World Journal of Nano Science and Engineering, 2012, 2, 103-109 Published Online June 2012 (
Enhancement in Mechanical Properties of Polystyrene
Filled with Carbon Nano-Particulates (CNPS)
Ayman A. Aly*, Moustafa M. Mahmoud, Adel A. Omar
Department of Mechanical Engineering, Faculty of Engineering, Assiut University, Assiut, Egypt
Department of Mechanical Engineering, College of Engineering, Taif University, Taif, Saudi Arabia
Email: *
Received March 24, 2012; revised April 30, 2012; accepted May 21, 2012
The idea of adding reinforcing materials, or fillers, to polymers has been around for many decades. The reason for the
creation of polymer composite materials came about due of the need for materials with specific properties for specific
applications. For example, composite materials are unique in their ability to allow brittle and ductile materials to be-
come softer and stronger. It is expected that good tribological properties can be obtained for polymers filled with
nano-scale fillers. A soft plastic can become harder and stronger by the addition of a light weight high stiffness material.
In the present work, the effect of adding different percentages of carbon nano-particulates to polystyrene (PS) on the
mechanical properties of nano-composites produced was investigated. Based on the experimental observations, it was
found that as the percentage of the carbon nano-particulates (CNPS) increased hardness increased and consequently fric-
tion coefficient remarkably decreased.
Keywords: Polymer Composites; Carbon Nano-Particulates (CNPS); Mechanical Properties; Tribological Properties
1. Introduction
In the past few decades, researchers and engineers interest
has been shifted from monolithic materials to reinforced
polymeric materials. These composite materials now
dominate the aerospace, leisure, automotive, construction,
and sporting industries [1].
Composite materials are typically made up of two ma-
terials, where one phase is the reinforcing phase, such as
fibers, sheets, or particles and the other phase is the ma-
trix material. The matrix material can be a metal, ceramic,
or polymer, where the reinforcing material typically is a
low density, high strength or toughness material [2].
A polymer nano-composite is defined as a composite
material with a polymer matrix and filler particles that
have at least one dimension less than 100 nm. These en-
gineering composites are desired due to their low density,
high corrosion resistance, ease of fabrication and low
cost [2-4].
Various kinds of polymers reinforced with metal parti-
cles have a wide range of industrial applications such as
heaters, electrodes, actuators etc. [5]. When silica nano-
particles are added into a polymer matrix to form a com-
posite, they play an important role in improving electrical,
mechanical, and thermal properties of composites [1,6].
The inclusion of inorganic fillers into polymers for com-
mercial applications is primarily aimed at the cost reduc-
tion and stiffness improvement [7].
The most commonly used filler materials for polymer
composites are carbon fibers, carbon nano-tubes, carbon
vapor grown nano-fibers, glass fibers, and metal or cera-
mic particulates. Glass fibers are added to polymeric ma-
terials to increase the specific strength and since both are
relatively inert materials, allows for application in corro-
sive environments [8,9].
Polymer composites can be fabricated by the incorpo-
ration of inorganic reinforcements into the polymer matrix.
The properties of the resulting polymer composites de-
pend on the characteristics, the dimensions, and the shapes
of the inorganic fillers, and also on the interfacial bond-
ing strength. It is proposed that with decreasing filler
dimension or increasing filler content a significant im-
provement on contact area between the filler and matrix
was carried out, and in turn this would greatly and effec-
tively improve the transfer of the load between the fillers
and the polymer matrix [8]. The inorganic nano-fillers,
ranging from 1 to 50 nm, were successfully incorporated
into the polymeric matrix to strengthen and improve the
ductile polymer to be more stiff and resistant for abrasion
The determination of the mechanical properties of
composite materials has proven challenging and remains
a subject of debate. There are several methods that can be
*Corresponding author.
opyright © 2012 SciRes. WJNSE
employed to theoretically determine composite properties.
These methods include; the rule of mixtures, the inverse
rule of mixtures, and the modified rule of mixtures [11].
The previous rules estimate properties only by the com-
position of the composite, but mechanical testing is nec-
essary, because the mechanical properties are dependent
on many factors. The full potential of the material isn’t
fully understood until samples can be made and mecha-
nical tests can be performed.
The mechanical properties of carbon nano-tubes com-
posites are largely dependent upon the quantity of CNTs
in the system, the dispersion and alignment of the tubes,
and the interfacial bonding between the carbon nano-
tubes and the matrix [1]. The ability to determine the
precise amount of carbon nano-tubes needed to increase
the stiffness is just the beginning. Therefore, there is a
need for these carbon nano-tubes to be dispersed, aligned,
and have favorable interactions with the matrix material.
