KR20180016054A - Method for preparing polyaniline gel for super capacitor electrode, method for preparing polyaniline fiber for super capacitor electrode using thereof and application thereof - Google Patents

Abstract

The present invention relates to a manufacturing method of a polyaniline gel for a super capacitor electrode, a manufacturing method of a polyaniline fiber using the same, and an application thereof. More specifically, the present invention relates to a technique of manufacturing a polyaniline fiber after synthesizing a polyaniline gel of a polymer through solution polymerization and wet-radiating the same, and using the fiber for a super capacitor electrode. According to the present invention, the fiber for a super capacitor electrode with high conductivity can be manufactured using a polyaniline and a carbon nanotube with high molecular weight synthesized through the solution polymerization, so an abstract-type flexible fiber super capacitor without a collector or a supporter can be easily manufactured. Also, since a polyaniline fiber having a broad surface can be manufactured, a super capacitor with high efficiency and high power using the same can be manufactured.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a polyaniline gel for a super capacitor electrode, a method for manufacturing a polyaniline fiber for a supercapacitor electrode, and an application thereof. BACKGROUND ART [0002]

The present invention relates to a method for producing a polyaniline gel for a supercapacitor electrode, a method for producing a polyaniline fiber for a supercapacitor electrode and an application thereof, and more particularly, to a method for producing a polyaniline gel, To a polyaniline fiber and to use it for supercapacitor electrodes.

Among the next generation energy storage devices that are replacing or supplementing lithium secondary batteries with rapid increase in demand in recent years, super capacitors are attracting attention as next generation energy storage devices due to fast charge / discharge rate, high stability, and environmentally friendly characteristics. Typical supercapacitors consist of a porous electrode, a collector, a separator, and an electrolyte. The supercapacitor is driven on the basis of an electrochemical reaction mechanism that applies a voltage to the porous electrodes and selectively adsorbs ions in the electrolyte composition to the porous electrode. The research on the composite material for the electrode material of the supercapacitor has been commercialized in Japan since the early 1980s with the ultra-high-capacity capacitor using the activated carbon, and at the present stage, the practical technical limit is approached, and as the carbon nanotube composite material, metal oxide or polyaniline and polyaniline (PANI).

However, in the case of using a metal oxide and a conductive polymer, the metal oxide and the conductive polymer have a low conductivity, and thus, In order to maximize the surface area, a nano-thickness deposition method is used. However, this method requires complicated process conditions and is difficult to mass-produce.

Korea Patent No. 10-1045001 Korean Patent Publication No. 10-2014-0096210

The present invention provides a method for manufacturing a polyaniline gel for a supercapacitor electrode capable of increasing the surface area of polyaniline, and a method for manufacturing a polyaniline fiber for a supercapacitor electrode.

The present invention also provides a supercapacitor electrode material comprising the polyaniline fiber produced by the above method and a supercapacitor comprising the same.

In order to achieve the above object, the present invention provides a method for preparing a polyaniline emeraldine salt powder, comprising the steps of: (1) obtaining a polyaniline emeraldine salt powder doped with camphorsulfonic acid by doping a solid phase polyaniline emeraldine base with camphorsulfonic acid; Mixing the powder obtained in Step 1 with metacresol, and adding chloroform to prepare a mixed solution (Step 2); And a step (step 3) of leaving the mixed solution of step 2 (step 3).

The polyaniline emeraldine base of step 1 is prepared by adding an inorganic acid to an organic solvent containing an aniline monomer to prepare a reaction solution (step a); Adding an inorganic acid in which the initiator is dissolved to the reaction solution of step a) to prepare a polyaniline emeraldine salt (step b); Treating the polyaniline emeraldine salt of step b) with a basic aqueous solution to obtain a solid polyaniline emeraldine base (step c).

The organic solvent of step a may include at least one selected from the group consisting of acetone, alcohol, chloroform, hexane, ethyl acetate, acetonitrile, tetrahydrofuran, ether and dichloromethane, preferably chloroform have.

