Porosity-adjustable PVDF / EVOH hollow fiber membrane and preparation method thereof

Abstract

The invention discloses a porosity-adjustable PVDF / EVOH hollow fiber membrane and a preparation method thereof.The preparation method comprises the steps that polyvinylidene fluoride serves as a matrix phase, a first substance or a second substance serves as a pore-foaming agent, the matrix phase and the pore-foaming agent are evenly mixed and dried, and a spinning raw material is obtained; putting the spinning raw material into a twin-screw spinning machine, extruding and granulating to obtain first particles; uniformly mixing the first particles with the dispersed phase, then putting the mixture into a twin-screw spinning machine, and performing extrusion and granulation to obtain spinning master batches; putting the spinning master batch into a twin-screw spinning machine, and extruding to obtain a primary PVDF / EVOH hollow fiber membrane; and stretching the primary PVDF / EVOH hollow fiber membrane: firstly carrying out cold stretching at 20-28 DEG C, then carrying out hot stretching at 90-130 DEG C to obtain the PVDF / EVOH hollow fiber membrane, and carrying out ultrasonic extraction and washing to obtain the porosity-adjustable PVDF / EVOH hollow fiber membrane. According to the invention, the interface pore-making principle is utilized to regulate and control multiple pore structures of dissolution pores, interface pores and stretching pores, so that the membrane pores are compact, the separation precision is high, and the permeability is good.

Description

Technical Field

[0001] The invention relates to the technical field of hollow fiber membranes, and in particular to a PVDF / EVOH hollow fiber membrane with adjustable porosity and a preparation method thereof. Background Art

[0002] The problem of water pollution is becoming increasingly serious, per capita water resources are constantly decreasing, and sewage treatment urgently needs an efficient solution. Membrane separation, as an important part of water treatment technology, has attracted widespread attention. However, a large amount of organic solvents are often used in the membrane preparation process, which will produce pollution emissions. In the membrane making process, the melt spinning method does not require the use of organic solvents and is relatively environmentally friendly and green. Polyvinylidene fluoride (PVDF) is widely used in the preparation of membrane materials due to its high chemical stability and strong mechanical properties. However, its low surface energy makes the PVDF membrane hydrophilic and easy to pollute. In addition, the PVDF hollow membrane prepared by the melt spinning method has a low porosity, the pores are usually larger, the macromolecular retention rate is low, the separation accuracy is poor, and the application range is limited.

[0003] Hollow fiber membranes are divided into microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes and loose nanofiltration membranes according to the size of the membrane pore size. Among them, the pore size of the microfiltration membrane is in the range of 0.1 to 10 μm; the pore size of the ultrafiltration membrane is in the range of 5 to 100 nm; the pore size of the nanofiltration membrane is generally in the range of 1 to 2 nm; the pore size of the reverse osmosis membrane is theoretically between 0.1 and 1 nm, and the pore size of the loose nanofiltration membrane is generally between 2 and 5 nm.

[0004] There are methods to regulate membrane pore structure, but an effective method to regulate porosity has not yet been developed. Summary of the invention

[0005] One object of the present invention is to provide a method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity. The hollow fiber membrane obtained by the method has dense pores, high separation accuracy and good permeability.

[0006] Another object of the present invention is to provide a PVDF / EVOH hollow fiber membrane with adjustable porosity obtained by the above preparation method.

[0007] To this end, the present invention adopts the following technical solutions:

[0008] A method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity comprises the following steps:

[0009] S1, preparation of spinning raw materials: using polyvinylidene fluoride (PVDF) as a matrix phase, a first substance or a second substance as a porogen, firstly mixing the matrix phase and the porogen evenly, and drying to obtain a spinning raw material, wherein the first substance is polyethylene oxide, the second substance is a mixture of polyethylene oxide and sodium chloride, the mass fraction of polyvinylidene fluoride is 35 to 65 parts, the mass fraction of the first substance is 5 to 15 parts, and the mass fraction of the second substance is 30 to 55 parts;

[0010] S2, primary granulation: the spinning raw material prepared in S1 is put into a twin-screw spinning machine, the temperature of the twin-screw spinning machine is set to 160-260°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, put into a pelletizer for granulation to obtain first particles;

[0011] S3, secondary granulation: the first particles prepared in S2 are mixed with a dispersed phase, wherein the dispersed phase is ethylene-vinyl alcohol copolymer (EVOH), and after being evenly mixed, they are put into a twin-screw spinning machine again, the temperature of the twin-screw spinning machine is set to 160-250°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, they are put into a pelletizer for granulation to obtain a spinning masterbatch, wherein the mass fraction of the ethylene-vinyl alcohol copolymer is 10-30wt%, and the sum of the mass fractions of the first particles and the ethylene-vinyl alcohol copolymer is 100wt%;

