Modified PVDF ultrafiltration membrane and preparation method thereof

Abstract

The invention relates to the technical field of water treatment, in particular to a modified PVDF ultrafiltration membrane and a preparation method thereof. The PVDF ultrafiltration membrane obtained by the conventional method has more surface defects and poor ultrafiltration performance. In order to solve the problems, the invention provides the modified PVDF ultrafiltration membrane, a specific mixed solvent system composed of DMI or TEP and DMAC is selected in the preparation process, the PVDF ultrafiltration membrane has good dissolving capacity to PVDF, the quality and stability of a membrane casting solution are guaranteed, and compared with a traditional toxic solvent, the introduction of the DMI and TEP as environment-friendly solvents has the advantages that the cost is low, and the application range is wide. And potential hazards to the environment and operators are reduced.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a modified PVDF ultrafiltration membrane and its preparation method. Background Technology

[0002] Ultrafiltration is a pressure-driven membrane separation technology that falls between ultrafiltration and reverse osmosis. Its molecular weight cutoff is typically between 100 and 1000 Da, and it has a high efficiency in removing divalent and multivalent ions and small organic molecules. With its advantages of low operating pressure, high flux, and low energy consumption, ultrafiltration technology shows broad application prospects in areas such as advanced drinking water treatment, material separation and concentration, wastewater reuse, and special separation.

[0003] Polyvinylidene fluoride (PVDF), as a semi-crystalline polymer, has become an ideal material for preparing separation membranes due to its excellent chemical stability, mechanical strength, antifouling properties, and weather resistance, and is widely used in microfiltration and ultrafiltration processes. However, directly using PVDF to prepare high-performance ultrafiltration membranes still faces significant challenges. First, PVDF's inherent strong hydrophobicity makes the membrane susceptible to fouling when treating aqueous solutions, causing a sharp drop in flux and requiring frequent chemical cleaning, increasing operating costs and maintenance difficulty. Second, conventional PVDF membrane formation methods struggle to create a separation layer with precise nanoscale pore sizes and narrow pore size distributions, which is crucial for achieving highly selective ultrafiltration separation.

[0004] To address the aforementioned issues, existing technologies typically employ methods such as blending modification, surface coating, or chemical grafting to hydrophilize and functionalize PVDF membranes. For example, hydrophilic polymers or nanoparticles are added to the casting solution to improve the membrane's hydrophilicity; or interfacial polymerization is performed on the surface of a pre-formed PVDF ultrafiltration membrane to construct an extremely thin polyamide separation layer, thereby endowing it with ultrafiltration separation performance. However, these methods often suffer from complex processes, insufficient stability of the modified layer, or the potential introduction of new interfacial defects. In particular, the interfacial polymerization process is extremely sensitive to monomer concentration, reaction time, and post-treatment conditions, requiring high process controllability, and the resulting polyamide layer exhibits poor chlorine resistance, limiting its long-term application in chlorine-containing environments.

[0005] Furthermore, in membrane fabrication processes, traditional phase inversion methods typically involve directly immersing a substrate containing a polymer solution into a non-solvent coagulation bath, with the substrate placement often being rather arbitrary. This approach can lead to an uneven initial membrane structure, or even macroscopic defects, before the polymer solution gels and solidifies, due to gravity or fluid disturbances, thus affecting the final membrane performance and consistency. Summary of the Invention

[0006] The problem with existing technologies is that PVDF ultrafiltration membranes obtained by conventional methods have many surface defects and poor ultrafiltration performance. To address these problems, this invention provides a modified PVDF ultrafiltration membrane, the preparation method of which includes the following steps: (1) Add PVDF powder to an organic solvent and stir at 90-100℃ until completely dissolved to obtain PVDF solution; (2) The PVDF solution is kept at a constant temperature of 90-100℃ to remove air bubbles, and then uniformly poured onto the surface of the nonwoven fabric on one side to obtain PVDF modified nonwoven fabric. (3) The PVDF modified nonwoven fabric is completely immersed in deionized water for phase transformation. During the immersion process, the PVDF modified layer on the surface of the PVDF modified nonwoven fabric is always parallel to the ground and located on the upper part of the nonwoven fabric. After the immersion is completed, an ultrafiltration membrane is obtained.

[0007] Preferably, the organic solvent in step (1) is a mixed solution formed by DMI or TEP and DMAC respectively.

