KR101101924B1 - Porous nanofiber webs and manufacturing method thereof - Google Patents

Abstract

The method for producing a porous nanofiber nonwoven fabric according to the present invention is obtained by dissolving 17-21 Wt% of an amorphous resin of acrylic resin in a mixed solvent mixed with dichloromethane and dimethylformamide in a weight ratio of 8: 2-7: 3. Obtaining a good spinning solution, and electrospinning the spinning solution to produce a nanofiber nonwoven fabric having a number of pores formed in the nanofiber yarn, the average size of the pores of the nanofiber yarn is 30 ~ 37Å, the ratio of the non-woven fabric The surface area is configured to be 125 ~ 150㎡ / g, can maximize the specific surface area of the nonwoven fabric to implement a nonwoven fabric with excellent adsorption performance, it can be usefully used for separation filters, electronic devices, high efficiency sensors, composite materials reinforcement. .

Nanofiber, non-woven fabric, pore, electrospinning, specific surface area

Description

POROUS NANOFIBER WEBS AND MANUFACTURING METHOD THEREOF

The present invention relates to a method of manufacturing a nanofiber nonwoven fabric, and more particularly, to a porous nanofiber nonwoven fabric and a method of manufacturing the same that can maximize the surface area.

 In recent years, with the rapid development of nanotechnology in many high-tech industries, a lot of interest and research has been progressed as the manufacturing technology of nanofibers having a diameter of several hundreds of nanometers is developed.

Such nanofibers can be prepared by the phase separation of each component of the block copolymer, nanofibers formed by electrospinning of polymer solution or melt, nanofibers by nanospinning, and nano-reactors having a nano-sized diameter. Nanofibers, which are incompatible with each other and have a large degree of carbonization, are manufactured from composite fibers of two polymers, and carbon nanofibers are obtained by carbonizing them.

Among these methods, the method of manufacturing nanofibers by electrospinning is a process for producing nanofibers by applying electrical force to a polymer solution dissolved or melted in a solvent, which is applicable to a wide range of polymer materials, and the manufacturing process is simple. Since the spun fiber has a smaller diameter than the existing fiber, the ratio of surface area to volume is extremely high, and the manufactured nonwoven fabric has high porosity, breathability, and wind resistance, and is considered as the best technology when considering various product technology applications.

Nanofiber nonwoven fabric produced by electrospinning method is applied to various fields such as separation filter, protection for biochemicals, medical industry application and electronic device, conductive nanofiber, high efficiency sensor, catalyst, carbon nanofiber, reinforcement for composite materials have.

The application strength of the nonwoven fabric of nanofibers is that nanofibers have a larger surface area than conventional fibers. Recently, researches to maximize the surface area by minimizing the diameter of nanofibers are being actively utilized. In addition, nanofibers of various structures, such as a double structure, a hollow structure, a porous structure, a honeycomb structure, and a regular structure, have been studied as a structure capable of maximizing the surface area of the nanofibers.

It is therefore an object of the present invention to provide a nanofiber nonwoven fabric having excellent adsorption performance by maximizing a specific surface area and a method of manufacturing the same.

In the method for producing the porous nanofiber nonwoven fabric of the present invention for achieving the above object, in the method for producing a nanofiber nonwoven fabric, 17 to 21 Wt% of an acrylic resin based on dichloromethane and dimethylformamide weight ratio 8: Dissolve in a mixed solvent of 2 to 7: 3 to obtain a spinning solution having good volatility and radioactivity, and electrospinning the spinning solution to prepare a nanofiber nonwoven fabric having a number of pores in the nanofiber yarn, the pores of the nanofiber yarn The average size of is 30 ~ 37Å, the specific surface area of the nanofiber nonwoven fabric is characterized in that it is configured to be 125 ~ 150㎡ / g.

The present invention can realize a nonwoven fabric having excellent adsorption performance by maximizing specific surface area, and has an advantage that it can be usefully used for separation filters, electronic devices, high efficiency sensors, and composite materials.

