Graft-modified PVDF (polyvinylidene fluoride) membrane and preparation method thereof

Abstract

The invention provides a graft modified PVDF (Polyvinylidene Fluoride) membrane and a preparation method thereof. The pollution resistance of the PVDF membrane is improved by adopting a physical blending-chemical grafting method. Firstly, the SMA-PVDF blended membrane is prepared by utilizing a thermally induced phase separation technology (TIPS), the SMA-PVDF blended membrane has the advantage that PVDF and SMA chain segments are entangled and are not easy to fall off, and a polyhydroxy (-OH) group or a polyamino (-NH2) group is fixed on the surface of the PVDF membrane by a subsequent grafting method, so that the hydrophilicity and the pollution resistance of the PVDF membrane can be improved, the modification effect can be lasting and stable, and the PVDF membrane can be used for preparing the PVDF membrane. And the prepared graft modified PVDF membrane has excellent performance.

Description

Technical Field

[0001] The invention belongs to the technical field of separation membrane preparation, and in particular relates to a grafted modified PVDF membrane and a preparation method thereof. Background Art

[0002] Polyvinylidene fluoride (PVDF) has become the core material for the preparation of separation membranes due to its excellent chemical stability, mechanical strength and weather resistance, and has been widely used in water treatment, new energy and other fields. However, the inherent strong hydrophobicity of PVDF materials makes it easy for pollutants to be adsorbed on the membrane surface, resulting in rapid flux attenuation and high cleaning frequency, which seriously restricts its large-scale application. Existing modification technologies mainly use physical blending of hydrophilic polymers (such as styrene-maleic anhydride copolymer SMA) or surface coating of hydrophilic layers, but due to the weak intermolecular forces, there are defects such as easy dissolution and shedding of modifiers and difficulty in maintaining hydrophilicity. Although surface grafting methods (such as sulfonation and plasma treatment) can enhance stability through chemical bonding, conventional grafting processes have two major technical bottlenecks: (1) When directly grafting to the PVDF matrix, the high crystallinity leads to insufficient active sites and limited grafting rate; (2) The entanglement degree of polymer segments in the existing blending-grafting system is low, and phase separation is prone to occur during the grafting process, resulting in uneven distribution of functional groups. For example, the SMA-PVDF blend membrane prepared by wet spinning has obvious microphase separation, and the hydrophilic groups are easily detached with the SMA segments after chemical grafting. Therefore, the development of PVDF membrane modification technology with both high grafting stability and long-term anti-fouling properties is still a key problem that needs to be solved in this field. Summary of the invention

[0003] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a technical solution for hydrophilic modification of PVDF membrane by physical blending-chemical grafting method, which has the advantages of hydrophilic groups not being easy to fall off and simple and effective preparation method through segment winding modification, and can broaden the application value of PVDF membrane. To achieve the above purpose, the present invention proposes a grafted modified PVDF membrane and a preparation method thereof.

[0004] The method for preparing a grafted modified PVDF membrane comprises the following steps: (1) Add PVDF, SMA and an organic solvent into container (1), heat and stir, maintain the temperature at 50 - 150 °C, maintain the stirring speed at 80 - 150 rpm, close the container and stir until completely dissolved to obtain a casting solution, where the content of PVDF is 15 wt% - 30 wt%, the content of SMA is 1 wt% - 10 wt%, and the content of the organic solvent is 60 wt% - 84 wt%; add water or a glycerol aqueous solution or an ethanol aqueous solution into another container (2) to obtain a core solution, and the concentration of the glycerol aqueous solution or the ethanol aqueous solution includes 0 wt% - 20 wt%; prepare an aqueous solution with a concentration of 1 wt% - 10 wt% of a polymer containing multiple hydroxyl groups or multiple amino groups, or make it into a liquid state by heating and melting to obtain a grafting solution; (2) Evacuate the container (1) containing the casting solution, maintain the speed of the stirring rod at 5 - 50 rpm and stir for 3 - 8 h to perform degassing treatment on the casting solution; (3) Extrude the casting solution from the outside of the spinneret (3), and the core solution passes through the inside of the spinneret (3), the extrusion speed is 5 rpm - 20 rpm, the casting solution and the core solution are successively cooled by air and a water bath, the distance from the spinneret (3) to the water bath pool (4) is 0.5 cm - 40 cm, the length of the water bath cooling is 0.2 m - 1 m, the water bath pool solution includes one or several aqueous solutions of N,N - dimethylformamide, N,N - dimethylacetamide, and ethanol, with a concentration of 0 - 30 wt%, the filaments after the water bath are wound by a winding device (5), and the wound filaments are placed in a cleaning solution to extract the organic solvent to obtain a PVDF / SMA blend membrane; (4) Immerse the PVDF / SMA blend membrane prepared in step (3) in the grafting solution, add an acidic or basic catalyst, the reaction temperature is 30 °C - 70 °C, the reaction time is 0.5 h - 6 h, the catalyst concentration is 0.2 wt% - 5 wt%, after the blend membrane is immersed, take it out and wash it with a cleaning solution to remove the unreacted polymer, and dry it to obtain a graft - modified PVDF membrane.

