KR101401163B1 - PVDF asymmetric porous hollow fiber membrane - Google Patents

Abstract

The present invention relates to a polyvinylidene fluoride (PVDF) asymmetric porous hollow fiber membrane, and more particularly, it relates to an asymmetric porous hollow fiber membrane having a diameter gradient, PVDF asymmetric hollow fiber membrane that forms a sphere-like structure can be provided. As a result of forming an asymmetric spherical structure, the PVDF hollow fiber membrane is superior in mechanical strength to the PVDF hollow fiber membrane manufactured by the conventional method, and thus can be effectively used for membrane cleaning such as backwashing. In addition, The present invention can provide a PVDF asymmetric porous hollow fiber membrane excellent in filtration efficiency at the same time.

Description

Polyvinylidene fluoride (PVDF) asymmetric porous hollow fiber membrane {PVDF asymmetric porous hollow fiber membrane}

TECHNICAL FIELD The present invention relates to a polyvinylidene fluoride (hereinafter abbreviated as "PVDF") asymmetric porous hollow fiber membrane, and more particularly to a PVDF as a fluorine-based material used for water treatment such as drainage treatment, water treatment, The present invention relates to a hollow fiber membrane used.

The separation membrane technology is a highly separation technology for almost completely separating and removing the materials to be treated present in the treatment water according to the pore size, the pore distribution and the membrane surface charge of the membrane. In the water treatment field, the production of high quality drinking water and industrial water, And clean production processes related to the development of waste water treatment and reuse, and free circulation systems are expanding and are becoming one of the key technologies to be noticed in the 21st century.

The membrane for water treatment may be a hollow fiber membrane. The hollow fiber membrane has a hollow-ring shape, which is advantageous in that it has a larger membrane area per module unit than a flat membrane. If the water treatment separator has a hollow fiber membrane structure, the membrane may be cleaned by backwashing to remove sediments by passing a clean liquid in a direction opposite to the filtration direction, air scrubbing for removing sediments by shaking the membrane by introducing air bubbles into the module Can be effectively used.

Typical properties required for water treatment hollow fiber membranes include adequate porosity (number of pores) for the purpose of separation efficiency, uniform pore distribution for the purpose of improving fractionation accuracy, It is required to have an optimum pore size. In addition, chemical resistance, chemical resistance, heat resistance, and the like for chemical treatment are required as material characteristics. In addition, properties that affect the operating capability are required to have good mechanical strength to extend service life, and water permeability associated with operating costs.

The membrane structure can be divided into a symmetric membrane having a uniform film as a whole and asymmetric membranes having different pore sizes formed in the thickness layer. The asymmetric membrane type has a lower permeation resistance from the viewpoint of mass permeability, The selectivity of the selective layer can be increased while ensuring the physical film strength.

Polymeric materials used in the water treatment process using membrane technology include polysulfone, polyethersulfone, polyacrylonitrile, polyethylene, polypropylene, cellulose (cellulose) actate) and polyvinyldene fluoride (hereinafter referred to as " PVDF "). In particular, in recent years, a fluorine-based polymer material having a stain resistance from an organic pollution source has been attracting attention as a water treatment separator material due to a negative charge atmosphere.

Recently, studies on PVDF hollow fiber membranes, which are fluorine resins, have been actively conducted. However, conventional PVDF hollow fiber membranes have problems in that the cross-sectional structure has a sponge-like structure and thus mechanical strength is weak and water permeability is remarkably decreased due to hydrophobicity of PVDF .

In addition, the conventional PVDF asymmetric hollow fiber membrane is manufactured by coating the PVDF solution on the support, so that the PVDF coating layer is easily peeled off, and the bonding force between the support layer and the coating layer is weak so that the pore size of the surface coating layer changes during backwashing there was.

The present invention has been conceived to overcome the above-mentioned problems, and it is an object of the present invention to provide a PVDF asymmetric porous hollow fiber membrane having improved filtration efficiency which simultaneously satisfies the high water permeability and rejection rate required for a water treatment membrane, .