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

The present invention focuses on the easy formation of pores of nanofiber yarns by using a solvent having high volatility by electrospinning method, and the nanofiber nonwoven fabric having pores on nanofiber yarns is prepared to realize a specific surface area. .

As the material of nanofiber nonwoven fabric, acrylic resin-based amorphous polymer is adopted because the crystallinity is not high and easy to form pores. In the present invention, polymethyl methacrylate (hereinafter referred to as PMMA) may be used as the amorphous polymer of the acrylic resin system. PMMA has strong resistance to chemicals such as sulfuric acid, hydrochloric acid, nitric acid and caustic soda at room temperature, and is widely used outdoors because of its excellent optical properties, transparency, transparency and weather resistance. In particular, PMMA nanofiber nonwovens are very useful in applications such as separation filters, medical applications and electronic devices, high efficiency sensors, and reinforcements for composites.

In addition, the inventors of the present invention showed that the PMMA showed good solubility in dichloromethane (hereinafter referred to as DCM) and dimethylformamide (hereinafter referred to as DMF). In order to obtain the nanofiber nonwoven fabric having pores, a solvent having a low boiling point, that is, a solvent having good volatility is advantageous, and thus, DCM was used as the main solvent in the present invention. However, as shown in Table 1 below, when only DCM is used as a solvent, it has good volatility and is advantageous to form pores. This also had a problem that makes radiation difficult.

menstruum
Boiling Point (℃) Dielectric constant Density (g / ml) DMF
153 38.3 0.94 DCM
40 9.08 1.33

Therefore, in the present invention, a mixed solvent was prepared by mixing DMF, which is widely used for electrospinning, having a higher boiling point and dielectric constant than DCM and having good solubility in PMMA, in the DCM.

The present invention mixes the mixed solvent of the DMF and DCM in PMMA to obtain a good volatile and radioactive spinning solution, and by electrospinning the spinning solution to prepare a nanofiber nonwoven fabric with a number of pores formed in the nanofiber yarn.

Here, the present inventors examined the effects of solution concentration, solvent ratio, and relative humidity on the structure and morphology of the fiber to examine the optimum conditions under which the porous nanofiber nonwoven fabric is formed. Looking at the concentration of the PMMA solution, the ratio of the solvent, the experimental example according to the relative humidity as follows.

1 is a viscosity curve according to the concentration change of the PMMA solution, Figure 2 is a nanofiber FE-SEM image diagram according to the concentration change of the PMMA solution, Figure 3 is a FE-SEM of the nanofiber nonwoven fabric according to the mixing ratio of DCM and DMF It is an image diagram. 4 is an FE-SEM image diagram of PMMA nanofiber nonwoven fabric according to relative humidity, and FIG. 5 is a FE-SEM image diagram showing a cross section of PMMA nanofiber yarn with or without pore formation.

In this case, important parameters to be considered for electrospinning include applied voltage, spinning distance, fluid injection speed and relative humidity. The applied voltage is 17 ~ 23Kv, the radiation distance is 12 ~ 18㎝, the fluid injection speed is 1.5 ~ 2.3mL / hr, the relative humidity can be 20 to 50%.

(Experimental Example 1)

First, the viscosity of the PMMA solution using a DMF solvent was measured at a temperature of 25 ° C. using a bismeter because the viscosity measurement should be preceded in the spinning of the nanofibers. The viscosity is an important factor in the fiberization obtained by electrospinning. When the viscosity is high, the flow of fluid due to the minimization of surface tension is significantly lowered, making injection difficult, and when the viscosity is low, the entanglement of the polymer chain is low. It is difficult to form the fiber by the fiber is not made. Therefore, in the present invention, the viscosity was measured by adjusting the concentration of PMMA to 9-25 wt%. As a result, when the polymer is dissolved in a solvent, the graph of the viscosity is represented by three straight lines, as shown in FIG. The above graph is expressed due to the rapid change of viscosity due to the entanglement of PMMA chain in each solution. The straight line ① represents a state where chain entanglement does not occur, and from the second straight line, chain entanglement occurs. Is an expression of increasing state, and the straight line ③ represents a state in which the viscosity is increased due to the entanglement of the chain being large enough to increase the chain entanglement.