[0005] According to some embodiments, when preparing the casting solution in step (1), it further includes adding an additive into container (1), and the content of the additive is 1 wt% - 5 wt%.

[0006] According to some embodiments, the organic solvent described in step (1) includes triacetin alone as the organic solvent or a mixture of one or two of N,N - dimethylformamide or N,N - dimethylacetamide as the organic solvent.

[0007] According to some embodiments, the additive includes one or two of polyethylene glycol or polyvinylpyrrolidone.

[0008] According to some embodiments, the polymer containing polyhydroxy or polyamino groups in step (1) includes one or more of polyvinyl alcohol, chitosan, polyethyleneimine, polypropyleneimine, and polydopamine.

[0009] According to some embodiments, the polymer containing polyhydroxy or polyamino groups in step (1) is replaced by polyethylene glycol (PEG), the concentration of the polyethylene glycol is 1 wt% - 10 wt%, and it is dissolved in water to form a grafting solution, or it is used for grafting modification after being melted into a liquid state by heating.

[0010] According to some embodiments, the cleaning solution in steps (2) and (4) includes one of clear water, deionized water, and ethanol.

[0011] According to some embodiments, the acidic or alkaline catalyst in step (4) includes one of concentrated sulfuric acid, concentrated hydrochloric acid, triethylamine, and sodium hydroxide.

[0012] According to some embodiments, the cleaning solution in step (3) is clear water, and the clear water is heated to 30 - 80 °C to accelerate the extraction rate of the organic solvent.

[0013] The present invention provides a graft-modified PVDF membrane prepared by using the graft-modification PVDF membrane preparation method described in any one of the above, including: the pure water contact angle is 43.4° - 72.3°, and the rejection rate of bovine serum albumin solution is 87.3% - 98.1%.

[0014] The preparation method in the present invention innovatively uses a physical blending - chemical grafting method to wind SMA inside the PVDF membrane and rivet hydrophilic groups on the surface of the PVDF membrane, thereby endowing the PVDF membrane with a large number of hydrophilic groups such as hydroxyl groups and amine groups, successfully carrying out the hydrophilic modification of the PVDF membrane, and improving the anti-pollution performance of the membrane. Therefore, this method has the following advantages: (1) This method is simple and easy to operate, and can ensure the stability between batch preparations; (2) The polymer can contain a large number of hydrophilic groups, so the hydrophilicity of the membrane can be improved, thereby improving the anti-pollution property; (3) The chain segment winding combined with chemical bonds can improve the stability of the groups, thereby prolonging the anti-pollution stability of the membrane.

[0015] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present invention. Other features, purposes, and advantages of the present invention will become apparent from the specification, drawings, and claims. Description of the Drawings

[0016] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the accompanying drawings required for the description of the embodiments. It is easily understood by those skilled in the art that these drawings are only for illustrative purposes and are not intended to limit the protection scope of the present invention. For illustrative purposes, these figures may not be drawn to scale exactly.

[0017] Figure 1 is the flow chart for preparing the graft-modified PVDF membrane.

[0018] In the figure: 1: container; 2: container; 3: spinneret; 4: water bath; 5: winding device.

[0019] Figure 2 is the summary table of the performance data of the graft-modified PVDF membranes prepared by the methods of Examples 2 to 9. Detailed implementation manners

[0020] Here, the exemplary embodiments will be described in detail, and the examples are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments of the present application. On the contrary, they are merely examples of devices consistent with some aspects of the present application as detailed in the appended claims.

