PMP composite membrane with gradient pore structure

Abstract

The invention provides a poly (4-methyl-1-pentene) (PMP) membrane with a gradient pore structure and a preparation method of the poly (4-methyl-1-pentene) membrane. The poly (4-methyl-1-pentene) membrane is suitable for an in-vitro membrane type artificial lung (ECMO). According to the PMP membrane, PMP and polyvinylidene fluoride (PVDF) are physically blended, multi-walled carbon nanotubes are combined for reinforcement, and the composite membrane with an asymmetric gradient pore structure is prepared through a multi-stage electrostatic spinning process. Wherein the compact layer effectively inhibits plasma leakage, and the porous layer optimizes the gas exchange efficiency. The preparation method is carried out at normal temperature and normal pressure, the limitation of high-temperature processing of a traditional PMP film is overcome, and meanwhile, the mechanical strength and the gas permeability of the film are remarkably improved. The PMP membrane has excellent biocompatibility, long-term stability and plasma leakage resistance, can meet the long-term use requirement of ECMO, and provides a better solution for an artificial lung membrane technology.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial lung oxygenators, and specifically provides a poly(4-methyl-1-pentene) (PMP) gas exchange membrane with a gradient pore structure and a preparation method thereof. The PMP membrane constructs an asymmetric structure through electrospinning technology, including a dense skin layer and a porous support layer, and has both high gas permeability, excellent anti-plasma leakage performance and long-term use stability, and is suitable for an extracorporeal membrane oxygenation (ECMO) system. Background Art

[0002] The extracorporeal membrane oxygenation (ECMO) is a key technology for treating severe respiratory failure, and its core functions are: (1) Oxygen transport: When blood flows through the oxygenator, oxygen in the mixed gas with a high oxygen partial pressure (P O2 ) (usually an O2 / air mixture) diffuses through the fiber membrane to the blood side with a low oxygen partial pressure; (2) Carbon dioxide removal: Carbon dioxide with a high partial pressure (P CO2 ) in the blood diffuses in the opposite direction to the gas environment outside the membrane. This membrane needs to meet the following requirements simultaneously: (1) Efficient gas exchange: Rapid exchange of CO2 and O2 in the blood is achieved through diffusion; (2) Anti-plasma leakage: Prevent plasma penetration from causing membrane pore blockage or a decrease in gas exchange efficiency; (3) Mechanical strength and biocompatibility: Ensure structural stability and blood compatibility during long-term circulation use.

[0003] Traditional membrane materials have certain limitations. For example, polypropylene (PP) has low gas exchange efficiency, insufficient mechanical strength (tensile strength < 10 MPa), and is prone to plasma leakage during long-term use; although traditional PMP membranes have excellent gas permeability, the existing preparation methods (such as thermally induced phase separation method, melt spinning method) have the following problems: The process is complex. For example, the thermally induced phase separation method is used in CN202210434903.5, which requires high-temperature (>200 °C) treatment, high energy consumption and is prone to material degradation; the porosity is insufficient. For example, the porosity of the PMP membrane described in CN202410823679.8 is only 45% - 65%, which limits the gas diffusion efficiency.

[0004] Polyvinylidene fluoride has become an ideal material for enhancing the structural stability of PMP membranes due to its excellent chemical stability (resistant to strong acids, strong bases and biological corrosion). In addition, the gradient pore structure can optimize gas exchange efficiency and blood compatibility. The present invention solves the problem of unbalanced performance of traditional membrane materials through the innovative combination of the PMP / PVDF blend system and the gradient electrospinning process, and provides a method for efficiently preparing a PMP membrane with both high oxygen permeability and a gradient pore structure. Summary of the Invention

[0005] In view of the technical defects of the existing PMP artificial lung membranes, such as complex preparation processes, insufficient mechanical properties, and single pore structure, the present invention provides a novel PMP membrane with a gradient pore structure and a preparation method thereof. The specific steps are as follows: (1) Prepare a PMP-PVDF polymer blend solution Mix poly(4-methyl-1-pentene) and polyvinylidene fluoride in a mass ratio of 1-5:1, and dissolve them in a ternary mixed solvent of cyclohexane, N,N-dimethylformamide, and acetone to form a homogeneous solution; (2) Prepare a PMP membrane casting solution Add multi-walled carbon nanotubes and a dispersant to the PMP-PVDF polymer blend solution. The addition amount of the multi-walled carbon nanotubes is 0.01-2% of the total mass of the casting solution, and stir until fully dispersed to obtain a casting solution; (3) Prepare a PMP membrane with a gradient pore structure by electrospinning Adjust the ratio of PMP and PVDF to different values in batches, and repeat steps (1) and (2) to obtain casting solutions of different batches. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; among them, the electrospinning parameters include: voltage 10-25 kV, flow rate 0.3-3.0 mL / h, distance between the nozzle and the collector 10-20 cm; after electrospinning, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0006] Preferably, in step (1), it is composed of cyclohexane, N,N-dimethylformamide, and acetone, and their mass ratio is 2-5:1-2:3-5.

