materials in the later stage.

[0019] Preferably, the polyvinylidene fluoride resin described in the present invention comprises one or more of PVDF6010, PVDF6015, and PVDF6020 of Solvay.

[0020] In the present invention, the specific gravity of the water-soluble latent solvent dissolved in water at room temperature is at least 5%, preferably 15%. A latent solvent refers to a solvent that does not dissolve the resin at room temperature but dissolves it at high temperature. Further, the water-soluble latent solvent includes one or more of ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, and triethyl phosphate.

[0021] In the present invention, the inorganic pore former includes one or more of nano-scale hydrophobic silica (specific surface area 90 - 130 m 2 / g), calcium carbonate (specific surface area 16 - 30 m 2 / g), zinc oxide (specific surface area > 48 m 2 / g), etc.

[0022] In the present invention, the additive includes one or more of an antioxidant, a heat stabilizer, an ultraviolet absorber, and an anti-aging agent.

[0023] In the present invention, in step 2), the coagulation bath is composed of water or a mixture of water and ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, or triethyl phosphate.

[0024] In the present invention, in step 2), the extraction includes the following steps: passing the membrane filaments through a 5 wt% sodium hydroxide solution or a 2 wt% hydrochloric acid solution at 30°C - 80°C for 10 - 60 minutes.

[0025] In the present invention, in step 2), the stretching includes the following steps: stretching the hollow fiber membrane filaments obtained by melt extrusion and coagulation in the length direction at a ratio of 1.5 - 3 times.

[0026] In the present invention, in step 2), the heat setting includes the following steps: heat setting the membrane filaments in a heat setting oven at 90 - 150°C for 10 - 60 minutes.

[0027] In the present invention, in step 2), the secondary coating includes the following steps: passing the heat-set and dried hollow fiber membrane filaments through the coating solution.

[0028] The coating solution of the present invention includes polyvinylidene fluoride resin, a hydrophilic polymer pore former, an amphiphilic block copolymer, a surfactant, and a solvent.

[0029] Preferably, the coating solution includes the following components:

[0030]

[0031] Preferably, the polyvinylidene fluoride resin in the coating solution is the same as the polyvinylidene fluoride resin in step 1).

[0032] Preferably, the hydrophilic polymer pore-forming agent comprises polyvinyl pyrrolidone (PVP) and / or polyethylene glycol (PEG).

[0033] Preferably, the amphiphilic block copolymer comprises poloxamer 188 and / or polylactic acid-polyethylene glycol-polylactic acid (PLA-PEG-PLA).

[0034] Preferably, the surfactant comprises Tween 80 or Span 20.

[0035] Preferably, the solvent comprises N,N-dimethylformamide and / or N,N-dimethylacetamide.

[0036] In the present invention, in the step 2), the solvent in the membrane filaments during the secondary coating process is removed by water washing.

[0037] The present invention adopts a water-soluble latent solvent as a plasticizer for FEP film formation. This latent solvent can be directly dissolved in the water of the coagulation bath during subsequent post-treatment, and the extraction is simple, pollution-free, and easy to recycle. In the interaction process between the latent solvent and water, the main layer of the cross section undergoes heat-induced phase separation, and the outer surface undergoes non-solvent-induced phase separation. The porosity of the main layer of the membrane cross section is greater than the porosity of the outer surface, and the membrane cross section forms a discontinuous change structure of a fine structure of a dense surface layer and a rough structure of the main layer. Only this structure is conducive to subsequent coating. Otherwise, the pores on the FEP surface are too large. During coating, the coating layer is not very pressure-resistant and is easy to break during use due to the large gap between the pores of the coating layer and the pores of the FEP surface, and the filtering effect is lost. At the same time, the inorganic pore-forming agent with a large specific surface area can adsorb a part of the water-soluble latent solvent to its surface, which can effectively control the dispersibility of the water-soluble latent solvent in the film-making process, so that the pore distribution of the FEP film obtained will be more uniform. At the same time, the water-soluble latent solvent can be dissolved in water, so that subsequent online extraction can be achieved, and subsequent online coating can be achieved at the same time. On the other hand, adding polyvinylidene fluoride resin into the formula, PVDF and FEP are blended, the two materials complement each other, can reduce the process temperature during the processing and improve the overall ductility of the material. The added PVDF on the surface of the film can be dissolved by the solvent in the coating liquid during the later coating process, so that the main film can be well combined with the coating layer, reducing the stratification phenomenon caused by the combination of two different materials in the later stage.