[0021] Example 1 The graft-modified PVDF membrane is prepared by using a hollow fiber membrane spinning machine, and the process includes the following steps: (1) Solution preparation: Add PVDF, SMA, and an organic solvent into container 1 and heat and stir, maintaining the temperature at 50 - 150 °C and the stirring speed at 80 - 150 rpm. After closing the container, stir until completely dissolved to obtain a casting solution, where the content of PVDF is 15wt% - 30wt%, the content of SMA is 1wt% - 10wt%, and the content of the organic solvent is 60wt% - 84wt%; Add water or an aqueous glycerol solution or an aqueous ethanol solution into another container (2) to obtain a core liquid, and the concentration of the aqueous glycerol solution or the aqueous ethanol solution includes 0wt% - 20wt%; Prepare an aqueous solution of a polymer containing multiple hydroxyl groups or multiple amino groups with a concentration of 1wt% - 10wt%, or make it into a liquid state by heating and melting. The polymer is a substance with a high molecular weight formed by covalent bonding of repeating monomers, and the multiple hydroxyl groups or multiple amino groups refer to polymers with a hydroxyl or amino group number greater than or equal to 3; (2) Vacuum degassing treatment of the casting solution: The container 1 filled with the casting solution is evacuated, and the speed of the stirring rod is maintained at 5 - 50 rpm for stirring for 3 - 8 h to defoam the casting solution; (3)Preparation of PVDF / SMA blend membrane: The casting solution is extruded from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 5 rpm - 20 rpm. The casting solution and the core liquid are successively cooled by air and water bath. The distance from the spinneret 3 to the water bath pool 4 is 0.5 cm - 40 cm, and the length of the water bath cooling is 0.2 m - 1 m. The water bath pool solution includes one or several aqueous solutions of N,N-dimethylformamide, N,N-dimethylacetamide, and ethanol, with a concentration of 0 - 30 wt%. The filaments after water bath cooling are wound by the winding device 5, and the wound filaments are soaked in the cleaning solution to extract the organic solvent to obtain the PVDF / SMA blend membrane; (4)Preparation of graft-modified PVDF membrane: The PVDF / SMA blend membrane prepared in step (3) is soaked in the grafting solution, and an acidic or alkaline catalyst is added. The reaction temperature is 30°C - 70°C, the reaction time is 0.5 h - 6 h, and the catalyst concentration is 0.2 wt% - 5 wt%. After the blend membrane is soaked, it is taken out and washed with the cleaning solution to remove the unreacted polymer, and then dried to obtain the graft-modified PVDF membrane.

[0022] The organic solvent described in step (1) can be existing ones including one or several of N-N dimethylformamide, N-N dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide, etc. Preferably, the organic solvent includes glycerol triacetate alone as the organic solvent or a mixture of one or two of N,N-dimethylformamide or N,N-dimethylacetamide. Glycerol triacetate has low toxicity, small irritation, a more environmentally friendly production process, and good biodegradability.

[0023] Preferably, when preparing the casting solution in step (1), an additive is further added to the container (1), and the additive content is 1 wt% - 5 wt%. The additive can be existing ones including one or more mixtures of polyethylene glycol, polypropylene glycol, polyvinylpyrrolidone, glycerol, ethylene glycol, water, ethanol, n-butanol, isopropanol, cationic surfactant, anionic surfactant, non-ionic surfactant, and methyl ethyl ketone, etc. Further preferably, the additive includes one or two of polyethylene glycol or polyvinylpyrrolidone, which can improve the hydrophilicity of the PVDF / SMA blend membrane and promote the formation of a microporous structure.

[0024] Preferably, the polymer containing multiple hydroxyl or amino groups in step (1) includes one or more of polyvinyl alcohol, chitosan, polyethyleneimine, polypropyleneimine, and polydopamine, which can fix the multiple hydroxyl (-OH) groups or amino (-NH2) groups on the surface of the PVDF membrane, thereby improving the hydrophilicity and anti-pollution property of the PVDF membrane, and being persistent and stable.

[0025] Alternatively, the polymer containing multiple hydroxyl or amino groups in step (1) can be replaced by polyethylene glycol (PEG). The concentration of the polyethylene glycol is 1 wt% - 10 wt%, and it is dissolved in water to form a grafting solution, or is used for grafting modification after being melted into a liquid state by heating.

[0026] The cleaning solutions in steps (3) and (4) can be existing ones including neutral detergents, soapy water, clear water, deionized water, ethanol, etc. Preferably, the cleaning solution includes one of clear water, deionized water, and ethanol, which can reduce the production cost.

