Thermo mechanical and morphological interrelationshio of polypropylene-multiwalled carbon nanotubes nanocomposites.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
29
THERMOMECHANICAL AND MORPHOLOGICAL INTERRELATIONSHIP OF
POLYPROPYLENE-MUTIWALLED CARBON NANOTUBES (PP/MWCNTs)
NANOCOMPOSITES
A.R., Jeefferiea, M.Y. Yuhazria, O. Nooririnaha, M.M. Haidira, Haeryip Sihombingb, M.A.,
Mohd Sallehc, N.A., Ibrahimd
a
Engineering Materials Department, bManufacturing Management Department, Faculty of Manufacturing Engineering,
Universiti Teknikal Malaysia Melaka, Durian Tunggal, 76109, Melaka, Malaysia.
c
Chemical Engineering Department, Faculty of Engineering, dChemistry Department, Faculty of Science, Universiti
Putra Malaysia, 43400 UPM, Serdang, Selangor Darul Ehsan, Malaysia.
Email: jeefferie@utem.edu.my
Abstract - In this research, the significance effects of
MWCNTs at lower percentage addition in affecting the
thermomechanical behavior of the fabricated PP/MWCNTs
nanocomposites
were
studied.
PP/MWCNTs
nanocomposites were compounded by using the internal
mixer, through the simple melt blending technique. The
improvement effects of MWCNTs addition were well
justified by the transmission electron microscopy (TEM)
surface morphological observation. The interrelationships
between the TEM surface observations with the
thermomechanical
results
were
established
by
manipulating the three major plots of dynamic mechanical
analysis of storage modulus, loss modulus and damping
modulus (tanδ). From this work, it was found that the
improvement of dynamic thermomechanical properties is
directly related to the amount of MWCNTs added and the
quality of MWCNTs dispersion within the PP matrix.
or materials stiffness. It provides the information on elastic
response to the deformation resistance [3]. The remarkable
increased in composite thermo-mechanical stability cannot
be only understood by the interactions between the
polymer chains and carbon nanotubes (CNTs) surface, but
the formation of a percolating entangled CNTs network
within the materials has to be taken seriously into
consideration [4]. Entanglements within a fibrous structure
are indeed responsible for the elastic response of the
composites structure [4].
1.0 INTRODUCTION
However, entanglements between the CNTs appear to have
a low effect on the mechanical reinforcement. Thus, the
increase in modulus is mainly due to stress transfer
between the matrix and CNTs. In filled polymer systems,
the presence of fibers perturbs the normal flow of polymer
and hinders the mobility of chain segments in flow. The
type of polymers (semicrystalline or amorphous), the glass
transition temperature of the polymers, the filler type,
geometry (including aspect ratio), concentration and the
interaction of the fillers to the matrix molecular chains are
all the factors which affecting the molecular motions
within the matrix [1]. These are the factor which affects the
behavior of the storage modulus curve.
Most fillers and reinforcements are purely elastic systems
while the polymer and the filler/polymer interface are
viscoelastic. A better understanding of the dynamic
thermo-mechanical properties of the composite will help to
define structure/property relationships and subsequently to
relate these properties to the product final performance [1].
Dynamic mechanical analysis (DMA), measures the
response of a given material to a cyclic deformation as a
function of temperature [2]. DMA provides information on
storage modulus, loss modulus and damping factor
behavior of materials. The dynamic storage modulus (G’)
is approximately similar to the Young or elastic modulus,
Loss modulus (G’’) indicates the materials ability to
dissipate energy, often in the form of heat or molecular
rearrangements when there is deformation occurred [5]. It
indicates the viscous nature of the polymer and gives
information about the viscous or energy dissipation during
the flow [6]. G’’ is also directly related to the amount of
amorphous PP chain involved in the transition [5]. As the
CNTs loading increased, there is a little mobility of the PP
chain. This limitation in the mobility of chain was
indicated by little amplitude differences, which indicates
that a slow movement of chain and the viscosity of
polypropylene (PP) filled multiwalled carbon nanotubes
Keywords:
Thermomechanical,
PP/MWCNTs
nanocomposites, Surface morphological, Interrelationships.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
(MWCNTs) composites were considerably higher or more
viscous [7]. The damping factor (tanδ) is the ratio of the
loss modulus to the storage modulus. It may also be
obtained as the ratio of the real part to the imaginary part
of the complex viscosity [1]. The damping factor (tanδ)
provides information on the relative contributions of the
viscous and elastic components of a viscoelastic material.
It is very useful for determining the occurrence of
molecular mobility transition such as the glass transition
temperature which also represents the ability to the heat
resistance [1].
Through this study, the effects of lower percentages of
MWCNTs filler addition to the thermomechanical
properties of fabricated PP/MWCNTs nanocomposites
were investigated. The efficacy of the internal mixer
method to compound the MWCNTs within the PP matrix
was tested in the course of transmission electron
microscopy (TEM) observation. The interrelationships
between the microscopy observations to the final
thermomechanical results were further established. It is
anticipated that the nanocomposites compounding by using
this route much probably will gives better nanofiller
homogenization within the polymer matrix which resulting
better end properties of the fabricated nanocomposites. In
parallel, it is also interesting to observe the significant
effect caused by the addition of extremely lower
percentages of MWCNTs to the mechanical properties,
subject to the thermal and mechanical effects.
30
2.3. DMA Thermomechanical Analysis of PP/MWCNTs
Nanocomposites
The compression molded sample plaques were cut into
rectangular shape with the dimension of ~12.6 mm in their
length, ~5.0 mm in their width and ~1.0 mm in their
thickness. The measurement was carried out using a three
point bending fixture of dynamic mechanical analyzer
(DMA) model Perkin Elmer TE. The samples were
subjected to an oscillating frequency of 1 Hz and 10 µm
oscillating amplitude in the temperature ranges of -50°C to
150°C at the heating rate of 2°C/min. The signals are
automatically used to determine the dynamic storage
modulus (G’), loss modulus (G’’) and the damping factor
(tanδ), which were plotted as a function of temperature.
The tanδ peak was taken as the glass transition temperature
(Tg) of the tested samples. To verify the thermomechanical
experimental results, the surface morphologies observation
from the transmission electron microscopy (TEM)
observation were conducted.
(a)
2.0 METHOD
(b)
2.1. Raw Materials
Thermoplastic PP grade Titan Pro SM950 used as matrix
material was purchased from Titan Petchem (M) Sdn. Bhd.
As-produced MWCNTs which synthesized by the floating
catalysts chemical vapor deposition (FC-CVD) method are
used as filler reinforcement. As-produced MWCNTs with
55% of purity are depicted as in the Figure 1.
Figure 1: As-produced MWCNTs observed through
HRTEM imaging
2.2. Preparation of PP/MWCNTs Nanocomposites
2.4.