The inorganic acid in step a may be lithium chloride dissolved. In the step a, the reaction may be carried out at -20 ° C to -40 ° C, preferably at -30 ° C. When the reaction proceeds in the above temperature range, the reaction rate is controlled to be slow so that a polymer having a high molecular weight can be obtained. However, at this time, there may occur a problem that a slurry is formed in the water layer. However, the present invention suppresses the slurry formation in the water layer by lowering the freezing point by adding lithium chloride to the inorganic acid. In addition, the addition of an anionic material such as lithium chloride to inorganic acid increases the ionic strength. The polymerization reaction in the present invention occurs at the interface. When lithium chloride is added, the ionic strength of the water layer is increased, so bi-phase separation of the two phases occurs well, and emeraldine salt having a high molecular weight can be provided.

The inorganic acid may be selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, fluoric acid and iodic acid, preferably hydrochloric acid, nitric acid, sulfuric acid and phosphoric acid, and more preferably hydrochloric acid .

The initiator of step b may be ammonium persulfate. At this time, the reaction can be carried out for 12 to 36 hours.

The basic aqueous solution of step c may be aqueous ammonia. In this case, the concentration of the basic aqueous solution may be 0.5 to 2 M, preferably 1 M.

The camphorsulfonic acid may be doped in a ratio of 0.2 to 0.8 mol, preferably 0.5 mol of camphorsulfonic acid, per mol of the polyaniline emeraldine base in the step 1.

The powder may be added in an amount of 1.2 to 1.6% by weight based on the total weight of the mixed solution of step 2, and the chloroform may be added in an amount of 5 to 40% by volume, preferably 10% by volume, However, it is not limited thereto.

In the mixed solution of step 2, a carbon material may be further added, wherein the carbon material may be carbon nanotubes.

The amount of the carbon nanotubes to be added may be 5 to 50 wt%, more preferably 15 to 45 wt%, based on the weight of the polyaniline emeraldine base.

In the present invention, the carbon material is used to improve the mechanical properties of the electrode. In the case of conductive polymers, the state changes according to the applied electric potential. The carbon material in the bulk polymer can give good electrical conductivity to the electrode even when the polymer is semiconducting or insulating state. .

The present invention also provides a method for producing a polyaniline gel for a supercapacitor electrode, Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And freezing the spinning fiber followed by vacuum drying to sublimate metacresol. The present invention also provides a method for producing a polyaniline fiber for a supercapacitor electrode.

The radiation may be wet radiation.

The step of sublimating the metacresol may further include a step of keeping the spinning fiber at room temperature before freeze-drying and vacuum drying. In this case, it is preferable to maintain the metacresol at room temperature for 2 to 8 hours.

As the solvent, at least one selected from alcohol such as ethanol, methanol, propanol, water, acetone, chloroform and the like can be used.

The step of freezing and vacuum-drying the fiber to sublimate the metacresol may be performed by freezing the spinning fiber with liquid nitrogen for 1 to 10 minutes and then vacuum drying the fiber for 3 to 8 hours. The freezing can be performed at minus 18 < 0 > C or lower.

In the present invention, metacresol is a secondary doping solvent containing a phenol functional group to induce π-π stacking and hydrogen bonding between polyaniline polymer chains. Metacresol is a nonvolatile solvent, which takes a long time to extract through an organic solvent, and a considerable amount of metacresol remains in the polyaniline fiber after extraction. This may affect the oxidation-reduction reaction and the electrochemical stability of the polyaniline in the electrolyte aqueous solution when the electrode for a capacitor is manufactured. Therefore, in order to solve this problem, the remaining metacresol is sublimated through freezing and vacuum drying through liquid nitrogen desirable. This makes it possible to manufacture a capacitor electrode having a structure of a polyaniline fiber and having electrochemical stability within a short time.

The present invention also provides a method for producing a polyaniline gel, Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And freezing the fiber and vacuum-drying it to sublimate metacresol. The present invention also provides a method of manufacturing a supercapacitor electrode material. The step of sublimating the metacresol may further include a step of keeping the spinning fiber at room temperature before freeze-drying and vacuum drying. In this case, it is preferable to maintain the metacresol at room temperature for 2 to 8 hours. The details of each step are as described above.

