KR20040077322A - Preparation of asymmetric polyethylene hollow fiber membrane having high strength - Google Patents

Abstract

PURPOSE: Provided is a method for preparing an asymmetric polyethylene hollow fiber membrane which is able to provide an asymmetric polyethylene hollow fiber membrane having high tensional strength and good porosity by changing melt spinning condition of a hollow fiber. CONSTITUTION: The method comprising the steps of (a) spinning polyethylene through a spinneret having a double nozzle; and (b) after cooling the polyethylene hollow fiber, annealing, cold stretching, hot stretching and thermal setting the cooled polyethylene hollow fiber. The method is characterized in that the crystallization speed of the outer surface and that of the polyethylene hollow fiber are different from each other by supplying nitrogen gas to the inner surface of the polyethylene hollow fiber while cocurrently spraying a solvent having a boiling point of 30 to 80 deg.C as a cooling media on the outer surface of the polyethylene hollow fiber in the cooling step.

Description

Manufacturing method of asymmetric polyethylene hollow fiber membrane with high strength {PREPARATION OF ASYMMETRIC POLYETHYLENE HOLLOW FIBER MEMBRANE HAVING HIGH STRENGTH}

The present invention relates to a method for producing a porous polyethylene hollow fiber membrane useful as a separation membrane for water treatment, and more specifically, a porous structure having a high asymmetry property and high tensile strength, water permeability, and particle removal ability, having a different pore size between the inner surface and the outer surface. A method for producing a polyethylene hollow fiber membrane.

Conventional methods for preparing a microfiltration membrane using a polyolefin material, which is a crystalline polymer, include a thermally induced phase separation method and a stretching method. The hollow fiber membranes prepared by the thermally induced phase separation method have excellent porosity, Since it does not impart a high draw ratio, it is difficult for polymer chains to have high orientation and generally has a weak tensile strength of hollow fiber membranes. In contrast, the hollow fiber membranes produced by the stretching method have high porosity as well as excellent porosity, so the orientation and tensile strength are very high. In addition, since it does not require specific additives such as solvents, diluents, extractants and chemicals during the manufacturing process, it can greatly contribute to cost reduction and work environment improvement.

In general, when morphology of polyolefin-based polymers are classified into several morphologies, polypropylene polymer chains are formed when the amount of external stress applied in a certain direction is small when transitioned from molten state to crystalline state. They grow concentrically around the nuclei and produce spherulite. In this case, the density inside the spearite is high, but the interspherulitic region between the spearlite and the spearite has a relatively low polymer density. At this time, the pores may be formed by cleaving the region between the sparite and the sparite. An example of the separation membrane thus produced has been illustrated in Korean Patent No. 0321133.

On the other hand, when the crystalline polymers such as polypropylene or polyethylene transition from the molten state to the crystalline state, when the external stress applied in a certain direction is large, the polymer chain grows perpendicularly to the stressed direction. (row nucleated lamella). At this time, approximately 5 rows of nucleated lamellas stacked vertically form a lamellar stack. An amorphous region exists between the lamellar stacks. The stretching method uses a method of cleaving the amorphous regions thus formed to form pores. The faster the cooling rate of the polymer during spinning, the smaller the final pore size and the slower the cooling rate, the larger the pore size. Cold drawing processes are performed to create microcrazes in these amorphous regions and draw at very high speeds at low temperatures. After the cold drawing process is completed, the heat drawing process is applied at a very slow speed at a high temperature to produce a microporous hollow fiber membrane having a very high porosity while cleaving the part where the microcraze is formed.

In US Patent 4,541,981 of Celanese Corporation, there is an example of manufacturing a polypropylene hollow fiber membrane having an outer diameter of about 300-400 μm and an oxygen permeability of 9 × 10 ⁴ L / m 2 hr 0.68 atm. In this patent, after the hollow fiber is spun, cold drawing and hot drawing are used in the stretching method. Since the membrane is used in gas permeation, the membrane has a relatively low porosity of about 40% and low oxygen permeability compared to the water treatment membrane.

In addition, Mitsubishi Rayon's U.S. Patent No. 5,294,338 has a rectangular pore form consisting of fine fibrils, the size of the pores is between 2㎛ 10㎛, air permeability 80 × 10 ⁴ L / ㎡ hr Polyethylene hollow fiber membranes having 0.5 atm or more were prepared. However, the internal and external surfaces of the hollow fiber membranes have the same symmetry, and after the manufacturing of the hollow fiber membranes, the hydrophilic polymer was secondarily coated on the outer surface to induce asymmetry.

