KR20110055825A - A tubular braid and composite hollow fiber membrane using the same - Google Patents

Abstract

PURPOSE: A tubular knitted fabric prepared by triangular multi filament and a composite hollow fiber using the same are provided to ensure splitting intensity and low dope penetration. CONSTITUTION: A tubular knitted fabric(1) is knitted by triangular multi filament. The multi filament comprises 20-300 monofilaments and the fineness is 20-100 denier. The total fineness of the tubular knitted fabric is 200-800 denier. The tubular knitted fabric is made of polyethylene terephthalate or nylon. A composite hollow fiber membrane comprises 20-300 monofilaments and fineness is 20-100 denier. The composite hollow fiber membrane comprises the tubular knitted fabric and polymeric resin thin film(2) coated on the surface of the tubular knitted fabric.

Description

Tubular knitted fabric and composite hollow fiber membrane using the same {A tubular braid and Composite Hollow Fiber Membrane using the same}

Embodiments of the present invention are directed to hollow fiber membranes that can be used in water treatment, and more particularly to composite hollow fiber membranes.

In general, it is well known that water treatment using a separation membrane is a purification technique using a selective permeation mechanism of a material. At this time, the water treatment using the membrane, that is, the separation of contaminated water is not only economical in terms of energy saving, facility simplification, and operation efficiency compared to the distillation method used in the conventional chemical treatment, A wide range of research and practical use has been made, ranging from laboratory scale to various industrial sectors. Such membranes may be morphologically listed as flat membranes, tubular membranes, hollow fiber membranes, etc. The flat membranes have high pollution resistance and are widely applied as wastewater treatment technologies, but are difficult to install economically due to their low density per unit volume. Hollow fiber membrane is morphologically shaped in the form of a yarn and can pack a lot of membranes per unit volume, thereby increasing throughput. However, hollow fiber membranes are often easily cut off during operation due to low mechanical strength, and in particular, these disadvantages act as a deterrent to securing high quality water. The composite hollow fiber membrane used as the separator must exhibit excellent permeability and at the same time exhibit excellent mechanical strength. Recently, the composite hollow fiber membrane is applied to a water treatment process in the form of an immersion type module, and the immersion type module is composed of an essential process for cleaning through aeration, and is operated by repeated cycles of operation / rest in order to minimize membrane contamination. In this case, friction, physical shock, and continuous operation and repetition of the hollow fiber membranes due to the aeration may cause the film to deviate from the support of the membrane and its own peeling at the interface between the module and the membrane. In order to apply such hollow fiber membranes to various water treatment fields, various characteristics such as excellent permeability, excellent mechanical strength, high filtration reliability, high peel strength, low dope penetration, and high stiffness are required.

Embodiments of the present invention are composed of a triangular multifilament to provide a tubular knitted fabric having excellent permeability, mechanical strength and peel strength, low dope permeability and high stiffness properties.

Embodiments of the present invention provide a composite hollow fiber membrane having improved mechanical strength by using the tubular knitted fabric.

One aspect of the present invention relates to a tubular knitted fabric knitted from triangular multifilament, wherein the multifilament is made by combining 20 to 300 monofilaments and has a fineness of 20 to 100 denier. will be.

Another aspect of the present invention is a composite hollow consisting of a tubular knitted fabric made of a combination of 20 to 300 monofilaments and knitted with a triangular structure multifilament having a fineness of 20 to 100 denier and a polymer resin thin film coated on the surface of the tubular knitted fabric. It's about the desert.

The triangular structure of the tubular knitted fabric according to the embodiments of the present invention can form a denser structure than a circular shape, so that the specific surface area is expanded, so that the peel strength between the tubular knitted fabric and the resin thin film is excellent and the voids between the tubular knitted fabric are minimized. Complete immersion of dope or blockage of hollow can be prevented. In addition, since the stiffness of the hollow fiber membrane can be increased, the mechanical strength is excellent, and the roundness of the support can be improved to obtain a polymer resin thin film having a uniform coating layer, as well as to improve the tensile strength and the pressure resistance.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a composite hollow fiber membrane according to an embodiment of the present invention.

As shown in Figure 1, the composite hollow fiber membrane according to an embodiment of the present invention is a tubular braid (1), a polymeric resin thin film (2) coated on the surface of the tubular knitted fabric (1) as a reinforcing material and treatment It consists of a hollow part 3 for receiving the material. The tubular knitted fabric 1 is knitted to a total fineness of 200 to 800 denier by recombining a triangular structure multifilament consisting of 20 to 100 denier and 20 to 300 pillars. The tubular knitted fabric (1) composed of triangular multifilaments makes the peel strength between the tubular knitted fabric (1) and the polymer resin thin film (2) excellent, and the packing density of the tubular knitted fabric is increased, so that the polymer resin thin film is used for forming the dope. Full impregnation or clogging of the hollow part is prevented.

