Method for preparing polymeric membrane by liquid level spreading method

Abstract

The invention discloses a method for preparing a polymeric membrane through a liquid level spreading method, and belongs to the technical field of separation membrane materials, according to the liquid level spreading method, a non-polar solvent of a polymer is dropwise added to the surface of a polar solvent, phase inversion is carried out, a polymeric porous membrane of an asymmetric structure with uniform pore diameter is obtained, and the method has a good application prospect in the field of membrane distillation. The preparation method is simple and rapid, and the membrane aperture is uniform.

Description

Technical Field

[0001] The invention belongs to the technical field of separation membrane materials and relates to a method for preparing a polymer membrane by a liquid surface spreading method. Background Art

[0002] In the field of liquid and gas separation, membrane technology has obvious advantages in terms of low energy consumption and operating temperature. Non-solvent phase separation (NIPS) and thermally induced phase separation (TIPS) are common methods for preparing polymer membranes. Liquid surface spreading method, as a method for preparing polymer membranes, has strong controllability, fast film formation, and is easy to produce ultra-thin films.

[0003] When a water-insoluble organic solvent is dropped onto the water surface, spreading can occur when the spreading coefficient is greater than 0 to form a thin layer. If a polymer is dissolved in an organic solvent and phase separation occurs after spreading on the liquid surface, a thinner polymer membrane can be obtained, which is simple to operate and highly controllable. For example, Jia et al. spread silicone rubber dissolved in n-heptane on the water surface to prepare a silicone rubber membrane with waterproof and breathable properties, and applied it in zinc-air batteries (ACS Sustainable Chemistry & Engineering, 2022, 10, (9): 2903-2913). In addition to spreading the oil phase on the water phase, some researchers also dripped an aqueous solution on the water surface to prepare a porous membrane. Zhao et al. spread a mixed aqueous solution containing polyethyleneimine (PEI) and sodium polystyrene sulfonate (PSSNa) on the acidic water surface to form a porous polyelectrolyte membrane (Nature communications, 2022, 13, (1): 3227). The low surface tension of the mixed solution drives the droplets to spread on the water surface, while the low pH acidic water triggers the rapid complexation of polyelectrolytes at the spreading interface, reducing the diffusion and miscibility of the droplets underwater. The two work together to promote the spontaneous spreading of large-sized aqueous solution droplets on the acidic water surface. The membrane is used to evaporate water under sunlight, and the water evaporation rate is 2.8kgm under 1 unit of sunlight. -2 h -1 The polymer membranes prepared by the liquid surface spreading method are generally non-porous or have irregular pores, and there are very few reports on the preparation of ultra-thin porous membranes with relatively uniform pore sizes. Summary of the invention

[0004] In order to prepare an ultra-thin porous membrane with relatively uniform pore size, the present invention provides a method for preparing a polymer membrane by a liquid surface spreading method. In order to achieve the above object, the present invention adopts the following technical scheme:

[0005] A method for preparing a polymer film by liquid surface spreading method, characterized in that a polymer solution dissolved in a non-polar solvent is dripped onto the surface of a polar solvent, and phase conversion occurs rapidly after the droplets spread.

[0006] Furthermore, the boiling point of the non-polar solvent is 55-95° C., the boiling point of the polar solvent is 100-250° C., and the time for phase inversion to occur after the droplets spread is 10 s-5 min.

[0007] The low boiling point non-polar solvent is one or more of n-hexane, cyclohexane, carbon tetrachloride, benzene, n-heptane and chloroform.

[0008] The polymer is one or more of poly-4-methyl-1-pentene, chlorinated polypropylene, polyethylene, and ethylene terephthalate.

[0009] The mass fraction of the polymer solution is 1-15wt%, and the dropwise addition amount of the polymer solution is 50-5000 μL.

[0010] The temperature of the polar solvent is between 10-60° C. and the polar solvent is one or more of water, formamide, dimethyl sulfoxide, N,N-dimethylformamide, and hexamethylphosphoramide.

[0011] The present invention also provides the application of the asymmetric polymer porous membrane prepared by the above method in the fields of seawater desalination, sewage treatment, biopharmaceuticals or petrochemicals.

[0012] Compared with the prior art, the present invention has the following beneficial effects: the asymmetric polymer porous membrane prepared by the liquid surface spreading method of the present invention has a special pore structure and pore structure controllability, the porous structure gives the porous membrane a higher water contact angle and a higher air and liquid permeability, and the preparation method is fast, simple and highly controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0014] Figure 1 This is a scanning electron microscope image of the upper surface of the asymmetric polymer porous membrane prepared in Example 1 of the present invention.

[0015] Figure 2 This is a scanning electron microscope image of the lower surface of the asymmetric polymer porous membrane prepared in Example 1 of the present invention.

[0016] Figure 3 This is a cross-sectional scanning electron microscope image of the asymmetric polymer porous membrane prepared in Example 1 of the present invention.

