KR20070113374A - Porous poly(vinylidene fluoride) hollow fiber membranes composed of spherical particles containing polymeric nanofibers - Google Patents

Abstract

A porous poly(vinylidene fluoride) hollow fiber membrane and a method for preparing the same are provided to exhibit excellent performance particularly in the microfiltration field by having good blocking ratio and good water permeability at the same time while maintaining superior tensile strength. A porous poly(vinylidene fluoride) hollow fiber membrane comprises: an inner layer(1) which is formed in the membranes, and in which a plurality of polymeric nanofibers having an average diameter of 500 nm or less are exposed on the section of the membranes, and a plurality of spherical fine particles with an average particle size of 1 to 5 micrometers(mum) are contained at the same time; an intermediate layer(2) which is formed on an upper part of the inner layer, and in which a plurality of polymeric nanofibers having an average diameter of 500 nm or less are exposed on the section of the membranes, and a plurality of middle-sized spherical particles with an average particle size of exceeding 5 micrometers(mum) to 10 micrometers(mum) are contained at the same time; and a surface layer(3) which is formed on an upper part of the intermediate layer, and in which a plurality of polymeric nanofibers having an average diameter of 500 nm or less are exposed on the section of the membranes, and a plurality of spherical fine particles with an average particle size of 1 to 5 micrometers(mum) are contained at the same time.

Description

Poly (vinylidene fluoride) hollow fiber membranes composed of spherical particles containing polymeric nanofibers}

1 is a schematic diagram of a cross section (a) and a surface (b) of a polyvinylidene fluoride-based porous hollow fiber membrane according to an embodiment of the present invention.

Figure 2a is an electron scanning microscope photograph of an enlarged 1,000 times the outer surface of the polyvinylidene fluoride-based porous hollow fiber membrane in accordance with an embodiment of the present invention.

Figure 2b is an electron scanning microscope photograph of an enlarged 5,000 times the outer surface of the polyvinylidene fluoride-based porous hollow fiber membrane cross-section according to an embodiment of the present invention.

Figure 2c is a scanning electron micrograph of the polyvinylidene fluoride-based porous hollow fiber membrane 75 times the entire cross-sectional view according to an embodiment of the present invention.

Figure 2d is an electron scanning microscope photograph of a 300-fold magnification of a cross section of a polyvinylidene fluoride-based porous hollow fiber membrane in accordance with an embodiment of the present invention.

2E is an electron scanning microscope photograph of a 1000-fold enlarged cross-section of an outer surface side of a polyvinylidene fluoride-based porous hollow fiber according to an embodiment of the present invention.

Figure 2f is an electron scanning microscope photograph of a 1000 times magnification of the inner surface side cross-section of the polyvinylidene fluoride-based porous hollow fiber membrane according to an embodiment of the present invention.

Figure 2g is an electron scanning micrograph of the polyvinylidene fluoride-based porous hollow fiber membrane intermediate side cross-sectional enlarged 5,000 times according to an embodiment of the present invention.

Figure 3a is a scanning electron micrograph of the polyvinylidene fluoride-based porous hollow fiber membrane 1,000 times magnification according to a conventional comparative example.

Figure 3b is a scanning electron micrograph of the polyvinylidene fluoride-based porous hollow fiber membrane 100 times the entire cross-sectional view according to a conventional comparative example.

Figure 3c is an electron scanning microscope photograph of a 1000 times magnification of the intermediate cross section of the polyvinylidene fluoride porous hollow fiber according to the conventional comparative example.

The present invention relates to a polyvinylidene fluoride-based porous hollow fiber membrane comprising a porous membrane structure composed of spherical particles containing polymer nanofibers, and a method of manufacturing the same, and more particularly, to maintain excellent tensile strength and at the same time block rate and water permeability The present invention relates to a polyvinylidene fluoride-based porous hollow fiber membrane and a method for producing the same, which exhibit excellent performance in the field of precision filtration.

Recently, a variety of membranes and membrane separation processes using the same have been actively developed for various energy saving and environmental protection. As is well known, microfiltration membranes have pores ranging in size from several micrometers to several tens of micrometers, so they have been applied to various filtration processes in various fields, including sewage treatment, water manufacturing, food and medical industry, etc. As the interest in the market increases, its use is gradually increasing.

