Study on Nano Polyacrylonitrile Fiber by Cotton Candy Method
Ryo Takematsu, Masayuki Okoshi, Hiroyuki Inoya and Hiroyuki Hamada,
Department of Advanced Fibro-Science, Kyoto Institute of Technology, Gosyokaidocho, Matsugasaki,
Sakyo-ku, Kyoto, 606-8585, Japan
Akihiro Tada,
OHGI TECHNOLOGICAL CREATION CO., LTD. 4-13, 3-chome, Nakano, Otsu City, Shiga
Prefecture 520-2114, Japan
Yoshifumi Aoi,
Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, Seta,
Otsu 520-2194, Japan
Abstract
In this research, nano polyacrylonitrile (PAN) fiber
was spun by Cotton Candy Method (CoCaM). CoCaM is
the novel method to fabricate a nano fiber. This technique
is expected to use in various field, because CoCaM has
excellent advantages, for example cost reduction, good
productivity and so on. We can find that PAN
concentration, air pressure and feeding speed affected
diameter of nano fiber. CoCaM can make a preparation of
various fiber sizes. The minimum and maximum number
average of nano PAN fiber diameter were ranged from
macro to nano meters. After carbonizing, the diameter of
nano fibers was decreased 16% compared to nano PAN
fibers. According to the result of Raman spectrometry, it is
revealed the high crystallinity of nano carbon fiber.
Introduction
Recently, it has been possible to make a preparation
of nano fibers in the technology field [1-4]. The diameter
of nano fibers is under several hundreds nano meters.
They have several excellent properties such as mechanical
properties and large surface area. Therefore, nano fibers
are expected to apply in various field including energy
sector, electronics sector, medical sector and so on.
Several methods for fabricating nano fibers were reported
by researchers, electrospinning method is one of the most
famous methods [5-9]. The electrospinning method can
fabricate the nano fibers by dissolved resin in the solution
with a high voltage. In the result, it is possible to make the
nano fibers to stretch the dissolved resin by electrostatic
repulsion. However, the electrospinning method results in
large cost because of keeping the high voltage during the
produce. Besides, the electrospinning method does not
have enough stretching process. Therefore, the nano fibers
that are fabricated by electrospinning method are low
crystallinity and weak mechanical properties.
On the other hands, carbon fibers have gotten a lot of
attention recently because they have excellent mechanical
properties and use in various fields [10-12]. Several ways
to produce carbon fibers are reported. Carbon fibers are
typically made from polyacrylonitrile (PAN) [13-14].
Carbonization of PAN fibers has two steps. The first step
is called flame-proofing which is heating in an oxygen
atmosphere at 200 to 300 ℃. In the second step, PAN is
carbonized between 700 and 1800 ℃ in a nitrogen
atmosphere.
In this research, the novel method that called Cotton
Candy Method (CoCaM) is introduced. PAN that is
precursor of carbon fiber was solved in Nmethylpyrrolidone (NMP). This solution was blown and
stretched by air. After that stretched nano fiber was caught
in water. NMP is a good solvent for PAN, whereas water
is a poor solvent for PAN. This simple process can
fabricate PAN nano fibers. Since the CoCaM does not
need a high voltage, this novel method is expected to
produce in large volume in a low cost way. For looking at
the effect of spinning condition on nano fibers, polymer
concentration, air pressure and feeding speed of polymer
were varied. After carbonization, Raman spectrometry
was carried out in order to evaluate crystallinity of nano
carbon fiber [15-16].
Experiment
Materials
Polyacrylonitrile (PAN, Mw: 150,000) was used, it
was manufactured by Sigma-Aldrich Co. LLC., America.
N-methyl-2-pyrrolidone (NMP) was used as solvent,
which was manufactured by NACALAI TESQUE, INC.,
Japan. PAN was dissolved in NMP, and the solutions that
contained 3%, 5%, 10% and 15% PAN were prepared
respectively.
Cotton Candy Method
Cotton Candy Method was used in this research.