[0027] Preferably, the acidic or basic catalyst in step (4) includes one of concentrated sulfuric acid, concentrated hydrochloric acid, triethylamine, and sodium hydroxide, which can accelerate the reaction process.

[0028] Preferably, the cleaning solution in step (3) is clear water, heated to 30 - 80 °C to accelerate the extraction rate of the organic solvent.

[0029] Example 2 (1) Solution preparation: Weigh 20 wt% PVDF, 2 wt% SMA, and 78 wt% triacetin (GTA) organic solvent and add them to container 1, heat and stir at a temperature of 140 °C and a stirring speed of 80 rpm until completely dissolved to form a casting solution.

[0030] Add water to another container 2 to prepare the core liquid.

[0031] Add polyvinyl alcohol (PVA) to water to prepare a PVA aqueous solution with a concentration of 10 wt%, which is the grafting solution.

[0032] (2) Vacuum degassing treatment of the casting solution: Vacuumize the container 1 containing the casting solution, and maintain the speed of the stirring rod at 5 rpm and stir for 8 h to degas the casting solution; (3) Preparation of the PVDF / SMA blend membrane: The casting solution is extruded from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 10 rpm. The casting solution and the core liquid are successively cooled by air and a water bath. The distance from the spinneret to the water bath tank 4 is 8 cm, the length of the water bath cooling is 0.8 m, and the solution in the water bath tank is an aqueous solution of N,N-dimethylformamide with a concentration of 20 wt%. The filaments after the water bath are wound up, and the wound filaments are immersed in an ethanol solution to extract the organic solvent, and then a PVDF / SMA blend film is prepared. (4)Preparation of graft-modified PVDF membrane: The PVDF / SMA blend film prepared in step (3) is immersed in a grafting solution, 0.5% concentrated sulfuric acid is added as a catalyst, the reaction temperature is 30 °C, and the immersion reaction is carried out for 6 h. After the immersion reaction of the blend film is completed, it is taken out and washed with water to remove the unreacted polymer, and then dried to obtain a graft-modified PVDF membrane. The prepared graft-modified PVDF membrane is tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane is 43.4°, and the rejection rate for a 1 g / mL bovine serum albumin (BSA) solution is 98.1%.

[0033] Example 3 (1)Solution preparation: Weigh 20 wt% PVDF, 2 wt% SMA, and 78 wt% triacetin (GTA) organic solvent with a balance and add them to container 1, then heat and stir at a temperature of 120 °C and a stirring speed of 80 rpm for 12 h to form a casting solution.

[0034] Water and glycerol are added to another container 2 and mixed to form a glycerol aqueous solution to obtain a core liquid, and the concentration of the glycerol aqueous solution is 20 wt%.

[0035] PEG2000 is heated to make it in a corresponding liquid state to obtain a grafting solution.

[0036] (2)Vacuum degassing treatment of the casting solution: The container 1 containing the casting solution is evacuated, and the speed of the stirring rod is maintained at 20 rpm and stirred for 7 h to degas the casting solution. (3)Preparation of PVDF / SMA blend film: The casting solution is extruded from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 5 rpm. The casting solution and the core liquid are successively cooled by air and a water bath. The distance from the spinneret to the water bath tank 4 is 0.5 cm, the length of the water bath cooling is 0.2 m, and the solution in the water bath tank is a clear aqueous solution. The filaments after the water bath are wound up, and the wound filaments are immersed in clear water at 30 °C to extract the organic solvent, and then a PVDF / SMA blend film is prepared. (4)Preparation of graft-modified PVDF membrane: The PVDF / SMA blend membrane prepared in step (3) was immersed in the grafting solution, with 0.6 wt% triethylamine as the catalyst, the reaction temperature was 65 °C, and the immersion reaction was carried out for 4 h. After the immersion reaction of the blend membrane was completed, it was taken out and washed with water to remove the unreacted polymer, and the grafted modified PVDF membrane was obtained after drying. The prepared grafted modified PVDF membrane was tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane was 58.6°, and the rejection rate for 1 g / mL bovine serum albumin (BSA) solution was 89.6%.

[0037] Example 4 (1) Solution preparation: Weigh 20 wt% PVDF, 2 wt% SMA, 78 wt% triacetin (GTA) organic solvent and additionally add 1 wt% polyethylene glycol (PEG) additive with a molecular weight of 20,000 into container 1, heat and stir at a temperature of 150 °C and a stirring speed of 80 rpm until completely dissolved to form a casting solution.