To this end, in view of the desirable microfiltration membrane characteristics, there is a need for a high pressure-permeable membrane having excellent mechanical properties without membrane damage even under high operating permeability and severe operating conditions capable of treating a large amount of water with a small membrane area. In addition, in order to fundamentally prevent the problem of membrane degradation due to the degradation of permeability due to contamination of the membrane surface and introduction of various water treatment agents to remove contaminants adhering to the membrane surface, a membrane material having excellent fouling resistance and chemical resistance is used. It is also required. For this purpose, a separator material that has recently attracted attention is a polyvinylidene fluoride-based polymer. Polyvinylidene fluoride-based polymer materials are known to have inherent low surface energy, excellent mechanical, chemical and ozone resistance properties than polysulfone-based or polyolefin-based hollow fiber membranes. Has received a lot of attention as a material. However, in order to use the polymer material as a microfiltration membrane, it is important to finely control the membrane structure to have an appropriate pore size and distribution. In particular, mechanical properties such as tensile strength are very important for ensuring stable water permeability without damaging the properties of the membrane during the water treatment process. In order to achieve this purpose, it is more desirable to strengthen the structure of the membrane using various polymer additives.

The conventional method of processing a polyvinylidene fluoride-based resin into a separator using a polymer additive is as follows.

For example, Korean Patent Publication No. 2005-0056245 discloses a hollow fiber membrane by melt-extrusion of a composition composed of a polymer plasticizer such as polyester and a good solvent such as N-methylpyrrolidone, and a plasticizer and a good solvent in the formed hollow fiber membrane. Disclosed is a method for producing a porous hollow fiber membrane by extraction using alcohols, chlorinated hydrocarbons, and the like, followed by stretching.

In addition, Korean Patent Publication No. 2005-0018624 discloses a method for producing a porous membrane having both a three-dimensional network structure and a spherical structure. In the method for producing a porous membrane of the above method, a method of simultaneously forming both a three-dimensional mesh structure and a spherical structure from one resin solution, a method of forming a mesh structure later on either side of the porous membrane having a spherical structure, and A method for producing a porous membrane by simultaneously discharging two or more kinds of resin solutions from a spinneret is disclosed. In particular, the method has shown that a porous membrane made of various mesh / spherical structures can be produced by varying the composition of a cooling liquid composed of a solvent, a poor solvent, and a non-solvent to solidify the discharged spinning solution.

However, the above method requires precise temperature control of the nozzle discharge part and the molten polymer solution temperature when discharging the polymer solution into the double nozzle for manufacturing the hollow fiber membrane, and the addition of stretching or the like to increase the water permeability. It requires a formal process. In addition, the treatment of an eluent consisting of a strong acid with a pH of 2 or less and a strong base of 12 or more is essential to improve the water permeability associated with the extraction of inorganic additives, which seriously affects the durability of the membrane by defluoric acid and degradation. .

In addition, Korean Patent Publication No. 2006-0022866 discloses a spinning solution composed of a first additive such as a polymer and a second additive such as an inorganic salt to a polyvinylidene fluoride resin at room temperature, and continuously passes through a dehumidification chamber and a coagulation bath. A method of manufacturing a porous hollow fiber membrane having a four-layer structure having a double active layer on the inside and outside surfaces of the membrane is disclosed. However, since the hollow fiber membrane prepared by the above method forms an amorphous dense layer having a thickness of 1 to 5 micrometers or less on the inner and outer surfaces thereof, it may be advantageous in terms of pressure resistance, but it is difficult to expect high water permeability and dehumidification. The use of chambers, etc., requires additional energy consumption in the manufacture of hollow fiber membranes.

In general, the hollow fiber membrane prepared from the polyvinylidene fluoride-based solution has a porous membrane structure composed of spherical particles of several to several tens of micrometers when cooled from high temperature to low temperature, and this structure has a high water permeability. Very preferred. The expression of these spherical particles is known to depend mainly on the solid-liquid phase separation represented by crystallization and gelation, depending on the solvent used and the cooling rate upon discharge from high temperature to low temperature (Journal of Appilied Polymer). For example, lactone-based poor solvents are very advantageous for the formation of spherical particles, while dimethylacetamide-based good solvents are less favorable for the formation of spherical particles. . Fast cooling rates are also well known for promoting the formation of spherical particles. However, in most cases, the porous membrane structure composed of simple spherical particles may be very advantageous in terms of water permeability, but because the blocking rate and mechanical properties are very weak due to the decrease in membrane density, the blocking rate and tensile strength are improved without decreasing the water permeability. Preference is given to the preparation of hollow fiber membranes with balanced membrane performance.

Therefore, in order to solve the conventional technical problems, the present inventors have tried to produce a hollow fiber membrane having a suitable water permeability and excellent tensile strength and blocking rate at the same time, polyvinyl fluoride having good water permeability and excellent blocking rate and tensile strength The present invention was completed by developing a lead-based porous hollow fiber membrane.

