Preparation method and application of modified polytetrafluoroethylene membrane

Abstract

The invention belongs to the technical field of membranes, and particularly relates to a preparation method and application of a modified polytetrafluoroethylene membrane. The preparation method comprises the following steps: providing a polytetrafluoroethylene microporous membrane; forming a polyimide layer on the polytetrafluoroethylene microporous membrane using at least one dianhydride monomer and diamine monomer; carrying out graft modification on the polyimide layer by using a compound containing a glycidyl ester group and polyethyleneimine; finally, polyvinyl alcohol and the grafted and modified polyimide layer are combined through a diisocyanate compound, and the modified polytetrafluoroethylene film is obtained.

Description

Technical Field

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

[0002] The development of membrane separation technology plays an important role in energy, environmental protection, chemical industry, medicine and other fields. Due to its advantages such as high efficiency and no secondary pollution, it has developed rapidly in the water treatment process 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 and directly determines the accuracy and efficiency of separation.

[0003] As a self-supporting porous membrane, polytetrafluoroethylene microporous membrane has the advantages of high strength, high packing density, backwashing ability, acid and alkali resistance, oxidation resistance, microbial corrosion resistance, and good biocompatibility. The filtration liquid flow rate is high, the flow is turbulent, it is not sensitive to clogging, it is easy to clean, the pressure loss in the membrane component is small, and it can operate under various extreme chemicals, temperatures and pressures. It is especially suitable for the separation of various high-viscosity, high-solid content, and high-pollution solid-liquid and gas-liquid.

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

[0005] The present invention provides a preparation method and application of a modified polytetrafluoroethylene membrane to solve the deficiencies in the related art.

[0006] According to a first aspect of an embodiment of the present disclosure, a method for preparing a modified polytetrafluoroethylene membrane is provided, the method comprising 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 diamine monomer contains at least one hydroxyl 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; 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.

[0007] In one aspect of the disclosed embodiments, the dianhydride monomer has the 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.

[0008] In one aspect of the embodiments of the present disclosure, the diamine monomer has the structure of the following formula III: Wherein, Ar1 and Ar2 are each independently selected from C3-30 cycloalkyl, C6-C30 aryl, 3-30 membered heterocyclic group or substituted or 5-30 membered heteroaryl.

[0009] In one aspect of the disclosed embodiment, the dianhydride monomer is selected from the following compound 2-1 (3,3',4,4'-biphenyltetracarboxylic acid dianhydride), and the diamine monomer is selected from the following compound 3-1 (3,3'-dihydroxy-4,4'-diaminobenzidine): In one aspect of the disclosed embodiments, the compound of formula I is selected from compound 1-1 (glycidyl methacrylate): 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.

[0010] In one aspect of the disclosed embodiment, in step 2, the molar ratio of the dianhydride monomer to the diamine monomer is 1:(0.8-1.2). Specifically, in step 2, the molar ratio of the dianhydride monomer to the diamine monomer is 1:1.

[0011] In one aspect of the disclosed embodiments, 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. Specifically, in step 3, the molar ratio of the compound having the structure of formula I to the dianhydride monomer used in step 2 is 4:1.

[0012] In one aspect of the disclosed embodiment, step 3 comprises: adding the intermediate modified polytetrafluoroethylene membrane of step 2 into water, and then adding glycidyl methacrylate and an initiator, and reacting at 60° C.-80° C. for 2-5 hours.

[0013] 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 to 2000. Specifically, the polyethyleneimine is a branched polyethyleneimine with an average weight average molecular weight of 1800.

[0014] In one aspect of the embodiments of the present disclosure, the diisocyanate compound is selected from any one of the following compounds: , , , , , , , , .

[0015] 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).

[0016] In one aspect of the embodiments of the present disclosure, the amount of polyethyleneimine used relative to the compound of formula I used is not specifically limited.

