KR101777568B1 - Preparing method of porous pvdf nanofaiber and porous pvdf nanofaiber prepared by the method - Google Patents
Preparing method of porous pvdf nanofaiber and porous pvdf nanofaiber prepared by the method Download PDFInfo
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- KR101777568B1 KR101777568B1 KR1020150138607A KR20150138607A KR101777568B1 KR 101777568 B1 KR101777568 B1 KR 101777568B1 KR 1020150138607 A KR1020150138607 A KR 1020150138607A KR 20150138607 A KR20150138607 A KR 20150138607A KR 101777568 B1 KR101777568 B1 KR 101777568B1
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/0007—Electro-spinning
- D01D5/0015—Electro-spinning characterised by the initial state of the material
- D01D5/003—Electro-spinning characterised by the initial state of the material the material being a polymer solution or dispersion
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/14—Other self-supporting filtering material ; Other filtering material
- B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
- B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
- B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/30—Polyalkenyl halides
- B01D71/32—Polyalkenyl halides containing fluorine atoms
- B01D71/34—Polyvinylidene fluoride
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/39—Electrospinning
Abstract
The present invention relates to a method for producing porous PVDF nanofibers, comprising mixing a PVDF and PEO together in a solvent to form a raw material; A molding step of molding the raw material into a nanofiber shape; And a pore forming step of selectively removing only PEO from the formed nanofibers to form a porous structure.
The manufacturing method of the present invention has the effect of manufacturing PVDF nanofibers having a porous structure by removing PEO after forming into a nanofiber form.
Further, the manufacturing method of the present invention has the effect of forming more pores by the vapor pressure difference and the liquid-liquid phase separation by mixing water together with the solvent dissolving the PVDF.
Furthermore, since the porous PVDF nanofiber according to the present invention has many pores and has a large specific surface area and a large contact angle with water, the porous PVDF nanofiber exhibits a very suitable property as a pre-filter used in the previous stage of the filter for removing oil- It is possible to increase the lifetime of the expensive filter.
Description
The present invention relates to a PVDF nanofiber and a manufacturing method thereof, and more particularly, to a PVDF nanofiber exhibiting a porous property and a manufacturing method thereof.
In recent years, separation materials that remove contaminated materials have been attracting attention as environmental problems have become more prominent. Demand is increasing due to diversification of active research and use fields for high performance of separation material functions and applications.
In particular, there is a high need for the separation and efficient treatment of water and oil mixtures in the oil and refining industries, food processing and metal finishing. However, it is very difficult to separate micrometer sized oil in the wastewater, and for the last decades technologies such as ultrasonic treatment and biological treatment have been developed.
Polymeric filtration membranes are considered to be a state-of-the-art technique for separating water and oil mixtures. However, because of the high cost of production due to plasma surface treatment and the like, there is a continuing need to increase the lifetime of membranes.
It is an object of the present invention to provide a method of manufacturing a porous nanofiber suitable for a pre-filter used in a previous stage of a filter for removing oil from oil-water oil.
In order to accomplish the above object, the present invention provides a method of preparing porous PVDF nanofibers, comprising: mixing PVDF and PEO together in a solvent to form a raw material; A molding step of molding the raw material into a nanofiber shape; And a pore forming step of selectively removing only PEO from the formed nanofibers to form a porous structure.
In order to produce a nanofiber having a porous surface, the present invention forms pores by selectively removing only PEO after forming into nanofibers.
At this time, it is preferable that the ratio of PEO in the raw material ranges from 3 wt% to 15 wt%. If the content of PEO is less than this range, pore formation due to removal is insufficient, and if it is contained in a large amount, PEO is not completely removed, and the physical properties of the nanofibers from which PEO is removed are deteriorated.
As the solvent for PVDF, DMF, DMAc (N, N-dimethyl acetamide), NMP (N-methyl pyrrolidone) and the like can be used.
When a solvent for dissolving PVDF as a solvent is mixed with water, more pores are formed by the vapor pressure difference and the liquid-liquid phase separation. At this time, the proportion of water is preferably 6 wt% or less, preferably 5 to 6 wt% Range.