[0038] Water and glycerol were added to another container 2 and mixed to prepare a glycerol aqueous solution as the core liquid, and the concentration of the glycerol aqueous solution was 3 wt%.

[0039] PEG2000 was heated to make it into the corresponding liquid state to prepare the grafting solution.

[0040] (2) Vacuum degassing treatment of the casting solution: The container 1 containing the casting solution was evacuated, and the speed of the stirring rod was maintained at 50 rpm and stirred for 3 h to degas the casting solution; (3) Preparation of PVDF / SMA blend membrane: The casting solution was extruded from the outside of the spinneret 3, and the core liquid passed through the inside of the spinneret 3. The extrusion speed was 20 rpm. The casting solution and the core liquid were cooled by air and water bath in sequence. The distance from the spinneret to the water bath pool 4 was 15 cm, the length of the water bath cooling was 0.8 m, the solution in the water bath pool was a clear water solution, and the filaments after the water bath were wound up. The wound filaments were immersed in 50 °C clear water to extract the organic solvent, and the PVDF / SMA blend membrane was obtained; (4) Preparation of grafted modified PVDF membrane: The PVDF / SMA blend membrane prepared in step (3) was immersed in the grafting solution, with 0.2 wt% triethylamine as the catalyst, the reaction temperature was 70 °C, and the immersion reaction was carried out for 0.5 h. After the immersion reaction of the blend membrane was completed, it was taken out and washed with water to remove the unreacted polymer, and the grafted modified PVDF membrane was obtained after drying. The prepared grafted modified PVDF membrane was tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane was 56.3°, and the rejection rate for 1 g / mL bovine serum albumin (BSA) solution was 90.5%.

[0041] Example 5 (1)Solution preparation: Weigh 20wt% PVDF, 2wt% SMA, 78wt% triacetin (GTA) organic solvent and additionally add 3wt% PEG20000 additive into container 1, heat and stir at a temperature of 50 °C and a stirring speed of 150 rpm until completely dissolved to form a casting solution.

[0042] Add water into another container 2 to prepare the core liquid.

[0043] Heat PEG2000 to its corresponding liquid state to prepare the grafting solution.

[0044] (2)Vacuum degassing treatment of the casting solution: Vacuumize the container 1 containing the casting solution, maintain the speed of the stirring rod at 35 rpm and stir for 6 h to degas the casting solution; (3)Preparation of PVDF / SMA blend membrane: Extrude the casting solution from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 10 rpm. The casting solution and the core liquid are cooled by air and water bath in sequence. The distance from the spinneret to the water bath pool 4 is 5 cm, the length of the water bath cooling is 1 m, and the solution in the water bath pool is an ethanol aqueous solution with a concentration of 10wt%. The filaments after the water bath are wound and collected by a winding roller, and the wound filaments are immersed in an ethanol solution to extract the organic solvent to obtain a PVDF / SMA blend membrane; (4)Preparation of graft-modified PVDF membrane: Immerse the PVDF / SMA blend membrane prepared in step (3) in the grafting solution, add triethylamine with a concentration of 3wt% as a catalyst, react at a temperature of 65 °C for 2 h. After the immersion reaction of the blend membrane is completed, take it out and wash it with water to remove the unreacted polymer, and dry it to obtain the graft-modified PVDF membrane. The prepared graft-modified PVDF membrane is tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane is 72.3°, and the rejection rate for 1 g / mL bovine serum albumin (BSA) solution is 87.3%.

[0045] Example 6 (1)Solution preparation: Weigh 16wt% PVDF, 4wt% SMA, 80wt% triacetin (GTA) organic solvent and additionally add 3wt% polyvinylpyrrolidone with a molecular weight of K30 (PVP-K30) as an additive into container 1, heat and stir at a temperature of 130 °C and a stirring speed of 100 rpm until completely dissolved to form a casting solution.

[0046] Add water into another container 2 to prepare the core liquid.

[0047] Heat PEG2000 to its corresponding liquid state to obtain a grafting solution.