Accordingly, the present inventors have diligently studied a new method for producing an asymmetric polyethylene hollow fiber membrane having high tensile strength and excellent porosity. As a result, the hollow fiber membrane itself is fundamentally changed by changing the spinning conditions of the hollow fiber rather than the surface coating method. A method for preparing polyethylene hollow fiber membranes having excellent asymmetric properties has been developed.

1 is a block diagram schematically showing an apparatus used for producing a polyethylene hollow fiber membrane according to the present invention,

2A and 2B are photographs of the outer surface and the inner surface when 40 ° C. air is supplied in co-current as a cooling medium of the cooling chamber.

3A and 3B are photographs of the outer surface and the inner surface when 20 ° C. air is supplied in co-current as a cooling medium of the cooling chamber.

4A and 4B are photographs of the outer surface and the inner surface when 20 ° C. freon injection liquid is supplied in co-current as a cooling medium of the cooling chamber.

5A and 5B are photographs of the outer surface and the inner surface when 40 ° C. air is supplied in countercurrent as a cooling medium of the cooling chamber.

6A and 6B are photographs of the outer surface and the inner surface when 20 ° C. air is supplied in countercurrent as a cooling medium of the cooling chamber.

7A and 7B are photographs of the outer surface and the inner surface when the 20 ° C. freon injection liquid is supplied countercurrently as a cooling medium of the cooling chamber.

<Short description of the symbols in the drawings>

1: Hopper 2: Extruder

3: gear pump 4: spinneret

5: baffle 6: cooling chamber

7: hollow fiber 8: suction pump

9: condenser 10: feed pump

11 drain valve 12 nitrogen tank

13: roller 14: winding bobbin

In order to achieve the above object, the present invention provides a method for producing a polyethylene hollow fiber membrane by spinning polyethylene through a spinneret having a double nozzle and cooling the spun polyethylene hollow fiber, followed by annealing, cold stretching, hot stretching and heat setting. In the cooling step, nitrogen gas is supplied to the inner surface of the spun polyethylene hollow yarn, and a solvent having a boiling point of 30 to 80 ° C. is co-flowed on the outer surface of the spun polyethylene hollow fiber as a cooling medium. Provided is a method for producing an asymmetric polyethylene hollow fiber, characterized by varying the crystallization rate.

Hereinafter, the present invention will be described in more detail.

In the present invention, a high density polyethylene having a density of 0.96 g / cm 3 or more is used as a raw material for manufacturing hollow fiber. The polyethylene is melt-spun under specific conditions and then subjected to an stretching process under specific conditions, thereby producing a microfiltration hollow fiber membrane having a very large pore size and porosity. High density polyethylenes that can be used in the present invention have a melt index in the range of 0.03 to 8.0 g / 10 minutes, preferably 0.1 to 5.5 g / 10 minutes. When the melt index is more than 8.0 g / 10 minutes, the strength is weak and the stretching is not possible much, so the pore size is small. The lower the melt index, the higher the draw ratio can be, the larger the pore size and the higher the strength, but 0.03 g / 10 If the melt index is less than minutes, it is difficult to uniformly spin.

1 schematically shows an example of an apparatus for producing unstretched fibers of an asymmetric polyolefin hollow yarn for applying the stretching method according to the present invention. As shown in FIG. 1, high-density polyethylene is injected through the hopper 1 to be melted by frictional heat between the screw and the barrel in the extruder 2 cylinder, and the melt is spun by a predetermined amount using the gear pump 3. 4) to supply.

The outlet of the spinneret (4) is provided with a double spinning nozzle, of which continuously supply hot nitrogen gas to the inner nozzle of the spinning nozzle, so that the polyethylene is spun with nitrogen inside. When the polyethylene melt is spun, the nozzle temperature is maintained at 150 ° C to 220 ° C, preferably 170 ° C to 220 ° C, and the draft ratio plays a decisive role in the crystallization behavior of polyethylene during spinning as well as the nozzle temperature. (Ie, the winding linear velocity / radiation linear velocity) is preferably maintained in the range of 100 to 800. If the draft ratio falls below 100, it is difficult to produce a low nucleated lamellar structure, and if it is 800 or more, hollow yarns having very fine pore sizes are produced.

