Application of a multifunctional isocyanate crosslinker in surface modification of aromatic polyamide composite membranes

Abstract

The present invention provides an application of a multifunctional isocyanate cross-linking agent in the surface modification of an aromatic polyamide composite membrane. Specifically, an aromatic isocyanate cross-linking agent containing diquaternary ammonium cations, disulfobetaine, and polyether chains in its molecular structure is used to graft and cross-link the surface of the aromatic polyamide composite membrane. After the modification, the membrane surface has high hydrophilicity. The intrinsic N-H groups of the aromatic polyamide separation layer are replaced by newly formed aromatic polyamide N-H groups, which participate in the reaction with residual chlorine or chlorine oxides in seawater, effectively ensuring the long-term stability of the aromatic polyamide composite membrane structure.

Description

Technical Field

[0001] The present invention relates to the application of a multifunctional isocyanate crosslinking agent in the surface modification of an aromatic polyamide composite membrane, and specifically relates to the application of a multifunctional isocyanate crosslinking agent containing diquaternary ammonium cations, disulfobetaine and polyether chains in the molecular structure in the surface modification of an aromatic polyamide composite membrane, and is applied to a seawater desalination process, belonging to the field of functional polymer materials. Technical Background

[0002] Aromatic polyamide reverse osmosis composite membranes have become a mainstream product for industrial applications in seawater and brackish water desalination. However, fouling of aromatic polyamide reverse osmosis composite membranes by marine organisms in seawater remains a pressing issue. One of the simplest and most cost-effective solutions is to disinfect the seawater before reverse osmosis with chlorine, completely killing marine organisms and ensuring that the seawater entering the reverse osmosis process is free of living organisms. To completely kill marine organisms in seawater, a certain residual amount of chlorine must be maintained in the seawater. However, aromatic polyamide reverse osmosis composite membranes, consisting of a support membrane and a separation layer, are sensitive to chlorine oxidation. Excessive chlorine in seawater chemically damages the polymer chain structure of the aromatic polyamide separation layer, rapidly degrading the membrane's separation performance and significantly reducing its service life. Consequently, for decades, research has focused on developing aromatic polyamide reverse osmosis composite membranes with high chlorine resistance.

[0003] Professionals are well aware that the aromatic polyamide separation layer structure of aromatic polyamide reverse osmosis composite membranes consists of three layers: the first is the aromatic polyamide polymer chain structure (referring to the polymer units, repeating units, bonding valence, chain crosslinking, etc.) formed by monomer polymerization; the second is the interchain structure (primarily interchain entanglement, stacking, hydrogen bonding, etc.) determined by the polymerization technology and process; and the third is the membrane surface properties (primarily referring to surface charge, hydrophilicity and hydrophobicity, surface smoothness, etc.). The structural characteristics of the aromatic polyamide separation layer are key factors in determining its desalination efficiency, permeate flux, stable and durable operation, regeneration and reuse, and other aspects of its low-cost and high-efficiency desalination operation. Therefore, in order to obtain aromatic polyamide composite membranes with excellent comprehensive properties such as high desalination performance, high permeate flux, high surface hydrophilicity, high surface antifouling properties, and high anti-chlorine and oxygen stability, research on the first and second structural layers is relatively limited. Surface modification is a relatively simple, effective, and flexible method to improve or enhance the membrane's overall performance.

