Dual modified polyethersulfone membrane and preparation method thereof

Abstract

The invention discloses a dual-modified polyethersulfone membrane and a preparation method thereof, and relates to the technical field of polyethersulfone membranes. According to the technical scheme, the preparation method comprises the following steps: carboxylating polyether sulfone to obtain carboxylated polyether sulfone; the preparation method comprises the following steps: carrying out cationization treatment on chitosan to prepare cationic chitosan; the prepared carboxylated polyether sulfone, cationic chitosan and an additive are prepared into the dual-modified polyether sulfone membrane through a phase inversion method. The problems of general membrane forming property, insufficient infiltration capacity, poor hydrophilicity, membrane body pollution and the like of the polyether sulfone membrane in the actual use process are solved, meanwhile, the biocompatibility of the polyether sulfone membrane is improved, and the service life of the membrane is also greatly prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of polyethersulfone membranes, in particular to a double-modified polyethersulfone membrane and a preparation method thereof. Background Art

[0002] Polyethersulfone has good stability and excellent mechanical properties, which is due to the flexibility of ether group, the rigidity of benzene ring and the large conjugated system formed by sulfone group and the whole structural unit in its molecular structure. In addition, polyethersulfone also has many excellent properties, such as flame retardant, heat resistant, radiation resistant, anti-oxidant, anti-solvent, etc., and has been more and more widely used in water treatment, reverse osmosis, etc. in recent years. At the same time, it is also increasingly valued in the medical field, especially in the field of blood purification, because of its excellent biocompatibility, it is applied to prepare hemodialysis membrane, composite membrane and plasma separation membrane, etc. However, with the development of membrane science and technology and the continuous expansion of its application field, the performance requirements of membrane are also gradually improved. The film forming property, insufficient permeability, poor hydrophilicity, membrane pollution and other phenomena existing in the actual use process are inevitable, which limits its application and promotion in many fields, and thus it is necessary to carry out functional modification to the membrane.

[0003] Chitosan is widely available in nature. It has become one of the focuses of attention and research in recent years due to its unique biocompatibility, biodegradability, antibacterial properties, film-forming properties, and low toxicity and pollution-free properties. It has broad application prospects in the fields of pharmaceuticals, biomedicine, agriculture, food, environmental protection, and functional materials. Moreover, the physical and chemical properties of chitosan can be further improved by introducing functional groups into the molecular structure of chitosan through chemical reactions such as acylation, etherification, N-alkylation, and esterification.

[0004] Chinese invention patent CN108295677A discloses a modified chitosan / sulfonated polyethersulfone cation exchange membrane and its preparation method, which uses sulfonated polyethersulfone as the membrane matrix and phthalated chitosan or maleated chitosan as an additive. The finished membrane has good mechanical strength, stability, high hydrophilicity and certain antibacterial properties, and is well used in the field of electrodialysis ion exchange membranes. However, the preparation process is complicated, and the contact angle of the modified membrane is still high, indicating that the hydrophilicity is insufficient; the raw materials used, such as sulfonating agents, phthalates, etc., are also dangerous and harmful to the human body during the preparation process, and the residues are difficult to handle, which will affect the environment.

[0005] Therefore, it is necessary to develop new polyethersulfone membrane modification methods to improve their performance. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a double-modified polyethersulfone membrane and a preparation method thereof, solve the problems of general film-forming property, insufficient permeability, poor hydrophilicity, membrane pollution, etc. existing in the actual use of the polyethersulfone membrane, and at the same time improve the biocompatibility of the polyethersulfone membrane, and greatly extend the service life of the membrane.

[0007] The technical solution of the present invention is: On the one hand, the present invention provides a preparation method of a double modified polyethersulfone membrane, comprising the steps of carboxylating polyethersulfone to obtain carboxylated polyethersulfone; cationizing chitosan to obtain cationic chitosan; and preparing the double modified polyethersulfone membrane by a phase inversion method using the prepared carboxylated polyethersulfone, cationic chitosan and an additive; wherein the mass ratio of carboxylated polyethersulfone, cationic chitosan and additive is 1:(0.1-0.3):(0.03-0.07); and the additive is PEG600, polyvinylpyrrolidone (PVP) or LiCl; the preparation method of the carboxylated polyethersulfone comprises the steps of: subjecting polyethersulfone, acetyl chloride and aluminum chloride to an acylation reaction to obtain acetylated polyethersulfone, and then subjecting the acetylated polyethersulfone to an oxidation reaction with potassium permanganate and sodium hydroxide to obtain carboxylated polyethersulfone; and the preparation method of cationic chitosan comprises the steps of: reacting chitosan with a cationic etherifying agent, glycidyl trimethylammonium chloride, to obtain cationic chitosan.

