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KyungHee Univ.
Carbon Nanotube Modification Using Gum
Arabic and Its Effect on the Dispersion and
Tensile Properties of Carbon Nanotubes/Epoxy
Nanocomposites
November 9th, 2010
Jorge Ivan
MECHANICAL ENGINEERING

Nano Composite Lab.
 Introduction
 Previous Study
Bandyopadhyaya et al. reported the formation of homogeneous dispersions of
individual MWCNT in Gum Arabic (GA) solution and demostrated that
adsorption of GA led to disruption of the intertube interactions in the crystalline
ropes. [ Nano Letters, Vol. 2, No. 1, 25]
 Bagheri et al. reported that more improved dispersion of MWCNTs was obtained
when MWCNTs were dispersed in GA/modified water soluable polyacrylonitrile
solution rather than in GA solution. [ Mat. Wiss. U. Werkstofftech, Vol. 41, No. 4.]
 Objective
 Find a friendly environmental modification of MWCNTs using natural materials for
MWCNT/epoxy nanocomposites instead of chemical surface modification as acid or
silane treatment and its effect on tensile properties of MWCNTs/epoxy
nanocomposites

Nano Composite Lab.
 Experiment
 MWCNTs CM-95 (Iljin Nanotech, Korea), as reagents nitric acid (60-62 %, Junsei,
Japan) sulfuric acid (95 %, Junsei, Japan), ethanol (99 % Aldrich, USA) distilled water,
 Baker pure water(J.T. Baker USA), Gum Arabic (Junsei, Japan)
Epoxy resin (DGEBA, Kukdo Chemical, Korea)
Hardener (PAA, Kukdo Chemical)
 Materials & Methods

Nano Composite Lab.
 The surface-modification of the MWCNTs was performed as follows :
 - Three grams of untreated MWCNTs were dispersed in 300 ml of
concentrated H2 SO4/HNO3 (3:2 v/v) solution at 50 C and stirred for 20 h.
The solution was filtered with distilled water until a neutral PH was
obtained to eliminate mixing and acid solution. The resulting oxidized
MWCNTs were then dried under vacuum at 80 C. for 12 H.

Nano Composite Lab.
 Experiment
The Gum Arabic modification of MWCNTs (G-MWCNTs) was performed as follows.
Ten grams of Gum Arabic (GA) was dissolved in 200 ml of distilled water and stirred
for 30 min.
Then, two grams of untreated CNTs was dispersed in the GA solution and stirred for
1 h. The Gum treated MWCNTs (G-MWCNTs) were separated by filtration using
ethanol and dried under vacuum ..

Nano Composite Lab.
 Experiment
Fabrication of MWCNT/epoxy nanocomposites and characterization:
 U-MWCNTs, O-MWCNTs, and G-MWCNTs were dispersed in the ethanol solution
and ultrasonication was performed for 5 min.
 After sonication, 0.3 wt. % each of U-MWCNTs, O-MWCNTs, and G-MWCNTs were
mixed with the epoxy resin and then stirred for approximately 2 h at 80 C to
completely evaporate the ethanol.

Nano Composite Lab.
Experiment
 . After removing the ethanol, a hardener was added (epoxy and hardener
at a 2:1 ratio) and the mixture poured into a Teflon mold.
 The mixture was de-gassed in a vacuum oven at 760 mm Hg for 30 min
and hardened in an oven at 60 C for 6 h.
 Tensile specimens were machined and tensile tests were performed in a
universal test machine according to the ASTM D 638. Fracture surfaces of
the nanocomposites were observed by high-resolution scanning electron
microscope (HR-SEM).

Nano Composite Lab.
Results & Discussion
Dispersed MWCNTs.
Fig. 1. Sedimentation of dispersed MWCNTs (A: unmodified MWCNTs, B: acid-
treated MWCNTs, C: Gum Arabic treated MWCNTs) in distilled water (a) 10 min
after ultrasonication, (b) 240 h after ultrasonication.

Nano Composite Lab.
http://web.khu.ac.kr/~nanocomp/
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Unmodified, acid-treated, and Gum-treated MWCNTs (U-MWCNTs, O-MWCNTs, and G-
MWCNTs) were dispersed in distilled water via ultrasonication to determine the effect of
Gum treatment on dispersion in the aqueous solution. As shown in Figure 1a, U-MWCNTs,
O-MWCNTs, and G-MWCNTs showed good dispersion in distilled water after 10 min of
ultrasonication.
 However, the U-MWCNTs gradually settled due to their agglomeration and hydrophobic
nature, whereas the O-MWCNTs and G-MWCNTs exhibited good suspension stability
even after 240 h of sonication.
 Results & Discussion

