Preparation Method and Application of a Modified Polytetrafluoroethylene Membrane

Abstract

The present disclosure belongs to the field of membrane technology, specifically a preparation method and application of a modified polytetrafluoroethylene membrane; the preparation method includes: providing a polytetrafluoroethylene microporous membrane; using at least one dianhydride monomer and diamine monomer to form a polyimide layer on the polytetrafluoroethylene microporous membrane; using a compound containing a glycidyl ester group and polyethyleneimine to graft-modify the polyimide layer; and finally combining polyvinyl alcohol and the graft-modified polyimide layer through a diisocyanate compound to obtain the modified polytetrafluoroethylene membrane.

Description

Technical Field

[0001] The present disclosure relates to the field of membrane technology, and in particular, to a method for preparing a modified polytetrafluoroethylene membrane and its application. Background Art

[0002] The development of membrane separation technology plays an important role in the fields of energy, environmental protection, chemical industry, medicine, etc. Due to its advantages such as high efficiency and no secondary pollution, it has developed rapidly in the process of water treatment and has become an important support for the technological upgrading of traditional industries and the development of emerging industries. Membrane is the key to separation technology, directly determining the separation accuracy and efficiency.

[0003] As a self-supporting porous membrane, polytetrafluoroethylene microporous membrane has the advantages of high strength, large packing density, being able to be backwashed, acid and alkali resistance, oxidation resistance, resistance to microbial erosion, good biocompatibility, etc. Its filtration liquid flow rate is high, it is in turbulent flow, insensitive to blockage, easy to clean, and the pressure loss in the membrane module is small. It can operate under various extreme chemicals, temperatures and pressures, and is especially suitable for the separation of various high-viscosity, high-solid-content, highly polluted solid-liquid and gas-liquid.

[0004] However, the inherent hydrophobicity of polytetrafluoroethylene material limits its application in the field of direct separation of liquid water permeation. Therefore, there is an urgent need for a polytetrafluoroethylene microporous membrane with long-lasting hydrophilicity. Summary of the Invention

[0005] The present disclosure provides a method for preparing a modified polytetrafluoroethylene membrane and its application to solve the deficiencies in the related art.

[0006] According to the first aspect of the embodiments of the present disclosure, a method for preparing a modified polytetrafluoroethylene membrane is provided. The preparation method includes the following steps:

[0007] Step 1: Provide a polytetrafluoroethylene microporous membrane and immerse the polytetrafluoroethylene microporous membrane in a first organic solvent;

[0008] Step 2: Add at least one dianhydride monomer and diamine monomer to the first organic solvent, and carry out a polymerization reaction at 30°C - 70°C under an inert gas atmosphere to form a polyimide layer on the polytetrafluoroethylene microporous membrane, obtaining an intermediate modified polytetrafluoroethylene membrane of Step 2; wherein, the diamine monomer contains at least one hydroxyl group;

[0009] Step 3: Use a compound having the following structural formula I to carry out graft copolymerization on the intermediate modified polytetrafluoroethylene membrane obtained in Step 2 to obtain an intermediate modified polytetrafluoroethylene membrane of Step 3;

[0010]

[0011] Wherein, R 1 and R2 Each independently selected from C1-10 alkyl or C1-10 alkoxy;

[0012] Step 4: Use polyethyleneimine to graft-modify the intermediate modified polytetrafluoroethylene membrane obtained in Step 3 to obtain the intermediate modified polytetrafluoroethylene membrane of Step 4;

[0013] Step 5: Immerse the intermediate modified polytetrafluoroethylene membrane obtained in Step 4 in a second organic solvent containing at least one diisocyanate compound. After soaking for 0.5 - 1.5 h, then add a second organic solvent containing polyvinyl alcohol, and react to obtain the modified polytetrafluoroethylene membrane.

[0014] In one aspect of the embodiments of the present disclosure, the dianhydride monomer has the structure of the following formula II:

[0015]

[0016] Wherein, R 3 and R 4 Each independently selected from hydrogen, amino group, halogen atom, hydroxyl group, nitro group, C1-10 alkyl or C1-10 alkoxy.

[0017] In one aspect of the embodiments of the present disclosure, the diamine monomer has the structure of the following formula III:

[0018]

[0019] Wherein, Ar 1 and Ar 2 Each independently selected from C3-30 cycloalkyl, C6-C30 aryl, 3-30 membered heterocyclic group or substituted or 5-30 membered heteroaryl.