[0004] So far, there are many examples of surface modification of aromatic polyamide reverse osmosis composite membranes, mainly including: (1) surface coating, (2) surface deposition, and (3) surface grafting. Among them, the chemical method of grafting water-soluble substances on the membrane surface, such as polyethylene glycol, polyacrylic acid, polyacrylamide, quaternary ammonium salt, zwitterionic polymer brush, betaine, etc., and grafting sulfide, sulfonamide, chlorohydantoin, polysaccharide, graphene oxide or carbon nanotubes, etc., have all played a positive role in improving its antifouling performance and anti-chlorine stability. However, the uniformity of the membrane surface modification using the above methods is poor, the density of the introduced functional groups is small, the membrane surface characteristics do not change much, and the water flux does not change much; some methods are also very easy to cause membrane pore blockage, but reduce water permeability; in addition, during the membrane surface graft copolymerization modification process, the monomer raw materials are seriously wasted due to the homopolymerization of monomers; finally, the prominent defect of these existing surface modification methods and technologies is that they only improve the performance of aromatic polyamide composite membranes in a single way. How to improve the comprehensive performance of the membrane in all directions is still a bottleneck problem in the field of reverse osmosis membrane desalination.

[0005] To address the shortcomings of existing surface modification technologies and grafting methods for aromatic polyamide composite membranes, CN103349922B proposed a method for "planting" a matrix containing quaternary ammonium salts and salicylaldehyde functional groups on the membrane surface through a chemical reaction. This method aims to utilize the different mechanisms of sterilization and biocidal activity of the quaternary ammonium salts and salicylaldehyde functional groups, as well as their selective complexation and adsorption of heavy metal ions in seawater, to produce a synergistic and highly effective anti-marine biofouling function, ensuring the cleanliness of the membrane surface. Furthermore, the salicylaldehyde units on the surface of the aromatic polyamide composite membrane react more rapidly with chlorine or chlorine oxides, making them useful as sacrificial materials to stabilize the membrane's intrinsic structure. Furthermore, grafting the quaternary ammonium salts onto the membrane surface effectively improves the membrane's hydrophilicity, which is beneficial for ensuring the membrane's water flux. However, as the membrane ages, the problem of marine biofouling persists. In 2015, CN105251372B disclosed a method for modifying a nascent aromatic polyamide composite membrane with an organic polyamine, followed by a condensation reaction with N,N,N-trialkyl-N-(4-hydroxy-3-formylbenzyl)ammonium chloride to produce a high-density grafted salicylaldehyde Schiff base and quaternary ammonium cation on the membrane surface. This method altered the hydrophilicity of the membrane surface and improved water flux. However, the process was complex, the modification targets were limited, and the application prospects were poor. Subsequently, CN201811305536.9 and CN201811011240.6 introduced the grafting modification of aromatic polyamide composite membrane surfaces with isocyanate-terminated polyurethane prepolymers containing quaternary ammonium cations, polyethers, and salicylaldehyde units in their molecular structures. However, the interchain structure of the aromatic polyamide separation layer was partially destroyed, affecting the membrane's separation efficiency.

[0006] The inventors have comprehensively analyzed the strengths, advantages and disadvantages of existing technologies and methods, and proposed a method for surface modification of aromatic polyamide composite membranes using a multifunctional isocyanate crosslinker containing diquaternary ammonium cations, disulfobetaine and polyether chains in its molecular structure. The method uses isocyanate groups as spacer arms to graft diquaternary ammonium cations, disulfobetaine and polyether chains onto the surface of the aromatic polyamide composite membrane through chemical bonding. Therefore, as long as the surface of the aromatic polyamide composite membrane has groups that can chemically react with isocyanate groups, they are included in the scope of membrane modification described in the present invention. Therefore, the aromatic polyamide composite membrane described in the present invention can be an aromatic polyamide composite membrane produced by completing a condensation reaction on a microporous polysulfone support membrane or a polyethersulfone support membrane using m-phenylenediamine and trimesoyl chloride as raw materials, referred to as a nascent membrane; an aromatic polyamide composite membrane obtained by hydrolyzing the nascent membrane, referred to as a hydrolyzed membrane; an aromatic polyamide composite membrane obtained by surface modification of the nascent membrane, hydrolyzed membrane or commercial membrane by other methods, referred to as a modified membrane; or an aromatic polyamide composite membrane that has been used and cleaned by physical or chemical methods, referred to as a regenerated membrane.

