A plasma-modified polyethylene / polyamide composite membrane, its preparation method and application

Abstract

This invention discloses a plasma-modified polyethylene / polyamide composite membrane, its preparation method, and its applications, belonging to the field of organic solvent-resistant forward osmosis membrane technology. First, by controlling the plasma treatment time and power, and subjecting both sides of the base membrane to different degrees of plasma treatment, a modified polyethylene membrane with one side moderately hydrophilic and the other side superhydrophilic can be obtained. Then, an aromatic polyamide dense selective layer is formed on the surface of the modified polyethylene membrane through interfacial polymerization. The polyethylene-based organic solvent forward osmosis composite membrane prepared by this invention has advantages such as strong chemical stability, high organic solvent permeation, low reverse lithium chloride flux, and high rejection rate for antibiotics such as tetracycline. It can be used in fields such as thermosensitive drug concentration, dye removal, and organic solvent recovery.

Description

Technical Field

[0001] This invention belongs to the field of organic solvent-resistant forward osmosis membrane technology, and relates to a plasma-modified polyethylene / polyamide composite membrane and its application in the fields of organic solvent recovery and drug concentration. Background Technology

[0002] The synthesis of active pharmaceutical ingredients typically involves multi-step molecular construction of the target compound in various organic solvents; therefore, multi-stage purification of the drug and its intermediates is essential. This makes organic solvent removal a crucial step in drug synthesis. Traditional methods such as distillation and extraction are costly to recover, and most pharmaceutical products are highly temperature-sensitive, potentially decomposing or degrading at high temperatures. Therefore, a single-step, non-thermal separation process capable of simultaneously recovering organic solvents and concentrating the drug is highly attractive.

[0003] Among various membrane separation technologies, organic solvent nanofiltration (OSN) is a commonly used technology for drug concentration and organic solvent recovery. However, the high pressure used in the OSN process may increase additional operating and maintenance costs. Compared to separation technologies such as distillation and organic solvent nanofiltration that require external pressure, forward osmosis relies on a chemical gradient to transport the solvent from the low-concentration side to the high-concentration side, exhibiting a lower tendency to fouling. Based on the same principle, researchers Lively and Sholl described organic solvent forward osmosis (OSFO) in detail. It can deliver organic solvents to the draw solution while simultaneously concentrating the drug on the feed side. Subsequently, the diluted draw solution can be regenerated through various methods such as direct filtration, distillation, and evaporation. Organic solvent forward osmosis places higher demands on the supporting membrane material. Traditional substrates used in water treatment, such as polysulfone, polyvinylidene fluoride, and polyethersulfone, have characteristics such as low mechanical strength, easy swelling, and poor solvent resistance, making them unsuitable for organic solvent environments.

[0004] Currently, most organic solvent forward osmosis composite membranes are TFC structures composed of a porous polyimide support membrane and a dense polyamide layer formed through interfacial polymerization, or thin film nanocomposite membranes (TFN) structures formed by introducing more nanochannels to further increase the selective permeability of the membrane. Compared with other substrate membranes, polyimide is first prepared into a substrate with finger-like macropores or honeycomb pore structures by immersion precipitation phase inversion method, and then placed in a hexamethylenediamine solution of a certain concentration for crosslinking to obtain organic solvent resistance. However, there are still some drawbacks to using polyimide as a substrate membrane: (1) The preparation process is complicated and time-consuming, and requires a large amount of organic solvent as a coagulation bath and additional crosslinking process; (2) The surface of the obtained polyimide membrane contains a dense skin layer, resulting in low surface porosity; (3) The thickness of the membrane cast by scraping is relatively high (above 100 micrometers); (4) As a support substrate, its mechanical strength is poor, making it difficult to ensure the long-term continuous and stable operation of the forward osmosis process.