PP/MWCNTs nanocomposites were prepared by melt
blending process in an internal mixer using Thermo Haake
PolyDrive with Rheomix R600/610 at 175°C of
compounding temperature and 60 rpm of roller rotor speed.
Eight minutes of compounding period were allocated and
required amount of MWCNTs (0, 0.25, 0.50, 0.75 & 1.00
wt %) were added at the midst of compounding duration.
The compounded recipes were then compression molded
using HSINCHU hot press machine for 5 minutes preheat
and another 5 minutes of compression period under the
pressure of 150 kg/cm2 at 185°C. The sheets obtained were
immediately cooled for 10 minutes of cooling cycle.
Surface Morphological Observation through TEM
TEM observation was performed to the ultra-thin section
of the PP/MWCNTs nanocomposites film as to check the
dispersion state of MWCNTs added within the PP matrix.
The observation was conducted by using the TEM-100
CX-II (JEOL Co., Japan), at an acceleration voltage of 120
kV. The specimens were prepared by using a Leica ultracut microtome equipped with a cyro-chamber. Thin
sections of about 100 nm were prepared by using a
diamond knife at -80°C of liquid nitrogen temperature.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
3.0 RESULTS AND DISCUSSION
Storage
Modulus
Nanocomposites
(G’)
9
4x10
of
PP/1.00 wt.% MWCNTs Composites
PP/0.75 wt.% MWCNTs Composites
PP/0.50 wt.% MWCNTs Composites
PP/0.25 wt.% MWCNTs Composites
PP Virgin (Control Sample)
PP/MWCNTs
Figure 2 displayed the plot of storage modulus (G’) as a
function of temperature for the PP/MWCNTs
nanocomposites with different weight percentage addition
of MWCNTs. Storage modulus curve for pure PP is
overlaid as for the comparison purpose. Basically, at the
initial stage of analysis, the Figure 2 shows the storage
modulus of the samples increases from about 1.50x109 to
3.25x109 Pa with the increasing amount of MWCNTs. A
mechanical reinforcement effects are increasing with the
nanotubes content [4], [8].
The stiffness effects introduced by MWCNTs enable the
PP to sustain high storage modulus value [1]. This also,
will suggest that the MWCNTs added behaves as good
reinforcement and allow homogeneous stress transferred
from the matrix to the fiber. As the fiber loading increased,
the stress is more evenly distributed and thus will increase
the storage modulus [9]. As can be seen, the initial value of
storage modulus is higher for each sample at the subambient temperature due to the facts that, at this stage the
molecules are in the frozen state, therefore they retain high
stiffness properties in the glassy condition [2]. E’ is higher
when the molecular movement is limited or restricted and
it consequently will caused the storage of mechanical
energy increased [10], [11]. The stiffening effect was more
remarkable at lower temperature. This phenomenon was
explained by the mismatch in coefficient of thermal
expansion between the matrix and inorganic fillers, which
might allow better stress transfer between matrices and
fillers at low temperatures [11].
The storage modulus curves for each sample is decrease
dramatically with the increase of temperature from -30 to
80°C. This finding is in agreement with the works done by
many researchers [1], [2], [4], [5], [10]. The pattern of
decrement in the storage modulus value with the increasing
temperature is due to the fact that PP reaches its softening
point therefore reduced the elastic response of the material.
With the increase of temperature to the melting
temperature, the storage modulus of the composites was
dominated by the matrix intrinsic modulus [1]. As the
temperatures approaches the glass transition temperature
region, there is a large drop in the storage modulus values,
indicating the phase transition from the rigid glassy state
where the molecular motions are restricted to a more
flexible rubbery state and the molecular chains have
greater freedom to move. When the polymer is viscous, as
only few entanglements exist between nanotubes, the
composite will flow because of interaction between
polymer chains and nanotubes [4].
9
3x10
E' (Pa)
3.1
31
9
2x10
9
1x10
0
-30
-20
-10
0
10
20
30
Temperature (°C)
40
50
60
70
Figure 2: Variation of storage modulus (G’) of
PP/MWCNTs composites as a function of temperature
When the PP polymer and its composites are heated above
their Tg, an increase in free volume typically occurs
followed by an increase in molecular mobility [10]. Under
this situation, the chain segments gradually align with the
applied force [5]. When this occurs, the E’ decreased.
However there is no distinct characteristic peak of the
storage modulus can be detected to determine the Tg for
the tested samples. Thus damping factor or loss modulus
curves will be utilized for this purpose.
As can be seen, the presence of different loading of
MWCNTs filler in the matrix of PP even at a lower
percentages of weight, is still capable to keep retain the
pattern of the curve where the higher the filler content, the
higher the storage value, with regards to the temperature
factor. This phenomenon is in agreement with the work
done by McNally et al., (2005), where they found that
addition of low loadings of MWCNTs were also more
effective at increasing the dynamic mechanical storage
modulus of polyethylene composites [12]. It is observed
that the curves tend to converge to that of pure PP when
approaching the melting temperature of PP. This
convergence at higher temperature explains the successful
exploitation of MWCNTs as reinforcements for PP. The
convergence also gives evidenced by the convergence of
mixing torque values after the mixing was stabilized [1].
However, composites with 0.75 and 1.00 wt.% of
MWCNTs addition creates a bit shifting in their
convergence with pure PP at higher temperature due to the
increased of viscosity factor, whereby the viscosity
increases with the nanotubes content [13].
80
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
Referring to Figure 3, loss modulus of unfilled PP
increased with addition of CNTs for PP/MWCNTs
nanocomposites. This finding seems to agreed the finding
by Yang et al., (2007) where they found that G” value was
increased along with the inclusion of nanofiller [1].
Khalina, 2005 reported that the increase pattern of loss
modulus amplitude with the presence of fibers indicating
that the filled PP system was experiencing the increasing
amount of amorphous part of PP chain which involved in
the transition. This indicates higher viscosity as a result of
the molecular movement restriction due to the presence of
the fillers [5]. Thus, the higher the CNTs content, the
higher the viscosity, which at the end requires higher needs
for energy dissipation [7].
When the composites were subjected to external stresses,
energy was dissipated by frictions between the fiber-fiber
and fiber-polymer interactions. Additionally, similar to the
storage modulus results, when approaching the melting
temperature of PP, the curves tend to converge and exhibit
the intrinsic properties of PP matrix. As can be seen, the
inclusion of MWCNTs showed negligible effect to the
peak temperature of loss modulus. The peak was not
significantly shifted with regard to the effect of different
MWCNTs loading. This condition indicates that the
inclusion of CNTs did not significantly affect the
relaxation behavior of PP. The relaxation transition peak
shown in E’’ is around -2 to 4°C is thought to be related to
the complex multi-relaxation process, which is mainly
concerned with the molecular motion of the crystalline
region of PP [1].
The G” peak reached a maximum peak near the Tg and
then decreased sharply with the increasing temperature.