[0017] In one aspect of the embodiments of the present disclosure, specifically, when the polyethyleneimine is a branched polyethyleneimine having an average weight average molecular weight of 1800, and the diisocyanate compound is selected from When the mass ratio of polyethyleneimine to diisocyanate compound is selected from (3-10):1.

[0018] In one aspect of the embodiments of the present disclosure, in step 5, the mass, average molecular weight and degree of polymerization of the polyvinyl alcohol used are not particularly limited.

[0019] According to a second aspect of an embodiment of the present disclosure, a modified polytetrafluoroethylene membrane is provided. The modified polytetrafluoroethylene membrane is obtained by the aforementioned preparation method.

[0020] The technical solution provided by the embodiments of the present disclosure may have the following beneficial effects: It can be seen from the above embodiments that the present disclosure provides a highly weather-resistant modified polytetrafluoroethylene membrane having excellent hydrophilic properties.

[0021] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0023] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.

[0024] In this article, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0025] In the description herein, unless otherwise specified, “above” and “below” include the number.

[0026] Unless otherwise specified, the terms used in this disclosure have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this disclosure can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this disclosure).

[0027] The term "about" is used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a range of variation less than or equal to ±10% of 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%. In addition, amounts, ratios, and other numerical values ​​are sometimes presented in this article in a range format. It should be understood that such a range format is for convenience and simplicity, and should be flexibly understood to include not only numerical values ​​explicitly designated as range limits, but also all individual numerical values ​​or subranges encompassed within the range, as if each numerical value and subrange were explicitly designated.

[0028] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, 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, 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 may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0029] In this disclosure, the term "alkyl" refers to an aliphatic hydrocarbon group, which can be straight or branched. Branched refers to one or more lower alkyl groups, such as methyl, ethyl or propyl, attached to a linear alkyl chain. "Lower alkyl" refers to a group containing about 1 to about 6 carbon atoms in the chain, which can be straight or branched.

[0030] In the present disclosure, the term "amino" refers to a -NR'R" group. The amino group may be optionally substituted. In an unsubstituted amino group, R' and R" are hydrogen. In a substituted amino group, R' and R" may 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" may be cyclized to form a cyclic amino group, such as a pyrrolidinyl or piperidinyl group. Such cyclic amino groups may incorporate other heteroatoms, for example to form piperazine or morpholine groups. Such cyclic amino groups may be optionally substituted, for example, by amino, hydroxyl or oxo groups.

[0031] In the present disclosure, the term "alkoxy" refers to -O-alkyl. Alkoxy can refer to a straight chain, branched or cyclic, saturated or unsaturated oxy-hydrocarbon chain, including, for example, methoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy and pentoxy. Alkoxy can be optionally substituted with one or more alkoxy substituents ("substituted alkoxy").

[0032] In this disclosure, the term "aryl" refers to an aromatic monocyclic or polycyclic ring system. The aryl group may be optionally substituted with one or more "ring system substituents", which may be the same or different, and are as defined herein. Non-limiting examples of suitable aryl groups include phenyl and naphthyl.

[0033] In the present disclosure, the term "heteroaryl" refers to an aromatic monocyclic or polycyclic ring system in which one or more of the ring atoms is an element other than carbon, such as nitrogen, oxygen or sulfur, either alone or in combination, with preferred heteroaryls containing about 5 to about 6 ring atoms. The "heteroaryl" may be optionally substituted with one or more "ring system substituents", which may be the same or different, as defined herein. The prefix aza, oxa or thia before the heteroaryl root name indicates that at least one nitrogen, oxygen or sulfur atom, respectively, is present as a ring atom. The nitrogen atom of the heteroaryl may be optionally oxidized to the corresponding N-oxide. Non-limiting examples of suitable heteroaryl groups include pyridinyl, pyrazinyl, furanyl, thiophenyl, pyrimidinyl, isoxazolyl, isothiazolyl, oxazolyl, thiazolyl, pyrazolyl, furazanyl, pyrrolyl, pyrazolyl, triazolyl, 1,2,4-thiadiazolyl, pyrazinyl, pyridazinyl, quinoxalinyl, 2,3-naphthyridinyl, imidazo[1,2-a]pyridinyl, imidazo[2,1-b]thiazolyl, benzofurazanyl, indolyl, azaindolyl, benzimidazolyl, benzothiophenyl, quinolinyl, imidazolyl, thienopyridinyl, quinazolinyl, thienopyrimidinyl, pyrrolopyridinyl, imidazopyridinyl, isoquinolinyl, benzazaindolyl, 1,2,4-triazinyl, benzothiazolyl, and the like.