[0012] S4, spinning: the spinning masterbatch prepared in S3 is put into a twin-screw spinning machine and N2 is introduced, the temperature of the twin-screw spinning machine is set to 160-230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air to obtain a primary PVDF / EVOH hollow fiber membrane;

[0013] S5, post-stretching: placing the nascent PVDF / EVOH hollow fiber membrane prepared in S4 into a stretching machine for stretching: first cold stretching and shaping at 20-28°C for 5-10 minutes, then hot stretching and shaping at 90°C-130°C for 1-2.5 hours to obtain a PVDF / EVOH hollow fiber membrane, and then ultrasonically washing it in ultrapure water at 50-100°C for 36-48 hours to obtain a PVDF / EVOH hollow fiber membrane with adjustable porosity, wherein the cold stretching ratio is 0-10%, and the hot stretching ratio is 100-250%, the cold stretching ratio is relative to the nascent PVDF / EVOH hollow fiber membrane, and the hot stretching ratio is relative to the nascent PVDF / EVOH hollow fiber membrane.

[0014] In S5, the cold stretching rate is 5 to 15 mm / min, and the hot stretching rate is 10 to 30 mm / min.

[0015] In S1, the particle size of the matrix phase is ≤20 μm, and the particle size of the porogen is ≤20 μm.

[0016] In S2, the speed of the pelletizer is 300-700 r / min, and in S3, the speed of the pelletizer is 400-800 r / min.

[0017] In S1, the drying temperature is 40-80°C, and the drying time is 24-48 hours.

[0018] When the second substance is used as a porogen, the mass ratio of polyethylene oxide to sodium chloride is (10-15):(20-40).

[0019] The above preparation method obtains a PVDF / EVOH hollow fiber membrane with adjustable porosity.

[0020] The porosity of the PVDF / EVOH hollow fiber membrane with adjustable porosity is 20-76%, and the pore size is 0.04-0.08 μm.

[0021] The bovine serum albumin (BSA) retention rate of the PVDF / EVOH hollow fiber membrane with adjustable porosity is greater than 90%.

[0022] The pure water flux of the adjustable porosity PVDF / EVOH hollow fiber membrane is 200-1400 L / m 2 h, breaking strength ≥20MPa.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention prepares a hydrophilic, multi-porous polyvinylidene fluoride hollow fiber membrane (PVDF / EVOH hollow fiber membrane with adjustable porosity) by melt spinning, and does not use organic solvents throughout the process, which is green and environmentally friendly. The preparation method does not discharge organic wastewater and has low cost.

[0025] 2. The present invention uniformly mixes the matrix phase and the dispersed phase through the dispersed phase mixing technology. In the melt spinning process, the membrane components are fully and evenly mixed through secondary granulation. The difference in compatibility and the principle of interface pore formation are utilized. After post-stretching at different ratios, the interface is induced to form pore structures of different forms, thereby obtaining hollow fiber membranes with different porosities and ideal porosity.

[0026] 3. The preparation method of the present invention utilizes the principle of interface pore formation in post-processing to regulate the multiple pore structures of dissolution pores, interface pores, and stretching pores. The functional particles (EVOH) are evenly distributed in the PVDF / EVOH hollow fiber membrane with adjustable porosity, making the membrane pores dense, the separation accuracy high, and the permeability good. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram of the outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 1;

[0028] Figure 2 This is a diagram of the outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2;

[0029] Figure 3 A cross-sectional view of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2;

[0030] Figure 4 This is a diagram of the outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2;

[0031] Figure 5 This is the outer surface image of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0033] Example 1

[0034] A method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity comprises the following steps:

[0035] S1, preparation of spinning raw materials: using polyvinylidene fluoride as a matrix phase and a first substance (polyethylene oxide) as a porogen, firstly putting the matrix phase and the porogen into a high-speed mixer and mixing them for 10 minutes until they are uniform, and then putting them into an oven and drying them at 40° C. for 48 hours, wherein the mass fraction of polyvinylidene fluoride is 65 parts and the mass fraction of polyethylene oxide is 5 parts;

[0036] S2, primary granulation: the spinning raw material prepared in S1 is put into a twin-screw spinning machine, the temperature of the twin-screw spinning machine is set to 250° C., extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, put into a pelletizer for granulation (the speed of the pelletizer is 500 r / min) to obtain the first particles;