[0008] Preferably, the preparation method of carboxylated polyether sulfone specifically comprises the following steps: (1) Acylation reaction: N-methylpyrrolidone (NMP) is used as a solvent, polyethersulfone is added and stirred thoroughly to form a homogeneous solution, acetyl chloride and aluminum chloride are added, and the mixture is refluxed and stirred at 80-100°C for 2-5 hours, then washed with deionized water, filtered, continued to be washed, and dried to obtain acetylated polyethersulfone; (2) Oxidation reaction: The acetylated polyethersulfone is further dissolved in NMP to form a homogeneous solution, and a mixed solution of potassium permanganate, sodium hydroxide and NMP is added. The mixture is stirred at 70-100°C for 5-8 hours, and then filtered, washed and dried to obtain carboxylated polyethersulfone.

[0009] Preferably, in step (1), the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride is 1:(6-8):(1-1.2), and the concentration of the homogeneous solution is 20-30wt.%; in step (2), the molar ratio of acetylated polyethersulfone, potassium permanganate and sodium hydroxide is 1:(0.2-0.4):(0.1-0.3), and the concentration of the homogeneous solution is 20-30wt.%.

[0010] Preferably, the preparation method of cationic chitosan is: chitosan is dissolved in a mixed solvent of isopropanol and water, the water content in the mixed solvent is 35-45wt.%, and then the cationic etherifying agent glycidyl trimethyl ammonium chloride is added dropwise for reaction, the dropping method is that the first 2min drop rate is 1-3mL / min, and then the drop rate increases by 1mL per minute until the drop addition is completed; finally, after acetone precipitation, it is repeatedly washed with anhydrous ethanol and dried to obtain cationic chitosan. Among them, the water content in the mixed solvent will affect the reaction, the water content is too low, the solution is viscous, and the reaction cannot proceed; the water content is too high, which will cause the cationic etherifying agent to hydrolyze, affecting the reaction efficiency and the degree of substitution of cationic chitosan.

[0011] Preferably, the molar ratio of the cationic etherifying agent to chitosan is (3-6):1, and the mass ratio of the cationic etherifying agent to isopropanol is (0.04-0.07):1; the acetone is added dropwise under continuous stirring until no new precipitate is generated; the reaction temperature is 70-90°C, and the reaction time is 7-9h. The amount of cationic etherifying agent added, the reaction temperature, and the reaction time will affect the cationization of chitosan. If the amount of cationic etherifying agent added is too little, the cationization is insufficient; but if the amount of cationic etherifying agent added is too much, it will be difficult to replace the hydroxyl group due to the increased steric hindrance, thereby affecting the reaction efficiency. If the reaction temperature is too low and the reaction time is too short, the reaction cannot be fully carried out; and if the reaction temperature is too high and the reaction time is too long, the cationic etherifying agent will decompose, thereby affecting the reaction efficiency and the degree of substitution of cationic chitosan.