[0008] Preferably, the organic solvent in step (1) is a mixed solution of DMI and DMAC in a mass ratio of 50:50.

[0009] Preferably, the organic solvent in step (1) is a mixed solution of TEP and DMAC in a mass ratio of 50:50.

[0010] Preferably, the mass ratio of PVDF powder to organic solvent is 14:86.

[0011] The present invention has the following beneficial effects: (1) This invention effectively avoids the problem of uneven initial membrane structure caused by gravity or fluid disturbance by strictly controlling the directional impregnation method of the PVDF modified nonwoven fabric during the phase transformation process, ensuring that the PVDF modified layer is always facing upward and parallel to the ground. This strongly ensures that the polymer solution can form a stable and uniform film before gel solidification, significantly reducing the generation of macroscopic defects, thereby obtaining an ultrafiltration base membrane with higher structural uniformity and performance consistency; (2) The present invention uses a specific mixed solvent system composed of DMI or TEP and DMAC, which not only has good solubility for PVDF and ensures the quality and stability of casting solution, but also the introduction of DMI and TEP as environmentally friendly solvents reduces the potential harm to the environment and operators compared with traditional toxic solvents. Attached Figure Description

[0012] Figure 1 SEM images of the surface and cross-section of the ultrafiltration membranes obtained in Examples 1-3 and Comparative Example 1, respectively.

[0013] Figure 2The ultrafiltration performance test results of the ultrafiltration membranes obtained in Examples 1-3 and Comparative Example 1 are presented.

[0014] Figure 3 SEM images of the surface and cross-section of the ultrafiltration membranes obtained in Examples 4-6 and Comparative Example 2.

[0015] Figure 4 The ultrafiltration performance test results of the ultrafiltration membranes obtained in Examples 4-6 and Comparative Example 2 are as follows.

[0016] Figure 5 The ultrafiltration retention performance test results of the ultrafiltration membranes obtained in Examples 1-3 and Comparative Example 1, respectively.

[0017] Figure 6 The ultrafiltration retention performance test results of the ultrafiltration membranes obtained in Examples 4-6 and Comparative Example 2.

[0018] Figure 7 The ultrafiltration retention performance test results of the ultrafiltration membranes obtained in Comparative Examples 3-6 are as follows: Detailed Implementation

[0019] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0020] Example 1

[0021] A method for preparing a modified PVDF ultrafiltration membrane is as follows: 2.8 g of PVDF powder was dried in an oven at 70℃ for 24 hours beforehand. The dried PVDF powder was then added to a mixed solution of 17.2 g of DMI and DMAC at a mass ratio of 30:70. The solution was heated and stirred in an oil bath at 100℃ until the PVDF powder was completely dissolved, yielding a PVDF casting solution. This solution was then allowed to stand at 100℃ for 2-3 hours to remove air bubbles. The PVDF casting solution was then uniformly cast onto a nonwoven fabric using a 150 μm thick doctor blade and immediately immersed in deionized water to undergo phase inversion. The phase inversion time was approximately 12 hours. Upon completion, a modified PVDF ultrafiltration membrane, designated as a 30% DMI membrane, was obtained.

[0022] Example 2 is the same as Example 1, except that in Example 2, the dried PVDF powder is added to a mixed solution of DMI and DMAC at a mass ratio of 50:50. The modified PVDF ultrafiltration membrane obtained in Example 2 is designated as a 50% DMI membrane.

[0023] Example 3 is the same as Example 1, except that in Example 3, the dried PVDF powder is added to a mixed solution of DMI and DMAC at a mass ratio of 70:30. The modified PVDF ultrafiltration membrane obtained in Example 2 is designated as the 70% DMI membrane.

[0024] Example 4 is the same as Example 1, except that DMI in Example 1 is replaced with TEP. The modified PVDF ultrafiltration membrane obtained in Example 4 is designated as a 30% TEP membrane.

[0025] Example 5 is the same as Example 2, except that DMI in Example 2 is replaced with TEP. The modified PVDF ultrafiltration membrane obtained in Example 5 is designated as a 50% TEP membrane.

[0026] Example 6 is the same as Example 3, except that DMI in Example 3 is replaced with TEP. The modified PVDF ultrafiltration membrane obtained in Example 6 is designated as a 70% TEP membrane.

