KR100429355B1 - Composition including polyethylene glycol for preparing microporous polyethersulfone membrane and method for preparing microporous membrane using the same - Google Patents

Abstract

The present invention relates to a polymer composition for producing a microporous polyether sulfone membrane and a method for producing a microporous membrane using the same. More specifically, a polymer composition comprising a solvent, a basic polymer polyethersulfone, and an additive polyethylene glycol for forming pores on the surface of the membrane, and casting it to a support, and then exposed to air having a predetermined temperature and humidity And a method for producing a membrane having fine pores of a desired size by nonsolvent deposition.

Description

COMPOSITION INCLUDING POLYETHYLENE GLYCOL FOR PREPARING MICROPOROUS POLYETHERSULFONE MEMBRANE AND METHOD FOR PREPARING MICROPOROUS MEMBRANE USING THE SAME

The present invention relates to a polymer solution for producing a microporous polyether sulfone membrane and a method for producing a microporous membrane using the same.

Separation membranes are widely used in various fields, and may be used for various purposes such as microfiltration membranes, ultrafiltration membranes, gas separation membranes, pervaporation membranes, and reverse osmosis membranes. In addition, various methods are known as a method of manufacturing the separator.

The present invention is based on a nonsolvent induced phase inversion (NIPI) process first attempted by Loeb and Sourirajan in 1963, among other methods of preparing a separator. Non-solvent induced phase transition method is a method of obtaining a solid film by dissolving a polymer in a suitable solvent to form a solution, then cast it thinly and deposited it in a non-solvent. Loeb and Surirajane have succeeded in producing asymmetric membranes based on cellulose acetate using a phase-transfer process, and since then, many studies have been conducted by various scientists including Kesting and others. Membranes used in a wide range from microfiltration to gas permeation are still manufactured by non-solvent induced phase transfer method.

In many cases, a polymer solution is prepared by adding a substance other than the basic polymer and a solvent to the polymer solution to improve the performance of the membrane. The solution thus prepared is referred to as an unstable casting solution, and the type and amount of the substance added to the polymer solution are recognized as an important factor in membrane production which greatly changes the properties and performance of the membrane. Many methods for producing membranes using unstable casting solutions are also presented in other patents. (US Patent No. 3,133,132, US Patent No. 3,133,137, etc.) However, these early patents use a cellulose acetate (Cellulous Acetate) system as a base polymer, which has great problems in resistance to bacteria and long-term storage of the membrane.

In determining the properties that the membrane to be prepared should have, the use of the membrane is of paramount importance. In the case of reverse osmosis membranes, which have been studied in the past, the desalination of seawater was the main purpose, and thus, a great deal of mechanical strength was required to satisfy high desalination and high pressure operating conditions. However, as the application fields of the membrane are expanded, such as wastewater and sewage treatment, purification of organic solvents, and concentration of high concentrations, the properties of the membranes are further diversified and characterized. For example, membranes used for wastewater treatment must have chemical resistance, and the membranes need to be resistant to microorganisms for use in sewage treatment. In order to meet the properties of these membranes, the selection of the basic polymer used in the membrane production must be prioritized. On the other hand, polyether sulfone has already been introduced as a polymer for membrane production through many patents due to its mechanical strength, high thermal stability and chemical resistance (US Pat. No. 5,886,059, US Pat. No. 4,968,733, etc.). The membrane production method proposed in the above patents has the disadvantage that there are many kinds of additives added to the polymer solution and its composition is very complicated. If there are many kinds of additives added to the polymer solution and the composition is very complicated, it means that there are many things to consider in changing the properties of the membrane such as the pore size and porosity of the membrane. This means that there are difficulties in the handling of and control of process variables.

The present invention, in order to solve the problems of the prior art that it is difficult to smoothly control the strength of the membrane and the size of the membrane pores, and a method for producing a porous polymer membrane capable of smoothly controlling the membrane pore size without being significantly affected by the process parameters and It is an object to provide a polymer solution used to prepare the separator.

1 shows a schematic view of a film forming apparatus used in the present invention.

Figure 2 shows an electron micrograph of the film surface prepared according to Example 1.

Figure 3 shows an electron micrograph of the film surface prepared according to Example 2.

Figure 4 shows an electron micrograph of the film surface prepared according to Example 3.

Figure 5 shows an electron micrograph of the film surface prepared according to Example 4.

