Hollow-fibre membrane having novel structure, and production method therefor

Abstract

The present invention relates to a hollow-fibre membrane having a novel structure and to a production method therefor. The hollow-fibre separation membrane of the present invention has an outermost shell surface pore size of between 0.001 and 0.05 m and a mean pore size of between 0.01 and 0.1 m while having, in sequence from the outermost shell surface, a dense sponge structure, a finger-like sponge structure and a mixed sponge-bead structure; and, because of this specific triple structure, the invention has outstanding mechanical strength, porosity and water permeability alike while also having a high performance whereby it is possible to eliminate even viruses.

Claims

1. A hollow fiber membrane in which (i) a dense sponge structure having pores with a size of 0.001 to 0.05 m, (ii) a finger-like sponge structure, and (iii) a sponge-bead mixed structure are formed in the order numbered from the outermost surface of the membrane.

2. The hollow fiber membrane of claim 1, wherein the pores formed on the outermost surface have a size of 0.001 to 0.01 m.

3. The hollow fiber membrane of claim 1, wherein the dense sponge structure has a thickness of 0.01 to 20 m, the finger-like sponge structure has a thickness of 10 to 100 m, and the sponge-bead mixed structure has a thickness of 50 to 200 m.

4. The hollow fiber membrane of claim 1, wherein the density of the beads contained in the sponge-bead mixed structure (iii) is gradually reduced from the central part to the internal coagulant-contacting part of a membrane.

5. The hollow fiber membrane of claim 1, wherein the hollow fiber membrane is polyvinylidene fluoride (PVDF)-based membrane.

6. The hollow fiber membrane of claim 1, wherein the membrane has an ability to remove viruses.

7. A method of preparing the hollow fiber membrane of claim 1 as a continuous process, the method comprising: (i) supplying a polyvinylidene fluoride (PVDF)-based resin to an extruder; (ii) supplying a good solvent and a poor solvent to the extruder; (iii) mixing the supplied materials by using a screw in a cylinder of the extruder; and (iv) extruding and spinning out the mixed solution.

8. The method of claim 7, wherein the supplied materials are mixed and molten by screw rotation at a cylinder temperature in step (iii).

9. The method of claim 8, wherein the temperature of the cylinder is adjusted to 50 to 250 C.

10. The method of claim 8, wherein the rotation speed of the screw is adjusted to 150 to 300 rpm.

11. The method of claim 7, wherein the mixed solution in step (iv) is spun out with an internal coagulant.

12. The method of claim 7, further comprising cooling and solidifying the solution spun out from (iv) using a coagulation bath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Scanning Electron Microscope (SEM) photographs of the separation membrane prepared in Example 1

(2) FIG. 1a illustrates a cross-section of the separation membrane prepared.

(3) FIG. 1b magnifies a cross-section (Region A in FIG. 1a) of an outermost surface portion of the separation membrane prepared. It can be confirmed that the pores formed on the outermost surface have a size of 0.01 m or less.

(4) FIG. 1c is the magnification of Region C in FIG. 1a, and a structure in which sponges and spherulite are mixed is identified.

(5) FIG. 1d is the magnification of Region D in FIG. 1a, and it can be confirmed that a structure in which sponge and beads are also mixed is formed, but the density of the bead structure is low as compared to FIG. 1c.

(6) FIG. 1e is a scanning electron microscope photograph of the outermost surface of the separation membrane, and FIG. 1f further magnifies the same. The pores formed have a size of 0.01 m or less.

(7) FIG. 2. Scanning Electron Microscope photographs of the separation membrane prepared in Example 2

(8) FIG. 2a illustrates a cross-section of the separation membrane prepared in the vicinity of the external surface thereof. A dense sponge structure having pores with a size of 0.01 m is identified.

(9) FIG. 2b illustrates an internal cross-section of the separation membrane prepared, and a structure in which sponge and beads are mixed may be identified.

(10) FIG. 3. Scanning Electron Microscope photographs of the separation membrane prepared in Example 3

(11) FIG. 3a illustrates a cross-section of the separation membrane prepared.

(12) FIG. 3b magnifies a cross-section (Region A in FIG. 3a) of the separation membrane prepared in the vicinity of there outermost surface. The pores formed on the outermost surface have a size of 0.02 to 0.03 m.

(13) FIG. 3c magnifies Region C in FIG. 3a, which is a structure in which sponge and beads are mixed.

(14) FIG. 3d is the magnification of Region D in FIG. 3a, and it can be confirmed that a structure in which sponge and beads are also mixed is formed, but the density of the bead structure is low as compared to FIG. 1c.

(15) FIG. 3e observes the outermost surface of the separation membrane, and FIG. 3f further magnifies the outermost surface. The pores formed have a size of 0.02 to 0.03 m.