[0005] Therefore, it is essential to find an ideal base membrane material with excellent performance in all aspects. Non-polar polyethylene porous membranes are widely used in lithium-ion batteries due to their relatively low cost, excellent mechanical strength, and chemical inertness. Their relatively uniform open and interconnected pore structure and high surface porosity are conducive to the formation of a uniform and highly cross-linked aromatic polyamide (PA) selective layer, thereby increasing solvent flux. Most researchers use polyethylene composite membranes for water forward osmosis. However, because polyethylene membranes are superhydrophobic, polymerizing polyamide layers at their surface interfaces is challenging. Pre-modification is usually achieved by depositing or coating hydrophilic macromolecular layers on the surface. However, this method not only reduces the surface porosity of the polyethylene membrane (PE), but also results in poor stability of the hydrophilic modified layer, limiting the improvement of water flux. Work on effectively overcoming the drawbacks of polyethylene as a support membrane material and applying it to the field of organic solvent forward osmosis to achieve high selective permeability of the feed liquid has almost never been reported. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a polyethylene-based organic solvent-resistant forward osmosis composite membrane, its preparation method, and its application in the fields of organic solvent recovery and drug concentration. It aims to solve the thorny problems in the prior art, such as the complex preparation process of the supporting membrane material, poor mechanical strength and large thickness, and the difficulty in improving the forward osmosis flux performance and retention performance of organic solvents.

[0007] The technical solution of the present invention is as follows:

[0008] A plasma-modified polyethylene / polyamide composite membrane includes a plasma-modified porous polyethylene membrane substrate and a polyamide selective layer. Both the upper and lower surfaces of the porous polyethylene membrane are treated with plasma. The water contact angle of the upper surface of the plasma-modified porous polyethylene membrane is 15-90°, and the water contact angle of the lower surface is 0-10°. Crosslinked aromatic polyamide is synthesized on the upper surface of the treated porous polyethylene membrane by interfacial polycondensation.

[0009] The polyethylene film is a commercial battery separator material, prepared by melt-stretching method.

[0010] Plasma-modified polyethylene porous membranes are organic solvent-resistant polyethylene porous membranes with high mechanical strength, uniform pore size distribution, high porosity, and ultra-thin thickness. The substrate thickness is 3–50 μm, preferably 5–30 μm; the average pore size is 0.1 μm–5.0 μm, preferably 0.15 μm–3.0 μm; and the porosity is 20%–60%, preferably 30%–55%. The thickness of the polyamide separation layer is 300–1000 nm.

[0011] A method for preparing a plasma-modified polyethylene / polyamide composite membrane includes the following steps:

[0012] (1) Preparation of hydrophilic polyethylene membrane: Plasma treatment is performed on the upper surface of the polyethylene porous membrane with a power of 5-70W and a treatment time of 3-60s; plasma treatment is performed on the lower surface of the polyethylene porous membrane with a power of 40-100W and a treatment time of 20-300s.

[0013] (2) A dense selective layer is prepared by interfacial polycondensation. The aqueous solution of polyamine monomer is spread on the surface of the modified polyethylene film. After wetting, the excess monomer aqueous solution is poured off and the surface is wiped. Then, a polyacrylamide chloride n-hexane solution is deposited on the surface of the above-wetted film for interfacial polymerization. After the interfacial polymerization is completed, the composite film is further crosslinked at 65-75℃.

[0014] This invention introduces polar groups (e.g., ester groups) into a nonpolar polyethylene membrane through plasma chemical etching, altering the membrane's polarity from nonpolar to polar, which facilitates the transport of polar solvents such as ethanol and increases permeation flux. Simultaneously, the introduced polar groups enhance the hydrophilicity of the polyethylene membrane, facilitating the formation of composite membranes with a polyamide layer. Furthermore, chemical etching can increase the pore size of the membrane material, thereby improving porosity.

[0015] The research revealed that strong chemical etching affects the strength of the polyethylene film and creates a superhydrophilic structure on its surface, making the polyamide layer on the upper surface prone to detachment. Therefore, only a mild plasma treatment of the upper surface is possible, followed by further plasma treatment of the lower surface to modify the morphology and polarity of the polyethylene film.