There are several different methods for dispersing
carbon nano particles, and the determination of the ideal
method proves challenging. These methods utilize poly-
mers, surfactants, acids, or a combination of several dif-
ferent materials to disperse carbon nano-tubes [12-14].
Several of these methods tend to utilize hazardous mate-
rials and lengthy procedures to produce the desired result,
while others require less dangerous materials with shorter
durations to produce a similar result [5,6,12-24]. There-
fore, these less dangerous methods used to dispersed
carbon nano-tube may not be thought of as “ideal meth-
ods”. Typically all of the methods utilize some degree of
sonification, from a few minutes to several hours, to ini-
tially mechanically disperse the carbon nano-tubes. This
method of mechanical dispersion in conjunction with the
use of both acetone and toluene surface active agents to
reduce the van der Waals forces, provided that, the dis-
persing agent can separate the carbon nano-tubes to pre-
vent re-aggregation [21,22].
Due to the interactions of the polymer chains with the
supporting surface and the air interface, the thinner films
required for such applications have distinctly different
properties than those of the well-defined bulk systems.
Many bulk polymer properties have been well defined
in the recent literature [23]. In addition, theories that offer
reasoning for changes in these bulk properties with tem-
perature, pressure, etc. have been developed. Focus has been
shifted in the past decade to polymers in thin film geome-
tries. These systems remain obscure to polymer scientists.
Thin films have become ubiquitous in the polymer indus-
try. Fueled by the microelectronics industry and its need
for miniature parts, polymer applications have become
more demanding. Polymers in these environments have
been tested and modeled in laboratories around the world:
from universities to automobile companies, research sur-
rounding thin films is quickly growing [8].
Two main areas of research have emerged that cover
thin polymer films. The first, free-standing films, inves-
tigates thin films unattached to a substrate. The main con-
cern in this field is how the air-polymer interface affects the
behavior of the polymer as the film decreases in thick-
ness. The second, polymer films on substrates, focuses
on the interactions at the polymer-substrate interface.
Both research fields have reported data and offered ex-
planations for what has been observed.
The present paper aims to study the effect of adding
different percentages of carbon nano-particulates (CNPS)
to polystyrene (PS) on the mechanical properties of nano-
composites produced. Current research has focused on
the task of defining thin film behavior when the polysty-
rene (PS) mixed (CNPS) is cast on a surface by using the
spin coating method.
2. Experimental Procedures
2.1. Materials
Polymer: Polystyrene.
Reinforcement: Carbon nano-particulates (CNPS) clus-
Solvent: Toluene.
2.2. Spin-Coating Method
Many techniques needed to be developed to create and
monitor these new thin film systems. An accurate method
for producing thin polymer films was the first objective
of this research. The proposed solution to the problem
was spin-coating.
First a polymer solution was made and was pipetted
onto the desired surface. Next, the substrate was “accel-
erated to a desired rotation rate”. Spinning continued
until an equilibrium film thickness was reached. This was
followed by annealing to alleviate radial orientation and
eliminate any remaining solvent.
Several variables can control the film thickness of the
final product. Extract looked at some parameters of spin-
coating experimental are in [17]. The solvent used to
make the solution does affect the final thickness of the
film. Different viscosity and solubility can make PMMA
films cast from a cyclohexane solution twice as thick as
those cast from a toluene solution. The research also
showed that thickness increased as spin speed decreased
as would be expected. The amount of solution applied to
the wafer did not affect the thickness as long as there was
enough present to cover the surface. Any excess was
simply flung off the surface by centripetal forces [17].
Because thin films are used in so many applications,
Bornside, Macosko, and Scriven developed a model for
achieving a desired film thickness [18]. They divided spin
coating into the four stages of deposition, spin-up, spin-off,
and evaporation (Figure 1). By taking both the force of
Copyright © 2012 SciRes. WJNSE
A. A. ALY ET AL. 105
Figure 1. Stages of spin-coating.
spinning and the concentration-controlled evaporation
into account, these researchers were able to predict film
thickness. This model was extremely useful because it
included the surface chemistry and the type of polymer
Because of the dependable nature of the method and
the ease of use, spin coating is frequently used to create
polymer thin films.
Solutions in toluene were prepared at 0.2%, 0.5%,
0.7%, and 1.0% by weight of CNPS.