2 is a schematic enlarged view of a tubular knitted fabric woven from circular filament yarns, and FIG. 3 is a schematic enlarged view of a tubular knitted fabric woven from triangular filament yarns. The use of triangular filament yarns allows the specific surface area to be expanded compared to circular filament yarns. Such a structural advantage is that when the dope liquid penetrates into the tubular knitted fabric to form the polymer resin film, the mutual contact surface can be enlarged, thereby improving adhesion to the polymer resin film. Therefore, peeling strength can be improved.

On the other hand, when the filament yarn of the triangular structure can be used to increase the packing density it is possible to prevent the hollow plug phenomenon by preventing the dope solution from penetrating into the hollow. In addition, the triangular structure diversifies the path to the inside of the hollow than the circular structure (see arrows in FIGS. 2 and 3) to induce a synergistic effect of friction force and low dope penetration, thereby preventing the hollow clogging phenomenon. An additional property that can be expressed due to increased packing density is that the stiffness is excellent. The importance of stiffness can be considered in two aspects, one of which is the roundness of the hollow fiber membrane. This is an important factor in determining the uniform coating of the composite film. In addition, the increase in stiffness in the application of water treatment can amplify the vibration action due to aeration can easily remove contaminants.

In one embodiment of the present invention, the multifilament is preferably made by combining a plurality of monofilament having a fineness of 0.3 to 50 denier. When the fineness of the monofilament exceeds 50 denier, the peeling strength between the tubular knitted fabric 1 and the polymer resin thin film 2 coated on the surface becomes low and the dope may penetrate. Decreased peel strength due to reduction of surface area. In addition, when the fineness of the monofilament is less than 0.3 denier, the water permeability is reduced, the elastic modulus of the filament is lowered, and the bending strength and the stiffness may be lowered. The multifilament is made by combining 20 to 300 monofilaments in terms of peel strength, easy doping penetration control, and economy, and the fineness of the formed filament may be 20 to 100 denier.

The multifilament of the tubular knitted fabric woven by one embodiment of the present invention has a high physical density due to the triangular structure. This increases the modulus of elasticity and contributes to securing the roundness of forming a uniform coating layer by increasing the stiffness of the tubular knitted fabric 1. At the same time, it is possible to manufacture a module having a pollution resistance property by having a desirable influence on the cleaning action through aeration in the water treatment process.

According to one embodiment of the invention, the total fineness of the yarn (yarn) consisting of triangular filaments is preferably 200 to 800 denier, more preferably in the range of 250 to 600 denier. When the total fineness of the yarn is less than 200 denier, the production speed is lowered, and when the total fineness of the yarn exceeds 800 denier, the outer diameter of the tubular knitted fabric 1 is expanded to reduce the density per unit volume.

The material of the tubular knitted fabric 1 according to the embodiment of the present invention may be a polyethylene terephthalate (PET), nylon (nylon), etc. containing a polar group, but is not necessarily limited thereto. Polyethylene, polypropylene, etc., which are composed of non-polar molecular chains, have poor adhesion with the coating layer, while polyester-based and polyamide-based materials containing polar groups have excellent interfacial adhesion with the coating layer.

According to one embodiment of the invention, the polymer resin thin film (2) is coated on the surface of the tubular knitted fabric (1) to form a composite hollow fiber membrane, the polymer resin thin film (2) is the mechanical strength of the composite hollow fiber membrane, the water permeability of the membrane And filtration reliability. The polymer resin thin film 2 has a mechanical strength such that the polymer resin thin film 2 itself is lower than the tubular knitted fabric 1, so that the polymer resin thin film 2 itself does not peel or break, and complements the tensile strength and the pressure resistance of the composite hollow fiber membrane.

According to one embodiment of the present invention, since the tubular knitted fabric 1 has a relatively large void compared to the polymer resin thin film 2, the filtrate passing through the polymeric resin thin film 2 has a tubular knitted fabric having a large void ( Passes 1) without great resistance. That is, the water permeability of the filtrate is affected by the polymer resin thin film 2 having small pores, and the water permeability of the entire composite hollow fiber membrane is determined by the micropore structure and porosity of the polymer resin thin film 2.

