KR101350866B1 - Method for preparing PVDF hollow fiber membranes based on thermally induced phase separation and stretching - Google Patents

Abstract

In the present invention, using a PVDF-based resin, to provide a PVDF hollow fiber membrane manufacturing method capable of producing an asymmetric hollow fiber membrane having a gradient of pore size. In addition, the present invention, to provide a PVDF hollow fiber membrane manufacturing method that can apply a relatively low temperature in the melt kneading step. PVDF hollow fiber membrane manufacturing method of the present invention, comprising: extruding a molten mixture comprising a PVDF-based resin, DEP (diethyl phthalate) and DBP (dibutyl phthalate) through a double nozzle to form a non-solidified hollow fiber; Rapidly cooling the unsolidified hollow fiber with a liquid refrigerant at about 0 to about 30 ° C. to obtain solidified hollow fiber; And extracting and removing DEP and DBP from the solidified hollow fiber.

Description

Method for preparing PVDF hollow fiber membranes based on thermally induced phase separation and stretching}

The present invention relates to a hollow fiber membrane manufacturing method, and more particularly to a method of manufacturing a polyvinylidene fluoride (PVDF) -based hollow fiber membrane based on thermally induced phase separation (TIPS) and stretching (stretching).

The hollow fiber membrane is a porous separator in the form of hollow fiber. As a material of such a hollow fiber membrane, PVDF (polyvinylidene fluoride) resin is attracting attention. Polyvinylidene fluoride (PVDF) resins not only have excellent resistance to physical cleaning and chemical cleaning but also have excellent mechanical properties.

As a method for producing a porous separator, a phase separation method, a stretching method, a track etching method, a sintering method, and the like are known. Phase separation can be further classified into non-solvent induced phase separation (NIPS) and thermally induced phase separation (TIPS). NIPS is a method of preparing a separator by dissolving a polymer in a solvent and then substituting the solvent with a non-solvent, and it is difficult to accurately control the three-component system of the polymer-solvent-non-solvent, forming macropores, generating pinholes, and low tensile strength. The disadvantages arise. TIPS is a method of manufacturing a separator by heating and dissolving the dispersed phase of the polymer and the diluent, solidifying by cooling, and extracting the diluent. Since the two-component system of the polymer and the diluent is involved, there are fewer control variables than the NIPS to control the structure of the separator. This is easy.

An example of a PVDF hollow fiber membrane manufacturing method based on TIPS is disclosed in Korean Patent Laid-Open Publication No. 10-2003-0001474. Korean Patent Laid-Open Publication No. 10-2003-0001474 discloses a mixture containing polyvinylidene fluoride and an organic liquid, or a mixture containing polyvinylidene fluoride, an organic liquid and an inorganic fine powder, followed by extrusion Forming a fiber, extracting an organic liquid or an organic liquid and an inorganic fine powder from the hollow fiber, stretching the hollow fiber before the end of the extraction or the hollow fiber after the end of the extraction, and continuing shrinkage. A method for producing a hollow fiber membrane is disclosed.

However, the PVDF hollow fiber membrane thus prepared has the form of a symmetric hollow fiber membrane having the same internal pore size and external pore size. In addition, the inconvenience of extracting inorganic fine powder such as hydrophobic silica occurs. In addition, due to the influence of the high temperature in the melt kneading step, there is a problem that the color of the finally produced hollow fiber membrane is browned. Therefore, an additional post treatment process for decolorization is needed.

In the present invention, to provide a method for producing a PVDF hollow fiber membrane based on TIPS, which can produce an asymmetric PVDF hollow fiber membrane having a gradient of pore size. In addition, the present invention, to provide a PVDF hollow fiber membrane manufacturing method that can apply a relatively low temperature in the melt kneading step.

PVDF hollow fiber membrane manufacturing method of the present invention,

Extruding a molten mixture including PVDF-based resin, DEP (diethyl phthalate) and DBP (dibutyl phthalate) through a double nozzle to form uncoagulated hollow fiber;

Rapidly cooling the unsolidified hollow fiber with a liquid refrigerant at about 0 to about 30 ° C. to obtain solidified hollow fiber; And

Extracting and removing DEP and DBP from the solidified hollow fiber;

.