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems,

In a polyvinylidene fluoride (PVDF) hollow fiber membrane, hollows; And a separation layer formed along the periphery of the hollow, the separation layer forming a plurality of spherical structures, the spherical structure having a diameter gradient increasing gradually from the outer surface of the separation layer to the inner surface The present invention also provides a PVDF asymmetric porous hollow fiber membrane.

According to a preferred embodiment of the present invention, the spherical structure of the separating layer may have a diameter of 5 to 30 탆.

According to another preferred embodiment of the present invention, the spherical structure of the isolation layer may have a diameter of 1 to 10 μm.

According to another preferred embodiment of the present invention, the thickness of the separation layer may be 150 to 550 μm.

According to another preferred embodiment of the present invention, the average pore size of the inner surface of the separation layer is 0.1 to 10 μm, and the average pore size of the outer surface of the separation layer is 0.01 to 3 μm.

According to another preferred embodiment of the present invention, the hollow fiber membrane may have a tensile strength of 9 MPa or more.

According to another preferred embodiment of the present invention, the hollow fiber membrane may have a water permeability of 1000 LMH or more and a BSA elimination rate of 96% or more.

The present invention also relates to a polyvinylidene fluoride (PVDF) hollow fiber membrane, A supporting layer formed along the outer periphery of the hollow; And a selective layer formed along the outer periphery of the support layer, wherein the support layer and the selection layer form a spherical structure, and a difference in diameter of the spherical structure at the interface between the support layer and the selective layer is 5 lt; RTI ID = 0.0 > m / m. < / RTI >

According to a preferred embodiment of the present invention, the spherical structure of the support layer may have a diameter of 5 to 30 탆.

According to another preferred embodiment of the present invention, the spherical structure of the selective layer may have a diameter of 1 to 10 μm.

According to another preferred embodiment of the present invention, the thickness of the support layer may be 200 to 340 μm, and the thickness of the selective layer may be 10 to 150 μm.

According to another preferred embodiment of the present invention, the average pore size of the support layer is 0.1 to 10 μm, and the average pore size of the selective layer is 0.01 to 3 μm.

According to another preferred embodiment of the present invention, the hollow fiber membrane may have a water permeability of 800 LMH or more and a BSA removal rate of 99% or more.

The PVDF asymmetric porous hollow fiber membrane of the present invention does not form a coating layer and is not peeled off, and there is no fear that the pore size of the coating layer changes after cleaning, and an aspherical like structure having a diameter gradient can be formed. As a result of forming an asymmetric spherical structure, the PVDF hollow fiber membrane is superior in mechanical strength to the PVDF hollow fiber membrane manufactured by the conventional method, and can be effectively used for membrane cleaning such as backwashing. In addition, The present invention can provide a PVDF asymmetric porous hollow fiber membrane excellent in filtration efficiency at the same time.

1 is a cross-sectional view of a PVDF asymmetric hollow fiber membrane according to a preferred embodiment of the present invention.
2 is a cross-sectional view of a PVDF asymmetric hollow fiber membrane according to another preferred embodiment of the present invention.
3 is a photograph of a section of a PVDF asymmetric hollow fiber membrane according to a preferred embodiment of the present invention.
4 is a cross-sectional view of a PVDF asymmetric hollow fiber membrane according to another embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawings.

 As described above, conventional PVDF hollow fiber membranes have poor mechanical strength, water permeability is significantly lowered due to hydrophobicity of PVDF, and PVDF asymmetric hollow fiber membranes prepared by coating a PVDF solution on a support easily peel off the PVDF coating layer There is a problem that the pore size of the coating layer changes after washing.

Therefore, in the present invention, And a separation layer formed along the periphery of the hollow, the separation layer forming a plurality of spherical structures, the spherical structure having a diameter gradient increasing gradually from the outer surface of the separation layer to the inner surface The present invention provides a PVDF asymmetric porous hollow fiber membrane which is characterized in that it has the above-mentioned problems. As a result, an asymmetric structure is formed without forming a coating layer, so that it can not be peeled off. It has high mechanical strength due to an asymmetric sphere structure and has a high permeability and a high rejection rate Satisfactory filtration efficiency can be obtained.