[0007] Numerous experimental results have demonstrated that structurally suitable quaternary ammonium salts and sulfobetaines possess strong hydration and sterilization and antibacterial properties, and exhibit excellent resistance to protein or microbial surface adhesion, making them a preferred choice for anti-biofouling materials. Furthermore, they can significantly improve the hydrophilicity of the membrane surface and reduce the membrane's water permeation resistance. The flexible stacking and hydration of polyether chains on the membrane surface also exhibit significant anti-biofouling properties. The aromatic isocyanate crosslinker not only chemically reacts with residual intrinsic primary amino groups or intrinsic aramid NH groups on the surface of the aromatic polyamide composite membrane, eliminating chemical degradation of the membrane's inherently vulnerable sites by active chlorine and improving the membrane's chlorine resistance, but also generates newly generated aramid NH units from the reaction of the aromatic isocyanate crosslinker with the residual intrinsic primary amino groups or intrinsic aramid NH groups on the membrane surface, which can replace the membrane's intrinsic aramid NH groups with higher reactivity in chemical reactions with active chlorine in water. Furthermore, the aromatic isocyanate crosslinker crosslinks the chain structure of the aromatic polyamide separation layer, strengthening the interchain structural strength of the separation layer and ensuring efficient and long-lasting operation of the aromatic polyamide composite membrane. In summary, the present invention provides an isocyanate crosslinker containing a quaternary ammonium cation, a bissulfobetaine, and a polyether chain in its molecular structure for surface modification of an aromatic polyamide composite membrane. The invention has the characteristics of wide adaptability of the modification method, multi-directional modification, comprehensive improvement of membrane performance, simple process, and adjustable and controllable operation. Summary of the Invention

[0008] The present invention discloses an application of a functional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite membrane, characterized by the following steps: an aromatic polyamide composite membrane with a clean and dry surface is immersed in a functional isocyanate crosslinking agent solution, or the functional isocyanate crosslinking agent solution is sprayed, brushed, or rolled on the surface of the aromatic polyamide composite membrane, followed by heat treatment at 60-130°C, and recovery of the organic solvent and diluent, to obtain an aromatic polyamide composite membrane with quaternary ammonium cations, sulfobetaine, and polyether chains grafted onto the surface.

[0009] The aromatic polyamide composite membrane is selected from one of a nascent membrane, a hydrolyzed membrane, a modified membrane or a regenerated membrane; the nascent membrane refers to an aromatic polyamide composite membrane directly produced by completing a condensation reaction on a porous polysulfone support membrane or a porous polyethersulfone support membrane using m-phenylenediamine and benzyltricarbonyl chloride as raw materials; the hydrolyzed membrane refers to an aromatic polyamide composite membrane obtained by hydrolysis of the nascent membrane; the modified membrane refers to an aromatic polyamide composite membrane obtained by surface modification of the nascent membrane, hydrolyzed membrane or commercially available aromatic polyamide composite membrane; the regenerated membrane refers to an aromatic polyamide composite membrane that has been used after cleaning using physical or chemical methods.

[0010] The mass percentage concentration of the functional isocyanate crosslinking agent in the multifunctional isocyanate crosslinking agent solution is 0.5-50%; the usage of the multifunctional isocyanate crosslinking agent solution is 5-500% of the mass of the aromatic polyamide composite film.

[0011] The multifunctional isocyanate cross-linking agent has a structure shown in general formula (A):

[0012]

[0013] Wherein R in the general formula (A) is selected from H or methyl, R1, R2, R3 and R4 are selected from C1 to C 18 Hydrocarbon group, R5 is selected from one of H, methyl or chloromethyl, n is selected from a natural number between 0 and 2000, Selected from C1~C 18 Hydrocarbylene, the Selected from C1~C 18 alkylene or One of , where p is selected from a natural number between 1 and 2000.