[0027] Comparative Example 1 is the same as Example 1, except that Comparative Example 1 uses DMAC instead of the "mixed solution of DMI and DMAC in a mass ratio of 30:70" in Example 1. The ultrafiltration membrane obtained in Comparative Example 1 is denoted as the DMAC membrane.

[0028] Comparative Example 2 is the same as Example 1, except that Comparative Example 2 uses TEP instead of the "mixed solution formed by DMI and DMAC at a mass ratio of 30:70" in Example 1. The ultrafiltration membrane obtained in Comparative Example 1 is referred to as the TEP membrane.

[0029] Comparative Example 3 is the same as Example 1, except that Comparative Example 3 uses the same amount of γ-valerol (GVL) instead of DMI in Example 1. The resulting ultrafiltration membrane is designated as a 30% GVL membrane.

[0030] Comparative Example 4 is the same as Example 1, except that Comparative Example 4 uses the same amount of GVL added to replace DMI in Example 2. The resulting ultrafiltration membrane is designated as a 50% GVL membrane.

[0031] Comparative Example 5 is the same as Example 1, except that Comparative Example 5 uses the same amount of GVL added to replace DMI in Example 3. The resulting ultrafiltration membrane is designated as a 70% GVL membrane.

[0032] Comparative Example 6 is the same as Example 1, except that Comparative Example 6 uses the same amount of GVL instead of the "mixed solution of DMI and DMAC at a mass ratio of 30:70" in Example 1. The resulting ultrafiltration membrane is denoted as the GVL membrane.

[0033] Performance testing

[0034] Membrane characterization

[0035] The surface and cross-sectional morphology of the membrane were characterized using field emission scanning electron microscopy (FESEM, ZEISS Sigma 300, Germany). The hydrophilicity of the membrane was verified by measuring the water contact angle on the membrane using a contact angle meter (JC2000D1).

[0036] Membrane performance evaluation

[0037] The membrane's permeability and retention rate are measured by a filtration area of ​​9.616 cm². 2 The cross-flow filtration device was evaluated. First, the membrane was pre-pressurized for 20 minutes at a constant transmembrane pressure (TMP) of 0.2 MPa. Then, the pure water flux (PWF, Lm) was measured at a stable TMP of 0.1 MPa at room temperature. -2 h -1 ), calculated using formula (1): (1); Where V is the water production rate (L) and A is the filtration area (cm2). The filtration time (s) was used. The rejection rate was assessed by filtering a BSA solution (300 ppm) and calculated using formula (2): (2); in and The concentrations of BSA in the permeate and feed during the filtration process were measured at a wavelength of 280 nm using an ultraviolet spectrophotometer (AOEUV-1900).

[0038] Anti-pollution performance test

[0039] Before the antifouling performance test, the membrane was pre-pressurized with deionized water at 0.2 MPa for 20 minutes. The cross-flow filtration unit was then run with deionized water at 0.1 MPa for 60 minutes, with PWF recorded every 10 minutes. Then, a 0.3 g / L BSA solution was used as the contaminant test. 60 minutes. Afterwards, wash the contaminated membrane with deionized water for 60 minutes, and test the recovered PWF again with deionized water. 60 minutes. Flux recovery rate (FRR) is calculated using formula (3): (3); Calculate the total fouling rate (Rt), reversible fouling rate (Rr), and irreversible fouling rate (Rir) according to equations (4), (5), and (6), respectively.

[0040] (4); (5); (6).

[0041] The surface and cross-sectional SEM images of the ultrafiltration membranes obtained in Examples 1-3 and Comparative Example 1 are shown in the appendix to the specification. Figure 1 As shown, Figure 1 (a) Corresponding to DMAC membrane; Figure 1 (b) Corresponding to 30% DMI membrane; Figure 1 (c) Corresponding to 50% DMI membrane; Figure 1 (d) Corresponding to the 70% DMI membrane. The image shows that compared with the DMAC-based membrane, the addition of DMI solvent reduces the surface pore size of the PVDF membrane. This may be because the casting solution is more likely to solidify at room temperature with increasing DMI content. Therefore, rapid cooling during immersion in the coagulation bath may cause rapid precipitation and solidification on the membrane surface, resulting in a smaller pore size surface layer. As the DMI solvent content increases, the finger pores first increase and then decrease, reaching their maximum at 50% DMI. This is because at lower DMI contents, the casting solution system is still dominated by hydrophilic DMAC. The addition of DMI reduces thermodynamic stability, making the phase separation rate faster than the pure DMAC system, thus increasing the finger pore size. At 70% DMI, the DMI content in the casting solution system is relatively high, and the exchange rate with water during phase transformation decreases, thereby inhibiting the increase of finger pore size.

