A hydrophilic modified polyvinylidene fluoride microfiltration membrane and preparation method thereof

Abstract

The present invention belongs to the technical field of microfiltration membranes, and provides a hydrophilic modified polyvinylidene fluoride microfiltration membrane and a preparation method thereof. When the pore size of the hydrophilic modified polyvinylidene fluoride microfiltration membrane is 0.22 μm, it is completely wetted within 1 second, and the protein recovery rate is ≥99%. The present invention utilizes free radical polymerization to achieve stable coating of hydrophilic substances on the surface of the membrane, and by adjusting the concentration, temperature, time and other process parameters of monomer polymerization and adjusting the appropriate molecular weight, a hydrophilic modified polyvinylidene fluoride microfiltration membrane with high flow rate, high bubble point and low protein adsorption can be prepared.

Description

Technical Field

[0001] The present application relates to the technical field of microfiltration membranes, and in particular to a hydrophilically modified polyvinylidene fluoride microfiltration membrane and a preparation method thereof. Background Art

[0002] Polyvinylidene fluoride (PVDF) material contains CF bonds with higher bond energy, and CC bonds with lower bond energy are surrounded, which makes it have excellent chemical stability, thermal stability and mechanical properties. After polyvinylidene fluoride is made into a microfiltration membrane material with a microporous structure, it is widely used in the field of water treatment. However, since the CF bonds on the surface of the polyvinylidene fluoride microfiltration membrane are hydrophobic, it is difficult to be wetted by water and it is difficult to meet the requirements for water flux in practical applications. Especially in the process of treating oily wastewater, it is easy to be contaminated by oil, causing the membrane pores to be blocked and the water flux to decrease. Its strong hydrophobicity limits the practical application of polyvinylidene fluoride microfiltration membrane.

[0003] Therefore, the prior art continuously performs hydrophilic modification on polyvinylidene fluoride membranes, and the modification method is generally to improve the hydrophilicity of the membrane by grafting a certain number of hydrophilic groups or hydrophilic polymers. For example, a patent application document with publication number CN109161041A discloses a modified polyvinylidene fluoride membrane and a preparation method thereof, comprising the following steps: adding at least one of acrylic acid and hydroxyethyl methacrylate, a crosslinking agent and an initiator to a polyvinylidene fluoride solution, and performing an in-situ crosslinking polymerization reaction to obtain a mixed solution; using a membrane-making method to make the mixed solution into a membrane material to obtain a modified polyvinylidene fluoride membrane. The pure water contact angle of the modified polyvinylidene fluoride membrane is less than 70°; the activated partial prothrombin time (APTT) is 50-120 seconds, and the thrombin time (TT) is 20-80 seconds; in the protein static adsorption test, the modified polyvinylidene fluoride membrane has a lower protein adsorption than the unmodified polyvinylidene fluoride membrane, and is maintained at 43μg / cm 2 The initiator is an azo initiator, and the amount used is preferably 0.3-1.5% of the total mass of acrylic acid and hydroxyethyl methacrylate, preferably 0.3-1%.

[0004] Another example is the patent with publication number CN105833732B, which discloses a separation membrane modified with a hydrophilic anti-pollution gel coating and a preparation method thereof. The preparation method comprises the following steps: (1) dispersing and dissolving a cross-linking monomer, a cross-linking agent and a photoinitiator in a solvent to obtain a monomer solution, wherein the cross-linking monomer is polyethylene glycol methyl methacrylate with a concentration of 0.01-0.5 g / mL; the cross-linking agent is ethylene glycol dimethacrylate with a volume concentration of 0.1-3%; the concentration of the photoinitiator is 0.1-2 mg / mL; (2) immersing the separation membrane in the monomer solution and placing it under ultraviolet light for irradiation cross-linking reaction, taking it out and drying it, thereby obtaining the separation membrane modified with the hydrophilic anti-pollution gel coating. The separation membrane modified with the hydrophilic anti-pollution gel coating has good hydrophilicity, stable anti-pollution performance, and is a composite separation membrane that will not cause pollution to the separated substance, and the graft layer thickness is thin and uniform and stable. The photoinitiator is potassium persulfate, ammonium persulfate or dibenzoyl peroxide.