[0020] In one aspect of the embodiments of the present disclosure, the dianhydride monomer is selected from the following Compound 2-1 (3,3',4,4'-biphenyltetracarboxylic dianhydride), and the diamine monomer is selected from the following Compound 3-1 (3,3'-dihydroxy-4,4'-diaminobenzidine):

[0021]

[0022] In one aspect of the embodiments of the present disclosure, the compound of formula I is selected from Compound 1-1 (glycidyl methacrylate):

[0023]

[0024] In one aspect of the embodiments of the present disclosure, the first organic solvent and the second organic solvent are each independently selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, ethanol or acetone.

[0025] In one aspect of the embodiments of the present disclosure, in step 2, the molar ratio of the dianhydride monomer to the diamine monomer used is 1:(0.8 - 1.2). Specifically, in step 2, the molar ratio of the dianhydride monomer to the diamine monomer used is 1:1.

[0026] In one aspect of the embodiments of the present disclosure, in step 3, the molar ratio of the compound having the structure of formula I used to the dianhydride monomer used in step 2 is (2 - 5):1. Specifically, in step 3, the molar ratio of the compound having the structure of formula I used to the dianhydride monomer used in step 2 is 4:1.

[0027] In one aspect of the embodiments of the present disclosure, step 3 includes: adding the intermediate modified polytetrafluoroethylene membrane of step 2 into water, then adding glycidyl methacrylate and an initiator, and reacting at 60°C - 80°C for 2 - 5 h.

[0028] In one aspect of the embodiments of the present disclosure, the polyethyleneimine is a branched polyethyleneimine with an average weight - average molecular weight of 1500 - 2000. Specifically, the polyethyleneimine is a branched polyethyleneimine with an average weight - average molecular weight of 1800.

[0029] In one aspect of the embodiments of the present disclosure, the diisocyanate compound is selected from any one of the following compounds:

[0030] 、 、 、 、 、 、 、 、 。

[0031] In one aspect of the embodiments of the present disclosure, preferably, the diisocyanate compound is selected from 、 、 。Specifically, the diisocyanate compound is selected from (3,3'-dimethyl - 4,4'-biphenyl diisocyanate; TODI).

[0032] In one aspect of the embodiments of the present disclosure, there is no specific limitation on the amount of polyethyleneimine used relative to the compound of formula I used.

[0033] In one aspect of the embodiments of the present disclosure, specifically, when the polyethyleneimine is a branched polyethyleneimine with an average weight-average molecular weight of 1800, and the diisocyanate compound is selected from the mass ratio of the polyethyleneimine to the diisocyanate compound is selected from (3 - 10):1.

[0034] In one aspect of the embodiments of the present disclosure, in step 5, there are no specific limitations on the mass, average molecular weight, and degree of polymerization of the polyvinyl alcohol used.

[0035] According to the second aspect of the embodiments of the present disclosure, a modified polytetrafluoroethylene membrane is provided, and the modified polytetrafluoroethylene membrane is obtained by the aforementioned preparation method.

[0036] The technical solutions provided by the embodiments of the present disclosure may include the following beneficial effects:

[0037] As can be seen from the above embodiments, the present disclosure provides a highly weather-resistant modified polytetrafluoroethylene membrane, which has excellent hydrophilic properties.

[0038] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. Detailed Embodiments

[0039] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

[0040] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0041] In this document, the terms "comprising", "including" or any other variation thereof are intended to cover non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus. Without further limitation, an element qualified by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.

[0042] In the description herein, unless otherwise specified, "above" and "below" include the number itself.

[0043] Unless otherwise specified, the terms used in this disclosure have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this disclosure can be measured by various common measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this disclosure).

[0044] The term "about" is used to describe and account for small variations. When used in conjunction with an event or circumstance, the term can refer to instances in which the event or circumstance occurs precisely as well as instances in which it occurs very nearly. For example, when used in conjunction with a numerical value, the term can refer to a variation range of ±10% or less than or equal to the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, sometimes quantities, ratios and other numerical values are presented in a range format in this document. It should be understood that such range formats are for convenience and brevity and should be understood flexibly to include not only the numerical values explicitly specified as range limits but also all individual numerical values or sub-ranges subsumed within the said range as if each numerical value and sub-range were explicitly specified.