[0037] S3, secondary granulation: the first particles prepared in S2 are mixed with the dispersed phase (EVOH), and after being evenly mixed, they are put into a twin-screw spinning machine again, the temperature of the twin-screw spinning machine is set to 230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after being cooled and solidified, they are put into a pelletizer for granulation (the speed of the pelletizer is 600r / min) to obtain a spinning masterbatch, wherein the mass fraction of EVOH is 30wt%, and the sum of the mass fractions of EVOH and the first particles is 100wt%;

[0038] S4, spinning: the spinning masterbatch prepared in S3 is put into a twin-screw spinning machine and N2 is introduced, the temperature of the twin-screw spinning machine is set to 230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air to obtain a primary PVDF / EVOH hollow fiber membrane;

[0039] S5, post-stretching: the nascent PVDF / EVOH hollow fiber membrane prepared in S4 is placed in a stretching machine for stretching: hot stretching and shaping at 90°C for 1 hour to obtain a PVDF / EVOH hollow fiber membrane, and then placed in ultrapure water at 80°C for ultrasonic treatment for 48 hours to obtain a PVDF / EVOH hollow fiber membrane with adjustable porosity, wherein the cold stretching ratio is 0% (i.e., no cold stretching is performed), and the hot stretching ratio is 100%.

[0040] The porosity of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 1 is 20.3%, the pore size is 0.04 μm, the breaking strength is 20 MPa, and the pure water flux of the PVDF / EVOH hollow fiber membrane with adjustable porosity is 230 L / m under 0.3 MPa. 2 h, BSA retention rate was 92%.

[0041] Example 2

[0042] A method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity comprises the following steps:

[0043] S1, preparation of spinning raw materials: using polyvinylidene fluoride as the matrix phase and the second substance (polyethylene oxide and sodium chloride) as the porogen, firstly putting the matrix phase and the porogen into a high-speed mixer and mixing them for 10 minutes until they are uniform, and then putting them into an oven and drying them at 40° C. for 48 hours, wherein the mass fraction of polyvinylidene fluoride is 50 parts, the mass fraction of the second substance is 30 parts, the mass fraction of polyethylene oxide in the second substance is 10 parts, and the mass fraction of sodium chloride in the second substance is 20 parts;

[0044] S2, primary granulation: the spinning raw material prepared in S1 is put into a twin-screw spinning machine, the temperature of the twin-screw spinning machine is set to 250° C., extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, put into a pelletizer for granulation (the speed of the pelletizer is 500 r / min) to obtain the first particles;

[0045] S3, secondary granulation: the first particles prepared in S2 are mixed with the dispersed phase (EVOH), and after being evenly mixed, they are put into a twin-screw spinning machine again, the temperature of the twin-screw spinning machine is set to 230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, they are put into a pelletizer for granulation (the speed of the pelletizer is 600r / min) to obtain a spinning masterbatch, wherein the mass fraction of EVOH is 20wt%, and the sum of the mass fractions of EVOH and the first particles is 100wt%;

[0046] S4, spinning: the spinning masterbatch prepared in S3 is put into a twin-screw spinning machine and N2 is introduced, the temperature of the twin-screw spinning machine is set to 230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air to obtain a primary PVDF / EVOH hollow fiber membrane;

[0047] S5, post-stretching: the nascent PVDF / EVOH hollow fiber membrane prepared in S4 is placed in a stretching machine for stretching: first, cold stretching and shaping at 25°C for 10 minutes, then hot stretching and shaping at 110°C for 1 hour to obtain a PVDF / EVOH hollow fiber membrane, and then it is placed in ultrapure water at 80°C for ultrasonic treatment for 48 hours to obtain a PVDF / EVOH hollow fiber membrane with adjustable porosity, wherein the cold stretching ratio is 5%, and the hot stretching ratio is 145%.

[0048] The porosity of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2 is 44.5%, the pore size is 0.06 μm, the breaking strength is 60 MPa, and the pure water flux of the PVDF / EVOH hollow fiber membrane with adjustable porosity is 400 L / m under 0.3 MPa. 2 h, BSA retention rate was 95%.