[0014] The organic solvent is selected from one or more of tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, chlorobenzene, chloroform, 1,2-dichloroethane, hexane, cyclohexane, toluene, xylene, decahydronaphthalene, ethyl acetate, N-methylpyrrolidone, N,N-dimethylaniline, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0015] The multifunctional isocyanate crosslinking agent described in the present invention has three types of functional groups in its molecular structure. The first is the isocyanate group (-NCO), which is a spacer arm that chemically reacts with residual NH2 or intrinsic aromatic amide NH on the surface of the aromatic polyamide composite membrane; the newly generated nascent aromatic amide NH can replace the intrinsic aromatic amide NH on the surface of the aromatic polyamide composite membrane to undergo a chlorine-oxygen reaction; secondly, the quaternary ammonium cation, sulfobetaine and polyether chain have hydrophilic, conductive, antibacterial, antifogging, antifouling or anticoagulant properties, and can produce a hydration layer, a bactericidal and antibacterial layer, and a soft and elastic layer on the membrane surface, all of which will have anti-marine biofouling effects; furthermore, the isocyanate crosslinking agent described in the present invention can chemically crosslink the intrinsic NH in the membrane chain structure, thereby improving physical, chemical or mechanical stability.

[0016] The specific preparation process of the multifunctional isocyanate crosslinking agent of general formula (A) of the present invention is as follows: at room temperature, dissolve general formula (B) in an organic solvent, start stirring and slowly add general formula (C), the amount of general formula (C) is 2.0 to 2.2 times the molar amount of general formula (B); after the addition of general formula (C) is completed, the reaction temperature is increased to 50 to 70°C, the reaction is continued for 2 to 6 hours, and the Michael addition reaction process is terminated; after the temperature of the reaction product system drops to room temperature, dry hydrogen chloride gas is introduced therein, the amount of hydrogen chloride introduced is 2.0 to 2.5 times the molar amount of general formula (B). times, and then slowly add alkylene oxide. After the addition of alkylene oxide is completed, the temperature of the reaction product system is increased to 50-70° C., and the reaction is continued for 2-6 hours. The temperature of the reaction system is maintained, and the catalyst, diluent and polyisocyanate are added to the reaction system in sequence. The stirring and heat-insulating reaction is continued for 2-12 hours. After the NCO content in the material in the reactor is detected to be consistent with the predetermined value, the addition reaction process is terminated; the temperature of the reaction product system is cooled to room temperature to obtain a solution of a multifunctional isocyanate crosslinking agent having a molecular structure represented by general formula (A) and containing a diquaternary ammonium cation, a bissulfobetaine and a polyether chain, which is set aside.

[0017] Wherein the general formula (B) has the following structure:

[0018]

[0019] Wherein R1 and R2 in the general formula (B) are selected from C1 to C18 Hydrocarbyl, Selected from C1~C 18 alkylene or One of , where p is selected from a natural number between 1 and 2000.

[0020] The organic solvent is selected from one or more of tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, chlorobenzene, chloroform, 1,2-dichloroethane, hexane, cyclohexane, toluene, xylene, decahydronaphthalene, ethyl acetate, N-methylpyrrolidone, N,N-dimethylaniline, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide. The amount of the organic solvent used is 1 to 10 times the mass of the general formula (B).

[0021] The general formula (C) refers to acryloyloxypolyether sulfobetaine, which has the structure shown in the general formula (C):

[0022]

[0023] Wherein R3 and R4 in the general formula (C) are selected from C1 to C 18 The hydrocarbon group, R is selected from H or methyl, and n is selected from a natural number between 0 and 2000.

[0024] The alkylene oxide refers to one of ethylene oxide, propylene oxide or epichlorohydrin, and the amount of the alkylene oxide used is 2.0 to 2.5 times the molar amount of the general formula (B).