[0045] A list of items connected by the terms "at least one of", "at least a", "at least one kind of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0046] In the present disclosure, the term "alkyl" refers to an aliphatic hydrocarbon group, which can be straight-chain or branched. A branched chain refers to one or more lower alkyl groups, such as methyl, ethyl or propyl, that are attached to a linear alkyl chain. "Lower alkyl" refers to a group containing from about 1 to about 6 carbon atoms in the chain, which can be straight-chain or branched.

[0047] In the present disclosure, the term "amino" refers to the -NR’R” group. The amino group can be optionally substituted. In an unsubstituted amino group, R’ and R” are hydrogen. In a substituted amino group, R’ and R” can each independently be, but are not limited to, hydrogen, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, alkylcycloalkyl, alkylheterocycloalkyl, alkoxy, sulfonyl, alkenyl, alkanoyl, aryl, arylalkyl or heteroaryl, provided that R’ and R” are not both hydrogen. In a substituted amino group, R’ and R” can cyclize to form a cyclic amino group, such as pyrrolidinyl or piperidinyl. Such cyclic amino groups can incorporate other heteroatoms, such as to form piperazine or morpholine groups. Such cyclic amino groups can be optionally substituted, for example, by amino, hydroxy or oxo groups.

[0048] In the present disclosure, the term "alkoxy" refers to -O-alkyl. Alkoxy can refer to a straight-chain, branched-chain or cyclic, saturated or unsaturated oxy-hydrocarbon chain, including, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy and pentyloxy. The alkoxy can be optionally substituted by one or more alkoxy substituents ("substituted alkoxy").

[0049] In the present disclosure, the term "aryl" refers to an aromatic monocyclic or polycyclic ring system. The aryl can be optionally substituted by one or more "ring system substituents", which can be the same or different and are as defined herein. Non-limiting examples of suitable aryls include phenyl and naphthyl.

[0050] In the present disclosure, the term "heteroaryl" refers to an aromatic monocyclic or polycyclic ring system in which one or more ring atoms are elements other than carbon, such as nitrogen, oxygen, or sulfur, either individually or in combination. Preferably, the heteroaryl contains about 5 to about 6 ring atoms. The "heteroaryl" may optionally be substituted with one or more "ring system substituents", which may be the same or different and are as defined herein. The prefixes aza, oxa, or thia before the heteroaryl root name indicate the presence of at least one nitrogen, oxygen, or sulfur atom, respectively, as a ring atom. The nitrogen atom of the heteroaryl may optionally be oxidized to the corresponding N-oxide. Non-limiting examples of suitable heteroaryls include pyridyl, pyrazinyl, furyl, phenylthio, pyrimidinyl, isoxazolyl, isothiazolyl, oxazolyl, thiazolyl, pyrazolyl, furazanyl, pyrrolyl, pyrazolyl, triazolyl, 1,2,4-thiadiazolyl, pyrazinyl, pyridazinyl, quinoxalinyl, cinnolinyl, imidazo[1,2-a]pyridyl, imidazo[2,1-b]thiazolyl, benzofurazanyl, indolyl, azaindolyl, benzimidazolyl, benzothienyl, quinolinyl, imidazolyl, thiophenopyridyl, quinazolinyl, thiophenopyrimidinyl, pyrrolopyridyl, imidazopyridyl, isoquinolinyl, benzazaindolyl, 1,2,4-triazinyl, benzothiazolyl, etc.

[0051] In the present disclosure, the polytetrafluoroethylene microporous membrane used in the present disclosure has a thickness of 15 - 80 μm; however, the thickness of the polytetrafluoroethylene microporous membrane used in the present disclosure is not limited thereto and can be adaptively selected according to actual needs.

[0052] In the present disclosure, the polytetrafluoroethylene microporous membrane used in the present disclosure has a membrane pore size of 0.03 - 10 μm; specifically, the polytetrafluoroethylene microporous membrane used in the present disclosure has 0.03 μm, 0.05 μm, 0.05 μm, 0.1 μm, 0.22 μm, 0.45 μm, 1 μm, 3 μm, 5 μm, or 10 μm; however, the membrane pore size of the polytetrafluoroethylene microporous membrane used in the present disclosure is not limited thereto and can be adaptively selected according to actual needs.

[0053] In the present disclosure, the first organic solvent and the second organic solvent are each independently selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, ethanol, or acetone; however, the organic solvents used in the present disclosure are not limited thereto.