 1 is a cross-sectional view of a PVDF asymmetric porous hollow fiber membrane according to an embodiment of the present invention. In the PVDF asymmetric porous hollow fiber membrane 200, the hollow 100 is located at the center, and an asymmetric separation layer 110 is formed along the periphery of the hollow 100.

 The hollow 100 preferably has a diameter of 600 to 900 μm. If the diameter of the hollow 100 is less than 600 μm, the permeation rate is disadvantageously reduced. If the diameter is more than 900 μm, the bearing capacity may be decreased.

 The cross-sectional thickness of the separation layer 110 may be in the range of 150 to 550 μm. If the separation layer 110 is less than 150 μm, separation efficiency and lifetime may be reduced. If the separation layer 110 is more than 550 μm, the permeation rate may be inhibited.

The separation layer 110 having the asymmetric structure of the PVDF hollow fiber membrane of the present invention has a spherical structure having a diameter gradient gradually increasing from the outer surface to the inner surface, The mechanical strength is increased and the water permeability can be improved compared with the PVDF hollow fiber membrane. In addition, the asymmetric structure of the present invention, in which the diameter of the spherical structure increases toward the inside of the hollow fiber membrane, is larger than that of the symmetrical spherical structure. The spherical structure of the present invention has a large spherical structure, There is an advantage to be improved.

The spherical structure of the inner surface of the separation layer 110 may have a diameter of 5 to 30 μm. If the diameter of the spherical structure of the inner surface is less than 5 μm, the water permeability may be lowered and the mechanical strength may be lowered. If the diameter is more than 30 μm, the density of the spherical structure is too weak, and the tensile strength may be lowered.

In addition, the spherical structure of the outer surface of the separation layer 110 may have a diameter of 1 to 10 μm. If the diameter of the spherical structure of the external surface is less than 1 μm, the separation efficiency increases but the permeation flow rate decreases sharply. If the diameter exceeds 10 μm, the selectivity decreases and the efficiency of the water treatment process may decrease.

The separating layer 110 may have a thickness of 150 to 550 μm, an inner surface of the separating layer 110 may have an average pore size of 0.1 to 10 μm, and an outer surface may have an average pore size of 0.01 to 3 μm.

The PVDF asymmetric porous hollow fiber membrane as described above has a tensile strength of 9 MPa or more and can secure the mechanical strength, and it is possible to prevent the problem of cutting over time in the actual process. In addition, the hollow fiber membrane produced by the method of coating a PVDF solution on a conventional support is liable to peel off the PVDF coating layer at a peel strength of about 6 MPa, but the PVDF asymmetric hollow fiber membrane of the present invention does not peel off.

In addition, the PVDF asymmetric hollow fiber membrane has a water permeability of 1000 LMH or more and satisfies a BSA removal rate of 96% or more, thereby exhibiting excellent filtration efficiency.

FIG. 2 is a cross-sectional view of a PVDF asymmetric porous hollow fiber membrane according to another embodiment of the present invention. In the PVDF asymmetric porous hollow fiber membrane 500, a hollow 300 is located at the center, A support layer 310 is formed and a selective layer 320 is formed along the outer periphery of the support layer 310. The supporting layer 310 and the selective layer 320 form a spherical structure and the difference in the spherical structure diameter at the interface between the supporting layer 310 and the selective layer 320 is 5 μm or more, The selective layer 320 acts to secure the physical strength of the hollow fiber membrane and effectively separates the material to be treated to enhance the selectivity.

The spherical structure of the support layer 310 may have a diameter of 5 to 30 μm. If the diameter of the spherical structure of the support layer 310 is less than 5 μm, the water permeability may be decreased and the mechanical strength may be lowered. If the diameter exceeds 30 μm, the density of the spherical structure may be too weak and the tensile strength may be lowered . The average pore diameter of the support layer 310 satisfying the spherical structure diameter may be 0.1 to 10 탆.