[0025] The catalyst is a compound of an organic tin and an organic amine; the organic tin is one of dibutyltin dilaurate, stannous octoate, stannous oxalate, dibutyltin dimaleate, di(dodecylsulfide)dibutyltin or dibutyltin diacetate; the organic amine is one of triethylamine, p-dimethylaminopyridine, N,N-dimethylformamide, triethylenediamine, 1,4-dialkylpiperazine, 1-alkylimidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylenediamine carboxylate, 1,4-dialkylpiperazine carboxylate or 1-alkylimidazole carboxylate; the mass ratio of the organic tin to the organic amine is 1:0 to 1.5; the amount of the catalyst is 0.05 to 5% of the mass of the polyisocyanate of general formula (D).

[0026] The diluent refers to one or more of acetone, butanone, cyclohexanone, methyl acetate, ethyl acetate, ether, tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, toluene, xylene, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylformamide, N,N-diethylformamide or hexamethylphosphoramide, and the amount of the diluent is 1 to 10 times the mass of the polyisocyanate of general formula (D).

[0027] The polyisocyanate has a structure shown in general formula (D):

[0028]

[0029] Wherein q in the general formula (D) is selected from a positive integer of 1 to 5, Selected from C1~C 18 alkylene;

[0030] The amount of the polyisocyanate used is 2.02 to 2.25 times the molar amount of the general formula (B).

[0031] Compared with the prior art, the modified aromatic polyamide composite membrane prepared by the present invention has the following advantages:

[0032] ① After the multifunctional isocyanate cross-linking agent of general formula (A) provided by the present invention is applied to the surface modification of the aromatic polyamide composite membrane, the surface of the obtained modified polyaromatic amide composite membrane has super hydrophilicity and high anti-fouling and chlorine resistance.

[0033] ② The multifunctional isocyanate cross-linking agent of the general formula (A) provided by the present invention is applied to the post-chemical modification of the surface of the aromatic polyamide composite membrane. The method is simple and easy to implement and can be easily controlled automatically. DETAILED DESCRIPTION

[0034] Example 1 Application of the multifunctional isocyanate cross-linking agent of formula (1) in the modification of aromatic polyamide composite membrane Preparation of the multifunctional isocyanate cross-linking agent of formula (1)

[0035] 25 g of N,N'-dibenzylethylenediamine was dissolved in 220 g of dimethyl sulfoxide and added to a reactor. Stirring was started and 95 g of methacryloyloxypolyether sulfobetaine of formula (C1) was slowly added at room temperature. After the addition of formula (C1) was completed, the reaction temperature was raised to 55-60 ° C. The reaction was continued for 4 hours to obtain an intermediate solution of formula (1-1). After the temperature of the reaction product system was lowered to room temperature, 10 g of dry hydrogen chloride gas was introduced, and then 12 g of ethylene oxide was slowly added. After the addition of ethylene oxide was completed, the reaction temperature was raised to 55-60 ° C. The reaction temperature was continued for 4 hours to obtain an intermediate solution of formula (1-1). The reaction product system temperature was lowered to room temperature, 10 g of dry hydrogen chloride gas was introduced, and then 12 g of ethylene oxide was slowly added. After completion, the temperature of the reaction product system is raised to 50-70° C., and the reaction is continued for 2 hours to obtain a solution of the intermediate formula (1-2); maintaining the temperature of the reaction system, a mixture of 0.22 g of triethylenediamine and 0.2 g of dibutyltin dilaurate, 180 g of acetone and 36 g of toluene diisocyanate is added to the reaction system, and the stirring reaction is continued for 4 hours to obtain a solution of a multifunctional isocyanate crosslinking agent containing a diquaternary ammonium cation, a bissulfobetaine and a polyether chain in the molecular structure shown in formula (1), which is set aside.

[0036]

[0037]

[0038] The isocyanate group content of an isocyanate crosslinker solution containing a diquaternary ammonium cation, a bissulfobetaine, and a polyether chain in the molecular structure of formula (1) was determined to be 1.51% using the method specified in GB / T 29493.6-2013. After being sealed and stored at room temperature for 180 days under nitrogen, a sample was taken and analyzed again, revealing a mass percentage of isocyanate groups of 1.38%. This indicates that the functional isocyanate crosslinker solution of formula (1) is relatively stable at room temperature and can be used for post-industrial modification of the surface of aromatic polyamide composite membranes.