[0034] 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 it can be adaptively selected according to actual needs.

[0035] In the present disclosure, the polytetrafluoroethylene microporous membrane used in the present disclosure has a membrane pore size of 0.03-10μm; specifically, the polytetrafluoroethylene microporous membrane used in the present disclosure has 0.03μm, 0.05μm, 0.05μm, 0.1μm, 0.22μm, 0.45μm, 1μm, 3μm, 5μm or 10μm; however, the membrane pore size of the polytetrafluoroethylene microporous membrane used in the present disclosure is not limited thereto, and it can be adaptively selected according to actual needs.

[0036] 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 solvent used in the present disclosure is not limited thereto.

[0037] In a specific embodiment of the present disclosure, in step 1 and step 2: a polytetrafluoroethylene microporous membrane is provided, the polytetrafluoroethylene microporous membrane has a thickness of 275 mm and a membrane pore size of 3-5 μm, the polytetrafluoroethylene microporous membrane is immersed in N, N-dimethylacetamide, a dianhydride monomer compound 2-1 (3,3',4,4'-biphenyltetracarboxylic acid dianhydride) and a diamine monomer compound 3-1 (3,3'-dihydroxy-4,4'-diaminobenzidine) are added to the N, N-dimethylacetamide, and a polymerization reaction is carried out at 45° C. under a nitrogen atmosphere to form a polyimide layer on the polytetrafluoroethylene microporous membrane, and the intermediate modified polytetrafluoroethylene membrane of step 2 is obtained, wherein the polyimide has the following structure: In step 3, the intermediate modified polytetrafluoroethylene membrane obtained in step 2 is graft copolymerized with compound 1-1 (glycidyl methacrylate) to obtain the intermediate modified polytetrafluoroethylene membrane of step 3; after graft copolymerization with polyimide, it has the following structure: The above structure is only used as an example. Polyethyleneimine can be grafted with other hydroxyl groups and carboxyl groups on the polyimide segment for copolymerization.

[0038] In step 4, polyethyleneimine is used to graft-modify the intermediate modified polytetrafluoroethylene membrane obtained in step 3 to obtain the intermediate modified polytetrafluoroethylene membrane of step 4; after the polyimide is graft-modified, it has the following structure: The above structure is only used as an example, and the structure formed by the branched polyethyleneimine used in the present disclosure after grafting modification is not limited thereto.

[0039] In step 5, the intermediate modified polytetrafluoroethylene membrane obtained in step 4 is immersed in N-methylpyrrolidone containing an isocyanate compound. After immersion for 45 minutes, N-methylpyrrolidone containing polyvinyl alcohol (average degree of polymerization of 50) is added. After reacting for 4 hours, a modified polytetrafluoroethylene membrane is obtained, which has the following structure: Wherein R7 is selected from , , or , the structure of R7 is determined by the specific diisocyanate compound used; T1 is a polyvinyl alcohol segment. The polyvinyl alcohol segment is combined with the branched polyethyleneimine through the diisocyanate compound bridge; the above structure is only used as an example, because the diisocyanate compound can be combined with any secondary amine on the branched polyethyleneimine.

[0040] The present invention is further described below by way of specific examples. The various 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 all weight contents. Unless otherwise specified, it is understood that the process is carried out at room temperature.