[0054] In a specific embodiment of the present disclosure, in Steps 1 and 2: Provide a polytetrafluoroethylene microporous membrane with a thickness of 275 mm and a membrane pore diameter of 3 - 5 μm. Immerse the polytetrafluoroethylene microporous membrane in N,N-dimethylacetamide. Add dianhydride monomer compound 2-1 (3,3',4,4'-biphenyltetracarboxylic dianhydride) and diamine monomer compound 3-1 (3,3'-dihydroxy-4,4'-diaminobiphenyl) to the N,N-dimethylacetamide. Carry out a polymerization reaction at 45°C under a nitrogen atmosphere to form a polyimide layer on the polytetrafluoroethylene microporous membrane, obtaining the intermediate modified polytetrafluoroethylene membrane of Step 2. Among them, the polyimide has the following structure:

[0055]

[0056] In Step 3, use compound 1-1 (glycidyl methacrylate) to carry out graft copolymerization on the intermediate modified polytetrafluoroethylene membrane obtained in Step 2, obtaining the intermediate modified polytetrafluoroethylene membrane of Step 3; after carrying out graft copolymerization on the polyimide, it has the following structure:

[0057]

[0058] The above structure is only taken as an example. Polyethyleneimine can carry out graft copolymerization reactions with other hydroxyl and carboxyl groups on the polyimide chain segments.

[0059] In Step 4, use polyethyleneimine to carry out graft modification on the intermediate modified polytetrafluoroethylene membrane obtained in Step 3, obtaining the intermediate modified polytetrafluoroethylene membrane of Step 4; after carrying out graft modification on the polyimide, it has the following structure:

[0060]

[0061] The above structure is only taken as an example. The branched polyethyleneimine used in the present disclosure, after carrying out graft modification, the formed structure is not limited to this.

[0062] In Step 5, immerse the intermediate modified polytetrafluoroethylene membrane obtained in Step 4 in N-methylpyrrolidone containing an isocyanate compound. After soaking for 45 min, add N-methylpyrrolidone containing polyvinyl alcohol (average degree of polymerization is 50), and after reacting for 4 h, obtain a modified polytetrafluoroethylene membrane, which has the following structure:

[0063]

[0064] Among them, R 7 is selected from 、 、 or , R7 The structure is determined by the specific diisocyanate compound used; T 1 is a polyvinyl alcohol chain segment. Through bridging with the diisocyanate compound, the polyvinyl alcohol chain segment is combined with branched polyethyleneimine; the above structure is only an example, because the diisocyanate compound can combine with any secondary amine on the branched polyethyleneimine.

[0065] The present invention will be further described below by way of specific examples. All kinds of chemical reagents used in the examples of the present invention are obtained through conventional commercial channels unless otherwise specified. Unless otherwise specified, the contents described below are mass contents. Unless otherwise specified, it is understood that the operations are carried out at room temperature.

[0066] Examples and Comparative Examples:

[0067] Example 1:

[0068] Example 1 includes the following steps:

[0069] Cut a 5 cm * 5 cm part from the PTFE membrane for experiments. The thickness of the PTFE membrane is 35 μm and the pore size is 3 μm. Immerse the PTFE membrane in 150 mL of N,N-dimethylacetamide;

[0070] Add HAB (0.05 mol, 10.8 g) to N,N-dimethylacetamide, introduce nitrogen, and then add BPDA (0.05 mol, 14.7 g) under nitrogen protection. Carry out a polymerization reaction at 45 °C to form a polyimide layer on the PTFE membrane to obtain Intermediate Product 1;

[0071] Dry the aforementioned Intermediate Product 1, then add it to 180 mL of deionized water, introduce nitrogen, and then add 20 mL of monomer GMA and 0.08 g of initiator K 2 S 2 O 8 , stir the reaction at a constant speed at 70 °C for 3 h. When the mixed reactants start to solidify and the reaction is basically completed, stop heating. Wash the product with deionized water and acetone to remove unreacted monomers and initiators to obtain Intermediate Product 2;

[0072] Dissolve 12 mL of branched polyethyleneimine (PEI) in 40 mL of DMF, add the aforementioned Intermediate Product 2, introduce nitrogen, and then react under nitrogen protection in a 70 °C water bath for 8 h. Wash the product repeatedly with deionized water and absolute ethanol to remove the reaction solvent and unreacted PEI to obtain Intermediate Product 3;

[0073] Dissolve isophorone diisocyanate (IPDI, 0.02 mmol) in 100 mL of N-methylpyrrolidone. Immerse the aforementioned intermediate product 3 in N-methylpyrrolidone. After soaking for 1 h, then add 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) to 50 mL of N-methylpyrrolidone, mix the two, and mechanically stir for 2 h to obtain the modified polytetrafluoroethylene membrane of Example 1.