[0038] After the main body structure is formed, it enters the coating liquid tank after subsequent extraction, stretching, and heat setting. The coating liquid needs to achieve the effects of uniform coating and firm combination with the main body. A PVDF casting solution with a low solid content (1%-10%) is used. A hydrophilic polymer pore-forming agent is added to the casting solution to improve the hydrophilicity of the membrane, and an amphiphilic block copolymer and a surfactant are added to improve the combination degree of the two materials. The finally formed coating layer is very thin, and the main strength structure of the membrane is determined by the main body layer. Only by combining the above preparation methods can the membrane filtration pore diameter with perfluoroethylenepropylene as the main body be effectively reduced to between 0.03 and 0.1 microns, with higher retention accuracy, and at the same time improve the hydrophilicity of the membrane. It reaches the pore diameter range of most current commercial membranes. The application feasibility and application field range are expanded.

[0039] This preparation method is green and environmentally friendly, the film-forming process is simple, there is no high-risk extraction process afterwards, the formed film has a small pore size, high mechanical strength, and good retention effect. Therefore, the present invention not only greatly reduces the three wastes and complex extraction processes generated during the film-making process, but also improves the separation performance of the membrane, expands the application field of the membrane, and the production method is economical and environmentally friendly, which has important practical significance and economic benefits. Brief Description of the Drawings

[0040] Figure 1 Scanning electron microscope picture of the outer surface of the hollow fiber membrane prepared in Example 1;

[0041] Figure 2 Scanning electron microscope picture of the cross-section of the hollow fiber membrane prepared in Example 1;

[0042] Figure 3 Scanning electron microscope picture of the outer surface of the hollow fiber membrane prepared in Comparative Example 1;

[0043] Figure 4 Scanning electron microscope picture of the cross-section of the hollow fiber membrane prepared in Comparative Example 1;

[0044] Figure 5 Pore size and its distribution diagram of the hollow fiber membrane prepared in Example 1;

[0045] Figure 6 Pore size and its distribution diagram of the hollow fiber membrane prepared in Comparative Example 1. Detailed Description of the Invention

[0046] The following further illustrates the present invention through specific examples. The examples described in the present invention are only for the illustration of the present invention and do not limit the scope of the present invention.

[0047] The sources of raw materials in the examples and comparative examples are as follows:

[0048] Fluorinated ethylene propylene resin (DS605 from Shandong Huaxia Shenzhou New Materials Co., Ltd. or FR460 from Shanghai San Ai Fu New Materials Co., Ltd.);

[0049] Ethylene glycol monomethyl ether acetate (Aite (Shandong) New Materials Co., Ltd.);

[0050] Ethylene glycol monoethyl ether acetate (Shandong Xinhui New Materials Co., Ltd.);

[0051] Diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate (Hubei Xinhongli Chemical Co., Ltd.);

[0052] Triethyl phosphate (Zhangjiagang Xinya Chemical Co., Ltd.);

[0053] Nano-silicon dioxide (Evonik Degussa (China) Co., Ltd., R972);

[0054] Nano calcium carbonate (Shanghai Yuanjiang Chemical Co., Ltd.);

[0055] Polyvinylidene fluoride (Solvay, Belgium, 6010, 6015, 6020)

[0056] Polyvinylpyrrolidone (PVP) (Gopico New Materials Technology (Shanghai) Co., Ltd.)

[0057] Polyethylene glycol (PEG)(Dow Chemical)

[0058] Poloxamer 188 (BASF)

[0059] PLA-PEG-PLA (Xi'an Qiyue Biotechnology Co., Ltd.)