[0005] In addition, in the prior art, for example, (Yang Hu et al., Study on the modification of polyvinylidene fluoride membrane surface by acrylic acid grafting, "Membrane Science and Technology", Vol. 26, No. 4) discloses a method for preparing a hydrophilic microporous membrane modified by acrylic acid grafting on a polyvinylidene fluoride membrane by a free radical polymerization method, and specifically discloses: immersing the PVDF microporous membrane in an aqueous solution of acrylic acid and an initiator, and after vacuum degassing, reacting at a constant temperature of 70°C for 5 hours, and gently scrubbing the surface of the flat membrane after the reaction with a sponge, and then immersing it in deionized water for 48 hours to complete the hydrophilic modification of the polyvinylidene fluoride membrane. For example, (Zeng Yunan, Study on the chemical modification of the surface of polyvinylidene fluoride ultrafiltration membrane and treatment of wastewater containing it, China Excellent Master's Degree Thesis Full-text Database Engineering Technology I, No. 5, 2012) discloses that the original polyvinylidene fluoride membrane is pre-treated and impregnated with an alcohol solution, and then immersed in pure water to gradually replace the ethanol in the membrane pores, so that the hydrophobic membrane pores are completely infiltrated with water.

[0006] The above-mentioned prior art usually prepares the modified solution by blending raw materials, and the initiator content is low. These methods are prone to block the membrane pores due to the polymerization of monomers during the modification process, affecting the flux. Secondly, during the use of the polyvinylidene fluoride membrane prepared by these methods, the polymer is easy to detach from the membrane surface, resulting in reduced hydrophilicity. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention provides a hydrophilically modified polyvinylidene fluoride microfiltration membrane and a preparation method thereof, so as to solve the problems in the prior art that the existing method for hydrophilic modification of polyvinylidene fluoride membranes easily causes the membrane pores to be blocked due to the polymerization of monomers during the modification process, thereby affecting the flux; secondly, during the use of the existing prepared polyvinylidene fluoride membrane, the polymer is easily separated from the membrane surface, resulting in reduced hydrophilicity, and the like.

[0008] To achieve the above and related purposes, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a hydrophilic modified polyvinylidene fluoride microfiltration membrane. When the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, it is completely wetted within 1 second, and the protein recovery rate is ≥99%.

[0010] In one embodiment of the present application, when the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, the flow rate is 13-15 mL / min / cm 2 .

[0011] In one embodiment of the present application, when the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, the bubble point is 0.4-0.45 MPa.

[0012] The second aspect of the present invention provides a method for preparing a hydrophilically modified polyvinylidene fluoride microfiltration membrane, comprising the following steps:

[0013] (1) preparing a monomer solution with a mass fraction of 5 to 20%, an initiator solvent with a mass fraction of 6 to 20%, and a cross-linking agent solution with a mass fraction of 0.6 to 1.2% respectively;

[0014] (2) The pre-moistened polyvinylidene fluoride membrane is sequentially immersed in a monomer solution, an initiator solution, and a cross-linking agent solution, washed with water, and dried to obtain a polyvinylidene fluoride microfiltration membrane.

[0015] In one embodiment of the present application, in step (1), the monomer used to prepare the monomer solution is acrylic acid or acrylamide.

[0016] In one embodiment of the present application, in step (1), the initiator used to prepare the initiator solvent is ammonium persulfate and / or potassium persulfate.

[0017] In one embodiment of the present application, in step (1), the crosslinking agent used to prepare the crosslinking agent solution is N,N-dimethylbisacrylamide or N-hydroxymethylacrylamide.

[0018] In one embodiment of the present application, in step (2), the pre-wetting method is: after wetting the original polyvinylidene fluoride film with alcohol, immersing it in deionized water to wash away the alcohol, thereby obtaining a polyvinylidene fluoride film.

[0019] In one embodiment of the present application, in step (2), the polyvinylidene fluoride membrane is immersed in the monomer solution for 5 to 15 minutes;

[0020] and / or, immersing in an initiator solution for 5 to 15 minutes;

[0021] and / or, immersing in a cross-linking agent solution for 7 to 10 minutes.

[0022] In one embodiment of the present application, the alcohol is one or a combination of methanol, ethanol, and isopropanol.

