Double modified polyethersulfone membrane and preparation method thereof

Abstract

The present invention discloses a double-modified polyethersulfone membrane and a preparation method thereof, relating to the technical field of polyethersulfone membranes. The technical solution comprises: carboxylating polyethersulfone to produce carboxylated polyethersulfone; cationizing chitosan to produce cationic chitosan; and then combining the prepared carboxylated polyethersulfone, cationic chitosan, and additives via a phase inversion method to produce the double-modified polyethersulfone membrane. The present invention addresses the problems of poor film-forming properties, insufficient permeability, poor hydrophilicity, and membrane contamination that often occur in polyethersulfone membranes during actual use. It also improves the biocompatibility of the polyethersulfone membrane and significantly extends the membrane's service life.

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 the ether group, the rigidity of the benzene ring and the large conjugated system formed by the sulfone group and the entire 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 increasingly widely used in water treatment, reverse osmosis, etc. in recent years. 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 membranes, composite membranes and plasma separation membranes. However, with the development of membrane science and technology and the continuous expansion of its application fields, the performance requirements of membranes are also gradually improved. The inevitable phenomena such as general film forming property, insufficient permeability, poor hydrophilicity and membrane body pollution in actual use have limited its application and promotion in many fields, thus requiring functional modification of membranes.

[0003] Chitosan, a widely available natural resource, has become a focus of recent research and attention due to its unique biocompatibility, biodegradability, antimicrobial properties, film-forming properties, and low toxicity and non-polluting properties. It holds broad application prospects in pharmaceuticals, biomedicine, agriculture, food, environmental protection, and functional materials. Furthermore, the physical and chemical properties of chitosan can be further improved by introducing functional groups into its molecular structure 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. The membrane is made with sulfonated polyethersulfone as the membrane matrix and phthalated chitosan or maleated chitosan as additives. The finished membrane exhibits good mechanical strength, stability, high hydrophilicity, and moderate antibacterial properties, and is well-suited for electrodialysis ion exchange membrane applications. However, the preparation process is complex, and the contact angle of the modified membrane remains high, indicating insufficient hydrophilicity. The raw materials used, such as the sulfonating agent and phthalate, are also hazardous and harmful to the human body during the preparation process. Furthermore, residual residues are difficult to dispose of and can have an impact on the environment.

[0005] Therefore, new polyethersulfone membrane modification methods need to be developed to improve their performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology, provide a double-modified polyethersulfone membrane and a preparation method thereof, solve the problems of general film forming properties, insufficient permeability, poor hydrophilicity, membrane contamination, 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:

[0008] On the one hand, the present invention provides a preparation method of a double-modified polyethersulfone membrane, comprising the following steps: 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 the 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; and preparing the carboxylated polyethersulfone by: performing an acylation reaction on polyethersulfone, acetyl chloride, and aluminum chloride to obtain acetylated polyethersulfone, and then performing an oxidation reaction on the acetylated polyethersulfone with potassium permanganate and sodium hydroxide to obtain carboxylated polyethersulfone; and preparing the cationic chitosan by: reacting chitosan with a cationic etherifying agent, glycidyltrimethylammonium chloride, to obtain cationic chitosan.

[0009] Preferably, the preparation method of carboxylated polyethersulfone specifically comprises the following steps:

[0010] (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, washed again, and dried to obtain acetylated polyethersulfone;

[0011] (2) Oxidation reaction: 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.

[0012] 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 20-30 wt.%; 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 20-30 wt.%.

[0013] Preferably, the preparation method of cationic chitosan is as follows: chitosan is dissolved in a mixed solvent of isopropanol and water, wherein the water content in the mixed solvent is 35-45wt.%, and then a cationic etherifying agent, glycidyl trimethylammonium chloride, is added dropwise to react, wherein the addition method is that the dropwise addition rate is 1-3mL / min for the first 2min, and then the dropwise addition rate is increased by 1mL per minute until the addition is complete; finally, after acetone precipitation, the mixture is repeatedly washed with anhydrous ethanol and dried to obtain cationic chitosan. Among them, the water content in the mixed solvent affects the reaction. If the water content is too low, the solution becomes viscous and the reaction cannot proceed; if the water content is too high, the cationic etherifying agent will be hydrolyzed, affecting the reaction efficiency and the degree of substitution of the cationic chitosan.