Nano Composite Lab.
TEM
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100 nm
(a)
20 nm
(b)
20 nm100 nm
100 nm 20 nm
(c)
Fig. 2. TEM images of dispersion states : (a) untreated MWCNTs, (b)
oxidized MWCNTs, (c) Gum treated MWCNTs

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The microscopic structures of MWCNTs with different surface modifications were
investigated using TEM. Figure 2 presents TEM images of U-MWCNTs, O-MWCNTs, and
G-MWCNTs. As shown in Fig. 2a, the U-MWCNTs were severely agglomerated and their
end tips were closed, which are the features of unmodified MWCNTs.
 for O-MWCNTs, as shown in Fig. 2b, the agglomeration of the carbon nanotubes was
reduced and the end tips of many carbon nanotubes were open, which enables the
generation of functional groups at the open ends. Similar dispersion results were obtained
for Gum treated MWCNTs.
As show in Fig. 2c, the dispersion of the nanotubes was significantly improved compared
to that of the U-MWCNTs. Figure 2 also shows that the MWCNTs retained their external
average diameter of 10-15 nm after oxidation and Gum treatment, which is in good
agreement with the suspension stabilities described in Fig. 1.

Nano Composite Lab.
Stress-Strain
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Fig. 3 Tensile stress-strain curves of unmodified, oxidized, and Gum
treated MWMWCNT/epoxy nanocomposites

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Figure 3 shows typical tensile stress-strain curves of the MWCNTs/epoxy
nanocomposites with unmodified, oxidized, and Gum-treated MWCNTs. As shown in the
figure, the stress increased almost linearly with strain at an early stage, and then nonlinear
behavior occurred before reaching the maximum stress for the three nanocomposites.
 In particular, the tensile strength and the modulus of the MWCNT/epoxy nanocomposites
were improved by the oxidation and Gum treatment of the nanotubes. However, the
functionalized MWCNTs resulted in more brittle tensile behavior.

Nano Composite Lab.
Tensile strength
Fig. 4. Comparison of tensile strength of unmodified, oxidized,
and Gum treated MWMWCNT/epoxy nanocomposites.

Nano Composite Lab.
Figure 4 shows the comparison of the tensile strengths of untreated, acid-treated, and
Gum-treated MWCNT/epoxy nanocomposites, in which the tensile strength was
determined as the maximun stress in the stress-strain curve.
 As shown in the figure, the tensile strength was on the order of the G-MWCNT, O-
MWCNT, and U-MWCNT/epoxy nanocomposites. Specifically, the tensile strength of the
G-MWCNT/epoxy nanocomposites was 22 % higher, and Oxidized-MWCNT/epoxy was
15 % higher than that of the U-MWCNT/epoxy nanocomposite.


Nano Composite Lab.
Elastic Modulus
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Fig. 5. Comparison of elastic modulus of unmodified, oxidized, and Gum
treated MWMWCNT/epoxy nanocomposites.

Nano Composite Lab.
RESULTS & DISCUSSION
The elastic modulus was determined by measuring the slope in a linear region of the
stress-strain curve. Figure 5 shows the comparison of the three nanocomposites. Similar
the tensile strength results, the elastic modulus was improved by the Gum treatment, with
the elastic modulus of the G-MWCNT/epoxy nanocomposite being higher than that of the
O-MWCNT/epoxy nanocomposites.
 The elastic modulus of the G- MWCNT/epoxy nanocomposites was 29 % higher, and the
O-MWCNT/epoxy nanocomposites was 13 % higher than that of the U-MWCNT/epoxy
nanocomposites.

Nano Composite Lab.
TEM
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TEM
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Fig. 6 SEM photographs of fracture
surfaces of (a) unmodified, (c) oxidized,
and (e) Gum treated MWMWCNT/epoxy
nanocomposites ; (b), (d), (f) are magnified
images of boxed region in (a), (c), (e),

Nano Composite Lab.
 Conclusions
 The improved dispersion stability of Gum treated MWCNTs was due their
enhanced negative ion abilities due to the functionalization effect on their
surfaces.
 TEM analysis showed that little damage occurred on Gum-treated
MWCNTs compared to acid-treated MWCNTs.
The Tensile strength and modulus of G-MWCNTs/epoxy nanocomposites
were improved by 22 % and 29 % respectively, compared to the U-
MWCNTs/epoxy nanocomposites, whereas the improvements were 15 %
and 13 % respectively, over O-MWCNTs/epoxy nanocomposites.

Nano Composite Lab.
 Conclusions
This enhacement is attributed to the good dispersibility and strong
interfacial bonding energy between the functionalized MWCNTs and the
epoxy matrix. It was concluded that the functionalization of MWCNTs with
Gum Arabic is effective in improving dispersion and adhesion in an epoxy
matrix.

Nano Composite Lab.
THANK YOU FOR YOUR
ATTENTION

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