In addition, the spherical structure of the selective layer 320 may have a diameter of 1 to 10 μm. When the diameter of the selective layer 320 is less than 1 탆, the separation efficiency increases but the permeation flow rate decreases sharply. If the diameter exceeds 10 탆, the selectivity decreases and the efficiency of the water treatment process may decrease . The average pore size of the selective layer 320 that satisfies the spherical structure diameter may be 0.01 to 3 占 퐉.

The cross-sectional thickness of the support layer 310 may be 200 to 340 占 퐉, and the thickness of the selective layer 320 may be 10 to 150 占 퐉. The cross-sectional thickness of the support layer 310 and the selective layer 320 can be controlled according to the content ratio of the mixed plasticizer contained in the PVDF asymmetric hollow fiber membrane. If the cross-sectional thickness of the selective layer 320 is less than 10 μm, There may be a problem of reduced lifetime, and if it exceeds 150 μm, the permeation rate may be inhibited.

The PVDF asymmetric porous hollow fiber membrane as described above has a tensile strength of 9 MPa or more and can secure the mechanical strength, and it is possible to prevent the problem of cutting over time in the actual process. In addition, the hollow fiber membrane produced by the method of coating a PVDF solution on a conventional support is liable to peel off the PVDF coating layer at a peel strength of about 6 MPa, but the PVDF asymmetric hollow fiber membrane of the present invention does not peel off.

In addition, the PVDF asymmetric hollow fiber membrane as described above has a water permeability of 800 LMH or more, satisfies BSA removal rate of 99% or more, and exhibits excellent filtration efficiency.

 In the PVDF asymmetric porous hollow fiber membrane of the present invention,

(1) preparing a crude liquid by melt-mixing a mixed plasticizer and polyvinylidene fluoride (PVDF) containing a plasticizer and a low-solubility plasticizer at a temperature of 170 to 300 ° C even if they are employed; (2) extruding the crude solution through a spinning nozzle to form a hollow fiber; And (3) dipping the formed hollow fiber in an external coagulating liquid.

 In the step (1), a mixed plasticizer containing a plasticizer and a low-solubility plasticizer and polyvinylidene fluoride (PVDF) are melt-mixed at a temperature of 170 to 300 ° C to prepare a crude liquid.

The polyvinylidene fluoride (PVDF) used in the hollow fiber membrane of the present invention preferably has an average molecular weight of 200,000 to 1,000,000. If the PVDF average molecular weight is less than 200,000, it may be difficult to form a hollow fiber membrane due to a low viscosity. If the PVDF average molecular weight is more than 1,000,000, moldability may be deteriorated due to high viscosity during melting.

The present invention relates to a method for producing a PVDF asymmetric membrane by melt-mixing a solution containing at least two mixed plasticizers. The solubility parameter difference between the solubilizing plasticizer and the low solubility plasticizer may be 5 (cal / ml) ^{2 or} more, more preferably 5 to 15 (cal / ml) ² Lt; / RTI >

In the present invention, the solubility parameter refers to the solubility constant of each polymer or solvent, and it can be said that a solvent having a small difference in the intrinsic solubility parameter of the polymer is easier to dissolve with the polymer. The difference in solubility between the polymer and each plasticizer can influence the formation and crystallinity of the primary nucleus when the polymer is solidified after melting, thereby determining the structure of the separator. The solubility parameter can be defined by the Hansen equation as follows:

In this formula,

[delta] = solubility parameter,

δ _d = solubility parameter by disperipon force for the solubility parameter,

δ _p = solubility parameter by dipolar intermolecular force for the solubility parameter,

δ _h = the solubility parameter of the hydrogen bonding force to the solubility parameter.

If the difference in solubility between the plasticizers and the low-solubility plasticizers is less than 5 (cal / ml) ^{2 even} when dissolved, it is difficult to form an asymmetric structure, and a large spherical structure may be formed as a whole to lower the porosity. When the solubility difference of the plasticizer and the low-solubility plasticizer is more than 15 (cal / ml) ² even if the solid solution is solubilized, the connection structure between the internal spheres of the separator may be broken and the tensile strength may be weakened.