When the forming step is carried out by an electrospinning process, it is easy to form the nanofiber into the nanofiber. However, the present invention is not limited thereto, and other methods can be applied without impairing the content of the present invention.
The pore forming step of removing PEO to form pores may be performed by dissolving PEO in water, and it is preferable that the dissolving step is performed at a temperature of water ranging from 50 to 70 ° C.
The porous PVDF nanofiber for prefilter according to the present invention is produced by one of the above-described methods and has a specific surface area of 10 to 20 m 2 / g.
The method of manufacturing the pre-filter used in the previous stage of the filter for removing oil according to the present invention includes a step of making a nanofiber mat using the porous PVDF nanofibers produced by one of the above methods. The nanofiber can be made into a mat shape and applied to a pre-filter for degreasing.
At this time, when the electrospun nanofiber is formed into a nanofiber mat shape, the electrospinning process and the nanofiber mat forming process can be simultaneously performed to produce the nanofiber mat.
And fixing the nanofiber mat to the support.
The pre-filter for removing oil according to the present invention is characterized by being manufactured by the above-described method.
The manufacturing method of the present invention configured as described above has the effect of manufacturing PVDF nanofibers having a porous structure by removing PEO after forming the nanofibers.
Further, the manufacturing method of the present invention has the effect of forming more pores by the vapor pressure difference and the liquid-liquid phase separation by mixing water together with the solvent dissolving the PVDF.
Furthermore, since the porous PVDF nanofiber according to the present invention has many pores and has a large specific surface area and a large contact angle with water, the porous PVDF nanofiber exhibits a very suitable property as a pre-filter used in the previous stage of the filter for removing oil- It is possible to increase the lifetime of the expensive filter.
FIGS. 1 to 4 are SEM photographs for measuring the surface shape of the nanofiber mat according to the embodiment of the present invention and the comparative example according to the content of PEO.
5 to 9 are SEM photographs for measuring the surface shape of the nanofiber mat according to the embodiment of the present invention and the comparative example according to the ratio of water.
10 is a graph showing the size distribution of pores with respect to the average diameter of the nanofibers of Examples and Comparative Examples of the present invention.
11 is a graph showing the results of measurement of elastic modulus of a nanofiber mat produced according to Examples and Comparative Examples of the present invention.
FIG. 12 shows the tensile strengths of nanofiber mat prepared according to Examples and Comparative Examples of the present invention.
13 shows the results of measurement of the elongation at break of the nanofiber mat prepared according to Examples and Comparative Examples of the present invention.
Fig. 14 shows FT-IR spectrum analysis results of the nanofibers of Examples and Comparative Examples of the present invention.
15 is an AFM scan image for NF.
16 and 17 are AFM scan images for the NFP.
Fig. 18 shows the results of filtration experiments on nanofiber mat according to Examples and Comparative Examples of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, embodiments of the present invention will be described in detail.
First, the raw materials are prepared and mixed to prepare the raw materials.
Poly (vinylidene fluoride) (PVDF), the main material, was dried in an oven for 4 hours. Polyethylene oxide (PEO) was commercially available with a molecular weight of 900,000. N, N-dimethylformamide (DMF) was used without further purification.
PVDF and PEO were dissolved in a mixed solvent of water and DMF, and the content of PVDF was fixed to 12.5 wt%. Various kinds of raw materials were prepared by mixing PEO and water at various weight ratios as shown in the following table.
NFP1 to NFP3 are cases in which the weight ratio of PEO is changed while maintaining the same amount of water, and NFPH1 to NFPH5 are those in which the weight ratio of PEO is kept the same while the ratio of water is adjusted. NF is a case where pure PVDF is dissolved in DMF without using PEO and water for comparison with the present invention.
The thus-mixed solution was stirred at 60 DEG C for 12 hours to prepare a homogeneous mixed solution.
Next, homogeneous mixed solution was electrospun and formed into fiber shape.
The spinnerette used for electrospinning had an inner diameter of 0.25 mm at the tip and the electrospinning process was carried out at a flow rate of 1.0 ml / h using a voltage of 15 kV and the gap between the spinnerette and the aluminum foil as collector was 15 cm. The temperature at which the electrospinning process was performed was in the range of room temperature to 23 ° C and the relative humidity was less than 55%, which is a condition selected from various experimental results.