(16) FIG. 4. Scanning Electron Microscope photographs of the separation membrane prepared in Example 4

(17) FIG. 4a illustrates a cross-section of the separation membrane prepared in the vicinity of the external surface thereof. It can be confirmed that the structure is a very dense sponge structure having pores with a size of 0.03 m.

(18) FIG. 4b illustrates an internal cross-section of the separation membrane prepared, and a structure in which sponge and beads are mixed may be identified.

(19) FIG. 5. compares the pore size of suspended materials including viruses with the pore size of the separation membrane.

BEST MODES FOR CARRYING OUT INVENTION

(20) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It will also be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

(21) Description will now be given in detail of a drain device and a refrigerator having the same according to an embodiment, with reference to the accompanying drawings.

EXAMPLE

Example 1

(22) A mixture ratio was set to 27 wt % of a polyvinylidene fluoride-based resin PVDF (solvay Co., Ltd. 6010 grade, molecular weight 322 kDa), 37 wt % of N-methyl-2-pyrrolidone (NMP), 18 wt % of diethyelene glycol (DEG), 9 wt % of polyvinylpyrrolidone (PVP K30), and 9 wt % of polyethylene glycol (PEG 200), the polyvinylidene-based resin was supplied to a hopper of an extruder, and NMP, DEG, PEG, and PVP K30 were supplied to a cylinder of the extruder through a liquid supply pump. As the temperature of extruder Regions 0 to 9 (C0 to C9), Regions C0 to C3, C4, C5 to C7, C8, and C9 were adjusted to 50 C., 120 C., 170 C., 150 C., and 120 C., respectively, and the temperature from the regions to the nozzle part was set to 120 C.

(23) The screw rotation speed was set to 300 revolution/min, the materials mixed in the cylinder of the extruder were molten and extruded in a biaxial extruder, and then finally spun through a gear pump and a nozzle, and entered a coagulation bath. The outer diameter and inner diameter of the nozzle was each 2.0 mm and 1.2 mm, the distance between the nozzle and the coagulation bath was 50 mm, and a mixture (NMP:ethylene glycol (EG)=7:3) was used as an inner coagulation solution.

(24) As the composition of the coagulation bath solution, pure water (deionized waer, DI) in which ions had been removed was used, and the temperature of the coagulation solution was 20 C. The ultrafiltration product of the present invention was prepared by extracting the separation membrane passing through the coagulation bath from the washing bath one day or more, and then drying the separation membrane at room temperature.

(25) Physical properties of the separation membrane prepared by the method were measured and are shown in the following Table 1, and as a result of the experiment, the separation membrane prepared in Example 1 had a tensile strength of 2.5 Mpa and an elongation of 20%, which is excellent in mechanical strength, and for the average pore size of the hollow fiber membrane, a pore size of 0.01 m was inferred by using a molecular weight cut off (MWCO) method to obtain 100% of the PEO 100,000 removal, and it can be confirmed that the hollow fiber membrane was a ultrafiltration membrane having a pure water permeation flow rate of 250 L/m2 and a porosity of 59% at 1 bar and 25 C.

(26) In order to more exactly confirm the film thickness, void size, cross-section and surface state of the hollow fiber separation membrane prepared by the method, the hollow fiber separation membrane was observed by scanning electron microscope (SEM), and the results are illustrated in FIG. 1 (FIGS. 1a to 1f).

(27) FIG. 1a illustrates the cross-section of the separation membrane prepared, and the PVDF hollow fiber separation membrane shows an outer diameter of 1 to 1.2 mm and an inner diameter of 0.5 to 0.8 mm. The cross-sectional structure has shown that a very dense sponge structure was formed on the outermost surface, macrovoids of the finger-like sponge structure were subsequently shown, a portion of the spherical structure by spherulite was present, but minimized inside thereof, and a structure having an interpenetrating network structure as a whole was formed.

(28) FIG. 1b further magnifies the cross-section (Region A in FIG. 1a) of the separation membrane prepared in the vicinity of the outermost surface, and it was confirmed that the outermost surface of the separation membrane had a very dense sponge structure having pores with a size of 0.01 m or a size even smaller than the aforementioned size, and particularly, a denser structure was shown as it goes toward the surface.

(29) The region (Region B in FIG. 1a) disposed in the inner side of the outermost surface is an interconnected finger-like sponge structure, and it was confirmed that the non-solvent induced phase separation was predominant, and the bead structure (spherulite) was rarely observed (FIG. 1a).

