U.S. patent application number 14/004837 was filed with the patent office on 2014-01-09 for graphene conjugate fiber and method for manufacturing same.
This patent application is currently assigned to IUCF-HYU (INDUSTRY-UNIVERSITY CORPERATION FOUNDATI ON HANYANG UNIVERSITY). The applicant listed for this patent is Seon Jeong Kim, Shi Hyeong Kim, Min Kyoon Shin. Invention is credited to Seon Jeong Kim, Shi Hyeong Kim, Min Kyoon Shin.
Application Number | 20140011027 14/004837 |
Document ID | / |
Family ID | 46831178 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140011027 |
Kind Code |
A1 |
Kim; Seon Jeong ; et
al. |
January 9, 2014 |
GRAPHENE CONJUGATE FIBER AND METHOD FOR MANUFACTURING SAME
Abstract
The present invention relates to a graphene conjugate fiber and
a method for manufacturing same, and more particularly, to a
conjugate fiber including graphene and a polymer, wherein a
wrinkled structure of the graphene is maintained in a fiber state.
The graphene conjugate fiber manufactured thereby has superior
mechanical properties, is flexible, and has high utility by being
manufactured as a fiber.
Inventors: |
Kim; Seon Jeong; (Seoul,
KR) ; Shin; Min Kyoon; (Seoul, KR) ; Kim; Shi
Hyeong; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Seon Jeong
Shin; Min Kyoon
Kim; Shi Hyeong |
Seoul
Seoul
Seoul |
|
KR
KR
KR |
|
|
Assignee: |
IUCF-HYU (INDUSTRY-UNIVERSITY
CORPERATION FOUNDATI ON HANYANG UNIVERSITY)
Seoul
KR
|
Family ID: |
46831178 |
Appl. No.: |
14/004837 |
Filed: |
March 9, 2012 |
PCT Filed: |
March 9, 2012 |
PCT NO: |
PCT/KR2012/001724 |
371 Date: |
September 12, 2013 |
Current U.S.
Class: |
428/367 ;
264/211.17 |
Current CPC
Class: |
D01F 6/16 20130101; Y10T
428/2918 20150115; D02J 13/00 20130101; B82Y 30/00 20130101; D01D
5/06 20130101; D01F 6/14 20130101; D01F 11/14 20130101; D01F 9/12
20130101; D01F 1/10 20130101; D01D 1/02 20130101; D01D 10/02
20130101 |
Class at
Publication: |
428/367 ;
264/211.17 |
International
Class: |
D01F 9/12 20060101
D01F009/12; D01F 11/14 20060101 D01F011/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 15, 2011 |
KR |
10-2011-0022833 |
Claims
1. A graphene composite fiber comprising graphene and a polymer
wherein the wrinkled structure of the graphene is maintained
unchanged.
2. The graphene composite fiber according to claim 1, wherein the
contents of the graphene and the polymer in the composite fiber are
from 20 to 90% by weight and from 10 to 80% by weight,
respectively.
3. The graphene composite fiber according to claim 1, wherein the
length of the graphene in the composite fiber is from 100 to 1000
nm.
4. The graphene composite fiber according to claim 1, wherein the
polymer is selected from polyvinyl alcohol and poly(methyl
methacrylate).
5. The graphene composite fiber according to claim 1, wherein the
graphene composite fiber is flexible.
6. The graphene composite fiber according to claim 1, wherein the
graphene composite fiber is capable of being formed into knot and
spring structures and being woven into a fabric.
7. The graphene composite fiber according to claim 1, wherein the
composite fiber has a toughness of 1 to 5.5 MJ/m.sup.3.
8. The graphene composite fiber according to claim 1, wherein the
composite fiber has a mechanical strength of 100 to 300 MPa.
9. The graphene composite fiber according to claim 1, wherein the
composite fiber has a modulus of elasticity of 5 to 30 GPa.
10. The graphene composite fiber according to claim 1, wherein the
composite fiber has a storage modulus of 1 to 10 GPa at 20 to
200.degree. C.