[0017] Figure 4 Schematic diagram of membrane distillation test equipment.

[0018] Figure 5 The membrane distillation performance of the asymmetric porous membrane prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The present invention is further described in detail below in conjunction with the examples, but this should not be construed as limiting the scope of the present invention to the following examples. Without departing from the above-mentioned ideas and methods of the present invention, various changes or substitutions made in accordance with common technical knowledge and customary means in the art should be included in the scope of the present invention. The methods are conventional methods unless otherwise specified. The materials can be obtained from public commercial channels unless otherwise specified.

[0020] Example 1 Method for preparing poly 4-methyl-1-pentene film by liquid surface spreading method

[0021] The steps include:

[0022] (1) 0.6 g of poly-4-methyl-1-pentene resin was mixed with 12 ml of cyclohexane, and heated at 65°C for 4 hours to obtain a homogeneous polymer solution, which was set aside. 100 ml of dimethyl sulfoxide was placed in a culture dish, and kept warm at 30°C for 1 hour, which was set aside. The ambient temperature was 25°C, and the ambient air flow rate was 0.5 m / s.

[0023] (2) Take 200 μL of the polymer solution and drop it on the surface of dimethyl sulfoxide. The polymer solution spreads on its own. After 1 minute, the polymer phase transformation is completed to form a translucent film. The film is taken out with tweezers or filter paper and placed in air to dry for 12 hours to obtain an asymmetric polymer porous membrane.

[0024] The upper surface of the poly-4-methyl-1-pentene membrane has a honeycomb pore structure with a pore diameter of 3 μm ( Figure 1 ), the surface porosity is 25.01%, and the bottom surface is dense ( Figure 2 ), the cross section is asymmetrical ( Figure 3 The membrane distillation performance of the porous membrane was tested using a vacuum flat membrane distillation device (VMD). The entire device mainly includes a heating system, a circulation pump, a condensation system and a vacuum pump ( Figure 4 ). Using 75℃, 30gL -1 The NaCl aqueous solution is the feed liquid. The membrane distillation flux can be obtained by the following formula:

[0025]

[0026] N——Membrane distillation flux, (Lm -2 h -1 );

[0027] V——The volume of the permeate obtained by membrane distillation operation, (L);

[0028] t——Membrane distillation operation time, (h).

[0029] Prepare 0.1gL -1 ~10gL -1 of standard sodium chloride solution and cool it to room temperature. According to the room temperature, calibrate the conductivity meter constant, adjust the conductivity meter to the appropriate measurement gear, and measure the conductivity of the sodium chloride solution in order from low to high concentration. Draw a standard curve of conductivity and salt concentration based on the measurement results. By measuring the conductivity of the raw liquid and the distillate to determine its salt concentration, the retention rate of the membrane during VMD operation can be calculated using the following formula:

[0030]

[0031] φ——membrane retention rate, (%);

[0032] c1——salt concentration of raw material solution, (gL -1 );

[0033] c2——salt concentration of permeate, (gL -1 ).

[0034] The performance of the membrane distillation device was evaluated and it was found that the membrane water flux reached 34.51LMH and the rejection rate reached 99.7% ( Figure 5 ).

[0035] Example 2-5 Method for preparing poly 4-methyl-1-pentene film by liquid surface spreading method

[0036] The phase transformation speed of the polymer solution is adjusted by changing the temperature of dimethyl sulfoxide to control the diameter of the honeycomb pores. Using Example 1 as a comparison, the experimental conditions and parameters of Examples 2-5 are listed in Table 1. As shown in Table 1, when the dimethyl sulfoxide temperature is 50°C, the polymer solution cannot be spread, and when the dimethyl sulfoxide temperature is 30°C, the membrane distillation performance is relatively excellent.

[0037] Table 1

[0038]

[0039] Example 6-9 Method for preparing poly 4-methyl-1-pentene film by liquid surface spreading method

[0040] The honeycomb pore diameter of the asymmetric polymer porous membrane is adjusted by changing the concentration of the polymer solution. Using Example 1 as a reference, the experimental conditions and parameters of Examples 6-9 are listed in Table 2. As can be seen from Table 2, the asymmetric polymer porous membrane obtained when the polymer concentration is 6wt% has excellent performance.

[0041] Table 2

[0042]

[0043] Example 10-13 Method for preparing poly 4-methyl-1-pentene film by liquid surface spreading method

[0044] The diameter of the honeycomb pores is controlled by changing the composition of the polymer solution. Using Example 1 as a control, the experimental conditions and parameters of Examples 10-13 are listed in Table 3. As shown in Table 3, the membrane distillation performance of the honeycomb asymmetric porous membrane prepared from the polymer solution without adding n-heptane is relatively excellent.