[0014] 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. Acetone is added dropwise with continuous stirring until no new precipitate forms. The reaction temperature is 70-90°C, and the reaction time is 7-9 hours. The amount of cationic etherifying agent added, the reaction temperature, and the reaction time all affect the cationization of chitosan. Too little cationic etherifying agent results in insufficient cationization; however, too much cationic etherifying agent increases steric hindrance, hindering hydroxyl substitution, thus affecting reaction efficiency. Too low a reaction temperature or too short a reaction time prevents the reaction from proceeding fully. Too high a reaction temperature or too long a reaction time causes decomposition of the cationic etherifying agent, thus affecting reaction efficiency and the degree of substitution of the cationic chitosan.

[0015] Preferably, the phase inversion method for preparing the double-modified polyethersulfone membrane comprises the following steps:

[0016] 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 to the homogeneous casting solution at 40-60°C and stir continuously. The dropwise addition method is as follows: the dropwise addition rate is 1-3 mL / min for the first 5 minutes, and then the dropwise addition rate increases by 0.5 mL per minute, and finally maintains at 5 mL / min; the stirring speed is 150-250 r / min for the first 5 minutes, and then increases by 50 r / min as the dropwise addition rate increases, and finally maintains at 500 r / min; continue stirring after the dropwise addition is completed After 0.5-1h, the mixture is filtered, allowed to stand, and degassed to obtain a cationic chitosan / carboxylated polyethersulfone homogeneous casting solution. The stirring speed and the dropwise addition method have a significant impact on the crosslinking reaction. The present invention adopts a method of slowly dropping and gradually increasing the dropwise addition rate, which can fully allow the cationic chitosan and the carboxylated polyethersulfone to undergo a crosslinking reaction, thereby increasing the final yield. In addition, if the stirring speed is too slow, the reaction efficiency will be reduced, while if the stirring speed is too fast, the cationic chitosan / carboxylated polyethersulfone homogeneous casting solution will not undergo a crosslinking reaction with the homogeneous solution containing the cationic chitosan added due to the action of centrifugal force.

[0017] 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting solution onto a glass plate and quickly scrape the membrane with a glass rod. After solidification and phase separation in deionized water, a double-modified polyethersulfone membrane is obtained on the glass plate. After the double-modified polyethersulfone membrane and the glass plate are evaporated to dryness, the glass plate is immersed in deionized water and separated to obtain the double-modified polyethersulfone membrane.

[0018] 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.%.

[0019] Preferably, in step 2), the evaporation method is: first evaporating at room temperature for 2-4 hours, then evaporating at 70-90°C for 12 hours, and finally drying 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.

[0020] On the other hand, the present invention provides a double-modified polyethersulfone membrane prepared by the above-mentioned preparation method of the double-modified polyethersulfone membrane.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention connects carboxylate ions to polyethersulfone, making the polyethersulfone negatively charged, so that the prepared double-modified polyethersulfone membrane has better permeability and anti-pollution performance, and at the same time has better retention performance. In addition, the present invention does not require the addition of a cross-linking agent, but instead utilizes 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.

[0023] 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 deal with membrane contamination and reduce bacterial adsorption.

[0024] 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, due to its biocompatibility, can prevent thrombosis. 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

[0025] Figure 1 Schematic diagram of the present invention showing that the positively charged cationic chitosan is attached to the surface of the negatively charged carboxylated polyethersulfone. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0027] Example 1

[0028] The preparation method of the double-modified polyethersulfone membrane of this embodiment comprises the following steps:

[0029] S1 prepares carboxylated polyethersulfone, including two steps of acylation and oxidation. The specific operation is as follows:

[0030] (1) Acylation reaction: NMP was used as solvent, polyethersulfone was added and stirred thoroughly to form a 25 wt.% homogeneous solution, acetyl chloride and aluminum chloride were added according to the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride of 1:7:1.1, poured into a flask and refluxed at 90 ° C for 3 h, then washed with deionized water, filtered, continued washing, and dried to obtain acetylated polyethersulfone;

[0031] (2) Oxidation reaction: 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 h, filtered, washed, and dried to obtain carboxylated polyethersulfone.