The hot nitrogen gas continuously supplied to the yarns through the spinneret 4 is naturally heated up to the same temperature as the nozzle body while being supplied into the spinneret 4 from the nitrogen tank 12 and supplied into the hollow fiber. The amount of nitrogen supplied is preferably introduced at a slow rate ranging from 0.1 m / min to 0.3 m / min.

The melt spun together with nitrogen through the spinneret from the spinneret (4) is cooled to room temperature by air or blown wind at a certain distance from the bottom of the nozzle and then immersed in a coagulation bath or continuously cooled in air. It is a process of crystallization. This cooling process is the most important part of the overall process in which the hollow fiber membrane is manufactured, and the pore size, shape, and porosity of the final hollow fiber membrane are largely determined by the cooling mechanism.

In general, the method of rapid cooling using a coagulation liquid causes the solidification phenomenon on the surface of the polymer so rapidly that it does not give adequate time for the crystallization to proceed as the polymer chains are arranged and the porosity of the final hollow fiber membrane is significantly lowered or almost pore. Is not generated. Therefore, the above method is not very preferable considering the specificity of the hollow fiber to which porosity is to be applied by applying the stretching method.

The method of gradually cooling the hollow fiber by air at the lower end of the nozzle is a more preferable method for preparing the hollow fiber membrane to which the stretching method is applied because the crystallization time can be adjusted relatively appropriately. In the conventional method, the air is flowed at a very low flow rate in the vicinity of room temperature, and cooling is performed. If the flow rate is large, there is a limit to increase the flow rate because the hollow fiber is caused to be uneven due to the shaking or surface friction of the hollow fiber.

In the present invention, by adjusting the crystallization rate of the outer surface and the inner surface of the hollow fiber in the cooling process differently, it can be obtained that the hollow fiber membrane having a different pore size of the outer surface and the inner surface in the final hollow fiber membrane, the inner surface of the hollow yarn In the continuous supply of hot nitrogen gas through the spinneret 4 to the outer surface of the hollow fiber, a low boiling point solvent, preferably air, which is not air, is preferably used as co-current flow. Spray. That is, in the present invention, in the cooling process of the hollow yarns, a low boiling point solvent is blown toward the outer surface of the hollow yarns radiated into the cooling chamber 6 through the micronozzle to increase the crystallization rate of the outer and inner surfaces of the hollow yarns. It is characterized by different adjustments. When the hollow fiber with the crystallinity is controlled as a final hollow fiber membrane through all processes, it becomes an asymmetric hollow fiber membrane having different internal and external pore sizes.

The low boiling point solvent usable in the present invention is an organic solvent having a boiling point of 30 to 80 ° C., specifically, methanol, ethanol, acetone, methyl ethyl ketone, ethyl formate, carbon tetrachloride, freon and the like.

In the present invention, the cooling chamber 6 is provided with a baffle 5 in the cooling process to spray a low boiling point solvent into fine liquid particles. In particular, the apparatus of FIG. 1 shows a case where freon is used as the cooling medium. The liquid freon injected into the cooling chamber 6 through the supply pump 10 vaporizes while depriving heat from the hollow fiber, and then the suction pump 8. By the condenser 9 (cooling water is circulated, not shown) to be condensed back to the liquid phase, the condensed freon is again supplied to the cooling chamber through the supply pump (10). Part of the water is produced during the condensation process, when using the Freon specific gravity of the water is less than the Freon is naturally separated and stored in the condenser, which can be separated through the drain valve 11 when a certain amount is accumulated.

According to the present invention, since the liquid low boiling point solvent has a very good cooling efficiency, even when supplied at a low flow rate of about 0.5 to 3 m / sec, it is possible to stably produce a uniform hollow fiber.

In the apparatus of FIG. 1, when other solvents are used without using a freon as a cooling solvent, they may be directly supplied from a separate storage tank without using a condenser.

The unstretched hollow fiber 7 emitted from the cooling chamber 6 is immediately wound on the winding bobbin 14 via the roller 13. Thereafter, the hollow fiber is subjected to annealing in a heated oven while wound on the winding bobbin 14, and then subjected to cold stretching and hot stretching on rollers, and then to a final hollow fiber membrane through a heat setting process while being wound on a bobbin. Will be made.