[0007] Preferably, the PMP membrane in step (2) is composed of a blend of poly(4-methyl-1-pentene) and polyvinylidene fluoride, and multi-walled carbon nanotubes are added to improve the mechanical strength, and its porosity changes in a gradient along the membrane thickness direction.

[0008] Preferably, one side of the PMP membrane with a gradient pore structure in step (3) is a dense layer for reducing the risk of plasma leakage, and the other side is a porous layer for enhancing gas diffusion.

[0009] Preferably, the tensile strength of the PMP membrane with a gradient pore structure in step (3) is 125 MPa, and the gas flux is 2.0-10.0 mL / (min·cm²·bar).

[0010] The present invention provides an electrospinning technique that is simpler and more controllable compared to traditional melt spinning and thermally induced phase separation methods. The film formation mechanism of the electrospinning process is that under the action of a high-voltage electric field, a polymer solution forms a Taylor cone at the nozzle and generates a charged jet. During the flight of the jet towards the receiving device, the solvent rapidly volatilizes or the melt cools and solidifies, and finally fibers are formed and deposited on the receiving device to form a film. Beneficial effects

[0011] Compared with the prior art, the present invention has significant advantages: 1. Process optimization By using a PMP / PVDF blend system and combining a ternary mixed solvent (cyclohexane / DMF / acetone), PMP can be dissolved at room temperature, avoiding material degradation caused by traditional high-temperature processing and reducing energy consumption.

[0012] 2. Precise regulation of the gradient pore structure Through a multi-stage electrospinning process, a gradient pore distribution along the film thickness direction is achieved, taking into account both high gas permeability and anti-plasma leakage performance.

[0013] 3. Significantly improved mechanical properties By introducing PVDF and multi-walled carbon nanotubes, the tensile strength of the PMP film is increased to 15 - 25 MPa, meeting the requirements for long-term cyclic use of ECMO.

[0014] 4. Long-term operation stability The PMP composite nanofiber membrane prepared by this patent has antibacterial properties, long-term operation stability, and corrosion resistance. Polyvinylpyrrolidone not only acts as a dispersant but also imparts a certain hydrophilicity to the membrane surface, which can effectively prevent plasma coagulation and ensure the long-term stability of the membrane. The oxygen flux is ≥2.0 mL / (min·cm²·bar), and the membrane hemolysis rate is ≤5%. Description of the drawings

[0015] Figure 1 Schematic diagram of the gas exchange process of the gradient pore PMP membrane Figure 2 Water contact angles of each layer of the PMP membrane with a gradient pore structure in Example 3: (a) porous layer; (b) transition layer; (c) dense layer. Detailed implementation manners

[0016] The following further elaborates the present invention in conjunction with specific embodiments. Embodiments

[0017] (1) Preparation of the PMP-PVDF polymer blend solution Add a magnetic stir bar to a reagent bottle, add 0.60 g of poly(4-methyl-1-pentene) and 0.60 g of poly(vinylidene fluoride) to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h at 50 °C under airtight conditions, with a stirring speed of 260 r / min, to make the mixture homogeneous and form a uniform solution, namely the PMP-PVDF polymer blend solution.

