Method for manufacturing hydrophilized hollow fiber membrane by continuous process using extruder

Abstract

The present invention relates to a method of manufacturing a hydrophilized hollow fiber membrane by a continuous process using an extruder. According to the method of the present invention, thermal curing agent in the form of a monomer or a oligomer is added to a polymer solution, and in the melt state before a separation membrane is manufactured, thermal polymerization occurs due to an initial reaction of a thermal initiator at the appropriate temperature within a cylinder of the extruder. Thus, a hydrophilic component is evenly distributed into the membrane at the micro-level, and the hydrophilic component is not washed out, resulting in very high stability. Another advantage is high economic value and efficiency because the process for hydrophilizing the membrane as well as the process for manufacturing the membrane is carried out by the continuous process using the extruder without using conventional extrusion equipment in the form of an agitator.

Claims

1. A method of manufacturing a hydrophilized hollow fiber membrane by a continuous process using an extruder, the method comprising: (i) supplying a polyvinylidene fluoride (PVDF)-based resin, a hydrophilic resin, a thermal curing agent, and a thermal initiator to an extruder; (ii) mixing and melting the supplied materials to a melt by temperature of a cylinder and rotation of a screw of the extruder; (iii) polymerizing the thermal curing agent in the melt, wherein the polymerization begins by initiating the thermal initiator using heat generated from temperature of the cylinder and rotation of the screw; and (iv) extruding and spinning the melt in which the thermal curing agent is being polymerized.

2. The method of claim 1, wherein the hydrophilic resin is selected from the group consisting of polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), an acrylamide resin, an acryl-based resin, an amine-based resin, polyetherimide (PEI), polyimide (PI), polyamide (PA), and cellulose acetate (CA).

3. The method of claim 1, wherein the thermal curing agent in the step (iii) is polymerized in the melt to form a polymerization network with each other.

4. The method of claim 1, wherein the thermal curing agent in the step (iii) is adhered to the polyvinylidene fluoride (PVDF)-based resin or the hydrophilic resin and graft-polymerized in the melt.

5. The method of claim 1, wherein the temperature of the cylinder is adjusted to 50 to 250 C.

6. The method of claim 1, wherein the rotation speed of the screw is adjusted to 150 to 300 rpm.

7. The method of claim 1, wherein the melt in step (iv) is extruded together with an internal coagulating solution.

8. A method of manufacturing a hydrophilized hollow fiber membrane by a continuous process using an extruder, the hollow fiber membrane in which (a) a dense sponge structure having pores with a size of 0.001 to 0.05 m, (b) a finger-like sponge structure, and (c) a sponge-bead mixed structure are formed in the order mentioned from the outermost surface of the membrane, the method comprising: (i) supplying a polyvinylidene fluoride (PVDF)-based resin, a hydrophilic resin, a good solvent, a poor solvent, a thermal curing agent, and a thermal initiator to an extruder; (ii) mixing and melting the supplied materials to a melt by temperature of a cylinder and rotation of a screw of the extruder; (iii) polymerizing the thermal curing agent in the melt, wherein the polymerization begins by initiating the thermal initiator using heat generated from temperature of the cylinder and rotation of the screw; and (iv) extruding and spinning the melt in which the thermal curing agent is being polymerized.

9. The method of claim 8, wherein the size of pores formed on the outermost surface of the membrane is 0.001 to 0.01 m.

10. The method of claim 8, 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 10 m, and the sponge-bead mixed structure has a thickness of 50 to 200 m.

11. The method of claim 8, wherein the density of the beads contained in the sponge-bead mixed structure (c) is gradually reduced from the central part to the internal coagulant-contacting part of the membrane.

12. The method of claim 8, wherein the hollow fiber membrane has an ability to remove virus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scanning electron microscope (SEM) photograph illustrating a cross-section of a separation membrane manufactured in Example 1.

(2) FIG. 2 is a magnification of the cross-section (Region A in FIG. 1) of the outermost surface portion of the manufactured separation membrane. It can be confirmed that the size of pores formed on the outermost surface thereof is 0.01 m or less.

