WO2020032684A1

WO2020032684A1 - Graphene wet spinning coagulation bath and method for manufacturing graphene oxide fiber using the same

Info

Publication number: WO2020032684A1
Application number: PCT/KR2019/010075
Authority: WO
Inventors: Tae Hee Han; Tae Hyun Sung; Won Sik Eom
Original assignee: Industry University Cooperation Foundation IUCF HYU
Current assignee: Industry University Cooperation Foundation IUCF HYU
Priority date: 2018-08-09
Filing date: 2019-08-09
Publication date: 2020-02-13
Anticipated expiration: 2021-02-09
Also published as: KR102467629B1; KR20200017679A

Abstract

Provided are a graphene wet spinning coagulation bath and a method of manufacturing a graphene oxide fiber using the same. The method of manufacturing a graphene oxide fiber of the disclosure includes preparing a graphene oxide dispersion containing graphene oxide sheets and a dispersion medium, preparing a graphene oxide gel fiber by spinning the dispersion into a coagulation bath containing a coagulating solvent which extracts the dispersion medium, a crosslinking agent which forms crosslinks between the graphene oxide sheets and an emulsifier for mixing the coagulating solvent and the crosslinking agent, and drying the graphene oxide gel fiber.

Description

GRAPHENE WET SPINNING COAGULATION BATH AND METHOD FOR MANUFACTURING GRAPHENE OXIDE FIBER USING THE SAME

Exemplary embodiments of the present invention relate in general to the field of a coagulation bath and more specifically to a coagulation bath for graphene wet spinning.

Nanocarbon-based materials such as graphene and carbon nanotubes (CNTs) are high-end materials which are used as next generation electronic materials, heat sink materials or ultra-high strength structural materials because of very excellent electrical properties, thermal properties, flexibility and mechanical strength.

Particularly, graphene is a two-dimensional carbon isotope in which carbon atoms form a sp²-hybridized hexagonal honeycomb lattice structure, and the thickness of monolayer graphene is 0.2 to 0.3 nm, which is the thickness of a single carbon atom. Due to high electronic conductivity and a large specific surface area, graphene has been used in various fields of electrodes (electrode active materials) for a super capacitor, a sensor, a battery, a touch panel, and a flexible display; an actuator, a high efficiency solar cell, a heat sink film, a coating material, a sea water desalination filter, an ultra-fast charger, etc.

The use of the excellent physical properties of the nanocarbon-based material is implemented using CNTs and graphene at the molecular level formed utilizing chemical vapor deposition. However, at the bulk unit, the excellent properties may not be effectively expressed due to the difficulty in implementing a large-size, massively synthesized and uniform nanocarbon crystal structure.

Recently, research has been conducted to enlarge the excellent physical properties of graphene to the bulk unit by making massively-produced graphene oxide and oxidized CNTs larger and densified using a connecting medium or a van der Waals force between graphene layers. In this technology, a nanocarbon fiber spinning technique is attracting attention as a technique that maximizes electrical and thermal properties as well as mechanical properties of nanocarbons by maximizing the orientation and interaction of the graphene layer. Here, the fiberization of nanocarbon may be generally realized by spinning nanocarbon dispersion into a coagulation bath which can reduce a repulsive force between graphene layers thereby linearly coagulating the nanocarbon.

A conventional coagulation bath only using a coagulating solvent such as ethyl acetate has a problem of very high shrinkage and drying speeds of a fiber. Such a high shrinkage speed is the cause of a structural defect of the fiber, and the high drying speed is the cause of difficult handling of the fiber.

Example embodiments of the present invention provide an organic coagulation bath which can control the shrinkage and drying speeds of a graphene gel fiber during spinning in manufacture of a graphene oxide fiber using wet spinning.