[0060] Twain 80, Span 20 (Aladdin)

[0061] N,N-dimethylformamide, N,N-dimethylacetamide (DuPont)

[0062] Unless otherwise specified, other raw materials and reagents can be obtained through common commercial channels.

[0063] The separation performance of the prepared small-pore perfluorinated hollow fiber porous membrane is evaluated mainly by characterizing three characteristic parameters, namely the average pore size of the membrane, pure water flux and mechanical strength.

[0064] (1) Average pore size of the membrane: measured using a POROLUX 1000 pore size analyzer. The test principle calculation formula is:

[0065] D=4δcosθ / P

[0066] In the formula: D—membrane pore diameter, μm;

[0067] δ—Liquid surface tension, N / m;

[0068] θ—Contact angle between the liquid and the pore wall, °;

[0069] P—Gas pressure, Pa;

[0070] (2) The definition of pure water flux (LMH) is: under certain operating pressure conditions, the volume of water passing through the effective membrane area per unit time, and its calculation formula is:

[0071] J = Q / At

[0072] Where: J—Flux, L / m 2 ·h@0.1 mPa;

[0073] Q—Permeation amount of pure water, L;

[0074] A—Filtration area of the membrane, m 2 ;

[0075] t—Time for collecting the permeate, h;

[0076] (3) Mechanical strength: The breaking strength (MPa) and elongation at break (%) of the hollow fiber membrane filaments are tested by a single fiber tensile machine at a certain pulling speed (50 mm / min).

[0077] Example 1

[0078] Weigh 35% of perfluoroethylene-propylene resin DS605, 10% of polyvinylidene fluoride resin 6020, 22% of ethylene glycol monomethyl ether acetate, 10% of diethylene glycol monoethyl ether acetate, and 23% of nano-silica by mass ratio, and mix them evenly in a high-speed mixer.

[0079] The mixed materials are passed through a twin-screw extruder (screw diameter Φ20mm, length-diameter ratio 60:1), and the barrel temperature is controlled at 270°C for kneading and melting. Then, it passes through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, and a nozzle die with a spinneret temperature controlled at 260°C. Air is injected into the inner diameter of the spinneret at an air flow rate of 40 mL / min. The extruded FEP hollow fiber membrane filaments are introduced into a coagulation cooling bath of an aqueous solution of ethylene glycol monomethyl ether acetate with a concentration of 20wt% and a temperature controlled at 30°C for shaping. Subsequently, it passes through an aqueous sodium hydroxide solution with a concentration of 5wt% at 70°C for a residence time of 30 minutes. After that, it is stretched by a stretching device at a stretching ratio of 2 times, and then heat-set in a heat-setting oven at 140°C for 20 minutes. The heat-set and dried membrane filaments are passed through a coating solution of PVDF resin 6010 at a mass ratio of 3%, PVP at 6%, poloxamer 188 at 6%, Tween 80 at 2.5%, and DMAC solvent at 82.5%. Finally, it is washed and wound to obtain a small-aperture perfluorinated hollow fiber porous membrane.

[0080] The outer surface and cross-section of the small-aperture perfluorinated hollow fiber porous membrane prepared in this example were photographed by a scanning electron microscope, as shown in Figure 1 、 Figure 2 respectively. A POROLUX1000 pore size analyzer was used to measure the pore size and its distribution of the membrane, as shown in Figure 5 respectively.

[0081] Comparative Example 1

[0082] Weigh 35% of polyperfluoroethylene propylene resin DS605 and 65% of dioctyl phthalate by mass ratio, and mix them evenly in a high-speed mixer.

[0083] The mixed materials are passed through a twin-screw extruder (screw diameter Φ20mm, length-diameter ratio 60:1), and the barrel temperature is controlled at 330°C for kneading and melting. Then, it passes through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, and a nozzle die with a spinneret temperature controlled at 320°C. Air is injected into the inner diameter of the spinneret at an air flow rate of 40 mL / min. The extruded FEP hollow fiber membrane filaments are introduced into a coagulation cooling bath of pure aqueous solution with a temperature controlled at 30°C for shaping. After that, it is stretched by a stretching device at a stretching ratio of 2 times, and then heat-set in a heat-setting oven at 140°C for 20 minutes. Then, it is wound to obtain a perfluorinated hollow fiber porous membrane.