[0049] Example 3

[0050] A method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity comprises the following steps:

[0051] S1, preparation of spinning raw materials: using polyvinylidene fluoride as the matrix phase and the second substance (polyethylene oxide and sodium chloride) as the porogen, firstly putting the matrix phase and the porogen into a high-speed mixer and mixing them for 10 minutes until they are uniform, and then putting them into an oven and drying them at 40° C. for 48 hours, wherein the mass fraction of polyvinylidene fluoride is 35 parts, the mass fraction of the second substance is 55 parts, the mass fraction of polyethylene oxide in the second substance is 15 parts, and the mass fraction of sodium chloride in the second substance is 40 parts;

[0052] S2, primary granulation: the spinning raw material prepared in S1 is put into a twin-screw spinning machine, the temperature of the twin-screw spinning machine is set to 250° C., extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, put into a pelletizer for granulation (the speed of the pelletizer is 500 r / min) to obtain the first particles;

[0053] S3, secondary granulation: the particles prepared in S2 are mixed with the dispersed phase (EVOH), and after being evenly mixed, they are put into a twin-screw spinning machine again, the temperature of the twin-screw spinning machine is set to 230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after being cooled and solidified, they are put into a pelletizer for granulation (the speed of the pelletizer is 600r / min) to obtain a spinning masterbatch, wherein the mass fraction of EVOH is 10wt%, and the sum of the mass fractions of EVOH and the first particles is 100wt%;

[0054] S4, spinning: the spinning masterbatch prepared in S3 is put into a twin-screw spinning machine and N2 is introduced, the temperature of the twin-screw spinning machine is set to 230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air to obtain a primary PVDF / EVOH hollow fiber membrane;

[0055] S5, post-stretching: the nascent PVDF / EVOH hollow fiber membrane prepared in S4 is placed in a stretching machine for stretching: first, cold stretching and shaping at 25°C for 10 minutes, then hot stretching and shaping at 130°C for 2 hours to obtain a PVDF / EVOH hollow fiber membrane, and then it is placed in ultrapure water at 80°C for ultrasonic treatment for 48 hours to obtain a PVDF / EVOH hollow fiber membrane with adjustable porosity, wherein the cold stretching ratio is 10% and the hot stretching ratio is 190%.

[0056] The porosity of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 3 is 61.7%, the pore size is 0.06 μm, the breaking strength is 55 MPa, and the pure water flux of the PVDF / EVOH hollow fiber membrane with adjustable porosity is 800 L / m at 0.3 MPa. 2 h.

[0057] Example 4

[0058] A method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity is basically the same as that in Example 3, except that:

[0059] 1) Replace “hot stretching and shaping at 130°C for 2 hours” with “hot stretching and shaping at 130°C for 2.5 hours”;

[0060] 2) The thermal stretching ratio in this embodiment is 240%.

[0061] The porosity of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 4 is 75.2%, the pore size is 0.05 μm, the breaking strength is 38 MPa, and the pure water flux of the PVDF / EVOH hollow fiber membrane with adjustable porosity is 1400 L / m under 0.3 MPa conditions. 2 h.

[0062] Comparative Example 1

[0063] A hollow fiber membrane, the preparation method of which is basically the same as that of Example 1, the only difference being that the "dispersed phase (EVOH)" is replaced by "sodium chloride".

[0064] At 0.3 MPa, the pure water flux of the hollow fiber membrane prepared in Comparative Example 1 was measured to be 135 L / m 2 h, pore size is 0.1 μm, BSA retention rate ≤5%.

[0065] Comparative Example 2

[0066] A hollow fiber membrane is a primary PVDF / EVOH hollow fiber membrane prepared by S4 of Example 2, that is, there is no post-treatment step in this comparative example.

[0067] At 0.3 MPa, the pure water flux of the hollow fiber membrane of Comparative Example 2 was measured to be ≤70 L / m 2 h, pore size is 0.04 μm, and BSA retention rate is 80%.

[0068] During the stretching process, due to the poor compatibility between the matrix phase and the dispersed phases, an interface is generated during the spinning process. As the post-stretching progresses, the interface further becomes an interface pore. As the stretching ratio increases, the pore structure also changes. Based on this mechanism, by setting different stretching ratios, the purpose of accurately controlling the pore structure and porosity can be achieved.

[0069] Figure 1 The outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 1 is shown in FIG. Figure 1 It can be seen that the outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity has multiple pore structures (interface pores, dissolution pores and stretching pores).

[0070] Figure 2 The outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2 is shown in FIG. Figure 2 It can be seen that after high-multiple stretching, the pores of the adjustable porosity PVDF / EVOH hollow fiber membrane are longitudinally elongated.

[0071] Figure 3 to Figure 5 The high-magnification images show the interface pores, dissolution pores and stretching pores in sequence. Figure 3 This is a cross-sectional view of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2. Figure 3 It can be seen that an interfacial pore structure is generated between EVOH and the matrix phase. Figure 4 The outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2 is shown in FIG. Figure 4 It can be seen that dissolution pores are generated after the porogen is extracted and washed out. Figure 5 The outer surface of the PVDF / EVOH hollow fiber membrane with adjustable porosity prepared in Example 2 is shown in FIG. Figure 5 It can be seen that longitudinally elongated stretching holes are formed in the film after cold-hot stretching treatment.