[0016] In step (1), the upper and lower surfaces of the polyethylene porous membrane are subjected to plasma treatment of different degrees. Specifically, the upper surface, which is relatively flat, is treated with a power of 5-70W and a treatment time of 3-60s, preferably with a power of 10-60W and a treatment time of 3-50s; the lower surface, which is relatively rough, is treated with a power of 40-100W and a treatment time of 20-300s, preferably with a power of 45-90W and a treatment time of 50-300s.

[0017] In step (1), the two surfaces of the hydrophilic polyethylene film exhibit different wettability and micromorphology. That is, the upper surface treated with low power and short time plasma does not undergo obvious etching, and the surface water contact angle is 15-90°, forming a moderately hydrophilic upper surface. The lower surface treated with high power and long time plasma undergoes obvious chemical etching, and the surface water contact angle drops to below 10° within 2s, forming a superhydrophilic lower surface. The average pore size of the polyethylene film is increased to 0.18-3.02μm (after plasma etching, the polyethylene molecular chains break, and the membrane pores become larger, increasing by 0.02-0.05μm compared to before treatment, thus increasing the porosity of the polyethylene support layer).

[0018] In step (2), the polyamine monomer is one of piperazine, m-phenylenediamine, pyromellitic triamine, or polyethyleneimine; the concentration of the polyamine monomer is 1-6 wt%, preferably 2.0-4.4 wt%; the polyacrylamide chloride monomer is 1,3,5-phenyltricarboxylic acid chloride, isophthalic acid chloride, or biphenyltetramethyl chloride; the concentration of the polyacrylamide chloride is 0.1-0.6 wt%, preferably 0.10-0.35 wt%.

[0019] In step (2), the interfacial polycondensation process involves spreading and wetting the polyamine monomer aqueous solution on the membrane surface for 2 to 25 minutes, preferably 2 to 20 minutes, the interfacial polymerization time for 1 to 10 minutes, preferably 1 to 5 minutes, and the crosslinking time at 65-75°C for 5 to 30 minutes, preferably 5 to 15 minutes.

[0020] The plasma-modified polyethylene / polyamide composite membrane is used as a forward osmosis membrane for the treatment of solutions containing organic solvents, such as for organic solvent recovery and the concentration of antibiotics or removal of dyes from organic solvents. When the solute used as the draw solution is any one of lithium chloride, PEG400, and citric acid, the methanol permeation flux is 5.0–11.4 LMH, the ethanol permeation flux is 4.2–8.5 LMH, the isopropanol permeation flux is 3.8–7.5 LMH, the reverse draw solution solute flux is 0.02–0.12 gMH, and the rejection rate for tetracycline or methylene blue is ≥98.0%.

[0021] The plasma-modified polyethylene / polyamide composite membrane has advantages such as high organic solvent permeation flux, low reverse salt permeation flux, high solute rejection rate, and high mechanical strength in the fields of organic solvent recovery and thermosensitive drug concentration.

[0022] Compared with the prior art, the present invention has the following advantages: (1) The present invention selects polyethylene porous membrane as support layer, which has advantages such as high annual output, low cost, excellent mechanical strength and good chemical inertness compared with other organic solvent forward osmosis membrane materials; (2) Compared with the use of dopamine or tannic acid to modify polyethylene membrane hydrophilically in the literature, plasma technology is convenient and efficient, and the hydrophilic modification effect is uniform and stable; (3) The polyethylene-based composite membrane prepared in the present invention has a very thin overall thickness, which is lower than that of traditional organic solvent forward osmosis membrane materials, which is beneficial to reduce solvent permeation resistance.

[0023] Figure and Table Description

[0024] Figure 1The images show scanning electron microscope (SEM) images of the polyethylene substrate films in Comparative Examples 1, 2 and Example 1. As can be seen from the images, dendritic fiber structures can be observed on both the upper and lower surfaces of the initial polyethylene substrate film, and the pore sizes on the upper and lower surfaces are not significantly different. After different degrees of plasma treatment, the morphology of the upper surface remains almost unchanged, while obvious etching is observed on the lower surface, with a significant increase in surface pore size and roughness.

[0025] Figure 2 The image shows a scanning electron microscope (SEM) image of the polyethylene / polyamide composite film in Example 2. As can be seen from the image, the polyethylene base film is relatively thin, only about 7 μm thick, and the polyamide layer after interfacial polycondensation is about 510 nm thick.