[0041] Embodiment and comparative example: Embodiment 1: Embodiment 1 comprises the following steps: A 5 cm*5 cm section was cut from a PTFE membrane for the experiment. The thickness of the PTFE membrane was 35 μm and the pore size was 3 μm. The PTFE membrane was immersed in 150 mL of N,N-dimethylacetamide. HAB (0.05 mol, 10.8 g) was added to N,N-dimethylacetamide, nitrogen was introduced, and then BPDA (0.05 mol, 14.7 g) was added under nitrogen protection, and polymerization reaction was carried out at 45°C to form a polyimide layer on the PTFE membrane to obtain intermediate product 1; The intermediate product 1 is dried and then added to 180 mL of deionized water, nitrogen is introduced, and then 20 mL of monomer GMA and 0.08 g of initiator K2S2O8 are added under nitrogen protection, and the mixture is stirred at a constant speed at 70°C for 3 h. When the mixed reactant begins to solidify and the basic reaction is completed, heating can be stopped, and the product is washed with deionized water and acetone to remove unreacted monomers and initiators, thereby obtaining an intermediate product 2; 12 mL of branched polyethyleneimine (PEI) was dissolved in 40 mL of DMF, and the intermediate product 2 was added, nitrogen was introduced, and then heated in a 70°C water bath under nitrogen protection for 8 h. The product was repeatedly washed with deionized water and anhydrous ethanol to remove the reaction solvent and unreacted PEI, thereby obtaining the intermediate product 3. Isophorone diisocyanate (IPDI, 0.02 mmol) was dissolved in 100 mL of N-methylpyrrolidone, and the intermediate product 3 was immersed in N-methylpyrrolidone for 1 hour. Then, 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) was added to 50 mL of N-methylpyrrolidone, and the two were mixed and mechanically stirred for 2 hours to obtain the modified polytetrafluoroethylene membrane of Example 1.

[0042] Embodiment 2: Embodiment 2 comprises the following steps: A 5 cm*5 cm section was cut from a PTFE membrane for the experiment. The thickness of the PTFE membrane was 35 μm and the pore size was 3 μm. The PTFE membrane was immersed in 150 mL of N,N-dimethylacetamide. HAB (0.05 mol, 10.8 g) was added to N,N-dimethylacetamide, nitrogen was introduced, and then BPDA (0.05 mol, 14.7 g) was added under nitrogen protection, and polymerization reaction was carried out at 45°C to form a polyimide layer on the PTFE membrane to obtain intermediate product 1; The intermediate product 1 is dried and then added to 180 mL of deionized water, nitrogen is introduced, and then 20 mL of monomer GMA and 0.08 g of initiator K2S2O8 are added under nitrogen protection, and the mixture is stirred at a constant speed at 70°C for 3 h. When the mixed reactant begins to solidify and the basic reaction is completed, heating can be stopped, and the product is washed with deionized water and acetone to remove unreacted monomers and initiators, thereby obtaining an intermediate product 2; 12 mL of branched polyethyleneimine (PEI) was dissolved in 40 mL of DMF, and the intermediate product 2 was added, nitrogen was introduced, and then heated in a 70°C water bath under nitrogen protection for 8 h. The product was repeatedly washed with deionized water and anhydrous ethanol to remove the reaction solvent and unreacted PEI, thereby obtaining the intermediate product 3. 3,3'-dimethyl-4,4'-biphenyl diisocyanate (TODI, 0.02mmol) was dissolved in 100mL N-methylpyrrolidone, and the intermediate product 3 was immersed in N-methylpyrrolidone for 1h. Then, 7g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) was added to 50mL N-methylpyrrolidone, and the two were mixed and mechanically stirred for 2h to obtain the modified polytetrafluoroethylene membrane of Example 2.