[0023] The beneficial technical effects of the present invention are:

[0024] The present invention prepares a hydrophilic modified polyvinylidene fluoride microfiltration membrane by pre-wetting, free radical polymerization, cross-linking and water washing to a hydrophobic polyvinylidene fluoride original membrane, and realizes stable coating of hydrophilic substances on the surface of the membrane, and the hydrophilicity thereof is greatly improved. Water droplets are immediately flattened on the microfiltration membrane and can be completely wetted within 1 second. The wetting speed is fast, the bubble point is high, the flow rate is high, and the protein recovery rate is high (i.e., low protein adsorption).

[0025] In the present invention, a cross-linking agent is added to the reaction system. Compared with the traditional blending modification, the hydrophilicity of the polyvinylidene fluoride microfiltration membrane of the present invention is more stable and is not affected by repeated washing or use.

[0026] The present invention controls the mass fractions of monomer, initiator and cross-linking agent solutions, the soaking sequence and process parameters, and adjusts the appropriate molecular weight, thereby ultimately achieving the effect of modifying the surface of the original polyvinylidene fluoride membrane without blocking the pore size of the polyvinylidene fluoride microfiltration membrane itself and having no effect on the flow rate and bubble point of the membrane itself. Surprisingly, the flow rate and bubble point of the modified polyvinylidene fluoride microfiltration membrane are improved compared with the flow rate and bubble point of the original polyvinylidene fluoride membrane.

[0027] The preparation method of the invention has readily available raw materials and is simple to operate, and can be applied to large-scale industrial production.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings herein are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present application, and together with the specification, are used to explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0030] Figure 1 A flow chart of the preparation method for this application;

[0031] Figure 2 This is an optical diagram of the wetting effect of the hydrophobic polyvinylidene fluoride original film;

[0032] Figure 3 This is an optical diagram of the wetting effect of the polyvinylidene fluoride microfiltration membrane in Example 1 of the present application. DETAILED DESCRIPTION

[0033] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as the general understanding of a person of ordinary skill in the art to which the present invention belongs. It should be understood that certain features of the present invention (described in the context of separate embodiments for clarity) may also be provided in combination in a single embodiment. On the contrary, multiple features of the present invention (described in the context of a single embodiment for brevity) may also be provided separately or in any suitable combination or in any other described embodiment of the present invention when appropriate. Certain features described in the context of various embodiments will not be considered as essential features of those embodiments unless the embodiment is inoperable without those elements. The present invention is further described below by specific specific examples, but it should be noted that the specific process conditions and results described in the embodiments of the present invention are only used to illustrate the present invention, and the protection scope of the present invention cannot be limited thereto. All equivalent changes or modifications made according to the spirit and essence of the present invention should be included in the protection scope of the present invention.

[0034] First of all, it should be noted that the chemical materials used in this application are all commercially available.

[0035] The present invention provides a method for preparing a hydrophilically modified polyvinylidene fluoride microfiltration membrane, comprising the following steps:

[0036] (1) preparing a monomer solution with a mass fraction of 5 to 20%, an initiator solvent with a mass fraction of 6 to 20%, and a cross-linking agent solution with a mass fraction of 0.6 to 1.2% respectively;

[0037] (2) The pre-moistened polyvinylidene fluoride membrane is sequentially immersed in a monomer solution, an initiator solution, and a cross-linking agent solution, washed with water, and dried to obtain a polyvinylidene fluoride microfiltration membrane.

[0038] Furthermore, if Figure 1 As shown, the present application first wets the hydrophobic polyvinylidene fluoride original membrane with alcohol, and then immerses it in deionized water for 10 to 20 minutes to gradually replace the alcohol in the membrane pores, thereby washing away the alcohol used for pre-wetting, so that the hydrophobic membrane pores are completely wetted by water to obtain a polyvinylidene fluoride membrane, wherein the alcohol is one or a combination of methanol, ethanol, and isopropanol;

[0039] Then, the pre-moistened polyvinylidene fluoride membrane is immersed in a monomer solution for 5 to 15 minutes, wherein the monomer solution is prepared using acrylic acid or acrylamide;

[0040] Then immerse in an initiator solution for 5 to 15 minutes, wherein the initiator solution is prepared using ammonium persulfate and / or potassium persulfate;

[0041] Finally, immerse in a crosslinking agent solution for 7 to 10 minutes, wherein the crosslinking agent solution is prepared using N, N-dimethylbisacrylamide or N-hydroxymethylacrylamide. After the immersion is completed, take out and dry at 80° C. for about 7 minutes.