[0026] Figure 3 The static water contact angle is the polyethylene film in Comparative Example 1 and Example 1. Detailed Implementation

[0027] To make the technical means, creative features, achieved objectives, and effects of this invention readily understandable, the invention is further described below with reference to specific illustrations. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0028] Comparative Example 1

[0029] (1) Clean the 7μm thick commercial polyethylene film with ethanol beforehand.

[0030] (2) Place the cleaned polyethylene film on a smooth and flat polytetrafluoroethylene plate, and place another polytetrafluoroethylene frame on top of the film, and clamp the edges to fix the polyethylene film.

[0031] (3) Add a 1.5 wt% piperazine aqueous solution to the polytetrafluoroethylene groove and let it stand for 5 min. Then pour off the excess monomer aqueous solution and wipe the surface. Subsequently, pour a 0.75 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 2 min, immediately remove the composite film and place it in a 70℃ oven for further crosslinking for 5 min to obtain a polyethylene / polyamide composite film.

[0032] Comparative Example 2

[0033] (1) A commercial polyethylene film with a thickness of 7 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 40 W for 7 s.

[0034] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the plasma-modified hydrophilic side facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the perimeter to fix the polyethylene film.

[0035] (3) Add a 3 wt% m-phenylenediamine aqueous solution to the polytetrafluoroethylene groove, let it stand for 3 minutes, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 0.23 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 3 minutes, immediately remove the composite film and place it in a 70℃ oven for further crosslinking for 5 minutes to obtain a polyethylene / polyamide composite film.

[0036] Example 1

[0037] (1) A commercial polyethylene film with a thickness of 7 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 40 W for 7 s; the lower surface of the polyethylene film was subjected to plasma treatment at a power of 90 W for 180 s.

[0038] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the top surface facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the edges to fix the polyethylene film.

[0039] (3) Add a 3 wt% m-phenylenediamine aqueous solution to the polytetrafluoroethylene groove, let it stand for 3 minutes, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 0.23 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 3 minutes, immediately remove it and place it in a 70℃ oven for further crosslinking for 5 minutes to obtain a polyethylene / polyamide composite film.

[0040] Example 2

[0041] (1) A commercial polyethylene film with a thickness of 9 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 10 W for 50 s; the lower surface of the polyethylene film was subjected to plasma treatment at a power of 40 W for 280 s.

[0042] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the top surface facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the edges to fix the polyethylene film.

[0043] (3) Add a 2.4 wt% piperazine aqueous solution to the polytetrafluoroethylene groove, let it stand for 5 min, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 0.18 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 2 min, immediately remove it and place it in a 70℃ oven for further crosslinking for 10 min to obtain a polyethylene / polyamide composite film.

[0044] Example 3

[0045] (1) A commercial polyethylene film with a thickness of 12 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 40 W for 15 s; the lower surface of the polyethylene film was subjected to plasma treatment at a power of 90 W for 120 s.

[0046] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the top surface facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the edges to fix the polyethylene film.

[0047] (3) Add a 1.80 wt% piperazine aqueous solution to the polytetrafluoroethylene groove, let it stand for 9 minutes, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 0.10 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 5 minutes, immediately remove it and place it in a 70℃ oven for another 5 minutes to continue crosslinking, thus obtaining a polyethylene / polyamide composite film.

[0048] Example 4

[0049] (1) A commercial polyethylene film with a thickness of 7 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 60 W for 7 s; the lower surface of the polyethylene film was subjected to plasma treatment at a power of 90 W for 240 s.

[0050] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the top surface facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the edges to fix the polyethylene film.

[0051] (3) Add a 1.25 wt% piperazine aqueous solution to the polytetrafluoroethylene groove, let it stand for 15 min, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 0.05 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 5 min, immediately remove it and place it in a 70℃ oven for further crosslinking for 5 min to obtain a polyethylene / polyamide composite film.