[0032] S2 Preparation of Cationic Chitosan

[0033] 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 trimethylammonium chloride, was added dropwise, and the reaction was carried out at 80° C. for 8 h; 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 addition method was a dropwise addition rate of 2 mL / min for the first 2 min, and then the dropwise addition rate was increased by 1 mL per minute until the addition 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.

[0034] S3 preparation of double modified polyethersulfone membrane

[0035] 1) The prepared carboxylated polyethersulfone and the additive LiCl 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 1:0.05:0.2; the homogeneous solution is dropwise added to the homogeneous casting solution at 50° C. and continuously stirred, and the dropping method is as follows: the dropping rate is 2 mL / min for the first 5 minutes, and the dropping rate is increased by 0.5 mL per minute thereafter, and finally maintained at 5 mL / min; the stirring speed is 200 r / min for the first 5 minutes, and then increased by 50 r / min as the dropping rate increases, and finally maintained at 500 r / min; after the dropwise addition is completed, stirring is continued for 0.5 h, 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 22 wt.%;

[0036] 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting solution onto a glass plate and quickly scrape the membrane with a glass rod. After solidification and phase separation in deionized water, a double-modified polyethersulfone membrane is obtained on the glass plate. The double-modified polyethersulfone membrane is evaporated together with the glass plate, first at room temperature for 3 hours, then evaporated in an oven at 80°C for 12 hours, and finally dried at 55°C for 12 hours. After immersion in deionized water for 12 hours, the double-modified polyethersulfone membrane is separated.

[0037] Example 2

[0038] The preparation method of the double-modified polyethersulfone membrane of this embodiment comprises the following steps:

[0039] S1 prepares carboxylated polyethersulfone, including two steps of acylation and oxidation. The specific operation is as follows:

[0040] (1) Acylation reaction: NMP was used as solvent, polyethersulfone was added and stirred thoroughly to form a 20 wt.% homogeneous solution, acetyl chloride and aluminum chloride were added according to the molar ratio of polyethersulfone, acetyl chloride and aluminum chloride of 1:6:1, poured into a flask and refluxed at 80 ° C for 5 h, then washed with deionized water, filtered, continued washing, and dried to obtain acetylated polyethersulfone;

[0041] (2) Oxidation reaction: 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 and reacted at 70°C for 8 h, filtered, washed, and dried to obtain carboxylated polyethersulfone.

[0042] S2 Preparation of Cationic Chitosan

[0043] Chitosan was dissolved in a mixed solvent of isopropanol and water, wherein the water content of the mixed solvent was 35 wt.%, and then a cationic etherifying agent, glycidyl trimethylammonium chloride, was added dropwise, and the reaction was carried out at 70°C for 9 hours; 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 addition method was that the dropwise addition rate was 1 mL / min for the first 2 minutes, and then the dropwise addition rate was increased by 1 mL per minute until the dropwise addition 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.

[0044] S3 preparation of double modified polyethersulfone membrane

[0045] 1) The prepared carboxylated polyethersulfone and the additive PVP 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 1:0.03:0.1; the homogeneous solution is added dropwise to the homogeneous casting solution at 40°C and continuously stirred, and the dropping method is that the dropping rate is 1 mL / min for the first 5 minutes, and the dropping rate is increased by 0.5 mL per minute thereafter, and finally maintained at 5 mL / min; the stirring speed is 150 r / min for the first 5 minutes, and then increases by 50 r / min as the dropping rate increases, and finally maintained at 500 r / min; after the dropwise addition is completed, the stirring is continued for 0.5 h, 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 18 wt.%;

[0046] 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting solution onto a glass plate and quickly scrape the membrane with a glass rod. After solidification and phase separation in deionized water, a double-modified polyethersulfone membrane is obtained on the glass plate. The double-modified polyethersulfone membrane is evaporated together with the glass plate, first at room temperature for 4 hours, then evaporated in an oven at 70°C for 12 hours, and finally dried at 50°C for 12 hours. The evaporated glass plate is placed in deionized water and soaked for 12 hours, and then separated to obtain a double-modified polyethersulfone membrane.