The low-solubility plasticizer satisfying the above-described preferable solubility may be a single or a mixed type such as dioctyl phthalate, dioctyl sebacate, dioctyl adipate, ethylene glycol, diethylene glycol, or polyethylene glycol, Butyl phthalate, dimethyl phthalate, glycerol triacetate or gamma-butylolactone, or the like, alone or in combination.

The mixed plasticizer containing the low solubility plasticizer and the solubilizing plasticizer may include 70 to 300 parts by weight based on 100 parts by weight of PVDF. When the amount of the mixed plasticizer is less than 70 parts by weight, the spherical structure is not formed and the structure of the hollow fiber membrane becomes totally dense and water permeability may be lowered. When the amount exceeds 300 parts by weight, the concentration of PVDF may be lowered, .

If the mixed plasticizer is low in solubility and if plasticizer is solubilized even though it is solubilized, a PVDF asymmetric hollow fiber membrane that forms a spherical structure having a diameter gradient gradually increasing from the outer surface to the inner surface can be produced, When three kinds of mixed plasticizers are used, the spherical structure does not form a gradual diameter gradient, but the spherical structure at the interface between the supporting layer and the selective layer is made of PVDF asymmetric hollow fiber membrane having a diameter difference of 5 μm or more can do.

It is possible to control the thicknesses of the asymmetric membrane supporting layer and the selective layer according to the mixing ratio of the plasticizer to the low solubility plasticizer and the solubilizing plasticizer. Preferably, the mixing ratio by weight of the low solubility plasticizer and the solubilizing plasticizer is 1: 9 to 7: 3. If the ratio exceeds 9, the membrane structure may be deformed to lower the tensile strength and water permeability. More specifically, when the plasticizer ratio is 9 or more, a large spherical structure is formed to lower porosity and water permeability And if the plasticizer ratio is 3 or less even when solubilized, the connecting structure between the spherical structures may be destroyed and the tensile strength may be lowered.

The melting temperature for preparing the crude liquid of the step (1) is preferably 170 to 300 ° C. When the temperature is lower than 170 ° C, the melting temperature is lower than the melting point of the PVDF polymer. Therefore, the melt can not be uniformly melted and the shape of the hollow fiber membrane may become unstable. If the temperature exceeds 300 ° C, the plasticizer may be vaporized and the water permeability may be lowered.

 In the step (2), the crude solution is extruded through a spinning nozzle to form a hollow fiber.

The crude solution may be manufactured outside the spinning nozzle and flowed into the extruder, or may be formed inside the extruder. The spinning nozzle of the step (2) may be maintained at a temperature of ± 20 ° C above the melting temperature of the step (1). If the temperature of the spinning nozzle deviates from the melting temperature of the step (1) by ± 20 ° C, the degree of crystallization of the polymer may change, Porosity and strength.

If the screw speed is less than 40 rpm, the additive or the like may be vaporized in the extruder. If the extruder is operated at 90 rpm or more, mixing of the polymer and the plasticizer is not smoothly performed, It can be difficult.

Conventionally, in order to manufacture a PVDF asymmetric hollow fiber membrane, a manufacturing process is complicated by separately preparing a support layer and an outer coating layer through a triple tubular spinning nozzle, and the coating layer is peeled off in an external harsh condition or washing process, There was a disadvantage that it changed. Accordingly, the present invention can easily produce a PVDF asymmetric hollow fiber membrane with a double tubular spinning nozzle by mixing a mixed plasticizer containing a plasticizer and a low solubility plasticizer at an appropriate mixing weight ratio.

The spinning stock solution of step (1) may be discharged to the outer tube of the double tubular spinning nozzle, and the inner coagulant may be simultaneously discharged to the inner tube of the double tubular spinning nozzle.