[0052] Example 5

[0053] (1) A commercial polyethylene film with a thickness of 15 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 40 W for 15 s; the lower surface of the polyethylene film was subjected to plasma treatment at a power of 90 W for 180 s.

[0054] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the top surface facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the edges to fix the polyethylene film.

[0055] (3) Add a 3.75 wt% piperazine aqueous solution to the polytetrafluoroethylene groove, let it stand for 3 minutes, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 1.25 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 2 minutes, immediately remove it and place it in a 70℃ oven for further crosslinking for 5 minutes to obtain a polyethylene / polyamide composite film.

[0056] Example 6

[0057] (1) A commercial polyethylene film with a thickness of 9 μm was pre-cleaned with ethanol. The upper surface of the polyethylene film was subjected to plasma treatment at a power of 90 W for 15 s; the lower surface of the polyethylene film was subjected to plasma treatment at a power of 90 W for 180 s.

[0058] (2) Place the plasma-treated polyethylene film on a smooth and flat polytetrafluoroethylene plate with the top surface facing up. Place another polytetrafluoroethylene frame on top of the film and clamp it around the edges to fix the polyethylene film.

[0059] (3) Add a 2.4 wt% piperazine aqueous solution to the polytetrafluoroethylene groove, let it stand for 5 min, then pour off the excess monomer aqueous solution and wipe the surface. Then pour a 0.18 wt% TMC cyclohexane solution on top of the polyethylene film for interfacial polymerization. After reacting for 2 min, immediately remove it and place it in a 70℃ oven for further crosslinking for 10 min to obtain a polyethylene / polyamide composite film.

[0060] The polyethylene / polyamide composite membranes synthesized in Comparative Examples 1-2 and Examples 1-6 were used for the concentration of thermosensitive drugs and the recovery of organic solvents. The ethanol flux and reverse lithium chloride flux are shown in Table 1 when pure ethanol is used as the feed liquid and 2M lithium chloride as the draw liquid. The specific rejection rates for tetracycline and rhodamine when using 1000 ppm tetracycline / ethanol solution and rhodamine / ethanol solution as feed liquids are shown in Table 1.

[0061] The organic solvent permeation flux is calculated according to the formula. The calculated reverse salt permeation flux is based on the formula... The calculated retention rates of macromolecules such as tetracycline and rhodamine are based on the formula... Calculation. Where Δm is the mass change of the liquid side per unit time, ρ is the density of the organic solvent, A is the effective membrane area, Δt is the flux test time, and ΔC is the flux measurement time. t To measure the change in lithium chloride concentration in the feed solution before and after the test, V t To measure the change in solution volume on the feed side before and after the test, C d To obtain the concentration of tetracycline or rhodamine on the liquid side, V dV is the final volume of liquid sample taken after the test. p For the osmotic volume, C f It refers to the concentration of tetracycline or rhodamine on the feed liquid side.

[0062] Table 1 summarizes the performance of the organic solvent forward osmosis membranes in the examples and comparative examples.

[0063] Solvent flux Reverse solute flux Tetracycline retention rate Rhodamine retention rate Comparative Example 1 0 0.41gMH 100％ 100％ Comparative Example 2 0.49 LMH 2.35gMH 100％ 100％ Example 1 5.45 LMH 0.44gMH 99.86％ 98.89％ Example 2 3.71 LMH 0.33gMH 99.15％ 98.24％ Example 3 4.71 LMH 0.45gMH 99.82％ 99.05％ Example 4 5.69 LMH 0.74gMH 99.06％ 98.13％ Example 5 3.57 LMH 0.39gMH 99.92％ 98.76％ Example 6 3.71 LMH 10.33gMH 99.15％ 99.15％

