CN115920669A

CN115920669A - Preparation method of perfluorinated hollow fiber porous membrane

Info

Publication number: CN115920669A
Application number: CN202211585031.9A
Authority: CN
Inventors: 魏汉辉; 赵伟国; 孙家宽
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2022-12-09
Filing date: 2022-12-09
Publication date: 2023-04-07

Abstract

The invention discloses a preparation method of a perfluorinated hollow fiber porous membrane, which comprises the following steps: 1) Uniformly mixing perfluoroethylene propylene resin, polyvinylidene fluoride resin, a water-soluble latent solvent, an inorganic pore-forming agent and an additive to obtain mixed powder for casting a film; 2) And (3) melting and extruding the mixed powder, cooling the mixed powder by a coagulating bath, extracting, stretching, heat setting, secondary coating, washing and rolling. The method is simple and effective, the generation of three wastes in the membrane preparation process is less, the water-soluble latent solvent is easy to extract and recover, and the prepared perfluorinated hollow fiber porous membrane has small pore diameter, excellent product performance and uniform pore diameter distribution.

Description

Preparation method of perfluorinated hollow fiber porous membrane

Technical Field

The invention belongs to the technical field of membranes, and particularly relates to a hollow porous membrane, in particular to a small-aperture perfluorinated hollow fiber porous membrane.

Background

The membrane separation technology is a novel separation technology, and is widely applied to the fields of chemical industry, energy, medicine, water treatment and the like at present. With the continuous expansion of the application field of the membrane, the membrane material has more advanced requirements: both high selectivity and permeability and sufficiently high mechanical strength, chemical resistance and thermal stability are required.

At the present stage, polyvinylidene fluoride (PVDF) is widely used in the preparation of industrial microfiltration and ultrafiltration membranes as an excellent membrane material. However, with the explosive growth of new energy automobiles, the PVDF is used as a binder of a battery material, the demand is increased dramatically, the market price is doubled and the supply is short, so that most film enterprises cannot purchase raw materials. Therefore, a membrane material capable of comprehensively replacing PVDF in various properties is urgently needed to be found.

Fluorinated Ethylene Propylene (FEP) is a typical perfluoropolymer having a fully fluorinated structure, which is copolymerized from Tetrafluoroethylene (TFE) and Hexafluoropropylene (HFP). Compared with the regular molecular structure of Polytetrafluoroethylene (PTFE), trifluoromethyl (CF) on the side chain of FEP macromolecule ₃ ) The original regularity of the FEP is destroyed by introducing the FEP, the crystallinity of the FEP is reduced, the FEP is endowed with good melt processability, and meanwhile, the FEP has chemical stability, high and low temperature resistance, ageing resistance and excellent mechanical property which are similar to those of PTFE, can be used as an excellent membrane material to be applied to a membrane separation system under severe conditions, and has strong competitive advantage.