[0084] The outer surface and cross-section of the perfluorinated hollow fiber porous membrane prepared in this comparative example were photographed by a scanning electron microscope, as shown in Figure 3 、 Figure 4 respectively. A POROLUX1000 pore size analyzer was used to measure the pore size and its distribution of the membrane, as shown in Figure 6as shown

[0085] Example 2

[0086] Weigh 30% of perfluoroethylene-propylene resin DS605, 20% of polyvinylidene fluoride resin 6015, 29% of diethylene glycol monobutyl ether acetate, and 21% of nano calcium carbonate by mass ratio, and mix them evenly in a high-speed mixer.

[0087] Pass the mixed materials through a twin-screw extruder (screw diameter Φ30mm, length-diameter ratio 40:1), control the barrel temperature at 230°C for kneading and melting, then pass through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, control the nozzle temperature at 220°C of the nozzle die, and inject air into the inner diameter of the spinneret at an air flow rate of 40 mL / min. Introduce the extruded FEP hollow fiber filaments into a coagulation and cooling bath of an aqueous solution of ethylene glycol monoethyl ether acetate with a concentration of 10wt% and a temperature controlled at 50°C for forming. Subsequently, pass through a hydrochloric acid aqueous solution with a concentration of 2%wt at 40°C for a residence time of 20 minutes, then stretch through a stretching device at a stretching ratio of 1.5 times, and then heat-set in a heat-setting oven at 150°C for 15 minutes. Pass the heat-set and dried filaments through a coating solution with a mass ratio of 2% of PVDF resin 6015, 4% of PVP, 5% of PLA-PEG-PLA, 2% of span 20, and 87% of DMF solvent, and finally obtain a small-aperture perfluoro hollow fiber porous membrane through water washing and winding.

[0088] Comparative Example 2

[0089] Weigh 30% of perfluoroethylene-propylene resin DS605, 20% of polyvinylidene fluoride resin 6015, and 50% of diethylene glycol monobutyl ether acetate by mass ratio, and mix them evenly in a high-speed mixer.

[0090] Pass the mixed materials through a twin-screw extruder (screw diameter Φ30mm, length-diameter ratio 40:1), control the barrel temperature at 230°C for kneading and melting, then pass through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, control the nozzle temperature at 220°C of the nozzle die, and inject air into the inner diameter of the spinneret at an air flow rate of 40 mL / min. Introduce the extruded FEP hollow fiber filaments into a coagulation and cooling bath of pure aqueous solution with a temperature controlled at 30°C for forming, then stretch through a stretching device at a stretching ratio of 1.5 times, and then heat-set in a heat-setting oven at 150°C for 15 minutes. Pass the heat-set and dried filaments through a coating solution with a mass ratio of 2% of PVDF resin 6015, 4% of PVP, 5% of PLA-PEG-PLA, 2% of span 20, and 87% of DMF solvent, and finally obtain a small-aperture perfluoro hollow fiber porous membrane through water washing and winding.

[0091] The coating layer on the membrane surface obtained in this comparative example is very uneven, resulting in different sizes of surface pores, a wide distribution, and the formed coating layer is locally not pressure-resistant.

[0092] Example 3

[0093] Weigh 60% of perfluoroethylene-propylene resin FR460, 5% of polyvinylidene fluoride resin 6010, 23% of triethyl phosphate, 10% of nano calcium carbonate, and 2% of antioxidant 330 by mass ratio respectively, and mix them evenly in a high-speed mixer.