[0042] The dried polyvinylidene fluoride membrane is placed in deionized water for washing for 10 to 30 minutes, taken out for drying, and the drying temperature and time are not specified, and drying is sufficient to obtain a hydrophilic modified polyvinylidene fluoride microfiltration membrane.

[0043] The present invention also provides a hydrophilic modified polyvinylidene fluoride microfiltration membrane, which is preferably prepared using the above preparation method. When the pore size of the prepared polyvinylidene fluoride microfiltration membrane is 0.22 μm, it is completely wetted within 1 second, and the protein recovery rate is ≥99%.

[0044] Furthermore, when the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, the flow rate is 13 to 15 mL / min / cm 2 .

[0045] Furthermore, when the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, the bubble point is 0.4 to 0.45 MPa.

[0046] The present invention is described in detail below by specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0047] Example 1

[0048] (1) Wetting the hydrophobic polyvinylidene fluoride original membrane with ethanol, then immersing it in deionized water for 10 minutes, washing away the ethanol, and obtaining a polyvinylidene fluoride membrane;

[0049] (2) preparing an acrylic acid solution with a mass fraction of 15% using acrylic acid as a monomer, stirring and heating at 60° C. for 4 h to form a uniform acrylic acid solution for later use;

[0050] Use ammonium persulfate as an initiator to prepare a 10% ammonium persulfate solution, stir and heat to 60°C for later use;

[0051] Prepare a 0.6% N,N-dimethylbisacrylamide solution using N,N-dimethylbisacrylamide as a crosslinking agent, stir until completely dissolved and set aside;

[0052] (3) immersing the polyvinylidene fluoride membrane in an acrylic acid solution for 7 minutes, then in an ammonium persulfate solution for 10 minutes, and finally in an N,N-dimethylbisacrylamide solution for 7 minutes, taking it out, and drying it at 80° C. for about 7 minutes;

[0053] (4) The dried polyvinylidene fluoride membrane was placed in deionized water for washing for 10 minutes, taken out, and dried to obtain a hydrophilic modified polyvinylidene fluoride microfiltration membrane with a pore size of 0.22 μm.

[0054] Example 2

[0055] (1) Wetting the hydrophobic polyvinylidene fluoride original membrane with isopropanol, then immersing it in deionized water for 10 minutes, washing away the isopropanol, and obtaining a polyvinylidene fluoride membrane;

[0056] (2) preparing a 15% acrylamide solution with acrylamide as a monomer, stirring and heating at 60° C. for 5 h to form a uniform acrylamide solution for later use;

[0057] Prepare a 15% potassium persulfate solution using potassium persulfate as an initiator, stir and heat to 65°C for later use;

[0058] Prepare a 0.6% N,N-dimethylbisacrylamide solution using N,N-dimethylbisacrylamide as a crosslinking agent, stir until completely dissolved and set aside;

[0059] (3) immersing the polyvinylidene fluoride membrane in an acrylamide solution for 7 minutes, then immersing it in a potassium persulfate solution for 10 minutes, and finally immersing it in an N,N-dimethylbisacrylamide solution for 7 minutes, taking it out, and drying it at 80° C. for about 7 minutes;

[0060] (4) The dried polyvinylidene fluoride membrane was placed in deionized water for washing for 10 minutes, taken out, and dried to obtain a hydrophilic modified polyvinylidene fluoride microfiltration membrane with a pore size of 0.22 μm.

[0061] Example 3

[0062] (1) Wetting the hydrophobic polyvinylidene fluoride original membrane with ethanol, then immersing it in deionized water for 10 minutes, washing away the ethanol, and obtaining a polyvinylidene fluoride membrane;

[0063] (2) preparing an acrylic acid solution with a mass fraction of 15% using acrylic acid as a monomer, stirring and heating at 60° C. for 6 h to form a uniform acrylic acid solution for later use;

[0064] Use ammonium persulfate as an initiator to prepare a 10% ammonium persulfate solution, stir and heat to 65°C for later use;

[0065] Prepare a 1% N,N-dimethylbisacrylamide solution using N,N-dimethylbisacrylamide as a crosslinking agent, stir until completely dissolved and set aside;

[0066] (3) immersing the polyvinylidene fluoride membrane in an acrylic acid solution for 10 minutes, then in an ammonium persulfate solution for 5 minutes, and finally in an N,N-dimethylbisacrylamide solution for 10 minutes, taking it out, and drying it at 80° C. for about 7 minutes;

[0067] (4) The dried polyvinylidene fluoride membrane was placed in deionized water for washing for 10 minutes, taken out, and dried to obtain a hydrophilic modified polyvinylidene fluoride microfiltration membrane with a pore size of 0.22 μm.