[0074] Example 2:

[0075] Example 2 includes the following steps:

[0076] Cut a 5 cm * 5 cm part from the PTFE membrane for experiment. The thickness of this PTFE membrane is 35 μm, and the pore size is 3 μm. Immerse this PTFE membrane in 150 mL of N,N-dimethylacetamide.

[0077] Add HAB (0.05 mol, 10.8 g) to N,N-dimethylacetamide, pass in nitrogen, and then add BPDA (0.05 mol, 14.7 g) under nitrogen protection. Carry out a polymerization reaction at 45 °C to form a polyimide layer on the PTFE membrane to obtain intermediate product 1.

[0078] Dry the aforementioned intermediate product 1, then add it to 180 mL of deionized water, pass in nitrogen, and then add 20 mL of monomer GMA and 0.08 g of initiator K 2 S 2 O 8 , stir the reaction at a constant speed at 70 °C for 3 h. When the mixed reactants start to solidify and the reaction is basically completed, stop heating. Wash the product with deionized water and acetone to remove the unreacted monomers and initiator to obtain intermediate product 2.

[0079] Dissolve 12 mL of branched polyethyleneimine (PEI) in 40 mL of DMF, add the aforementioned intermediate product 2, pass in nitrogen, and then react under nitrogen protection in a 70 °C water bath for 8 h. Wash the product repeatedly with deionized water and absolute ethanol to remove the reaction solvent and unreacted PEI to obtain intermediate product 3.

[0080] Dissolve 3,3'-dimethyl-4,4'-biphenyl diisocyanate (TODI, 0.02 mmol) in 100 mL of N-methylpyrrolidone. Immerse the aforementioned intermediate product 3 in N-methylpyrrolidone. After soaking for 1 h, then add 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) to 50 mL of N-methylpyrrolidone, mix the two, and mechanically stir for 2 h to obtain the modified polytetrafluoroethylene membrane of Example 2.

[0081] Example 3:

[0082] The steps of Example 3 are basically the same as those of Example 1, except that equimolar amount of 2,2'-methylenediphenyl diisocyanate (MDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0083] Example 4:

[0084] The steps of Example 4 are basically the same as those of Example 1, except that equimolar amount of terephthalic diisocyanate (2,6-TDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0085] Example 5:

[0086] The steps of Example 5 are basically the same as those of Example 1, except that equimolar amount of terephthalic diisocyanate (2,4-TDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0087] Example 6:

[0088] The steps of Example 6 are basically the same as those of Example 1, except that equimolar amount of dicyclohexylmethane diisocyanate (HMDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0089] Comparative Example 1:

[0090] Comparative Example 1 includes the following steps:

[0091] Cut a 5 cm * 5 cm part from the PTFE membrane for experiment. The thickness of the PTFE membrane is 35 μm;

[0092] Add buffer salt tris(hydroxymethyl)aminomethane hydrochloride to 100 mL of dopamine hydrochloride solution (5 mg / mL), adjust the pH of the solution to 8.5, then slowly add polytetrafluoroethylene powder, stir at high speed, and carry out polymerization reaction at 0 °C for 15 h; after the reaction is completed, filter and wash the solid with water for many times until the filtrate is clear and transparent, and then dry the solid under vacuum at 120 °C for 10 h to obtain Intermediate Product 1;

[0093] Dry the aforementioned Intermediate Product 1, then add it to 180 mL of deionized water, introduce nitrogen, and then add 20 mL of monomer GMA and 0.08 g of initiator K 2 S 2 O 8, react with constant stirring at 70 °C for 3 h. When the mixed reactants start to solidify and the reaction is basically completed, stop heating. Wash the product with deionized water and acetone to remove the unreacted monomers and initiator, and obtain intermediate product 2;

[0094] Dissolve 12 mL of branched polyethyleneimine (PEI) in 40 mL of DMF, add the aforementioned intermediate product 2, introduce nitrogen gas, and then react under nitrogen protection by heating in a water bath at 70 °C for 8 h. Wash the product repeatedly with deionized water and absolute ethanol to remove the reaction solvent and unreacted PEI, and obtain intermediate product 3;

[0095] Dissolve 3,3'-dimethyl-4,4'-biphenyl diisocyanate (TODI, 0.02 mmol) in 100 mL of N-methylpyrrolidone. Immerse the aforementioned intermediate product 3 in N-methylpyrrolidone. After soaking for 1 h, then add 7 g of polyvinyl alcohol (polyvinyl alcohol (type 17-99)) to 50 mL of N-methylpyrrolidone, mix the two, and stir mechanically for 2 h to obtain the modified polytetrafluoroethylene membrane of Comparative Example 1.