(30) It was shown that the inner part (Regions C and D in FIG. 1a) of the separation membrane prepared had a structure in which sponge+beads (spherulite) were mixed, and it was because the heat-induced phase separation effects by heat were still remaining. FIG. 1c magnifies Region C in FIG. 1a, FIG. 1d magnifies Region D, Region D showed that the bead structure (spherulite) was present, but the number thereof was smaller than that in Region C, and it can be confirmed that a sponge bead mixed structure in which the density of the bead structure was smaller as it went from Region C to Region D was observed.

Example 2

(31) A film was formed under the same condition in the same manner as in Example 1, except that a nucleating agent adipic acid was added in an amount of 0.1 wt % based on the weight of the polyvinylidene-based resin (PVDF). Basic physical properties of the thus prepared separation membrane were measured, and are shown in the following Table 1, and the images observed by scanning electron microscope (SEM) are illustrated in FIG. 2.

(32) As a result of observation, it was confirmed that as in the hollow fiber membrane prepared in Example 1, the outermost surface was a very dense sponge structure having pores with a size of 0.01 m (FIG. 2a), a finger-like sponge structure was subsequently observed, and the inner part of the separation membrane was a structure in which sponge and beads are mixed (FIG. 2b).

Example 3

(33) A separation membrane was prepared by performing the experiment in the same manner as in Example 1, using the coagulation bath solution in a mixture of water and ethanol at a ratio of 8:2, and making the other conditions the same as those of Example 1 to form a film, and the basic physical properties thereof were measured, and are shown in Table 1. Further, the images observed by scanning electron microscope (SEM) are illustrated in FIGS. 3 (FIGS. 3a to 3f).

(34) FIG. 3a illustrates a cross-section of the separation membrane, and FIG. 3b magnifies a cross-section (Region A in FIG. 3a) of the separation membrane prepared in the vicinity of the outermost surface. FIGS. 3e and 3f further magnifies and observes in detail the outermost surface of the separation membrane, and as a result of observation, it was confirmed that the size of pores formed on the outermost surface was 0.02 to 0.03 m, which is slightly larger than the size of the separation membrane prepared in Example 1 (FIGS. 3e and 3f).

(35) Subsequent to the outermost surface, macrovoids with a finger-like sponge structure were formed, and the macrovoids became slightly smaller than in Example 1 (FIG. 3a).

(36) It was shown that the inner part (Regions C and D in FIG. 3a) of the separation membrane prepared had a structure in which sponge+beads (spherulite) were mixed, and it was because the heat-induced phase separation effects by heat were still remaining. FIG. 3c magnifies Region C in FIG. 3a, FIG. 3d magnifies Region D, Region D showed that the bead structure (spherulite) was present, but the number thereof was smaller than that in Region C, and it can be confirmed that a sponge bead mixed structure in which the density of the bead structure was smaller as it went from Region C to Region D was observed.

Example 4

(37) A film was formed by making the other conditions the same as those of Example 1 in the same manner as in Example 1, except that the poor solvent used in the polymer solution was changed from DEG to hexyl carbitol (HC). Basic physical properties of the thus prepared separation membrane were measured, and are shown in the following Table 1, and the images observed by scanning electron microscope are illustrated in FIG. 4.

(38) As a result of observation, it was shown that as in the hollow fiber membrane prepared in Example 1, the outermost surface formed a very dense sponge structure having a pore size of 0.03 m, a macrovoid structure of a finger-like sponge structure was subsequently observed (FIG. 4a), and the middle part had a structure in which sponge and beads were mixed (FIG. 4b).

(39) Basic physical properties measured for the separation membranes prepared in Examples 1 to 4 are summarized in the following Table 1, the content of each constituent component of the present invention is not limited to the numerical value described in Table 1, and those skilled in the art can make rational summary and inference based on the numerical value range of the Table. Parameters of Table 1 are only one of the exemplary embodiments of the present invention, and should not be interpreted as an essential condition of the present invention.

(40) TABLE-US-00002 TABLE 1 Example No. 1 2 3 4 Ratio of PVDF (%) 27 27 27 27 Polymer PVP (%) 9 9 9 9 Solution PEG (%) 9 9 9 9 Component NMP (%) 37 37 37 37 DEG (%) 18 18 18 0 HC (%) 0 0 0 18 Nucleating Adipic 0 0.1 0 0 agent acid (%, compared to pvdf) Temperature of polymer 120 120 120 120 solution ( C.) Air gap (mm) 50 50 50 50 Constitution Water (%) 100 100 80 100 of Cooling Ethanol (%) 0 0 20 0 Solution Cooling temperature ( C.) 20 20 20 20 MWCO (PEG #100,000) 100 85 67 2 (%) Pure water permeation 228 150 265 314 flow rate (L/m2h) Tensile strength (MPa) 2.3 3 2.4 3.0 Pore size (m) of 0.001~0.01 0.01 0.02~0.03 0.03 outermost surface