[0012] Preferably, the phase inversion method for preparing the double modified polyethersulfone membrane comprises the following steps: 1) Dissolve carboxylated polyethersulfone and additives in NMP to form a homogeneous casting solution, and then dissolve cationic chitosan in NMP to form a homogeneous solution; add the homogeneous solution dropwise into the homogeneous casting solution at 40-60°C and stir continuously, the dropping method is that the dropping rate is 1-3mL / min in the first 5 minutes, and then the dropping rate increases by 0.5mL per minute, and finally maintains at 5mL / min; the stirring speed is 150-250r / min in the first 5 minutes, and then increases by 50r per minute as the dropping rate increases, and finally maintains at 500r / min; continue stirring after the dropping is completed After 0.5-1h, the mixture is filtered, allowed to stand and degassed to obtain a cationic chitosan / carboxylated polyethersulfone homogeneous film casting solution; wherein the stirring speed and the dripping method have a great influence on the crosslinking reaction, and the present invention adopts a method of slowly dripping and gradually accelerating the dripping rate, so that the cationic chitosan and the carboxylated polyethersulfone can fully undergo a crosslinking reaction, and the final yield is higher; in addition, if the stirring speed is too slow, the reaction efficiency will be reduced, and if the stirring speed is too fast, the cationic chitosan / carboxylated polyethersulfone homogeneous film casting solution will not undergo a crosslinking reaction with the homogeneous solution containing the cationic chitosan added due to the effect of centrifugal force; 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting liquid onto a glass plate, quickly scrape the membrane with a glass rod, and obtain a double-modified polyethersulfone membrane on the glass plate after solidification and phase separation in deionized water; evaporate the double-modified polyethersulfone membrane together with the glass plate, soak the glass plate in deionized water, and separate the double-modified polyethersulfone membrane.

[0013] Preferably, in step 1), the content of cationic chitosan and carboxylated polyethersulfone in the cationic chitosan / carboxylated polyethersulfone homogeneous casting solution is 18-25 wt.%.

[0014] Preferably, in step 2), the evaporation method is: first evaporate at room temperature for 2-4 hours, then evaporate at 70-90°C for 12 hours, and finally dry at 50-60°C for 12 hours; the glass plate is immersed in deionized water for more than 8 hours, after which the double modified polyethersulfone membrane can be directly removed from the glass plate.

[0015] On the other hand, the present invention provides a double modified polyethersulfone membrane, which is prepared by the above-mentioned preparation method of the double modified polyethersulfone membrane.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention connects carboxylate ions to polyethersulfone to make the polyethersulfone negatively charged, so that the prepared double-modified polyethersulfone membrane has better permeability and anti-pollution performance, and also has better interception performance. In addition, the present invention does not need to add a crosslinking agent, but uses the electrostatic attraction between positive and negative charges to connect the positively charged cationic chitosan to the surface of the negatively charged carboxylated polyethersulfone (such as Figure 1 As shown in the figure, the double-modified polyethersulfone membrane has the advantages of both carboxylated polyethersulfone and cationic chitosan, and has excellent hydrophilicity, permeability, biocompatibility, good film-forming performance, and a longer service life than ordinary polyethersulfone membranes.

[0017] 2. Since the negatively charged carboxylated polyethersulfone and the positively charged cationic chitosan in the present invention both have excellent antibacterial and sterilization properties, the prepared double-modified polyethersulfone membrane has better antibacterial and sterilization capabilities than general antibacterial membranes, and can better cope with membrane contamination and reduce bacterial adsorption.

[0018] 3. The double-modified polyethersulfone membrane prepared by the present invention can be applied to a wider range of fields and has good use effects. It can be used for hemodialysis and can prevent thrombosis due to its biocompatibility. It can also be used for wastewater purification, for flocculation and sterilization of wastewater and for adsorption of heavy metal ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1It is a schematic diagram of the present invention in which the cationic chitosan with positive charge is connected to the surface of the negatively charged carboxylated polyethersulfone. DETAILED DESCRIPTION

[0020] In order to enable persons skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0021] Example 1 The preparation method of the double modified polyethersulfone membrane of this embodiment comprises the following steps: S1 prepares carboxylated polyethersulfone, including two steps of acylation and oxidation, and the specific operation is as follows: (1) Acylation reaction: NMP is used as a solvent, polyethersulfone is added and stirred thoroughly to form a 25wt.% homogeneous solution, acetyl chloride and aluminum chloride are added according to the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride of 1:7:1.1, poured into a flask, refluxed and stirred at 90°C for 3h, then washed with deionized water, filtered, continued to wash, and dried to obtain acetylated polyethersulfone; (2) Oxidation reaction: The acetylated polyethersulfone is further dissolved in NMP to form a 25 wt.% homogeneous solution, which is then poured into a flask. A mixed solution of potassium permanganate, sodium hydroxide and NMP is then added according to a molar ratio of acetylated polyethersulfone, potassium permanganate and sodium hydroxide of 1:0.3:0.25. The mixture is stirred at 85°C for 7 hours, filtered, washed and dried to obtain carboxylated polyethersulfone.