[0042] The ultrafiltration performance test results of the ultrafiltration membranes obtained in Examples 1-3 and Comparative Example 1 are shown in the appendix to the specification. Figure 2 As shown. Figure 2 (a) Water permeability of different DMI and DMAC membranes; Figure 2 (b) BSA (bovine serum albumin) permeability and retention rate of different DMI and DMAC membranes; Figure 2 (c) FRR (flux recovery rate), Rr (reversible fouling rate), and Rir (irreversible fouling rate) for different DMI and DMAC membranes. Figure 2(d) shows the water contact angle of different DMI membranes. The image shows that replacing some DMAC with DMI increases both the pure water flux and BSA flux of the prepared PVDF membrane. With increasing DMI replacement content, the pure water flux and BSA flux first increase and then slightly decrease. Compared to the 50% DMI membrane, the pure water flux and BSA flux of the 70% DMI membrane decrease slightly. This is because at lower DMI contents, the thermodynamic stability of the casting solution decreases due to the addition of DMI, leading to an increase in finger-like pores and thus membrane flux. When the DMI replacement reaches 70%, the DMI proportion is large, reducing the exchange rate with water during phase transformation and slowing down the phase separation rate, thereby inhibiting the enlargement of finger-like pores. Therefore, the flux of the 70% DMI membrane decreases. The DMI membrane rejection rate also first increases and then decreases. The increase in rejection rate is due to the rapid precipitation and solidification that occurs instantaneously on the membrane surface during phase transformation, which reduces the pore size and thus increases the membrane's BSA rejection effect. When the DMI content reaches 70%, the rejection rate decreases, possibly because the excessively high DMI content causes defects in some membrane structures, thus reducing the rejection rate. The best-performing membrane is the 50% DMI membrane, with a pure water flux of 99 Lm. -2 h -1 BSA flux 45.13 Lm -2 h -1 The rejection rate reached 94.19%. Calculations showed that the membrane with added DMI exhibited improved recovery rate, increased reversible fouling rate, and decreased irreversible fouling rate, indicating improved antifouling performance. However, the improvement was minor, and the increase in DMI content did not significantly affect the recovery rate or reversible fouling rate. This may be because the addition of DMI improved the hydrophilicity of the membrane surface, which is corroborated by the smaller water contact angle of the DMI membrane compared to the pure DMAC-based membrane. However, the improvement was limited, hence the smaller increase in recovery rate.

[0043] The surface and cross-sectional SEM images of the ultrafiltration membranes obtained in Examples 4-6 and Comparative Example 1 are shown in the appendix to the specification. Figure 3 As shown. Figure 3 (a) Corresponding to 30% TEP membrane; Figure 3 (b) Corresponding to 50% TEP membrane; Figure 3 (c) Corresponding to 70% TEP membrane; Figure 3(d) Corresponding TEP membrane. The image shows that, compared with the base membrane, the addition of TEP solvent reduces the surface pores of the PVDF membrane, while slightly increasing the cross-sectional finger pores. With increasing TEP content, the surface pores gradually decrease, especially when the TEP content reaches 100%, where the surface pores decrease significantly. This may be because TEP has lower hydrophilicity than DMAC; the higher the content, the lower the solvent-water exchange rate, tending to form a denser, more complete surface layer with smaller pore sizes and a large number of interconnected sponge pores. The finger pores initially increase and then decrease with increasing TEP solvent content. This may be because at lower TEP contents, the addition of TEP reduces the thermodynamic stability of the casting solution system, but since both have similar Hansen solubility, the decrease in thermodynamic stability is less, thus slightly accelerating the phase separation rate and resulting in a smaller increase in finger pores. When the TEP content is higher, TEP dominates the system, the hydrophilicity of the mixed solvent decreases more, and the phase separation rate is slower, thus promoting the formation of a large number of interconnected sponge-like micropores. However, since the number of sponge pores is large and the connectivity is good, the flux of 70% TEP membrane and TEP membrane decreases less.