The silicon wafers were positioned on the spin coater
and several drops of solution were placed on the wafer.
Immediately, each sample began rotating at a constant
speed to acquire the desired film thickness (2500 rpm).
The samples were spun for one minute.
2.3. Test Rig
Initially the test rig built on the idea to utilize the possi-
bilities of a small lathe machine such as the different cutting
speeds and the automatic movement of the carriage. The
used lathe machine is suitable for laboratory applications.
In fact, the machine tool can expand its function with
various accessories to modify the test nature.
For measuring the friction and wear resistance a test
rig was built. The test specimen assembly was carried on
the compound cross slide of the lathe, which automa-
tically operated for positioning purposes in the direction
of adhesion, driven by controlled speeds. The test speci-
men was mounted on a platen supported on the tool post
and restrained by a load cell, which senses tangential
force on the test surface in the direction of sliding. The
details of the test rig are shown in Figure 2. The indenter,
used in experiments, was a spherical and hardened steel
ball having diameter of 1.588 mm, (see Figure 2). The
friction force was measured by the deflection of the load
cell. The ratio of the friction force to the normal load was
considered as friction coefficient. The load was applied
Figure 2. (a)-(b) used test rig (1. Screen; 2. Indenter Holder;
3. Load Cell; 4. Ball Indenter; 5. Specimen Holder).
by weights. The test speed was nearly controlled by
automatically turning the power screw feeding the indenter
in the adhesion direction. The adhesion velocity was 0.05
mm/s. All measurements were performed at 28˚C ± 2˚C
and 50% ± 10% humidity.
3. Results and Discussion
The Vickers test is often easier to use than other hardness
tests since the required calculations are independent of
the size of the indenter, and the indenter can be used for
all materials irrespective of hardness. The basic principle,
as with all common measures of hardness, is to observe
the questioned material’s ability to resist plastic defor-
mation from a standard source.
The unit of hardness given by the test is known as the
Vickers Pyramid Number (HV) or Diamond Pyramid Hard-
ness (DPH). The hardness number is determined by the
load over the surface area of the indentation and not the
area normal to the force, and is therefore not a pressure.
Accordingly, loads of various magnitudes are applied
Specimen holder
Ball indenter
Copyright © 2012 SciRes. WJNSE
to a flat surface, depending on the hardness of the material
to be measured. The HV number is then determined by
the ratio F/A where F is the force applied to the diamond
in kilograms-force and A is the surface area of the result-
ing indentation in square millimeters.
Figure 3 represents the effect of carbon nano-parti-
culates content added on the micro-hardness of com-
posite produced. It obvious that the micro-hardness in-
creased with the increase in CNPS content and this is
attributed primarily to the presence of nano-size reinfor-
cement carbon particulates. This result agrees with the
previous fact that addition of small amount of CNPS (<3
wt%) to a matrix system can increase mechanical proper-
ties without compromising the processability of the com-
posite [25]. The micro-hardness increased nearly linearly
with the CNPS content at 0.2 wt%. This means that the
maximum utilization of the properties of carbon CNPS
was achieved throughout its uniform dispersion and good
wetting within the polystyrene matrix.
Figure 4 represents the relationship between estimated
tensile strength and CNPS content. It is clear that the esti-
mated tensile strength increased with the increase in car-
bon content. A drastic improvement in the mechanical
properties of CNTs/polymer composites already men-
tioned in many researches [26-30]. These researches have
shown that many factors play an important role and in-
fluence the interface affecting therefore properties in car-
bon nanotube composites. Thus, interesting properties
are obtained, depending on the conditions used in the
synthesis, dispersion quality and raw material features,
showing that, in some cases, it is possible to obtain some
interesting properties using carbon nanotubes as-syn-
thesized. In addition, the good interfacial bonding between
carbon nanotubes (CNTs) and Polymer matrix could one
of these reasons which are responsible for this higher
values of strength in this present work.
The effect of the CNPS content on the friction coeffi-
cient of composites is shown in Figure 5 at different
applied loads (4, 5 and 6 N). Generally, the figure shows
scattering values for the frictional behavior of PS nano-
composites containing different CNPS contents.
00.2 0.4 0.6 0.811.2
content, wt%
Hardness, H
Figure 3. Effect of carbon nano-particulates content on the
micro-hardness of produced comp os ite.
content wt%
ncrease o
Increase of Tensile Strength. %
Figure 4. Effect of carbon nano-particulates content on the
tensile strength of produced composite.