The present invention also provides a method for producing a polyaniline gel, comprising: preparing a polyaniline gel by the above method; Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And freezing the fiber followed by vacuum drying to sublimate metacresol. The present invention also provides a supercapacitor electrode material comprising the polyaniline fiber. The step of sublimating the metacresol may further include a step of keeping the spinning fiber at room temperature before freeze-drying and vacuum drying. In this case, it is preferable to maintain the metacresol at room temperature for 2 to 8 hours.

The present invention also provides a method for producing a polyaniline gel, Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And freezing the fiber followed by vacuum drying to sublimate the metacresol. The flexible supercapacitor includes an electrode made of polyaniline fiber. The step of sublimating the metacresol may further include a step of keeping the spinning fiber at room temperature before freeze-drying and vacuum drying. In this case, it is preferable to maintain the metacresol at room temperature for 2 to 8 hours. Here, the supercapacitor may be an abstraction type flexible super capacitor. The details of each step are as described above.

According to the present invention, it is possible to manufacture the supercapacitor electrode material through a simpler process than the conventional method, thereby reducing the processing time and cost and improving the productivity.

In addition, the present invention can produce fibers for supercapacitor electrodes having high electrical conductivity by using high molecular weight polyaniline and carbon nanotubes synthesized through solution polymerization. Accordingly, it is possible to manufacture fibers for supercapacitor electrodes of high electrical conductivity, Can be easily produced. Also, according to the present invention, it is possible to produce a polyaniline fiber having a wide surface area, and a super capacitor having high efficiency and high output characteristics can be manufactured using the same.

In addition, the present invention can mass-produce electrodes for supercapacitors of various shapes and thicknesses at low cost by applying the wet spinning technique. In addition, the electrode manufactured according to the present invention is lightweight because the matrix is made of a polymer, and has a high molecular weight and a high density of polyaniline compared with the conventional vapor deposition methods. Thus, a super capacitor having a unit area and an excellent performance per unit volume Production is possible.

1 is an image of a fiber structure produced by wet-spinning a polyaniline fiber for a supercapacitor electrode.
2A shows the results of measurement of the current density (over), area and volume capacitance (below) of the pure polyaniline fiber, and FIG. 2B shows the results of measurement of the current density (over), area and volume capacitance of the polyaniline fiber including 20 wt% (Below).
FIG. 3A is a chart showing current density (over) and area energy density (below) of the fiber according to the carbon nanotube content, and FIG. 3B is a SEM image and a cross-sectional view showing a cross section of the polyaniline fiber including 20 wt% 3C is an SEM image showing the surface of the polyaniline fiber including 40 wt% of carbon nanotubes.
FIG. 4 is an image of the surface structure of the fiber produced by dividing the fiber in the fiber manufacturing process (upper, lower magnification) and rough (lower: left: lower magnification;
FIG. 5A is an image obtained by observing the surface of a fiber prepared by adding chloroform with an optical microscope, and FIG. 5B is a result of comparing the performance of a fiber to which chloroform was not added and a fiber to which chloroform was added (below).
6A is an electrochemical test using a polyaniline fiber containing 20 wt% of carbon nanotubes as an electrode and FIG. 6B is a view showing a state in which a superconducting cell Time (below).

Hereinafter, the present invention will be described in more detail with reference to Examples. The objects, features and advantages of the present invention will be readily understood through the following examples. The present invention is not limited to the embodiments described herein, but may be embodied in other forms. The embodiments described herein are provided to enable those skilled in the art to fully understand the spirit of the present invention. Therefore, the present invention should not be limited by the following examples.

Example 1: Preparation method of polyaniline gel for supercapacitor electrode

Example 1-1

Aniline monomer 20 ml was dissolved in 800 ml of chloroform and then cooled. 300 ml of 4 M aqueous hydrochloric acid solution in which 3 g of lithium chloride was dissolved was prepared and added to the chloroform solution containing aniline monomer. In order to obtain a polymer having a high molecular weight, the reaction rate was controlled to be slow and the reaction was carried out at -30 ° C. Then, 9 g of initiator (ammonium persulfate) was dissolved in 80 ml of 4 M hydrochloric acid, slowly dropped at a constant rate of 10 ml / h into the reaction solution, and the reaction was continued for 12 hours or more. After cooling at room temperature, the polyaniline emeraldine salt was treated with 500 ml of ammonia water (500 ml) to obtain 2 g of powdered emeraldine base.