Perfluoropolymers have recently been receiving attention from many researchers as a film-forming material having excellent properties. Chinese patent CN101884878B discloses a preparation method of a perfluoropolymer hollow fiber porous membrane, which is to forcibly mix a perfluoropolymer, a polymer additive, a composite pore-forming agent and an organic low-molecular liquid according to a proportion, then inject the mixture into a double-screw extruder, melt-spin the mixture, and finally obtain the perfluoropolymer hollow fiber porous membrane through conventional post-treatment. The added organic low molecular liquid selects one of dioctyl phthalate or dibutyl phthalate or a mixture of dioctyl phthalate and dibutyl phthalate in any proportion as a plasticizer in the organic low molecular liquid, so that the perfluoropolymer has good meltability. Patent CN109351209A also discloses a preparation method of a fluorinated ethylene propylene hollow fiber porous membrane, which is to mix FEP, pore-forming agent, plasticizer and auxiliary additive uniformly in proportion, granulate, then extrude, stretch, heat-set, extract pore-forming agent, wash, finally obtain a fluorinated ethylene propylene hollow fiber membrane with a multi-pore structure of stretching pores, dissolving pores and interface pores. Wherein the plasticizer is at least one of dibutyl phthalate, diethyl phthalate or dioctyl phthalate. JP2899903B2 discloses a porous polyvinylidene fluoride membrane having a narrower pore size distribution and a three-dimensional network structure, which is produced by using a phthalate-based substance as an organic additive and simultaneously adding hydrophobic nano-silica, and a method for producing the same. Chinese patent CN104941464A discloses a catalytic hollow fiber membrane and a preparation method thereof, wherein the adopted composite pore-forming agent comprises a soluble pore-forming agent and a non-soluble pore-forming agent, the soluble pore-forming agent comprises one of lithium chloride, calcium chloride, sodium chloride and potassium chloride, the non-soluble pore-forming agent is one of silicon dioxide and calcium carbonate or a mixture of any proportion, and the organic low molecular liquid still adopts phthalate substances. In the four patents, phthalate substances are used as plasticizers of resin, and the plasticizers can be extracted from the film to form holes in the film only by using substances such as ethanol, chloroform or normal hexane and the like in subsequent post-treatment, so that the solvents are high in risk and heavy in pollution, are not easy to recover, and have high safety risk and environmental hidden danger.

U.S. Pat. No. 20090283469A1 discloses a method for preparing a polyvinylidene fluoride hollow fiber type microporous membrane, which adopts a method that water-soluble latent solvent such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate and the like and polyvinylidene fluoride resin are dissolved together at high temperature to obtain spinning solution, the spinning solution is introduced into a cooling bath formed by water or mixed liquid of water and the water-soluble latent solvent by a dry-wet method, a section main body layer is prepared by a thermally induced phase separation method, the outer surface is prepared by a non-solvent induced phase separation method, the porosity of the prepared membrane section main body layer is larger than the aperture ratio of the outer surface, and the membrane section forms a compact discontinuous change structure of a fine surface layer and a rough surface layer. The patent adopts the water-soluble latent solvent to optimize the technical process, so that the high-risk extractant used in the post-treatment can be reduced, but the used system is single, the preparation process easily causes the problems of uneven mixing, agglomeration of the latent solvent and wider pore size distribution of the membrane.

Chinese patent CN102580573B discloses a preparation method of a perfluoropolymer hollow fiber membrane, which adopts the following processes: firstly, uniformly mixing a perfluorinated polymer, polystyrene, a polymer additive and a composite pore-foaming agent, uniformly mixing the obtained mixture with the organic liquid, carrying out melt spinning at the temperature of 300-350 ℃ by using a double-screw extruder, extruding by using a hollow spinneret assembly, soaking in water for 48 hours, then drying in the air, then carrying out sulfonation treatment on the dried hollow fiber membrane, and finally cleaning and drying by using deionized water to obtain the perfluorinated polymer hollow fiber membrane with hydrophilicity; the sulfonation treatment process comprises the following steps: concentrated sulfuric acid is used as a solvent and a sulfonating agent, the mass of the concentrated sulfuric acid is 5-10 times of that of the sulfonated hollow fiber membrane, the sulfonation reaction temperature is 50-80 ℃, and the sulfonation reaction time is 5-10 hours. In order to improve the hydrophilicity of the FEP membrane, the membrane is subjected to sulfonation treatment, and the treatment process is complex, heavy in pollution and long in reaction time. The pore diameter range of the fluorinated ethylene propylene hollow fiber membrane prepared by the patent is about 0.5 mu m, which seriously limits the application field and range thereof.