[0044] The ultrafiltration performance test results of the ultrafiltration membranes obtained in Examples 4-6 and Comparative Example 1 are shown in the appendix to the specification. Figure 4 As shown. Figure 4 (a) Water permeability of different TEP membranes; Figure 4 (b) BSA permeability and rejection rate of different TEP membranes; Figure 4 (c) FRR, Rr and Rir of different TEP membranes; Figure 4 (d) Water contact angles of different TEP membranes. As shown in the figure, replacing some DMAC with TEP increases the pure water flux of the prepared PVDF membrane, while the BSA flux changes relatively little. With increasing TEP replacement, the pure water flux first increases and then slightly decreases. This is because at lower TEP contents, the thermodynamic stability of the casting solution decreases but changes little, and the phase separation rate slightly increases, resulting in a slight but not significant increase in finger-like pores, thus leading to a slight increase in flux. When the TEP content increases, TEP dominates the system, further reducing hydrophilicity and slowing the phase separation rate, thereby promoting the formation of a large number of interconnected sponge pores. These sponge pores are numerous and highly interconnected, therefore the pure water flux decreases only slightly. The BSA flux shows a similar trend, with even smaller changes. The TEP membrane's rejection rate increases with increasing TEP content. The TEP membrane surface becomes denser, more complete, and has fewer and smaller surface pores with increasing TEP content, thus the TEP membrane has a more significant BSA rejection effect. Calculations showed that membranes with added TEP exhibited significantly improved recovery rates, increased reversible fouling rates, and significantly reduced irreversible fouling rates, indicating a marked improvement in the antifouling performance of membranes with added TEP. This is likely because the surface of the TEP membrane is more dense and intact, making it less prone to contaminant adhesion, thus making the membrane easier to clean and exhibiting higher antifouling performance.

[0045] The ultrafiltration retention performance test results of the ultrafiltration membranes obtained in Examples 1-3 and Comparative Example 1 of this invention are shown in the appendix to the specification. Figure 5 As shown. Figure 5 (a) Water permeability of different DMI and DMAC membranes; Figure 5 (b) HA (humic acid) permeability and retention rate of different DMI and DMAC membranes; Figure 5 (c) FRR, Rr, and Rir of different DMI and DMAC membranes; The test results of ultrafiltration of 0.1 g / L humic acid (HA) showed that with the increase of DMI replacement, the filtration flux and rejection rate of humic acid first increased and then decreased. The 50% DMI membrane performed best, with the highest filtration flux and rejection rate. Calculations showed that the recovery rate of the DMAC-based membrane was 81.23%, while the recovery rate of the DMI membrane ranged from 94.49% to 95.59%. Compared with the DMAC-based membrane, the reversible fouling rate of the DMI membrane increased, while the irreversible fouling rate decreased. Compared with the recovery rates of DMAC-based and DMI membranes after filtering BSA, both showed improved recovery rates. This may be due to the strong adsorption effect of the membrane materials on humic acid; while increasing the rejection rate, some humic acid is also adsorbed and remains on the membrane. Because humic acid is hydrophilic, the humic acid molecules remaining on the membrane form a hydrophilic layer on the inner wall of the membrane pores and the surface of the membrane, thereby enhancing the membrane's hydrophilicity and improving its recovery flux and recovery rate. Compared with DMAC-based membranes, DMI membranes have a higher recovery rate, possibly because the addition of DMI enhances the membrane's adsorption of humic acid, resulting in better hydrophilicity of the filtered membrane and thus a better recovery rate. Membrane fouling is divided into reversible fouling and irreversible fouling. Reversible fouling means fouling that can be removed by washing with water, while irreversible fouling means fouling that cannot be removed by washing with water. Recovery rate refers to the membrane flux after washing compared to the initial membrane flux.