Accordingly, an object of the present invention is to provide a porous polyvinylidene fluoride-based hollow fiber membrane having excellent water permeability through a simple manufacturing process and low cost without additional processes such as stretching.

It is another object of the present invention to provide a polyvinylidene fluoride-based porous hollow fiber membrane having improved blocking rate and tensile strength without significant decrease in water permeability.

Still another object of the present invention is to provide a polyvinylidene fluoride-based porous hollow fiber having excellent pressure resistance so that it can be operated for a long time even at high pressure.

Still another object of the present invention is to provide a method of manufacturing the porous hollow fiber membrane.

In order to achieve the above object, the present invention is located from the hollow center of the hollow fiber membrane to the outside, a plurality of polymer nanofibers which are located inside the membrane and the average diameter of 500 nm or less are exposed on the cross-sectional surface, at the same time 1 to 5 micro An inner layer comprising a plurality of microspheres of less than a meter (μm),

An intermediate layer comprising a plurality of mesosphere particles having an average diameter of more than 5 micrometers to 10 micrometers (μm) and exposed to the cross-sectional surface of the polymer nanofibers, which are located on top of the inner layer and have an average diameter of 500 nm or less. , And

A surface layer including a plurality of microspherical particles having an average diameter of 1 to 5 micrometers (μm) and exposed to a cross-sectional surface of a plurality of polymer nanofibers which are positioned on top of the intermediate layer and have an average diameter of 500 nm or less.

It provides a polyvinylidene fluoride-based porous hollow fiber membrane comprising a surface layer comprising a.

In addition, the present invention a) preparing a spinning solution comprising a polyvinylidene fluoride-based polymer, a polymer additive and a good solvent,

b) The spinning solution is transferred to an outer tube of a double nozzle maintaining a temperature of at least 120 ° C. or higher, and then discharged into an external coagulation liquid containing a good solvent and a non-solvent maintained at 40 ° C. or lower, and the amount of room temperature Manufacturing a hollow fiber membrane by transferring a hollow forming agent including a solvent, a non-solvent, and a polymer into the inside of the double nozzle;

It provides a method for producing a polyvinylidene fluoride-based porous hollow fiber membrane comprising a.

More preferably, the method for producing a porous hollow fiber of the present invention

a) a polyvinylidene fluoride-based polymer, a polymer additive, and a solvent capable of dissolving and dispersing the polyvinylidene fluoride-based resin and the polymer additive substantially uniformly at 90 to 180 ° C. to prepare a spinning solution,

b) the spinning solution is transferred to an outer tube of a double nozzle maintained at a temperature of 120 to 180 ° C., and then composed of a mixture of a good solvent and a non-solvent for the polymer, and is kept at -40 to 40 ° C. At the same time as discharging into a solid solution, the hollow tube containing a mixture of a good solvent, a non-solvent, and a polymer at room temperature is discharged into the inner tube of the double nozzle to contain nanofibers from the hollow center of the hollow fiber membrane toward the outermost surface. Forming a hollow fiber membrane comprising a three-layered structure of mesospheres and microspheres; And c) washing the hollow fiber membranes with water.

In the following, the present invention is described in more detail.

The present invention allows the microspheres of about 10 μm to be evenly distributed inside the entire cross-section of the membrane, and at the same time, the fine spherical particles of about 5 μm are appropriately distributed on the surface of the membrane. It is characterized by providing a hollow fiber membrane with improved water permeability by adjusting.

The present invention is also characterized by providing spherical particles having polymer nanofibers with an average diameter of 500 nm or less on the outer surface and cross section of the hollow fiber membrane, thereby providing a hollow fiber membrane with improved blocking rate and tensile strength.

Hereinafter, with reference to the accompanying drawings illustrating a preferred embodiment of the hollow fiber membrane of the present invention.

1 is a schematic view of a cross section (a) and a membrane surface (b) of a polyvinylidene fluoride-based porous hollow fiber according to one embodiment of the present invention. At this time, (a) in Figure 1 is a porous inner layer consisting of fine spherical particles, 2 is an intermediate layer of porous composed of intermediate spherical particles, 3 shows a surface layer of a fine spherical.

