World Journ
a
doi: 10.4236/w
j
Copyright © 2
0
En
h
Abstract:
Nanocompo
s
standard cal
e
epoxy resin
man spectro
epoxy resin
c
and Raman
i
laser power.
toughness o
f
Keywords:
1. Introdu
c
Iijima discov
e
Single-walle
d
b
ased structu
r
graphite rolle
d
and 1 nm in
d
(MWCNT) a
r
of graphite s
h
several micro
pending on t
h
like structure
,
chanical pro
p
dynamics mo
d
His study su
g
CNT are not
s
the Young’s
m
be  0.45 TP
a
Yu et al [4]
u
measure the
found the ten
s
of 11-63 GPa
Their exc
e
length to dia
m
composite re
i
b
ased compo
s
a
l o
f
Nano Sc
i
j
nse.2011.1100
1
0
11 SciRes.
h
ancem
e
Departmen
t
Recei
v
s
ites consisti
n
e
ndaring tec
h
by weight t
o
scopy tests
w
c
omposite.
T
i
ntensity also
Also, nano
h
f
epoxy resin
Epoxy Resi
n
Elasticity
c
tion
e
red carbon n
a
d
carbon nanot
u
r
es that can b
e
d
into a cylin
d
d
iameter [2].
M
r
e similar to S
W
h
eets in the cy
l
ns in length
a
h
e number of
l
,
CNT are ex
p
p
erties. Lu [3]
d
el to predict
t
g
gested that t
h
s
ensitive to si
z
m
odulus to be
a
, and the bul
k
u
sed an atomi
c
mechanical
p
s
ile strength a
n
and 270-950
G
e
llent mechan
i
m
eter ratio
m
i
nforcement.
R
s
ites has focus
e
i
ence and En
g
1
Published On
l
e
nt of
E
C
t
of Mechanic
a
v
ed February
1
n
g of multi
w
h
nique. In t
h
o
produce th
e
w
ere used to
T
he results sh
o
affected wit
h
h
ardness incr
improved w
i
n
; Multiwall
a
notubes (CN
u
bes (SWCN
T
e
viewed as a
d
er several m
i
M
ultiwalled c
WCNT but w
l
inder structur
e
a
nd 5-50 nm
i
l
ayers. Due t
o
p
ected to hav
e
adopted an
e
t
he elastic pro
p
h
e elastic pro
p
z
e and chirali
t
1 TPa, the s
h
k modulus to
c
force micro
s
pr
operties of
n
d modulus to
G
Pa respectiv
e
i
cal propertie
m
ake CNT ve
r
R
ecent researc
e
d on polyme
r
g
ineerin
g
, 201
l
ine March 201
1
E
lastic
M
C
arbo
n
Vijay K
u
a
l Engineerin
g
a
1
, 2011; revise
d
w
all carbon n
a
h
is study, 3
%
e
multiwall c
a
obtain the
m
o
w that the
R
h
the reinfor
c
eased with i
n
i
th the additi
o
Carbon Nan
o
T) in 1991 [1
T
) are fulleren
e
single sheet
o
i
crons in leng
t
arbon nanotu
b
ith many laye
r
e
. MWCNT a
r
i
n diameter d
e
o
their graphit
e
e
excellent m
e
e
mpirical latti
c
p
erties of CN
T
p
e
r
ties of S
W
t
y and predict
e
h
ear modulus
t
be  0.74 TP
s
cope (AFM)
t
MWCNT a
n
be in the ran
g
e
ly.
s and superi
o
r
y attractive f
o
h on nanotub
e
r
matrix comp
o
1, 1, **
1
(http://www.s
c
M
odul
u
n
Nano
t
u
mar Srivas
t
g
, Indian
I
nstit
u
a
d
March 4, 20
a
notubes (M
W
%
multiwall
a
rbon nanot
u
m
odulus of
e
R
aman intens
c