Another embodiment of the PVDF hollow fiber membrane manufacturing method of the present invention further comprises the step of stretching the solidified hollow fiber before or after the step of extracting and removing DEP and DBP from the solidified hollow fiber.

In the PVDF hollow fiber membrane production method of the present invention, by rapidly cooling uncoagulated hollow fiber with a low temperature liquid refrigerant, the difference in the solidification rate between the outside and inside of the non-solidified hollow fiber can be increased. The outer surface of the unsolidified hollow yarn in direct contact with the low temperature liquid refrigerant is rapidly cooled. The interior of the unsolidified hollow yarn, which is not in direct contact with the low temperature liquid refrigerant, is cooled at a relatively low speed.

In the course of cooling the non-solidified hollow yarn, the PVDF polymer phase and the DEP-DBP phase are separated. The slower the cooling, the higher the growth rate of the spheres made of PVDF polymer. On the outer surface of the non-solidified hollow fiber rapidly cooled, growth of PVDF polymer spherical structure is suppressed, so that a dense structure having a relatively small pore size is formed compared to the interior of the unsolidified hollow fiber. Inside the slow cooled unsolidified hollow yarn, relatively large pores are formed due to sufficient growth of the PVDF polymer spheres. By this action, since the pore size of the inside and outside of the non-solidified hollow yarn is changed, it becomes possible to manufacture an asymmetric hollow fiber membrane.

Moreover, in the manufacturing method of this invention, PVDF hollow fiber membrane can be manufactured, without using inorganic fine powder like hydrophobic silica.

In addition, in the production method of the present invention, a relatively low temperature can be applied in the melt kneading step. Accordingly, the decolorization phenomenon of the manufactured PVDF hollow fiber membrane does not occur, thereby eliminating the need for an additional post treatment process for decolorization.

1 is an electron micrograph of a cross section of the hollow fiber membrane of Example 1. FIG.
FIG. 2 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 1. FIG.
3 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 1. FIG.
4 is an electron micrograph of a cross section of the hollow fiber membrane of Example 1-2.
5 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 1-2.
6 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 1-2.
7 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 8. FIG.
8 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 8. FIG.
9 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 8-1.
10 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 8-1.
11 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 1. FIG.
12 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 1. FIG.
13 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 2. FIG.
14 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 2. FIG.
15 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 3. FIG.
16 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 3. FIG.
17 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 4. FIG.
18 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 4. FIG.
19 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 5. FIG.
20 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 5. FIG.
21 is an electron micrograph of the inner surface of the hollow fiber membrane prepared by applying a water bath temperature of 8 ℃.
FIG. 22 is an electron micrograph of the outer surface of a hollow fiber membrane prepared by applying a bath temperature of 8 ° C. FIG.
FIG. 23 is an electron micrograph of the inner surface of a hollow fiber membrane prepared by applying a water bath temperature of 25 ° C. FIG.
24 is an electron micrograph of the outer surface of the hollow fiber membrane prepared by applying a water bath temperature of 25 ℃.
25 is an electron micrograph of the inner surface of a hollow fiber membrane prepared by applying a water bath temperature of 50 ℃.
FIG. 26 is an electron micrograph of an outer surface of a hollow fiber membrane prepared by applying a water bath temperature of 50 ° C. FIG.
27 is an electron micrograph of the inner surface of the hollow fiber membrane prepared by applying a water bath temperature of 80 ℃.
28 is an electron micrograph of the outer surface of the hollow fiber membrane prepared by applying a water bath temperature of 80 ℃.

Hereinafter, the PVDF hollow fiber membrane manufacturing method of this invention is demonstrated in more detail. PVDF hollow fiber membrane manufacturing method of the present invention, comprising: extruding a molten mixture comprising a PVDF-based resin, DEP (diethyl phthalate) and DBP (dibutyl phthalate) through a double nozzle to form a non-solidified hollow fiber; Rapidly cooling the unsolidified hollow fiber with a liquid refrigerant at about 0 to about 30 ° C. to obtain solidified hollow fiber; And extracting and removing DEP and DBP from the solidified hollow fiber.