As shown in Figure 1, the hollow fiber membrane of the present invention comprises a plurality of nanofibers and porous spherical particles. Specifically, the hollow fiber membrane of the present invention is a three-layer structure including an inner layer, an intermediate layer and a surface layer from the hollow center of the hollow fiber membrane to the outside, wherein the inner layer includes a plurality of microporous spherical particles and some polymer nanofibers. The intermediate layer comprises a plurality of mesoporous porous spherical particles and a plurality of polymer nanofibers, and the surface layer comprises a plurality of microporous spherical particles and some polymer nanofibers. That is, the hollow fiber membrane of the present invention is exposed to the outer surface on the membrane surface and includes a plurality of nanofibers of about 500 nm in diameter and a plurality of spherical particles of about 5 micrometers (µm) in average diameter, and also on the outer surface of the membrane Surface layer and intermediate layer containing nanofibers and having a mean particle diameter of about 5 micrometers (μm) and a plurality of microspheres containing nanofibers and a mean particle diameter of about 10 micrometers (μm) It comprises a porous composed of mesosphere particles.

The hollow fiber membrane of the present invention having the above structure is formed by using a hollow forming agent at room temperature while discharging the spinning solution of 120 ° C. or higher to an external coagulation solution of 40 ° C. or lower, and the spinning solution is a polyvinylidene fluoride-based polymer. It includes a polymer additive and a solvent, it is characterized by forming the nanofibers by specifying the polymer additive. In addition, the external coagulation solution includes a solvent and a non-solvent, and the hollow forming agent includes a solvent, a non-solvent and a polymer.

In the present invention, the nanofiber is formed by a polymer additive, a part of which includes spherical particles and is evenly distributed on the cross-section and the surface of the hollow fiber desert and has an average diameter of 100 to 500 nm and its length of 10 to 1000. In addition, the surface average pores of the hollow fiber membranes are formed from spherical particles and nanofibers exposed on the surface, and are mainly located between the spherical particles and have an average pore diameter of 10 μm. It is defined as inside and outside, and it is preferable that the average pore size on an outer surface is 0.01-10 micrometers or less. In addition, the microspherical particles are defined as having an average particle diameter of about 5 μm evenly located on the inner and outer surfaces of the membrane. Preferably, the average particle diameter of the microsphere particles of the inner layer and the surface layer containing the nanofibers is preferably 1 to 5 ㎛ or less. In addition, the meso-spherical particles are defined to have an average particle diameter of about 10 μm, which is evenly positioned inside the membrane, and preferably greater than 5 to 10 μm.

In the present invention, the spherical particles and nanofibers are preferably included in a weight ratio of 50 to 100: less than 50, preferably 50 to 100: 5 to 50.

In addition, it is preferable that the outer diameter of the hollow fiber membrane is 0.8 to 1.2 mm, the inner diameter is 0.4 to 0.6 mm, and the film thickness is 0.1 to 0.4 mm.

On the other hand, the method for producing a porous hollow fiber membrane of the present invention, a) preparing a spinning solution comprising a polyvinylidene fluoride-based polymer, a polymer additive and a good solvent, b) a good solvent to the spinning solution at a temperature of at least 120 ℃ And microspheres containing nanofibers by using a hollow forming agent composed of a good solvent, a nonsolvent, and a polymer, while discharging into an external coagulating solution maintaining a temperature of at least 40 ° C. made of a nonsolvent, and And simultaneously preparing a hollow fiber membrane having a three-layered structure of mesosphere particles.

Hereinafter, the manufacturing process of the hollow fiber membrane of this invention is demonstrated concretely.

(a) Manufacturing process of spinning solution

As described above, the spinning solution is composed of polyvinylidene fluoride resin, a polymer additive, and a good solvent forming a hollow fiber membrane, and refers to a uniform mixture without formation of precipitates or suspended solids at a temperature of 90 ° C or higher. Therefore, in the present invention, the spinning solution is preferably prepared at 90 to 180 ° C, and generally exists as a polymer solution of a uniform composition at a temperature of 100 ° C or more, and forms a hollow fiber membrane by phase separation upon contact with a non-solvent. Promote. In addition, when forming a hollow fiber membrane, it is preferable to discharge a spinning liquid to an external coagulating liquid through the nozzle which maintains temperature of at least 120 degreeC or more.

In the spinning solution, the composition ratio of each component preferably comprises 15 to 55% by weight of polyvinylidene fluoride polymer, 1 to 15% by weight of a polymer additive, and 30 to 84% by weight of a solvent based on the whole composition. Preferably it consists of 25 to 45 weight% of polyvinylidene fluoride type polymer, 1 to 10 weight% of a polymer additive, and 45 to 74 weight% of a solvent.