The annealing process is performed in a hot air dryer at 80 ° C. to 130 ° C., preferably 120 ° C. to 127 ° C., for 2 hours to 24 hours, preferably 6 hours to 24 hours. The reason for this is to induce non-crystalline regions that do not participate in the crystallization to participate additionally in the crystal regions, thereby increasing the degree of crystallization and distributing the crystal regions and the amorphous regions well.

The unstretched yarn after the annealing process is subjected to a cold draw process at a temperature of from room temperature to 40 ° C. or less, in order to generate fine crazes throughout the hollow fiber by applying a shock at a very uniform and high speed. In this case, the deformation rate should be within 50% / second to 200% / second, preferably within 150% / second, and the draw ratio should be within the range of 5% to 100%.

At the end of the cold drawing process, no pores are formed yet. Therefore, the heat drawing process is immediately performed on the hollow fiber after the cold drawing process without an additional heat treatment process, wherein the temperature is in the range of 80 to 130 ° C., preferably 105 to 120 ° C., and the heat drawing ratio is 300 to 1,000. It is carried out within% and the strain rate is within the range of about 1 to 10% / second. It is finally formed through the hollow fiber membrane having a large porosity during the thermal stretching process. When the strain exceeds 10% / sec, the thickness of the hollow yarn becomes very thin, the bending phenomenon becomes severe, and the porosity is very low.

After the heat stretching process, the hollow fiber membrane is finally manufactured by hollow fiber through a thermal setting process in a range of 0.5 to 30 minutes between 110 and 130 ° C. to remove elastic recovery force.

As described above, according to the method of the present invention, the tensile strength is very high and more than 1,000 gf / filament and excellent porosity, as well as the pore size of the inner surface and the outer surface without the need for a separate surface coating for imparting asymmetry Different one can produce an asymmetric polyethylene hollow fiber membrane that can act to increase the particle removal efficiency and the other can increase the water permeability.

Hereinafter, the present invention will be described in detail with examples and test examples, which are not intended to limit the present invention. In the examples below, the performance measurements of the hollow fiber membranes were used in the methods described below.

(1) Gas Permeability

15 ends of the hollow fiber membranes were fixed to both ends with an epoxy adhesive in an acrylic tube of 15 cm in length, 1 cm in outer diameter and 0.7 cm in inner diameter so that the effective length was 12 cm. Then, the air was hollowed at a temperature of 25 ° C. with 0.5 atm pressure. After the injection into the desert, the volume of air transmitted to the outside through the cross section of the hollow fiber membrane was measured.

(2) Pure Permeability

Since the polyolefin-based polymer has a hydrophobic surface property, the surface and the inside of the polymer should be hydrophilized using a surfactant before performing the water permeation experiment. Produced by As the surfactant, an aqueous solution of 20% by volume of Tween 80 (Aldrich) was used. With the supply pressure maintained at 1 kgf / ㎠ and the back pressure regulator open, crossflow filtration was used to supply the surfactant to the feed for 15 minutes, then the back pressure regulator was completely closed and dead The supply of the surfactant was stopped when the pressure gradually decreased while permeating through a dead-end filtration method and remained constant without any further drop. Distilled water was supplied for 5 minutes by applying crossflow filtration with the back pressure regulator open to replace the surface and the inside with water.Then, the back pressure regulator was completely shut off, and the feed solution was continuously permeated for at least 10 minutes and the pressure was stabilized. After waiting until the pressure was stabilized, the volume of permeate collected for 10 minutes was measured.

(3) tensile strength

Instron (INSTRON) was used to measure the tensile strength of the hollow fiber membrane. The hollow fiber membrane for measurement was 100 mm in length and the test speed was 50 mm / min.

(4) pore size

In order to measure the pore size of the hollow fiber membrane, an image of a surface magnified 15,000 times using a scanning electron microscope (SEM) was obtained, and then 50 pores were arbitrarily selected using an image analyzer, and then the average of long and short axes was obtained. The length was measured.

(5) particle removal ability

Polystyrene particles having an average size of 0.1 to 0.62 μm prepared by the emulsion polymerization method were mixed to prepare a 0.1 wt% aqueous solution, and then filtered from the outside of the hollow fiber membrane to the inside to measure the polystyrene particle size distribution of the filtered permeate.