The temperature range from -10 to 10°C represent a
transition region from the glassy state to a rubbery state
[5]. Above the transition temperature, the G” curve
dropped gradually indicating the increases flow of the
chain movement, thus reducing the viscosity.
G” can be used to indicate the rheological change (phase
and flow) which occur during the processing of materials.
As the temperature increase, the viscosity of the materials
decreased gradually. The maximum dissipation of heat per
unit deformation occurs at the temperature where G” is
maximum. Above the phase transition region, the decrease
in the G” is sharper indicating a sharp decrease in their
viscosity. In this research, the peaks of loss modulus can be
detected varies from -2 to 4°C with negligible influence of
different amount of MWCNTs loading. As can be seen,
after the maximum peak of the curves, the loss modulus
values dropped significantly with the increasing of
temperature until ~ 30°C, before it form stabilization
plateau prior to the convergence of the curves caused by
the melting temperature.
8
1.8x10
PP/1.00 wt.% MWCNTs Composites
PP/0.75 wt.% MWCNTs Composites
PP/0.50 wt.% MWCNTs Composites
PP/0.25 wt.% MWCNTs Composites
PP Virgin (Control Sample)
8
1.5x10
8
1.2x10
E'' (Pa)
3.2 Loss Modulus (G’’) of PP/MWCNTs Composites
32
8
0.9x10
8
0.6x10
8
0.3x10
-30
-20
-10
0
10
20
30
Temperature (°C)
40
50
60
70
Figure 3: Variation of loss modulus (G’’) of PP/MWCNTs
composites as a function of temperature
3.3 Damping Factor (tanδ) of PP/MWCNTs Composites
Tanδ indicates the relative importance of both viscous and
elastic behaviors of materials, whereby tanδ < 1 exhibits
more elastic behavior and may behave like solid, while
tanδ > 1 exhibits more viscous behavior and behaves more
like liquid [10]. Referring to the Figure 4, it shows that the
range of tanδ is < 1, exhibits that the fabricated composites
behave like a solid. It was also shown that the composites
showed a slightly higher damping than the pure PP owing
to the viscoelastic energy dissipation as a result of fiberfiber friction and fiber-PP interaction. However, this
finding is not in agreement with the findings obtained by
Fateme (2006), where the author found that the tanδ value
is decreased with the increasing amount of carbon fiber
content in the PP matrix [10].
From the damping factor curves, Tg of the composites can
be determined by the tanδ peak temperature [8]. The Tg of
the MWCNTs/Phenoxy nanocomposites was increased by
increasing the amount of CNTs loading [3]. This
phenomenon is due to the factor that MWCNTs restrict the
thermally induced segmental motions of the polymer
chains in the composites, resulting a higher Tg [3], [8].
From the Figure 5, it is clearly shown that the formation of
the Tg peaks is in the range of -10 to 20°C, where it is
associated to the relaxation of unrestricted amorphous
phase in PP of β relaxation [14]. This relaxation stage is a
80
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
secondary relaxation due to the movement of short chain
segments. It can be assigned as glass transition temperature
(Tg). However, by referring to the Figure 4, it was also
shown that there is no significant shift in the Tg
temperatures, with respect to the difference amount of
MWCNTs added into the PP matrix. The maximum peak
for each curve falls at slightly the same Tg temperature,
which is ~ 7°C. This phenomenon may be contributed by
the factor of extremely low percentages of CNTs used,
where it does not gives any little changes to the Tg
properties of the tested nanocomposites. The relatively no
changes in transition temperature of composites suggest
that there is no change in the rigidity of the fiber matrix
interfacial zone and no change in the mobility of the
interfacial region. This situation was consistent with the
work done by Zhang & Zhang (2007) which found that
addition of 1 wt.% MWCNTs into PP matrix does not
gives any significance increase to the glass temperature,
where it fall around ~13°C which is almost equivalent with
the Tg of the tested virgin PP [11]. However, addition of
MWCNTs even at lower percentages of filler loading is
still capable to gives identical separated peak position with
respect to the tanδ value, where addition of only 1.00 wt.%
MWCNTs to the PP, make intense shift to their tanδ value,
almost 0.8 compared to the virgin PP which only had
maximum peak of tanδ around 0.65.
0.16
PP/1.00 wt.% MWCNTs Composites
PP/0.75 wt.% MWCNTs Composites
PP/0.50 wt.% MWCNTs Composites
PP/0.25 wt.% MWCNTs Composites
PP Virgin (Control Sample)
Tanδ
0.12
0.08
0.04
0
-30
-20
-10
0
10
20
30
Temperature (°C)
40
50
60
70
Figure 4: Variation of damping factor (tanδ) of
PP/MWCNTs composites as a function of temperature
3.4 TEM Analysis of PP/MWCNTs Composites Surfaces
33
Magnification at about 35 500 times was applied in this
observation. In overall, as can be seen from Figures 5, the
dispersion patterns of MWCNTs were totally influenced by
the percentages of MWCNTs loading. It is obviously can
be seen as depicted in the Figure 5(a) and Figure 5(b), that
the CNTs added were successfully dispersed, whereby the
CNTs were isolated into the single nanotubes and
homogeneously distributed between each other in certain
remarkable distance. Referring to the Figure 5(a), CNTs
seem likes embedded within the PP matrix. This is an
indication of good compatibility between the matrix and
the filler used. Well distribution of CNTs will provide
good stress transfer during the mechanical loading which
resulting better mechanical properties of the fabricated
nanocomposites. Thus, it can be said that this observation
well
supported
the
positive
results
of
the
thermomechanical properties as obtained from the DMA
testing.
As depicted in the Figure 5(b), it is clearly observed that
the embedded CNTs have different thickness and diameter
between each other or even at the same single nanotubes.
MWCNTs seem to be shorter and the presence of CNTs in
one single observation region is much dominant as clearly
depicted in the Figure 5(b), in comparison with the Figure
5(a), since the quantity of CNTs loading was increased and
the observation done at relatively small thickness of
specimen [4]. All the nanotubes showed very well
separation between each other in both fabricated
nanocomposites. Micrograph of Figure 5(c) showed that
the nanocomposites revealed the layer of PP that seems to
cover the CNTs surfaces, indicating some degree of
wetting and phase adhesion, unlike the hydrophobic
polymer system. Good wettability of MWCNTs will
creates good interphase between the filler and matrix
which later will creates strong interfacial bonding between
them (Liao, 2003). Addition of up to 0.75wt.% of
MWCNTs exhibits excellence nanotubes dispersion where
each of MWCNTs bundle has been isolated. It is known
that good dispersion will lead better thermomechanical
properties of nanocomposites [3]. Good dispersion of the
tubes will increase the available surface area of the tubes to
be bonded with the matrix of PP. TEM coupled with all the
thermomechanical properties results, provides strong
evidence that CNTs isolation is the prime key to
maximizing reinforcement effects, which finally affecting
the thermal and mechanical properties [15].