[0022] S2 Preparation of Cationic Chitosan Chitosan was dissolved in a mixed solvent of isopropanol and water, wherein the water content of the mixed solvent was 38 wt.%, and then a cationic etherifying agent, glycidyl trimethyl ammonium chloride, was added dropwise, and the mixture was reacted at 80°C for 8 hours; wherein the molar ratio of the cationic etherifying agent to chitosan was 4:1, and the mass ratio of the cationic etherifying agent to isopropanol was 0.05:1; the dropping method was that the dropping rate was 2 mL / min for the first 2 minutes, and then the dropping rate was increased by 1 mL per minute until the dropping was completed; finally, acetone was added dropwise under continuous stirring until no new precipitate was generated, and the mixture was repeatedly washed with anhydrous ethanol and dried to obtain cationic chitosan.

[0023] Preparation of double modified polyethersulfone membrane by S3 1) The prepared carboxylated polyethersulfone and the additive LiCl are dissolved in NMP to form a homogeneous casting solution, and then the cationic chitosan is dissolved in NMP to form a homogeneous solution, wherein the mass ratio of the carboxylated polyethersulfone, the additive and the cationic chitosan is 1:0.05:0.2; the homogeneous solution is added dropwise to the homogeneous casting solution at 50°C and stirred continuously, and the dropping method is that the dropping rate is 2mL / min in the first 5min, and the dropping rate increases by 0.5mL per minute thereafter, and finally maintained at 5mL / min; the stirring speed is 200r / min in the first 5min, and then increases by 50r per minute as the dropping rate increases, and finally maintained at 500r / min; after the dropping is completed, the stirring is continued for 0.5h, and then filtered, allowed to stand, and degassed to obtain a cationic chitosan / carboxylated polyethersulfone homogeneous casting solution with a cationic chitosan and carboxylated polyethersulfone content of 22wt.%; 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting liquid onto a glass plate, quickly scrape the membrane with a glass rod, and obtain a double-modified polyethersulfone membrane on the glass plate after solidification and phase separation in deionized water; evaporate the double-modified polyethersulfone membrane together with the glass plate, first evaporate at room temperature for 3 hours, then evaporate in an oven at 80°C for 12 hours, and finally dry at 55°C for 12 hours; soak the evaporated glass plate in deionized water for 12 hours, and separate the double-modified polyethersulfone membrane.

[0024] Example 2 The preparation method of the double modified polyethersulfone membrane of this embodiment comprises the following steps: S1 prepares carboxylated polyethersulfone, including two steps of acylation and oxidation, and the specific operation is as follows: (1) Acylation reaction: NMP is used as a solvent, polyethersulfone is added and stirred thoroughly to form a 20wt.% homogeneous solution, acetyl chloride and aluminum chloride are added according to the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride of 1:6:1, poured into a flask, refluxed and stirred at 80°C for 5h, then washed with deionized water, filtered, continued to wash, and dried to obtain acetylated polyethersulfone; (2) Oxidation reaction: The acetylated polyethersulfone is further dissolved in NMP to form a 20 wt.% homogeneous solution, which is then poured into a flask. A mixed solution of potassium permanganate, sodium hydroxide and NMP is then added according to a molar ratio of acetylated polyethersulfone, potassium permanganate and sodium hydroxide of 1:0.2:0.1. The mixture is stirred at 70°C for 8 h, filtered, washed and dried to obtain carboxylated polyethersulfone.

[0025] S2 Preparation of Cationic Chitosan Chitosan was dissolved in a mixed solvent of isopropanol and water, wherein the water content of the mixed solvent was 35wt.%, and then a cationic etherifying agent, glycidyl trimethyl ammonium chloride, was added dropwise, and the reaction was carried out at 70°C for 9h; wherein the molar ratio of the cationic etherifying agent to chitosan was 3:1, and the mass ratio of the cationic etherifying agent to isopropanol was 0.04:1; the dropping method was that the dropping rate was 1mL / min for the first 2min, and then the dropping rate was increased by 1mL per minute until the dropping was completed; finally, acetone was added dropwise under continuous stirring until no new precipitate was generated, and the cationic chitosan was obtained after repeated washing with anhydrous ethanol and drying.