[0018] (2)Preparation of the PMP membrane casting solution Add 0.05 g of polyvinylpyrrolidone to the above-mentioned PMP-PVDF polymer blend solution and keep stirring while heating for 2 h. After uniform dispersion, add 0.05 g of multi-walled carbon nanotubes to the above-mentioned mixed solution. After ultrasonic treatment for 30 min, a uniformly dispersed solution is formed. Continue to keep stirring while heating at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain the casting solution; (3)Preparation of the PMP membrane with a gradient pore structure by electrospinning Adjust the ratio of PMP to PVDF in batches to different values (PMP:PVDF = 1.0:1.0, 1.3:1.1, 7.0:5.0), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of the PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil flat on the roller of the electrospinning device. Add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe so that the casting solution just slightly flows out of the syringe needle. Apply a voltage to the needle to make the casting solution into filaments. Electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0019] Perform performance tests on the PMP nanofiber membrane prepared in Example 1. The oxygen flux of the membrane is 4.68 mL / (min·cm²·bar), the hemolysis rate of the membrane is 3.6%, the porosity is 60%, and the tensile strength is 18 MPa; Perform experiments on the PMP nanofiber membrane for 48 h continuously, and its performance can still reach 96%. Example

[0020] (1)Preparation of the PMP-PVDF polymer blend solution Add a magnetic stir bar to a reagent bottle. Add 0.65 g of poly(4-methyl-1-pentene) and 0.55 g of poly(vinylidene fluoride) to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h at 50 °C under air isolation conditions, with a stirring speed of 260 r / min, to make them mix evenly and form a homogeneous solution, that is, obtain a PMP-PVDF polymer blend solution.

[0021] (2)Prepare a PMP membrane casting solution Add 0.05 g of polyvinylpyrrolidone to the above PMP-PVDF polymer blend solution, and keep stirring while heating for 2 h. After uniform dispersion, add 0.05 g of multi-walled carbon nanotubes to the above mixed solution. After ultrasonic treatment for 30 min, a uniformly dispersed solution is formed. Continue to keep stirring while heating at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain a casting solution; (3)Prepare a PMP membrane with a gradient pore structure by electrospinning Adjust the ratio of PMP to PVDF in batches to different values (PMP:PVDF = 1.3:1.1, 7.0:5.0, 5.0:3.0), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil flat on the roller of the electrospinning device. Add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe to make the casting solution just flow out slightly from the syringe needle. Apply a voltage to the needle to make the casting solution form filaments. Electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0022] Perform performance tests on the PMP nanofiber membrane prepared in Example 2. The oxygen flux of the membrane is 5.23 mL / (min·cm²·bar), the hemolysis rate of the membrane is 3.9%, the porosity is 64%, and the tensile strength is 20 MPa; Perform an experiment on the PMP nanofiber membrane for 48 h continuously, and its performance can still reach 95%. Example

[0023] (1)Prepare a PMP-PVDF polymer blend solution Add a magnetic stir bar to a reagent bottle, add 0.70 g of poly(4-methyl-1-pentene) and 0.50 g of poly(vinylidene fluoride) to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h at 50 °C under airtight conditions, with a stirring speed of 260 r / min, to make the mixture homogeneous and form a uniform solution, i.e., obtain a PMP-PVDF polymer blend solution.

[0024] (2)Preparation of PMP membrane casting solution Add 0.04 g of polyvinylpyrrolidone to the above PMP-PVDF polymer blend solution and keep stirring while heating for 2 h. After uniform dispersion, add 0.06 g of multi-walled carbon nanotubes to the above mixed solution. After ultrasonic treatment for 30 min, a uniformly dispersed solution is formed. Continue to keep stirring while heating at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain a casting solution; (3)Preparation of PMP membrane with gradient pore structure by electrospinning Adjust the ratio of PMP to PVDF in batches to different values (PMP:PVDF = 7.0:5.0, 5.0:3.0, 2.0:1.0), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil flat on the roller of the electrospinning device. Add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe to make the casting solution just flow out slightly from the syringe needle. Apply a voltage to the needle to make the casting solution form filaments. Electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0025] Perform performance tests on the PMP nanofiber membrane prepared in Example 3. The oxygen flux of the membrane is 6.15 mL / (min·cm²·bar), the hemolysis rate of the membrane is 3.7%, the porosity is 66%, and the tensile strength is 24 MPa; The performance of the PMP nanofiber membrane can still reach 95% after continuous experiments for 48 h. Example

[0026] (1)Preparation of PMP-PVDF polymer blend solution Add a magnetic stir bar to a reagent bottle. Add 0.75 g of poly(4-methyl-1-pentene) and 0.45 g of polyvinylidene fluoride to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h at 50 °C under airtight conditions, with a stirring speed of 260 r / min, to make them mix evenly and form a homogeneous solution, namely the PMP-PVDF polymer blend solution.