Chinese patent CN102166484A discloses a preparation method of a hydrophilic polyvinylidene fluoride composite membrane, wherein an amphiphilic copolymer is added in the process to increase the compatibility of polyvinylidene fluoride and a matrix PET braided tube. But the product is affected by the processing characteristics of the braided tube, such as unevenness, burrs and the like, and the defect rate of the product is high. Chinese patent CN1128176A discloses a preparation method of a wet-process polyvinylidene fluoride porous membrane, which adopts the performance complementation and synergistic effect of a polymer pore-forming agent, a surfactant and a non-solvent to prepare the porous membrane with the pore diameter of 0.05-0.22 mu m, the flux of 100-1500LMH and the porosity of 80-90 percent. In order to prepare a homogeneous hollow fiber membrane, the solid content of the resin used is relatively high in order to meet the self-supporting strength requirement of the membrane, which results in high application cost.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide the preparation method of the perfluorinated hollow fiber porous membrane, which is simple and effective, has less three wastes in the membrane preparation process, is easy to extract and recover a latent solvent, and is coated for the second time, so that the prepared perfluorinated hollow fiber porous membrane has excellent product performance, small aperture, uniform aperture distribution and high interception precision.

In order to realize the purpose, the technical scheme adopted by the invention is as follows:

a preparation method of a perfluorinated hollow fiber porous membrane comprises the following steps:

1) Uniformly mixing perfluoroethylene propylene resin, polyvinylidene fluoride resin, a water-soluble latent solvent, an inorganic pore-forming agent and an additive to obtain mixed powder for casting a film;

2) And (3) melting and extruding the mixed powder, cooling the mixed powder by a coagulating bath, extracting, stretching, heat setting, secondary coating, washing and rolling.

In step 1) of the invention, the raw materials comprise the following components:

in the invention, the perfluoroethylene propylene resin is powdery resin, the melt index of the perfluoroethylene propylene resin needs to be more than 10g/10min, if the melt index is too small, the perfluoroethylene propylene resin is difficult to completely melt in an extruder, and the mechanical strength of a final film is influenced.

Preferably, the perfluoroethylene propylene resin of the present invention comprises DS605 of Shandong Huashen boat New Material Co., ltd or FR460 of Shanghai Sanai Rich New Material Co., ltd.

The polyvinylidene fluoride resin is a polyvinylidene fluoride homopolymer or copolymer with the weight-average molecular weight of 20-70 ten thousand, on one hand, the addition of the polyvinylidene fluoride resin can improve the processing performance of the perfluoroethylene propylene resin in the melting process, on the other hand, the polyvinylidene fluoride resin migrates to the surface of the film along with the latent solvent in the solidification process after the latent solvent is added, and the polyvinylidene fluoride can be dissolved in the solvent of the coating liquid in the subsequent coating process, so that the coating interface is firmer, and the problem of delamination caused by the compatibility of materials in the later period is reduced.

Preferably, the polyvinylidene fluoride resin of the present invention comprises one or more of PVDF6010, 6015 and 6020, from solvay.

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%. The latent solvent is a solvent which does not dissolve the resin at room temperature and dissolves it at high temperature. Further, the water-soluble latent solvent comprises one or more of ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate and triethyl phosphate.

In the present invention, the inorganic pore-forming agent comprises nanoscale hydrophobic silica (specific surface area 90 to 130 m) ² Per gram), calcium carbonate (specific surface area 16-30 m) ² Per gram), zinc oxide (specific surface area > 48 m) ² /g), etc.

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

In the invention, the component of the coagulating bath in the step 2) is water or a mixture of water and ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate or triethyl phosphate.

In the invention, the extraction in the step 2) comprises the following steps: the membrane silk is passed through 5wt% sodium hydroxide solution or 2wt% hydrochloric acid solution at 30-80 deg.c for 10-60 min.

In the invention, the stretching in the step 2) comprises the following steps: the hollow fiber membrane yarn obtained by melting, extruding and solidifying is stretched in the length direction by a ratio of 1.5 to 3 times.

In the invention, the heat setting in the step 2) comprises the following steps: the membrane silk is heated and set in a baking oven at 90-150 ℃ for 10-60 minutes.

In the invention, the secondary coating in the step 2) comprises the following steps: the heat-set and dried hollow fiber membrane filaments are passed through a coating liquid.