[0026] Preparation of double modified polyethersulfone membrane by S3 1) The prepared carboxylated polyethersulfone and the additive PVP are dissolved in NMP to form a homogeneous casting liquid, and then cationic chitosan is dissolved in NMP to form a homogeneous solution, wherein the mass ratio of carboxylated polyethersulfone, additive and cationic chitosan is 1:0.03:0.1; the homogeneous solution is added dropwise to the homogeneous casting liquid at 40°C and stirred continuously, and the dropping method is that the dropping rate is 1mL / min in the first 5min, and then the dropping rate increases by 0.5mL per minute, and finally maintained at 5mL / min; the stirring speed is 150r / min in the first 5min, and then increases by 50r per minute as the dropping rate increases, and finally maintained at 500r / min; after the dropwise addition is completed, the stirring is continued for 0.5h, and then filtered, allowed to stand, and degassed to obtain a cationic chitosan / carboxylated polyethersulfone homogeneous casting liquid with a cationic chitosan and carboxylated polyethersulfone content of 18wt.%; 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting liquid onto a glass plate, quickly scrape the membrane with a glass rod, and obtain a double-modified polyethersulfone membrane on the glass plate after solidification and phase separation in deionized water; evaporate the double-modified polyethersulfone membrane together with the glass plate, first evaporate at room temperature for 4 hours, then evaporate in an oven at 70°C for 12 hours, and finally dry at 50°C for 12 hours; soak the evaporated glass plate in deionized water for 12 hours, and separate the double-modified polyethersulfone membrane.

[0027] Example 3 The preparation method of the double modified polyethersulfone membrane of this embodiment comprises the following steps: S1 prepares carboxylated polyethersulfone, including two steps of acylation and oxidation, and the specific operation is as follows: (1) Acylation reaction: NMP is used as a solvent, polyethersulfone is added and stirred thoroughly to form a 30wt.% homogeneous solution, acetyl chloride and aluminum chloride are added according to the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride of 1:8:1.2, poured into a flask, refluxed and stirred at 100°C for 2h, then washed with deionized water, filtered, continued to wash, and dried to obtain acetylated polyethersulfone; (2) Oxidation reaction: The acetylated polyethersulfone is further dissolved in NMP to form a 30 wt.% homogeneous solution, which is then poured into a flask. A mixed solution of potassium permanganate, sodium hydroxide and NMP is then added according to a molar ratio of acetylated polyethersulfone, potassium permanganate and sodium hydroxide of 1:0.4:0.3. The mixture is stirred at 100°C for 5 h, filtered, washed and dried to obtain carboxylated polyethersulfone.

[0028] S2 Preparation of Cationic Chitosan Chitosan was dissolved in a mixed solvent of isopropanol and water, wherein the water content of the mixed solvent was 45wt.%, and then a cationic etherifying agent, glycidyl trimethyl ammonium chloride, was added dropwise, and the reaction was carried out at 90°C for 7h; wherein the molar ratio of the cationic etherifying agent to chitosan was 6:1, and the mass ratio of the cationic etherifying agent to isopropanol was 0.07:1; the dropping method was that the dropping rate was 3mL / min for the first 2min, and then the dropping rate was increased by 1mL per minute until the dropping was completed; finally, acetone was added dropwise under continuous stirring until no new precipitate was generated, and the cationic chitosan was obtained after repeated washing with anhydrous ethanol and drying.