[0043] Embodiment 3: The steps of Example 3 are substantially the same as those of Example 1, except that an equal molar amount of 2,2'-methylenediphenyl diisocyanate (MDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0044] Embodiment 4: The steps of Example 4 are substantially the same as those of Example 1, except that an equimolar amount of isophorone diisocyanate (2,6-TDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0045] Embodiment 5: The steps of Example 5 are substantially the same as those of Example 1, except that an equimolar amount of phenylene diisocyanate (2,4-TDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0046] Embodiment 6: The steps of Example 6 are substantially the same as those of Example 1, except that an equimolar amount of dicyclohexylmethane diisocyanate (HMDI, 0.02 mmol) is used instead of isophorone diisocyanate (IPDI, 0.02 mmol).

[0047] Comparative Example 1: Comparative Example 1 comprises the following steps: A 5 cm*5 cm section was cut from the PTFE membrane for the experiment, and the thickness of the PTFE membrane was 35 μm; 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 perform polymerization reaction at 0°C for 15 hours; after the reaction is completed, filter and wash the solid with water several times until the filtrate is clear and transparent, then dry the solid under vacuum at 120°C for 10 hours to obtain intermediate 1; The intermediate product 1 is dried and then added to 180 mL of deionized water, nitrogen is introduced, and then 20 mL of monomer GMA and 0.08 g of initiator K2S2O8 are added under nitrogen protection, and the mixture is stirred at a constant speed at 70°C for 3 h. When the mixed reactant begins to solidify and the basic reaction is completed, heating can be stopped, and the product is washed with deionized water and acetone to remove unreacted monomers and initiators, thereby obtaining an intermediate product 2; 12 mL of branched polyethyleneimine (PEI) was dissolved in 40 mL of DMF, and the intermediate product 2 was added, nitrogen was introduced, and then heated in a 70°C water bath under nitrogen protection for 8 h. The product was repeatedly washed with deionized water and anhydrous ethanol to remove the reaction solvent and unreacted PEI, thereby obtaining the intermediate product 3. 3,3'-dimethyl-4,4'-biphenyl diisocyanate (TODI, 0.02mmol) was dissolved in 100mL of N-methylpyrrolidone, and the intermediate product 3 was immersed in N-methylpyrrolidone for 1h. Then, 7g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) was added to 50mL of N-methylpyrrolidone, and the two were mixed and mechanically stirred for 2h to obtain the modified polytetrafluoroethylene membrane of Comparative Example 1.

[0048] The difference between Comparative Example 1 and Example 2 is that, in Comparative Example 1, a polydopamine layer is formed on the surface instead of a polyimide layer.

[0049] Comparative Example 2: Comparative Example 2 comprises the following steps: A 5 cm*5 cm section was cut from the PTFE membrane for the experiment, and the thickness of the PTFE membrane was 35 μm; 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 perform polymerization reaction at 0°C for 15 hours; after the reaction is completed, filter and wash the solid with water several times until the filtrate is clear and transparent, then dry the solid under vacuum at 120°C for 10 hours to obtain intermediate 1; The intermediate product 1 is dried and then added to 180 mL of deionized water, nitrogen is introduced, and then 20 mL of monomer GMA and 0.08 g of initiator K2S2O8 are added under nitrogen protection, and the mixture is stirred at a constant speed at 70°C for 3 h. When the mixed reactant begins to solidify and the basic reaction is completed, heating can be stopped, and the product is washed with deionized water and acetone to remove unreacted monomers and initiators, thereby obtaining an intermediate product 2; 12 mL of branched polyethyleneimine (PEI) was dissolved in 40 mL of DMF, and the intermediate product 2 was added, nitrogen was introduced, and then heated in a 70°C water bath under nitrogen protection for 8 h. The product was repeatedly washed with deionized water and anhydrous ethanol to remove the reaction solvent and unreacted PEI, thereby obtaining the intermediate product 3. Isophorone diisocyanate (IPDI, 0.02 mmol) was dissolved in 100 mL of N-methylpyrrolidone, and the intermediate product 3 was immersed in N-methylpyrrolidone for 1 hour. Then, 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) was added to 50 mL of N-methylpyrrolidone, and the two were mixed and mechanically stirred for 2 hours to obtain the modified polytetrafluoroethylene membrane of Comparative Example 1.