The micropore structure and porosity of the polymer resin thin film 2 is determined according to the difference in thermodynamic stability according to the composition of the dope. In more detail, when the solvent or additives constituting the dope solution strongly interact with the polymer, a sponge-like structure is formed due to the "demixing delay effect" between the polymer and the coagulation bath solution. As the interaction with the polymer becomes weaker, the 'mixing effect' proceeds rapidly to form a finger-like structure. The sponge structure is advantageous over the finger structure in terms of mechanical strength, but disadvantageous in terms of water permeability. The reason is that the sponge structure has a strong hydraulic resistance compared to the finger structure. On the other hand, the surface pore size distributed on the surface shows an important function for imparting reliability of the filtration characteristics. That is, the formation of surface pore having the same distribution excludes particles of a certain size or more, thereby imparting stability of the water quality in the water treatment process.

According to one embodiment of the present invention, the polymer resin thin film (2) forms a sponge structure up to 50 ~ 190 ㎛ in the lower layer and the finger structure up to 0.1 ~ 10 ㎛ in the lower layer in order to simultaneously express mechanical strength, water transmission rate, filtration reliability To minimize the distribution of surface porosity. Micropores having a pore size of 0.01 to 1 μm may be formed in the surface layer, and micropores having a pore size of 0.01 to 10 μm may be formed in the inner layer. In addition, when the diameter of the micropores formed in the inner layer of the composite hollow fiber membrane gradually increases toward the center direction to increase the asymmetry, the water permeability can be enhanced.

Next, the polymer resin thin film 2 is applied to the tubular knitted fabric 1 and undergoes a solidification process. As the organic solvent is released during the solidification process, a pore is formed inside. At this time, since the surface layer of the polymer resin thin film 2 has a faster solidification rate than the inner layer, the pore size of the surface layer is formed relatively smaller than the pore size of the inner layer.

In one embodiment of the present invention, the thickness of the polymer resin thin film (2) is preferably in the range of 10 to 200㎛, when the thickness of the polymer resin thin film 20 is less than 10㎛ falls in mechanical strength, if larger than 200㎛ There is a drop in water permeability. The distance that the polymer resin thin film 2 penetrates into the tubular knitted fabric 1 is preferably in the range of 10 to 30% of the thickness of the tubular knitted fabric 1 (that is, the difference between the outer diameter and the inner diameter of the tubular knitted fabric 1). This is because the mechanical strength drops when the thickness of the knitted fabric 1 is smaller than 10%, and the water permeability decreases when the thickness is larger than 30%.

The polymer resin thin film 2 according to an embodiment of the present invention is formed by coating a surface of the tubular knitted fabric 1 with a spinning dope composed of a polymer resin, an organic solvent, and an additive polyvinylpyrrolidone and a hydrophilic compound. .

In the process of manufacturing a composite hollow fiber membrane according to an embodiment of the present invention, the tubular knitted fabric (1) passes through the tubular knitted fabric (1) to the center of the double tubular nozzle and flows the spinning dope into the surface of the tubular knitted fabric (1). Coating the spin dope on the surface of the substrate). Subsequently, the spinning dope may be discharged into the air outside the nozzle, coagulated with an external coagulation liquid, and then washed with water and dried.

In one embodiment of the present invention, the spinning dope is prepared by dissolving a polymer resin, an additive polyvinylpyrrolidone, and a hydrophilic compound in an organic solvent. The preferred content range is 10 to 50% by weight of the polymer resin, polyvinylpyrrolidone and 1 to 30% by weight of the hydrophilic compound, and 20 to 89% by weight of the organic solvent.

The polymer resin used in one embodiment of the present invention is polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, polyvinylidene fluoride (PVDF) resin, polyacrylonitrile (PAN) resin, polyimide resin , Polyamideimide resin, and at least one selected from the group consisting of polyesterimide resin can be used. At this time, at least one selected from the group consisting of dimethylacetamide and dimethylformamide may be used as the organic solvent. As the surface pore-forming agent, at least one selected from the group consisting of water or polypyrrolidone-based compounds may be used. If the polypyrrolidone compound is less than 1% does not form a uniform surface pore, if the polypyrrolidone compound is 30% or more, the mechanical strength is lowered by the brittleness of the thin film.

Hereinafter, after the composite hollow fiber membranes are prepared through Examples and Comparative Examples, the properties of the composite hollow fiber membranes prepared according to the Examples of the present invention will be described by measuring physical properties thereof. The listed examples are for ease of understanding and are not intended to limit the invention.