[0094] Feed the mixed materials through a twin-screw extruder (screw diameter Φ20mm, length-diameter ratio 80:1), control the barrel temperature at 250 °C for kneading and melting, then pass through an annular spinneret with an outer diameter of 1.8 mm and an inner diameter of 0.9 mm, control the nozzle temperature at 230 °C with a nozzle die, and inject air into the inner diameter of the spinneret at an air flow rate of 40 mL / min. Introduce the extruded FEP hollow fiber membrane filaments into a coagulation cooling bath of pure aqueous solution with a temperature controlled at 30 °C for shaping. Subsequently, pass through a hydrochloric acid aqueous solution with a concentration of 2 wt% at 30 °C for 10 minutes, then stretch with a stretching ratio of 3 times through a stretching device, and then heat-set in a heat-setting oven at 120 °C for 30 minutes. Pass the heat-set and dried membrane filaments through a coating solution with a mass ratio of 1% of PVDF resin 6010, 2% of PEG, 15% of poloxamer 188, 1% of Tween 80, and 81% of DMAC solvent, and finally obtain a small-aperture perfluoro hollow fiber porous membrane after washing and winding.

[0095] Example 4

[0096] Weigh 20% of perfluoroethylene-propylene resin FR460, 15% of polyvinylidene fluoride resin 6020, 24% of ethylene glycol monoethyl ether acetate, 40% of nano silicon dioxide, and 1% of anti-aging agent UV326 by mass ratio respectively, and mix them evenly in a high-speed mixer.

[0097] The mixed materials are passed through a twin-screw extruder (screw diameter Φ20mm, length-diameter ratio 40:1), and the barrel temperature is controlled at 260°C for kneading and melting. Then, it passes through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, and a nozzle die with the spinneret temperature controlled at 260°C. Air is injected into the inner diameter of the spinneret at an air flow rate of 40 mL / min. The extruded FEP hollow fiber filaments are introduced into a coagulation and cooling bath of an aqueous solution of ethylene glycol monoethyl ether acetate with a concentration of 5wt% and a temperature controlled at 40°C for shaping. Subsequently, it passes through an aqueous sodium hydroxide solution with a concentration of 5wt% at 80°C for a residence time of 25 minutes. After that, it is stretched by a stretching device at a stretching ratio of 1.5 times, and then heat-set in a heat-setting oven at 90°C for 20 minutes. The heat-set and dried filaments are passed through a coating solution with a mass ratio of 10% PVDF resin 6020, 2% PVP, 3% poloxamer 188, 8% Tween 80, and 77% DMAC solvent. Finally, a small-aperture perfluorinated hollow fiber porous membrane is obtained through water washing and winding.

[0098] Example 5

[0099] Weigh 40% of perfluoroethylene-propylene resin DS605, 7% of polyvinylidene fluoride resin 6015, 20% of propylene glycol monomethyl ether acetate, 30% of nano calcium carbonate, and 3% of antioxidant 330 by mass ratio, and mix them evenly in a high-speed mixer.

[0100] The mixed materials are passed through a twin-screw extruder (screw diameter Φ30mm, length-diameter ratio 60:1), and the barrel temperature is controlled at 260°C for kneading and melting. Then, it passes through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, and a nozzle die with the spinneret temperature controlled at 240°C. Air is injected into the inner diameter of the spinneret at an air flow rate of 50 mL / min. The extruded FEP hollow fiber filaments are introduced into a coagulation and cooling bath of pure aqueous solution with a temperature controlled at 35°C for shaping. Subsequently, it passes through an aqueous hydrochloric acid solution with a concentration of 2% at 30°C for a residence time of 20 minutes. After that, it is stretched by a stretching device at a stretching ratio of 1.8 times, and then heat-set in a heat-setting oven at 130°C for 30 minutes. The heat-set and dried filaments are passed through a coating solution with a mass ratio of 4% PVDF resin 6015, 10% PVP, 12% poloxamer 188, 4% Tween 80, and 70% DMAC solvent. Finally, a small-aperture perfluorinated hollow fiber porous membrane is obtained through water washing and winding.

[0101] Example 6

[0102] Weigh 36% of perfluoroethylene propylene resin FR460, 4% of polyvinylidene fluoride resin 6010, 50% of diethylene glycol monoethyl ether acetate, 8% of nano-silica, and 2% of ultraviolet absorber UV531 respectively by mass ratio, and mix them evenly in a high-speed mixer.