[0050] The difference between Comparative Example 2 and Example 1 is that a polydopamine layer instead of a polyimide layer is formed on the surface of Comparative Example 1.

[0051] Comparative Example 3: The steps of Comparative Example 3 are substantially the same as those of Comparative Example 1, except that the dopamine hydrochloride solution used in Comparative Example 3 is 1.5 mg / mL.

[0052] Comparative Example 4: 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.

[0053] Comparative Example 5: Comparative Example 5 comprises the following steps: A 5 cm*5 cm section was cut from the PTFE membrane for the experiment, and the thickness of the PTFE membrane was 35 μm; 0.05 mol 2-HEA and the PTFE membrane were added to 100 mL N,N-dimethylacetamide, and nitrogen was introduced after stirring for 5 min. Then 0.12 g of initiator BPO was weighed and dissolved in 5 mL DMF, which was slowly added to the above solution at 75°C. After the addition was completed, the temperature was raised to 85°C and the reaction was continued for 5 h to obtain intermediate product 1. The intermediate product 1 is dried and then added to 180 mL of deionized water, nitrogen is introduced, and then 20 mL of monomer GMA and 0.08 g of initiator K2S2O8 are added under nitrogen protection, and the mixture is stirred at a constant speed at 70°C for 3 h. When the mixed reactant begins to solidify and the basic reaction is completed, heating can be stopped, and the product is washed with deionized water and acetone to remove unreacted monomers and initiators, thereby obtaining an intermediate product 2; 12 mL of branched polyethyleneimine (PEI) was dissolved in 40 mL of DMF, and the intermediate product 2 was added, nitrogen was introduced, and then heated in a 70°C water bath under nitrogen protection for 8 h. The product was repeatedly washed with deionized water and anhydrous ethanol to remove the reaction solvent and unreacted PEI, thereby obtaining the intermediate product 3. Isophorone diisocyanate (IPDI, 0.02 mmol) was dissolved in 100 mL of N-methylpyrrolidone, and the intermediate product 3 was immersed in N-methylpyrrolidone for 1 hour. Then, 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) was added to 50 mL of N-methylpyrrolidone, and the two were mixed and mechanically stirred for 2 hours to obtain the modified polytetrafluoroethylene membrane of Comparative Example 1.

[0054] The difference between Comparative Example 5 and Example 1 is that a polyhydroxyethyl acrylate layer is formed on the surface of Comparative Example 5 instead of a polyimide layer.

[0055] Comparative Example 6: Comparative Example 6 comprises the following steps: A 5 cm*5 cm section was cut from a PTFE membrane for the experiment. The thickness of the PTFE membrane was 35 μm and the pore size was 3 μm. The PTFE membrane was immersed in 150 mL of N,N-dimethylacetamide. HAB (0.05 mol, 10.8 g) was added to N,N-dimethylacetamide, nitrogen was introduced, and then BPDA (0.05 mol, 14.7 g) was added under nitrogen protection, and polymerization reaction was carried out at 45°C to form a polyimide layer on the PTFE membrane to obtain intermediate product 1; Isophorone diisocyanate (IPDI, 0.02 mmol) was dissolved in 100 mL of N-methylpyrrolidone, and the intermediate product 1 was immersed in N-methylpyrrolidone for 1 hour. Then, 7 g of polyvinyl alcohol (polyvinyl alcohol (17-99 type)) was added to 50 mL of N-methylpyrrolidone, and the two were mixed and mechanically stirred for 2 hours to obtain the modified polytetrafluoroethylene membrane of Comparative Example 6.