[0068] Example 4

[0069] (1) Wetting the hydrophobic polyvinylidene fluoride original membrane with isopropanol, then immersing it in deionized water for 10 minutes, washing away the isopropanol, and obtaining a polyvinylidene fluoride membrane;

[0070] (2) preparing a 15% acrylamide solution with acrylamide as a monomer, stirring and heating at 60° C. for 6 h to form a uniform acrylamide solution for later use;

[0071] Prepare a 15% potassium persulfate solution using potassium persulfate as an initiator, stir and heat to 60°C for later use;

[0072] Prepare a 0.8% N-hydroxymethyl acrylamide solution using N-hydroxymethyl acrylamide as a crosslinking agent, and stir until completely dissolved for later use;

[0073] (3) immersing the polyvinylidene fluoride membrane in an acrylamide solution for 12 minutes, then immersing it in a potassium persulfate solution for 8 minutes, and finally immersing it in N-hydroxymethyl acrylamide for 7 minutes, taking it out, and drying it at 80° C. for about 7 minutes;

[0074] (4) The dried polyvinylidene fluoride membrane was placed in deionized water for washing for 10 minutes, taken out, and dried to obtain a hydrophilic modified polyvinylidene fluoride microfiltration membrane with a pore size of 0.22 μm.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is:

[0077] A monomer solution with a mass fraction of 15% was prepared with acrylamide and acrylic acid as monomers, wherein the mass ratio of acrylic acid to acrylamide was 1:1.

[0078] Comparative Example 2

[0079] The difference between this comparative example and Example 1 is:

[0080] Ammonium persulfate solution with a mass fraction of 2% was prepared using ammonium persulfate as an initiator.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is:

[0083] Ammonium persulfate solution with a mass fraction of 25% was prepared using ammonium persulfate as an initiator.

[0084] Comparative Example 4

[0085] The difference between this comparative example and Example 1 is:

[0086] A 10% by mass dibenzoyl peroxide solution was prepared with dibenzoyl peroxide as an initiator.

[0087] Comparative Example 5

[0088] The difference between this comparative example and Example 1 is:

[0089] The acrylic acid solution, the ammonium persulfate solution and the N,N-dimethylbisacrylamide solution are mixed to prepare a modified solution;

[0090] The polyvinylidene fluoride membrane was immersed in the modified solution for 24 minutes, taken out, and dried at 80° C. for about 7 minutes.

[0091] Comparative Example 6

[0092] The difference between this comparative example and Example 1 is:

[0093] The polyvinylidene fluoride membrane was immersed in an acrylic acid solution for 7 minutes, then immersed in an N,N-dimethylbisacrylamide solution for 7 minutes, and finally immersed in an ammonium persulfate solution for 10 minutes, taken out, and dried at 80°C for about 7 minutes.

[0094] Comparative Example 7

[0095] The difference between this comparative example and Example 1 is:

[0096] The polyvinylidene fluoride membrane was immersed in N,N-dimethylbisacrylamide solution for 7 minutes, then immersed in ammonium persulfate solution for 10 minutes, and finally immersed in acrylic acid solution for 7 minutes, taken out, and dried at 80°C for about 7 minutes.

[0097] Performance Testing

[0098] Flow rate and bubble point detection: The polyvinylidene fluoride microfiltration membranes of Examples 1 to 4 and Comparative Examples 1 to 7 were subjected to flow rate and bubble point detection according to GB / T32361-2015 "Bubble point and average flow rate method for separation membrane pore size test method". In this process, a polyvinylidene fluoride membrane without any modification was used as a blank control group. The test results are shown in Table 1:

[0099] Wetting ability: Water was dropped on the polyvinylidene fluoride microfiltration membranes of Examples 1 to 4 and Comparative Examples 1 to 7, respectively, and their complete wetting speed, i.e., the time when the water contact angle dropped to 0°, was tested. In this process, the polyvinylidene fluoride based membrane without any modification was used as the blank control group. The test results are shown in Table 1.