Figure 1 shows the schematic of CoCaM machine. Three
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holes for feeding solution are located above an air outlet.
The solution was feeding thorough a routed screw, after
that it was blown and stretched by air. The stretched PAN
solution was corrected in water and deposited as nano
PAN fiber.
of nano carbon fiber. From this result, the ratio of the D
and G peak intensities (ID/IG) was calculated.
Fiber Diameter Determination
Diameter of nano fiber was measured by SEM
photograph. From these results, fiber diameter distribution
was determined. The number average fiber diameter (DN)
was defined by the following equation.
(1)
DN =
∑ Ni Di
∑N
i
where Ni is number of fiber at the diameter Di
Carbonization
!
Figure 1. Schematic of CoCaM machine.
Carbonization was carried out in two steps. The first
step is flame-proofing. The nano PAN fibers were heated
room temperature to 270 ℃ with heating rate of 5℃/min,
held for an hour under compressed air atmosphere.
In second step, carbonizing was carried out. The
flame-proofed fibers were heated until 1400 ℃ with
heating rate 7 ℃/min. And then held at 1400 ℃ for 10
minutes in nitrogen atmosphere.
In this method, 3 processing parameters were
revealed. For looking at the effect of PAN concentration
in NMP, 4 various contents of PAN solution (3%, 5%,
10% and 15%) were prepared and tested. screw speed for
feeding solution was set 30 rpm with air pressure of 0.1
MPa in this test.
In addition, the effect of air pressure was studied at
0.05 MPa, 0.2 MPa and 0.4 MPa by using PAN solution
of 10%. And screw speed for feeding solution was set 30
rpm.
After that, experiment was focused on the effect of
feeding screw speed of solutions. The screw for feeding
was varied at 5 rpm and 30 rpm. In this experiment, PAN
concentration of 10% was used, and Air pressure was set
0.2 MPa.
Results and Discussion
Mechanism of CoCaM
High-Speed Camera
PAN was dissolved in NMP and this solution was
injected at a constant feed rate though the nozzle. The
observation by high-speed camera is shown in Figure 2.
PAN solution was stretched by swirled flow of air. The
swirl flow could make PAN solution blanched efficiently.
The blanched solution was stretched until diameter of that
became nano size.
Air outlet
High-speed camera (PHOTRON LIMITED : model
FASTCAM SA4 ) was used for observing mechanism of
CoCaM.
Branching
Scanning Electron Microscope
Scanning electron microscope (JEOL: model
JSM5200) was conducted to observe configuration of
nano fiber. The specimen was mounted on aluminum
holder and gold sputtered for 2 minutes prior observation.
Raman Spectrometry
Raman spectrometer (JASCO Corporation: model
RMP-510RS) was used in order to evaluate crystallinity
Stretched PAN
!
Figure 2. Photograph of stretched PAN solution by High–
speed camera
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Effects of PAN concentration on fiber diameter
SEM photographs of nano PAN fibers are presented
in Figure 5. Shapes of nano PAN fibers are almost
constant and their surfaces are smooth. The diameters of
nano fibers are decreased with the increasing of air
pressure.
SEM photographs of nano PAN fiber that fabricated
by different concentration are presented in Figure 3. The
diameters of nano fibers are decreased with the reducing
of PAN concentration. Moreover, they also reveal
inconstant shapes along nano PAN fibers.
(a)
(e)
(f)
(b)
!
!
(g)
!
!
(c)
(d)
!
Figure 5. SEM observation of nano PAN fiber produced
by different magnitude of air pressure (e) 0.05 MPa, (f)
0.2 MPa and (g) 0.4 MPa.
!
!
Figure 3. SEM photographs of nano PAN fiber produced
by different PAN concentration (a) 3%, (b) 5%, (c) 10%
and (d) 15%.
