Method for regulating and controlling surface appearance of hollow fiber membrane by changing composition of gel bath

Abstract

The invention provides a method for regulating and controlling the surface appearance of a hollow fiber membrane by changing the composition of a gel bath, which comprises the following steps: (a) respectively spraying a membrane casting solution and a core solution from an outer cavity and an inner cavity of a spinning nozzle at the same time to form a hollow molded product with an inner surface and an outer surface; (b) passing the hollow molded article through a section of air path; and (c) immersing the product in the step (b) into a gel bath for split-phase curing and forming to form a green film, the gel bath is an aqueous solution containing a first organic matter or inorganic salt, the temperature of the gel bath is 30-80 DEG C, the mass concentration of the organic matter in the aqueous solution is 5-50%, and the concentration of the inorganic salt in the aqueous solution is 5-30 g / L. By changing the components and concentration of the gel bath, the mass transfer velocity of the solvent and the non-solvent is controlled, and then the phase splitting process is changed, so that the hollow fiber membrane which is high in surface porosity, moderate in pore size, narrow in pore size distribution and excellent in performance is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and relates to a method for preparing a hollow fiber membrane, and in particular to a method for regulating the surface morphology of the hollow fiber membrane by changing the composition of a gel bath. Background Art

[0002] Hollow fiber membrane is a self-supporting membrane with a fiber-like appearance. It is a kind of asymmetric membrane, and its dense layer can be located on the outer surface of the fiber (such as reverse osmosis membrane) or on the inner surface of the fiber (such as microfiltration membrane, nanofiltration membrane and ultrafiltration membrane). According to the different water inlet methods, hollow fiber membranes are divided into two types: internal pressure type and external pressure type.

[0003] The external pressure hollow fiber membrane is the most widely used product in water treatment ultrafiltration. Its characteristic is that the filter cortex is located on the outer surface of the hollow fiber section, that is, the outer surface plays a real filtering / retention role, so the morphology of its outer surface (porosity, pore size, pore size distribution, etc.) is crucial to its filtration / retention performance. Generally speaking, the external pressure hollow fiber membrane with high porosity, pore size similar to or slightly smaller than the target retained material, and narrow pore size distribution range on the outer surface has a larger filtration flux, is more stable, and is more resistant to pollution in actual engineering applications.

[0004] The Chinese invention patent with application number 202111186634.7 discloses a casting solution and a preparation method thereof and its application in the preparation of Janus hollow fiber membrane. The casting solution is obtained by dissolving 8-30wt% of a film-forming polymer, 5-20wt% of a hydrophilic polymer and 1-20wt% of a porogen in an organic solvent. The casting solution is formed by blending a hydrophilic polymer and a film-forming polymer, and the Janus hollow fiber membrane is prepared by controlling the phase separation rate of the casting solution and the surface segregation path of the hydrophilic polymer using a gel bath and a core liquid. The Chinese invention patent with application number 202010965026.5 discloses a hemodialysis membrane containing a diazinone structure copolyethersulfone and a preparation method thereof. The hemodialysis membrane containing a diazinone structure copolyethersulfone uses polyethersulfone containing a diazinone structure of different structures and compositions as the membrane material, and is dissolved in a solvent with an additive to prepare a casting solution. The content of the copolyethersulfone containing diazinone structure in the casting solution is 5-30wt%, and the content of the additive is 1-25wt%. Under certain temperature and humidity conditions, a hollow fiber hemodialysis membrane is prepared by a phase inversion method using a hollow fiber membrane spinning machine. Since the polymer molecular chain contains a twisted non-coplanar diazinone structure, it has a high glass transition temperature, good mechanical properties and ultrafiltration properties, so the copolyarylethersulfone hemodialysis membrane containing diazinone structure has good application prospects in the field of hemodialysis.

[0005] It can be seen that the technical inspiration given by the prior art is that the technical route usually adopted to adjust the performance of hollow fiber membranes is to adjust the composition of the casting solution. For example, in order to obtain a dense outer skin, the usual method is to increase the polymer content, use a small molecule porogen, or use a complex core solution, which leads to high production costs and complex production processes. Summary of the invention

[0006] In order to solve the above technical problems, the object of the present invention is to provide a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath.