[0072] The adjustable porosity PVDF / EVOH hollow fiber membrane of the present invention has a multiple pore structure of dissolution pores, interface pores, and stretching pores. Functional particles (ethylene-vinyl alcohol copolymer, EVOH) are evenly distributed in the adjustable porosity PVDF / EVOH hollow fiber membrane, making the membrane pores dense, the separation accuracy high, and the permeability good.

Claims

1. A method for preparing a PVDF / EVOH hollow fiber membrane with adjustable porosity, characterized in that: The following steps are involved: S1, preparation of spinning raw materials: using polyvinylidene fluoride as a matrix phase and a first substance or a second substance as a porogen, firstly mixing the matrix phase and the porogen evenly, and drying to obtain a spinning raw material, wherein the first substance is polyethylene oxide, the second substance is a mixture of polyethylene oxide and sodium chloride, the mass fraction of polyvinylidene fluoride is 35 to 65 parts, the mass fraction of the first substance is 5 to 15 parts, and the mass fraction of the second substance is 30 to 55 parts; S2, primary granulation: the spinning raw material prepared in S1 is put into a twin-screw spinning machine, the temperature of the twin-screw spinning machine is set to 160-260°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, put into a pelletizer for granulation to obtain first particles; S3, secondary granulation: the first particles prepared in S2 are mixed with a dispersed phase, wherein the dispersed phase is an ethylene-vinyl alcohol copolymer, and after being evenly mixed, they are put into a twin-screw spinning machine again, the temperature of the twin-screw spinning machine is set to 160-250°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air, and after cooling and solidification, they are put into a pelletizer for granulation to obtain a spinning masterbatch, wherein the mass fraction of the ethylene-vinyl alcohol copolymer is 10-30wt%, and the sum of the mass fractions of the first particles and the ethylene-vinyl alcohol copolymer is 100wt%; S4, spinning: the spinning masterbatch prepared in S3 is put into a twin-screw spinning machine and N2 is introduced, the temperature of the twin-screw spinning machine is set to 160-230°C, extruded from the spinneret of the twin-screw spinning machine and cooled and solidified in the air to obtain a primary PVDF / EVOH hollow fiber membrane; S5, post-stretching: the nascent PVDF / EVOH hollow fiber membrane prepared in S4 is placed in a stretching machine for stretching: firstly cold-stretched at 20-28°C and shaped for 5-10 minutes, then hot-stretched at 90°C-130°C and shaped for 1-2.5 hours to obtain a PVDF / EVOH hollow fiber membrane, and then ultrasonically washed in ultrapure water at 50-100°C for 36-48 hours to obtain a PVDF / EVOH hollow fiber membrane with adjustable porosity.

2. The preparation method according to claim 1, characterized in that: In S1, the mass ratio of polyethylene oxide to sodium chloride is (10-15):(20-40).

3. The preparation method according to claim 1, characterized in that: In S1, the particle size of the matrix phase is ≤20 μm, and the particle size of the porogen is ≤20 μm.

4. The preparation method according to claim 1, characterized in that: In S1, the drying temperature is 40-80°C, and the drying time is 24-48 hours.

5. The preparation method according to claim 1, characterized in that: In S2, the speed of the pelletizer is 300-700 r / min, and in S3, the speed of the pelletizer is 400-800 r / min.

6. The preparation method according to claim 1, characterized in that: In S5, the cold stretching rate is 5-15 mm / min, the hot stretching rate is 10-30 mm / min, the cold stretching ratio is 0-10%, the hot stretching ratio is 100-250%, the cold stretching ratio is relative to the ratio of the nascent PVDF / EVOH hollow fiber membrane, and the hot stretching ratio is relative to the ratio of the nascent PVDF / EVOH hollow fiber membrane.

7. The PVDF / EVOH hollow fiber membrane with adjustable porosity obtained by the preparation method according to any one of claims 1 to 6.

8. The PVDF / EVOH hollow fiber membrane with adjustable porosity according to claim 7, characterized in that: The porosity of the PVDF / EVOH hollow fiber membrane with adjustable porosity is 20-76%, and the pore size is 0.04-0.08 μm.

9. The PVDF / EVOH hollow fiber membrane with adjustable porosity according to claim 7, characterized in that: The bovine serum albumin retention rate of the PVDF / EVOH hollow fiber membrane with adjustable porosity is greater than 90%.

10. The PVDF / EVOH hollow fiber membrane with adjustable porosity according to claim 7, characterized in that: The pure water flux of the adjustable porosity PVDF / EVOH hollow fiber membrane is 200-1400 L / m 2 h, breaking strength ≥20MPa.

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