80
Figure 5(d) clearly viewed the clustered region of filler due
to high concentration of MWCNTs used (1 wt.%).
MWCNTs are not fully dispersed as individual CNT,
wherein some are entangled together in the form of random
orientation, which also creates the interconnecting
structure [13]. However, addition of 1 wt.% of MWCNTs
caused the presence of nanotubes bundles and
agglomerates seem to be more critical compared to the
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
produced nanocomposites with 0.75 wt.% MWCNTs
addition. The agglomerates and bundles of the tubes can be
recognized as a black or big dark spots in the composites
surfaces. Formation of CNTs agglomerates is due to high
intermolecular van der Waals interactions between the
CNTs which induced tangled intertwined aggregates as
shown in the TEM observations [16]. Presence of all these
entities caused the weakening to the mechanical properties
of the fabricated nanocomposites. Agglomerates and
bundles of CNTs in polymer nanocomposites will act as
stress concentration sites that caused early failure due to
the factor of uneven stress transfer during the mechanical
loading of the nanocomposites. Liao (2003) successfully
explained the mechanism of failure due to this
phenomenon [3].
In this study, the formation of agglomerates of tubes
aggregation can be detected clearly since the dispersion
process was solely rely on the capability of the melt
blending process to separate the CNTs bundles without
assistance from any chemical surface modification onto the
surface of CNTs. Surprisingly, at lower filler content,
MWCNTs were successfully dispersed quite well,
especially for the PP/MWCNTs composites with filler
loading of lower than 1.00 wt.%.
4.0 CONCLUSION
PP/MWCNTs nanocomposites were successfully prepared
through the simple melt blending technique. Addition of
low loading of nanotubes provides extensive improvement
to the thermomechanical properties for the fabricated
nanocomposites. This situation was assisted by the
contribution of well dispersion of MWCNTs within the
matrix of PP, as validated through the surface observation
by TEM. This phenomenon further revealed the
importance of filler dispersion and distribution in affecting
the resulted thermal-mechanical properties of the
fabricated composites. In addition, through this study, the
interaction between the morphological natures with the
resulted dynamic thermomechanical behavior was
understood and established. In overall, MWCNTs have a
great potential to influence the characteristic and
engineering behavior of the produced nanocomposites,
even though at the extremely lower percentages of filler
addition.
5.0 REFERENCES
[1]
Yang, S., Tijerina, J.T., Diaz, V.S., Hernandez, K.,
and Lozano, K. : Dynamic Mechanical and Thermal
Analysis of Aligned Vapor Grown Carbon Nanofibre
Reinforced Polyethylene, Composites Part B, 38,
2007, p.228-235.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
34
Jamaliah, S.: Preparation and Characterization of
Natural
Rubber/Clay,
Poly(ethylene-co-vinyl
acetate)/Clay
Nanocomposites.
PhD.
Thesis,
Universiti Putra Malaysia, 2005.
Liao, Y. H. : Processing Technique and Mechanical
Properties of Functionalized SWNT-Reinforced
Composites. MSc. Thesis. The Florida State
University, College of Engineering, 2003.
Dalmas, F., Cavaille, J.-Y., Gauthier, C., Chazeau,
L., and Dendievel, R. : Viscoelastic Behavior and
Electrical Properties of Flexible Nanofober Filled
Polymer Nanocomposites. Influences of Processing
Conditions. Composites Science and Technology. 67,
2007, p.829 – 839.
Khalina, A. : Rheological Behavior and Properties of
Injection Moulded Oil Palm (Elaeis Guineensis Jacq.)
Empty Fruit Bunch Fibres / Polypropylene
Composites. PhD Thesis. Universiti Putra Malaysia,
2005.
Green, J., and Wilkes: Steady State and Dynamic
Properties
of
Concentrated
Fiber
Filled
Thermoplastic. Polymer Engineering and Science,
35: 21, 1995, p. 1670-1681.
Abdel-Goad, M., and Potschke, P.: Rheological
Characterization of Melt Pressed PolycarbonateMultiwalled Carbon Nanotube Composites. Journal
Non-Newtonian Fluid Mechanics, 128, 2005, p.2-6.
Choi, Y.-K., Gotoh, Y., Sugimoto, K.I., Song, S.-M.,
Yanagisawa, T., and Endo, M.: Processing and
Characterization
of
Epoxy
Nanocomposites
Reinforced by Cup-Stacked Carbon Nanotubes.
Polymer, 46, 2005, p.11489-11498.
Joseph, P.V., Mathew, G., Joseph, K., Groeninckx,
G., and Sabu, T. : Dynamic Mechanical of Short Sisal
Fiber Reinforced Polypropylene Composites.
Composites Part A, 34, 2003, p.275-290.
Fateme, R. : Development of Short Carbon Fibre
Reinforced Polypropylene Composites for Car
Bonnet Application. MSc. Thesis. Universiti Putra
Malaysia, 2006.
Zhang, H., and Zhang, Z. : Impact Behaviour of
Polypropylene Filled with Multi-Walled Carbon
Nanotubes.
Macromolecular
Nanotechnology.
European Polymer Journal, 43, 2007, p.3197-3207.
McNally, T., Potschke, P., Halley, P., Murphy, M.,
Martin, D., Bell, S.E.J., Brennane, G.P., Beinf, D.,
Lemoine, P. and Ouinn, J.P. : Polyethylene
Multiwalled
Carbon
Nanotubes Composites.
Polymer. 46, 2005, p. 8222-8232.
Seo, M.K., and Park, S.J. : Electrical Resistivity and
Rheological Behaviors of Carbon Nanotubes-Filled
Polypropylene Composites. Chemical Physics
Letters. 395, 2004, p.44-48.
Schawe, J. : Interpreting DMA Curves, Part 2.
Mettler Toledo Thermal Analysis System. UserCom
2/2002, p. 1-5.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
[15] Ryan, K.P., Cadek, M., Nicolosi, V., Blond, D.,
Ruether., Armstrong, G., Swan, H., Fonseca, A.,
Nagy, J.B., Maser, W.K., Blau, W.J., and Coleman,
J.N. : Carbon Nanotubes Reinforcement of Plastics?
A Case Study with Poly(vinyl alcohol). Composites
Science
and
Technology,
2006.
.
(a)
35
[16] Potschke, P., Bhattacharyya, A.R., and Janke, A. :
Carbon Nanotubes-Filled Polycarbonate Composites
Produced by Melt Mixing and Their Use in Blends
with Polyethylene. Carbon. 42, 2004, p. 965-969.