[0103] Pass the mixed materials through a twin-screw extruder (screw diameter Φ20mm, length-diameter ratio 60:1), control the barrel temperature at 280°C for mixing and melting, then pass through a nozzle die with an annular spinneret having an outer diameter of 1.8mm and an inner diameter of 0.9mm, control the spinneret temperature at 260°C, and inject air into the inner diameter of the spinneret at an air flow rate of 45 mL / min. Introduce the extruded FEP hollow fiber membrane filaments into a coagulation cooling bath of pure water with a temperature controlled at 40°C for forming. Subsequently, pass through a 5% sodium hydroxide aqueous solution at 75°C for a residence time of 25 minutes, then stretch with a stretching ratio of 1.5 times through a stretching device, and then heat-set in a heat-setting oven at 90°C for 50 minutes. Pass the heat-set and dried membrane filaments through a coating solution with a mass ratio of 6% of PVDF resin 6010, 3% of PVP, 3% of poloxamer 188, 1% of Tween 80, and 87% of DMAC solvent, and finally obtain a small-aperture perfluoro hollow fiber porous membrane after washing and winding.

[0104] Comparative Example 3

[0105] After heat setting, no treatment with the coating solution was carried out, and the rest was the same as in Example 6 to obtain a perfluoro hollow fiber porous membrane.

[0106] Example 7

[0107] Weigh 70% of perfluoroethylene propylene resin FR460, 14% of polyvinylidene fluoride resin 6010, 10% of diethylene glycol monobutyl ether acetate, 5% of nano-calcium carbonate, and 1% of antioxidant 330 respectively by mass ratio, and mix them evenly in a high-speed mixer.

[0108] The mixed materials are passed through a twin-screw extruder (screw diameter Φ35mm, length-diameter ratio 60:1), and the cylinder temperature is controlled at 270°C for mixing and melting. Then, it passes through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, and a nozzle die with a spinneret temperature controlled at 270°C. Air is injected into the inner diameter of the spinneret at an air flow rate of 50 mL / min. The extruded FEP hollow fiber filaments are introduced into a coagulation cooling bath of pure water with a temperature controlled at 80°C for shaping. Subsequently, it passes through a hydrochloric acid aqueous solution with a concentration of 2% at 30°C for a residence time of 30 minutes. After that, it is stretched by a stretching ratio of 1.8 times through a stretching device, and then heat-set in a heat-setting oven at 110°C for 50 minutes. The heat-set and dried filaments are passed through a coating solution with a mass ratio of 3% PVDF resin 6010, 3% PVP, 3% poloxamer 188, 1% Tween 80, and 90% DMAC solvent. Finally, a small-aperture perfluorinated hollow fiber porous membrane is obtained through water washing and winding.

[0109] Comparative Example 4

[0110] Weigh 70% perfluoroethylene-propylene resin FR460, 24% diethylene glycol monobutyl ether acetate, 5% nano calcium carbonate, and 1% antioxidant 330 by mass ratio, and mix them evenly in a high-speed mixer.

[0111] The mixed materials are passed through a twin-screw extruder (screw diameter Φ35mm, length-diameter ratio 60:1), and the cylinder temperature is controlled at 330°C for mixing and melting. Then, it passes through an annular spinneret with an outer diameter of 1.8mm and an inner diameter of 0.9mm, and a nozzle die with a spinneret temperature controlled at 320°C. Air is injected into the inner diameter of the spinneret at an air flow rate of 50 mL / min. The extruded FEP hollow fiber filaments are introduced into a coagulation cooling bath of pure water with a temperature controlled at 80°C for shaping. Subsequently, it passes through a hydrochloric acid aqueous solution with a concentration of 2wt% at 30°C for a residence time of 30 minutes. After that, it is stretched by a stretching ratio of 0.8 times through a stretching device, and then heat-set in a heat-setting oven at 110°C for 50 minutes. The heat-set and dried filaments are passed through a coating solution with a mass ratio of 3% PVDF resin 6010, 3% PVP, 3% poloxamer 188, 1% Tween 80, and 90% DMAC solvent. Finally, a small-aperture perfluorinated hollow fiber porous membrane is obtained through water washing and winding.