To attain the above-mentioned object, in some example embodiments, a method of manufacturing a graphene oxide fiber may include preparing a graphene oxide dispersion containing graphene oxide sheets and a dispersion medium, preparing a graphene oxide gel fiber by spinning the dispersion into a coagulation bath containing a coagulating solvent which extracts the dispersion medium, a crosslinking agent which forms crosslinks between graphene oxide sheets and an emulsifier for mixing the coagulating solvent and the crosslinking agent, and drying the graphene oxide gel fiber.

The dispersion medium may be a polar organic solvent. The coagulating solvent may be an amine-based solvent of a secondary amine or tertiary amine. The coagulating solvent may be triethylamine, diethylamine, or dipropylamine. The crosslinking agent may be a monovalent metal salt or an ammonium salt. The monovalent metal salt or the ammonium salt may include a nitrate ion (NO₃ ^-), a chloride ion (Cl^-), a sulfide ion (S₂ ^-), a sulfate ion (SO₄ ^2-), a carbonate ion (CO₃ ^2-) or a thiocyanate ion (SCN^-) as an anion. The crosslinking agent may be ammonium thiocyanate or sodium thiocyanate.

The emulsifier may be an amphipathic solvent exhibiting Lewis basicity. The emulsifier may be acetonitrile. In the coagulation bath, the coagulating solvent and the emulsifier may be contained at a volume ratio of 1:0.7 to 1:2.5. In the coagulation bath, the crosslinking agent is contained at a ratio of 0.005 to 0.23 g per 1 ml of the coagulating solvent. In the coagulation bath, the coagulating solvent, the emulsifier and the crosslinking agent are contained at a ratio of 1:1:0.005 to 1:1:0.23 (ml:ml:g).

In other example embodiments, a coagulation bath for graphene wet spinning comprises a coagulating solvent which extracts a dispersion medium from a spun graphene oxide dispersion containing graphene oxide sheets and the dispersion medium, a crosslinking agent which forms crosslinks between the graphene oxide sheets, and an emulsifier which mixes the coagulating solvent and the crosslinking agent. The coagulation bath has a pH ranging from 10.1 to 10.55.

According to the disclosure, to manufacture the graphene oxide fiber using wet spinning, an organic coagulation bath which can control the shrinkage and drying speeds of a graphene gel fiber during spinning may be provided. Therefore, the manufactured graphene oxide fiber may exhibit excellent structural stability and facilitate hybridization with various materials.

Example embodiments of the present invention will become more apparent by describing in detail example embodiments of the present invention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a process of manufacturing a graphene oxide fiber using a coagulation bath according to example embodiments of the present invention;

FIG. 2 is a set of images showing graphene oxide fibers manufactured according to Preparation Example 5 and 6;

FIG. 3A is a graph showing the pH of a coagulation bath according to the volume ratio of acetonitrile to triethylamine under the condition that the composition ratio of ammonium thiocyanate to triethylamine is fixed at 0.01 g/ml; and

FIG. 3B is a graph showing the pH of the coagulation bath according to the composition ratio of ammonium thiocyanate to triethylamine (g/ml) under the condition that the volume ratio of acetonitrile and ethylamine is fixed at 1:1 (v:v).

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

Accordingly, while the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

FIG. 1 is a schematic diagram illustrating a process of manufacturing a graphene oxide fiber using a coagulation bath according to example embodiments of the present invention.

Referring to FIG. 1, a graphene oxide dispersion 100 may be prepared. The dispersion 100 may be a spinning solution for performing wet spinning. Specifically, the dispersion 100 may contain graphene oxide sheets which are dispersed in a dispersion medium.

The graphene oxide sheet may be generally obtained by chemically delaminating graphite and have several to tens or hundreds of stacked layers of graphene unit layers to have a thickness ranging from several to tens of nanometers. The graphene oxide sheet may include an oxygen functional group such as a hydroxide group (-OH), a carboxyl group (-COOH) or a carbonyl group (-C=O) binding to an edge part and an upper or lower part thereof.