At this time, when the content of the total polymer material within the above temperature range is less than 15% by weight, it is impossible to manufacture a continuous membrane due to the low viscosity, and even if manufactured, a hollow fiber membrane having a very low tensile strength is produced, and exceeds 55% by weight. In this case, due to the high viscosity of the spinning solution, the production of the membrane is almost impossible, and the prepared membrane also exhibits low water permeability.

The polyvinylidene fluoride-based polymer may be a homopolymer or a copolymer, but is preferably a single polymer such as polyvinylidene fluoride (PVDF), hexafluoropropylene (PVDF-HFP) or chlorotrile in the polymer. It may be selected from the group consisting of copolymers containing fluoroethylene (PVDF-TCFE) and the like and mixtures thereof. In addition, the polyvinylidene fluoride-based polymer is more preferably used a mixture of a single polymer and a copolymer rather than a homopolymer in order to improve the mechanical strength, such as tensile strength, when using a mixture, the ratio of the single polymer is 5 to 50 More preferably used in weight percent. Moreover, it is preferable that it is the weight average molecular weight of 50,000-500,000 or less about all the polymers with respect to molecular weight, More preferably, it is good to use 100,000-400,000 or less. In addition, the crystallinity of all polymers is preferably at least 50% and more advantageously at least 70% in order to ensure adequate strength and stable spinning continuity.

In particular, the polymer additive in the present invention means substantially promoting the formation of nanofibers. Representative polymer additives include polyimide (polyetherimide), polyimide (polyimide), polyiskeketone (polyetherketone), polyiser ketone (polyetheretherketine) and the like, these may be used alone or in combination of one or more. More preferably, polyimide is used as the polymer additive. When the polymer additive is not added, the nanofibers are not formed, and both the surface and the cross section of the film are composed of spherical particles, which is very advantageous in water permeability but very low in blocking rate and tensile strength. On the contrary, when the polymer additives are added, nanofibers are formed on the surface and the cross-section of the membrane, thereby increasing the density of the surface and the cross-section of the membrane.

The good solvent used in the preparation of the spinning solution may be defined as uniformly dissolving and dispersing 55% by weight or less of polyvinylidene fluoride resin at room temperature of 90 ° C or higher. Solvents that can be used include N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide, dimethylformamide and mixtures of two or more thereof. For the formation of spherical particles of more uniform size, more preferably dimethylacetamide is used. The polyvinylidene fluoride polymer solution containing such a good solvent and a polymer additive is generally present as a polymer solution with a uniform composition without forming spherical particles at a temperature of 100 degrees or higher, and is due to crystallization and gelation upon cooling to room temperature. It is expressed to have spherical particles and nanofibers by one solid-liquid phase separation.

(b) Preparation of hollow fiber membranes

(Composition of External Coagulant and Temperature Control of Coagulant)

In the present invention, the spinning solution prepared above is discharged to an external coagulating solution, and at the same time, a hollow fiber membrane including a porous layer composed of a nanofiber structure and spherical particles without a structure of a dense layer using a hollow former is prepared.

At this time, the external coagulation solution used in the present invention is composed of a non-solvent containing a certain amount of solvent, and when the contact with the solvent in the spinning solution rapidly reduces the concentration of the polymer at the interface to improve the porosity in the outer surface layer and At the same time, it is defined as maximally suppressing liquid-liquid phase separation to serve to promote the formation of spherical particles by solid-liquid phase separation without the formation of a dense layer. In addition, the non-solvent is defined as being able to be uniformly mixed with the good solvent without substantially dissolving the polymer at all over the entire temperature range. The good solvent may be defined as completely dissolving polyvinylidene fluoride-based polymer and polymer additive up to 55% by weight at 100 ° C. uniformly without formation of a precipitate . Representative good solvents usable in the present invention include dimethylformamide, dimethylacetamide, N-methylpyrrolidone and the like, and these may be used alone or in combination of one or more thereof, and more preferably dimethylacetamide is used. . Examples of the non-solvent include glycerol, ethylene glycol, propylene glycol, low molecular weight polyethylene glycol and mixtures thereof, and more preferably ethylene glycol.

The composition ratio of the external coagulating solution is preferably 15 to 65% by weight of the good solvent and 35 to 85% by weight of the non-solvent, more preferably 30 to 60% by weight of the good solvent and 40 to non-solvent, based on the total solvent mixture. 70 weight percent. If the content of the good solvent in the coagulation solution is less than 15% by weight, a dense layer is formed on the outer surface, which causes a problem in the membrane performance. When the content exceeds 65% by weight, the spinning is almost impossible due to the actual dissolution of the film. In addition, when the non-solvent content is less than 35% by weight, there is a problem in that continuous film production is impossible due to single yarn, and when the non-solvent content exceeds 85% by weight, a dense layer is formed on the surface of the hollow fiber to produce a membrane having low water permeability.