The effects of PAN concentration on number average
fiber diameter is shown in Figure 4. The minimum and
maximum number average fiber diameter are range from
70 nm to 1980 nm. The reducing of PAN content led to
the decreasing of number average fiber diameter. It is
guessed that PAN content in solution that shaped fiber
was reducing.
Figure 6 shows the relative of air pressure and
number average fiber diameter. The minimum and
maximum number average fiber diameter are range from
340 nm to 2090 mm. The increasing of air pressure led the
decreasing of number average fiber diameter. This result
indicates that high pressure air blow can stretch solution
more efficiently than low pressure air blow.
!
Figure 6. The effects of air pressure on number average
fiber diameter
!
Figure 4. The effects of PAN concentration on number
average fiber diameter
Effects of magnitude of Air pressure on fiber
diameter
Effects of feeding speed on fiber diameter
Figure 7 shows SEM photographs of nano fibers that
were fabricated by using5 rpm and 30 rpm feeding speed.
The nano fibers fabricated by feeding screw speed of 5
rpm are not smooth. These diameters of nano fibers are
decreased with the reducing of rotating screw speed for
feeding solution.
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(h)
The comparison between diameter of nano PAN fiber
and that of nano carbon fiber is presented in Figure 10.
The number average fiber diameter of nano carbon fiber
was decreased about 16% by carbonization.
(i)
!
!
Figure 7. SEM photograph of nano PAN fiber produced
by different feeding speed (h) 5 rpm, (i) 30 rpm.
The effect of a number average fiber diameter by
different feeding speed is shown in Figure 8. The
minimum and maximum number average fiber diameter
are range from 350 nm to 2230 nm. The decreasing of a
number average fiber diameter with the reducing of
amount of feed solution is observed.
!
Figure 10. The comparison between diameter of nano
PAN fiber and that of nano carbon fiber
Raman spectrometry
!
The Raman spectra of nano carbon fiber is shown in
Figure 11. D band has a very shape peak at 1342 cm-1 and
FWHM of D peak is 66.95. G band has a small peak at
1573 cm-1 and FWHM of G peak is 23.87. These peaks
separate completely. The ratio of the D and G peak
intensities (ID/IG) is 0.58. This value indicates high
crystallinity of nano carbon fiber. It is guessed that nano
fiber fabricated by CoCaM is stretched strongly and
polymer chain is aligned.
Figure 8. The effects of feeding speed on number average
fiber diameter
Carbonization
The nano PAN fiber at 3% PAN concentration was
selected to make nano carbon fiber, because they were the
finest nano PAN fibers. As shown in figure 9, SEM
photograph exhibits the remained nano fibers from
carbonization process.
G peak
D peak
!
!
Figure 11. Raman spectra of nano carbon fiber
Figure 9. SEM observation of nano carbon fiber
Conclusions
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In this research, we can find that nano
polyacrylonitrile (PAN) fibers were spun by Cotton Candy
Method (CoCaM) in several processing conditions. After
spinning nano PAN fibers, carbonization of those fibers
were carried out.
Under the observation of High-speed camera, it is
become apparent mechanism of CoCaM. PAN solution
was stretched by swirled flow of air. The swirl flow could
make PAN solution blanched efficiently.
The changing of PAN content, air pressure and
feeding speed have an effect on diameter of nano fibers.
The diameters of nano fibers are decreased with the
reducing of PAN concentration. The diameters of nano
fibers are decreased with the increasing of air pressure.
The diameters of nano fibers are decreased with the
reducing of amount of feed solution.
After carbonizing, shapes of nano fibers were
remained. The number average fiber diameter of nano
carbon fiber decreased about 16% by carbonization.
Raman spectrometry of nano carbon fiber by CoCaM
shows high crystallinity. The ratio of the D and G band
intensities (ID/IG) of carbon nano fiber is 0.58. It is
guessed that nano fibers by CoCaM are stretched strongly
and polymer chain is aligned. CoCaM is a new process for
fabricating nano fibers without high voltage and ion dope.
This technology provides us high-volume production of
nano fibers in a low-cost way.
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