As the PVDF resin, for example, vinylidene fluoride homopolymer, vinylidene fluoride copolymer, or a mixture thereof can be used. As a vinylidene fluoride copolymer, the copolymer of vinylidene fluoride and 1 or more types of monomers chosen from the group which consists of ethylene tetrafluoride, hexafluoro propylene, ethylene trifluoride chloride, and ethylene, for example can be used. The weight average molecular weight of the PVDF-based resin used may be about 100,000 to about 1,000,000.

DEP (diethyl phthalate) and DBP (dibutyl phthalate) are extracted and removed from the hollow fiber, thereby acting to leave pores in the hollow fiber. Preferably, the mixed weight ratio of DEP to DBP is about 2: 8 to about 8: 2. If the mixing ratio is outside this range, there is a very high possibility of a similar result to using DEP or using DEP alone.

As a diluent showing compatibility with the PVDF polymer, dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP) and the like are known. However, according to the present invention, in the case of using DMP or DEP alone, the growth of the reticulated PVDF spherical structure during the low temperature rapid cooling process is large, and the tensile strength of the manufactured hollow fiber membrane may be very weak. In the case of using DBP alone, the size of pores formed in the hollow fiber membrane manufactured by the low temperature rapid cooling process may be excessively fine, and even in the case of using a combination of DEP and DMP, The growth of reticulated PVDF spherical structure is large, and the tensile strength of the manufactured hollow fiber membrane may be very weak, and even when the combination of DBP and DMP is used, the growth of reticulated PVDF spherical structure is large during low temperature rapid cooling. It has been found that the tensile strength of the manufactured hollow fiber membrane becomes very weak. In the present invention, by using a combination of DEP and DBP as a diluent, it was possible to effectively produce an asymmetric PVDF hollow fiber membrane by rapid cooling at low temperature. In addition, asymmetric PVDF hollow fiber membranes prepared using a combination of DEP and DBP as diluent could be stretched very effectively.

The content of PVDF-based resin in the mixture comprising the PVDF-based resin, DEP and DBP is preferably from about 20% to about 45% by weight. If the content of the PVDF resin is too small, the tensile strength of the manufactured hollow fiber membrane may be excessively weak. If the content of the PVDF resin is too large, the porosity of the manufactured hollow fiber membrane may be excessively lowered.

Preferably, the temperature at which the PVDF resin, the DEP, and the DBP are melt mixed is about 140 ° C to about 200 ° C. DEP and DBP exhibit good compatibility with PVDF even at temperatures below the melting point (about 174 ° C.) of PVDF. Thus, even at temperatures up to about 200 ° C., uniform mixing of PVDF and DEP and DBP can be achieved. As such, since the melt mixing is performed at a relatively low temperature, the problem that the color of the finally produced hollow fiber membrane is browned does not occur.

Melt mixing of the mixture comprising PVDF-based resins, DEP and DBP can be accomplished, for example, by V-blenders, ribbon blenders, Henschel mixers, Benbury mixers, proshare mixers, and the like. have. Alternatively, melt mixing of the mixture comprising PVDF-based resin, DEP and DBP may be done directly in the melt mixing extrusion apparatus of the twin screw extruder used for hollow fiber spinning.

In the step of extruding the molten mixture comprising the PVDF resin, DEP and DBP through the double nozzle, the temperature of the molten mixture is preferably about 140 ℃ to about 200 ℃.

By melt extruding the PVDF-based resin, DEP and DBP, through the double nozzle into the air gap at the bottom of the double nozzle, unsolidified hollow fiber can be formed. Inside the double nozzle, nitrogen or air is supplied as the hollow forming agent. Air gap means the space between the liquid refrigerant tank from the outlet of the double nozzle. The distance through which the non-solidified hollow yarn passes through the air gap may be about 50 mm to about 500 mm.

The non-solidified hollow yarn thus obtained passes through an air gap and is then introduced into a low temperature liquid refrigerant tank and rapidly cooled. As the liquid refrigerant, for example, water may be used. If the temperature of the liquid refrigerant is too high, it is difficult to achieve rapid cooling of the non-solidified hollow yarn. If the temperature of the liquid refrigerant is too low, the inside of the non-solidified hollow yarn may also be rapidly cooled. The temperature of the liquid refrigerant is preferably about 0 to about 30 ° C. More preferably, the temperature of the liquid refrigerant may be about 5 to about 25 ° C. The time for the uncoagulated hollow fiber to pass through the liquid refrigerant is preferably about 25 seconds to less than 120 seconds. In less than about 25 seconds, the cooling to the hollow form may be incomplete due to insufficient cooling, and in the case of more than about 120 seconds, the effect of cooling on the structure is minimal and there is a fear of over-installation.