(b)
(a)
CNTs
(c)
CNTs Entanglement
CNTs
(d)CNTs
Network
CNTs Coiled
and Entangled
Structure
(c)
Figure 5: TEM observation of cryo thin sectioning of (a) PP/ 0.25wt.%; (b) PP/0.50wt.%; (c) PP/0.75wt.% and (d)
PP/1.00wt.% MWCNTs nanocomposites surfaces with 35 500X of magnification power
29
THERMOMECHANICAL AND MORPHOLOGICAL INTERRELATIONSHIP OF
POLYPROPYLENE-MUTIWALLED CARBON NANOTUBES (PP/MWCNTs)
NANOCOMPOSITES
A.R., Jeefferiea, M.Y. Yuhazria, O. Nooririnaha, M.M. Haidira, Haeryip Sihombingb, M.A.,
Mohd Sallehc, N.A., Ibrahimd
a
Engineering Materials Department, bManufacturing Management Department, Faculty of Manufacturing Engineering,
Universiti Teknikal Malaysia Melaka, Durian Tunggal, 76109, Melaka, Malaysia.
c
Chemical Engineering Department, Faculty of Engineering, dChemistry Department, Faculty of Science, Universiti
Putra Malaysia, 43400 UPM, Serdang, Selangor Darul Ehsan, Malaysia.
Email: jeefferie@utem.edu.my
Abstract - In this research, the significance effects of
MWCNTs at lower percentage addition in affecting the
thermomechanical behavior of the fabricated PP/MWCNTs
nanocomposites
were
studied.
PP/MWCNTs
nanocomposites were compounded by using the internal
mixer, through the simple melt blending technique. The
improvement effects of MWCNTs addition were well
justified by the transmission electron microscopy (TEM)
surface morphological observation. The interrelationships
between the TEM surface observations with the
thermomechanical
results
were
established
by
manipulating the three major plots of dynamic mechanical
analysis of storage modulus, loss modulus and damping
modulus (tanδ). From this work, it was found that the
improvement of dynamic thermomechanical properties is
directly related to the amount of MWCNTs added and the
quality of MWCNTs dispersion within the PP matrix.
or materials stiffness. It provides the information on elastic
response to the deformation resistance [3]. The remarkable
increased in composite thermo-mechanical stability cannot
be only understood by the interactions between the
polymer chains and carbon nanotubes (CNTs) surface, but
the formation of a percolating entangled CNTs network
within the materials has to be taken seriously into
consideration [4]. Entanglements within a fibrous structure
are indeed responsible for the elastic response of the
composites structure [4].
1.0 INTRODUCTION
However, entanglements between the CNTs appear to have
a low effect on the mechanical reinforcement. Thus, the
increase in modulus is mainly due to stress transfer
between the matrix and CNTs. In filled polymer systems,
the presence of fibers perturbs the normal flow of polymer
and hinders the mobility of chain segments in flow. The
type of polymers (semicrystalline or amorphous), the glass
transition temperature of the polymers, the filler type,
geometry (including aspect ratio), concentration and the
interaction of the fillers to the matrix molecular chains are
all the factors which affecting the molecular motions
within the matrix [1]. These are the factor which affects the
behavior of the storage modulus curve.
Most fillers and reinforcements are purely elastic systems
while the polymer and the filler/polymer interface are
viscoelastic. A better understanding of the dynamic
thermo-mechanical properties of the composite will help to
define structure/property relationships and subsequently to
relate these properties to the product final performance [1].
Dynamic mechanical analysis (DMA), measures the
response of a given material to a cyclic deformation as a
function of temperature [2]. DMA provides information on
storage modulus, loss modulus and damping factor
behavior of materials. The dynamic storage modulus (G’)
is approximately similar to the Young or elastic modulus,
Loss modulus (G’’) indicates the materials ability to
dissipate energy, often in the form of heat or molecular
rearrangements when there is deformation occurred [5]. It
indicates the viscous nature of the polymer and gives
information about the viscous or energy dissipation during
the flow [6]. G’’ is also directly related to the amount of
amorphous PP chain involved in the transition [5]. As the
CNTs loading increased, there is a little mobility of the PP
chain. This limitation in the mobility of chain was
indicated by little amplitude differences, which indicates
that a slow movement of chain and the viscosity of
polypropylene (PP) filled multiwalled carbon nanotubes
Keywords:
Thermomechanical,
PP/MWCNTs
nanocomposites, Surface morphological, Interrelationships.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
(MWCNTs) composites were considerably higher or more
viscous [7]. The damping factor (tanδ) is the ratio of the
loss modulus to the storage modulus. It may also be
obtained as the ratio of the real part to the imaginary part
of the complex viscosity [1]. The damping factor (tanδ)
provides information on the relative contributions of the
viscous and elastic components of a viscoelastic material.
It is very useful for determining the occurrence of
molecular mobility transition such as the glass transition
temperature which also represents the ability to the heat
resistance [1].
Through this study, the effects of lower percentages of
MWCNTs filler addition to the thermomechanical
properties of fabricated PP/MWCNTs nanocomposites
were investigated. The efficacy of the internal mixer
method to compound the MWCNTs within the PP matrix
was tested in the course of transmission electron
microscopy (TEM) observation. The interrelationships
between the microscopy observations to the final
thermomechanical results were further established. It is
anticipated that the nanocomposites compounding by using
this route much probably will gives better nanofiller
homogenization within the polymer matrix which resulting
better end properties of the fabricated nanocomposites. In
parallel, it is also interesting to observe the significant
effect caused by the addition of extremely lower
percentages of MWCNTs to the mechanical properties,
subject to the thermal and mechanical effects.
30
2.3. DMA Thermomechanical Analysis of PP/MWCNTs
Nanocomposites
The compression molded sample plaques were cut into
rectangular shape with the dimension of ~12.6 mm in their
length, ~5.0 mm in their width and ~1.0 mm in their
thickness. The measurement was carried out using a three
point bending fixture of dynamic mechanical analyzer
(DMA) model Perkin Elmer TE. The samples were
subjected to an oscillating frequency of 1 Hz and 10 µm
oscillating amplitude in the temperature ranges of -50°C to
150°C at the heating rate of 2°C/min. The signals are
automatically used to determine the dynamic storage
modulus (G’), loss modulus (G’’) and the damping factor
(tanδ), which were plotted as a function of temperature.
The tanδ peak was taken as the glass transition temperature
(Tg) of the tested samples. To verify the thermomechanical
experimental results, the surface morphologies observation
from the transmission electron microscopy (TEM)
observation were conducted.
(a)
2.0 METHOD
(b)
2.1. Raw Materials
Thermoplastic PP grade Titan Pro SM950 used as matrix
material was purchased from Titan Petchem (M) Sdn. Bhd.
As-produced MWCNTs which synthesized by the floating
catalysts chemical vapor deposition (FC-CVD) method are
used as filler reinforcement. As-produced MWCNTs with
55% of purity are depicted as in the Figure 1.
Figure 1: As-produced MWCNTs observed through
HRTEM imaging
2.2. Preparation of PP/MWCNTs Nanocomposites
2.4.
PP/MWCNTs nanocomposites were prepared by melt
blending process in an internal mixer using Thermo Haake
PolyDrive with Rheomix R600/610 at 175°C of
compounding temperature and 60 rpm of roller rotor speed.