In order to prepare a gel-like composition, 1 g of polyaniline emeraldine base in solid form and 1.3 g of camphorsulfonic acid doped with camphorsulfonic acid were added to a mortar and the mixture was finely ground. Then, by chemical reaction by physical mixing and collision, camphorsulfonic acid- 2.3 g of a lardin-base polymer powder was obtained. At this time, in order to obtain the highest electric conductivity, 0.5 mol of camphorsulfonic acid was doped to 1 mol of polyaniline emeraldine base (4 mol of aniline molecular unit is defined as 1 mol). The solution composition was prepared by mixing 0.16 g of the polymer powder composition with 10.25 ml of metacresol as a solvent, mixing and then allowing the solution composition to stand at room temperature for 1 to 3 hours to prepare a polyaniline gel composition for a supercapacitor electrode.

Examples 1-2

Aniline monomer 20 ml was dissolved in 800 ml of chloroform and then cooled. 300 ml of 4 M aqueous hydrochloric acid solution in which 3 g of lithium chloride was dissolved was prepared and added to the chloroform solution containing aniline monomer. In order to obtain a polymer having a high molecular weight, the reaction rate was controlled to be slow and the reaction was carried out at -30 ° C. Next, 9 g of initiator (ammonium persulfate) was dissolved in 80 ml of 4 M hydrochloric acid, slowly dropped at a constant rate of 10 ml / h into the reaction solution, and the reaction was continued for 12 hours or more. After cooling at room temperature, the polyaniline emeraldine salt was treated with 500 ml of ammonia water (500 ml) to obtain 2 g of powdered emeraldine base.

In order to prepare a gel-like composition, 1 g of polyaniline emeraldine base in solid form and 1.3 g of camphorsulfonic acid doped with camphorsulfonic acid were added to a mortar and the mixture was finely ground. Then, by chemical reaction by physical mixing and collision, camphorsulfonic acid- 2.3 g of a lardin-base polymer powder was obtained. At this time, in order to obtain the highest electric conductivity, 0.5 mol of camphorsulfonic acid was doped to 1 mol of polyaniline emeraldine base (4 mol of aniline molecular unit is defined as 1 mol). The solution composition was prepared by adding 10 ml of metacresol as a solvent to 0.16 g of the polymer powder composition and adding 1 ml of chloroform to the solution composition and then allowing the solution composition to stand at room temperature for 1 to 3 hours to prepare a polyaniline gel composition for a supercapacitor electrode .

Example 2: Manufacturing method of polyaniline fiber for supercapacitor electrode

The spinning solution containing the polyaniline gel composition for each supercapacitor electrode prepared according to Examples 1-1 and 1-2 was prepared by adjusting the concentration so that the concentration of camphorsulfonic acid was 1 M using ethanol as a solvent Then, the polyaniline fiber was wet-radiated at a speed of 0.8 ml / m (Fig. 1). Thereafter, the spun fiber was dried for 2 hours to evaporate ethanol, freeze with liquid nitrogen for 5 minutes, and vacuum-dried for 6 hours to sublimate metacresol to finally produce a polyaniline fiber for a supercapacitor electrode.

Experimental Example 1: Confirmation of performance of polyaniline fiber for supercapacitor electrode

In order to confirm the performance of the polyaniline fiber for a supercapacitor electrode, a pure polyaniline fiber prepared by the method of Example 2 and a solution composition containing the polymer powder in Example 1-1 were prepared, and then 20 wt% (0.014 g) of carbon nanotubes were prepared, and current density, areal capacitance and volumetric capacitance were measured and compared. In this experimental example and subsequent experiments, an electrochemical test was conducted using a 1M aqueous solution of sulfuric acid, an Ag / AgCl reference electrode, and a platinum electrode as a counter electrode.

As a result of the experiment, it was confirmed that the width of the single-walled carbon nanotube-containing fiber increases as the electric potential given to the pure polyaniline fiber increases (FIG. 2A). In addition, area and volume capacitance values were also higher (FIG. 2B). This is because the carbon nanotubes are uniformly dispersed in the polyaniline matrix in the fiber including single-walled carbon nanotubes, thereby increasing the internal density and forming a dense structure, thereby contributing to the improvement of the conductivity, thereby improving not only the energy density but also the constant output density .