[0096] The difference between Comparative Example 1 and Example 2 is that a polydopamine layer rather than a polyimide layer is formed on the surface in Comparative Example 1.

[0097] Comparative Example 2:

[0098] Comparative Example 2 includes the following steps:

[0099] Cut a 5 cm * 5 cm part from the PTFE membrane for experiments. The thickness of this PTFE membrane is 35 μm;

[0100] Add buffer salt tris(hydroxymethyl)aminomethane hydrochloride to 100 mL of dopamine hydrochloride solution (5 mg / mL), adjust the pH of the solution to 8.5, then slowly add polytetrafluoroethylene powder, stir at high speed, and carry out a polymerization reaction at 0 °C for 15 h; after the reaction is completed, filter and wash the solid with water multiple times until the filtrate is clear and transparent. Subsequently, dry the solid under vacuum conditions at 120 °C for 10 h to obtain intermediate product 1;

[0101] Dry the aforementioned intermediate product 1, then add it to 180 mL of deionized water, introduce nitrogen gas, and then add 20 mL of monomer GMA and 0.08 g of initiator K 2 S 2 O 8 , react with constant stirring at 70 °C for 3 h. When the mixed reactants start to solidify and the reaction is basically completed, stop heating. Wash the product with deionized water and acetone to remove the unreacted monomers and initiator, and obtain intermediate product 2;

[0102] Dissolve 12 mL of branched polyethyleneimine (PEI) in 40 mL of DMF, add the aforementioned intermediate 2, introduce nitrogen gas, and then react under nitrogen protection by heating in a 70 °C water bath for 8 h. Wash the product repeatedly with deionized water and absolute ethanol to remove the reaction solvent and unreacted PEI, obtaining intermediate 3;

[0103] Dissolve isophorone diisocyanate (IPDI, 0.02 mmol) in 100 mL of N-methylpyrrolidone. Immerse the aforementioned intermediate 3 in N-methylpyrrolidone. After soaking for 1 h, then add 7 g of polyvinyl alcohol (polyvinyl alcohol (type 17-99)) to 50 mL of N-methylpyrrolidone, mix the two, and stir mechanically for 2 h to obtain the modified polytetrafluoroethylene membrane of Comparative Example 1.

[0104] The difference between Comparative Example 2 and Example 1 is that a polydopamine layer rather than a polyimide layer is formed on the surface in Comparative Example 1.

[0105] Comparative Example 3:

[0106] The steps of Comparative Example 3 are basically the same as those of Comparative Example 1, except that the dopamine hydrochloride solution used in Comparative Example 3 is 1.5 mg / mL.

[0107] Comparative Example 4:

[0108] The steps of Comparative Example 4 are basically the same as those of Comparative Example 2, except that the dopamine hydrochloride solution used in Comparative Example 2 is 1.5 mg / mL.

[0109] Comparative Example 5:

[0110] Comparative Example 5 includes the following steps:

[0111] Cut a 5 cm * 5 cm part from the PTFE membrane for experiments. The thickness of this PTFE membrane is 35 μm;

[0112] Add 0.05 mol of 2-HEA and this PTFE membrane to 100 mL of N,N-dimethylacetamide, stir for 5 min and then introduce nitrogen gas; then weigh 0.12 g of initiator BPO and dissolve it in 5 mL of DMF, slowly add it to the aforementioned solution at 75 °C, and after the dropping is completed, raise the temperature to 85 °C and continue to react for 5 h to obtain intermediate 1;

[0113] Dry the aforementioned intermediate 1, then add it to 180 mL of deionized water, introduce nitrogen gas, and then add 20 mL of monomer GMA and 0.08 g of initiator K under nitrogen protection 2 S 2 O 8, stir the reaction at a constant speed at 70 °C for 3 h. When the mixed reactants start to solidify and the basic reaction is completed, stop heating. Wash the product with deionized water and acetone to remove the unreacted monomers and initiators, and obtain intermediate product 2;