[0007] In order to achieve the above technical purpose, the present invention provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, comprising the following steps:

[0008] (a) simultaneously ejecting a casting liquid and a core liquid from an outer cavity and an inner cavity of a spinneret, respectively, to form a hollow molded product having an inner surface and an outer surface;

[0009] (b) passing the hollow molded product through an air process;

[0010] (c) immersing the product of step (b) in a gel bath to form a raw film by phase separation solidification; the gel bath is an aqueous solution containing a first organic matter or an inorganic salt, the temperature of the gel bath is 30 to 80° C., the mass concentration of the organic matter in the aqueous solution is 5 to 50%, and the concentration of the inorganic salt in the aqueous solution is 5 to 30 g / L.

[0011] Optimally, in step (c), the first organic matter is a mixture of one or more selected from dimethylacetamide, polyethylene glycol, ethylene glycol and ethanol.

[0012] Furthermore, in step (c), the mass concentration of organic matter in the aqueous solution is 20-30%.

[0013] Optimally, in step (c), the inorganic salt is a mixture of one or more selected from sodium chloride, calcium chloride and magnesium chloride.

[0014] Optimally, in step (c), the concentration of the inorganic salt in the aqueous solution is 10-15 g / L.

[0015] Furthermore, in step (a), the temperature of the casting liquid is 60-80°C, and the temperature of the core liquid is 50-70°C; in step (c), the temperature of the glue bath is 60-75°C.

[0016] Optimally, in step (a), the casting solution comprises the following raw material components in percentage by weight:

[0017] High molecular weight polymer 15-25%;

[0018] Solvent 15-40%;

[0019] Porogen 40-65%;

[0020] The high molecular polymer is a mixture of one or more selected from polyethersulfone, polysulfone, polyvinylidene fluoride and polyvinyl chloride; the solvent is a mixture of one or more selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and triethyl phosphate; and the porogen is a mixture of one or two selected from polyvinylpyrrolidone and polyethylene glycol.

[0021] Furthermore, in step (a), the core liquid is a mixture of dimethylacetamide and water.

[0022] Furthermore, the mass contents of dimethylacetamide and water in the core liquid are 20-70% and 30-80% respectively.

[0023] Optimally, in step (b), the length of the air path is 3 to 10 cm.

[0024] The present invention discloses a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath. By changing the components and concentration of the gel bath, the mass transfer rate between the solvent and the non-solvent is controlled, and the phase separation process is changed to obtain a hollow fiber membrane with high surface porosity, moderate pore size and narrow pore size distribution and excellent performance. The method has the characteristics of easy operation, high adjustment accuracy and strong applicability (applicability to polymer main materials prepared by various NIPs (non-solvent induced phase separation) methods). BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the hollow fiber membrane in Comparative Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the hollow fiber membrane in Example 5;

[0027] Figure 3 This is a scanning electron microscope image of the hollow fiber membrane in Example 6;

[0028] Figure 4 This is a scanning electron microscope image of the hollow fiber membrane in Example 7. DETAILED DESCRIPTION

[0029] The method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath of the present invention comprises the following steps: (a) simultaneously ejecting a casting liquid and a core liquid from the outer cavity and the inner cavity of a spinneret respectively to form a hollow molded product having an inner surface and an outer surface; (b) allowing the hollow molded product to pass through an air process; (c) immersing the product of step (b) in a gel bath to solidify and form a raw membrane by phase separation; the gel bath is an aqueous solution containing a first organic matter or an inorganic salt, the temperature of the gel bath is 30 to 80° C., the mass concentration of the organic matter in the aqueous solution is 5 to 50%, and the concentration of the inorganic salt in the aqueous solution is 5 to 30 g / L. By changing the components and concentration of the gel bath, the mass transfer rate of the solvent and the non-solvent is controlled, and the phase separation process is changed to obtain a hollow fiber membrane with high surface porosity, moderate pore size and narrow pore size distribution; the method has the characteristics of easy operation, high adjustment accuracy and strong applicability (applicability to polymer main materials prepared by various NIPs (non-solvent induced phase separation) methods).