The coating liquid provided by the invention comprises polyvinylidene fluoride resin, a hydrophilic polymer pore-forming agent, an amphiphilic block copolymer, a surfactant and a solvent.

Preferably, the coating liquid comprises the following composition:

preferably, the polyvinylidene fluoride resin in the coating liquid is the same as the polyvinylidene fluoride resin in step 1).

Preferably, the hydrophilic polymer pore-forming agent comprises polyvinylpyrrolidone (PVP) and/or polyethylene glycol (PEG).

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

Preferably, the surfactant comprises tween 80 or span 20.

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

In the invention, in the step 2), the solvent in the membrane wire in the secondary coating process is removed by water washing.

The invention adopts the water-soluble latent solvent as the plasticizer of the FEP film forming, the latent solvent can be directly dissolved in the water of the coagulating bath during the subsequent post-treatment, the extraction is simple, the pollution is avoided, and the recovery is easy. In the interaction process of the latent solvent and water, the section main body layer is subjected to thermally induced phase separation, the outer surface is subjected to non-solvent induced phase separation, the porosity of the membrane section main body layer is greater than the aperture ratio of the outer surface, and the membrane section forms a compact discontinuous change structure of a fine structure of the surface layer and a rough structure of the main body layer. Only this structure is beneficial for subsequent coating, otherwise the FEP surface pores are too large, and the coating is not very pressure resistant and is easy to break during use, and the filtering effect is lost due to too large difference between the coating pores and the FEP surface pores during coating. Meanwhile, the inorganic pore-forming agent with large specific surface area can adsorb a part of water-soluble latent solvent on the surface of the inorganic pore-forming agent, and can effectively control the dispersibility of the water-soluble latent solvent in the film-making process, so that the prepared FEP film has more uniform pore distribution. Meanwhile, the water-soluble latent solvent can be dissolved in water, so that the subsequent on-line extraction and the subsequent on-line coating can be realized. And on the other hand, polyvinylidene fluoride resin is added into the formula, and PVDF and FEP are blended, so that the advantages are complementary, the process temperature in the processing process can be reduced, the whole ductility of the material can be improved, the PVDF on the film surface of the added PVDF can be dissolved by a solvent in coating liquid in the later coating process, the main body film can be well combined with a coating layer, and the later layering phenomenon generated when two different materials are combined is reduced.

After the main body structure is formed, the main body structure is subjected to subsequent extraction, stretching and heat setting and then enters a coating liquid tank, the coating liquid needs to achieve the effects of uniform coating and firm combination with the main body, PVDF casting solution with low solid content (1% -10%) is adopted, hydrophilic high-molecular pore-forming agent is added into the casting solution to improve the hydrophilicity of the membrane, and amphiphilic block copolymer and surfactant are added to improve the combination degree of the two materials. The resulting coating is thin and the bulk strength structure of the film is determined by the bulk layer. Only by combining the preparation method, the aperture of the membrane filter mainly made of the fluorinated ethylene propylene can be effectively reduced to 0.03-0.1 micron, the interception precision is higher, and the hydrophilicity of the membrane is improved. Reaching the pore size range of most commercial membranes today. The application feasibility and the application field range of the composite material are expanded.

The preparation method is green and environment-friendly, the film forming process is simple, the subsequent high-risk extraction process is not needed, the film forming aperture is small, the mechanical strength is high, and the interception effect is good. Therefore, the invention not only greatly reduces the three wastes generated in the membrane preparation process and the complex extraction process, but also improves the separation performance of the membrane, expands the application field of the membrane, has economic and environment-friendly preparation method, and has important practical significance and economic benefit.