The internal coagulant is used for internal hollow formation and is not particularly limited as long as it is uniformly mixed with PVDF and can be mixed at the time of immersion in an external coagulating liquid. More preferred is dibutyl phthalate, dimethyl phthalate Dimethyl phthalate, diethyl phthalate, dioctyl phthalate, dioctyl sebacate, glycerol triacetate, polyethylene glycol, ethylene glycol, Propylene glycol, diethylene glycol, and the like.

In the step (3), the formed hollow fiber is discharged or immersed in an external coagulating solution to produce a hollow fiber membrane. The external coagulating solution in the step (3) is not particularly limited as long as it can be mixed with a plasticizer and an internal coagulant, and more preferably water, dibutyl phthalate, dimethyl phthalate, diethyl phthalate Diethyl phthalate, dioctyl phthalate, dioctyl sebacate, glycerol triacetate, polyethylene glycol, ethylene glycol, propylene glycol, Diethylene glycol, and the like.

The external coagulation liquid in the step (3) may be -10 to 120 캜. If the cooling rate in the external coagulation solution is low, the spherical size inside the hollow fiber membrane may become large, and the spherical size may become small at a high cooling rate. If the temperature of the external coagulating solution is less than -10 ° C, the cooling rate is too fast and the water permeability may be reduced due to too small spherical structure. If the temperature exceeds 120 ° C, the cooling rate becomes too slow. The density and the connection sites between the spherical structures are reduced, and the porosity and tensile strength may be lowered.

The hollow fiber membrane produced in the step (3) may further include (4) continuously feeding and stretching the hollow fiber membrane into a stretching machine including a stretching solution. In the above stretching step, the stretching solution may be ethylene glycol, glycerol, polyethylene glycol having a molecular weight of 400 or less, water, or the like, and may be stretched at a stretching ratio of 1.1 to 2.0 times at a stretching temperature of 15 to 150 캜.

When the stretching temperature is less than 15 ° C, partial stretching may occur and the hollow fiber membrane may not be uniformly stretched. When the stretching temperature is more than 150 ° C, film shrinkage and trimming are likely to occur. If the stretching ratio is less than 1.1 times the length of the hollow fiber, the effect of pore control and strength increase due to stretching is insufficient. If the stretching ratio is more than 2.0 times, the film thickness may decrease and the mechanical properties may become weak.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

≪ Example 1 >

60 parts by weight of glycerol triacetate (solubility: 20 (cal / ml) ² ), 60 parts by weight of diethylene glycol (solubility: 29.9 (cal / ml) ² ) were added to 100 parts by weight of PVDF (Solef 6013, Solvay) 90 parts by weight were simultaneously introduced into the twin-screw extruder (screw diameter: 30 mm). In the extruder at 220 DEG C, the molten mixture was transferred to a nozzle maintained at 200 DEG C using a gear pump. Then, the mixed solution was discharged using glycerol triacetate as an internal coagulant, and the air gap between the nozzle and the coagulation bath was maintained at 1 cm.

The discharged mixture was cooled through a coagulation bath maintained at 35 ° C to induce phase separation, and then wound in a water bath at 80 ° C at a rate of 20 m / min.

As shown in FIG. 3, the hollow fiber membrane thus formed formed a spherical structure gradually increasing in size toward the inner surface. The spherical structure average diameter of the outer surface was 6 μm and the average diameter of the spherical structure of the inner surface was 18 μm.

≪ Example 2 >

Diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) 90 parts by weight in place of parts of diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) 40 parts by weight of dimethyl phthalate ^{(solubility: 10.8 (cal / ml) 2} ) Was prepared in the same manner as in Example 1,

As shown in FIG. 4, the hollow fiber membrane thus formed had an asymmetric structure with a diameter difference of 20 μm at the interface between the support layer and the selective layer. The cross-sectional thickness of the support layer was 270 μm and the cross-sectional thickness of the selective layer was 80 μm .

≪ Example 3 >

Glycerol triacetate ^{(solubility: 20 (cal / ml) 2} ) 60 parts by weight of diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) 90 parts by weight in place of parts of dimethyl phthalate ^{(solubility: 10.8 (cal / ml) 2} ) , And 90 parts by weight of glycerin (solubility: 33.8 (cal / ml) ² ) were mixed in the same manner as in Example 1.