In the process of collecting the electrospun nanofibers, the nanofiber mat was naturally formed as a nanofiber mat.
Only the PEO was removed from the electrospun nanofiber mat to form pores.
Specifically, the PEO contained in the nanofiber mat was selectively dissolved and removed by using water at 60 ° C for 1 hour to form pores in the place where the PEO was located.
The nanofiber mat with pores was washed again with distilled water and acetone, and then dried in a vacuum oven at 80 DEG C for 12 hours.
The physical properties of the nanofiber mat prepared in the above process were measured and filtration experiments were performed.
FIGS. 1 to 4 are SEM photographs for measuring the surface shape of the nanofiber mat according to the embodiment of the present invention and the comparative example according to the content of PEO.
FIG. 1 is a SEM photograph of a comparative example (NF) in which the weight ratio of PEO is 0%, and FIGS. 2 to 4 show SEM photographs of NFP1 with PEO weight ratio of 5 wt%, NFP2 with 7 wt% and NFP3 with 10 wt% SEM picture. On the right is a 20,000 magnification image of the surface. The photo on the right photo shows the contact angle of the water droplet to confirm the hydrophobicity of each nanofiber surface.
As shown in the figure, NF without PEO had a smooth surface and a contact angle of water drop of 146.3 지만, but it was confirmed that many pores were formed on the surface in PEO-added NFP1 to NFP3, and the contact angle of the water droplet was larger than NF .
In the case of NFP1 and NFP2, the contact angle was increased with the addition of PEO, but the contact angle of NFP3 with PEO was more than NFP1 and NFP2. This shows that the pore size becomes too large, which leads to a decrease in the hydrophobic property. From this, it can be seen that the PEO content of the raw material is not unconditionally good.
5 to 9 are SEM photographs for measuring the surface shape of the nanofiber mat according to the embodiment of the present invention and the comparative example according to the ratio of water.
FIG. 5 is a SEM image of NFPH5 in which the weight ratio of water is 0%. FIGS. 6 to 9 show NFPH1 having a weight ratio of water of 1.43 wt%, NFPH2 of 2.86 wt%, NFPH3 of 4.29 wt% and 5.71 wt% SEM image of NFPH4. On the right is a 20,000 magnification image of the surface. The photo on the right photo shows the contact angle of the water droplet to confirm the hydrophobicity of each nanofiber surface.
As shown, the contact angle increased from 148.4 156 to 156.5 ㅀ as the weight ratio of water increased from 0 wt% to 2.86 wt%, but decreased to 151.9 4.2 in 4.29 wt% and decreased to 148.0 5. in 5.71 wt% .
The difference in the amount of water added is due to the difference in vapor pressure between water and DMF. At room temperature, water exhibits a vapor pressure of about 2.34 kPa which is higher than the vapor pressure of DMF at 0.36 kPa. As the water evaporates relatively quickly, the higher the water content, the more pores are formed on the surface of the nanofibers, resulting in a high contact angle with the rough surface. In addition, since water functions as a non-solvent for DMF, it is suitable for removing PEO after electrospinning when used as a solution for dissolving PEO. On the other hand, the diameter of the nanofibres increases with increasing water content, which is the result of increased viscosity of the spinning solution. Furthermore, the addition of water causes phase separation which leads to the formation of pores through liquid-liquid phase separation in the electrospinning process.
In the following examples, NFP (NFP2 = NFPH2) in which 7 wt% PEO and 2.86 wt% water having the best small cure characteristics are added is shown below, and various characteristics are confirmed based on this.
10 is a graph showing the size distribution of pores with respect to the average diameter of the nanofibers of Examples and Comparative Examples of the present invention.
It can be confirmed that pores having a uniform size are formed due to narrow distribution in both the embodiment of the present invention represented by NFP and the comparative example indicated by NF.
Table 2 shows the BET measurement results for the nanofibers.
Experiments named NFBP showed PVDF / PEO / H 2 O complex state without electroposition and PEO removal, and the specific surface area was reduced to 69.1% compared with NF composed pure PVDF alone. Also,
In NFBP, the specific surface area and the total pore volume were greatly increased in NFP selectively removing only PEO. The diameter of the pores formed in the sample was measured to be in the range of 30 to 50 nm.