Experimental Example 2: Capacitance, surface and cross-sectional structure of polyaniline fiber for supercapacitor electrode according to carbon nanotube content

On the other hand, since the electrically conductive carbon material has a lower non-storage capacity than the polyaniline fiber, it is essential to control the amount of the carbon material considering all of the high non-storage capacity, the energy density, the output density and the life stability. Specifically, a fiber including a single-walled carbon nanotube has a faster charge-discharge transition than a pure polyaniline fiber. In a conductive polymer, a state changes depending on a potential applied. In a bulk polymer, Because it gives the electrode good electrical conductivity even when the polymer is semiconducting or insulating state. In order to confirm the performance of the single-walled carbon nanotubes contained in the polyaniline fiber for the supercapacitor electrode, the solution composition containing the polymer powder was prepared in the same manner as in Example 1, (0.014 g), 30 wt% (0.021 g) and 40 wt% (0.028 g) of carbon nanotubes were further prepared to measure the current density and the energy density per unit area. As a result, single-walled carbon nanotubes Was 30 wt%, it was confirmed that the current density was the highest. Also, the Ragone plot showed that the energy density per area was the highest when the single wall carbon nanotube content was 30 wt% (FIG. 3A).

In addition, the surface structure and cross-sectional structure of the fiber according to the content of single-walled carbon nanotubes were observed by SEM (scanning electron microscope) (FIGS. 3B and 3C). As a result, it was impossible to observe the carbon nanotubes on the surface of the polyaniline fiber until the single-walled carbon nanotube content was up to 30 wt%, but it was possible to observe the single-walled carbon nanotubes on the surface.

Experimental Example 3: Confirmation of performance improvement according to the surface structure of polyaniline fiber for supercapacitor electrode

In order to confirm the performance of supercapacitor electrodes according to the surface structure of the fiber, the following two methods were performed. 1) (When the process is melted) The radiated fiber was dried for 2 hours to evaporate the ethanol, freeze the fiber for 5 minutes through liquid nitrogen, and then hold it at 18 ° C for 6 hours before sublimating the metacresol through the vacuum to shrink and expand the polyaniline The structure was modified. After that, it was frozen with liquid nitrogen for 5 minutes, followed by a vacuum drying process for 6 hours to sublimate metacresol. 2) (when not subjected to the melting process) The spun fiber was dried for 2 hours as in Example 2 to evaporate the ethanol. After that, it was frozen for 5 minutes using liquid nitrogen and then vacuum dried for 6 hours to sublimate metacresol.

As a result of the experiment, it was confirmed that the increase of the surface area of the fiber after the melting process as shown in Fig. 4 was confirmed in the image of 100K magnification (the surface is more rugged). On the other hand, no trace could be seen in the 100K magnification image without the melting process. Then, the capacitances of the fibers having different surface structures were measured and compared. As a result, it was confirmed that the fiber having a larger surface area had a higher specific storage amount. It was confirmed that the surface structure of the capacitor electrode material affects the ion diffusion and migration as the surface area is larger and contributes to the enhancement of the non - storage capacity.

Experimental Example 4: Confirmation of performance of polyaniline fiber for supercapacitor electrode according to presence or absence of chloroform

The performance difference was tested using the polyaniline fibers prepared by the methods of Examples 1-1 and 2 and the polyaniline fibers prepared by the methods of Examples 1-2 and 2 (with chloroform added). Since chloroform is extracted much faster than metacresol when ethanol is used, pores are formed on the surface of the polyaniline fiber when chloroform is removed (FIG. 5A). The diameter of the fiber was about 115 μm.

As a result of the experiment, it was confirmed that the fiber added with chloroform showed a larger area and volume capacitance than the fiber not added with chloroform (FIG. 5B).

Experimental Example 5: Confirmation of performance of a full cell of a supercapacitor

The full cell of the supercapacitor was a PVA electrolyte and an electrolyte was prepared by the method of Example 1 and Example 2 so as to prevent a shot at a ratio of PVA 9 g / H ₂ SO ₄ 6 g / H ₂ O 60 ml After application to the fabricated fiber, vacuum was applied for 5 minutes to remove any air bubbles near the fiber, minimizing defects and allowing the electrolyte to penetrate the fiber surface better. Subsequently, an electrochemical test of a polyaniline fiber supercapacitor containing 20 wt% of single-walled carbon nanotubes was performed (FIG. 6A).