11. A method for producing a graphene composite fiber, the method
comprising a) dispersing graphene and a surfactant in a solvent to
prepare a dispersion, and b) incorporating the dispersion into a
polymer solution, wet spinning the resulting solution, followed by
drying to produce a fiber.
12. The method according to claim 11, further comprising c)
annealing the fiber obtained in b) at a high temperature of 140 to
160.degree. C.
13. The method according to claim 11, further comprising c')
dipping the fiber obtained in b) in methanol or acetone to improve
the degree of crystallization of the fiber.
14. The method according to claim 11, wherein the graphene is
chemically reduced graphene.
15. The method according to claim 11, wherein the graphene is
chemically reduced graphene with acid functional groups.
16. The method according to claim 15, wherein the chemically
reduced graphene is prepared by reducing an aqueous dispersion of
graphene with hydrazine at 90 to 100.degree. C. for 1 to 24
hours.
17. The method according to claim 11, wherein the surfactant is
selected from sodium dodecyl benzene sulfonate (SDBS), sodium
dodecyl sulfonate (SDS), Triton X-100, and cetyltrimethylammonium
bromide (CTAB).
Description
TECHNICAL FIELD
[0001] The present invention relates to a polymer composite fiber
including graphene and a method for producing the same. More
specifically, the present invention relates to a flexible graphene
composite fiber with outstanding mechanical properties and a method
for producing the graphene composite fiber.
BACKGROUND ART
[0002] Graphene is a two-dimensional nanostructure of covalently
bonded carbon atoms and exhibits surprising mechanical, electrical,
and thermal properties. Graphene flakes consist of single or
several graphene sheets exfoliated from graphite. Graphene flakes
have been reconstituted into bulky structures that have a modulus
exceeding that of flexible graphite while possessing high
strength.
[0003] A major challenge for graphene structures with high strength
and toughness is to maintain the inherent active surface of
graphene by preventing restacking of graphene tending to form
close-packed layer structures. Single-layer graphene or a graphene
flake has a wrinkled structure due to high area-to-thickness ratio
thereof, but a graphene paper or composite including a large amount
of graphene usually has a dense layer structure similar to
graphite. The dense layered structure of graphene is an obstacle in
achieving maximum mechanical properties owing to the short length
of graphene that reduces the van der Waals force and tensile
strength between graphene layers (by 1% or less).
[0004] There is no report on graphene composites including a
considerable concentration of graphene while maintaining the
inherent wrinkled structure of graphene. Little is also known about
the development of fibers from graphene composites.
DISCLOSURE
Technical Problem
[0005] It is an object of the present invention to provide a
graphene composite fiber that is flexible and has outstanding
mechanical properties in terms of strength, toughness, and modulus
of elasticity, and a method for producing the graphene composite
fiber.
Technical Solution
[0006] According to an aspect of the present invention, there is
provided a graphene composite fiber including graphene and a
polymer wherein the wrinkled structure of the graphene is
maintained unchanged.
[0007] In one embodiment of the present invention, the contents of
the graphene and the polymer in the composite fiber are preferably
from 20 to 90% by weight and from 10 to 80% by weight,
respectively. Within these ranges, the wrinkled structure of the
graphene composite fiber can be maintained.
[0008] The length of the graphene in the composite fiber is
preferably from 100 to 1000 nm.
[0009] In one embodiment of the present invention, the polymer may
be selected from polyvinyl alcohol and poly(methyl
methacrylate).
[0010] The graphene composite fiber of the present invention may be
formed into knot and spring structures due to flexibility thereof,
and several strands thereof may also be woven into a fabric.
[0011] The graphene composite fiber of the present invention has a
toughness of 1 to 5.5 MJ/m.sup.3, a mechanical strength of 100 to
300 MPa, a modulus of elasticity of 5 to 30 GPa, and a storage
modulus of 1 to 10 GPa at 20 to 200.degree. C.