Comparative Example 1

High density polyethylene (MI = 0.35 g / 10 min) was melt spun at 180 ° C. while nitrogen was injected into the internal nozzle using a double slit nozzle. The spinning hollow fiber was cooled with air and then wound on a winding roller. The injected air was maintained at a temperature of 40 ° C. and an injection speed of 2 m / sec, and injected in parallel with the direction in which the hollow yarns were radiated. The undrawn yarn was subjected to an annealing process for 24 hours at a temperature of 120 ° C. The undrawn yarn, which has undergone an annealing process, has undergone a cold drawing process of 50% of its initial length at a strain rate of 110% / second. After the addition of a hot stretching process of 600% of the length of the cold-drawn yarn at a strain rate of 5% / second in a heating chamber at 110 ℃ to achieve a total draw ratio of 950%, it was heat set at 115 ℃ 10 minutes.

The physical properties of the finally obtained hollow fiber membranes were measured, and the results are shown in Table 1, and the photographs of the outer surface are shown in FIG. 2A and the photographs of the inner surface in FIG. 2B, respectively. The pore sizes of the outer and inner surfaces are almost the same.

Comparative Example 2

The air used for cooling the spun yarn was maintained in the same manner as in Comparative Example 1 except that air was maintained at a temperature of 20 ° C. and a feed rate of 2 m / sec, and injected in a co-current manner. The results are shown in Table 1, and the photograph of the outer surface is shown in FIG. 3A and the photograph of the inner surface in FIG. 3B, respectively.

Under the condition of using the same air and only lowering the temperature, it showed a similar pattern to Comparative Example 1.

Example 1

Instead of air for cooling the spun yarn, the same procedure as in Comparative Example 1 was carried out except that the Freon liquid was sprayed in a cocurrent flow at a rate of 2 m / sec while maintaining an air temperature of 20 ° C. The physical properties of and the results are shown in Table 1, and the photograph of the outer surface is shown in Figure 4a and the photograph of the inner surface in Figure 4b, respectively.

As shown in FIGS. 4A and 4B, the internal pore size was almost unchanged and the external pore size was decreased, but the porosity increased and the air permeability and pure permeability remained unchanged.

Example 2

Instead of air for cooling the spun yarn, it was carried out in the same manner as in Comparative Example 1 except that acetone was sprayed in a cocurrent flow at a rate of 2 m / sec while maintaining an air temperature of 20 ° C., and finally obtained hollow fiber membrane properties Was measured and the results are shown in Table 1. In terms of pore size, the results were almost similar to those of Example 1, but the air permeability and the net permeability were slightly decreased compared to those using Freon due to the poor porosity of the outer surface.

Example 3

The cooling was performed in the same manner as in Comparative Example 1, except that methanol was sprayed in a cocurrent flow at a rate of 2 m / sec while maintaining an air temperature of 20 ° C. instead of air to cool the spun yarn. Physical properties were measured and the results are shown in Table 1. In terms of pore size, the results were almost similar to those of Example 1, but the porosity of the outer surface was also lowered, so that the air permeability and the net permeability were slightly decreased than those of Freon.

Comparative Example 3

Except for injecting air used for cooling the spun yarn at 40 ° C., 2 m / sec in countercurrent, the same procedure as in Comparative Example 1 was carried out, and the physical properties of the finally obtained hollow fiber membrane were measured. The results are shown in Table 1, and the photograph of the outer surface is shown in FIG. 5A and the photograph of the inner surface in FIG. 5B, respectively.

Although the pore structure shows asymmetry, the porosity of the outer surface was reduced, resulting in a decrease in air permeation and water permeation compared to the results of Example 1.

Comparative Example 4

Except for injecting air used for cooling the spun yarn at a temperature of 20 ℃, 2 m / sec in a countercurrent flow was carried out in the same manner as in Comparative Example 1 was measured by measuring the physical properties of the final hollow fiber membrane The results are shown in Table 1, and the photograph of the outer surface is shown in FIG. 6A and the photograph of the inner surface in FIG. 6B, respectively.

In addition, although the pore structure exhibits asymmetry, the porosity of the outer surface is reduced, resulting in a decrease in air permeation and water permeation compared to the results of Example 1.

Comparative Example 5

The cooling was carried out in the same manner as in Comparative Example 1 except for spraying the freon liquid at a constant temperature of 5 m / sec at 20 ° C. to cool the spun yarn, and measured the physical properties of the final hollow fiber membrane. The results are shown in Table 1, and the photograph of the outer surface is shown in FIG. 7A and the photograph of the inner surface in FIG. 7B, respectively.