(3) FIG. 3 is a magnification of Region C in FIG. 1, and it is confirmed that there is a structure in which sponges and beads (spherulite) are mixed together.

(4) FIG. 4 is a magnification of Region D in FIG. 1, and it can be confirmed that a structure in which sponges and beads are also mixed together is formed, but the structure has a density lower than that of the bead structure in FIG. 3.

(5) FIG. 5 is a scanning electron microscope photograph observing the outermost surface of the separation membrane, and FIG. 6 is a further magnification of this. The size of pores formed is 0.01 m or less.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

(6) Hereinafter, the present invention will be described in more detail through the Examples. These Examples are provided only for more specifically describing The present invention, and it will be obvious to a person with ordinary skill in the art to which the present invention pertains that the scope of the present invention is not limited by these Examples according to the gist of The present invention.

EXAMPLE

Example 1

Manufacture of Hydrophilized High-Performance Ultra-Filtration Membrane Having Three-Layered Structure in which Micropores are Formed on Outermost Surface Thereof

(7) The mixture ratio was determined as 27 wt % of a polyvinylidene fluoride-based resin PVDF (Solvay, 6010 grade, and a molecular weight of 322 kDa), 37 wt % of 2-methyl-2-pyrrolidone (NMP), 18 wt % of diethyelene glycol (DEG), 9 wt % of polyvinyl pyrrolidone (PVP K30), and 9 wt % of polyethylene glycol (PEG 200). The polyvinylidene fluoride-based resin and polyvinyl pyrrolidone (PVP K30) were supplied to the hopper of the extruder, and NMP, DEG, and PEG were supplied through a liquid supply pump to the cylinder of the extruder. The temperature for regions 0 to 9 (C0 to C9) of the extruder was adjusted to 50 C. for C0 to C3, 120 to 140 C. for C4, 170 to 200 C. for C5 to C7, 150 to 170 C. for C8, and 120 C. for C9, and the temperature for up to the nozzle part was set 120 C.

(8) The rotation speed of the screw was set as 300 rpm/min, and the materials mixed in the cylinder of the extruder was melt and extruded using a twin-screw extruder, finally spun through a gear pump and a nozzle, and entered into a coagulation bath. The outer diameter and inner diameter of the nozzle were each 2.0 mm and 1.2 mm, the distance between the nozzle and the coagulation bath was 50 mm, and as an internal coagulating solution, a mixture of (NMP:EG (ethylene glycol)=7:3) was used.

(9) As a coagulation bath solution, deionized water (DI) was used, and the temperature of the coagulating solution was set to room temperature (20 C.). A hollow fiber separation membrane product of the present invention was manufactured by extracting the hollow fiber membrane which had passed through the coagulation bath in a washing bath one overnight or more, and then drying the hollow fiber membrane at room temperature.

(10) Physical properties of the separation membrane manufactured by the above method are shown in the following Table 1, and as a result of experiment, the separation membrane manufactured in Example 1 was excellent in mechanical strength, such as a tensile strength of 2.5 Mpa and an elongation rate of 20%. The pore size was inferred as 0.01 m by obtaining 100% removal rate of PEO 100,000 using a molecular weight cut off (MWCO) method, and it was confirmed that the separation membrane was a ultra-filtration membrane having a net permeation flow rate of 228 L/m.sup.2.Math.hr and a porosity of 59% at 1 bar and 25 C.

(11) In order to more exactly confirm the membrane thickness, void size, and cross-section and surface state of the hollow fiber separation membrane manufactured by the method, observation by a scanning electron microscope (SEM) was performed, and the result is shown in FIG. 1. The PVDF hollow fiber separation membrane manufactured by the above method exhibited an outer diameter in a range of 1 to 1.2 mm and an inner diameter of 0.5 to 0.8 mm. The cross-sectional structure was as follows: a very dense sponge structure was formed in the outermost part of the separate membrane; next to the sponge structure, macrovoids with finger-like sponge structure was formed; and inside part of the separate membrane, a spherical spherulite structure was partially observed but it was minimized, and an interpenetrating network structure was principally formed. It was confirmed that the outermost surface of the separation membrane had a pore size of 0.01 m or even smaller, and in particular, the closer to the surface of the separate membrane, the much denser structure was observed.