Figure 6 shows an electron micrograph of the film surface prepared according to Example 5.

Figure 7 shows an electron micrograph of the film surface prepared according to Example 6.

8 is a graph showing the pore distribution of the membrane surface prepared according to Example 4.

The present invention relates to a polymer composition for producing a microporous polyether sulfone membrane and a method for producing a microporous membrane using the same.

More specifically, the present invention is fine containing N, N-dimethylformamide as a solvent, and containing 15 to 25 parts by weight of polyethersulfone as a basic polymer and 0.5 to 40 parts by weight of polyethylene glycol as an additive per 100 parts by weight of the solvent. Provided is a composition for preparing a porous polyether sulfone membrane.

In addition, the present invention

(1) preparing a polymer solution in which 15 to 25 parts by weight of polyether sulfone and 0.5 to 40 parts by weight of polyethylene glycol are dissolved in 100 parts by weight of a solvent,

(2) casting the polymer solution on a support;

(3) exposing the support on which the polymer solution is cast to air at a constant humidity under a certain temperature, and then depositing it in a non-solvent, and

(4) providing a method for producing a solid microporous polyether sulfone membrane having fine pores formed on the surface of the membrane, the method including washing and drying the deposited membrane to remove residual solvents and additives.

In step (1) of the composition for preparing a microporous polyether sulfone membrane and the method for preparing a membrane according to the present invention, it is preferable to use N, N-dimethylformamide as the solvent, in addition to N-methyl-2- Pyrrolidone (N-methyl-2-pyrrolidone, NMP) or dimethyl acetamide (N, N-Dimethyl Acetamide, DMAc) can be used. It is preferable to use polyethersulfone having a molecular weight of at least 50,000 or more as the basic polymer. This is because satisfactory mechanical strength of the membrane and viscosity of the polymer solution of the membrane can be easily obtained when the molecular weight of the polyether sulfone as the basic polymer is 50,000 or more. Moreover, it is preferable that the polyethyleneglycol used as an additive has a molecular weight about 6,000-20,000. The reason is that when the molecular weight of polyethylene glycol is greater than 20.000, it is difficult to obtain a polymer solution at room temperature, and it is not easy to extract the polyethylene glycol at the time of final film formation, and when the molecular weight is lower than 6,000, sufficient porosity is achieved. This is because it cannot be obtained and the viscosity is so low that it is difficult to cast on the support.

In the preparation of the polymer solution, in order to completely mix and dissolve the polyether sulfone and polyethylene glycol, it is preferable to prepare the polymer solution by stirring the solvent, the polymer and the additive at 45 ° C to 60 ° C. This is because below 45 ° C requires a lot of time for complete dissolution, and the temperature above 60 ° C is not very effective compared to the temperature. The polymer solution thus prepared may be stored at room temperature to about 35 ° C.

In step (2), the thickness of casting the polymer solution on the support is preferably about 50 μm to 400 μm. At this time, the type of the support does not affect the present invention, it can be used by selecting the one having a desired surface properties from the support commonly used, such as nonwoven fabric of polyester or PET material. In addition, the temperature at the time of casting does not affect the present invention, in the embodiment of the present invention was carried out at room temperature. The method of performing casting is also not limited, and casting knives having a predetermined range of knife spacings can be used, in addition to conventional use such as roll coating or one side dip-coating. Can be used.

In forming the fine pores on the surface of the membrane by exposing the support on which the polymer solution of step (3) is cast in the air, at about 5 seconds in a constant humidity of 30% or more under a constant temperature of 20 to 60 ℃ It is preferable to expose about 3 minutes. In addition, when performing the non-solvent deposition process to gel the microporous formed film, using water or alcohol as a non-solvent under a temperature of 20 to 60 ℃, each 5 minutes in the first deposition and the second deposition It is preferable to perform the above.

In addition, in the step (4), it is possible to wash by soaking in water or alcohol for more than one day when washing the deposited film, and in this case, it is advantageous in terms of cost in using water as a washing liquid. Such washed membrane may be naturally dried in an air at room temperature to prepare a microporous polyether sulfone membrane from which residual solvent, additives, and water are removed.

The microporous polyether sulfone membrane prepared by the above method can be prepared using the film forming apparatus shown in FIG. According to Figure 1, the nonwoven fabric is released from the nonwoven roll used as a support at a constant speed while passing through the coating knife is cast as a polymer solution, after the constant temperature and humidity section in the humidity control tank, the first flocculation tank and the second The microporous polyethersulfone membrane is removed in the form of a roll in which most solvents and additives have been removed by being deposited while passing through a coagulation bath.