The temperature of the external coagulation liquid controls the size of the spherical particles across the membrane cross section, which is similar to the results of solid-liquid phase separation in crystalline polymer and solvent mixtures. In the present invention, the lower the temperature of the coagulation solution, the more advantageous it is to change the spherical particle size of the outer and inner surface layer. Therefore, the temperature of a preferable coagulation liquid is 40 degrees C or less, More preferably, it is 5 degrees C or less, Most preferably, it is -40 degreeC-5 degreeC. If the temperature of the coagulation liquid exceeds 40 ℃, the outer dense layer is formed or the membrane is partially dissolved to form a desirable hollow fiber membrane.

The hollow forming agent includes a non-solvent, a good solvent, and a polymer, and the temperature is maintained at 5 to 40 ° C., preferably at room temperature. The non-solvent may be selected from one or more of the above-mentioned non-solvent crowds, more preferably ethylene glycol. In addition, the preferred good solvent in the hollow forming agent may be selected from one or more of the aforementioned solvent groups, more preferably dimethylacetamide. Polymers used in the hollow forming agent include polyethylene glycol, polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone, and the like, and these may be used alone or in combination of one or more, and more preferably, polyvinylpyrrolidone. The composition ratio of the hollow forming agent is preferably composed of 10 to 60% by weight of the solvent, 30 to 80% by weight of the non-solvent, within 10% by weight of the polymer, more preferably 30 to 60% by weight of the total mixture. Weight percent, non-solvent 65 to 35 weight percent, and polymer 5 weight percent. If the polymer is not included in the hollow forming agent, it is difficult to continuously manufacture a hollow fiber membrane having a uniform outer diameter at a high temperature, and if the content of the solvent exceeds 60% by weight, uniform blow molding is impossible due to the actual dissolution of the membrane. . In addition, when the non-solvent content exceeds 65% by weight, a dense layer is formed on the hollow inner surface, resulting in the formation of a membrane having a low water permeability.

(Washing process)

In addition, the present invention may further include a washing process to remove the organic matter including the solvent remaining in the membrane of the hollow fiber membrane transferred to the air from the coagulation solution. Water is preferably used as the washing liquid, and the washing time is not particularly limited, but at least one day or more and five days or less is preferable.

Hereinafter, the configuration and operation of the present invention will be described through the following examples. However, the present invention is not limited by the following examples.

EXAMPLE

(Examples 1 to 3)

Preparation of hollow fiber membrane composed of spherical particles containing nanofibers

Dimethylacetamide (DMAC) (64% by weight) polyvinylidene fluoride (Solvay, Mw: 261,000) (34% by weight) and the amount of polyimide (PEI, Ultem, Mw: 100,000) added 140 A uniform spinning solution was prepared at ℃. Then, bubbles contained in the prepared spinning solution were removed using a vacuum pump, and then the spinning solution was transferred to a double nozzle maintained at 140 ° C. with an inner diameter of 0.6 mm and an outer diameter of 1.6 mm using a gear pump. . Thereafter, the temperature of the external coagulation solution composed of ethylene glycol / dimethylacetamide (60/40% by weight) was maintained at −20 ° C., followed by spinning to prepare a hollow fiber membrane. At this time, the solution discharge amount is 3.8 cc / min, a dimethylacetamide / ethylene glycol / polyvinylpyrrolidone mixture (55/45/5% by weight) of room temperature was used as the hollow forming agent. Subsequently, the hollow fiber membrane that passed the external coagulating solution was continuously transferred to the atmosphere for 30 seconds, immediately wound up through a winding bobbin immersed in water for about 1/2 second, and then washed in a water washing tank to remove organic solvent remaining in the membrane. Washed for 96 h. The fully washed hollow fiber membrane was immersed in 50% by weight aqueous solution of glycerin for 24 hours, and dried at room temperature. The membrane area was approximately 21 cm with an effective length of about 300 strands of hollow fiber membrane having an inner diameter of 0.6 mm and an outer diameter of 1.4 mm. A membrane module having this 0.28 m ² was prepared.