ement of m
u
n
crease of
m
o
n of multiw
a
o
tubes; Nan
o
].
e
-
o
f
t
h
b
e
r
s
r
e
e
-
e
-
e
-
c
e
T
.
W
-
e
d
t
o
a.
t
o
n
d
g
e
o
r
o
r
e
-
o
-
sites.
Q
showe
d
42% i
n
in the
t
p
osites
electro
n
able t
o
reinfor
c
extrao
r
interfa
c
is ver
y
interfa
c
p
redict
using
t
calcul
a
b
e in t
h
mole c
u
tions t
o
PS co
m
CNT f
r
cial fi
b
fibres
i
it was
efficie
n
compo
s
strengt
h
c
irp.org/journal
/
w
u
s of E
p
t
ubes
t
ava
u
te of Techno
l
il.com
11; accepted
M
W
CNT) and
carbon nano
u
bes/epoxy c
o
e
lasticity an
d
ity increased
u
ltiwall carb
o
m
odulus of el
a
a
ll carbon na
n
o
hardness; R
Q
ian et al [5]
c
d
that the addi
t
n
crease in the
t
ensile strengt
h
. They observ
n
microscope
o
bridge the c
r
c
ements in co
m
r
dinary mecha
n
c
ial bonding b
e
y
critical. Wa
n
c
ial shear str
e
the CNT-
p
o
l
t
he critical le
n
a
ted the CNT-
p
h
e range of 50
u
lar mechanic
s
o
predict the
i
m
posite syste
m
r
om the matri
x
b
re-
p
olymer s
h
i
n epoxy matr
i
concluded th
a
n
t interfacial
s
s
ites. In addi
t
h
, it was repo
w
jnse)
p
oxy R
e
l
ogy, Varanasi
,
M
arch 10, 201
epoxy resin
tube particl
e
o
mposite. N
a
d
Raman int
e
with the inc
r
o
n nanotubes
a
sticity, whi
c
n
otubes.
a
man Spectr
o
c
onducted an
e
t
ion of 1 wt%
elastic stiffne
s
h
for polystyr
e
d CNT pull-
o
(TEM) that
r
ack in the P
S
m
posites. In o
r
n
ical properti
e
e
tween CNT
a
n
ger [6] obtai
n
e
ngth to the c
l
ymer interfa
c
n
gth from 10
0
p
olymer inter
f
-250 MPa. Li
o
s
simulations
i
nterfacial cha
r
m
. They sim
u
x
and calculat
e
h
ear strength o
f
i
x usually ran
g
a
t a CNT-
p
oly
m
s
tress transfer
t
ion to the i
m
r
ted that Vic
k
e
sin wi
t
,
I
ndia
1
were produ
c
e
s were disp
e
a
nohardness
a
e
nsity of M
W
r
ease of Ra
m
and 1% exp
o
c
h indicated
o
scopy; Mo
d
e
xperimental s
t
CNT resulte
d
s
s and a 25%
ene (PS) –
b
a
s
o
ut in the tran
s
suggested C
N
S
matrix and
r
der to fully u
t
e
s of CNT, t
h
a
nd the polym
e
n
ed the fibre
-
ritical aspect
c
ial shear str
e
0
to 500 nm.
f
acial bond st
r
o
and Li [7] p
e
and elasticity
r
acteristics o
f
u
lated the pu
l
e
d the CNT-P
S
f
high modul
u
g
es from 50-1
m
er can achi
e
than current
a
m
provement i
n
k
ers hardness
o
WJNSE
t
h
c
ed by a
e
rsed in
a
nd Ra-
W
CNTs/
m
an shift
o
sure of
that the
d
ulus of
t
udy and
d
in a 36-
increase
s
ed com-
s
mission
N
T were
serve as
t
ilize the
h
e strong
e
r ma
t
rix
-
polymer
ratio, to
e
ngth by
Wagner
r
ength to
e
rformed
calcula-
f
a CNT-
l
l-out of
S
interfa-
u
s carbon
00 MPa,
e
ve more
a
dvanced
n
tensile
o
f epoxy