FN=4 N
5 N
6 N
0.0 CNP- Content, wt%
icient o
FN = 4 N
FN = 5 N
FN = 6 N
Figure 5. Friction coefficient of the carbon nano-particu-
lates-PS composites.
It is clear that there are two different behaviors in the
figure; one of them belongs to the unfilled specimens and
the other concerning with filled specimens. The unfilled
specimen exhibits a continuous decrease in the coeffi-
cient of friction with increasing normal load as a result of
the frictional heating that reduced the shear strength of
the PS specimens. Moreover, the topography of the sur-
face becomes smoother with increasing the load causing
a decrease in the values of friction. Whereas the second
trend which concerning with the carbon nano-particulates
filled PS based composites shows a variation of friction
coefficient with increasing normal load. Friction coeffi-
cient of PS samples filled by carbon nano-particulates
with different weight contents is shown in the previous
Figure too. PS composites containing carbon nano-parti-
culates of 0.5 wt% showed the smallest coefficient of
friction at applied load of 6 N while the maximum values
Copyright © 2012 SciRes. WJNSE
A. A. ALY ET AL. 107
always displayed at applied load of 5 N. The increase in
the coefficient of friction during adhesion is attributed to
increasing plowing of the coating by the indenter with
increasing normal load but the abrupt decrease of friction
at applied load of 6 N may be attributed to the direct
contact with the carbon nano-particulates which its nature as
a solid lubricant.
The dependence of PS wear scar width on carbon nano-
particulates content at different applied normal loads and
constant speed is exhibited in Figure 6. It is shown that
the wear scar width increased up to maximum value then
decreased with increasing normal load and carbon nano-
particulates content. The increase in wear is attributed to
the increase in the contact area with increasing normal
load. The decrease in the width of wear scar after the
maximum is possibly due to the plasticization at loads
higher than a critical value. This means there is a direct
contact with the hardened carbon nano-particulates caus-
ing a high wear resistance appears in small wear scars. It
can relate this interpretation with the directly propor-
tional relationship of hardness and carbon nano-parti-
culates content as shown in Figure 6.
When the samples were examined following testing, it
was apparent from measurements of the width of the wear
tracks that considerable macroscopic plastic deformation
had taken place. There was evidence of roughening and
galling of the hardened steel ball as shown in microscopic
image (Figures 7 and 8). It was shown that the width of
the wear tracks on the contact surface of the unfilled PS
specimens under different normal loads is measured.
Moreover the width of wear tracks can express about the
amount of the plastic deformation localization in the wear
tracks, see Figures 7 and 8. This amount decreased with
FN = 4 N
6 N
CNP- Content
, m
= 4 N
= 6 N
Figure 6. Dependence of PS wear scar width on carbon
nano-particulates content.
4 N5 N 6 N
Figure 7. Panorama picture of a wear track on unfilled PS
specimens at different normal loads and constant speed 0.05
6 N4 N
Figure 8. Wear track on 0.7 wt% carbon nano-particulates
filled PS specimens at normal loads 4 and 6 N and constant
speed 0.05 mm/s.
increasing the CNPS content.
4. Conclusion
In this work, we produced the composite material (filled
with Nanoparticles). A challenging issue that improving
the tribological properties of the produced material. In
the produced composite material, the micro-hardness
increased nearly linearly with the CNPS content at 0.2%.
This means that the maximum utilization of the proper-
ties of CNPS was achieved throughout its uniform dis-
persion and good wetting within the polystyrene matrix.
The estimated tensile strength increased with the increase
in carbon content. This is attributed to the reinforcement
effect of CNPS in the polystyrene matrix which conse-
quently improves the mechanical properties in general.
The friction and wear properties of PS-carbon nano-par-
ticulates composites were promising. The carbon nano-
particulates filled PS based composites shows a variation
of friction coefficient with increasing normal load. PS
composites containing CNPS of 0.5 wt% showed the
smallest coefficient of friction at applied load of 6 N
while the maximum values always displayed at applied
load of 5 N. Generally the values of coefficient of fric-
tion are low enough to have many practical applications.
CNPS-PS composites, particularly 0.7 and 1 wt%, exhib-
ited high wear resistance owing to the possibly plastici-
zation which occurred at loads higher than a critical
value and the direct contact with hardened CNPS.
5. Acknowledgements
The authors would like to express their sincere gratitude
to Taif University for its fully funding this research pro-
ject (project number 1171/1431).
Copyright © 2012 SciRes. WJNSE
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