Eight minutes of compounding period were allocated and
required amount of MWCNTs (0, 0.25, 0.50, 0.75 & 1.00
wt %) were added at the midst of compounding duration.
The compounded recipes were then compression molded
using HSINCHU hot press machine for 5 minutes preheat
and another 5 minutes of compression period under the
pressure of 150 kg/cm2 at 185°C. The sheets obtained were
immediately cooled for 10 minutes of cooling cycle.
Surface Morphological Observation through TEM
TEM observation was performed to the ultra-thin section
of the PP/MWCNTs nanocomposites film as to check the
dispersion state of MWCNTs added within the PP matrix.
The observation was conducted by using the TEM-100
CX-II (JEOL Co., Japan), at an acceleration voltage of 120
kV. The specimens were prepared by using a Leica ultracut microtome equipped with a cyro-chamber. Thin
sections of about 100 nm were prepared by using a
diamond knife at -80°C of liquid nitrogen temperature.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
3.0 RESULTS AND DISCUSSION
Storage
Modulus
Nanocomposites
(G’)
9
4x10
of
PP/1.00 wt.% MWCNTs Composites
PP/0.75 wt.% MWCNTs Composites
PP/0.50 wt.% MWCNTs Composites
PP/0.25 wt.% MWCNTs Composites
PP Virgin (Control Sample)
PP/MWCNTs
Figure 2 displayed the plot of storage modulus (G’) as a
function of temperature for the PP/MWCNTs
nanocomposites with different weight percentage addition
of MWCNTs. Storage modulus curve for pure PP is
overlaid as for the comparison purpose. Basically, at the
initial stage of analysis, the Figure 2 shows the storage
modulus of the samples increases from about 1.50x109 to
3.25x109 Pa with the increasing amount of MWCNTs. A
mechanical reinforcement effects are increasing with the
nanotubes content [4], [8].
The stiffness effects introduced by MWCNTs enable the
PP to sustain high storage modulus value [1]. This also,
will suggest that the MWCNTs added behaves as good
reinforcement and allow homogeneous stress transferred
from the matrix to the fiber. As the fiber loading increased,
the stress is more evenly distributed and thus will increase
the storage modulus [9]. As can be seen, the initial value of
storage modulus is higher for each sample at the subambient temperature due to the facts that, at this stage the
molecules are in the frozen state, therefore they retain high
stiffness properties in the glassy condition [2]. E’ is higher
when the molecular movement is limited or restricted and
it consequently will caused the storage of mechanical
energy increased [10], [11]. The stiffening effect was more
remarkable at lower temperature. This phenomenon was
explained by the mismatch in coefficient of thermal
expansion between the matrix and inorganic fillers, which
might allow better stress transfer between matrices and
fillers at low temperatures [11].
The storage modulus curves for each sample is decrease
dramatically with the increase of temperature from -30 to
80°C. This finding is in agreement with the works done by
many researchers [1], [2], [4], [5], [10]. The pattern of
decrement in the storage modulus value with the increasing
temperature is due to the fact that PP reaches its softening
point therefore reduced the elastic response of the material.
With the increase of temperature to the melting
temperature, the storage modulus of the composites was
dominated by the matrix intrinsic modulus [1]. As the
temperatures approaches the glass transition temperature
region, there is a large drop in the storage modulus values,
indicating the phase transition from the rigid glassy state
where the molecular motions are restricted to a more
flexible rubbery state and the molecular chains have
greater freedom to move. When the polymer is viscous, as
only few entanglements exist between nanotubes, the
composite will flow because of interaction between
polymer chains and nanotubes [4].
9
3x10
E' (Pa)
3.1
31
9
2x10
9
1x10
0
-30
-20
-10
0
10
20
30
Temperature (°C)
40
50
60
70
Figure 2: Variation of storage modulus (G’) of
PP/MWCNTs composites as a function of temperature
When the PP polymer and its composites are heated above
their Tg, an increase in free volume typically occurs
followed by an increase in molecular mobility [10]. Under
this situation, the chain segments gradually align with the
applied force [5]. When this occurs, the E’ decreased.
However there is no distinct characteristic peak of the
storage modulus can be detected to determine the Tg for
the tested samples. Thus damping factor or loss modulus
curves will be utilized for this purpose.
As can be seen, the presence of different loading of
MWCNTs filler in the matrix of PP even at a lower
percentages of weight, is still capable to keep retain the
pattern of the curve where the higher the filler content, the
higher the storage value, with regards to the temperature
factor. This phenomenon is in agreement with the work
done by McNally et al., (2005), where they found that
addition of low loadings of MWCNTs were also more
effective at increasing the dynamic mechanical storage
modulus of polyethylene composites [12]. It is observed
that the curves tend to converge to that of pure PP when
approaching the melting temperature of PP. This
convergence at higher temperature explains the successful
exploitation of MWCNTs as reinforcements for PP. The
convergence also gives evidenced by the convergence of
mixing torque values after the mixing was stabilized [1].
However, composites with 0.75 and 1.00 wt.% of
MWCNTs addition creates a bit shifting in their
convergence with pure PP at higher temperature due to the
increased of viscosity factor, whereby the viscosity
increases with the nanotubes content [13].
80
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
Referring to Figure 3, loss modulus of unfilled PP
increased with addition of CNTs for PP/MWCNTs
nanocomposites. This finding seems to agreed the finding
by Yang et al., (2007) where they found that G” value was
increased along with the inclusion of nanofiller [1].
Khalina, 2005 reported that the increase pattern of loss
modulus amplitude with the presence of fibers indicating
that the filled PP system was experiencing the increasing
amount of amorphous part of PP chain which involved in
the transition. This indicates higher viscosity as a result of
the molecular movement restriction due to the presence of
the fillers [5]. Thus, the higher the CNTs content, the
higher the viscosity, which at the end requires higher needs
for energy dissipation [7].
When the composites were subjected to external stresses,
energy was dissipated by frictions between the fiber-fiber
and fiber-polymer interactions. Additionally, similar to the
storage modulus results, when approaching the melting
temperature of PP, the curves tend to converge and exhibit
the intrinsic properties of PP matrix. As can be seen, the
inclusion of MWCNTs showed negligible effect to the
peak temperature of loss modulus. The peak was not
significantly shifted with regard to the effect of different
MWCNTs loading. This condition indicates that the
inclusion of CNTs did not significantly affect the
relaxation behavior of PP. The relaxation transition peak
shown in E’’ is around -2 to 4°C is thought to be related to
the complex multi-relaxation process, which is mainly
concerned with the molecular motion of the crystalline
region of PP [1].
The G” peak reached a maximum peak near the Tg and
then decreased sharply with the increasing temperature.
The temperature range from -10 to 10°C represent a
transition region from the glassy state to a rubbery state
[5]. Above the transition temperature, the G” curve
dropped gradually indicating the increases flow of the
chain movement, thus reducing the viscosity.