The method according to the invention is characterized by being able to control the pore size, porosity and membrane strength of the membrane prepared according to the composition of the polymer solution used. That is, the pore size and porosity of the membrane can be controlled by casting a polymer solution having a predetermined composition according to the present invention on a support and then exposing the membrane to air having a predetermined temperature and humidity to prepare the membrane. This is because the polymer solution cast on the support passes through the air at a constant temperature and a constant humidity, and thus the pore size and porosity unique to each condition are formed.

As can be seen by the following examples, it is possible to prepare a polyether sulfone membrane having a desired pore size by adjusting the content, humidity or exposure time of polyethylene glycol. In particular, the lower the content of polyethylene glycol in the polymer solution, the lower the humidity of the air to which the support on which the polymer solution is applied is exposed, and the shorter the time of exposure to the air at a constant humidity, the smaller the size of the fine pores. can do. Therefore, when preparing the microporous polyether sulfone membrane in the composition and method of the present invention, it is possible to control the size of the membrane pores in the range of 0.05 to 1 ㎛.

In addition, the present invention provides a microporous polyether sulfone membrane prepared by the above method and having pores of uniform size on the membrane surface. By controlling the content, humidity and exposure time of the polyethylene glycol in the manufacturing process, it is possible to obtain a polyether sulfone membrane having variously controlled pores in the range of 0.05 to 1 ㎛ on the membrane surface.

<Example>

Example 1

100 g of N, N-dimethylformamide as a solvent, 17 g of polyethersulfone as a basic polymer, and 35 g of polyethylene glycol as an additive were placed in a glass reactor and stirred at 60 ° C. for at least 24 hours to obtain a polymer solution.

The polymer solution obtained here was cast on a polyester nonwoven fabric using a casting knife adjusted to have a gap of 150 μm. The solution cast on the nonwoven fabric was passed for 40 seconds in a humidity control tank maintained at 80% humidity, and then deposited in a primary coagulation bath filled with water at 50 ° C. It was allowed to stay for about 5 minutes by using several rollers in the coagulation tank, and was then deposited for about 5 minutes in the secondary coagulation tank maintained at 30 ° C to obtain a membrane.

The membrane thus obtained was soaked in water at room temperature for one day to completely remove the solvent and nonsolvent in the membrane, and then dried at room temperature.

An electron micrograph of the film thus obtained is shown in FIG. 2. 2 is an enlarged 8000 times the surface of the film, it can be seen that the fine pores of about 0.5 ㎛ evenly distributed.

The precise pore size and distribution of the obtained membrane were measured using a capillary flow porosimeter (CFP-1200AEL) using the bubble point method. The maximum pore size was 0.89 μm and the average pore size was 0.63 μm.

Example 2

After reducing the polyethylene glycol to 15g in the polymer solution composition of Example 1 to prepare a polymer solution by stirring at 60 ℃, and then cast to 150 ㎛ on a nonwoven fabric passed through the humidity control tank maintained at 80% for 40 seconds, 1 The membrane was prepared by dipping for 5 minutes in the secondary flocculation tank and the secondary flocculation tank, and then washed and dried as in Example 1.

An electron micrograph of the membrane prepared in this example is shown in FIG. 3. The maximum pore size of the membrane was 0.88 μm, and the average pore size was 0.38 μm, measured by Mercury perfusion meter.

Example 3

After reducing the polyethylene glycol to 5g in the polymer solution composition of Example 1 to prepare a polymer solution by stirring at 60 ℃ to prepare a membrane under the same conditions as in Example 1.

An electron micrograph of the prepared membrane is shown in FIG. 4, and the maximum pore size of the membrane was 0.66 μm and the average pore size was 0.28 μm.

Example 4

Using the polymer solution of the same composition as in Example 2, a membrane was prepared with a pass time of a humidity control tank having a humidity of 80% as 20 seconds. Electron micrographs of the resulting membrane are shown in FIG. 5, and the maximum pore size and average pore size were 0.21 μm and 0.18 μm, respectively. This means that the membrane produced has a very narrow range of pore distribution. An electron micrograph of the surface of the membrane prepared in this manner is shown in FIG. 5, and the pore distribution of the prepared membrane is shown in FIG. 8. As can be seen in FIG. 8, it can be seen that the membrane exhibits a sharp pore distribution at portions of 0.18 μm and 0.19 μm.