[0030] In step (c), the first organic matter is preferably a mixture of one or more selected from dimethylacetamide, polyethylene glycol, ethylene glycol and ethanol, the mass concentration of the organic matter in the aqueous solution is preferably 10-40%, more preferably 20-30%, and the inorganic salt is preferably a mixture of one or more selected from sodium chloride, calcium chloride and magnesium chloride (the above-mentioned polyethylene glycol can be dissolved in water and reach the required concentration at the corresponding temperature, and the specific molecular weight is not limited). In step (c), the more preferred concentration of the inorganic salt in the aqueous solution is 10-15g / L. In step (a), the temperature of the casting solution is 60-80°C, and the temperature of the core solution is 50-70°C; in step (c), the more preferred temperature of the glue bath is 60-75°C.

[0031] In step (a), the casting solution includes the following raw material components in percentage by weight: 15-25% of high molecular polymer; 15-40% of solvent; 40-65% of porogen; the high molecular polymer is a mixture of one or more selected from polyethersulfone, polysulfone, polyvinylidene fluoride and polyvinyl chloride, the solvent is a mixture of one or more selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and triethyl phosphate, and the porogen is a mixture of one or two selected from polyvinylpyrrolidone and polyethylene glycol (similarly, the above polymers can be dissolved in the solvent and reach the required concentration at the corresponding temperature, and the specific molecular weight is not limited). The core liquid is a mixture of dimethylacetamide and water, wherein the mass content of dimethylacetamide and water is 20-70% and 30-80% respectively. In step (b), the length of the air path is 3-10 cm, preferably 3-5 cm.

[0032] The above method of changing the composition of the gel bath to regulate the surface morphology of the hollow fiber membrane may also include: step (d) washing the raw membrane with water, and then drawing and winding it with a collection wheel to obtain the hollow fiber membrane filament (i.e., the collection wheel is wound).

[0033] The preferred embodiments of the present invention will be described in detail below.

[0034] Comparative Example 1

[0035] This example provides a method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath, as follows:

[0036] (a) preparing a casting solution: adding polyethersulfone (BASF6020P), polyethylene glycol (PEG-200), polyvinyl pyrrolidone (PVP-K90), and dimethylacetamide (in this embodiment, 2000 g, 3000 g, 500 g, and 4500 g of polyethersulfone, polyethylene glycol, polyvinyl pyrrolidone, and dimethylacetamide, respectively) with a mass percentage of 20%, 30%, 5%, and 45% to a reaction kettle, heating to 80° C. and setting a rotation speed of 100 RPM to stir for about 12 hours; after the stirring is completed, evacuating the reaction kettle to remove bubbles to obtain a casting solution;

[0037] Preparation of core liquid: pure water and dimethylacetamide are mixed into a solution in a mass ratio of 4:1 and stirred, and heated to 50°C as the core liquid (i.e., 1000g of dimethylacetamide and 4000g of pure water are weighed to prepare a core liquid with a mass concentration of 20%);

[0038] The casting liquid and the core liquid are respectively ejected from the outer cavity and the inner cavity of the spinneret through respective metering pumps (the flow rates of the metering pumps are adjusted to 100 g / min and 40 g / min, respectively) (the casting liquid is ejected from the outer cavity, and the core liquid is ejected from the outer cavity) to form a hollow molded product with an inner surface and an outer surface;

[0039] (b) passing the hollow molded product through an air path, and setting the air path to 5 cm;

[0040] (c) immersing the product of step (b) in a gel bath (pure water, heated to 70° C.) to form a green film by phase separation solidification;

[0041] (d) The raw membrane is washed with water and then drawn and wound by a take-up wheel to obtain a hollow fiber membrane filament, the surface of which is as follows: Figure 1 As shown (at this time the membrane surface porosity is relatively low, which is only 5.6% after analysis and calculation, and the average pore size is about 80 microns).

[0042] Example 1

[0043] This embodiment provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, which is basically the same as that in Comparative Example 1, except that in step (c), the gel bath is an ethylene glycol aqueous solution with a mass concentration of 10%.

[0044] Example 2

[0045] This embodiment provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, which is basically the same as that in Comparative Example 1, except that in step (c), the gel bath is an ethylene glycol aqueous solution with a mass concentration of 20%.

[0046] Example 3

[0047] This embodiment provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, which is basically the same as that in Comparative Example 1, except that in step (c), the gel bath is an ethylene glycol aqueous solution with a mass concentration of 30%.