[0100] Protein recovery rate: Under the conditions of conductivity of 32.5 mS / cm and pH of 6.5, the recoveries of proteins RFP, mAb1, mAb2 and RuBisCO were averaged using the polyvinylidene fluoride microfiltration membranes of Examples 1 to 4 and Comparative Examples 1 to 7 to obtain the protein recovery rate. In this process, a polyvinylidene fluoride based membrane that had not undergone any modification was used as a blank control group. The test results are shown in Table 1.

[0101] The experimental data and analysis are as follows:

[0102] Table 1 Performance test table of polyvinylidene fluoride microfiltration membrane of Examples 1 to 4 and Comparative Examples 1 to 7

[0103]

[0104]

[0105] As can be seen from Table 1, the wetting time of the polyvinylidene fluoride-based membrane without any modification is infinite, it is not easy to wet, the flow rate and bubble point are low, and there is no protein recovery, which indicates that the base membrane has poor hydrophilicity, low water flux, and high protein adsorption, and it cannot meet the filtration requirements in actual applications.

[0106] The polyvinylidene fluoride microfiltration membranes of Examples 1 to 4 of the present application can be completely wetted within 1 second, which indicates that their wetting ability is significantly improved. In addition, the polyvinylidene fluoride microfiltration membranes of the present application examples have a high flow rate, which indicates that their membrane pores are not blocked, their water flux is high, and they have excellent throughput; and the bubble point is smaller than that of Comparative Examples 1 to 7, which indicates that their wetting performance is better.

[0107] In addition, the protein recovery rate of the polyvinylidene fluoride microfiltration membrane in the examples of the present application is higher than that of the microfiltration membrane in the comparative example, which indicates that it has extremely low protein adsorption and good hydrophilicity.

[0108] The monomer solution of Comparative Example 1 is a mixture of two monomers. During the polymerization process, the free radical polymerization rates of different monomers are inconsistent, and multi-polymerization is carried out. The product is a copolymer microfiltration membrane, and its flow rate and protein recovery rate are lower than those of the homopolymer microfiltration membrane of the embodiment of the present application, while the bubble point is high, which indicates that its hydrophilicity is not as good as the polyvinylidene fluoride microfiltration membrane of the embodiment of the present application.

[0109] The initiator mass fraction in Comparative Example 2 is low, that is, the initiator content in the reaction system is low, and its initiation speed is slow. Within the same time, its free radical polymerization degree is not as good as the polyvinylidene fluoride microfiltration membrane in the embodiment of the present application, and thus its hydrophilicity is poor and the water flux is small.

[0110] The mass fraction of the initiator in Comparative Example 3 exceeds the specified range of the preparation method of the present application, that is, the initiator content in the reaction system is too high and the initiation speed is too fast, which makes the physical properties of the prepared polyvinylidene fluoride microfiltration membrane unstable, the product is not fully cured, the membrane pores are blocked, and the hydrophilicity of the polyvinylidene fluoride microfiltration membrane is affected.

[0111] In Comparative Example 4, an organic peroxide initiator is selected as the initiator, which is an oily initiator with low activity. When an organic initiator is used for free radical polymerization, it introduces an oily solvent and cannot be completely removed during water washing. Therefore, the polyvinylidene fluoride microfiltration membrane prepared therefrom contains a certain amount of oiliness, which in turn affects its hydrophilicity.

[0112] Comparative Example 5 was modified by blending, and Comparative Examples 6 and 7 changed the immersion order of the monomer solution, the initiator solution and the cross-linking agent solution. It can be seen from Table 1 that although the methods of Comparative Examples 5 to 7 showed a hydrophilic modification effect on the base membrane, their flow rate and protein recovery rate were not as good as those of the embodiments of the present application, which indicates that the methods of Comparative Examples 5 to 7 may cause blockage of the pore size of the original polyvinylidene fluoride membrane itself, ultimately affecting its hydrophilicity.

[0113] Further, if Figure 2 As shown, Figure 2 This is an optical diagram of the wetting effect of the hydrophobic polyvinylidene fluoride original film. It can be seen from the figure that the unmodified original film has no wetting ability and has extremely poor hydrophilicity.