Drawings

FIG. 1 is a scanning electron microscope image of the outer surface of the hollow fiber membrane prepared in example 1;

FIG. 2 is a scanning electron micrograph of a cross section of the hollow fiber membrane prepared in example 1;

FIG. 3 is a scanning electron microscope picture of the outer surface of the hollow fiber membrane prepared in comparative example 1;

FIG. 4 is a scanning electron microscope picture of a cross section of the hollow fiber membrane prepared in comparative example 1;

FIG. 5 is a graph showing the pore diameter and distribution thereof of the hollow fiber membrane prepared in example 1;

fig. 6 is a graph showing the pore diameter and distribution thereof of the hollow fiber membrane prepared in comparative example 1.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative of the invention and are not to be construed as limiting the scope of the invention.

The raw material sources in the examples and the comparative examples are as follows:

fluorinated ethylene propylene resin (Shandong Huaxia Shenzhou New materials Co., ltd., DS605 or Shanghai Sanai Fuyu New materials Co., ltd., FR 460);

ethylene glycol monomethyl ether acetate (ait (Shandong) New Material Co., ltd.);

ethylene glycol monoethyl ether acetate (Shandong Xinhui New Material Co., ltd.);

diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate (Hubeixin Hongli chemical Co., ltd.);

triethyl phosphate (zhanggang new Asia chemical Co., ltd.);

nano silicon dioxide (win chuang degusse (china) ltd., R972);

nano calcium carbonate (shanghai yuan river chemical limited);

polyvinylidene fluoride (belgium Solvay,

6010，6015，6020)

polyvinylpyrrolidone (PVP) (Gaobike New Material science and technology (Shanghai) Co., ltd.)

Polyethylene glycol (PEG) (Dow chemical)

Poloxamer 188 (Basifu)

PLA-PEG-PLA (Xian Qi Yue Biotechnology Co., ltd.)

Tween 80, span 20 (Aladdin)

N, N-dimethylformamide, N-dimethylacetamide (DuPont)

Other raw materials and reagents may be obtained by ordinary commercial routes unless otherwise specified.

The separation performance of the prepared small-aperture perfluorinated hollow fiber porous membrane is evaluated and is characterized by three characteristic parameters, namely the average aperture of the membrane, pure water flux and mechanical strength.

(1) Average pore diameter of membrane: the measurement is carried out by using a POROLUX1000 aperture analyzer, and the test principle calculation formula is as follows:

D＝4δcosθ/P

in the formula: d, the diameter of a membrane pore is μm;

delta-surface tension of the liquid, N/m;

θ -the contact angle, degree, between the liquid and the pore wall;

p is gas pressure, pa;

(2) Pure water flux (LMH) is defined as: under a certain operating pressure condition, the volume of water penetrating through the effective membrane area in unit time is calculated by the following formula:

J＝Q/At

wherein: j-flux, L/m ² ·h@0.1mPa；

Q is the permeability of pure water, L;

a-filtration area of the membrane, m ² ；

t is the time for collecting the permeate, h;

(3) Mechanical strength: the breaking strength (MPa) and elongation at break (%) of the hollow fiber membrane filaments were measured by a single fiber tensile machine at a certain drawing speed (50 mm/min).

Example 1

Respectively weighing 35% of poly-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 in mass ratio, and uniformly mixing in a high-speed mixer.

The mixed material is passed through a double screw extruder (screw diameter phi 20mm, length-diameter ratio 60.

The external surface and the cross section of the small-pore-diameter perfluoro hollow fiber porous membrane prepared in this example were photographed by a scanning electron microscope, and are shown in fig. 1 and fig. 2, respectively. The pore size of the membrane and its distribution were measured using a POROLUX1000 pore size analyzer, as shown in fig. 5.

Comparative example 1

Weighing 35% of fluorinated ethylene propylene resin DS605 and 65% of dioctyl phthalate according to the mass ratio, and uniformly mixing in a high-speed mixer.

And (2) mixing and melting the mixed materials by a double-screw extruder (the diameter of a screw is phi 20mm, the length-diameter ratio is 60.

The external surface and the cross section of the perfluoro hollow fiber porous membrane prepared in the comparative example were photographed by a scanning electron microscope, and are shown in fig. 3 and 4, respectively. The pore size of the membrane and its distribution were measured using a POROLUX1000 pore size analyzer, as shown in fig. 6.