In Experimental Example 1, the minimum concentration at which fibrosis occurred was determined using these straight lines. As a result, it can be seen that 17wt% of the straight line ② with the slope of 1.7808 and the straight line ③ with the slope of 4.6742 are the minimum concentrations at which fibrosis occurs.

Based on this viscosity measurement data, the other process elements, DCM and DMF, are mixed at a 9: 1 ratio, and electrospinning by applying an applied voltage of 20 kV, a spinning distance of 15 cm, a fluid injection rate of 2.0 ml / h, and a relative humidity of 20%. The nanofiber nonwoven fabric was prepared with the concentrations of (a) 12 wt%, (b) 15 wt%, (c) 18 wt%, and (d) 21 wt%. As a result, it is confirmed that the beads and the nanofiber yarns are accumulated in the form of a continuous phase in FIGS. 2A and 2B, and that the nanofiber yarns without the droplets are obtained in FIGS. 2C and 2D. It was.

Therefore, in the present invention, in order to obtain the nanofiber nonwoven fabric by electrospinning, it was found that the concentration of PMMA is preferably 17 to 21 Wt%.

(Experimental Example 2)

Next, to determine the proper mixing ratio of DCM and DMF solvent, DCM and DMF were mixed in the ratio of (a) 10: 0, (b) 9: 1, (c) 8: 2, and (d) 7: 3. Nanofiber nonwoven fabrics were prepared. During electrospinning, the concentration of PMMA was fixed at 18wt%, applied voltage 20kV, spinning distance 15cm, fluid injection speed 2.0 ml / h, relative humidity 20%. As shown in FIG. 3, as the proportion of DCM increases, nanofiber yarns having pores are formed, and as the proportion of DMF increases, nanofiber yarns having a clean cylindrical surface can be prepared. This was confirmed that it is easy to form pores on the surface of the nanofiber yarn due to the volatilization of the solvent as the proportion of DCM increases due to the low boiling point of DCM.

However, in the mixing ratio of (a) 10: 0 of FIG. 3, the polymer solution is hardened at the end of the radiator due to the low boiling point of DCM, so that the electrospinning is not easy, and the low dielectric constant does not facilitate the electrospinning. It was another factor. (B) Although the nanofiber yarn began to form well below the mixing ratio of 9: 1, pores decreased as the ratio of DMF was increased.

Therefore, in the present invention, it was confirmed that it is preferable to use a solvent in which DCM and DMF are mixed in a weight ratio of 9: 1 to 7: 3 to prepare a porous nanofiber nonwoven fabric.

Experimental Example 3

Next, paying attention to the fact that the relative humidity during electrospinning directly affects the surface structure of the nanofiber yarn of the nanofiber nonwoven fabric. Using a solvent mixed with DMF in a weight ratio of 8: 2, electrospinning was performed by applying an applied voltage of 20 kV, a spinning distance of 15 cm, a fluid injection speed of 2.0 mL / hr, and changing only relative humidity to 15 to 60%.

As a result, in Figure 4 (a) it can be seen that there is a slight surface change without pores. In (b) of FIG. 4 in which the humidity is increased from (a) of FIG. 4, it was confirmed that pores were formed on the surface of the nanofiber yarn. In FIG. 4 (c), nanofiber yarns having many pores on the surface were obtained. In (d) of FIG. 4, nanofiber yarns having more pores on the surface could be obtained.

However, since the very high humidity is not good for electrospinning, it was confirmed that the proper relative humidity is 20 to 50%, and most preferably 30 to 40% to prepare the nanofiber nonwoven fabric having pores.

As described above, in order to prepare a nanofiber nonwoven fabric with pores is formed by dissolving PMMA in a mixed solvent mixed with DCM and DMF weight ratio of 9: 1 to 7: 3 to obtain a spinning solution, the applied voltage 17 ~ 23Kv to the spinning solution , Spinning distance 12 ~ 18㎝, fluid injection speed was 1.5 ~ 2.3 mL / hr, it was confirmed that the electrospinning is preferable in the spinning conditions of 20 ~ 50% relative humidity.