The dispersion medium may be an organic solvent, specifically, a polar organic solvent, capable of uniformly dispersing the graphene oxide sheets. Therefore, the graphene oxide sheet, specifically, the graphene oxide sheet including the oxygen functional group having polarity may be more uniformly mixed in the dispersion medium. For example, the dispersion medium may be dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate (EA), an alcohol such as methanol, ethanol, ethylene glycol or n-butanol or the combination thereof. In one example, the dispersion medium may be DMF or DMSO.

A concentration of the graphene oxide dispersion 100 may be 1 mg/ml to 80 mg/ml, specifically, 1 mg/ml to 50 mg/ml, more specifically, 1 mg/ml to 10 mg/ml, and further more specifically, approximately 5 mg/ml.

A graphene oxide gel fiber 30a may be manufactured by spinning the dispersion 100, that is, the spinning solution, into a coagulation bath 200 through a nozzle 101. The coagulation bath 200 may contain a crosslinking agent, an emulsifier and a coagulating solvent.

When the spinning solution (100) is spun or extruded into the coagulation bath 200 through the nozzle 101, the dispersion medium conatained between the graphene oxide sheets in the spun or extruded solution may be exchanged with the coagulating solvent in the coagulation bath 200. In other words, the coagulating solvent may rapidly extract the dispersion medium from the spun or extruded solution to promote coagulation of the spun or extruded solution to provide the graphene oxide gel fiber 30a. For example, the coagulating solvent may be an organic solvent, specifically, an amine-based solvent of a secondary amine or tertiary amine, a ketone-based solvent such as acetone, an acetate-based solvent such as ethyl acetate or an alcohol-based solvent such as ethanol or propanol. For example, the coagulating solvent may be an alkylamine having 1 to 3 carbon atoms, and specifically, a dialkylamine or a trialkylamine having 1 to 3 carbon atoms. For example, the coagulating solvent may be triethylamine, diethylamine or dipropylamine, and specifically, triethylamine.

The crosslinking agent may enter into the spun or extruded solution along with the coagulating solvent to form crosslinks between the graphene oxide sheets, thereby improving a strength of the graphene oxide gel fiber 30a. Therefore, a conventional problem of the low strength of the graphene oxide fiber, which was made by only using, for example, a coagulating solvent such as ethyl acetate in the coagulating bath, may be compensated. In addition, the shrinkage and drying speeds of the graphene oxide gel fiber 30a may be controlled by controlling a content of the crosslinking agent with respect to the coagulating solvent.

More specifically, as the coagulating solvent enters and fills between the graphene oxide sheets, the crosslinking agent forms crosslinks between the graphene oxide sheets; therefore, rapid shrinkage of the graphene oxide gel fiber 30a may be prevented and a time to dry the gel fiber 30a may be slowed down. Therefore, it is possible to reduce the probability that a structural detect of a graphene oxide fiber (not shown) will be formed later.

In other words, as the coagulation bath according to example embodiments of the present invention includes a crosslinking agent that forms crosslinks between the graphene oxide sheets, conventional problems caused by the high shrinkage and drying speeds generated when only the coagulating solvent is used in the coagulating bath are prevented, and therefore an effect of increasing the structural stability of the finally-formed graphene oxide fiber may be exhibited.

The crosslinking agent may have a component ratio to be contained at a sufficient amount with respect to the coagulating solvent in order to slow down the shrinkage and drying speeds of the graphene oxide gel fiber, and to prevent undrying of the gel fiber, which may be caused by a too high content of the crosslinking agent. For example, in the coagulation bath, the crosslinking agent may be contained in an amount of 0.005 to 0.23g, specifically 0.01 to 0.2g, more specifically 0.05 to 0.2g, more specifically 0.09 to 0.2g, more specifically 0.1 to 0.16g, per 1 ml of the coagulating solvent.