[0012] The diameter of the graphene composite fiber is from 30 to
100 .mu.m.
[0013] The present invention also provides a method for producing a
graphene composite fiber, including a) dispersing graphene and a
surfactant in a solvent to prepare a dispersion, and b)
incorporating the dispersion into a polymer solution, wet spinning
the resulting solution, followed by drying to produce a fiber.
[0014] In one embodiment of the present invention, the method may
further include annealing the fiber obtained in b) at a high
temperature of 140 to 160.degree. C. or dipping the fiber obtained
in b) in methanol or acetone to improve the degree of
crystallization of the fiber.
[0015] In one embodiment of the present invention, the surfactant
may be selected from sodium dodecyl benzene sulfonate (SDBS),
sodium dodecyl sulfonate (SDS), Triton X-100, and
cetyltrimethylammonium bromide (CTAB). The use of sodium dodecyl
benzene sulfonate (SDBS) is more preferred.
[0016] In one embodiment of the present invention, the graphene is
preferably chemically reduced graphene, more preferably chemically
reduced graphene with acid functional groups.
[0017] In one embodiment of the present invention, the chemically
reduced graphene may be prepared by reducing an aqueous dispersion
of graphene with hydrazine at 90 to 100.degree. C. for 1 to 24
hours.
Advantageous Effects
[0018] The graphene composite fiber of the present invention, which
includes graphene whose wrinkled structure is maintained, exhibits
far superior mechanical properties to conventional graphene papers,
graphene composite films, and flexible graphite. In addition, the
graphene composite fiber of the present invention can be formed
into knot or spring structures due to flexibility thereof and can
also be woven into a fabric. Therefore, the graphene composite
fiber of the present invention can find application in various
fields. Furthermore, the graphene composite fiber of the present
invention can be mass-produced in a simple and economical manner
and its length can be extended to tens of meters in a continuous
process. Therefore, the graphene composite fiber of the present
invention is ideally suited to industrial applications.
DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a conceptual diagram showing the procedure for
producing a fiber composed of graphene flakes having directivity
and wrinkles according to the present invention.
[0020] FIG. 2 shows SEM images of the surface and cross-sectional
morphologies of a graphene/PVA fiber according to the present
invention: (A) a low magnification image, (B) a surface image, (C)
a side image of the graphene fiber aligned along the fiber axis,
and (D) a side image of graphene flakes having a wrinkled structure
in the graphene/PVA composite fiber.
[0021] FIG. 3 shows XRD and Raman spectra showing the
layer-to-layer distances of graphene flakes and the number of
graphene flake layers.
[0022] FIG. 4 graphically shows the mechanical properties of
graphene composite fibers: FIG. 4A shows stress-strain curves of a
pure graphene/PVA fiber (the solid line represents values measured
at room temperature and the dotted line represents values measured
at 150.degree. C.); FIG. 4B shows cyclic stress-strain curves of a
graphene/PVA fiber, the inset shows variations in the modulus of
elasticity of the graphene/PVA fiber with increasing strain, as
calculated from the cyclic stress-strain curves according to
loading (filled squares) or unloading (open squares); FIG. 4C shows
stress-strain curves of a GF/PVA fiber measured under different
conditions: when the fiber was annealed at 150.degree. C. (solid
line), and when annealed at 150.degree. C. after dipping in
methanol for 8 hours; and FIG. 4D graphically shows the toughness
and mechanical strength values of a pure fiber (red filled square),
a GF/PVA fiber annealed at 150.degree. C. (red triangle), and a
GF/PVA fiber treated with methanol (red filled circle) when
compared to those of graphene oxide papers (open circles), reduced
graphene papers (filled circles), an ion-modified graphene paper
(filled square), and graphene/PVA films (filled triangles)
including 44, 60, and 72% by weight of graphene reported in the
literature.
[0023] FIG. 5 shows 2-dimensional X-ray images of a graphene/PVA
(A) before and (B) after the fiber was thermally drawn by 30%. The
broad rings indicate that the PVA chains showed no change
associated with better alignment thereof.