By rapidly cooling the unsolidified hollow fiber with a low temperature liquid refrigerant, the difference in the solidification rate between the outside and the inside of the unsolidified hollow fiber can be increased. The outer surface of the unsolidified hollow yarn in direct contact with the low temperature liquid refrigerant is rapidly cooled. The interior of the unsolidified hollow yarn, which is not in direct contact with the low temperature liquid refrigerant, is cooled at a relatively low speed.

In the course of cooling the non-solidified hollow yarn, the PVDF polymer phase and the DEP-DBP phase are separated. The slower the cooling, the higher the growth rate of the spheres made of PVDF polymer. On the outer surface of the non-solidified hollow fiber rapidly cooled, growth of PVDF polymer spherical structure is suppressed, so that a dense structure having a relatively small pore size is formed compared to the interior of the unsolidified hollow fiber. Inside the slow cooled unsolidified hollow yarn, relatively large pores are formed due to sufficient growth of the PVDF polymer spheres. By this action, since the pore size of the inside and outside of the non-solidified hollow yarn is changed, it becomes possible to manufacture an asymmetric hollow fiber membrane. The large pores inside reduce the passage resistance of the filtered water from the outside, which is advantageous for the development of high water permeability, and the small outside pores are advantageous for the expression of high rejection rate characteristics.

DEP and DBP are extracted and removed from the solidified hollow fiber. As an extraction solvent used for extraction of DEP and DBP, ethanol, methanol, acetone, methylene chloride, etc. can be used, for example. By extracting DEP and DBP from the solidified hollow fiber, the solidified hollow fiber becomes a hollow fiber membrane rich in pores.

In another embodiment of the present invention, before the extraction step or after the extraction step, it may further comprise the step of stretching the solidified drawn yarn. By extending | stretching, the physical strength of a hollow fiber membrane can be improved, and also porosity can be increased. That is, by stretching, it is possible to generate microcracks of the PVDF polymer matrix or to increase the pore size. The stretching temperature is preferably about -10 ° C to about 30 ° C. If the stretching temperature is too low, stretching may be difficult. If the stretching temperature is too high, it may cause a change in pore shape, and also may cause a decrease in physical properties such as tensile strength due to a change in crystallinity of the PVDF polymer matrix. Elongation is preferably about 100% to about 200%.

<Examples>

Example  One

PVDF 30 wt%, DEP 35 wt% and DBP 35 wt% having a weight average molecular weight of 573,000 were melt mixed at 200 ° C. for 6 hours using a V-mixer. The molten mixture at 200 DEG C thus obtained was introduced into a double toroidal nozzle by a metering pump, and nitrogen was supplied to the hollow forming agent. The uncoagulated hollow yarns radiated from the double nozzles were passed through an air gap of 100 mm, and then solidified in a 10 ° C. water bath and then wound up. At this time, the winding speed was 8 m / min, the time for the hollow fiber to pass through the tank was 25 seconds. The solidified hollow fiber thus obtained was extracted with ethanol for 3 hours and then dried to obtain a final hollow fiber membrane. 1 is an electron micrograph of a cross section of the hollow fiber membrane of Example 1. FIG. FIG. 2 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 1. FIG. 3 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 1. FIG. 2 and 3, the pore size of the outer surface of the hollow fiber membrane of Example 1 is smaller than the pore size of the inner surface. That is, the hollow fiber membrane of Example 1 is asymmetrical.

Example  1-1

The solidified hollow fiber wound in Example 1 was extracted at the same conditions as in Example 1 after stretching 100% on a roller running at constant speed at 25 ° C. at an introduction speed of 8 m / min and an outlet speed of 16 m / min. After drying, a final hollow fiber membrane was obtained.