[0047] Example 3

[0048] The preparation method of the double-modified polyethersulfone membrane of this embodiment comprises the following steps:

[0049] S1 prepares carboxylated polyethersulfone, including two steps of acylation and oxidation. The specific operation is as follows:

[0050] (1) Acylation reaction: NMP is used as a solvent, polyethersulfone is added and stirred thoroughly to form a 30 wt.% 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 and refluxed at 100 ° C for 2 h, then washed with deionized water, filtered, continued to wash, and dried to obtain acetylated polyethersulfone;

[0051] (2) Oxidation reaction: 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 and reacted at 100°C for 5 h, filtered, washed, and dried to obtain carboxylated polyethersulfone.

[0052] S2 Preparation of Cationic Chitosan

[0053] Chitosan was dissolved in a mixed solvent of isopropanol and water, wherein the water content of the mixed solvent was 45 wt.%, and then a cationic etherifying agent, glycidyl trimethylammonium chloride, was added dropwise, and the reaction was carried out at 90° C. for 7 h; 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 addition method was a dropwise addition rate of 3 mL / min for the first 2 min, and then the dropwise addition rate was increased by 1 mL per minute until the addition 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.

[0054] S3 preparation of double modified polyethersulfone membrane

[0055] 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 continuously stirred, and the dropping method is that the dropping rate is 3 mL / min for the first 5 minutes, and the dropping rate is increased by 0.5 mL per minute thereafter, and finally maintained at 5 mL / min; the stirring speed is 250 r / min for the first 5 minutes, and then increases by 50 r / min as the dropping rate increases, and finally maintained at 500 r / min; after the dropwise addition is completed, the stirring is continued for 1 hour, 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 25 wt.%;

[0056] 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous casting solution onto a glass plate and quickly scrape the film with a glass rod. After solidification and phase separation in deionized water, a double-modified polyethersulfone membrane is obtained on the glass plate. The double-modified polyethersulfone membrane is evaporated together with the glass plate, first at room temperature for 2 hours, then evaporated in an oven at 90°C for 12 hours, and finally dried at 60°C for 12 hours. After immersion in deionized water for 12 hours, the double-modified polyethersulfone membrane is separated.

[0057] Comparative Example 1

[0058] The difference from Example 1 is that step S1 is not performed, and in step S3, polyethersulfone is used instead of carboxylated polyethersulfone.

[0059] Comparative Example 2

[0060] The difference from Example 1 is that step S2 is not performed, and in step S3, chitosan is used instead of cationic chitosan.

[0061] Comparative Example 3

[0062] The difference from Example 1 is that step S2 is not performed, and in step 1), the prepared carboxylated polyethersulfone and the additive LiCl are dissolved in NMP at a mass ratio of 1:0.05 to form a homogeneous casting solution, stirred for 0.5 h, filtered, allowed to stand, and degassed to obtain a carboxylated polyethersulfone homogeneous casting solution.

[0063] Comparative Example 4

[0064] The difference from Example 1 is that in step S2, the molar ratio of the cationic etherifying agent to chitosan is 8:1.

[0065] Comparative Example 5

[0066] The difference from Example 1 is that in step S2, the reaction temperature is 100° C. and the reaction time is 11 h.

[0067] Comparative Example 6

[0068] The difference from Example 1 is that in step S2, the water content in the mixed solvent is 55 wt.%.

[0069] Comparative Example 7

[0070] The difference from Example 1 is that in step 1), a uniform speed dropwise addition method is adopted during the dropwise addition process, the dropwise addition rate is 3 mL / min, and the stirring speed is 350 r / min.

[0071] Comparative Example 8

[0072] The difference from Example 1 is that in step 1), a uniform speed dropwise addition method is adopted during the dropwise addition process, the dropwise addition rate is 5 mL / min, and the stirring speed is 500 r / min.