[0039] The application of the multifunctional isocyanate crosslinker of formula (1) in the surface modification of the new aromatic polyamide composite membrane is carried out according to the method of Journal Membrane Science 428 (2013) 403–409 or Journal Membrane Science 457(2014)88–97, CN103349922B or CN105251372B disclosed methods and steps, using m-phenylenediamine and trimesoyl chloride as monomers, through interfacial polymerization on the surface of a porous polysulfone support membrane, to prepare a nascent aromatic polyamide composite membrane with an area of ​​1*1 cm and containing acyl chloride groups on the surface, immersing the nascent aromatic polyamide composite membrane in a solution of a multifunctional isocyanate crosslinker of formula (1) with a mass percentage concentration of 4-6%, then taking out the membrane and placing it in a press plate at 120°C for heat treatment for 30 minutes, then cooling and washing with deionized water to neutrality to obtain a modified membrane (denoted as A1-1) of the nascent aromatic polyamide composite membrane modified with the multifunctional isocyanate crosslinker of formula (1).

[0040] The application of the multifunctional isocyanate cross-linking agent of formula (1) in the surface modification of a commercial aromatic polyamide composite membrane is to cut a commercial aromatic polyamide composite membrane (BW-30, DuPont FilmTec RO membrane, USA) into 1*1 cm sample membranes, adopt the modification procedure and process of the above-mentioned new aromatic polyamide composite membrane, and use the multifunctional isocyanate cross-linking agent solution of formula (1) to treat the sample membranes to obtain a modified BW-30 membrane (denoted as A1-2) of the commercial aromatic polyamide composite membrane modified with the functional isocyanate cross-linking agent of formula (1).

[0041] Example 2: Application of the multifunctional isocyanate crosslinking agent of formula (2) in the modification of aromatic polyamide composite membrane

[0042] According to the method and operating steps of Example 1, the N,N'-dibenzylethylenediamine in Example 1 is replaced with N,N'-didodecanediamine, ethylene oxide is replaced with epichlorohydrin, and toluene diisocyanate is replaced with diphenylmethane diisocyanate to prepare a solution of a multifunctional isocyanate crosslinking agent of formula (2) for later use.

[0043]

[0044] According to the method and operating steps of Example 1, the surface of the nascent membrane and the commercial membrane were modified using the multifunctional isocyanate crosslinker solution of formula (2) to obtain the modified nascent modified membrane (denoted as A2-1) and the modified BW-30 membrane (denoted as A2-2), respectively.

[0045] Example 3: Application of the multifunctional isocyanate crosslinking agent of formula (3) in the modification of aromatic polyamide composite membrane

[0046] According to the method and operating steps of Example 1, the N,N'-dibenzylethylenediamine in Example 1 is replaced with N,N'-didodecyl-p-phenylenediamine, the methacryloyloxypolyether sulfobetaine of formula (C1) is replaced with the methacryloyloxypolyether sulfobetaine of formula (C2), and the toluene diisocyanate is replaced with diphenylmethane diisocyanate to prepare a solution of a multifunctional isocyanate crosslinking agent of formula (3) for later use.

[0047]

[0048]

[0049] According to the method and operating steps of Example 1, the surface of the nascent membrane and the commercial membrane was modified using the multifunctional isocyanate crosslinker solution of formula (3) to obtain the modified nascent modified membrane (denoted as A3-1) and the BW-30 modified membrane (denoted as A3-2), respectively.

[0050] Example 4: Application of the multifunctional isocyanate crosslinking agent of formula (4) in the modification of aromatic polyamide composite membrane

[0051] According to the method and operating steps of Example 1, the N,N'-dibenzylethylenediamine in Example 1 is replaced with α,ω-bis(benzylamino)polyether-2000, the methacryloyloxypolyether sulfobetaine of formula (C1) is replaced with the methacryloyloxypolyether sulfobetaine of formula (C2), and toluene diisocyanate is replaced with diphenylmethane diisocyanate to prepare a solution of a multifunctional isocyanate crosslinking agent of formula (4) for later use.