The thus produced hollow fiber membrane was not formed properly due to a large effect of non-solvent, and the tensile strength was lowered.

<Example 4>

Glycerol triacetate ^{(solubility: 20 (cal / ml) 2} ) 60 parts by weight of diethylene glycol ^{(solubility: 29.9 (cal / ml) 2} ) in place of 90 parts by weight of dibutyl phthalate (solubility: 19 (cal / ml) ² ) And 90 parts by weight of a polyethylene glycol (solubility: 23 (cal / ml) ² ) were mixed in the same manner as in Example 1.

The hollow fiber membrane thus formed formed a symmetrical structure having a large spherical shape larger than a predetermined size without forming an asymmetric structure that the spherical size became smaller toward the outer surface, thereby exhibiting a low water permeability.

&Lt; Example 5 >

Except that 60 parts by weight of dimethyl phthalate (solubility: 10.8 (cal / ml) ² ) was used instead of 60 parts by weight of glycerol triacetate (solubility: 20 (cal / ml) ² ) Respectively.

The hollow fiber membrane thus produced does not have a double structure, and the thickness of the outer dense layer becomes thick, thereby lowering the water permeability.

&Lt; Example 6 >

Except that 90 weight parts of diethylene glycol (solubility: 29.9 (cal / ml) ² ) was replaced by 90 weight parts of dioctyl phthalate (solubility: 18.5 (cal / ml) ² ) .

The hollow fiber membrane thus produced has no double structure and has low tensile strength due to poor interconnection between crystal structures.

&Lt; Comparative Example 1 &

Except that diethylene glycol (solubility: 29.9 (cal / ml) ² ) was not mixed.

 The hollow fiber membrane thus formed formed a spherical symmetrical membrane, and the spherical structure had an average diameter of 8 μm.

&Lt; Comparative Example 2 &

240 parts by weight of N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone) was mixed with 100 parts by weight of PVDF polymer at 120 DEG C to prepare a crude liquid. And then discharged to the external coagulation bath. The mixed solution thus discharged was cooled through a coagulation bath maintained at 35 ° C., and a hollow fiber was produced by a conventional heat-induced phase separation method. Thereafter, the hollow fiber was wound at a rate of 20 m / min in a water bath of 80 ° C.

The hollow fiber membrane thus formed formed a symmetric membrane of sponge like structure.

&Lt; Comparative Example 3 &

240 parts by weight of dimethylacetamide as a solvent was mixed with 100 parts by weight of PVDF polymer at 120 캜 to prepare a crude liquid. The liquid was transferred to a nozzle through a transfer line maintained at a constant temperature, and then discharged into an external coagulation bath. At this time, when the hollow fiber was discharged through a triple nozzle, the same polymer was coated on the surface of the hollow fiber. The composition of the polymer solution to be coated is 630 parts by weight of dimethylacetamide as a solvent and 39 parts by weight of polyvinylpyrrolidone based on 100 parts by weight of PVDF, and is transported through a coating nozzle. The mixed solution thus discharged was cooled through a coagulation bath maintained at 35 ° C., and a hollow fiber was produced by a conventional heat-induced phase separation method. Thereafter, the hollow fiber was wound at a rate of 20 m / min in a water bath of 80 ° C.

The thus prepared hollow fiber membrane was formed into a double hollow structure in which a coating layer was formed on the outside of the hollow fiber having the support layer.

<Experimental Example>

The pure water permeability, tensile strength, rejection rate and backwash strength of the hollow fiber membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were measured by the following methods, and the results are shown in Table 2.

1. Measurement of pure water permeability

The hollow fiber membrane module thus prepared was supplied with pure water at a room temperature at a pressure of 1.0 atm on one side of the module by a DEAD-END method, and the amount of permeated water was measured

After which the permeation amount per unit time, unit membrane area, and unit pressure was calculated.