V. K. SRIVASTAVA
increased by 20% with an additional 2 wt% CNT [8-12].
It is evident that CNT can be potentially used to rein-
force the polymer and improve the mechanical properties.
However, no experiment has come ever demonstrated a
CNT based composite with better performance than cur-
rent advanced polymer composites. For further advances
in this area, researchers pointed out that several critical
issues such as improvement in polymer interfacial bond-
ing, MWCNT interwall sliding under tension, CNT dis-
persion and alignment and polymer matrix shrinkage
during the process must be addressed [11]. These issues
may contribute to the uncertainty of manufacturing
CNT/polymer composites with desired characteristics.
Raman spectroscopy has historically played an impor-
tant role in the study and characterization of graphite
materials, being widely used over the last four decades to
characterize pyrolytic graphite, carbon fibres, glassy and
carbon nanotubes [12]. For sp2 nanocarbons such as
Graphene and carbon nanotubes, Raman spectroscopy
can give complete information about crystallite mate-
rials. In this article, Raman spectroscopy, nanohardness
and scanning electron microscopy were used to see the
effect of multiwall carbon nanotubes in the elastic mod-
ulus of epoxy resin. Our hypothesis is that the CNT will
serve as an excellent reinforcement to toughen the epoxy
resin due to its small scale, excellent mechanical proper-
ties and good chemical compatibility with the composite
adherends.
2. Experimental Details
Araldite, LY-556 (55%), hardener, HY-917 (49%) and
accelerator, DY-070 (0.28%) were used as epoxy resin.
3% multiwall carbon nanotubes filled epoxy resin (LY-
556) were produced using a lab-scale three-roll-mill (Ex-
akt 120 E), which enables the introduction of very high
shear forces (up to 200,000 s–1) throughout the suspen-
sion. The pre-dispersed suspension was then given bat-
chwise onto the roll with dwell times of 2 min. The dis-
persive forces on the suspension were acting in the gap
(5 µm) between the rolls. After dispersion of the nano-
particles in the resin LY-556, the hardener and accelera-
tor are usually added in a vacuum dissolver in order to
avoid trapped air in the suspension. Then the mixture
was placed in a vacuum chamber for 20 min to eliminate
the bubbles introduced during the rolling process.
Raman spectroscopy is nondestructive and readily
available and measurements can be made over a wide
range of temperature or pressures. It can provide unique
information about vibrational and electron properties of
the material. Even though it is not a direct method, it can
also be used to determine the structure of the material
and allows the identification of materials through the
characteristics vibrations of certain structures. Because
the Raman intensity of a vibration in a crystal depends
on the relative directions of the crystal axis and the elec-
tric wave polarization of the incident and scattered light.
Therefore, Raman spectroscopy was used to determine
the differences in Raman intensity of epoxy resin, MW-
CNTs/epoxy resin composite and 1% laser power ex-
posed MWCNTs/epoxy resin composite.
The indentation method has become a standard way to
measure the mechanical properties of thin-film and small-
scale structures. A depth-sensing indenter, i.e. nanoin-
denter, can measure the indentation displacement (h) and
elastic contact stiffness (S) during a programmed inden-
tation loading process, where S is defined as:
d
dc
P
Sh  (1)
where P is the indentation load, and ݄௖ is the elastic
component of h. Using the data analysis method pro-
posed by Oliver and Pharr [13], the contact depth, ݄௖,
can be estimated by
€
cP
hh S  (2)
where € is a constant, 0.75. Then, based on the predeter-
mined indenter tip geometry, we can calculate the pro-
jected contact area (A) from ݄௖. Finally, the elastic mod-
ulus (E) and the hardness (H) of materials can be calcu-
lated by
2
r
J
IS
E
A
 (3)
P
H
A