Example  1: Preparation of Composite Hollow Fiber Membrane

A total of 50 denier triangular yarns consisting of 36 filaments of polyethylene terephthalate (PET) monofilament having 1.4 deniers of fineness were spliced into 6 strands so that the total fineness of one yarn was 300 deniers. Then, using the 26 yarns prepared to prepare a tubular knitted fabric woven so that the outer diameter is 1.9 mm. The SEM image of the prepared triangular filament yarn is shown in FIG.

As a dope solution, a composition composed of 17% polyvinylidene fluoride (PVDF), 10% polyvinylpyrrolidone, and 73% dimethyl acrylamide was sufficiently dissolved at 40 ° C., and then degased to remove the generated gas. Placed at room temperature. The prepared dope solution was supplied to a double tubular nozzle and the dope solution was coated on the outside of the tubular knitted fabric by passing through the tubular knitted fabric prepared in the center. At this time, the thickness of the coating was 0.2mm. The knitted fabric passed through the air gap (5 cm) was coagulated in an external coagulation bath at 30 ° C. Thereafter, in order to remove residual solvents and additives, the mixture was post-treated in a hydrothermal apparatus at 60 ° C. for 1 day, immersed in 20 wt% alcohol solution for 2 hours, and then dried in a dryer at 40 ° C. for 24 hours to obtain a composite hollow fiber membrane.

The prepared composite membrane had the characteristics of 1.10 Mpa peel strength, 0.132 kg stiffness and 500 LMH water permeability, and obtained an excellent membrane which did not penetrate the dope solution into the hollow.

Example  2: Preparation of Composite Hollow Fiber Membrane

A total of 50 denier triangular yarns consisting of 100 filaments of polyethylene terephthalate (PET) monofilament having 0.5 denia of fineness were spliced into 6 strands so that the total fineness of one yarn was 300 denia. Then, using the 26 yarns prepared to prepare a tubular knitted fabric woven so that the outer diameter is 1.9 mm. Formation of the coating layer was performed according to the same preparation and process as in Example 1.

The obtained composite membrane showed the characteristics of 1.22 MPa peel strength, 0.103 kg of stiffness, and 492 LMH of water transmission. Compared with Example 1, it can be seen that the denia number of the fineness was low, and the contact area with the dope liquid was widened, thereby increasing the peel strength. Stiffness, on the other hand, showed low results.

Example 3: Preparation of Composite Hollow Fiber Membrane

A total of 50 denier triangular yarns consisting of 100 filaments of polyethylene terephthalate (PET) monofilament having 5 deniers were spliced into 6 strands so that the total fineness of one yarn was 300 denia. Then, using the 26 yarns prepared to prepare a tubular knitted fabric woven so that the outer diameter is 1.9 mm. Formation of the coating layer was performed according to the same preparation and process as in Example 1.

The obtained composite membrane exhibited characteristics of peel strength of 0.92 MPa, stiffness of 0.170 kg, and water permeability of 486 LMH. Compared with Example 1, it can be seen that the denia number of the fineness is high and the contact area with the dope liquid is small, so that the peel strength is lowered. Stiffness, on the other hand, showed elevated results.

Comparative example  1: Preparation of Composite Hollow Fiber Membrane

A total of 6 yarns of 50 denier circular structure yarns consisting of 36 PET monofilament yarns having 1.4 deniers of fineness were combined so that the total fineness of one yarn was 300 deniers. Then, using the 26 yarns prepared to prepare a tubular knitted fabric woven so that the outer diameter is 1.9 mm. SEM pictures of the manufactured circular structure filament yarn are shown in FIG. 5. Subsequent processes were performed under the same processes and conditions as in Example 1 to obtain a composite hollow fiber membrane.

The obtained composite film had a low peel strength of 0.72 MPa. This is considered to be because the tubular knitted fabric of circular structure has a low contact specific surface area with the dope solution. Although the stiffness was relatively high at 0.112 kg, the function of the hollow fiber membrane was lost due to the penetration of the dope solution.

Comparative example  2: Preparation of Composite Hollow Fiber Membrane

Six strands of 50 denier circular structural yarns composed of 100 filaments of polyethylene terephthalate (PET) monofilament with 0.5 degree of fineness were synthesized to give a total fineness of 300 dennes per yarn. Thereafter, using the 26 strands of yarn, a tubular knitted fabric having an outer diameter of 1.9 mm was prepared. Formation of the coating layer was performed according to the same preparation and process as in Example 1.