[0048] (2) Vacuum degassing treatment of the casting solution: Vacuumize the container 1 filled with the casting solution, and maintain the speed of the stirring rod at 10 rpm to stir for 8 h to degas the casting solution; (3) Preparation of PVDF / SMA blend membrane: Extrude the casting solution from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 20 rpm. The casting solution and the core liquid are cooled by air and water bath in sequence. The distance from the spinneret to the water bath pool 4 is 10 cm, the length of the water bath cooling is 0.8 m, and the solution in the water bath pool is a mixed aqueous solution of N,N-dimethylacetamide and ethanol with a concentration of 30 wt%. The filaments after the water bath are wound and collected by a winding roller, and the wound filaments are soaked in an 80°C aqueous solution to extract the organic solvent to obtain a PVDF / SMA blend membrane; (4) Preparation of graft-modified PVDF membrane: Soak the PVDF / SMA blend membrane prepared in step (3) in the grafting solution, add triethylamine with a concentration of 5 wt% as a catalyst, the reaction temperature is 65°C, soak and react for 5 h. After the blend membrane soaking reaction is completed, take it out and wash it with water to remove the unreacted polymer, and dry it to obtain a graft-modified PVDF membrane. The prepared graft-modified PVDF membrane is tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane is 52.6°, and the rejection rate for a 1 g / mL bovine serum albumin (BSA) solution is 93.5%.

[0049] Example 7 (1) Solution preparation: Weigh 30 wt% PVDF, 10 wt% SMA, 60 wt% triacetin (GTA) organic solvent and additionally add 3 wt% PEG20000 as an additive into container 1, heat and stir at a temperature of 70°C and a stirring speed of 145 rpm until completely dissolved to form a casting solution.

[0050] Add water and ethanol into another container 2 to obtain an ethanol aqueous solution, that is, the core liquid, and the concentration of the ethanol aqueous solution is 10 wt%.

[0051] Heat PEG2000 to its corresponding liquid state to obtain a grafting solution.

[0052] (2) Vacuum degassing treatment of the casting solution: Vacuumize the container 1 filled with the casting solution, and maintain the speed of the stirring rod at 45 rpm to stir for 4 h to degas the casting solution; (3) Preparation of PVDF / SMA blend membrane: The casting solution is extruded from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 20 rpm. The casting solution and the core liquid are sequentially cooled by air and a water bath. The distance from the spinneret to the water bath pool 4 is 40 cm, the length of the water bath cooling is 0.2 m, and the solution in the water bath pool is a mixed aqueous solution of N,N-dimethylformamide, N,N-dimethylacetamide, and ethanol with a concentration of 15 wt%. The filaments after the water bath are wound and collected by a winding roller, and the wound filaments are soaked in an ethanol solution to extract the organic solvent, and then a PVDF / SMA blend membrane is prepared; (4)Preparation of graft-modified PVDF membrane: The PVDF / SMA blend membrane prepared in step (3) is soaked in a grafting solution, and triethylamine with a concentration of 0.2 wt% is added as a catalyst. The reaction temperature is 68 °C, and the soaking reaction is carried out for 2 h. After the soaking reaction of the blend membrane is completed, it is taken out and washed with water to remove the unreacted polymer, and then a graft-modified PVDF membrane is prepared after drying. The prepared graft-modified PVDF membrane is tested for hydrophilicity and anti-pollution performance. The pure water contact angle of the membrane is 71.0°, and the rejection rate for a 1 g / mL bovine serum albumin (BSA) solution is 88.8%.

[0053] Example 8 (1)Solution preparation: Weigh 16 wt% PVDF, 4 wt% SMA, 80 wt% triacetin (GTA) organic solvent with a balance, and additionally add 5 wt% polyvinylpyrrolidone (PVP-K30) with a molecular weight of K30 as an additive to container 1, heat and stir at a temperature of 140 °C and a stirring speed of 85 rpm until completely dissolved to form a casting solution.

[0054] Water is added to another container 2 to prepare a core liquid.

[0055] PEG2000 is heated to make it in a corresponding liquid state to prepare a grafting solution.