Now, in order to evaluate the characteristics of the porous nanofiber nonwoven fabric prepared by the above-described manufacturing method, the increase in specific surface area and the size of the formed pores, and the increase in the specific surface area are compared with those of general nanofiber nonwoven fabrics without pores. Adsorption experiments of iodine, methylene blue, and phenol, which can be easily identified, examined the effect of specific surface area on adsorption.

First, in order to confirm the increase or decrease of specific surface area depending on the presence or absence of pores, as shown in FIG. 4, using a solvent in which a PMMA 18wt% solution is mixed with DCM and DMF in a weight ratio of 8: 2, an applied voltage of 20 kV and a spinning distance of 15 cm, Fixed the fluid injection rate at 2.0 mL / hr, and electrospinning by changing the relative humidity to 15 to 40% to prepare nanofibers with no pores and nanofibers without pores, and use the specific surface area analyzer to measure the specific surface area. By measuring the difference in specific surface area according to the pore formation. The results are shown in Table 2 below.

Polymer
Specific surface area (m < 2 > / g) PMMA nonwoven fabric with no pores 20.36 Porous PMMA Nonwoven Fabric 139.0

That is, the inventors of the present invention was able to confirm that the specific surface area of the PMMA nonwoven fabric having pores is much larger than that of the PMMA nonwoven fabric without pores.

In addition, in order to confirm the structure of the cross section of the PMMA nanofiber yarn having pores, the PMMA nonwoven fabric having no pores and the PMMA nonwoven fabric having pores were appropriately cut and the cross section was measured by a scanning electron micrograph. As a result, in the case of PMMA nanofiber yarn without pores formed on the surface, as shown in (a) of FIG. 5, the cross section showed a clean cross section without any features inside, but in the case of PMMA nanofiber yarn with pores formed thereon, FIG. As shown in 5 (b), pores were formed not only on the surface but also on the inside. The structure of PMMA nanofiber yarns in which such pores were formed was confirmed that the specific surface area was maximized by the principle similar to that of activated carbon, thereby making the specific surface area difference as shown in Table 2.

Next, in order to determine the average pore diameter and pore diameter of the PMMA nanofiber yarn, the diameters of the pores and the pores were measured using a specific surface area and a porosity measuring instrument (BET). The PMMA nanofiber nonwoven fabric used in this experiment was mixed at a weight ratio of 18 wt%, DCM and DMF at 8: 2, and applied voltage 20kV, spinning distance 15cm, fluid injection speed 2.0 ml / h, relative humidity 15-40%. Prepared. The results are shown in Table 3 below.

Polymer
Average pore and pore diameter PMMA without pores 37.8
Porous PMMA
34.8

The numerical value of Table 3 indicates the average diameter value of the pores in the case of PMMA nanofiber yarn without pores, and the average diameter value of the pores and pores in the case of PMMA nanofiber yarn with pores. In Table 3, the pore-formed PMMA nanofiber yarn was found to have a smaller average pore size and pore diameter than the pore-formed PMMA nanofiber yarn. If the nonwoven fabric formed of PMMA nanofiber yarn having a very small pore and pore diameter is applied to a filter or the like, the fine particles can be filtered out, and the specific surface area will be very high.

Now, in order to determine the adsorption power of the PMMA nanofiber nonwoven fabric by increasing the specific surface area, an adsorption force experiment was conducted using iodine, methylene blue, and phenol. The PMMA nanofiber nonwoven fabric used in this experiment was mixed at 18wt%, DCM and DMF at 8: 2 ratio, and applied at 20kV applied voltage, spinning distance 15cm, fluid injection speed 2.0ml / h, and relative humidity 15 ~ 40%. .