Using the hollow fiber membrane and the module, pure permeability, particle blocking rate (polystyrene monodisperse particles; diameter 120 nm), and tensile strength at break were measured by the following method, and the results are shown in Table 1 below. In addition, the cross section and the microstructure of the hollow fiber membrane are shown in Figs. At this time, Figure 2a is an electron scanning micrograph of 1,000 times the outer surface of the polyvinylidene fluoride-based porous hollow fiber membrane in accordance with an embodiment of the present invention, Figure 2b is a polyvinylidene fluoride according to an embodiment of the present invention An electron scanning microscope photograph of an enlarged outer surface of the densoid porous hollow fiber membrane section 5,000 times, Figure 2c is an electron scanning microscope image of a 75 times magnification of the entire cross-section of the polyvinylidene fluoride-based porous hollow fiber membrane according to an embodiment of the present invention. . In addition, Figure 2d is a scanning electron micrograph of a portion of the polyvinylidene fluoride-based porous hollow fiber membrane 300 times magnification according to an embodiment of the present invention, Figure 2e is a polyvinylidene fluoride-based porous hollow according to an embodiment of the present invention An electron scanning microscope photograph of a 1,000 times enlarged cross section of the desert outer surface side, FIG. 2F is an electron scanning microscope photograph of a 1000 times enlarged cross section of the inner surface side of a polyvinylidene fluoride-based porous hollow fiber membrane according to an embodiment of the present invention. 2g is an electron scanning microscope photograph in which the cross section of the middle side of the polyvinylidene fluoride-based porous hollow fiber membrane is enlarged 5,000 times.

(1) Measurement of pure permeability

For the manufactured hollow fiber membrane module, pure water at room temperature was supplied to one side of the module in a dead-end manner at 1.0 atm, and the amount of water permeated was measured, and then converted into unit time, unit membrane area, and permeate per unit pressure.

(2) measurement of blocking rate

A 500 ppm aqueous particle solution was prepared by dispersing an aqueous monodisperse polystyrene particle (polyscience, 120 nm size) in pure water at room temperature. Particle aqueous solution was supplied to one side of the prepared module at a pressure of 0.5 kg / cm ² , and the polystyrene concentration dispersed in the permeated aqueous solution and the initially supplied raw water was measured using an ultraviolet spectrometer (Shimadzu, UV-1601PC). . Thereafter, the blocking ratio was determined by converting the relative ratio of the absorption peaks measured at the wavelength of 240 nm into percentage using the following equation.

(Equation 1)

Percentage Blocked (%) = (Stock Concentration-Permeate Concentration) ÷ Stock Concentration x 100

(3) Measurement of tensile breaking strength

Tensile strength was measured by using a tensile tester and a sample having a holding distance of 60 mm was measured five times at a crosshead speed of 50 mm / min.

Example Composition (wt%) Coagulation liquid temperature (℃) Pure Permeability (l / m ² hr) Polystyrene Particle Blocking Rate (%) Tensile Strength at Break (kg / piece) Membrane Structure Particles (External Surface + Inside) One PVDF / PEI / DMAC 37/3/60 -20 1182 97.2 0.75 Nano Fiber + Spherical 2 PVDF / PEI / DMAC 35/1/64 -20 1248 93.7 0.87 Nano Fiber + Spherical 3 PVDF / PEI / DMAC 34/2/64 -20 1993 71.6 0.71 Nano Fiber + Spherical

(Comparative Examples 1 and 2)

Fabrication of porous hollow fiber without nanofiber

A hollow fiber membrane was prepared under the same conditions as in Example 1, except that the polymer additive was not included in the spinning solution. Thereafter, the performance of the hollow fiber membranes was measured in the same manner as above, and the results are shown in Table 2. In addition, electron micrographs of the film surface and the cross-sectional structure are shown in FIGS. 3A to 3C.

Comparative example Composition (wt%) Coagulation liquid temperature (℃) Pure Permeability (l / m ² hr) Polystyrene Particle Blocking Rate (%) Tensile Strength at Break (kg / cm ² ) Membrane Structure Particles (External Surface + Inside) One PVDF / DMAC 34/66 -20 2568 3.4 0.41 Sphere + Sphere 2 PVDF / DMAC 40/60 -20 1400 8.8 0.54 Sphere + Sphere

From the results of the Examples and Comparative Examples of Tables 1 and 2, in the production of polyvinylidene fluoride-based hollow fiber membrane, when using a high-temperature spinning solution containing a specific polymer additive, as in the embodiment of the present application including nanofibers Compared with the comparative example, a preferable hollow fiber membrane with improved blocking rate and tensile strength was prepared without a significant decrease in water permeability. This improved fine filtration performance can be seen that the fine nanofibers and spherical particles in the membrane structure is evenly and selectively distributed on a part of the porous surface layer to increase the density of the membrane surface.