Example 2

Respectively weighing 30% of fluorinated ethylene propylene resin DS605, 20% of polyvinylidene fluoride resin 6015, 29% of diethylene glycol monobutyl ether acetate and 21% of nano calcium carbonate according to the mass ratio, and uniformly mixing in a high-speed mixer.

The mixed material is passed through a double screw extruder (screw diameter phi 30mm, length-diameter ratio 40.

Comparative example 2

Respectively weighing 30% of fluorinated ethylene propylene resin DS605, 20% of polyvinylidene fluoride resin 6015 and 50% of diethylene glycol monobutyl ether acetate according to the mass ratio, and uniformly mixing the materials in a high-speed mixer.

The mixed materials are mixed and melted by a double screw extruder (the diameter of a screw is 30mm, the length-diameter ratio is 40.

The coating layer on the surface of the film obtained by the comparative example is very uneven, so that the size of the pores on the surface is different, the distribution is very wide, and the formed coating layer is locally very weak in pressure resistance.

Example 3

Respectively weighing 60% of fluorinated ethylene propylene resin FR460, 5% of polyvinylidene fluoride resin 6010, 23% of triethyl phosphate, 10% of nano calcium carbonate and 2% of antioxidant 330 in mass ratio, and uniformly mixing in a high-speed mixer.

The mixed materials are mixed and melted by a double screw extruder (the diameter of a screw is 20mm, the length-diameter ratio is 80.

Example 4

20 percent of fluorinated ethylene propylene resin FR460, 15 percent of polyvinylidene fluoride resin 6020, 24 percent of ethylene glycol monoethyl ether acetate, 40 percent of nano silicon dioxide and 1 percent of age resister UV326 are respectively weighed according to the mass ratio and are evenly mixed in a high-speed mixer.

The mixed material is passed through a double screw extruder (screw diameter phi 20mm, length-diameter ratio 40.

Example 5

Weighing 40% of fluorinated ethylene 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 according to the mass ratio, and uniformly mixing in a high-speed mixer.

The mixed materials are mixed and melted by a double screw extruder (the diameter of a screw is 30mm, the length-diameter ratio is 60.

Example 6

36% of fluorinated ethylene propylene resin FR460, 4% of polyvinylidene fluoride resin 6010, 50% of diethylene glycol monoethyl ether acetate, 8% of nano silicon dioxide and 2% of ultraviolet absorbent UV531 are weighed respectively according to the mass ratio and are mixed uniformly in a high-speed mixer.

The mixed materials are mixed and melted by a double screw extruder (the diameter of a screw is 20mm, the length-diameter ratio is 60.

Comparative example 3

After heat setting, the perfluoro hollow fiber porous membrane was obtained in the same manner as in example 6 except that the treatment with the coating liquid was not performed.

Example 7

70 percent of fluorinated ethylene propylene resin FR460, 14 percent of polyvinylidene fluoride resin 6010, 10 percent of diethylene glycol monobutyl ether acetate, 5 percent of nano calcium carbonate and 1 percent of antioxidant 330 are respectively weighed according to the mass ratio and are evenly mixed in a high-speed mixer.

The mixed materials are mixed and melted by a double screw extruder (the diameter of a screw is 35mm, the length-diameter ratio is 60.

Comparative example 4

70 percent of fluorinated ethylene propylene resin FR460, 24 percent of diethylene glycol monobutyl ether acetate, 5 percent of nano calcium carbonate and 1 percent of antioxidant 330 are weighed according to the mass ratio and are mixed evenly in a high-speed mixer.