Example 2

Manufacture of High-Performance Ultra-Filtration Membrane Having Extra Hydrophilicity by Continuous Process (First Hydrophilization Manufacturing Method)

(12) A separate membrane was prepared in the same way as explained in Example 1, except that a thermal curing process was performed in an extruder using 10 wt % of 2-hydroxy ethyl acrylate (HEA)/triethylene glycol diacrylate (TEGDA) as a curing material (thermal curing agent) based on the polymer solution, and 5 wt % of diisopropyl diazene as a thermal initiator based on the thermal curing agent. Specifically, the thermal initiator was initiated by heat generated from the temperature of the cylinder and rotation of the screw, and thereby monomers which are curing materials were polymerized to form a hydrophilic network.

(13) With respect to the separation membrane manufactured by the above method, the time for which the flux is reduced to 50% level as compared to the initial flux was measured by using bovine serum albumin (BAS) as a contaminant. As a result, it was observed that the flux reduction rate was slower than that of Example 1, which shows the hydrophilic effect and the improved contamination resistance.

Example 3

Manufacture of High-Performance Ultra-Filtration Membrane Having Extra Hydrophilicity by Continuous Process (Second Hydrophilization Manufacturing Method)

(14) The mixture ratio was determined as 27 wt % of a polyvinylidene fluoride-based resin PVDF (a molecular weight of 322,000), 37 wt % of N-methyl-2-pyrrolidone (NMP), 18 wt % of diethyelene glycol (DEG), 9 wt % of polyvinyl pyrrolidone, and 9 wt % of polyethylene oxide (a molecular weight of 100,000). A separate membrane was prepared in the same way as explained in Example 1, except that 10 wt % 2-hydroxy methacrylate (HEMA) was used as a curing material (thermal curing agent) based on the polymer solution and 5 wt % of diisopropyl diazene was used as a thermal initiator based on the thermal curing agent, and the monomers (curing material) were adhered to the polyethylene oxide chain and graft-polymerized by heat generated from temperature of the cylinder and rotation of the screw in the extruder. Specifically, the temperature of the extruder was adjusted to 50 C. to 170 C., and the temperature for up to the nozzle part was set to 120 C. The rotation speed of the screw was 300 rpm/min, and the materials mixed in the cylinder of the extruder was melt and extruded from a twin-screw extruder, finally spun through a gear pump and a nozzle, and entered into a coagulation bath. The outer diameter and inner diameter of the nozzle were each 2.0 mm and 1.2 mm, and as an internal coagulating solution, a mixture (NMP:EG (ethylene glycol)=7:3) was used. The other manufacturing processes are the same as in Example 1.

(15) Basic physical properties measured with respect to the separation membranes manufactured in Examples 1 to 3 are summarized in the following Table 1, the content of each constituting component of the present invention is not limited to the numerical values described in Table 1, and those with ordinary skill in the art may conduct rational summary and reasoning based on the numerical range in the Table. The parameters in Table 1 are only one of the exemplary embodiments of the present invention, and should not be interpreted as the essential condition of the present invention.

(16) TABLE-US-00002 TABLE 1 No. of Example 1 2 3 Ratio of polymer PVDF (wt %) 27 27 27 solution component PVP (wt %) 9 9 9 PEG/PEO (wt %) 9 9 9 NMP (wt %) 37 37 37 DEG (wt %) 18 18 18 Thermal curing HEA/TEGDA (wt %, 10 agent as compared to the polymer solution) Thermal curing HEMA (wt %, as 10 agent compared to the polymer solution) Thermal initiator Diisopropyl diazene 5 5 (wt %, as compared to the thermal curing agent) Temperature ( C.) of the polymer 120 120 140 solution Air gap (mm) 50 50 50 Constitution of Water (%) 100 100 100 the cooling solution Cooling temperature ( C.) 20 20 20 Net permeation flow rate (L/m .Math. 2 h) 228 190 215 Reduction in flux by resistance to 50 59 62 contamination (min) @J/J0 = 50%, concentration of BSA (50 mg/L)