The crosslinking agent may be in the form of a salt, specifically, a metal salt or a non-metal salt, and in one example, may be one which can be dissolved in a solvent like water to yield a metal cation or non-metal cation, and an anion. The metal cation may be a monovalent metal cation, for example, a sodium ion (Na⁺) or a potassium ion (K⁺), and the non-metal cation may be an ammonium ion (NH₄ ⁺). The anion may be a nitrate ion (NO₃ ^-), a chloride ion (Cl^-), a sulfide ion (S₂ ^-), a sulfate ion (SO₄ ^2-), a carbonate ion (CO₃ ^2-) or a thiocyanate ion (SCN^-). For example, the crosslinking agent may be ammonium thiocyanate (NH₄SCN) or sodium thiocyanate (NaSCN), and more specifically, ammonium thiocyanate (NH₄SCN).

The emulsifier may be used to mix the coagulating solvent with the crosslinking agent in the coagulation bath 200, and may be an amphipathic solvent having both hydrophobicity and hydrophilicity. Accordingly, the emulsifier may be used to well dissolve the crosslinking agent in the coagulating solvent which is an organic solvent.

The emulsifier may have a Lewis base characteristic. In other words, the emulsifier may be amphipathic and exhibit Lewis basicity. Therefore, the emulsifier may allow the coagulating bath to have basicity without a pH adjustor. As a result, an attractive force between the negatively-charged graphene oxide in the dispersion spun into the coagulation bath and the positively-charged crosslinking agent may be increased. The pH and characteristics of the coagulation bath will be described in further detail with respect to experimental examples below.

Although there is no limit to the type of the emulsifier, for example, the emulsifier may be acetonitrile. To maintain the graphene oxide gel fiber 30a in a gel form without phase separation, in the coagulation bath 200, the coagulating solvent and the emulsifier may be contained at a volume ratio of 1:0.7 to 1:2.5, specifically 1:0.7 to 1:2, more specifically 1:1 to 1:2, and most specifically 1:1.

The coagulation bath may exhibit basicity. This may be due to the emulsifier in the coagulation bath. Therefore, an attractive force between the negatively-charged graphene oxide spun into the coagulating bath and the positively-charged crosslinking agent may be increased.

More specifically, the characteristics of the graphene oxide negatively charged due to an oxygen functional group are changed according to a pH environment. For example, in an acidic environment, a negative charge characteristic is weakened, and in a basic environment, the negative charge characteristic is strengthen. Therefore, when the spinning solution is spun into the coagulation bath exhibiting basicity, a difference in charge potential between the positive charge of the crosslinking agent and the negative charge of the graphene oxide is larger, and thus an attractive force between the graphene oxide and the crosslinking agent is further increased. Therefore, the structural stability of the formed graphene oxide gel fiber 30a may be more improved.

For example, the coagulation bath 200 may have a pH of 10 or more, specifically a pH of 10.1 to 10.55, more specifically a pH of 10.36 to 10.46, further more specifically a pH of 10.37 to 10.45, and still further more specifically a pH of 10.38 to 10.44. Within the above-mentioned pH range, the coagulation bath 200 may increase the attractive force between the graphene oxide and the crosslinking agent, and therefore the structural stability of the formed gel fiber 30a may be improved.

The pH of the coagulation bath 200 may be controlled by a component ratio of the coagulating solvent, the emulsifier and the crosslinking agent. For example, in order for the coagulation bath 200 to have the above-mentioned pH range, in the coagulation bath 200, the coagulating solvent and the emulsifier may be contained at a volume ratio of 1:0.7 to 1:2.5, specifically 1:0.7 to 1:2, more specifically 1:1 to 1:2, and further more specifically 1:1. As an example, in the coagulation bath 200, the coagulating solvent, the emulsifier and the crosslinking agent may be contained at a ratio of 1:1:0.005 to 1:1:0.23 (ml:ml:g), specifically 1:1:0.01 to 1:1:0.2 (ml:ml:g), specifically 1:1:0.05 to 1:1:0.2 (ml:ml:g), more specifically 1:1:0.09 to 1:1:0.20 (ml:ml:g), and further more specifically 1:1:0.1 to 1:1:0.16 (ml:ml:g).