Example 5

Using the polymer solution of the composition as in Example 2 to lower the humidity of the humidity control tank to 60% and passed through for 40 seconds to prepare a membrane. Electron micrographs of the prepared membrane are shown in FIG. 6, and the maximum pore size and average pore size were 0.13 μm and 0.08 μm, respectively.

Example 6

Using the polymer solution of the same composition as in Example 2 to adjust the humidity of the humidity control tank to 60% and to prepare a membrane with a passage time of 20 seconds.

Electron micrographs are shown in FIG. 7, and the maximum pore size and average pore size were 0.06 μm and 0.05 μm, respectively.

Example 7

100 g of N, N-dimethylacetamide as a solvent, 17 g of polyether sulfone as a basic polymer, and 15 g of polyethylene glycol as an additive were mixed to obtain a polymer solution in the same manner as in Example 1. Thereafter, a membrane was prepared in the same manner as in Example 4.

The maximum pore size of the membrane obtained in this example was 0.18 mu m and the average pore size was 0.12 mu m.

Example 8

100 g of N-methyl-2-pyrrolidone as a solvent, 17 g of polyether sulfone as a basic polymer, and 15 g of polyethylene glycol as an additive were mixed to obtain a polymer solution in the same manner as in Example 1, and then as in Example 4 The membrane was prepared by the method.

The maximum pore size and average pore size were 0.16 μm and 0.10 μm, respectively.

From the results of the above examples, it can be seen that the polyether sulfone membrane having the desired pore size can be prepared by controlling the content of polyethylene glycol, humidity or exposure time. In particular, the lower the content of polyethylene glycol, the lower the humidity, the shorter the exposure time in the humidity control tank was able to produce a membrane having fine pores of a smaller size.

When the membrane is prepared by the process according to the present invention using the polymer solution provided in the present invention, a membrane having a uniform distribution of pores can be obtained. In addition, the size of the pores can be variously controlled from 1 μm to 0.05 μm. Membranes obtainable by the present invention can be used for microfiltration and ultrafiltration. Furthermore, it can be used for ultra-precision filtration.

The method according to the present invention can be an economical membrane production method because the type and amount of components added to the polymer solution is small, and the membrane manufacturing process is also very simple, which leads to a reduction of the membrane manufacturing cost, thereby reducing the maintenance cost of the filtration process. It will be a great help to the generalization of the film.

Claims (13)

delete delete delete (1) 15 to 25 parts by weight of polyethersulfone and 0.5 to 40 parts by weight of 100 parts by weight of solvent in the solvent, using N, N-dimethylformamide, N-methyl-2-pyrrolidone or dimethylacetamide as a solvent. Preparing a polymer solution in which parts of polyethylene glycol are dissolved, (2) casting the polymer solution on a support; (3) exposing the support on which the polymer solution is cast to non-solvent after exposing it to air for about 5 seconds to about 3 minutes in a constant humidity of at least 30% at a temperature in the range of 20 to 60 ° C. , And (4) washing and drying the deposited film to completely remove residual solvents and additives, The molecular weight of the polyether sulfone is 50,000 or more, the molecular weight of the polyethylene glycol is 6,000 to 20,000, the method for producing microporous polyether sulfone membrane for water treatment microfiltration. delete delete The method of claim 4, wherein the polymer solution is prepared at 45 ° C. to 60 ° C. for complete mixing and complete dissolution of a solvent, a polymer, and an additive. The method of claim 4, wherein the polymer solution is cast to a support having a thickness of about 50 to 400 μm. delete 5. The method of claim 4, wherein the deposition process of step (3) is performed in the primary and secondary flocculation tanks for at least 5 minutes, respectively. 5. The membrane surface of claim 4, wherein the pore of the desired size is controlled by controlling the content of polyethylene glycol in the above range, the time for exposing the support on which the polymer solution is cast in air, or the humidity in the air during which the support on which the polymer solution is cast is exposed. Method for producing microporous polyether sulfone membrane that can be formed uniformly on 12. The method of claim 11, wherein the size of the pores formed on the surface of the membrane is controlled by controlling the size of the pores within the range of 0.05 to 1 [mu] m. A microporous polyethersulfone membrane prepared according to the method of any one of claims 4, 7, 8 and 10-12.