FIG. 11 shows the results of measurement of the elastic modulus of the nanofiber mat prepared according to Examples and Comparative Examples of the present invention. FIG. 12 shows the tensile strength of the nanofiber mat prepared according to Examples and Comparative Examples of the present invention FIG. 13 shows the results of measurement of the elongation at break of the nanofiber mat prepared according to Examples and Comparative Examples of the present invention.
As shown, in the case of NFBP containing 7 wt% of PEO, the modulus of elasticity increased by about 161% from 13.18 MPa to 34.4 MPa, and the tensile strength increased by about 40% from 2.99 MPa to 4.19 MPa. This result is due to the fact that evenly dispersed PEO acts as a fixed barrier to limit the mobility of the PVDF polymer chain in the nanofiber and also because the applied force is efficiently transferred from the PVDF matrix to the PEO, .
In the case of NFP with PEO removed, the modulus of elasticity increased by 7.8% from 34.4MPa to 37.1MPa, and the tensile strength increased by about 11.4% from 4.19MPa to 4.67MPa, compared to NFBP. This increase in elastic modulus and tensile strength is a result of the internal pores formed in the nanofiber imparting brittleness characteristics to the nanofiber.
On the other hand, the elongation at fracture increased to 115.4% in NFBP and decreased to 23.1% in NFP with PEO removed.
From the above results, it can be seen that the porous PVDF nanofiber of the present embodiment has not only an improvement in the hydrophobic properties of the surface but also an improvement in the elastic modulus and tensile strength.
Fig. 14 shows FT-IR spectrum analysis results of the nanofibers of Examples and Comparative Examples of the present invention.
Among the absorption band check in NF samples consisting of pure PVDF 760cm -1 and 795cm -1, and 972cm -1 is consistent with the phase of PVDF, and α, 840cm -1 and 1273cm -1 are consistent onto a PVDF β. Peak of 875cm -1 will by the CH 2 wagging vibrations (wagging) of vinylidene fluoride (Vinylidene), 1068cm -1 band will by symmetrical CF stretching (stretching), 1404cm -1 peak scissoring of vinylidene It is by scissoring.
The spectrum of the PEO 841cm -1, 949cm -1, 964cm -1, 1057cm -1, 1118cm -1, 1242cm -1, 1281cm -1, 1385cm -1 and 1466cm -1 peak is CH 2, each right and left shaking motion (rocking) , COC deformation, helical shape, deformed zigzag shape, COC stretching vibration, CH 2 twisting, CH 2 swing vibration and CH 2 scissile vibration.
When PEO was added to PVDF, a new peak was observed, and some peaks were strengthened and some peaks shifted. In the PEO is added NFBP 840cm -1, 875cm -1, 1068cm -1 and 1404cm -1, the strength of the absorption peak was stronger in, the NFP these peaks by the removal of the PEO is 833cm -1, 856cm -1, 1065cm - 1 and has moved to 1366cm -1. And 1734 cm -1 and 2916 cm -1 peaks were newly observed in PEO added NFBP, which correspond to the C = O stretching vibration and OH stretching vibration of PEO, respectively. The NFP decreases the intensity of these peaks by the removal of PEO, and was moved each to 1728m and 2908m -1 -1.
From these results, it can be seen that PEO was added to NFBP and PEO was removed in NFP.
15 is an AFM scan image for NF, and FIGS. 16 and 17 are AFM scan images for NFP.
As a result of recording the signal while moving the probe in the horizontal direction in the area of 10 탆 to 10 탆, the NFN nanofiber showed a rough surface, as shown in FIG. 15 and FIG. 16, Is slightly smoothed. The difference in morphological change is the effect of pores of NFP nanofibers selectively removed from PEO. This is the same result as in the previous SEM photograph that NF has a smooth contact surface without porosity and a low contact angle.
Table 3 shows the roughness (roughness) measured for NF and NFP.