Example  1-2

The solidified hollow fiber wound in Example 1 was stretched 200% at 25 ° C., followed by extraction and drying under the same conditions as in Example 1 to obtain a final hollow fiber membrane. 4 is an electron micrograph of a cross section of the hollow fiber membrane of Example 1-2. 5 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 1-2. 6 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 1-2. 5 and 6, the pore size of the outer surface of the hollow fiber membrane of Example 6 is smaller than the pore size of the inner surface. That is, the hollow fiber membrane of Example 6 is asymmetrical. 5 and 6 show that microfibrils are formed between PVDF polymer spheres by stretching.

Example  2

PVDF 30wt%, DEP 21wt% and DBP 49wt% having a weight average molecular weight of 573,000 were mixed at 200 ° C. for 6 hours to obtain a hollow fiber membrane in the same manner as in Example 1.

Example  2-1

The solidified hollow fiber wound in Example 2 was stretched to 100% at 25 ° C. and extracted and dried under the same conditions as in Example 1 to obtain a final hollow fiber membrane.

Example  2-2

The solidified hollow fiber wound in Example 2 was stretched to 200% at 25 ° C. and extracted and dried under the same conditions as in Example 1 to obtain a final hollow fiber membrane.

Example  3

A hollow fiber membrane was manufactured under the same film forming conditions as in Example 1 except that PVDF 30wt% having a weight average molecular weight of 687,000 was used.

Example  3-1

The solidified hollow fiber wound in Example 3 was stretched to 100% at 25 ° C and extracted and dried under the same conditions as in Example 1 to obtain a final hollow fiber membrane.

Example  3-2

The solidified hollow fiber wound in Example 3 was stretched to 200% at 25 ° C. and extracted and dried under the same conditions as in Example 1 to obtain a final hollow fiber membrane.

Example  4

A hollow fiber membrane was manufactured under the same film forming conditions as in Example 1 except that the air gap length condition was changed to 200 mm.

Example  5

A hollow fiber membrane was manufactured under the same film forming conditions as in Example 1 except that the mixing temperature and the spinning temperature of the molten mixture were changed to 180 ° C.

Example  6

A hollow fiber membrane was manufactured under the same film forming conditions as in Example 1 except that the mixing temperature and the spinning temperature of the molten mixture were changed to 160 ° C.

Example  7

A hollow fiber membrane was manufactured under the same film forming conditions as in Example 1 except that the mixing temperature and the spinning temperature of the molten mixture were changed to 140 ° C.

Example  8

A hollow fiber membrane was prepared under the same film forming conditions as in Example 1 except that PVDF 40wt%, DEP 30wt%, and DBP 30wt% having a weight average molecular weight of 573,000 were used. 1 is an electron micrograph of a cross section of the hollow fiber membrane of Example 1. FIG. 7 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 8. FIG. 8 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 8. FIG. As shown in FIG. 7 and FIG. 8, the outer surface of the hollow fiber membrane of Example 8 shows a dense structure, and the inner surface shows porosity. That is, the hollow fiber membrane of Example 8 is asymmetrical. In the hollow fiber membrane of Example 8, due to the high content of PVDF and rapid cooling at low temperature, the uncoagulated hollow fiber undergoes a liquid-liquid phase separation process very shortly, resulting in a dense structure of the outer surface as shown in FIG. 8. Showed. In addition, it was confirmed that the internal matrix (that is, the structure or skeleton composed only of PVDF) was thicker than the hollow fiber membrane of Example 1. Accordingly, the hollow fiber membrane of Example 8 showed an increased tensile strength compared to the hollow fiber membrane of Example 1. On the other hand, the hollow fiber membrane of Example 8 had a dense structure of the outer surface, and exhibited a reduced permeate flux compared to the hollow fiber membrane of Example 1.

Example  8-1

The solidified hollow fiber wound in Example 8 was stretched at 100C at 25 ° C., and then extracted and dried under the same conditions as in Example 1 to obtain a final hollow fiber membrane. 9 is an electron micrograph of the inner surface of the hollow fiber membrane of Example 8-1. 10 is an electron micrograph of the outer surface of the hollow fiber membrane of Example 8-1. As shown in FIG. 9, compared with Example 8, the pore size of the inner surface of the hollow fiber membrane of Example 8-1 was increased. However, as shown in FIG. 10, despite being stretched, the outer surface of the hollow fiber membrane of Example 8-1 still showed a dense structure. The permeate flux of the hollow fiber membrane of Example 8-1 was increased compared to the hollow fiber membrane of Example 8 due to the increase in the internal porosity and the thinning of the outer dense layer. The hollow fiber membranes of Example 8 and Example 8-1 can be used, for example, as ultrafiltration membranes.