[0027] (2)Preparation of PMP membrane casting solution Add 0.05 g of polyvinylpyrrolidone to the above PMP-PVDF polymer blend solution and keep stirring while heating for 2 h. After uniform dispersion, add 0.05 g of multi-walled carbon nanotubes to the above mixed solution. After ultrasonic treatment for 30 min, a uniformly dispersed solution is formed. Continue to keep stirring while heating at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain the casting solution; (3)Preparation of PMP membrane with gradient pore structure by electrospinning Adjust the ratios of PMP and PVDF in batches to different values (PMP:PVDF = 5.0:3.0, 2.0:1.0, 1.7:0.7), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil flat on the roller of the electrospinning device. Add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe so that the casting solution just slightly flows out of the syringe needle. Apply a voltage to the needle to make the casting solution form filaments, and electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0028] Perform performance tests on the PMP nanofiber membrane prepared in Example 4. The oxygen flux of the membrane is 5.61 mL / (min·cm²·bar), the hemolysis rate of the membrane is 3.1%, the porosity is 68%, and the tensile strength is 21 MPa; The performance of the PMP nanofiber membrane can still reach 94% after 48 h of continuous experiment. Example

[0029] (1)Preparation of PMP-PVDF polymer blend solution Add a magnetic stir bar to a reagent bottle. Add 0.80 g of poly(4-methyl-1-pentene) and 0.40 g of poly(vinylidene fluoride) to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h under the conditions of heating to 50 °C and isolating from air, with a stirring speed of 260 r / min, to make it uniformly mixed and form a homogeneous solution, that is, a PMP-PVDF polymer blend solution is obtained.

[0030] (2)Preparation of PMP membrane casting solution Add 0.05 g of polyvinylpyrrolidone to the above-mentioned PMP-PVDF polymer blend solution, and keep heating and stirring for 2 h. After uniform dispersion, add 0.05 g of multi-walled carbon nanotubes to the above-mentioned mixed solution. After ultrasonic treatment for 30 min, a uniformly dispersed solution is formed. Continue to keep heating and stirring at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain a casting solution; (3)Preparation of PMP membrane with gradient pore structure by electrospinning Adjust the ratios of PMP and PVDF in batches to different values (PMP:PVDF = 2.0:1.0, 1.7:0.7, 3.0:1.0), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil paper flat on the roller of the electrospinning machine. Add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe to make the casting solution just slightly flow out from the syringe needle. Apply a voltage to the needle to make the casting solution into filaments. Electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0031] Perform performance tests on the PMP nanofiber membrane prepared in Example 5. The oxygen flux of the membrane is 5.41 mL / (min·cm²·bar), the hemolysis rate of the membrane is 2.8%, the porosity is 72%, and the tensile strength is 24 MPa; Conduct an experiment on the PMP nanofiber membrane for 48 h continuously, and its performance can still reach 98%. Example

[0032] (1)Preparation of PMP-PVDF polymer blend solution Add a magnetic stir bar to a reagent bottle, add 0.85 g of poly(4-methyl-1-pentene) and 0.35 g of poly(vinylidene fluoride) to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h under the conditions of heating to 50 °C and isolating from air, with a stirring speed of 260 r / min, to make it mix evenly and form a homogeneous solution, that is, obtain the PMP-PVDF polymer blend solution.

[0033] (2)Prepare the PMP membrane casting solution Add 0.05 g of polyvinylpyrrolidone to the above-mentioned PMP-PVDF polymer blend solution, and keep stirring while heating for 2 h. After dispersing evenly, add 0.05 g of multi-walled carbon nanotubes to the above-mentioned mixed solution, and ultrasonically treat for 30 min to form a uniformly dispersed solution. Continue to keep stirring while heating at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain the casting solution; (3)Prepare the PMP membrane with a gradient pore structure by electrospinning Adjust the ratio of PMP to PVDF in batches to different values (PMP:PVDF = 1.7:0.7, 3.0:1.0, 4.0:1.0), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of the PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin yarns in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil flat on the roller of the electrospinning machine, add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe to make the casting solution just slightly flow out from the syringe needle. Apply a voltage to the needle to make the casting solution into filaments, and electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

[0034] Perform performance tests on the PMP nanofiber membrane prepared in Example 6. The oxygen flux of the membrane is 5.27 mL / (min·cm²·bar), the hemolysis rate of the membrane is 3.5%, the porosity is 71%, and the tensile strength is 26 MPa; Perform experiments on the PMP nanofiber membrane for 48 h continuously, and its performance can still reach 97%. Example

[0035] (1)Prepare the PMP-PVDF polymer blend solution Add a magnetic stir bar to the reagent bottle. Add 0.90 g of poly(4-methyl-1-pentene) and 0.30 g of poly(vinylidene fluoride) to the reagent bottle, and then slowly add 8.7 g of a ternary mixed solvent. Continuously stir for 4 h under the conditions of heating to 50 °C and isolating from air, with a stirring speed of 260 r / min, to make them mix evenly and form a homogeneous solution, that is, obtain the PMP-PVDF polymer blend solution.