[0073] The performance of the polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 was tested using the following method:

[0074] Hydrophilicity test: The contact angle of the polyethersulfone membrane was directly tested using a contact angle meter.

[0075] Antibacterial performance test: Using unmodified polyethersulfone membrane as a blank control sample, and polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 as samples, the blank control sample and samples of the same area were respectively treated with the bacterial suspension for 2 hours and then cultured. The antibacterial rate was calculated according to the following formula:

[0076] Inhibition rate = ;

[0077] Wherein, B is the average number of recovered bacteria in blank control samples, and C is the average number of recovered bacteria in polyethersulfone membrane samples,

[0078] Retention performance test: The feed solution was bovine serum albumin (BSA) at a concentration of 1000 mg / L. The polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 were tested for BSA concentration in the permeate after continuous passage of BSA for 24 hours at the same simulated flow rate (200 mL / min) and membrane inner diameter (0.3 mm). The retention rate was calculated using the following formula:

[0079] Retention rate = ;

[0080] Where C f -BSA concentration in feed solution, mg / L; C p -BSA concentration in the permeate, mg / L.

[0081] The performance test results of the polyethersulfone membranes prepared in Examples 1-3 and Comparative Examples 1-8 are shown in Table 1:

[0082] Table 1 Performance test results of polyethersulfone membranes of Examples 1-3 and Comparative Examples 1-8

[0083]

[0084] In Example 1, carboxylated polyethersulfone is first prepared, and then cationic chitosan is grafted onto the carboxylated polyethersulfone using the electrostatic attraction of positive and negative charges. This allows the prepared double-modified polyethersulfone membrane to possess both properties, with improved hydrophilicity, antibacterial properties, and retention performance, as well as good film-forming properties and a longer service life. In Comparative Example 1, carboxylated polyethersulfone is not prepared, and in Comparative Example 2, chitosan is not cationized. Therefore, the electrostatic attraction of positive and negative charges cannot be used to graft cationic chitosan onto the carboxylated polyethersulfone, resulting in a poor grafting effect. Furthermore, a crosslinking agent must be added to initiate the crosslinking reaction, otherwise the effect of Example 1 cannot be achieved.

[0085] Compared with the double-modified polyethersulfone membrane of Example 1, the carboxylated polyethersulfone membrane prepared in Comparative Example 3 exhibited inferior hydrophilicity, antibacterial properties, and retention performance. Overall, the double-modified polyethersulfone membrane outperformed the carboxylated polyethersulfone membrane in all aspects. This is due to the unique biocompatibility, biodegradability, antibacterial properties, film-forming properties, and low toxicity and pollution-free properties of cationic chitosan, which resulted in the superior performance of the prepared double-modified polyethersulfone membrane.

[0086] As shown in Example 1 and Comparative Examples 4-6, the amount of cationic etherifying agent used, reaction temperature, reaction time, and the water content of the mixed solvent all affect the reaction efficiency and degree of substitution of the prepared cationic chitosan. Excessive use of the cationic etherifying agent increases steric hindrance, making hydroxyl groups less likely to be replaced, and thus reduces reaction efficiency. Excessive reaction time, high reaction temperature, or high water content of the mixed solvent all lead to hydrolysis of the cationic etherifying agent, which in turn affects the degree of substitution of the cationic chitosan and reduces reaction efficiency.

[0087] As can be seen from Example 1 and Comparative Examples 7-8, both the dropping method and the stirring speed will have an impact on the cross-linking reaction of carboxylated polyether sulfone and cationic chitosan. Using a dropping method that is first slow and then accelerated is more conducive to the cationic chitosan being dispersed into the homogeneous film casting liquid and then undergoing a cross-linking reaction with the carboxylated polyether sulfone; if a uniform dropping method is adopted, the cationic chitosan in the system will adhere and aggregate, making it difficult to disperse and undergo a cross-linking reaction with the carboxylated polyether sulfone. At the same time, using a stirring method that is first slow and then gradually accelerated is also conducive to the cross-linking reaction after the reactants are dispersed. If the faster uniform stirring method in Comparative Example 8 is always adopted, a portion of the homogeneous film casting liquid may not react with the solution containing cationic chitosan added due to the effect of centrifugal force, thereby affecting the yield.