[0048] Example 4

[0049] This embodiment provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, which is basically the same as that in Comparative Example 1, except that in step (c), the gel bath is an ethylene glycol aqueous solution with a mass concentration of 40%.

[0050] The hollow fiber membranes in Comparative Example 1 and Examples 1-4 were tested for performance, and the results are listed in Table 1.

[0051] Table 1 Performance data of hollow fiber membranes in comparative example 1 and examples 1-4

[0052]

[0053] Example 5

[0054] This embodiment provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, which is basically the same as that in Embodiment 3, except that in step (c), the gel bath is a dimethylacetamide aqueous solution of a corresponding concentration. Figure 2 As shown, it can be seen intuitively from the electron microscope photograph that the outer surface morphology of the membrane filament obtained in Example 6 is significantly improved compared with the outer surface morphology in Comparative Example 1, and its porosity is significantly improved.

[0055] Example 6

[0056] This embodiment provides a method for adjusting the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, which is basically the same as that in Comparative Example 1, except that in step (c), the gel bath is a 10 g / L calcium chloride solution. Figure 3As shown, it can be seen intuitively from the electron microscope photos that, compared with Example 5, the surface pore size of the membrane filaments obtained in Example 6 is further reduced, the porosity is further improved, and the pore size distribution range is further narrowed; it can be seen that when the gel bath is an inorganic salt aqueous solution, the external surface morphology of the product has obvious advantages.

[0057] Example 7

[0058] This embodiment provides a method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath. The method is basically the same as that in Embodiment 2, except that in step (c), the gel bath is a polyethylene glycol (PEG-200) solution having a mass fraction of 20%, and the surface of the final product is as follows: Figure 4 As shown (at this time, the surface pore diameter of the obtained membrane filament becomes larger and the porosity decreases); it can be seen that when the gel bath is a polymer solution, the product performance is lower than the product performance corresponding to the gel bath being an ordinary organic solution.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath, characterized in that: The following steps are involved: (a) simultaneously ejecting a casting liquid and a core liquid from an outer cavity and an inner cavity of a spinneret, respectively, to form a hollow molded product having an inner surface and an outer surface; (b) passing the hollow molded product through an air process; (c) immersing the product of step (b) in a gel bath to form a raw film by phase separation solidification; the gel bath is an aqueous solution containing a first organic matter or an inorganic salt, the temperature of the gel bath is 30 to 80° C., the mass concentration of the organic matter in the aqueous solution is 5 to 50%, and the concentration of the inorganic salt in the aqueous solution is 5 to 30 g / L.

2. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 1, characterized in that: In step (c), the first organic matter is a mixture of one or more selected from dimethylacetamide, polyethylene glycol, ethylene glycol and ethanol.

3. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 2, characterized in that: In step (c), the mass concentration of organic matter in the aqueous solution is 20-30%.

4. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 1, characterized in that: In step (c), the inorganic salt is a mixture of one or more selected from sodium chloride, calcium chloride and magnesium chloride.

5. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 1, characterized in that: In step (c), the concentration of the inorganic salt in the aqueous solution is 10-15 g / L.

6. The method for regulating the surface morphology of a hollow fiber membrane by changing the composition of a gel bath according to any one of claims 1 to 5, characterized in that: In step (a), the temperature of the casting solution is 60-80°C, and the temperature of the core solution is 50-70°C; in step (c), the temperature of the glue bath is 60-75°C.

7. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 1, characterized in that: In step (a), the casting solution comprises the following raw material components in percentage by weight: High molecular weight polymer 15-25%; Solvent 15-40%; Porogen 40-65%; The high molecular polymer is a mixture of one or more selected from polyethersulfone, polysulfone, polyvinylidene fluoride and polyvinyl chloride; the solvent is a mixture of one or more selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and triethyl phosphate; and the porogen is a mixture of one or two selected from polyvinylpyrrolidone and polyethylene glycol.

8. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 1 or 7, characterized in that: In step (a), the core liquid is a mixture of dimethylacetamide and water.

9. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 8, characterized in that: The mass contents of dimethylacetamide and water in the core liquid are 20-70% and 30-80% respectively.

10. The method for regulating the surface morphology of hollow fiber membrane by changing the composition of gel bath according to claim 1, characterized in that: In step (b), the length of the air path is 3 to 10 cm.

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