(4)
Here ܧ௥ is the reduced modulus defined as
2 21
1i
ri
EEE




 (5)
where E and µ are Young’s modulus and Poisson’s ratio
of the indented material respectively; and Ei and µi are
the corresponding values of the indenter tip. H is the
mean pressure under the indenter.
The nanohardness and the elastic modulus of the
epoxy resin and MSCNTs/epoxy resin composite were
determined using a Nano Indentation tester (CSM in-
strument). A triangular pyramid Berkovich indenter was
used, its indent shape and side view angles were 65.3 and
77.05 respectively. The poisson’s ratio of the samples
were estimated as µ = 0.3, because in the calculations of
elastic modulus, an error in the estimation of the Poisson
ratio does not produce a significant effect on the result-
ing value of the elastic modulus. Three indentations were
carried out to depth of 1000 nm where the indentation
was kept for 10 s before unloading. The loading and the
unloading rate were 10 mN min–1.
Finally, scanning electron microscopy was used to
identify the effect of MWCNTs in the epoxy resin.

V. K. SRIVASTAVA
3. Results and Discussion
In this study MWCNT were dispersed by three mill roll-
ing machine in an epoxy resin, with the aim of improving
mechanical properties of MWCNTs/epoxy resin compo-
site. First of all the effect of the presence of MWCNT in
the epoxy resin was investigated by Raman spectroscopy
technique. Figure 1 shows the Raman spectrum of epoxy
resin, MWCNT/epoxy resin and 1% laser power exposed
MWCNT/epoxy resin. These spectral features are clearly
distinguishing the variation in Raman intensity. Because,
when the bond lengths and angles of graphene are mod-
ified by strain, caused by the interaction with a substrate
or with other graphene layers or due to external perturba-
tion, the hexagonal symmetry of graphene is broken. It
was observed that the Raman spectra intensity increases
with increasing the shift angle up to 300 cm–1 and gradu-
ally decreases with increasing of shift angle after 400 cm–1.
These spectral features are similar for epoxy resin,
MWCNTs/epoxy resin and 1% exposed laser power
MWCNTs/epoxy resin composites. Eight peak signal
bands are identified from epoxy resin sample at different
Raman shift values; 620, 835, 1140, 1240, 1460, 1600 cm–1.
The height of these eight signals is gradually reduced
with the addition of MWCNTs and exposure of laser
power of epoxy resin, indicating a dilution effect of the
MWCNTs when blended with epoxy resin. It is believe
that epoxy resin exerts a pressure on the individual tubes,
which leads to an increase of the breathing mode fre-
quencies. Therefore bands are highly sensitive to micro-
structure effects and can be used to probe any modifica-
tion to the flat geometric structure of resin. The micro-
structure effects induced by multiwall carbon nanotubes
or by exposure of laser power. This shows the effect of
CNTs and laser power exposure on epoxy resin, because,
the interaction between nanotubes and resin polymer is
reflected by a peak shift or peak width change. Visible
change in the epoxy resin peak locations as a result of the
insertion of nanotubes could be detected.
The Raman intensity can vary when multiwall nano-
tubes interact with elements; this can be used to examine
the structure of the interface and obtain information
about the nature, localization and force of the interaction.
After the nanotubes were dispersed in epoxy resin, Ra-
man intensity was observed towards lower intensities,
evidence that MWCNTs were no longer in direct contact
with one another tubes. Also, Raman intensities were
decreased with the exposure of laser power. These show
that Raman spectroscopy is a useful and reliable tool for
the investigation of nanotubes dispersion in epoxy resin.
The influence of scratch load on mechanical response
of multiwall carbon nanotubes in epoxy resin was inves-
tigated by nanoindentation test. Nanohardness and elastic
modulus patterns of the epoxy resin and MWCNT/epoxy
resin specimens are reported in Figure 2. The results
show that the nanohardness increases with increase of
elastic modulus. MWCNTs filled epoxy resin gives
higher value than the epoxy resin, because MWCNTs
improve the mechanical properties of epoxy resin [5-7].
Based on the experimental observation, one can derived
that following expression to obtain modulus of elasticity
from nardness,