The graphene oxide gel fiber 30a may be dried, for example, at room temperature, under an atmospheric environment. Accordingly, a graphene oxide fiber in which a plurality of graphene oxide sheets are stacked in a thickness direction, and the stacked graphene oxide sheets are arranged in a length-wise direction i.e., in a axial direction of the fiber can be manufactured to have a structure in which the inner surface of the graphene oxide sheet is shrunk. The graphene oxide fiber may have a higher mechanical strength than the conventional graphene oxide fiber, and exhibit internal structural stability between the graphene oxide sheets.

The dried graphene oxide fiber may be thermally treated. The thermal treatment may reduce graphene oxide in the graphene oxide fiber, and thus reduced graphene oxide fiber having excellent structural stability may be manufactured. At this time, due to the thermal treatment, almost all of the materials introduced into the fiber from coagulation bath 200 may be removed, but in some cases, a small amount of material from the coagulation bath 200, that is, the crosslinking agent, the emulsifier and the coagulating solvent may be still contained in the reduced graphene oxide fiber. Due to high volatility, the coagulating solvent may remain at an ultimately smaller amount than the crosslinking agent and the emulsifier. The thermal treatment may be performed in an inert gas atmosphere such as an argon gas at a temperature ranging from 800°C to 1300°C, and specifically, approximately 1200°C.

In other words, in the method of manufacturing a graphene oxide fiber according to example embodiments of the present invention, the strength and structural stability of the formed graphene oxide fiber may be improved by controlling a component and a component ratio in the coagulation bath.

That is, unlike the conventional coagulating bath only using a coagulating solvent, the coagulation bath according to example embodiments of the present invention may include a crosslinking agent capable of forming crosslinks between the graphene oxide sheets, a coagulating solvent, which is an amine-based solvent for rapid extraction of a dispersion medium from a spun spinning solution extruded through a nozzle, and an emulsifier for mixing the crosslinking agent and the coagulating solvent. Therefore, the shrinkage and drying speeds of the graphene oxide gel fiber may be controlled.

In addition, in example embodiments of the present invention, to slow down the drying and shrinkage speeds of the graphene oxide gel fiber and reduce a shrinkage rate of the gel fiber, specifically, the thickness-direction shrinkage rate of the gel fiber, the crosslinking agent may be contained in an amount of 0.005 to 0.23g, specifically 0.01 to 0.2g, specifically 0.05 to 0.2g, more specifically 0.09 to 0.2g, more specifically 0.1 to 0.16g, per 1 ml of the coagulating solvent in the coagulation bath. In addition, in order for the gel fiber to exhibit an excellent coagulating property without phase separation and enable active spinning, the coagulating solvent and the emulsifier may be contained at a volume ratio of 1:0.7 to 1:2.5, specifically 1:0.7 to 1:2, more specifically, 1:1 to 1:2, and further more specifically 1:1.

In addition, in order for the coagulating bath 200 to have a pH of 10 or more, specifically a pH of 10.1 to 10.55, more specifically a pH of 10.36 to 10.46, further more specifically a pH of 10.37 to 10.45, and still further more specifically a pH of 10.38 to 10.44, in the coagulating bath 200, the coagulating solvent and the emulsifier may be mixed at a volume ratio of 1:0.7 to 1:2.5, and specifically 1:1 to 1:2. As an example, in the coagulation bath 200, the coagulating solvent, the emulsifier and the cross-linking agent may be mixed at a ratio of 1:1:0.005 to 1:1:0.23 (ml:ml:g), specifically 1:1:0.01 to 1:1:0.2 (ml:ml:g), specifically 1:1:0.05 to 1:1:0.2 (ml:ml:g), more specifically 1:1:0.09 to 1:1:0.20 (ml:ml:g), and further more specifically 1:1:0.1 to 1:1:0.16 (ml:ml:g).