As a result, it was confirmed that the full-cell of the supercapacitor has a similar variation of the fiber of Experimental Example 1, and the variation of the current density increases with the increase of the potential. It was also confirmed that as the current density increases, the time to reach the maximum potential is shortened (FIG. 6B).

Claims (19)

Doping the solid polyaniline emeraldine base with camphorsulfonic acid to obtain a camphorsulfonic acid-doped polyaniline emeraldine salt powder (step 1);
Mixing the powder obtained in Step 1 with metacresol, and adding chloroform to prepare a mixed solution (Step 2); And
And leaving the mixed solution of step 2 (step 3).
The method according to claim 1,
The polyaniline emeraldine base of the above step 1 may be,
Adding an inorganic acid to an organic solvent containing an aniline monomer to prepare a reaction solution (step a);
Adding an inorganic acid in which the initiator is dissolved to the reaction solution of step a) to prepare a polyaniline emeraldine salt (step b); And
(C) treating the polyaniline emeraldine salt of step (b) with a basic aqueous solution to obtain a solid polyaniline emeraldine base (step c).
The method of claim 2,
Wherein the organic solvent of step a comprises at least one selected from the group consisting of acetone, alcohol, chloroform, hexane, ethyl acetate, acetonitrile, tetrahydrofuran, ether and dichloromethane. Gel manufacturing method.
The method of claim 2,
A method for producing a polyaniline gel for a supercapacitor electrode, wherein lithium chloride is dissolved in the inorganic acid of the step (a).
The method of claim 2,
Wherein the step (a) is carried out at -20 ° C to -40 ° C.
The method of claim 2,
Wherein the initiator of step (b) is ammonium persulfate.
The method according to claim 1,
The method for producing a polyaniline gel for supercapacitor electrode according to claim 1, wherein a carbon material is further added to the mixed solution.
The method of claim 7,
Wherein the carbon material is a carbon nanotube. ≪ RTI ID = 0.0 > 11. < / RTI >
Preparing a polyaniline gel by the method according to any one of claims 1 to 8;
Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And
And freezing the fiber and vacuum drying it to sublimate metacresol.
The method of claim 9,
Wherein the spinning is a wet spinning process.
The method of claim 9,
Wherein the step of sublimating the metacresol further comprises a step of maintaining the fiber at room temperature before freeze-drying and vacuum drying.
The method of claim 11,
Wherein the step of maintaining the polyaniline fiber at the normal temperature is performed for 2 to 8 hours.
The method of claim 9,
The step of sublimating metacresol by freeze-drying the fiber after freezing is performed by freezing the spun fiber with liquid nitrogen for 1 to 10 minutes, followed by vacuum drying for 3 to 8 hours. The supercapacitor (Method for manufacturing polyaniline fiber for electrodes).
Preparing a polyaniline gel by the method according to any one of claims 1 to 8; Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And freezing the fiber followed by vacuum drying to sublimate the metacresol.
15. The method of claim 14,
Wherein the step of sublimating the metacresol further comprises the step of maintaining the fiber at room temperature before freeze-drying and vacuum drying.
Preparing a polyaniline gel by the method according to any one of claims 1 to 8; Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And freezing the fiber and vacuum-drying it to sublimate metacresol. The super-capacitor electrode material is made of polyaniline fiber.
18. The method of claim 16,
Wherein the step of sublimating the metacresol further comprises the step of maintaining the fiber at room temperature before freeze-drying and vacuum drying.
Preparing a polyaniline gel by the method according to any one of claims 1 to 8; Preparing a fiber by spinning a spinning liquid prepared by mixing the polyaniline gel in a solvent; And an electrode made of polyaniline fiber, which is fabricated by freezing the fiber and vacuum drying the metacresol fiber.
19. The method of claim 18,
Wherein the step of sublimating the metacresol further comprises a step of holding the fiber at room temperature before freeze-drying and vacuum drying.

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