[0024] FIG. 6 shows (A) an AFM image and (B) a SEM image of
graphene flakes deposited on a silicon substrate from an aqueous
dispersion.
[0025] FIG. 7 shows (A) a plot of tangent delta vs. temperature and
(B) a plot of storage modulus vs. temperature for a pure
graphene/PVA fiber.
[0026] FIG. 8 shows TG-DTA spectra of a pure graphene/PVA fiber
(black line) and a PVA powder (blue line).
[0027] FIG. 9A shows stress-strain curves of a pure graphene/PVA
fiber (dotted line), a graphene/PVA fiber annealed at 150.degree.
C., and a graphene/PVA fiber (dashed line) annealed at 150.degree.
C. and 213.degree. C.; and FIG. 9B shows DSC curves of a
graphene/PVA fiber (black line) and a PVA powder (blue line).
MODE FOR INVENTION
[0028] The present invention will now be described in more detail
with reference to exemplary embodiments thereof.
[0029] FIG. 1 is a conceptual diagram showing the procedure for
producing a fiber composed of graphene flakes having directivity
and wrinkles according to the present invention. According to the
method of the present invention, graphene can be prevented from
restacking in the individual steps of producing a fiber from a
graphene solution in order to maintain a wrinkled structure.
[0030] First, chemically converted graphene flakes (RCCGFs) with
functional groups such as COOH groups are dispersed in
dimethylformamide (DMF). An electrostatic repulsive force induced
by the functional groups allows stable maintenance of the
dispersion state of the graphene for at least 3 months without
serious aggregation of the graphene. In this case, the following
relationship is satisfied:
F.sub.R.gtoreq.F.sub.G+F.sub.V.D.W.
[0031] where F.sub.R, F.sub.G, and F.sub.V.D.W. represent the
electrostatic repulsive force, the force of gravity, and the van
der Waals force between the graphene flakes, respectively. The
relations of forces in the graphene solution during the overall
fiber production procedure are as follows.
[0032] 1. The chemically converted graphene is well dispersed in
DMF under the following condition:
Electrostatic repulsive force.gtoreq.(van der Waals force)+(force
of gravity)
[0033] 2. For a wet spinning solution, when DMF is exchanged with
distilled water by centrifugation:
Electrostatic repulsive force.gtoreq.(van der Waals force)+(force
of gravity by graphene)+(centrifugal force)
[0034] 3. The step of sufficiently dispersing graphene in distilled
water with the help of SDBS as a surfactant:
Electrostatic repulsive forces (graphene+SDBS)+dispersion force by
sonication.gtoreq.(van der Waals force)+(force of gravity by
graphene)
[0035] This condition may be varied with increasing time when a
large amount of graphene is loaded, and as a result, the graphene
may aggregate.
[0036] 4. During wet spinning, PVA chains replace SDBS and the
wrinkled graphene surrounded by the PVA chains is aligned in a
graphene fiber by a shear force induced by a shear flow.
[0037] 5. After wet spinning, a graphene gel in the solution
undergoes a hydrostatic force. The hydrostatic force does not
greatly affect restacking of the graphene.
[0038] 6. Drying
[0039] Gravimetric force is applied during drying, but stacking
occurs only in the axial direction, thus maintaining the wrinkled
structure of the graphene.
[0040] Since hydrophobic interaction between graphene flakes is
necessary for fiber production during wet spinning, the degree of
reduction of the chemically converted graphene flakes is of
importance. In other words, hydrophilicity of graphene flakes or
somewhat less reduced graphene flakes impedes sufficient
hydrophobic interaction between the graphene flakes, making the
formation of a gel-fiber difficult.
[0041] Accordingly, appropriate reduction of graphene is essential
for the preparation of a stable dispersion and the production of an
assembly by wet spinning. The atomic fractions of carbon and oxygen
in the reduced graphene flakes (RCCGF) determined from XPS data are
88.05% and 9.75%, respectively.