[0029] Preparation of double modified polyethersulfone membrane by S3 1) The prepared carboxylated polyethersulfone and the additive PEG600 are dissolved in NMP to form a homogeneous casting solution, and then cationic chitosan is dissolved in NMP to form a homogeneous solution, wherein the mass ratio of carboxylated polyethersulfone, additive and cationic chitosan is 1:0.07:0.3; the homogeneous solution is added dropwise to the homogeneous casting solution at 60°C and stirred continuously, and the dropping method is that the dropping rate is 3mL / min in the first 5min, and the dropping rate increases by 0.5mL per minute thereafter, and finally maintained at 5mL / min; the stirring speed is 250r / min in the first 5min, and then increases by 50r per minute as the dropping rate increases, and finally maintained at 500r / min; after the dropping is completed, the stirring is continued for 1h, and then filtered, allowed to stand, and degassed to obtain a cationic chitosan / carboxylated polyethersulfone homogeneous casting solution with a cationic chitosan and carboxylated polyethersulfone content of 25wt.%; 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting liquid onto a glass plate, quickly scrape the membrane with a glass rod, and obtain a double-modified polyethersulfone membrane on the glass plate after solidification and phase separation in deionized water; evaporate the double-modified polyethersulfone membrane together with the glass plate, first evaporate at room temperature for 2 hours, then evaporate in an oven at 90°C for 12 hours, and finally dry at 60°C for 12 hours; soak the evaporated glass plate in deionized water for 12 hours, and separate the double-modified polyethersulfone membrane.

[0030] Comparative Example 1 The difference from Example 1 is that step S1 is not performed, and in step S3, polyethersulfone is used instead of carboxylated polyethersulfone.

[0031] Comparative Example 2 The difference from Example 1 is that step S2 is not performed, and in step S3, chitosan is used instead of cationic chitosan.

[0032] Comparative Example 3 The difference from Example 1 is that step S2 is not performed, and in step 1), the prepared carboxylated polyether sulfone and the additive LiCl are dissolved in NMP at a mass ratio of 1:0.05 to form a homogeneous casting solution, which is stirred for 0.5 h and then filtered, allowed to stand, and degassed to obtain a carboxylated polyether sulfone homogeneous casting solution.

[0033] Comparative Example 4 The difference from Example 1 is that in step S2, the molar ratio of the cationic etherifying agent to chitosan is 8:1.

[0034] Comparative Example 5 The difference from Example 1 is that in step S2, the reaction temperature is 100° C. and the reaction time is 11 h.

[0035] Comparative Example 6 The difference from Example 1 is that in step S2, the water content in the mixed solvent is 55 wt.%.

[0036] Comparative Example 7 The difference from Example 1 is that in step 1), a uniform dropping method is adopted during the dropping process, the dropping rate is 3 mL / min, and the stirring speed is 350 r / min.

[0037] Comparative Example 8 The difference from Example 1 is that in step 1), a uniform dropping method is adopted during the dropping process, the dropping rate is 5 mL / min, and the stirring speed is 500 r / min.

[0038] The performance of the polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 was tested in the following manner: Hydrophilicity test: The contact angle of the polyethersulfone membrane was directly tested using a contact angle meter.

[0039] Antibacterial performance test: The unmodified polyethersulfone membrane was used as a blank control sample, and the polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 were used as samples. The blank control samples and samples of the same area were cultured with the bacterial suspension for 2 hours, and the antibacterial rate was calculated according to the following formula: Antibacterial rate = ; Wherein, B-the average number of recovered bacteria of blank control sample, pieces; C-the average number of recovered bacteria of polyethersulfone membrane sample, pieces.

[0040] Retention performance test: bovine serum albumin (BSA) was used as the feed liquid at a concentration of 1000 mg / L. The polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 were tested at the same simulated flow rate (200 mL / min) and the same membrane inner diameter (0.3 mm) to simulate the concentration of BSA in the permeate after BSA continuously passed through the polyethersulfone membrane for 24 hours. The retention rate was calculated according to the following formula: Retention rate = ; In the formula, C f - BSA concentration in feed solution, mg / L; C p -BSA concentration in the permeate, mg / L.

[0041] The performance test results of the polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 are shown in Table 1: Table 1 Performance test results of polyethersulfone membranes of Examples 1-3 and Comparative Examples 1-8

[0042] In Example 1, carboxylated polyethersulfone is first prepared, and then cationic chitosan is grafted onto the carboxylated polyethersulfone by utilizing the electrostatic attraction of positive and negative charges, so that the prepared double-modified polyethersulfone membrane has both characteristics, and has better hydrophilicity, antibacterial property and interception performance, and also has better film-forming property and longer service life. However, in Comparative Example 1, carboxylated polyethersulfone is not prepared, and in Comparative Example 2, chitosan is not cationized, so cationic chitosan cannot be grafted onto the carboxylated polyethersulfone by utilizing the electrostatic attraction of positive and negative charges, and the grafting effect at this time is poor, and a cross-linking agent must be added to carry out the cross-linking reaction, otherwise the effect of Example 1 cannot be achieved.