[0052]

[0053] According to the method and operating steps of Example 1, the surface of the newly formed aromatic polyamide composite membrane and the commercial aromatic polyamide composite membrane of BW-30 were modified using the multifunctional isocyanate crosslinker solution of formula (4) to obtain the modified newly formed modified membrane (denoted as A4-1) and the modified BW-30 membrane (denoted as A4-2), respectively.

[0054] Example 5 Surface properties of membrane before and after modification

[0055] The water contact angles of the modified fresh membranes, commercial BW-30 membranes, and modified BW-30 membranes prepared in Examples 1 to 4 were measured according to the methods disclosed in Journal of Membrane Science 428 (2013) 403–409 or Journal of Membrane Science 457 (2014) 88–97, CN103349922B, or CN105251372B. The results are shown in Table 1.

[0056] Table 1 Surface properties of membranes before and after modification

[0057]

[0058] The experimental results in Table 1 clearly show that, regardless of whether it is a newly prepared aromatic polyamide composite membrane or a commercial aromatic polyamide composite membrane, after being treated with the multifunctional isocyanate crosslinking agent of the present invention, its surface hydrophilicity is greatly improved, and both exhibit water-wetting phenomenon, indicating that quaternary ammonium cations, sulfobetaine and polyether chains have been successfully grafted onto the surface of the aromatic polyamide composite membrane.

Claims

1. Application of a multifunctional isocyanate crosslinking agent in surface modification of aromatic polyamide composite membrane, characterized in that The method is as follows: the surface of an aromatic polyamide composite membrane after cleaning and drying is hot-dipped in a multifunctional isocyanate crosslinking agent solution, or the multifunctional isocyanate crosslinking agent solution is sprayed, brushed, or rolled on the surface of the aromatic polyamide composite membrane, followed by heat treatment at 60 to 130° C. for 0.2 to 20 hours. The membrane is taken out and cooled to obtain an aromatic polyamide composite membrane with quaternary ammonium cations, sulfobetaine, and polyether chains grafted onto its surface; The multifunctional isocyanate crosslinking agent solution has a mass percentage concentration of 0.5 to 50%; the amount of the multifunctional isocyanate crosslinking agent solution used is 5 to 500% of the mass of the aromatic polyamide composite film; The multifunctional isocyanate cross-linking agent has a structure shown in general formula (A): Wherein R in the general formula (A) is selected from H or methyl, R1, R2, R3 and R4 are selected from C1 to C 18 Hydrocarbon group, R5 is selected from one of H, methyl or chloromethyl, n is selected from a natural number between 0 and 2000, Selected from C1~C 18 Hydrocarbylene, the Selected from C1~C 18 alkylene or One of , where p is selected from a natural number between 1 and 2000.

2. Use of a multifunctional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite film according to claim 1, characterized in that The aromatic polyamide composite membrane is selected from one of a new membrane, a hydrolyzed membrane, a modified membrane or a regenerated membrane; The nascent membrane refers to an aromatic polyamide composite membrane produced by completing a condensation reaction on a porous polysulfone support membrane or a porous polyethersulfone support membrane using m-phenylenediamine and trimesoyl chloride as raw materials; the hydrolyzed membrane refers to an aromatic polyamide composite membrane obtained by hydrolysis of the nascent membrane; the modified membrane refers to an aromatic polyamide composite membrane obtained by surface modification of the nascent membrane, hydrolyzed membrane or commercially available aromatic polyamide composite membrane; the regenerated membrane refers to an aromatic polyamide composite membrane that has been cleaned using physical or chemical methods.