The present invention will now be described in more detail with reference to Preparation Examples, however its scope is not limited thereto.

Preparation Example: Preparation of graphene oxide fiber

After graphene oxide powder was obtained from graphite powder using Hummers method, a graphene oxide dispersion i.e., a graphene oxide DMF dispersion was prepared in which the graphene oxide powder was dispersed in DMF at a concentration of 5 mg/ml. The graphene oxide dispersion was formed by dispersing the graphene oxide powder in water, putting a large amount of DMF therein, and then removing most of water using a centrifuge. The graphene oxide dispersion was spun into a coagulation bath containing triethylamine (TEA) which is a coagulating solvent, acetonitrile (ACN) which is an emulsifier and ammonium thiocyanate(NH₄SCN) which is a crosslinking agent to prepare graphene oxide gel fibers. Thereafter, the gel fibers were dried at room temperature (25 ℃) to prepare the graphene oxide fiber.

The content of TEA, ACN, and NH₄SCN in the preparation of graphene oxide fibers according to the preparation example was varied as shown in Table 1 below. At each condition, the gel fiber strength, the physical properties of the fibers, the pH of the coagulation bath were measured and are shown in Table 1 below.

	TEA:ACN ratio(v:v)	TEA(ml)	ACN(ml)	NH₄SCN(g)	Gel fiber strength	Other physical properties of fiber	pH of coagulation bath
ComparativeExample
1	1:0	5	0	0	very weak	dried very quickly	2
ComparativeExample 2	1:1	5	5	0	weak	dried quickly	12.06
PreparationExample 1	1:0.5	5	2.5	0.05	weak	phase separation occurred	10.07
PreparationExample 2	1:0.5	5	2.5	0.2	weak	phase separation occurred	10.07
PreparationExample 3	1:1	5	5	0.05	strong	spinnable/dried slowly	10.36
PreparationExample 4				0.4	strong	spinnable/dried slowly	10.45
PreparationExample 5				0.5	very strong	spinnable/dried slowly/ reduced shrinkage rate	10.38
PreparationExample 6				0.8	very strong	spinnable/dried slowly/ reduced shrinkage rate	10.44
PreparationExample 7				1.2	strong	undried	10.48
PreparationExample 8	1:2	5	10	0.05	Interme-diate	spinnable	10.5
PreparationExample 9	1:2	5	10	0.2	strong	spinnable	10.45
PreparationExample 10	1:3	5	15	0.05	weak	due to high emulsifier content,cohesive strength is low and spinning does not optimally proceed	10.6
PreparationExample 11	1:4	5	20	0.05	weak	due to high emulsifier content,cohesive strength is low and and fiber is weak	11.24

Referring to Table 1, it was expected that, when the coagulation bath in Comparative Example 1 was used, the graphene oxide fiber would have an internal structural defect due to a high drying speed of the gel fiber, and it was confirmed that the strength of the gel fiber was very weak.

When the amount of ACN as the emulsifier was less than that of TEA as the coagulating solvent, for example,when ACN was contained in a volume ratio of 0.5 or less with respect to TEA as shown in Preparation Examples 1 or 2, it was difficult for the resulting mixture to be mixed with NH₄SCN as the crosslinking agent in the coagulation bath, thereby generating the phase separation of the gel fiber. As shown in Preparation Examples 10 and 11, when the amount of ACN with respect to that of TEA was too much, for example, when the volume ratio of ACN with respect to TEA was 3 or more, the cohesive strength of the spun dispersion is reduced to make spinning somewhat difficult due to the high volume of the emulsifier contained in the coagulation bath, regardless of the strength of the fiber.

Meanwhile, when the volume ratio of TEA and ACN is 1:2 as shown in Preparation Examples 8 and 9, a cohesive strength of the spun dispersion is found to be good enough to enable the spinning process, but the drying speed and (thickness-direction) shrinkage rate of the fiber are not found to be very good. However, it is interpreted that the increase in strength of the fiber obtained from Preparation Example 9, compared to that of Preparation Example 8, results from the effect of a crosslinking agent.