[0043] Compared with the double modified polyethersulfone membrane of Example 1, the hydrophilicity, antibacterial property and interception performance of the carboxylated polyethersulfone membrane prepared in Comparative Example 3 are all poor. Overall, the various properties of the double modified polyethersulfone membrane are better than those of the carboxylated polyethersulfone membrane. This is because the unique biocompatibility, biodegradability, antibacterial property, film-forming property and low toxicity and pollution-free characteristics of cationic chitosan make the various properties of the prepared double modified polyethersulfone membrane better.

[0044] It can be seen from Example 1 and Comparative Examples 4-6 that the amount of cationic etherifying agent used, the reaction temperature, the reaction time, and the water content of the mixed solvent will affect the reaction efficiency and substitution degree of the prepared cationic chitosan. Excessive use of the cationic etherifying agent will increase the steric hindrance, making it difficult for the hydroxyl group to be substituted, thereby reducing the reaction efficiency; too long a reaction time, too high a reaction temperature, or too high a water content of the mixed solvent will all lead to the hydrolysis of the cationic etherifying agent, thereby affecting the substitution degree of the cationic chitosan and reducing the reaction efficiency.

[0045] It can be seen from Example 1 and Comparative Examples 7-8 that both the dripping method and the stirring speed will affect the cross-linking reaction of carboxylated polyether sulfone and cationic chitosan. The dripping method of slowing down first and then accelerating is more conducive to the dispersion of cationic chitosan into the homogeneous film casting liquid, and then cross-linking reaction with the carboxylated polyether sulfone; if the uniform dripping method is adopted, the cationic chitosan in the system will adhere and aggregate, and it will not be easy to disperse and cross-link with the carboxylated polyether sulfone. At the same time, the stirring method of slowing down first and then gradually accelerating is also conducive to the cross-linking reaction after the reactants are dispersed, and if the faster uniform stirring method in Comparative Example 8 is always adopted, a part of the homogeneous film casting liquid may not react with the solution containing cationic chitosan added due to the effect of centrifugal force, affecting the yield.

[0046] In summary, the present invention utilizes the electrostatic attraction between positive and negative charges, and does not need to add a cross-linking agent, so that the positively charged cationic chitosan is connected to the surface of the negatively charged carboxylated polyethersulfone, so that the prepared double modified polyethersulfone membrane has the advantages of carboxylated polyethersulfone and cationic chitosan at the same time, has excellent hydrophilicity, permeability, and biocompatibility, and has good film-forming performance, strong antibacterial ability, can better deal with membrane pollution, reduce bacterial adsorption, and has a longer service life than general polyethersulfone membranes. These advantages enable the double modified polyethersulfone membrane of the present invention to be applied to a wider range of fields and have better use effects.

Claims

1. A method for preparing a double modified polyethersulfone membrane, characterized in that: Carboxylation of polyethersulfone is performed to obtain carboxylated polyethersulfone; chitosan is cationized to obtain cationic chitosan; the obtained carboxylated polyethersulfone, cationic chitosan and additives are used to prepare a double modified polyethersulfone membrane through a phase inversion method; wherein the mass ratio of carboxylated polyethersulfone, cationic chitosan and additive is 1:(0.1-0.3):(0.03-0.07); the additive is PEG600, polyvinylpyrrolidone or LiCl; the preparation method of carboxylated polyethersulfone is as follows: polyethersulfone, acetyl chloride and aluminum chloride are subjected to acylation reaction to obtain acetylated polyethersulfone, and the acetylated polyethersulfone is then subjected to oxidation reaction with potassium permanganate and sodium hydroxide to obtain carboxylated polyethersulfone; the preparation method of cationic chitosan is as follows: chitosan is reacted with a cationic etherifying agent, glycidyl trimethylammonium chloride, to obtain cationic chitosan.