[0112] Perform performance tests on the perfluorinated hollow fiber porous membranes prepared in the above examples and comparative examples. The test data are shown in Table 1:

[0113] Table 1 Performance test results of perfluorinated hollow fiber porous membranes

[0114]

[0115]

[0116] From the performance test results of the perfluorinated hollow fiber porous membranes in Examples 1-7 and Comparative Examples 1-4, it can be seen that the outer diameter of the perfluorinated hollow fiber porous membranes prepared by the above preparation method is 1.18-1.22 mm, the wall thickness is 0.2-0.3 mm, the porosity is 74-82%, the membrane pore size is 0.03-0.09 μm, and the pure water flux is 1152-2385 L / m 2 ·h@0.1 mPa, 25 °C, the tensile fracture strength is 16.58-27.24 Mpa, and the tensile fracture elongation is 86-175%.

[0117] In addition, by comparing Figure 1 and 3 it can be known that the surface pores of the hollow fiber membrane prepared in Example 1 of the present invention are smaller, which can be clearly seen from Figure 5 the pore size and its distribution diagram, which makes its interception accuracy higher; by comparing Figure 2 and 4 it can be known that the cross section of the hollow fiber membrane prepared in Example 1 of the present invention has an obvious surface coating layer, the bottom layer is a sponge-like structure and is denser, and there are no cavity defects, which can ensure the interception performance of the membrane, and has high mechanical strength and long-term service life during the later use of the membrane.

[0118] Therefore, the perfluorinated hollow fiber porous membrane obtained by the present invention and its process has smaller pore size and higher interception accuracy, expanding the application field of FEP hollow fiber membranes. And the extraction in the post-treatment stage is simple, the latent solvent extraction and recovery are easy, effectively reducing the use of Class A materials and the potential safety and environmental protection hazards brought.

[0119] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the method of the present invention, several improvements and supplements can be made, and these improvements and supplements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a perfluorinated hollow fiber porous membrane, comprising the following steps: 1) Mix uniformly perfluoroethylene propylene resin, polyvinylidene fluoride resin, water-soluble latent solvent, inorganic pore former, and additive to obtain a mixed powder for casting a membrane; 2) After melting and extruding the mixed powder, cool it in a coagulation bath, then extract, stretch, thermally set, apply a second coating, wash with water, and wind up; The water-soluble latent solvent includes one or more of diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and triethyl phosphate; In step 1), the raw materials include the following components: The coating solution used for the second coating includes polyvinylidene fluoride resin, hydrophilic polymer pore former, amphiphilic block copolymer, surfactant, and solvent; the coating solution includes the following components:

2. The method according to claim 1, wherein In step 1), the raw materials include the following components:

3. The method according to claim 1, wherein The perfluoroethylene propylene resin is a powdery resin, and its melt index needs to be greater than 10 g / 10 min.

4. The method according to claim 1, characterized in that, The perfluoroethylene propylene resin is DS605 of Shandong Huaxia Shenzhou New Materials Co., Ltd. and / or FR460 of Shanghai 3F New Materials Co., Ltd.

5. The method according to claim 1, wherein The polyvinylidene fluoride resin is a polyvinylidene fluoride homopolymer or copolymer with a weight-average molecular weight of 200,000 to 700,000.

6. The method according to claim 1, wherein The polyvinylidene fluoride resin is one or more of PVDF6010, PVDF6015, and PVDF6020 of Solvay Company.

7. The method according to claim 1, characterized in that The inorganic pore-forming agent includes one or more of hydrophobic silica with a nanoscale specific surface area of 90 - 130 m 2 / g, calcium carbonate with a specific surface area of 16 - 30 m 2 / g, and zinc oxide with a specific surface area > 48 m 2 / g.

8. The method according to claim 1, characterized in that, The coating solution includes the following components:

9. The method according to claim 1, wherein The hydrophilic polymer pore former includes polyvinylpyrrolidone and / or polyethylene glycol.

10. The method according to claim 1, wherein The amphiphilic block copolymer includes poloxamer 188 and / or poly(lactic acid)-poly(ethylene glycol)-poly(lactic acid).

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