First, the iodine adsorption power of the PMMA nanofiber nonwoven fabric without pores and the PMMA nanofiber nonwoven fabric with pores was tested. As a result, as shown in Table 4 below, the PMMA without pores was adsorbed 202.8052 mg per g in the case of PMMA having pores, whereas the PMMA without pores was adsorbed per 1 g. As a result, it was confirmed that the difference in specific surface area has a great influence on the adsorption of iodine between the PMMA having no pores and the PMMA having no pores.

Polymer
Adsorption amount (mg / g) PMMA without pores
117.4119 Porous PMMA
202.8052

And, using the properties of absorbing light at 665 nm of methylene blue, the decolorizing ability of the PMMA with no pores and the PMMA with pores was tested. As a result, as shown in Table 5, the adsorption and decolorizing power of PMMA without pore formation was 1.0449 mg and 0.8707 mg per 1 g, and the adsorption and decolorizing power of PMMA with pores was 1.0520 mg and 0.8761 mg per 1 g. Little difference was found.

Polymer
Adsorption amount (mg / g) Decolorizing power (ml / g) PMMA without pores 1.0449
1.0520 Porous PMMA 0.8707
0.8761

This is a factor that greatly influences the adsorption of PMMA, which is affinity between specific surface area and adsorbent. Since PMMA adsorbs more polar material than non-polar material and acidic material than neutral or base, the result is pore on the surface. The formed PMMA nonwoven fabric has a larger specific surface area, but has a small affinity with methylene blue.

Finally, the adsorption performance of the phenol of PMMA with no pores and the PMMA with pores was tested using the light absorbing property at 269 nm of phenol.

As a result, as shown in Table 6, in the case of PMMA without pores, the adsorption amount was 1.78047 mg per 1 g of sample, whereas the PMMA with pores was 3.73127 mg per 1 g of sample. . In addition, it was confirmed that the difference in specific surface area has a great influence on the adsorption of phenol between PMMA having pores and PMMA having no pores.

Polymer
Adsorption amount (mg / g) PMMA without pores
1.78047 Porous PMMA
3.73127

Confirmation through this comparison proves that the porous nanofiber nonwoven fabric prepared according to the embodiment of the present invention maximizes the specific surface area and has excellent adsorption performance.

Porous nanofiber nonwoven fabric of the present invention can be particularly useful for separation filters, electronic devices, high efficiency sensors, composite materials reinforcement.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the equivalent of claims and claims.

1 is a viscosity curve according to the concentration change of the PMMA solution,

2 is a nanofiber FE-SEM image diagram according to the concentration change of the PMMA solution,

3 is a FE-SEM image of the nanofiber nonwoven fabric according to the mixing ratio of DCM and DMF,

4 is a FE-SEM image of the PMMA nanofiber nonwoven fabric according to relative humidity,

5 is a FE-SEM image showing a cross section of PMMA nanofiber yarn with or without pore formation.

Claims (5)

In the method of manufacturing a nanofiber nonwoven fabric, 17-21 Wt% of an acrylic resin of acrylic resin was dissolved in a mixed solvent mixed with dichloromethane and dimethylformamide in a weight ratio of 9: 1 to 7: 3 to obtain a volatile and radioactive spinning solution. To prepare a nanofiber nonwoven fabric with a plurality of pores formed on the nanofiber yarn, the average size of the pores of the nanofiber yarn is 30 ~ 37Å, the specific surface area of the nanofiber nonwoven fabric is configured to be 125 ~ 150㎡ / g Method for producing a porous nanofiber nonwoven fabric characterized in that. delete The method of claim 1, Applied voltage is 17 ~ 23Kv, spinning distance is 12 ~ 18㎝, fluid injection speed is 1.5 ~ 2.3 mL / hr, relative humidity is 20 ~ 50% electrospinning method of producing a porous nanofiber nonwoven fabric, characterized in that. The method of claim 1, The acrylic resin amorphous polymer is a method of producing a porous nanofiber nonwoven fabric, characterized in that composed of polymethyl methacrylate. Porous nanofiber nonwoven fabric prepared by the method of producing a porous nanofiber nonwoven fabric of any one of claims 1, 3 or 4.

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