The pores of the outer surface were hardly found within the range that can be observed by the electron microscope, and the air permeability and the pure water permeability tended to decrease significantly.

Properties Outer Diameter (㎛) Wall thickness (㎛) Air permeation amount (ℓ / ㎡hr0.5 bar) Pure permeation amount (ℓ / ㎡hrbar) Tensile Strength (g _f / fil.) Average external pore diameter (㎛, short axis / long axis) Average internal pore diameter (㎛, short axis / long axis) Particle cut-off (㎛) Comparative Example 1 600 110 185 × 10 ⁴ 14,000 1,000 0.75 / 3.8 0.8 / 3.5 > 0.6 Comparative Example 2 600 110 185 × 10 ⁴ 14,000 1,100 0.7 / 3.5 0.8 / 3.7 0.58 Example 1 610 115 185 × 10 ⁴ 14,000 1,300 0.4 / 1.5 0.8 / 4.2 0.37 Example 2 610 115 165 × 10 ⁴ 13,000 1,350 0.42 / 1.7 0.8 / 4.0 0.39 Example 3 610 115 150 × 10 ⁴ 12,500 1,350 0.45 / 1.8 0.8 / 4.0 0.39 Comparative Example 3 620 117 80 × 10 ⁴ 9,000 1,300 0.2 / 2.5 0.4 / 3.4 0.17 Comparative Example 4 620 117 75 × 10 ⁴ 8,500 1,300 0.1 / 1.5 0.4 / 3.4 0.13 Comparative Example 5 625 122 50 × 10 ² 50 1,500 - 0.4 / 3.4 <0.1

According to the present invention, the method of cooling the outer surface of the spun polyethylene hollow yarn using a low boiling point solvent such as liquid freon as a cooling medium, followed by annealing, cold drawing, hot drawing and heat setting has very high tensile strength and porosity. In addition to providing excellent asymmetric polyethylene hollow fiber membranes with different internal and external pore sizes, these asymmetric polyethylene hollow fiber membranes can be effectively applied to immersion type membrane systems with high vibration due to air bubbles and removal efficiency. It is also applicable to the field of water treatment where the durability of the membrane is required.

Claims (12)

A method of producing polyethylene hollow fiber membranes by spinning polyethylene through a spinneret having a double nozzle and cooling the spun polyethylene hollow fiber and then annealing, cold stretching, hot stretching and heat setting, in the cooling step, the spun polyethylene hollow Nitrogen gas is supplied to the inner surface of the yarn, and a solvent having a boiling point of 30 to 80 ° C is co-flowed on the outer surface of the spun polyethylene hollow yarn as a cooling medium to vary the crystallization rate of the outer and inner surfaces of the hollow yarn. , Method for producing asymmetric polyethylene hollow fiber membrane. The method of claim 1, Wherein the polyethylene has a melt index (MI) in the range of 0.1 to 5.5 g / 10 minutes. The method of claim 1, And the temperature of the nozzle during spinning is in the range of 170 ° C to 220 ° C. The method of claim 1, The draft ratio of the hollow fiber during spinning is in the range of 100 to 800. The method of claim 1, And a solvent selected from methanol, ethanol, acetone, methyl ethyl ketone, ethyl formate, carbon tetrachloride and freon as the cooling medium. The method of claim 1, Method characterized in that the cooling medium is supplied at a speed of 0.5 to 3 m / second The method of claim 1, Characterized in that the temperature of the nitrogen gas ranges from 170 ° C. to 220 ° C. and is supplied at a rate of 0.1 to 0.3 m / sec. The method of claim 1, Annealing is carried out in a hot air dryer at 80 ° C. to 130 ° C. for 6 to 24 hours. The method of claim 1, Cold drawing is carried out at a temperature ranging from room temperature to 40 ° C., cold drawing ratio in the range of 5 to 100%, deformation rate in the range of 50 to 200% / second. The method of claim 1, And wherein the hot drawing is carried out at a temperature in the range of 80 ° C. to 130 ° C., at a hot draw ratio of 300 to 1,000%, and a strain of 1 to 10% / second. The method of claim 1, Heat-setting is carried out for 0.5 to 30 minutes at a temperature in the range from 110 ℃ to 130 ℃. An asymmetric polyethylene hollow fiber membrane prepared according to the method of any one of claims 1 to 11.