[0046] The ultrafiltration retention performance test results of the ultrafiltration membranes obtained in Examples 4-6 and Comparative Example 2 of this invention are shown in the appendix to the specification. Figure 6 As shown. Figure 6 (a) Water permeability of different TEP membranes; Figure 6 (b) HA permeability and rejection rate of different TEP membranes; Figure 6(c) FRR, Rr, and Rir of different TEP membranes; Ultrafiltration of 0.1 g / L humic acid (HA) showed that compared with DMAC-based membranes, TEP membranes improved both the humic acid filtration flux and the rejection rate. With increasing TEP replacement, the humic acid filtration flux first increased and then decreased, while the rejection rate slightly increased. Comparatively, the 50% TEP membrane performed best, exhibiting the highest humic acid filtration flux and a relatively high rejection rate. Calculations showed that compared with DMAC-based membranes, TEP membranes exhibited a higher reversible fouling rate and a lower irreversible fouling rate. Compared with the recovery rates of DMAC-based and TEP membranes after filtering BSA, TEP membranes showed a higher recovery rate after filtering humic acid, exceeding 100%. This is likely because the surface of the TEP membrane is more dense and intact, making it less prone to contaminant adhesion, thus resulting in higher antifouling performance and a higher recovery rate. Secondly, the adsorption of humic acid by the membrane material may also be a factor. While increasing the rejection rate, the humic acid molecules remaining on the membrane adsorb onto the inner wall of the membrane pores and the surface of the membrane, forming a hydrophilic layer. This enhances the membrane's hydrophilicity, promotes pure water transport, and further improves the recovery flux and recovery rate of the TEP membrane. Therefore, the recovery rate of humic acid filtered by the TEP membrane is significantly improved.

[0047] The ultrafiltration retention performance test results of the ultrafiltration membranes obtained in Comparative Examples 3-6 of this invention are shown in the appendix to the specification. Figure 7 As shown. Figure 7 (a) Water permeability of different GVL membranes; Figure 7 (b) BSA permeability and rejection rate of different GVL membranes; Figure 7 (c) FRR, Rr, and Rir of different GVL membranes; (a is pure water, b is BSA solution, solvent is pure water) Ultrafiltration tests were performed on the BSA solution. The results showed that after partially replacing DMAC with GVL, the pure water flux of the prepared GVL membrane was significantly lower than that of the DMAC-based membrane. The BSA flux of the GVL membrane was also much lower than that of the DMAC-based membrane, but the rejection rate increased. Compared with DMI and TEP membranes, the GVL membrane showed only a small increase in the BSA rejection rate. However, the BSA flux of the GVL membrane was significantly lower than that of the DMI and TEP membranes. Furthermore, calculations of the recovery rate, reversible fouling rate, and irreversible fouling rate of the GVL membrane did not show any significant advantage. Therefore, GVL was not chosen as a green solvent to replace DMAC.

[0048] The performance test results of various membranes obtained by this invention are shown in Table 1.

[0049] Table 1

[0050] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A modified PVDF ultrafiltration membrane, characterized in that, The preparation method includes the following steps: (1) Add PVDF powder to an organic solvent and stir at 90-100℃ until completely dissolved to obtain PVDF solution; (2) The PVDF solution is kept at a constant temperature of 90-100℃ to remove air bubbles, and then uniformly poured onto the surface of the nonwoven fabric on one side to obtain PVDF modified nonwoven fabric. (3) The PVDF modified nonwoven fabric is completely immersed in deionized water for phase transformation. During the immersion process, the PVDF modified layer on the surface of the PVDF modified nonwoven fabric is always parallel to the ground and located on the upper part of the nonwoven fabric. After the immersion is completed, an ultrafiltration membrane is obtained.

2. The modified PVDF ultrafiltration membrane according to claim 1, characterized in that, The organic solvent in step (1) is a mixed solution of DMI or TEP and DMAC.

3. The modified PVDF ultrafiltration membrane according to claim 2, characterized in that, The organic solvent in step (1) is a mixed solution of DMI and DMAC in a mass ratio of 50:

50.

4. The modified PVDF ultrafiltration membrane according to claim 2, characterized in that, The organic solvent in step (1) is a mixed solution of TEP and DMAC in a mass ratio of 50:

50.

5. The modified PVDF ultrafiltration membrane according to claim 1, characterized in that, The mass ratio of PVDF powder to organic solvent is 14:

86.

6. An ultrafiltration device, characterized in that, The modified PVDF ultrafiltration membrane according to any one of claims 1-5 is used as the ultrafiltration membrane material of the ultrafiltration device.

7. The ultrafiltration device according to claim 6, characterized in that, Ultrafiltration can be performed on humic acid or BSA.

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