[0042] The graphene composite fiber of the present invention is
produced by the following procedure. First, a graphene/DMF solution
is prepared. The DMF is exchanged with distilled water by
sonication and centrifugation, and the graphene is well dispersed
in distilled water with the help of a surfactant to prepare a
graphene solution. The graphene solution is incorporated into a
coagulation bath containing polyvinyl alcohol (PVA). The graphene
solution incorporated into the polymer is changed to a graphene
gel-fiber by an assembly process through hydrophobic interaction
between the graphene flakes surrounded by the PVA chains replacing
the surfactant bonded to the graphene flakes. The graphene
gel-fiber is washed with distilled water to remove excess PVA.
[0043] Although hydrostatic forces are applied to the graphene
gel-fiber in the PVA solution and distilled water, the wrinkled
structure of the graphene flakes can be maintained because the
magnitudes of the hydrostatic forces in the x, y, and z directions
are equal. Then, the graphene gel-fiber is suspended vertically and
dried in air. As a result, the graphene-based fiber having a
wrinkled structure is formed.
[0044] The present invention will be explained in detail with
reference to the following examples and accompanying drawings.
However, these examples are provided to assist in further
understanding of the invention and are not to be construed as
limiting the scope of the invention.
EXAMPLE1
Preparation of Solution of Graphene (RCCG) Chemically Converted by
Reduction
[0045] In accordance with the method illustrated in FIG. 1, RCCG
was dispersed in dimethylformamide (DMF) in the presence of an
appropriate amount of triethylamine to obtain a stable graphene
dispersion. Several grams of RCCG was obtained by reducing an
aqueous dispersion of CCG with excess hydrazine at 95.degree. C.
over 2 h in accordance with previously reported methods (Li, D.,
Muller, M. B., Gilje, S., Kaner, R. B. & Wallace, G. G.
Processable aqueous dispersions of graphene nanosheets. Nature
Nanotech. 3, 101 (2008)). As a result of the reduction reaction,
the graphene aggregated in the aqueous solution. The graphene
aggregates were acidified with dilute sulfuric acid under vigorous
stirring to a pH of 2 or less, and transferred to a sintered
funnel. The aggregates were washed with a large amount of Milli-Q
water on the funnel until the pH reached about 7. The filtered
material was dried under vacuum at 70.degree. C. for 48 h to obtain
RCCG as a solid. The dried RCCG powder was dissolved in DMF to
prepare a 0.47-0.5 mg/mL RCCG/DMF solution. The length of the
graphene flakes was about 400 nm, as measured using a Zetasizer.
The particle size and zeta potential remained stable for several
months. The dispersion was filtered under vacuum to obtain a paper
having a resistance of 30-40 .OMEGA./sq.
EXAMPLE2
Production of Graphene Flakes/PVA Composite Fiber
[0046] The solvent (DMF) of the graphene flake dispersion was
exchanged with distilled water by centrifugation. The G/F aqueous
solution was mixed with sodium dodecyl benzene sulfonate (SDBS) by
ultrasonication.
[0047] The graphene dispersion was slowly injected into a
coagulation bath containing PVA (molecular weight=89,000-124,000,
degree of hydrolysis=.about.99%) through a syringe (26 gauge) and
wet spun to continuously produce a uniform graphene/PVA fiber.
[0048] After dipping in a coagulation bath for one day, the
graphene/PVA fiber was thoroughly washed with distilled water and
vertically dried in air at room temperature. The graphene/PVA fiber
was annealed at 150.degree. C. and dipped in methanol for 8 h to
obtain thermally drawn, methanol-treated GF/PVA. The annealing and
methanol treatment increased the crystallinity of the PVA.