12
4.9 0.86EH (6)
where E and H are the elastic modulus and nanohardness.
The micrograph shows the dispersion of MWCNT in
an epoxy resin area as can be seen in Figure 3. Only few
small aggregates are remaining, which are smeared out
and well penetrated by the epoxy resin matrix. MWCNT/
epoxy resin composite containing 3% MWCNT exhibit a
significant increase in fracture toughness and strength, as
well as an enhancement of stiffness, due to resistance of
cracks propagation [8], as can be identified from Figure
4. It is also clear that CNT particles resist the formation
of crack path due to increase of toughness of MWCNT
filled epoxy resin. The mechanisms of increasing the
fracture toughness of polymers due to incorporation of
particles have been extensively studied within the last
three decades [14]. The application of micro-particles
exhibits the highest effect in brittle matrix systems. A
clear difference in the distribution pattern and agglome-
rate sizes can be seen between MWCNT and epoxy resin
and their interface appears to be much more homogene-
ous, suggesting a greater dispersion. Figure 5 shows that
MWCNT particles strongly bonded with the epoxy resin
and it appears like sprouts, because of toughening effects
of particle [7]. The epoxy resin is modified by the ad-
dition of MWCNT, which participates in minimizing
the crack initiation or the propagation by crack block-
ing or bridging, as can be identified in Figure 4. The
extensive MWCNT bridging seen in micrographs are
well in agreement with the prior explained mechanisms,
MWCNT-bridging effect enhanced the fracture tough-
ness [6].
The most important micro-mechanical mechanism
leading to an increase in fracture toughness are due to
localized inelastic matrix deformation and void nuclea-
tion, particle/fibre debonding and deformations [5]. The
characteristics of the matrix polymer are also important
for the reinforcing effect of nano-scaled fillers. In gener-
al, the plastic zone size of brittle epoxy resin is relatively
small. When a resin is filled with nano-particles, a signif-
icant amount of particles occur in the plastic zone, while
in a composite with micro-particles, only a minor num-
ber of them are involved in the plastic zone deformation
process. This is clear evidence that the main fracture
mechanical mechanism is related to the enormous surface

V. K. SRIVASTAVA
Figure 1. Variation of Raman intensity versus Raman shift from (a). epoxy resin, (b). MWCNTs/epoxy resin
and (c). 1% laser power exposed MWCNTs/epoxy resin.
Figure 2. Variation of nanohardness with elastic modulus of epoxy resin and MWCNTs/epoxy resin composites.
area of nano-particles in general. Since, all composites
exhibited a partly agglomerated dispersion of the filler,
leading to increase in the toughness can be expected to
localized inelastic matrix deformation, void nucleation
and crack deflection at the agglomerates [7]. Therefore,
it is clear from micrographs that resin rich area fractured
due to the appearance of shear stress, which increases the
adhesive bond strength of ceramic composites. This can
be explained by the higher surface area of the double
wall carbon nanotubes, which may result in a better load
transfer efficiency at the interface region as well as
amine functional groups over CNTs which is supposed to
promote the dispersion and pronounced covalent bonding
to some extent.
4. Concluding Remarks
In this article, the effect of multiwall carbon nanotubes in
epoxy resin was characterized by the Raman spectrosco-
py and nanohardness indentation methods. The elastic
0.2
0.22
0.24
0.26
0.28
0.3
0.32
4.9555.05 5.1 5.15 5.2 5.255.3 5.35
Nanohardness,GPa
Elasticmodulus,GPa
Epoxy resin
MWCNT with epoxy resin

V. K. SRIVASTAVA
Figure 3. SEM micrograph showing the dispersion of MWCNT particles in the resin rich area.
Figure 4. SEM micrograph showing the enhancement of cracks path with MWCNT particles.
Figure 5. SEM micrograph shows the interface bond of MWCNTs with resin.

V. K. SRIVASTAVA
modulus and nanohardness can be related as

12
4.9 0.86EH . Also, it was found that 3 wt%
MWCNT loading showed good dispersion capability in
the epoxy resin, which increases the elastic modulus of
neat epoxy resin up to 15%. However, elastic modulus
increases with increase of nanohardness, whereas Raman
intensity reduces abruptly with the inclusion of MW-
CNTs and exposure of 1% laser power.
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