[0045] Table 3

[0046]

[0047] Example 14 Method for preparing chlorinated polypropylene film by liquid surface spreading method

[0048] The steps include:

[0049] (1) Mix 1 g of chlorinated polypropylene resin with 10 ml of toluene, heat at 80°C for 4 hours to obtain a homogeneous polymer solution, and set aside. Place 100 ml of a 30 g / L calcium chloride aqueous solution in a petri dish, keep it warm at 30°C for 1 hour, and set aside. The ambient temperature is 25°C, and the ambient air flow rate is 0.5 m / s.

[0050] (2) Take 200 μL of the polymer solution and drop it on the surface of the calcium chloride aqueous solution. The polymer solution spreads on its own. After 3 minutes, the polymer phase transformation is completed to form a translucent film. The film is taken out with tweezers or filter paper and placed in the air to dry for 12 hours to obtain an asymmetric polymer porous membrane.

[0051] The upper surface of the chlorinated polypropylene film has a honeycomb pore structure with a pore diameter of 1 μm and a surface porosity of 26.1%; the bottom surface is dense.

[0052] Comparative Example 1

[0053] The preparation method of this comparative example is as follows: 0.6g of poly 4-methyl-1-pentene resin is mixed with 12ml of cyclohexane, and heated at 65°C for 4 hours to obtain a homogeneous polymer solution for standby use. 100ml of water is placed in a culture dish, kept warm at 30°C for 1 hour, and set aside. The ambient temperature is 25°C, and the ambient air flow rate is 0.5m / s. Take 200μL of the polymer solution, add it dropwise on the water surface, and wait for the polymer solution to spread by itself. It was finally found that the polymer solution could not spread on the water surface, and gathered on the liquid surface in a lens shape, and ultimately could not form a polymer porous membrane.

[0054] Comparative Example 2

[0055] The preparation method of this comparative example is as follows: 0.6g of poly 4-methyl-1-pentene resin is mixed with 12ml of cyclohexane, and heated at 65°C for 4 hours to obtain a homogeneous polymer solution for standby use. 100ml of dimethyl sulfoxide is placed in a culture dish, kept warm at 70°C for 1 hour, and set aside. The ambient temperature is 25°C, and the ambient air flow rate is 0.5m / s. Take 200μL of the polymer solution, add it dropwise on the water surface, and wait for the polymer solution to spread by itself. It was finally found that the polymer solution could not spread in dimethyl sulfoxide at a higher temperature, and gathered on the liquid surface in a lens shape, and ultimately could not form a polymer porous membrane.

[0056] Comparative Example 3

[0057] The preparation method of this comparative example is as follows: 0.6g of poly-4-methyl-1-pentene resin is mixed with 12ml of cyclohexane, and heated at 65°C for 4 hours to obtain a homogeneous polymer solution for standby use. 100ml of dimethyl sulfoxide is placed in a culture dish, kept warm at 30°C for 1 hour, and set aside. The ambient temperature is 25°C, and the ambient air flow rate is 0.5m / s. 1000μL of the polymer solution is taken and dripped on the surface of the dimethyl sulfoxide, and the polymer solution is allowed to spread by itself. The polymer solution is partially spread to form an uneven non-porous membrane.

[0058] The disclosed embodiments are described to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a polymer film by a liquid surface spreading method, characterized in that: A polymer solution dissolved in a non-polar solvent is dropped onto the surface of a polar solvent, and phase inversion occurs rapidly after the droplets spread.

2. The method for preparing a polymer film by a liquid surface spreading method according to claim 1, characterized in that: The boiling point of the non-polar solvent is 55-95° C., the boiling point of the polar solvent is 100-250° C., and the time for phase inversion to occur after the droplets spread is 10s-5min.

3. The method for preparing a polymer film by a liquid surface spreading method according to claim 1, characterized in that: The low boiling point non-polar solvent is one or more of n-hexane, cyclohexane, carbon tetrachloride, benzene, n-heptane and chloroform.

4. The method for preparing a polymer film by a liquid surface spreading method according to claim 1, characterized in that: The polymer is one or more of poly-4-methyl-1-pentene, chlorinated polypropylene, polyethylene, and ethylene terephthalate.

5. The method for preparing a polymer film by a liquid surface spreading method according to claim 1, characterized in that: The mass fraction of the polymer solution is 1-15wt%.

6. The method for preparing a polymer film by a liquid surface spreading method according to claim 1, characterized in that: The amount of the polymer solution added was 50-5000 μL.

7. The method for preparing a polymer film by a liquid surface spreading method according to claim 1, characterized in that: The temperature of the polar solvent is between 10-60° C. and the polar solvent is one or more of water, formamide, dimethyl sulfoxide, N,N-dimethylformamide, and hexamethylphosphoramide.

8. The method for preparing a polymer membrane by a liquid surface spreading method according to claim 1, wherein the asymmetric polymer porous membrane prepared by the method is used in the fields of seawater desalination, sewage treatment, biopharmaceuticals or petrochemicals.

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