2. Measurement of rejection rate

BSA (bovine serum albumin, Aldrich, Mw 66,000) was added to pure water at room temperature

To prepare an aqueous solution having a concentration of 1,000 ppm. The aqueous solution was supplied to one side of the prepared hollow fiber membrane module at a pressure of 1.0 kg / cm 2, and the BSA concentration dissolved in the permeated aqueous solution and the raw water initially supplied was measured using an ultraviolet spectrophotometer (Cary-100) Respectively.

Thereafter, the relative ratio of the absorption peaks measured at a wavelength of 278 nm was calculated using the following equation

The BSA exclusion rate was determined as a percentage.

Excretion rate (%) = ((concentration of raw liquid - permeation concentration) / concentration of raw liquid) × 100

3. Measurement of tensile strength

The tensile strength and tensile elongation of the hollow fiber membranes prepared through the tensile tester were measured. The tensile test was carried out at room temperature at a gripping distance of 10 cm and a crosshead speed of 3 cm / min.

(Initial sample length: 100 mm, crosshead speed: 200 mm / min) at a temperature of 23 DEG C and a relative humidity of 50% using a tensile tester ("RTM-100" manufactured by Toyo Baldwin Co., Ltd.).

4. Measurement of pressure test

The filtration water side of the membrane module is closed while the test water is filled in the manufactured hollow fiber membrane module, and the pressure is applied to the feed water side at least 1.5 times the condition of the membrane module for 1 minute and the state is observed.

division Pure permeability
(L / m ² hr) BSA exclusion rate
(%) The tensile strength
(MPa) Example 1 1000 96 9 Example 2 800 99 9 Example 3 900 93 6 Example 4 700 90 8 Example 5 500 93 9 Example 6 800 91 5 Comparative Example 1 600 90 8 Comparative Example 2 600 95 4 Comparative Example 3 600 96 6

 As can be seen from Table 1, when the asymmetric spherical structure including the mixed plasticizer according to the present invention is formed, the mechanical strength and the filtration efficiency are superior to those of Comparative Example 1 containing only a single plasticizer. Compared with Comparative Example 2, which is manufactured according to the conventional method and has a sponge structure, the BSA elimination rate is maintained at a high level while the pure water permeability is increased, and the tensile strength is improved to show excellent mechanical strength. In Comparative Example 3, which was manufactured through a triple tubular spinning nozzle, the manufacturing process was complicated, and it was not only costly but also ineffective in terms of water permeability and pore size after backwashing.

Specifically, in Examples 3 to 6 in which the difference in solubility between the plasticizer and the low-solubility plasticizer was more than 15 (cal / ml) ² or less than 5 (cal / ml) ^{2 even} when dissolved, water permeability And the tensile strength was lowered. Example 2 in which the boundary between the support layer and the selective layer was formed using the three-component mixed plasticizer was found to be the most excellent in terms of the filtration efficiency.

Claims (13)

delete delete delete delete delete delete delete In the polyvinylidene fluoride (PVDF) hollow fiber membrane,
Hollow;
A supporting layer formed along the outer periphery of the hollow; And
And a selective layer formed along the periphery of the support layer,
Wherein the support layer and the selection layer form a spherical structure, the support layer has a cross-sectional thickness of 200 to 340 占 퐉, the selective layer has a cross-sectional thickness of 10 to 150 占 퐉, Spherulite like structure A PVDF asymmetric porous hollow fiber membrane with a diameter difference of 5 μm or more.
9. The method of claim 8,
Wherein the spherical structure of the support layer has a diameter of 5 to 30 占 퐉 asymmetric porous hollow fiber membrane.
9. The method of claim 8,
Wherein the spherical structure of the selective layer has a diameter of 1 to 10 [mu] m.
delete 9. The method of claim 8,
Wherein the support layer has an average pore size of 0.1 to 10 占 퐉, and the average pore size of the selective layer is 0.01 to 3 占 퐉.
9. The method of claim 8,
Wherein the hollow fiber membrane has a water permeability of 800 LMH or more and a BSA removal rate of 99% or more.

Images