3. Use of a multifunctional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite film according to claim 1, characterized in that The specific preparation process of the multifunctional isocyanate crosslinking agent of general formula (A) is as follows: at room temperature, general formula (B) is dissolved in an organic solvent, and general formula (C) is slowly added with stirring, wherein the amount of general formula (C) is 2.0 to 2.2 times the molar amount of general formula (B); After the addition of the general formula (C) is completed, the reaction temperature is increased to 50-70° C., the reaction is continued for 2-6 hours, the temperature of the reaction system is lowered to room temperature, and dry hydrogen chloride gas is introduced into the reaction system in an amount of 2.0-2.5 times the molar amount of the general formula (B). Then, alkylene oxide is slowly added. After the addition of the alkylene oxide is completed, the temperature of the reaction product system is increased to 50-70° C., the reaction is continued for 2-6 hours, the temperature of the reaction system is maintained, the catalyst, diluent and polyisocyanate are sequentially added to the reaction system, the stirring and heat-insulating reaction is continued for 2-12 hours, and the addition reaction process is terminated after the NCO content of the material in the reactor is detected to be consistent with the predetermined value; the temperature of the reaction product system is lowered to room temperature to obtain a solution of a multifunctional isocyanate crosslinking agent having a molecular structure represented by the general formula (A) and containing a diquaternary ammonium cation, a bissulfobetaine and a polyether chain, which is set aside; Wherein the general formula (B) has the following structure: Wherein R1 and R2 in the general formula (B) are selected from C1 to C 18 Hydrocarbyl, Selected from C1~C 18 alkylene or One of , where p is a natural number between 1 and 2000; The organic solvent is selected from one or more of tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, chlorobenzene, chloroform, 1,2-dichloroethane, hexane, cyclohexane, toluene, xylene, decahydronaphthalene, ethyl acetate, N-methylpyrrolidone, N,N-dimethylaniline, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide, and the amount of the organic solvent is 1 to 10 times the mass of the general formula (B). The general formula (C) refers to acryloyloxypolyether sulfobetaine, which has the structure shown in the general formula (C): Wherein R3 and R4 in the general formula (C) are selected from C1 to C 18 The hydrocarbon group, R is selected from H or methyl, and n is selected from a natural number between 0 and 2000.

4. Use of a multifunctional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite film according to claim 3, characterized in that The alkylene oxide refers to one of ethylene oxide, propylene oxide or epichlorohydrin, and the amount of the alkylene oxide used is 2.0 to 2.5 times the molar amount of the general formula (B).

5. Use of a multifunctional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite film according to claim 3, characterized in that The catalyst is a compound of an organic tin and an organic amine; the organic tin is one of dibutyltin dilaurate, stannous octoate, stannous oxalate, dibutyltin dimaleate, di(dodecylsulfide)dibutyltin or dibutyltin diacetate; the organic amine is one of triethylamine, p-dimethylaminopyridine, N,N-dimethylformamide, triethylenediamine, 1,4-dialkylpiperazine, 1-alkylimidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylenediamine carboxylate, 1,4-dialkylpiperazine carboxylate or 1-alkylimidazole carboxylate; the mass ratio of the organic tin to the organic amine is 1:0 to 1.5; the amount of the catalyst is 0.01 to 5% of the mass of the polyisocyanate of general formula (D).

6. Use of a multifunctional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite film according to claim 3, characterized in that The diluent refers to one or more of acetone, butanone, cyclohexanone, methyl acetate, ethyl acetate, ether, tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, toluene, xylene or dimethyl sulfoxide; the amount of the diluent is 1 to 10 times the mass of general formula (B).

7. Use of a multifunctional isocyanate crosslinking agent in surface modification of an aromatic polyamide composite film according to claim 3, characterized in that The polyisocyanate has a structure shown in general formula (D): Wherein q in the general formula (D) is selected from a positive integer of 1 to 5, Selected from C1~C 18 alkylene; The amount of the polyisocyanate used is 2.02 to 2.25 times the molar amount of the general formula (B).

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