[0036] (2)Preparation of the PMP membrane casting solution Add 0.05 g of polyvinylpyrrolidone to the above PMP-PVDF polymer blend solution and keep stirring while heating for 2 h. After dispersing evenly, add 0.05 g of multi-walled carbon nanotubes to the above mixed solution. After ultrasonic treatment for 30 min, form a uniformly dispersed solution, and continue to keep stirring while heating at 50 °C for 12 h, with a stirring speed of 260 r / min, to obtain the casting solution; (3)Preparation of the PMP membrane with a gradient pore structure by electrospinning Adjust the ratio of PMP and PVDF to different values in batches (PMP:PVDF = 3.0:1.0, 4.0:1.0, 5.0:1.0), and repeat steps (1) and (2) to obtain casting solutions of different batches. The content of the PMP-PVDF polymer in the casting solution is 12%. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; Fix the aluminum foil flat on the roller of the electrospinning device. Add the casting solution prepared in (2) to a syringe, connect the electrospinning machine, turn on the machine and set the spinning parameters of the injection pump. The spinning volume is 6 mL, and the spinning rate is 1.2 mL / h. Push the injection pump to the bottom of the syringe to make the casting solution just flow out slightly from the syringe needle. Apply a voltage to the needle to make the casting solution into filaments. Electrospin for 5 h. After electrospinning is completed, peel the PMP membrane from the receiving substrate and dry it to obtain the PMP membrane with a gradient pore structure.

[0037] Perform performance tests on the PMP nanofiber membrane prepared in Example 7. The oxygen flux of the membrane is 4.78 mL / (min·cm²·bar), the hemolysis rate of the membrane is 3.3%, the porosity is 72%, and the tensile strength is 27 MPa; The performance of the PMP nanofiber membrane can still reach 97% after 48 h of continuous experiments.

Claims

1. A method for preparing a PMP membrane with a gradient pore structure, characterized in that, It includes the following steps: (1) Prepare a PMP-PVDF polymer blend solution Mix poly(4-methyl-1-pentene) and polyvinylidene fluoride in a mass ratio of 1-5:1, and dissolve them in a ternary mixed solvent of cyclohexane, N,N-dimethylformamide, and acetone to form a homogeneous solution; (2) Prepare a PMP membrane casting solution Add multi-walled carbon nanotubes and a dispersant to the PMP-PVDF polymer blend solution. The addition amount of the multi-walled carbon nanotubes is 0.01-2% of the total mass of the casting solution, and stir until fully dispersed to obtain a casting solution; (3) Prepare a PMP membrane with a gradient pore structure by electrospinning Adjust the ratio of PMP and PVDF to different values in batches, and repeat steps (1) and (2) to obtain casting solutions of different batches. Use the electrospinning process to spin the fibers in sequence to form a PMP membrane with a three-layer structure; among them, the electrospinning parameters include: voltage 10-25 kV, flow rate 0.3-3.0 mL / h, distance between the nozzle and the collector 10-20 cm; after electrospinning, peel the PMP membrane from the receiving substrate and dry it to obtain a PMP membrane with a gradient pore structure.

2. The preparation method according to claim 1, wherein The mass ratio of cyclohexane, DMF, and acetone in the ternary mixed solvent is 2-5:1-2:3-5.

3. The preparation method according to claim 1, wherein The PMP membrane is composed of a blend of poly(4-methyl-1-pentene) and polyvinylidene fluoride, and multi-walled carbon nanotubes are added to improve the mechanical strength, and its porosity changes in a gradient along the membrane thickness direction.

4. The preparation method according to claim 1, wherein, One side of the PMP membrane is a dense layer for reducing the risk of plasma leakage, and the other side is a porous layer for enhancing gas diffusion.

5. The gradient pore structure PMP film according to claim 1, wherein The tensile strength of the membrane is 125 MPa, and the gas flux is 2.0-10.0 mL / (min·cm²·bar).

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