[0056] Pure water flux test: Under a certain negative pressure, the pure water flux of the PTFE membrane before and after hydrophilic modification was tested according to the following formula; J=V / At Where: J is the flux of PTFE membrane, unit is L / (m 2 ·h); V is the volume of deionized water used, in L; A is the effective passage area of ​​PTFE membrane, in m 2 ; t is the time for deionized water to pass through, in h.

[0057] The prepared Examples 1-6 and Comparative Examples 1-6 were subjected to a 1-hour pure water flux test, and the pure water flux value at this time was recorded. The pure water flux test was then continued for 5 hours, and the pure water flux value at this time was recorded again. The pure water flux values ​​were then placed at room temperature for 15 days and 45 days, respectively, and then subjected to a pure water flux test, and the pure water flux values ​​of each were recorded respectively. The results are shown in Table 1 below, and the units are L / (m 2 h): Table 1 Example Initial pure water flux Pure water flux after 5h Pure water flux after 15 days of storage Pure water flux after 45 days of storage 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 Blockage - - - Comparative Example 2 Blockage - - - 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 It can be seen that the present invention prepares a highly hydrophilic and highly weather-resistant modified polytetrafluoroethylene membrane; by comparing Examples 1-2 with Comparative Examples 1-4, it can be seen that since there are too many hydroxyl active groups on the polydopamine layer and they are unevenly distributed, after grafting modification, the polydopamine layer combines with too many grafted groups, resulting in the pores of the modified polytetrafluoroethylene membranes obtained in Comparative Examples 1 and 2 being blocked, and if the concentration of the dopamine hydrochloride solution is reduced during the preparation process, as shown in Comparative Examples 3 and 4, the hydrophilicity is not as good as that of Examples 1 and 2.

[0058] Comparative Example 5 uses polyhydroxyethyl acrylate 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 polyhydroxyethyl acrylate and polytetrafluoroethylene membrane is not very good. After long-term use, the polyhydroxyethyl acrylate layer is damaged.

[0059] The structure of the polyimide layer obtained in the embodiment of the present disclosure is shown below. The aromatic ring structure not only provides rigidity, but also has uniform distribution of hydroxyl and carboxyl groups, so that the pore size will not be blocked after grafting modification.

[0060] Comparing Example 6 with Example 1, it can be seen that the newly prepared product in Example 6 has good hydrophilicity, but after being placed for many days, the hydrophilicity has significantly decreased. This is because the hydrophilic polyvinyl alcohol is directly connected to the polyimide layer, which is directly exposed to the outside world and easily loses its hydrophilicity after repeated use and long-term placement. The hydrophilic polyvinyl alcohol in the disclosed embodiment is protected by branched polyethyleneimine, so it has good weather resistance and still has hydrophilicity after repeated use and long-term placement. In Examples 1-6, due to the small steric hindrance of the HMDI group, Example 6 has a very prominent hydrophilic effect.

[0061] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the disclosure disclosed 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 common knowledge or customary technical means in the art that are 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 diamine monomer contains at least one hydroxyl 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; 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 has the 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.

3. The preparation method according to claim 1, characterized in that: The diamine monomer has the structure of the following formula III: Wherein, Ar1 and Ar2 are each independently selected from C3-30 cycloalkyl, C6-C30 aryl, 3-30 membered heterocyclic group or substituted or 5-30 membered heteroaryl.

4. The preparation method according to claim 2 or 3, 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: 。 5. 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).

6. The preparation method according to claim 5, 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.

7. The preparation method according to claim 1, characterized in that: The polyethyleneimine is a branched polyethyleneimine with an average weight average molecular weight of 1500-2000.

8. The preparation method according to claim 1, characterized in that: The diisocyanate compound is selected from any one of the following compounds: 、 、 、 、 、 、 、 、 。 9. The preparation method according to claim 8, characterized in that: The diisocyanate compound is selected from , , .

10. 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 9.

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