[0114] Dissolve 12 mL of branched polyethyleneimine (PEI) in 40 mL of DMF, add the aforementioned intermediate product 2, introduce nitrogen, and then react under nitrogen protection by heating in a water bath at 70 °C for 8 h. Wash the product repeatedly with deionized water and absolute ethanol to remove the reaction solvent and unreacted PEI, and obtain intermediate product 3;

[0115] Dissolve isophorone diisocyanate (IPDI, 0.02 mmol) in 100 mL of N-methylpyrrolidone. Immerse the aforementioned intermediate product 3 in N-methylpyrrolidone. After soaking for 1 h, then add 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) to 50 mL of N-methylpyrrolidone, mix the two, and mechanically stir for 2 h to obtain the modified polytetrafluoroethylene membrane of Comparative Example 1.

[0116] The difference between Comparative Example 5 and Example 1 is that a hydroxyethyl acrylate layer instead of a polyimide layer is formed on the surface in Comparative Example 5.

[0117] Comparative Example 6:

[0118] Comparative Example 6 includes the following steps:

[0119] Cut a 5 cm * 5 cm part from the PTFE membrane for experiment. The thickness of this PTFE membrane is 35 μm and the pore size is 3 μm. Immerse this PTFE membrane in 150 mL of N,N-dimethylacetamide;

[0120] Add HAB (0.05 mol, 10.8 g) to N,N-dimethylacetamide, introduce nitrogen, and then add BPDA (0.05 mol, 14.7 g) under nitrogen protection. Carry out a polymerization reaction at 45 °C to form a polyimide layer on the PTFE membrane and obtain intermediate product 1;

[0121] Dissolve isophorone diisocyanate (IPDI, 0.02 mmol) in 100 mL of N-methylpyrrolidone. Immerse the aforementioned intermediate product 1 in N-methylpyrrolidone. After soaking for 1 h, then add 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) to 50 mL of N-methylpyrrolidone, mix the two, and mechanically stir for 2 h to obtain the modified polytetrafluoroethylene membrane of Comparative Example 6.

[0122] Pure water flux test:

[0123] Under a certain negative pressure condition, the pure water flux before and after the hydrophilic modification of the PTFE membrane was tested according to the following formula;

[0124] J = V / At

[0125] In the formula: J is the flux of the PTFE membrane, with the unit of L / (m 2 ·h); V is the volume of deionized water used, with the unit of L; A is the effective passing area of the PTFE membrane, with the unit of m 2 ; t is the time for the deionized water to pass through, with the unit of h.

[0126] The prepared Examples 1-6 and Comparative Examples 1-6 were subjected to a 1-hour pure water flux test, and the values of the pure water flux at this time were recorded. Then, they were continued for a 5-hour pure water flux test, and the values of the pure water flux at this time were recorded again; then they were respectively placed at room temperature for 15 days and 45 days, and then the pure water flux test was carried out again, and the values of the pure water flux of each were recorded respectively; the results are shown in Table 1 below, and the units are all L / (m 2 ·h):

[0127] Table 1

[0128] Example Initial pure water flux Pure water flux after 5 h Pure water flux after standing for 15 days Pure water flux after standing for 45 days Example 1 3688 3589 3254 3147 Example 2 2975 2855 2742 2662 Example 3 3215 3021 2821 2793 Example 4 3056 2980 2685 2769 Example 5 3189 3048 2895 2810 Example 6 4415 4317 4124 4081 Comparative example 1 Clogging - - - Comparative example 2 Clogging - - - Comparative example 3 2025 1785 1564 1453 Comparative example 4 2251 2170 1995 1850 Comparative example 5 3914 2218 2084 1986 Comparative example 6 4151 3065 2017 1543

[0129] It can be seen that the present disclosure has prepared a modified polytetrafluoroethylene membrane with high hydrophilicity and high weather resistance; by comparing Examples 1-2 and Comparative Examples 1-4, it can be seen that because there are too many hydroxyl active groups on the polydopamine layer and they are unevenly distributed, therefore, after grafting modification, the polydopamine layer binds too many grafting groups, resulting in the pores of the modified polytetrafluoroethylene membranes obtained in Comparative Example 1 and Comparative Example 2 being blocked. If the concentration of the dopamine hydrochloride solution is reduced during the preparation process, as shown in Comparative Examples 3 and 4, their hydrophilic properties are not as good as those of Examples 1 and 2.