G” can be used to indicate the rheological change (phase
and flow) which occur during the processing of materials.
As the temperature increase, the viscosity of the materials
decreased gradually. The maximum dissipation of heat per
unit deformation occurs at the temperature where G” is
maximum. Above the phase transition region, the decrease
in the G” is sharper indicating a sharp decrease in their
viscosity. In this research, the peaks of loss modulus can be
detected varies from -2 to 4°C with negligible influence of
different amount of MWCNTs loading. As can be seen,
after the maximum peak of the curves, the loss modulus
values dropped significantly with the increasing of
temperature until ~ 30°C, before it form stabilization
plateau prior to the convergence of the curves caused by
the melting temperature.
8
1.8x10
PP/1.00 wt.% MWCNTs Composites
PP/0.75 wt.% MWCNTs Composites
PP/0.50 wt.% MWCNTs Composites
PP/0.25 wt.% MWCNTs Composites
PP Virgin (Control Sample)
8
1.5x10
8
1.2x10
E'' (Pa)
3.2 Loss Modulus (G’’) of PP/MWCNTs Composites
32
8
0.9x10
8
0.6x10
8
0.3x10
-30
-20
-10
0
10
20
30
Temperature (°C)
40
50
60
70
Figure 3: Variation of loss modulus (G’’) of PP/MWCNTs
composites as a function of temperature
3.3 Damping Factor (tanδ) of PP/MWCNTs Composites
Tanδ indicates the relative importance of both viscous and
elastic behaviors of materials, whereby tanδ < 1 exhibits
more elastic behavior and may behave like solid, while
tanδ > 1 exhibits more viscous behavior and behaves more
like liquid [10]. Referring to the Figure 4, it shows that the
range of tanδ is < 1, exhibits that the fabricated composites
behave like a solid. It was also shown that the composites
showed a slightly higher damping than the pure PP owing
to the viscoelastic energy dissipation as a result of fiberfiber friction and fiber-PP interaction. However, this
finding is not in agreement with the findings obtained by
Fateme (2006), where the author found that the tanδ value
is decreased with the increasing amount of carbon fiber
content in the PP matrix [10].
From the damping factor curves, Tg of the composites can
be determined by the tanδ peak temperature [8]. The Tg of
the MWCNTs/Phenoxy nanocomposites was increased by
increasing the amount of CNTs loading [3]. This
phenomenon is due to the factor that MWCNTs restrict the
thermally induced segmental motions of the polymer
chains in the composites, resulting a higher Tg [3], [8].
From the Figure 5, it is clearly shown that the formation of
the Tg peaks is in the range of -10 to 20°C, where it is
associated to the relaxation of unrestricted amorphous
phase in PP of β relaxation [14]. This relaxation stage is a
80
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
secondary relaxation due to the movement of short chain
segments. It can be assigned as glass transition temperature
(Tg). However, by referring to the Figure 4, it was also
shown that there is no significant shift in the Tg
temperatures, with respect to the difference amount of
MWCNTs added into the PP matrix. The maximum peak
for each curve falls at slightly the same Tg temperature,
which is ~ 7°C. This phenomenon may be contributed by
the factor of extremely low percentages of CNTs used,
where it does not gives any little changes to the Tg
properties of the tested nanocomposites. The relatively no
changes in transition temperature of composites suggest
that there is no change in the rigidity of the fiber matrix
interfacial zone and no change in the mobility of the
interfacial region. This situation was consistent with the
work done by Zhang & Zhang (2007) which found that
addition of 1 wt.% MWCNTs into PP matrix does not
gives any significance increase to the glass temperature,
where it fall around ~13°C which is almost equivalent with
the Tg of the tested virgin PP [11]. However, addition of
MWCNTs even at lower percentages of filler loading is
still capable to gives identical separated peak position with
respect to the tanδ value, where addition of only 1.00 wt.%
MWCNTs to the PP, make intense shift to their tanδ value,
almost 0.8 compared to the virgin PP which only had
maximum peak of tanδ around 0.65.
0.16
PP/1.00 wt.% MWCNTs Composites
PP/0.75 wt.% MWCNTs Composites
PP/0.50 wt.% MWCNTs Composites
PP/0.25 wt.% MWCNTs Composites
PP Virgin (Control Sample)
Tanδ
0.12
0.08
0.04
0
-30
-20
-10
0
10
20
30
Temperature (°C)
40
50
60
70
Figure 4: Variation of damping factor (tanδ) of
PP/MWCNTs composites as a function of temperature
3.4 TEM Analysis of PP/MWCNTs Composites Surfaces
33
Magnification at about 35 500 times was applied in this
observation. In overall, as can be seen from Figures 5, the
dispersion patterns of MWCNTs were totally influenced by
the percentages of MWCNTs loading. It is obviously can
be seen as depicted in the Figure 5(a) and Figure 5(b), that
the CNTs added were successfully dispersed, whereby the
CNTs were isolated into the single nanotubes and
homogeneously distributed between each other in certain
remarkable distance. Referring to the Figure 5(a), CNTs
seem likes embedded within the PP matrix. This is an
indication of good compatibility between the matrix and
the filler used. Well distribution of CNTs will provide
good stress transfer during the mechanical loading which
resulting better mechanical properties of the fabricated
nanocomposites. Thus, it can be said that this observation
well
supported
the
positive
results
of
the
thermomechanical properties as obtained from the DMA
testing.
As depicted in the Figure 5(b), it is clearly observed that
the embedded CNTs have different thickness and diameter
between each other or even at the same single nanotubes.
MWCNTs seem to be shorter and the presence of CNTs in
one single observation region is much dominant as clearly
depicted in the Figure 5(b), in comparison with the Figure
5(a), since the quantity of CNTs loading was increased and
the observation done at relatively small thickness of
specimen [4]. All the nanotubes showed very well
separation between each other in both fabricated
nanocomposites. Micrograph of Figure 5(c) showed that
the nanocomposites revealed the layer of PP that seems to
cover the CNTs surfaces, indicating some degree of
wetting and phase adhesion, unlike the hydrophobic
polymer system. Good wettability of MWCNTs will
creates good interphase between the filler and matrix
which later will creates strong interfacial bonding between
them (Liao, 2003). Addition of up to 0.75wt.% of
MWCNTs exhibits excellence nanotubes dispersion where
each of MWCNTs bundle has been isolated. It is known
that good dispersion will lead better thermomechanical
properties of nanocomposites [3]. Good dispersion of the
tubes will increase the available surface area of the tubes to
be bonded with the matrix of PP. TEM coupled with all the
thermomechanical properties results, provides strong
evidence that CNTs isolation is the prime key to
maximizing reinforcement effects, which finally affecting
the thermal and mechanical properties [15].
80
Figure 5(d) clearly viewed the clustered region of filler due
to high concentration of MWCNTs used (1 wt.%).