[0088] In summary, the present invention utilizes the electrostatic attraction between positive and negative charges, without the need for adding a crosslinking agent, to allow positively charged cationic chitosan to be attached to the surface of negatively charged carboxylated polyethersulfone. This allows the prepared double-modified polyethersulfone membrane to simultaneously possess the advantages of both carboxylated polyethersulfone and cationic chitosan, resulting in excellent hydrophilicity, permeability, and biocompatibility. Furthermore, the membrane-forming performance is good, the antibacterial ability is strong, and the membrane can better cope with membrane contamination, reduce bacterial adsorption, and have a longer service life than conventional polyethersulfone membranes. These advantages enable the double-modified polyethersulfone membrane of the present invention to be applied in a wider range of fields and to provide better results.

Claims

1. A method for preparing a double-modified polyethersulfone membrane, characterized in that: Carboxylated polyethersulfone is prepared by carboxylating polyethersulfone; chitosan is cationized to prepare cationic chitosan; the prepared carboxylated polyethersulfone, cationic chitosan and additives are used in a phase inversion method to prepare a double-modified polyethersulfone membrane; 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 an acylation reaction to prepare acetylated polyethersulfone, and the acetylated polyethersulfone is then subjected to an oxidation reaction with potassium permanganate and sodium hydroxide to prepare 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; 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: 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, filtered, washed and dried to obtain carboxylated polyethersulfone. The preparation method of cationic chitosan comprises the following steps: dissolving chitosan in a mixed solvent of isopropyl alcohol and water, wherein the water content of the mixed solvent is 35-45 wt.%, then dropping a cationic etherifying agent, glycidyl trimethylammonium chloride, to react, wherein the dropping method is to dropwise add chitosan at a rate of 1-3 mL / min for the first 2 minutes, and then increase the dropping rate by 1 mL per minute until the dropping is complete; finally, adding acetone for precipitation, repeatedly washing with anhydrous ethanol, and drying to obtain cationic chitosan.

2. The method for preparing a double-modified polyethersulfone membrane according to claim 1, wherein: 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 20-30 wt.%; 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 20-30 wt.%.

3. The method for preparing a double-modified polyethersulfone membrane according to claim 1, wherein: 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. 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 7-9 hours.

4. The method for preparing a double-modified polyethersulfone membrane according to claim 1, wherein: The preparation of double modified polyethersulfone membrane by phase inversion method includes the following steps: 1) dissolving carboxylated polyethersulfone and additives in N-methylpyrrolidone to form a homogeneous casting solution, and then dissolving cationic chitosan in N-methylpyrrolidone to form a homogeneous solution; adding the homogeneous solution dropwise to the homogeneous casting solution at 40-60° C. while stirring continuously, with a dropping rate of 1-3 mL / min for the first 5 minutes, then increasing the dropping rate by 0.5 mL per minute, and finally maintaining it at 5 mL / min; the stirring speed for the first 5 minutes is 150-250 r / min, then increasing by 50 r / min as the dropping rate increases, and finally maintaining it at 500 r / min; after the dropwise addition is completed, stirring is continued for 0.5-1 hour, and then filtered, allowed to stand, and degassed to obtain a cationic chitosan / carboxylated polyethersulfone homogeneous casting solution; 2) Pour the cationic chitosan / carboxylated polyethersulfone homogeneous membrane casting solution onto a glass plate and quickly scrape the membrane with a glass rod. After solidification and phase separation in deionized water, a double-modified polyethersulfone membrane is obtained on the glass plate. After the double-modified polyethersulfone membrane and the glass plate are evaporated to dryness, the glass plate is immersed in deionized water and separated to obtain the double-modified polyethersulfone membrane.

5. The method for preparing a double-modified polyethersulfone membrane according to claim 4, wherein: In step 1), the contents of cationic chitosan and carboxylated polyethersulfone in the cationic chitosan / carboxylated polyethersulfone homogeneous casting solution are 18-25 wt.%.

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

7. 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 6.

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