As shown in Preparation Examples 3 to 7, when the volume ratio of TEA and ACN was 1:1, spinning was smoothly performed. Here, it was confirmed that the higher the content of the crosslinking agent, i.e. ammonium thiocyanate(NH₄SCN), the higher the strength of the fiber. Among Preparation Examples 3 to 7, Preparation Examples 4 to 6 showed decreases in drying speed and (thickness-direction) shrinkage rate during the formation of the fiber. In Preparation Example 7, the content of the crosslinking agent was so high that the drying speed of the fiber was too low and thereby producing fiber not completely dried.

As stated, when the crosslinking agent is contained in the coagulation bath of the above-described embodiments while the coagulation solvent and emulsifier are mixed at a ratio of 1: 1 to 1: 2, phase separation does not occur and the spinning can proceed well. Furthermore, when the coagulating solvent and the emulsifier are contained in a ratio of 1: 1 and the crosslinking agent is contained, the gel fiber drying rate is slowed and the shrinkage in the thickness direction is reduced. Particularly, when the crosslinking agent is contained at a ratio of 0.05 to 0.16 g per 1 ml of the coagulation solvent while the coagulating solvent and emulsifier is contained in a ratio of 1:1, the shrinkage in the thickness direction can be further reduced. Accordingly, it is possible to reduce the possibility of occurrence of structural defects in the fiber and to exhibit excellent strength characteristics of the fiber.

FIG. 2 is a set of images showing graphene oxide fibers manufactured according to Preparation Example 5 and 6.

Referring to FIG. 2, it was confirmed that the gel fiber was more uniformly and stably spun into the coagulation bath, and the spun fiber exhibited a strength sufficiently high so as to facilitate continuous spinning.

FIG. 3A is a graph showing the pH of a coagulation bath according to the volume ratio of acetonitrile to triethylamine under the condition that the composition ratio of ammonium thiocyanate to triethylamine is fixed at 0.01 g/ml, FIG. 3B is a graph showing the pH of the coagulation bath according to the composition ratio of ammonium thiocyanate to triethylamine (g/ml) under the condition that the volume ratio of acetonitrile and ethylamine is fixed at 1:1 (v:v).

Referring to FIGS. 3A and 3B, when neither acetonitrile nor ammonium thiocyanate was added, that is, when triethylamine alone was present (Comparative Example 1), the pH of the coagulation bath was strongly acidic to 2, and when acetonitrile was added in the absence of ammonium thiocyanate (Comparative Example 2), the pH of the coagulation bath was 12.06, indicating strong basicity. When the component ratio of ammonium thiocyanate to triethylamine (g/ml) was in the range of 0.01 to 0.24 in the condition that the volume ratio of acetonitrile and triethylamine was fixed at 1:1 (v:v) (Preparation Examples 3-7), the pH of the coagulation bath was 10.36 to 10.48, and the pH value was slightly decreased due to the addition of ammonium thiocyanate, and the coagulation solution enabled smooth spinning (FIG. 3B). In addition, when the volume ratio (v/v) of acetonitrile to triethylamine is in the range of 0.5 to 4 in a state where the component ratio (g/ml) of ammonium thiocyanate to triethylamine is fixed to 0.01 (Preparation Examples 1, 3, 8, 10, and 11), the pH of the coagulation bath ranged from 10.7 to 11.24, indicating that the pH increase with increasing volume ratio of acetonitrile was not significant when the volume ratio of acetonitrile to triethylamine is 3 or less. In addition, in Preparation Examples 1, 3, 8, 10, and 11, spinning optimally or well proceeded when the coagulation bath was in the pH range of 10.36 to 10.5.