[0049] Experimental Example: Characterization of the Graphene
Composite Fiber
[0050] The graphene composite fiber was sufficiently flexible and
thus could be wound on a glass tube having a small diameter of 6.5
mm without mechanical damage, unlike graphene papers tending to be
brittle (FIG. 1B). Complete knots of the graphene composite fiber
were difficult to form, but the formation of sufficiently strong,
flexible, small diameter knots of the graphene fiber was possible
(FIG. 1C). Difficulty in the formation of complete knots was due to
the small length of the graphene flakes and the frictional force of
the rough surface of the graphene composite fiber composed of the
graphene flakes (FIGS. 2B, 2F).
[0051] FIG. 2 shows SEM images of the surface and cross-sectional
morphologies of the graphene/PVA fiber. The wrinkled graphene
flakes were aligned along the axis of the fiber (FIG. 2C) and were
formed into highly porous petals (FIG. 2D). These images
demonstrate that the graphene flakes were formed into the fiber
without serious restacking. The present inventors also discovered
that even after the graphene/PVA was stretched by about 30% at
150.degree. C., the wrinkled structure was maintained in the fiber.
Good dispersibility of the graphene flakes in the PVA can be
confirmed from
[0052] XRD data. The layer-to-layer distances (d-spacings) before
and after 20-30% thermal drawing were 28 and 27 .ANG.,
respectively. The large d-spacings indicate a good interaction
between the hydrophilic PAV chains having a number of hydroxyl
groups through hydrogen bonding at the hydrophilic edges of the
chemically reduced graphene flakes. Further, the small difference
in d-spacing indicates that the well-dispersed wrinkled structure
was maintained despite the serious structural changes. The thermal
drawing of 20-30% did not bring about a considerable increase in
the alignment and crystallinity of the PVA chains.
[0053] In the present invention, the average size of the graphene
flakes and the number of the graphene layers were analyzed. The
size of the graphene flakes was calculated according to the
equation described in the literature [U. Khan, A. O'Neill, M.
Lotya, S. De, J. N. Coleman, Small 6, 864 (2010).].
I.sub.DI.sub.G=x/16+0.2(x=1/<w>+1<L>) (2)
[0054] where I.sub.D, I.sub.G, <w>, and <L> are the
intensities of the D and G bands of the Raman spectrum, the area of
the graphene flakes, and the length of the graphene flakes,
respectively.
[0055] The size of the graphene flakes calculated according to
Equation (2) was about 180 nm. This value is smaller than the size
(300-400 nm) of graphene flakes deposited on a silicon (Si)
substrate. This size was obtained from AFM and SEM data (see FIGS.
3 and 6). The smaller size of the graphene flakes in the fiber
demonstrates the wrinkled structure of the graphene flakes.
Meanwhile, the broad 2D band appeared at around 2700 cm.sup.-1 in
the Raman spectrum indicates that the wrinkled graphene flakes
consisted of two to four graphene layers in the fiber. No peak
shift was observed in the fiber. Therefore, it is thought that the
number of the graphene layers was not changed even after annealing
and acid treatment.
[0056] FIG. 4A shows stress-strain curves of the pure graphene/PVA
fiber. In FIG. 4A, the solid line represents values measured at
room temperature and the dotted line represents values measured at
150.degree. C. The average mechanical strength and modulus of
elasticity of the pure graphene/PVA fiber measured at room
temperature were 125 MPa and 8.8 GPa, respectively. The mechanical
strength values of the graphene composite fiber were similar to
those of previously reported graphene papers and were much higher
than those (5-10 MPa) of flexible graphite. The graphene composite
fiber had much higher toughness than the graphene papers (FIG. 4D,
Table 1). The mechanical properties of the graphene/PVA fiber were
similar to those of single-walled carbon nanotubes/PVA fibers
produced by wet spinning (mechanical strength: .about.150 MPa,
modulus of elasticity: 9-15 GPa).
[0057] The glass transition temperature (T.sub.g) and crystal
relaxation temperature (T.sub..beta.) of the pure graphene/PVA
fiber determined from changes in tangent delta and the storage
modulus with increasing temperature were .about.80.degree. C. and
.about.150.degree. C., respectively (FIG. 7). The graphene/PVA
fiber was stretched by 25-35% above the glass transition
temperature (near T.sub..beta.). The increased stretching of the
graphene/PVA fiber above the glass transition temperature is
because of high porosity of the fiber resulting from the wrinkled
structure of the graphene flakes despite the high content
(.about.70 wt %) of the PVA (FIG. 8).