[0064] Test results show that, although the forward osmosis membrane prepared in Comparative Example 1 without plasma treatment has a high rejection rate for tetracycline and rhodamine, its permeability to the polar solvent ethanol is very poor, making it impractical. The forward osmosis membrane prepared in Comparative Example 2, with plasma treatment only on the upper surface, still exhibits poor permeability to the polar solvent ethanol. Examples 1-5, which involve low-power, short-time plasma treatment of the upper surface and high-power, long-time plasma treatment of the lower surface, show significantly improved permeability to the polar solvent ethanol, lower reverse salt permeation flux, and higher antibiotic rejection rate. Example 6, which involves high-power, short-time plasma treatment of the upper surface and high-power, long-time plasma treatment of the lower surface, shows reduced permeability to the polar solvent ethanol and increased reverse salt permeation flux. This is because the polyethylene membrane surface treated with high-intensity plasma has high hydrophilicity, becoming strongly hydrophilic. In this case, the composite stability between the polyethylene membrane surface and the dense polyamide layer is actually poor, with some polyamide layers detaching, leading to salt leakage.

[0065] Table 2 shows the water contact angles of the upper and lower surfaces of the polyethylene films after treatment in Comparative Examples 1-2 and Examples 1-6, as well as the thickness of the prepared films.

[0066]

[0067]

Claims

1. A plasma-modified polyethylene / polyamide composite film, characterized by, The porous polyethylene membrane substrate is modified by plasma, and the upper surface and the lower surface of the porous polyethylene membrane are treated by plasma, the water contact angle of the upper surface of the plasma-modified porous polyethylene membrane is 15-90 o , the water contact angle of the lower surface is 0 o ~10 o , and the cross-linked aromatic polyamide is synthesized on the upper surface of the treated porous polyethylene membrane by interfacial polycondensation.

2. The plasma-modified polyethylene / polyamide composite film according to claim 1, characterized in that, The modified polyethylene porous membrane substrate has a thickness of 3-50 μm, an average pore size of 0.1 μm-5.0 μm, and a porosity of 20%-60%.

3. The plasma-modified polyethylene / polyamide composite film according to claim 1, characterized in that, The thickness of the polyamide selective layer is 300-1000 nm.

4. A method for producing the plasma-modified polyethylene / polyamide composite film according to any one of claims 1 to 3, characterized by, The method comprises the following steps: (1) preparation of a hydrophilic polyethylene membrane, the upper surface of the polyethylene porous membrane is subjected to plasma treatment at a power of 5-70 W for 3-60 s, and the lower surface of the polyethylene porous membrane is subjected to plasma treatment at a power of 40-100 W for 20-300 s; (2) preparation of a polyamide selective layer by interfacial polycondensation, a polyamine monomer aqueous solution is spread on the upper surface of the modified polyethylene membrane, the excess monomer aqueous solution is removed after wetting, and the surface is wiped, then a polybasic acid chloride n-hexane solution is deposited on the wet membrane surface for interfacial polymerization, and the composite membrane is further crosslinked at 65-75 ℃ after the interfacial polymerization is completed.

5. The method of claim 4, wherein the plasma-modified polyethylene / polyamide composite film is prepared by a process comprising: (a) providing a polyethylene / polyamide composite film; (b) exposing the polyethylene / polyamide composite film to a plasma; and (c) annealing the polyethylene / polyamide composite film. In the step (2), the polyamine monomer is one of piperazine, m-phenylenediamine, murexide or polyethyleneimine; the concentration of the polyamine monomer is 1-6 wt%; the polybasic acid chloride monomer is 1,3,5-benzene tricarboxylic chloride, m-phenyldicarboxylic chloride or biphenyl tetracarboxylic chloride, and the concentration of the polybasic acid chloride is 0.1-0.6 wt%.

6. The method for preparing plasma-modified polyethylene / polyamide composite membrane according to claim 4, characterized in that, In the step (2), the interfacial polycondensation process is that the polyamine monomer aqueous solution is spread and wetted on the membrane surface for 2-25 min, the interfacial polymerization time is 1-10 min, and the further crosslinking at 65-75 ℃ is performed for 5-30 min.

7. The plasma-modified polyethylene / polyamide composite membrane according to any one of claims 1-3 is used as a forward osmosis membrane for treatment of a solution containing an organic solvent.

8. The plasma-modified polyethylene / polyamide composite membrane according to any one of claims 1-3 is used as a forward osmosis membrane for organic solvent recovery and antibiotic concentration or dye removal in an organic solvent.

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