[0056] (2)Vacuum degassing treatment of the casting solution: The container 1 containing the casting solution is evacuated, and the speed of the stirring rod is maintained at 30 rpm and stirred for 5 h to degas the casting solution; (3)Preparation of PVDF / SMA blend membrane: The casting solution is extruded from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 15 rpm. The casting solution and the core liquid are sequentially cooled by air and a water bath. The distance from the spinneret to the water bath pool 4 is 20 cm, the length of the water bath cooling is 0.8 m, and the solution in the water bath pool is a mixed aqueous solution of N,N-dimethylformamide and N,N-dimethylacetamide with a concentration of 20 wt%. The filaments after the water bath are wound and collected by a winding roller. The wound filaments are immersed in an ethanol solution to extract the organic solvent, and then a PVDF / SMA blend membrane is prepared. (4)Preparation of graft-modified PVDF membrane: The PVDF / SMA blend membrane prepared in step (3) is immersed in the grafting solution, and concentrated sulfuric acid with a concentration of 0.6 wt% is added as a catalyst. The reaction temperature is 65 °C, and the immersion reaction is carried out for 4 h. After the immersion reaction of the blend membrane is completed, it is taken out and washed with water to remove the unreacted polymer, and then dried to obtain the graft-modified PVDF membrane. The prepared graft-modified PVDF membrane is tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane is 56.5°, and the rejection rate for a 1 g / mL bovine serum albumin (BSA) solution is 90.2%.

[0057] Example 9 (1)Solution preparation: Weigh 15 wt% PVDF, 1 wt% SMA, and 84 wt% triacetin (GTA) organic solvent with a balance and add them to container 1, then heat and stir at a temperature of 140 °C and a stirring speed of 80 rpm until completely dissolved to form a casting solution.

[0058] Water is added to another container 2 to prepare the core liquid.

[0059] Polyvinyl alcohol (PVA) is added to water to prepare a PVA aqueous solution with a concentration of 1 wt%, which is the grafting solution.

[0060] (2)Vacuum degassing treatment of the casting solution: The container 1 containing the casting solution is evacuated, and the speed of the stirring rod is maintained at 25 rpm and stirred for 5 h to degas the casting solution. (3)Preparation of PVDF / SMA blend membrane: The casting solution is extruded from the outside of the spinneret 3, and the core liquid passes through the inside of the spinneret 3. The extrusion speed is 15 rpm. The casting solution and the core liquid are sequentially cooled by air and a water bath. The distance from the spinneret to the water bath pool 4 is 30 cm, the length of the water bath cooling is 0.5 m, and the solution in the water bath pool is an N,N-dimethylformamide aqueous solution with a concentration of 20 wt%. The filaments after the water bath are wound and collected. The wound filaments are immersed in an ethanol solution to extract the organic solvent, and then a PVDF / SMA blend membrane is prepared. (4)Preparation of graft-modified PVDF membrane: The PVDF / SMA blend film prepared in step (3) was immersed in the grafting solution, and concentrated sulfuric acid with a concentration of 3 wt% was added as a catalyst. The reaction temperature was 60 °C, and the immersion reaction was carried out for 6 h. After the immersion reaction of the blend film was completed, it was taken out, washed with water to remove the unreacted polymer, and dried to obtain the graft-modified PVDF membrane. The prepared graft-modified PVDF membrane was tested for hydrophilicity and anti-fouling performance. The pure water contact angle of the membrane was 45.1°, and the rejection rate of the 1 g / mL bovine serum albumin (BSA) solution was 97.9%.

[0061] Example 10 Based on the same technical concept as the above method embodiments, the embodiment of the present invention also provides a graft-modified PVDF membrane, including the product prepared by the above embodiments, with a pure water contact angle of 43.4° - 72.3° and a rejection rate of 87.3% - 98.1% for the 1 g / mL bovine serum albumin solution.

[0062] Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of this application. The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", and "the" used in this application are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0063] Spatial relative position terms such as "upper", "lower", "left", "right", "front", "rear", "thickness", "radial", "axial", etc. that may be used herein are for the purpose of facilitating the description of the relationship between one feature and another as shown in the drawings, and are not limited to a position or a spatial orientation. It can be understood that depending on the placement position of the product, the spatial relative position terms may be intended to include different orientations other than those shown in the figures and should not be construed as limiting. In addition, the descriptive term "horizontal" used herein is not completely equivalent to being perpendicular to the direction of gravity and allows for a certain degree of inclination. The terms "including" or "comprising" used herein are intended to indicate that the elements or items appearing before "including" or "comprising" cover the elements or items listed after "including" or "comprising" and their equivalents, and do not exclude other elements or items.

[0064] It should be understood that the "first", "second", and similar terms used in the specification of this application do not denote any order, quantity, or importance, but are only used to distinguish different components.

[0065] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of this application.