The perfluor hollow fiber porous membranes prepared in the above examples and comparative examples were subjected to performance tests, and the test data are shown in table 1:

TABLE 1 perfluor hollow fiber porous membrane Performance test results

As can be seen from the results of the performance tests of the perfluorinated hollow fiber porous membranes of examples 1 to 7 and comparative examples 1 to 4, the perfluorinated hollow fiber porous membrane prepared by the preparation method has an outer diameter of 1.18 to 1.22mm, a wall thickness of 0.2 to 0.3mm, a porosity of 74 to 82%, a membrane pore diameter of 0.03 to 0.09 μm, and a pure water flux of 1152 to 2385L/m ² H @0.1mPa,25 ℃, tensile breaking strength of 16.58-27.24 MPa, and tensile breaking elongation of 86-175%.

In addition, as can be seen from comparing fig. 1 and 3, the hollow fiber membrane prepared by the invention in example 1 has smaller surface pores, which is also apparent from the pore diameter and distribution diagram in fig. 5, which makes the interception precision higher; as can be seen from comparison of FIGS. 2 and 4, 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 structure and is denser, and has no void defects, and the hollow fiber membrane not only can ensure the retention performance of the membrane, but also has high mechanical strength and long-term service life in the later use process of the membrane.

Therefore, the perfluorinated hollow fiber porous membrane obtained by the method and the process has smaller aperture and higher interception precision, and the application field of the FEP hollow fiber membrane is expanded. And the extraction in the post-treatment stage is simple, the extraction and recovery of the latent solvent are easy, and the use of class A materials and the potential safety and environmental protection hazards brought by the class A materials are effectively reduced.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for a person skilled in the art, several modifications and additions can be made without departing from the method of the present invention, and these modifications and additions should also be considered as the protection scope of the present invention.

Claims

1. A preparation method of a perfluorinated hollow fiber porous membrane comprises the following steps:

2) And melting and extruding the mixed powder, cooling the mixed powder by a coagulating bath, extracting, stretching, heat setting, secondary coating, washing and rolling.

2. The method according to claim 1, wherein in step 1), the raw materials comprise the following composition:

20 to 70wt%, preferably 30 to 60wt% of perfluoroethylene-propylene resin;

2 to 20 weight percent of polyvinylidene fluoride resin, preferably 5 to 15 weight percent;

10 to 60wt%, preferably 20 to 50wt% of a water-soluble latent solvent;

5 to 40wt%, preferably 10 to 30wt% of an inorganic pore-forming agent;

additives 0 to 5 wt.%, preferably 0 to 3 wt.%.

3. The process according to claim 1 or 2, wherein the perfluoroethylene-propylene resin is a powdered resin having a melt index of more than 10g/10min, preferably DS605 of Shandong Huashen boat New materials Co., ltd and/or FR460 of Shanghai Sanai Rich New materials Co., ltd.

4. A method according to any one of claims 1 to 3, wherein the polyvinylidene fluoride resin is a polyvinylidene fluoride homopolymer or copolymer having a weight average molecular weight of from 20 to 70 ten thousand, preferably one or more of PVDF6010, 6015 and 6020 of solvay.

5. A process according to any one of claims 1 to 4 wherein the water soluble cosolvent comprises one or more of ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate and triethyl phosphate.

6. The method of any one of claims 1 to 5, wherein the inorganic pore former comprises a specific surface area on the order of nanometers of 90 to 130m ² Hydrophobic silica/g, specific surface area 16-30m ² Calcium carbonate/g, specific surface area > 48m ² One or more of zinc oxide per gram.

7. The method according to any one of claims 1 to 6, wherein the coating liquid comprises polyvinylidene fluoride resin, a hydrophilic polymer pore-forming agent, an amphiphilic block copolymer, a surfactant and a solvent.

8. The method according to any one of claims 1 to 7, wherein the coating liquid comprises the following composition:

9. the method of any one of claims 1-8, wherein the hydrophilic polymeric porogen comprises polyvinylpyrrolidone and/or polyethylene glycol.

10. The method of any one of claims 1-9, wherein the amphiphilic block copolymer comprises poloxamer 188 and/or polylactic acid-polyethylene glycol-polylactic acid.