The obtained composite membrane had a low water permeability of 492 LMH, a peel strength of 0.91 MPa, and a stiffness of 0.062.

As shown in the Examples and Comparative Examples, the yarn having a triangular structure has a higher packing density than the yarn having a circular structure, which shows excellent dope permeability and stiffness, and promotes peel strength by expanding a specific surface area. have.

Peel strength

The load at the moment of peeling of the polymer resin thin film from the tubular knitted fabric was measured by a tensile tester, and the peel strength was calculated by dividing this by the area (㎡) to which the shear force was applied. Specific measurement conditions are shown in Table 1 below.

TABLE 1

Peel strength is defined as shear strength per unit area applied to the coated polymer resin thin film when the specimen is tensioned, and the area (m ² ) to which shear force is applied is π × outer diameter of the composite hollow fiber membrane (m) × Calculated by the adhesion length (m). The calculation is as follows.

Peel strength (Pa) = load at yield point (kg) / area under shear (m ² )

Dope permeability

The cross section of the prepared composite hollow fiber membrane was cut and the degree of penetration of the dope into the tubular knitted fabric was observed through a microscope.

Stiffness ( Stiffness )

Using the sample holder provided by Instron, the composite hollow fiber membrane was pressed in the compression mode to evaluate the stiffness with the maximum load generated when bending occurred. Specific measurement conditions are shown in Table 2 below.

TABLE 2

Permeability  Measure

A compact pressure module with a membrane area of 0.0057 m ² was fabricated and placed in a device with a pressure gauge. The interlayer differential pressure was kept constant at 100 kPa and RO water of 24 ± 1 ° C. was supplied to measure the water permeation rate for 2 minutes. The unit of permeation amount is LMH (L / m ² × h).

Although the present invention has been described in detail with reference to preferred embodiments of the present invention, it will be apparent to those skilled in the art that the present invention may be variously changed or modified without departing from the spirit and scope of the present invention. Modifications and variations are also to be construed as being included in the scope of protection of the present invention.

The following drawings illustrate one embodiment of the present invention, and together with the detailed description of the present invention serve to assist in understanding the present invention, the present invention should not be construed as limited to the matters set forth in these drawings.

1 is a cross-sectional view of a composite hollow fiber membrane according to an embodiment of the present invention.

2 is a schematic enlarged view of a tubular knitted fabric woven from circular filament yarns. Figure 3 is a tubular woven of triangular structure filament yarn according to an embodiment of the present invention

A schematic enlarged view of a knitted fabric.

4 is a SEM photograph of the triangular structure filament yarn according to Example 1. FIG.

5 is a SEM photograph of a circular structure filament yarn according to Comparative Example 1. FIG.

<Explanation of symbols for the main parts of the drawings>

1: tubular knitted fabric 2: polymer resin thin film

3: hollow part

Claims (10)

A tubular knit knitted from triangular multifilament, wherein the multifilament is made by combining 20 to 300 monofilaments, and has a fineness of 20 to 100 denier. The tubular knitted fabric of claim 1, wherein the monofilament has a fineness of 0.3 to 50 denier. The tubular knit fabric of claim 1, wherein the total fineness of the tubular knit fabric is between 200 and 800 denier. The tubular knitted fabric of claim 1, wherein the tubular knitted fabric is made of at least one selected from the group consisting of polyethylene terephthalate and nylon. A composite hollow fiber membrane comprising a tubular knitted fabric made of a combination of 20 to 300 monofilaments and knitted with a triangular structure multifilament having a fineness of 20 to 100 denier, and a polymer resin thin film coated on the surface of the tubular knitted fabric. 6. The polymer resin thin film of claim 5, wherein the polymer resin thin film forms a sponge-like structure from 50 to 190 mu m in the lower layer and a finger-like structure from 0.1 to 10 mu m in the upper layer. Composite hollow fiber membrane. The composite hollow fiber membrane of claim 5, wherein the polymer resin thin film is formed of a surface layer having a pore size of 0.01 to 1 μm and an inner layer having a pore size of 0.01 to 10 μm. The composite hollow fiber membrane of claim 5, wherein the polymer resin thin film has a thickness of 10 μm to 200 μm. 6. The composite hollow fiber membrane according to claim 5, wherein the total fineness of the tubular knitted fabric is 200 to 800 denier. 6. The composite hollow fiber membrane according to claim 5, wherein the tubular knitted fabric is made of at least one selected from the group consisting of polyethylene terephthalate and nylon.

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