Comparative Example  One

A hollow fiber membrane was prepared under the same film forming conditions as in Example 1, except that DEP 35wt% and DMP 35wt% were used instead of DEP 35wt% and DBP 35wt%. 11 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 1. FIG. 12 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 1. FIG. As shown in FIG. 11, excessive growth of PVDF spheres occurred in the inner surface layer of the hollow fiber membrane of Comparative Example 1, and accordingly, the tensile strength of the hollow fiber membrane of Comparative Example 1 was weak.

Comparative Example  2

A hollow fiber membrane was prepared under the same film forming conditions as in Example 1, except that DBP 35wt% and DMP 35wt% were used instead of DEP 35wt% and DBP 35wt%. 13 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 2. FIG. 14 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 2. FIG. As shown in FIG. 13, excessive growth of PVDF spheres occurred in the inner surface layer of the hollow fiber membrane of Comparative Example 2, and accordingly, the tensile strength of the hollow fiber membrane of Comparative Example 2 was weak.

Comparative Example  3

A hollow fiber membrane was prepared under the same film forming conditions as in Example 1, except that DMP 70 wt% was used instead of 35 wt% of DEP and 35 wt% of DBP. 15 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 3. FIG. 16 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 3. FIG. As shown in FIG. 15, excessive growth of PVDF spheres occurred in the inner surface layer of the hollow fiber membrane of Comparative Example 3, and accordingly, the tensile strength of the hollow fiber membrane of Comparative Example 3 was weak.

Comparative Example  4

A hollow fiber membrane was prepared under the same film forming conditions as in Example 1 except that DEP 70wt% was used instead of DEP 35wt% and DBP 35wt%. 17 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 4. FIG. 18 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 4. FIG. As shown in FIG. 17, excessive growth of PVDF spheres occurred in the inner surface layer of the hollow fiber membrane of Comparative Example 4, and accordingly, the tensile strength of the hollow fiber membrane of Comparative Example 4 was weak.

Comparative Example  5

A hollow fiber membrane was prepared under the same film forming conditions as Example 1 except that DBP 70wt% was used instead of DEP 35wt% and DBP 35wt%. 19 is an electron micrograph of the inner surface of the hollow fiber membrane of Comparative Example 5. FIG. 20 is an electron micrograph of the outer surface of the hollow fiber membrane of Comparative Example 5. FIG. As shown in Fig. 19 and Fig. 20, on the inner surface and the outer surface of the hollow fiber membrane of Comparative Example 5 was not excessive growth of PVDF spheres, but the formation of pores is very weak, the permeate flux of the hollow fiber membrane of Comparative Example 5 Very low.

Comparative Example  6

A hollow fiber membrane was prepared under the same film forming conditions as in Example 1 except that DEP 70wt% was used instead of DEP 35wt% and DBP 35wt%, and the temperature of the water bath was increased to 8 ° C, 25 ° C, 50 ° C, and 80 ° C. In other cases, the change of the inner surface and the outer surface of the hollow fiber membrane according to the temperature of the tank was observed by electron micrograph. 21 is an electron micrograph of the inner surface of the hollow fiber membrane prepared by applying a water bath temperature of 8 ℃. FIG. 22 is an electron micrograph of the outer surface of a hollow fiber membrane prepared by applying a bath temperature of 8 ° C. FIG. FIG. 23 is an electron micrograph of the inner surface of a hollow fiber membrane prepared by applying a water bath temperature of 25 ° C. FIG. 24 is an electron micrograph of the outer surface of the hollow fiber membrane prepared by applying a water bath temperature of 25 ℃. 25 is an electron micrograph of the inner surface of a hollow fiber membrane prepared by applying a water bath temperature of 50 ℃. FIG. 26 is an electron micrograph of an outer surface of a hollow fiber membrane prepared by applying a water bath temperature of 50 ° C. FIG. 27 is an electron micrograph of the inner surface of the hollow fiber membrane prepared by applying a water bath temperature of 80 ℃. 28 is an electron micrograph of the outer surface of the hollow fiber membrane prepared by applying a water bath temperature of 80 ℃. As shown in Figures 25 to 28, when the cooling temperature of the non-solidified hollow yarn is 50 ℃ and 80 ℃, the difference in the spherical growth degree of the inner surface and the outer surface of the hollow fiber membrane was very slight. However, as shown in Figs. 21 to 24, when the cooling temperatures of the non-solidified hollow yarns were 8 ° C and 25 ° C, the difference in spherical growth between the inner surface and the outer surface of the hollow fiber membrane was very remarkable. From this, it can be seen that the asymmetric hollow fiber membrane can be obtained by low temperature rapid cooling of the non-solidified hollow yarn.