MWCNTs are not fully dispersed as individual CNT,
wherein some are entangled together in the form of random
orientation, which also creates the interconnecting
structure [13]. However, addition of 1 wt.% of MWCNTs
caused the presence of nanotubes bundles and
agglomerates seem to be more critical compared to the
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
produced nanocomposites with 0.75 wt.% MWCNTs
addition. The agglomerates and bundles of the tubes can be
recognized as a black or big dark spots in the composites
surfaces. Formation of CNTs agglomerates is due to high
intermolecular van der Waals interactions between the
CNTs which induced tangled intertwined aggregates as
shown in the TEM observations [16]. Presence of all these
entities caused the weakening to the mechanical properties
of the fabricated nanocomposites. Agglomerates and
bundles of CNTs in polymer nanocomposites will act as
stress concentration sites that caused early failure due to
the factor of uneven stress transfer during the mechanical
loading of the nanocomposites. Liao (2003) successfully
explained the mechanism of failure due to this
phenomenon [3].
In this study, the formation of agglomerates of tubes
aggregation can be detected clearly since the dispersion
process was solely rely on the capability of the melt
blending process to separate the CNTs bundles without
assistance from any chemical surface modification onto the
surface of CNTs. Surprisingly, at lower filler content,
MWCNTs were successfully dispersed quite well,
especially for the PP/MWCNTs composites with filler
loading of lower than 1.00 wt.%.
4.0 CONCLUSION
PP/MWCNTs nanocomposites were successfully prepared
through the simple melt blending technique. Addition of
low loading of nanotubes provides extensive improvement
to the thermomechanical properties for the fabricated
nanocomposites. This situation was assisted by the
contribution of well dispersion of MWCNTs within the
matrix of PP, as validated through the surface observation
by TEM. This phenomenon further revealed the
importance of filler dispersion and distribution in affecting
the resulted thermal-mechanical properties of the
fabricated composites. In addition, through this study, the
interaction between the morphological natures with the
resulted dynamic thermomechanical behavior was
understood and established. In overall, MWCNTs have a
great potential to influence the characteristic and
engineering behavior of the produced nanocomposites,
even though at the extremely lower percentages of filler
addition.
5.0 REFERENCES
[1]
Yang, S., Tijerina, J.T., Diaz, V.S., Hernandez, K.,
and Lozano, K. : Dynamic Mechanical and Thermal
Analysis of Aligned Vapor Grown Carbon Nanofibre
Reinforced Polyethylene, Composites Part B, 38,
2007, p.228-235.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
34
Jamaliah, S.: Preparation and Characterization of
Natural
Rubber/Clay,
Poly(ethylene-co-vinyl
acetate)/Clay
Nanocomposites.
PhD.
Thesis,
Universiti Putra Malaysia, 2005.
Liao, Y. H. : Processing Technique and Mechanical
Properties of Functionalized SWNT-Reinforced
Composites. MSc. Thesis. The Florida State
University, College of Engineering, 2003.
Dalmas, F., Cavaille, J.-Y., Gauthier, C., Chazeau,
L., and Dendievel, R. : Viscoelastic Behavior and
Electrical Properties of Flexible Nanofober Filled
Polymer Nanocomposites. Influences of Processing
Conditions. Composites Science and Technology. 67,
2007, p.829 – 839.
Khalina, A. : Rheological Behavior and Properties of
Injection Moulded Oil Palm (Elaeis Guineensis Jacq.)
Empty Fruit Bunch Fibres / Polypropylene
Composites. PhD Thesis. Universiti Putra Malaysia,
2005.
Green, J., and Wilkes: Steady State and Dynamic
Properties
of
Concentrated
Fiber
Filled
Thermoplastic. Polymer Engineering and Science,
35: 21, 1995, p. 1670-1681.
Abdel-Goad, M., and Potschke, P.: Rheological
Characterization of Melt Pressed PolycarbonateMultiwalled Carbon Nanotube Composites. Journal
Non-Newtonian Fluid Mechanics, 128, 2005, p.2-6.
Choi, Y.-K., Gotoh, Y., Sugimoto, K.I., Song, S.-M.,
Yanagisawa, T., and Endo, M.: Processing and
Characterization
of
Epoxy
Nanocomposites
Reinforced by Cup-Stacked Carbon Nanotubes.
Polymer, 46, 2005, p.11489-11498.
Joseph, P.V., Mathew, G., Joseph, K., Groeninckx,
G., and Sabu, T. : Dynamic Mechanical of Short Sisal
Fiber Reinforced Polypropylene Composites.
Composites Part A, 34, 2003, p.275-290.
Fateme, R. : Development of Short Carbon Fibre
Reinforced Polypropylene Composites for Car
Bonnet Application. MSc. Thesis. Universiti Putra
Malaysia, 2006.
Zhang, H., and Zhang, Z. : Impact Behaviour of
Polypropylene Filled with Multi-Walled Carbon
Nanotubes.
Macromolecular
Nanotechnology.
European Polymer Journal, 43, 2007, p.3197-3207.
McNally, T., Potschke, P., Halley, P., Murphy, M.,
Martin, D., Bell, S.E.J., Brennane, G.P., Beinf, D.,
Lemoine, P. and Ouinn, J.P. : Polyethylene
Multiwalled
Carbon
Nanotubes Composites.
Polymer. 46, 2005, p. 8222-8232.
Seo, M.K., and Park, S.J. : Electrical Resistivity and
Rheological Behaviors of Carbon Nanotubes-Filled
Polypropylene Composites. Chemical Physics
Letters. 395, 2004, p.44-48.
Schawe, J. : Interpreting DMA Curves, Part 2.
Mettler Toledo Thermal Analysis System. UserCom
2/2002, p. 1-5.
International Journal of Basic & Applied Sciences IJBAS-IJENS Vol: 10 No:04
[15] Ryan, K.P., Cadek, M., Nicolosi, V., Blond, D.,
Ruether., Armstrong, G., Swan, H., Fonseca, A.,
Nagy, J.B., Maser, W.K., Blau, W.J., and Coleman,
J.N. : Carbon Nanotubes Reinforcement of Plastics?
A Case Study with Poly(vinyl alcohol). Composites
Science
and
Technology,
2006.
.
(a)
35
[16] Potschke, P., Bhattacharyya, A.R., and Janke, A. :
Carbon Nanotubes-Filled Polycarbonate Composites
Produced by Melt Mixing and Their Use in Blends
with Polyethylene. Carbon. 42, 2004, p. 965-969.
(b)
(a)
CNTs
(c)
CNTs Entanglement
CNTs
(d)CNTs
Network
CNTs Coiled
and Entangled
Structure
(c)
Figure 5: TEM observation of cryo thin sectioning of (a) PP/ 0.25wt.%; (b) PP/0.50wt.%; (c) PP/0.75wt.% and (d)
PP/1.00wt.% MWCNTs nanocomposites surfaces with 35 500X of magnification power