From this, it can be seen that when the coagulation bath is prepared by adding acetonitrile as an emulsifier as well as ammonia thiocyanate as a crosslinking agent to triethylamine as a coagulating solvent, spinning can proceed smoothly. Specifically, when the coagulating solvent and the emulsifier were mixed in a ratio of 1: 1 to 1: 2 and the crosslinking agent is contained 0.01 to 0.24 g per 1 ml of the coagulating solvent, the spinning was smoothly proceeded. Further, when the crosslinking agent is contained at a ratio of 0.01 to 0.16 g relative to 1 ml of the coagulating solvent while the coagulating solvent and the emulsifying agent are mixed at a ratio of 1:1, the strength of the fiber is increased while the fiber is dried properly together with the smooth spinning. When the crosslinking agent is contained at a ratio of 0.1 to 0.16 g per 1 ml of the coagulating solvent, the shrinkage in the thickness direction can be further reduced and the strength of the fiber can be greatly increased. Further, it can be seen that the pH of the coagulation bath which enables smooth or optimal spinning is in the range of 10.36 to 10.5, and that the pH of the coagulation bath is preferably in the range of 10.38 to 10.44 in consideration of the strength of the fiber.

Meanwhile, the example embodiments disclosed in the specification and drawings are merely provided to present specific examples for the purpose of understanding the present invention and not intended to limit the scope of the present invention. It will be apparent to those of ordinary skill in the art that modifications, other than the example embodiments of the present invention, based on the technical idea of the present invention can be implemented.

Claims

A method of manufacturing a graphene oxide fiber, comprising:

preparing a graphene oxide dispersion containing graphene oxide sheets and a dispersion medium;

preparing a graphene oxide gel fiber by spinning the dispersion into a coagulation bath containing a coagulating solvent which extracts the dispersion medium, a crosslinking agent which forms crosslinks between graphene oxide sheets and an emulsifier for mixing the coagulating solvent and the crosslinking agent; and

drying the graphene oxide gel fiber.
The method of claim 1, wherein the dispersion medium is a polar organic solvent.
The method of claim 1, wherein the coagulating solvent is an amine-based solvent of a secondary amine or tertiary amine.
The method of claim 3, wherein the coagulating solvent is triethylamine, diethylamine, or dipropylamine.
The method of claim 1, wherein the crosslinking agent is a monovalent metal salt or an ammonium salt.
The method of claim 5, wherein the monovalent metal salt or the ammonium salt includes a nitrate ion (NO₃ ^-), a chloride ion (Cl^-), a sulfide ion (S₂ ^-), a sulfate ion (SO₄ ^2-), a carbonate ion (CO₃ ^2-) or a thiocyanate ion (SCN^-) as an anion.
The method of claim 6, wherein the crosslinking agent is ammonium thiocyanate or sodium thiocyanate.
The method of claim 1, wherein the emulsifier is an amphipathic solvent exhibiting Lewis basicity.
The method of claim 1, wherein the emulsifier is acetonitrile.
The method of claim 1, wherein, in the coagulation bath, the coagulating solvent and the emulsifier are contained at a volume ratio of 1:0.7 to 1:2.5.
The method of claim 1, wherein, in the coagulation bath, the crosslinking agent is contained at a ratio of 0.005 to 0.23 g per 1 ml of the coagulation solvent.
The method of claim 1, wherein, in the coagulation bath, the coagulating solvent, the emulsifier and the crosslinking agent are contained at a ratio of 1:1:0.005 to 1:1:0.23 (ml:ml:g).
A coagulation bath for graphene wet spinning, comprising:

a coagulating solvent which extracts a dispersion medium from a spun graphene oxide dispersion containing graphene oxide sheets and the dispersion medium,

a crosslinking agent which forms crosslinks between the graphene oxide sheets; and

an emulsifier which mixes the coagulating solvent and the crosslinking agent.
The coagulation bath of claim 13, wherein the coagulation bath has a pH ranging from 10.1 to 10.55.