Pure permeation Flux  Measure

The prepared hollow fiber membrane was made into a module having an effective membrane length of 100 mm. The number of strands of the hollow fiber membranes used in the module was 10, both ends of the hollow fiber membranes were sealed with epoxy resin, and the hollow portion of the hollow fiber membranes was opened at the upper end of the module. The module was immersed in 100% ethanol for 10 minutes and then supplied with ultrapure water at 25 ° C. at a pressure of 100 kPa to measure the permeate flow rate per unit time per unit area.

Outer diameter / Inner  Measure

The prepared hollow fiber membrane was broken immediately after freezing with liquid nitrogen for 5 seconds, and then the outer diameter / inner diameter of the cross section of the hollow fiber membrane was measured by an electron scanning microscope.

The tensile strength  And Elongation at break  Measure

Tensile strength and elongation at break of the prepared hollow fiber membrane was measured by an Instron Universal Testing Machine (UTM) (Model No .: 5844) under a tensile speed of 100 mm / min. The measurement was performed indoors at 25 ° C. and 30% relative humidity.

Average pore size measurement

It was measured by half-dry method (ASTM F-316-03) using a "capillary flow porometer" (Model No .: CFP-1200AE) from Porous Materials, Inc. (PMI). The liquid used was Galwick (surface tension of 15.9 dynes / cm), measuring temperature of 25 ℃, working pressure of 15 psi minimum and 100 psi maximum.

The physical properties of the hollow fiber membranes obtained in Examples and Comparative Examples are summarized in Table 1.

Pure Permeate Flux
(ℓ / ㎡hr, at 100kpa) Outer diameter / inner diameter
(탆) The tensile strength
(gf / fil.) Elongation at break
(%) Average pore size
(탆) Example 1 1800 1380/790 670 250 0.1 Example 1-1 7000 1290/680 860 100 0.2 Examples 1-2 9000 1130/490 950 30 0.42 Example 2 1200 1390/720 800 280 0.1 Example 2-1 6500 1310/690 1000 120 0.17 Example 2-2 8500 1050/450 1100 30 0.35 Example 3 1000 1380/680 900 260 0.1 Example 3-1 3800 1280/630 1100 100 0.15 Example 3-2 5000 1000/450 1300 20 0.42 Example 4 2500 1380/790 570 200 0.2 Example 5 1200 1380/790 750 300 - Example 6 800 1380/790 850 320 - Example 7 600 1380/790 950 350 - Example 8 270 1380/720 1000 350 0.05 Example 8-1 1800 1290/630 1400 200 0.08 Comparative Example 1 1200 1250/630 200 5 - Comparative Example 2 1000 1280/650 350 8 -

Claims (2)

Extruding a molten mixture including PVDF-based resin, DEP (diethyl phthalate) and DBP (dibutyl phthalate) through a double nozzle to form uncoagulated hollow fiber;
Rapidly cooling the unsolidified hollow fiber using a liquid refrigerant at 0 to 25 ° C. to obtain solidified hollow fiber; And
Extracting and removing DEP and DBP from the solidified hollow fiber;
PVDF hollow fiber membrane manufacturing method comprising a. The method of claim 1, further comprising stretching the solidified hollow fiber before or after the step of extracting and removing DEP and DBP from the solidified hollow fiber.

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