[0130] In Comparative Example 5, 2-hydroxyethyl acrylate was used instead of polyimide. The newly prepared product has good hydrophilic properties, but after long-term use, the value of its pure water flux decreases significantly. This is because the combination of 2-hydroxyethyl acrylate and the PTFE membrane is not very good, and after long-term use, the 2-hydroxyethyl acrylate layer is damaged.

[0131] The structure of the polyimide layer obtained in the examples of the present disclosure is as follows. The aromatic ring structure not only provides rigidity, and the hydroxyl and carboxyl groups are evenly distributed, so the pore diameter will not be blocked after grafting modification.

[0132]

[0133] Comparing Comparative Example 6 with Example 1, it can be seen that the newly prepared product in Example 6 has very good hydrophilic properties. However, after being placed for several days, the hydrophilic properties have significantly decreased. This is because the hydrophilic polyvinyl alcohol is directly connected to the polyimide layer and is directly exposed to the outside, making it easy to lose its hydrophilic ability after multiple uses and long-term placement. In the embodiments of the present disclosure, the hydrophilic polyvinyl alcohol is protected by branched polyethyleneimine, so it has good weather resistance and still has hydrophilic ability after multiple uses and long-term placement. Among Examples 1-6, due to the small steric hindrance of the HMDI group, Example 6 has a very prominent hydrophilic effect.

[0134] Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the specification and practice of the disclosure herein. The present disclosure is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include well-known common general knowledge or conventional technical means in the technical field not disclosed in the present disclosure.

Claims

1. A method for preparing a modified polytetrafluoroethylene membrane, characterized in that: The preparation method comprises the following steps: Step 1: providing a polytetrafluoroethylene microporous membrane, and immersing the polytetrafluoroethylene microporous membrane in a first organic solvent; Step 2: adding at least one dianhydride monomer and a diamine monomer to the first organic solvent, and performing a polymerization reaction at 30° C. to 70° C. under an inert gas atmosphere to form a polyimide layer on the polytetrafluoroethylene microporous membrane to obtain the intermediate modified polytetrafluoroethylene membrane of step 2; wherein the dianhydride monomer has a structure of the following formula II: wherein R3 and R4 are each independently selected from hydrogen, amino, halogen atom, hydroxyl, nitro, C1-10 alkyl or C1-10 alkoxy; The diamine monomer has the structure of the following formula III: wherein Ar1 and Ar2 are each independently selected from a C3-30 cycloalkyl group, a C6-C30 aryl group, a 3-30 membered heterocyclyl group or a 5-30 membered heteroaryl group; Step 3: using a compound having the structure of the following formula I to graft copolymerize the intermediate modified polytetrafluoroethylene membrane obtained in step 2 to obtain the intermediate modified polytetrafluoroethylene membrane of step 3; Wherein, R1 and R2 are each independently selected from C1-10 alkyl or C1-10 alkoxy; Step 4: using polyethyleneimine to graft-modify the intermediate modified polytetrafluoroethylene membrane obtained in step 3 to obtain the intermediate modified polytetrafluoroethylene membrane of step 4; The polyethyleneimine is a branched polyethyleneimine with an average weight average molecular weight of 1500-2000; Step 5: Immerse the intermediate modified polytetrafluoroethylene membrane obtained in step 4 in a second organic solvent containing at least one diisocyanate compound for 0.5-1.5 hours, then add a second organic solvent containing polyvinyl alcohol, and obtain the modified polytetrafluoroethylene membrane after reaction.

2. The preparation method according to claim 1, characterized in that: The dianhydride monomer is selected from the following compound 2-1, and the diamine monomer is selected from the following compound 3-1: 。 3. The preparation method according to claim 1, characterized in that: In step 2, the molar ratio of the dianhydride monomer to the diamine monomer is 1:(0.8-1.2).

4. The preparation method according to claim 3, characterized in that: In step 3, the molar ratio of the compound having the structure of formula I to the dianhydride monomer used in step 2 is (2-5):

1.

5. The preparation method according to claim 1, characterized in that: The diisocyanate compound is selected from any one of the following compounds: 、 、 、 、 、 、 、 、 。 6. The preparation method according to claim 5, characterized in that: The diisocyanate compound is selected from 、 、 。 7. A modified polytetrafluoroethylene membrane, characterized in that: The modified polytetrafluoroethylene membrane is obtained by the preparation method according to any one of claims 1 to 6.

Images