As described above in detail, the porous hollow fiber according to the present invention includes a porous structure composed of fine nanofibers and spherical particles by spinning at a high temperature of 100 ° C. or higher using a polyvinylidene fluoride-based resin and a specific polymer additive. Therefore, since the performance of the hollow fiber membrane of the present invention has superior blocking rate, tensile strength and good water permeability compared to the conventional porous hollow fiber membrane, it can provide many advantages to the high efficiency separation process industry using next-generation microfiltration and ultrafiltration processes. .

Claims (10)

From the hollow center of the hollow fiber membrane outward, An inner layer including a plurality of microspheres having a mean diameter of 1 to 5 micrometers (µm) and exposed to a cross-section of a plurality of polymer nanofibers which are located inside the film and have an average diameter of 500 nm or less; An intermediate layer comprising a plurality of mesospheres having a mean diameter of more than 5 micrometers and 10 micrometers (µm) exposed to a cross-sectional surface of a plurality of polymer nanofibers which are located on top of the inner layer and have an average diameter of 500 nm or less. , And A surface layer comprising a plurality of microspherical particles having an average diameter of 1 to 5 micrometers (µm) and exposed to a cross-sectional surface of a plurality of polymer nanofibers, which are located on top of the intermediate layer and have an average diameter of 500 nm or less. Polyvinylidene fluoride-based porous hollow fiber membrane comprising a. The polyvinylidene fluoride-based porous hollow fiber of claim 1, wherein the hollow fiber membrane has a surface average pore diameter of 0.01 to 10 μm on the membrane surface, and an average diameter of the nanofibers is 1 to 500 nm. The polyvinylidene fluoride-based porous hollow fiber of claim 1, wherein the hollow fiber membrane has an outer diameter of 0.8 to 1.2 mm and a film thickness of 0.1 to 0.4 mm. The method of claim 1, wherein the hollow fiber membrane is formed by using a hollow forming agent at room temperature while discharging the spinning solution of 120 ℃ or more to the external coagulation solution below 40 ℃, the spinning solution is a polyvinylidene fluoride-based polymer A polyvinylidene fluoride-based porous hollow fiber membrane comprising a polymer additive and a good solvent, wherein the external coagulating solution includes a good solvent and a non-solvent, and the hollow former includes a good solvent, a non-solvent, and a polymer. a) preparing a spinning solution comprising a polyvinylidene fluoride polymer, a polymer additive, and a good solvent, b) The spinning solution is transferred to an outer tube of a double nozzle maintaining a temperature of at least 120 ° C. or higher, and then discharged into an external coagulation liquid containing a good solvent and a non-solvent maintained at 40 ° C. or lower, and the amount of room temperature Manufacturing a hollow fiber membrane by transferring a hollow forming agent including a solvent, a non-solvent, and a polymer into the inside of the double nozzle; Method for producing a polyvinylidene fluoride-based porous hollow fiber membrane comprising a. The method of claim 5, wherein the temperature of the double nozzle is maintained at a temperature of 120 to 180 ° C., and the temperature of the external coagulation solution is maintained at −40 to 40 ° C. 7. . The method of claim 5, wherein the method further comprises the step of washing the hollow fiber membrane with water. The method of claim 5, wherein the spinning solution comprises 15 to 55% by weight of polyvinylidene fluoride-based polymer, 1 to 15% by weight of a polymer additive, and 30 to 84% by weight of a good solvent, the external coagulation solution is a good solvent 10 To 60 wt% and non-solvent 40 to 90 wt%, wherein the hollow former comprises 10 to 60 wt% of good solvent, 30 to 80 wt% of non-solvent, and 10 wt% of polymer Method for producing a vinylidene fluoride porous hollow fiber membrane. 6. The polyvinylidene fluoride-based porous hollow fiber membrane of claim 5, wherein the polymer additive used in the spinning solution is selected from the group consisting of polyimide, polyimide, polyisketone, polyiserketone and mixtures thereof. Manufacturing method. The method of claim 5, wherein the polyvinylidene-based polymer is selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichlorofluoroethylene, and mixtures thereof. The good solvent used in the spinning solution is selected from the group consisting of N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide, dimethylformamide and mixtures thereof, The solvent included in the hollow forming agent and the external coagulant is selected from the group consisting of γ N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide, dimethylformamide and mixtures thereof, and the non-solvent is glycerol, ethylene Glycol, propylene glycol, low molecular weight polyethylene glycol and mixtures thereof, The polymer used in the hollow forming agent is polyethylene glycol, polyvinyl alcohol, polyethyleneimine, polyvinylpyrrolidone and a method for producing a polyvinylidene fluoride-based porous hollow fiber membrane is selected from the group consisting of.

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