[0058] FIG. 4B shows that the modulus of elasticity of the pure
graphene/PVA fiber varies depending on the strains calculated from
the cyclic stress-strain curves. The modulus of the graphene fiber
increased by factors of 2.2 and 4.7 according to the loading and
unloading cycles, respectively. The significantly increased modulus
according to the unloading cycle is thought to be due to the
wrinkled structure of graphene, which makes the recovery of the
sliding motion of the graphene difficult.
[0059] From the cyclic stress-strain curves of the graphene/PVA
fiber, the present inventors could conceive that the drawing
assists in increasing the mechanical properties of the fiber. In
order to increase the mechanical properties of the graphene/PVA
fiber, the fiber was annealed at 150.degree. C. for 1 h. The
mechanical strength, modulus of elasticity, and toughness of the
thermally drawn graphene/PVA fiber increased by 105%, 120%, and
95%, respectively, compared to those of the pure graphene/PVA
fiber. The graphene/PVA fiber drawn under the above conditions
after dipping in methanol for 8 h showed a maximum toughness of
4932 kJ/m.sup.3. This value is higher than any other kind of
graphene material known to date. Graphene papers produced from
graphene flakes reduced by vacuum filtration had maximum mechanical
properties when annealed at 220.degree. C. for 1 h. However, the
mechanical properties of the graphene/PVA fiber annealed at
213.degree. C. decreased because the PVA was thermally modified
(FIG. 9).
[0060] The mechanical properties of the inventive graphene/PVA
fiber were not better than the other graphene materials. However,
the graphene/PVA composite fiber of the present invention showed
superior toughness. Particularly, the thermally drawn graphene/PVA
fiber showed much higher strength and toughness than graphene oxide
papers and graphene oxide films (FIG. 4D).
[0061] Specifically, the mechanical strength, the modulus of
elasticity, and toughness of the graphene/PVA composite fiber
before annealing were 100-150 MPa, 5-10 GPa, and 1-2 MJ/m.sup.3,
respectively. In contrast, the mechanical strength, the modulus of
elasticity, and toughness of the graphene/PVA composite fiber after
annealing at 150.degree. C. were 250-300 MPa, 15-30 GPa, and
4.5-5.5 MJ/m.sup.3, respectively. The mechanical strength, the
modulus of elasticity, and toughness of the graphene/PVA composite
fiber treated with methanol or acetone (the graphene composite
dried after dipping in methanol for 12 h) were 100-200 MPa, 5-10
GPa, and 3-4 MJ/m.sup.3, respectively. The mechanical properties of
the graphene composite fiber according to the present invention
were measured using a dynamic mechanical analyzer. As a result, the
graphene composite fiber of the present invention was found to have
a storage modulus of 1-10 GPa in the temperature range of
20-200.degree. C., a tensile strength of 40-60 MPa at 150.degree.
C., and a modulus of elasticity of 1-3 GPa, which demonstrate its
superior thermal stability. As a result of the TG-DTA test on the
graphene composite fiber, no weight loss was observed in the range
of 0-300.degree. C. From these results, it is expected that the
composite fiber of the present invention can be applied at high
temperature.
INDUSTRIAL APPLICABILITY
[0062] As is apparent from the foregoing, the graphene composite
fiber of the present invention has outstanding mechanical
properties. In addition, the graphene composite fiber of the
present invention can be formed into knot and spring structures due
to flexibility thereof and can also be woven into a fabric.
Therefore, the graphene composite fiber of the present invention is
applicable to a wide variety of fields. The graphene composite
fiber of the present invention can be mass-produced in a simple and
economical manner and its length can be extended to tens of meters
in a continuous process.
* * * * *