[0114] Further, if Figure 3 As shown, Figure 3 This is an optical diagram of the wetting effect of the polyvinylidene fluoride microfiltration membrane in Example 1 of the present application. It can be seen from the figure that when water drops on the polyvinylidene fluoride microfiltration membrane prepared in the present application, it is immediately flattened, and its water contact angle quickly drops to 0°, completely wetting the polyvinylidene fluoride microfiltration membrane.

[0115] Depend on Figure 2 and Figure 3 It can be seen from the comparison that the polyvinylidene fluoride microfiltration membrane prepared in the present application has high wetting ability and strong hydrophilicity.

[0116] In summary, the present application can achieve the effect of hydrophilic modification of the base membrane surface by controlling the types, contents, proportions, immersion sequence, temperature, time and other process steps of monomers, initiators and cross-linking agents, and will not block the pore size of the polyvinylidene fluoride microfiltration membrane itself, and has no effect on the flow rate and bubble point of the membrane itself. Unexpectedly, the flow rate and bubble point of the hydrophilically modified polyvinylidene fluoride microfiltration membrane prepared by the present application are improved relative to the flow rate and bubble point of the base membrane, and the final protein recovery rate is also greatly improved.

[0117] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A hydrophilic modified polyvinylidene fluoride microfiltration membrane, characterized in that: When the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, it is completely wetted within 1 second, and the protein recovery rate is ≥99%; The preparation method of the hydrophilic modified polyvinylidene fluoride microfiltration membrane comprises the following steps: (1) preparing a monomer solution with a mass fraction of 5-20%, an initiator solution with a mass fraction of 6-20%, and a crosslinker solution with a mass fraction of 0.6-1.2% respectively; the monomer used to prepare the monomer solution is acrylic acid or acrylamide, the initiator used to prepare the initiator solution is ammonium persulfate and / or potassium persulfate, and the crosslinker used to prepare the crosslinker solution is N,N-dimethylbisacrylamide or N-hydroxymethylacrylamide; (2) The pre-moistened polyvinylidene fluoride membrane is sequentially immersed in the monomer solution, the initiator solution, and the cross-linking agent solution, washed with water, and dried to obtain the polyvinylidene fluoride microfiltration membrane.

2. The hydrophilic modified polyvinylidene fluoride microfiltration membrane according to claim 1, characterized in that: When the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, the flow rate is 13-15 mL / min / cm 2 .

3. The hydrophilic modified polyvinylidene fluoride microfiltration membrane according to claim 1, characterized in that: When the pore size of the polyvinylidene fluoride microfiltration membrane is 0.22 μm, the bubble point is 0.4-0.45 MPa.

4. A method for preparing a hydrophilic modified polyvinylidene fluoride microfiltration membrane, characterized in that: The following steps are involved: (1) preparing a monomer solution with a mass fraction of 5-20%, an initiator solution with a mass fraction of 6-20%, and a crosslinker solution with a mass fraction of 0.6-1.2% respectively; the monomer used to prepare the monomer solution is acrylic acid or acrylamide, the initiator used to prepare the initiator solution is ammonium persulfate and / or potassium persulfate, and the crosslinker used to prepare the crosslinker solution is N,N-dimethylbisacrylamide or N-hydroxymethylacrylamide; (2) The pre-moistened polyvinylidene fluoride membrane is sequentially immersed in the monomer solution, the initiator solution, and the cross-linking agent solution, washed with water, and dried to obtain the polyvinylidene fluoride microfiltration membrane.

5. The preparation method according to claim 4, characterized in that: In the step (2), the pre-wetting method is: after wetting the original polyvinylidene fluoride membrane with alcohol, immersing it in deionized water, washing away the alcohol, and obtaining the polyvinylidene fluoride membrane.

6. The preparation method according to claim 4, characterized in that: In the step (2), the polyvinylidene fluoride membrane is immersed in the monomer solution for 5 to 15 minutes; and / or, immersing in the initiator solution for 5 to 15 minutes; And / or, immersing in the cross-linking agent solution for 7 to 10 minutes.

7. The preparation method according to claim 5, characterized in that: The alcohol is one or a combination of methanol, ethanol and isopropanol.

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