Claims

1. A preparation method of a graft-modified PVDF membrane, characterized in that It includes the following steps: (1) Add PVDF, SMA and an organic solvent into container (1), heat and stir, maintain the temperature at 50 - 150 °C, maintain the stirring speed at 80 - 150 rpm, close the container and stir until completely dissolved to obtain a casting solution, where the content of PVDF is 15 wt% - 30 wt%, the content of SMA is 1 wt% - 10 wt%, and the content of the organic solvent is 60 wt% - 84 wt%; add water or a glycerol aqueous solution or an ethanol aqueous solution into another container (2) to obtain a core liquid, and the concentration of the glycerol aqueous solution or the ethanol aqueous solution includes 0 wt% - 20 wt%; prepare an aqueous solution with a concentration of 1 wt% - 10 wt% from a polymer containing multiple hydroxyl groups or multiple amino groups, or make it into a liquid state by heating and melting to obtain a grafting solution; (2) Evacuate the container (1) containing the casting solution, maintain the speed of the stirring rod at 5 - 50 rpm and stir for 3 - 8 h to conduct degassing treatment on the casting solution; (3) Extrude the casting solution from the outside of the spinneret (3), the core liquid passes through the inside of the spinneret (3), the extrusion speed is 5 rpm - 20 rpm, the casting solution and the core liquid are successively cooled by air and a water bath, the distance from the spinneret (3) to the water bath pool (4) is 0.5 cm - 40 cm, the length of the water bath cooling is 0.2 m - 1 m, the water bath pool solution includes one or several aqueous solutions of N,N - dimethylformamide, N,N - dimethylacetamide, ethanol, with a concentration of 0 - 30 wt%, the filaments after the water bath are wound by a winding device (5), and the wound filaments are placed in a cleaning solution to extract the organic solvent to obtain a PVDF / SMA blend membrane; (4) Immerse the PVDF / SMA blend membrane prepared in step (3) in the grafting solution, add an acidic or basic catalyst, the reaction temperature is 30 °C - 70 °C, the reaction time is 0.5 h - 6 h, the catalyst concentration is 0.2 wt% - 5 wt%, after the blend membrane is immersed and completed, take it out and wash it with a cleaning solution to remove the unreacted polymer, and dry it to obtain a graft - modified PVDF membrane.

2. The preparation method of the graft-modified PVDF membrane according to claim 1, wherein, When preparing the casting solution in step (1), it also includes adding an additive into container (1), and the content of the additive is 1 wt% - 5 wt%.

3. The preparation method of the graft-modified PVDF membrane according to claim 1, wherein, The organic solvent in step (1) includes glycerol triacetate alone as the organic solvent or a mixture of one or two of N,N - dimethylformamide or N,N - dimethylacetamide as the organic solvent.

4. The preparation method of the graft-modified PVDF membrane according to claim 2, characterized in that, The additive includes one or two of polyethylene glycol or polyvinylpyrrolidone.

5. The preparation method of the graft-modified PVDF membrane according to claim 1, characterized in that, The polymer containing multiple hydroxyl groups or multiple amino groups in step (1) includes one or several of polyvinyl alcohol, chitosan, polyethyleneimine, polypropyleneimine, polydopamine.

6. The preparation method of the graft-modified PVDF membrane according to claim 1, wherein, Replace the polymer containing multiple hydroxyl groups or multiple amino groups in step (1) with polyethylene glycol, the concentration of the polyethylene glycol is 1 wt% - 10 wt%, and dissolve it in water to form a grafting solution, or make it into a liquid state by heating and melting and then use it for grafting modification.

7. The preparation method of the graft-modified PVDF membrane according to claim 1, characterized in that, The cleaning solution in steps (2) and (4) includes one of clear water, deionized water, ethanol.

8. The preparation method of the graft-modified PVDF membrane according to claim 1, characterized in that, The acidic or basic catalyst in step (4) includes one of concentrated sulfuric acid, concentrated hydrochloric acid, triethylamine, sodium hydroxide.

9. The preparation method of the graft-modified PVDF membrane according to claim 6, wherein, The cleaning liquid described in step (3) is clean water, and the clean water is heated to 30 - 80 °C to accelerate the extraction rate of the organic solvent.

10. A graft-modified PVDF membrane prepared by the method according to any one of claims 1-9, characterized in that, It includes: The contact angle of pure water is 43.4° - 72.3°, and the rejection rate of 1 g / mL bovine serum albumin solution is 87.3% - 98.1%.

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