2. The method for preparing a double modified polyethersulfone membrane according to claim 1, characterized in that: The preparation method of carboxylated polyether sulfone specifically comprises the following steps: (1) Acylation reaction: N-methylpyrrolidone is used as a solvent, polyethersulfone is added and stirred thoroughly to form a homogeneous solution, acetyl chloride and aluminum chloride are added, and the mixture is refluxed and stirred at 80-100°C for 2-5 hours, then washed with deionized water, filtered, washed again, and dried to obtain acetylated polyethersulfone; (2) Oxidation reaction: The acetylated polyethersulfone is further dissolved in N-methylpyrrolidone to form a homogeneous solution, and a mixed solution of potassium permanganate, sodium hydroxide and N-methylpyrrolidone is added. The mixture is stirred at 70-100°C for 5-8 hours, and then filtered, washed and dried to obtain carboxylated polyethersulfone.

3. The method for preparing a double modified polyethersulfone membrane according to claim 2, characterized in that: In step (1), the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride is 1:(6-8):(1-1.2), and the concentration of the homogeneous solution is 20-30wt.%; in step (2), the molar ratio of acetylated polyethersulfone, potassium permanganate and sodium hydroxide is 1:(0.2-0.4):(0.1-0.3), and the concentration of the homogeneous solution is 20-30wt.%.

4. The method for preparing a double modified polyethersulfone membrane according to claim 1, characterized in that: The preparation method of cationic chitosan is as follows: dissolving chitosan in a mixed solvent of isopropanol and water, wherein the water content in the mixed solvent is 35-45wt.%, and then dropping a cationic etherifying agent, glycidyl trimethylammonium chloride, to react, wherein the dropping method is that the dropping rate is 1-3mL / min in the first 2 minutes, and then the dropping rate is increased by 1mL per minute until the dropping is completed; finally, acetone is added for precipitation, and the mixture is repeatedly washed with anhydrous ethanol and dried to obtain cationic chitosan.

5. The method for preparing a double modified polyethersulfone membrane according to claim 4, characterized in that: The molar ratio of the cationic etherifying agent to chitosan is (3-6):1, and the mass ratio of the cationic etherifying agent to isopropanol is (0.04-0.07):1; the acetone is added dropwise under continuous stirring until no new precipitate is generated; the reaction temperature is 70-90°C, and the reaction time is 7-9h.

6. The method for preparing a double modified polyethersulfone membrane according to claim 1, characterized in that: The phase inversion method for preparing the double modified polyethersulfone membrane comprises the following steps: 1) Dissolve the carboxylated polyethersulfone and the additive in N-methylpyrrolidone to form a homogeneous casting solution, and then dissolve the cationic chitosan in N-methylpyrrolidone to form a homogeneous solution; add the homogeneous solution dropwise into the homogeneous casting solution at 40-60°C and stir continuously, the dropping method is that the dropping rate is 1-3mL / min in the first 5 minutes, and then the dropping rate increases by 0.5mL per minute, and finally maintains at 5mL / min; the stirring speed is 150-250r / min in the first 5 minutes, and then increases by 50r per minute as the dropping rate increases, and finally maintains at 500r / min; after the dropping is completed, continue stirring for 0.5-1h, filter, stand, and degas, and obtain a cationic chitosan / carboxylated polyethersulfone homogeneous casting solution; 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting liquid onto a glass plate, quickly scrape the membrane with a glass rod, and obtain a double-modified polyethersulfone membrane on the glass plate after solidification and phase separation in deionized water; evaporate the double-modified polyethersulfone membrane together with the glass plate, soak the glass plate in deionized water, and separate the double-modified polyethersulfone membrane.

7. The method for preparing a double modified polyethersulfone membrane according to claim 6, characterized in that: In step 1), the content of cationic chitosan and carboxylated polyethersulfone in the cationic chitosan / carboxylated polyethersulfone homogeneous casting solution is 18-25wt.%.

8. The method for preparing a double modified polyethersulfone membrane according to claim 6, characterized in that: In step 2), the evaporation method is: first evaporate at room temperature for 2-4 hours, then evaporate at 70-90°C for 12 hours, and finally dry at 50-60°C for 12 hours; the glass plate is immersed in deionized water for more than 8 hours.

9. Double modified polyethersulfone membrane, characterized in that: The double-modified polyethersulfone membrane is prepared by the preparation method of any one of claims 1 to 8.

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