Rq is the root mean square roughness, Ra is the average roughness, and Rpv is the "peak-to-valley" roughness. The difference in roughness between NF nanofibers and NFP nanofibers is due to the difference in the internal porosity. The Rpv of NFP nanofibers was found to be highly non-uniform on the surface compared to the other roughness parameters for NF nanofibers as well as NF nanofibers, which seems to be due to the large specific surface area of the NFP.
Meanwhile, FIG. 17 shows other characteristics of the NFP measured in the error signal, and it can be confirmed that there are many internal pores in the NFP nanofibers.
Fig. 18 shows the results of filtration experiments on nanofiber mat according to Examples and Comparative Examples of the present invention.
Filtration experiments were carried out by constructing a laboratory end-of-dead-end filtration unit containing Millipore stirred cells with an effective area of 13.4 cm 2 .
As the feed solution, vegetable oil (5 wt%), surfactant (0.5 wt%, Brij 35) and deionized water (94.5 wt%) were mixed and stirred vigorously for 24 hours at the same rotational speed to obtain a homogeneous oil- in-water emulsion was prepared and used. The filtration experiments were carried out over a range of 0.1 to 0.3 bar at room temperature.
Flux rate of the NFP at a pressure of 0.1bar shows a 3 times higher than the flux rate of the 813.4lm -2 h -1 NF as 2462.3lm -2 h -1. As shown, increasing the pressure further reduced eoteuna the difference in flux rates, the flux rate of the NFP in a 0.3 bar pressure as compared 5746.27lm -2 h -1 to the flux rate of the 5067.16lm -2 h -1 NF still High. The reduction of this difference is due to the compression and deformation of the NFP nanofibers as the pressure increases and the porosity decreases. Also, deformation of the nanofibers increases the torsion due to pore blocking, which leads to a decrease in pore size.
Therefore, it can be confirmed that the nanofiber mat of the present invention exhibits further improved efficiency at a low pressure of 0.3 bar or less.
Table 4 shows the filtration efficiency (?) Of the nanofiber mat measured at 0.2 bar.
The filtration efficiency (η) of the nanofiber mat was calculated by the following equation.
Cf and Cp represent the oil concentrations of the feed and permeate solutions, respectively, and were measured at 230 nm wavelength using a UV spectrophotometer (
While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Those skilled in the art will understand. Therefore, the scope of protection of the present invention should be construed not only in the specific embodiments but also in the scope of claims, and all technical ideas within the scope of the same shall be construed as being included in the scope of the present invention.
Claims (13)
A molding step of molding the raw material into a nanofiber shape; And
And forming a porous structure by selectively removing only PEO from the formed nanofibers.
Wherein the ratio of PEO in the raw material ranges from 3 wt% to 15 wt%.
Wherein the solvent for dissolving the PVDF is one selected from the group consisting of DMF, N-dimethyl acetamide (DMAc), and N-methyl pyrrolidone (NMP).
Wherein the solvent is a mixture of a solvent in which PVDF is dissolved and water.
And the ratio of water in the raw material is 6 wt% or less.
Wherein the forming step is performed in an electrospinning process.
Wherein the pore forming step is performed by dissolving the PEO in water.
Wherein the step of dissolving the PEO in water is carried out at a temperature in the range of 50 to 70 占 폚.
Wherein the nanofibers are formed into a nanofiber mat in the course of obtaining the electrospun nanofibers.
Further comprising the step of fixing the nanofiber mat to a support.
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| WO2007119850A1 (en) * | 2006-04-19 | 2007-10-25 | Asahi Kasei Chemicals Corporation | Highly durable porous pvdf film, method of producing the same and washing method and filtration method using the same |
| JP2013535314A (en) | 2010-06-30 | 2013-09-12 | アモグリーンテック カンパニー リミテッド | Filter medium for liquid filter using electroradiated nanofiber web, manufacturing method thereof, and liquid filter using the same |
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| WO2007119850A1 (en) * | 2006-04-19 | 2007-10-25 | Asahi Kasei Chemicals Corporation | Highly durable porous pvdf film, method of producing the same and washing method and filtration method using the same |
| JP2013535314A (en) | 2010-06-30 | 2013-09-12 | アモグリーンテック カンパニー リミテッド | Filter medium for liquid filter using electroradiated nanofiber web, manufacturing method thereof, and liquid filter using the same |
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