Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 841-847
Published Online August 2012 (http://www.SciRP.org/journal/jmmce)
Computational Approach to Modelling Fracture
Behaviour of Polypropylen e/Talc Composites
Chinedum Ogonna Mgbemena1*, Obuora Anozie Okoye2
1National Engineering Design Development Institute, Nnewi, Nigeria
2Nnamdi Azikiwe University, Awka, Nigeria
Received June 20, 2012; revised July 30, 2012; accepted August 14, 2012
ABSTRACT
Fracture represents one of the major problems associated with the selection and use of engineering materials for high
temperature applications. The fracture toughness is of special relevance on the design of components. In this work, the
fracture behavior of Polypropylene/Talc composites was studied. From the results of the tensile and flexural tests con-
ducted on the composite, scatter diagrams were made using Microsoft Excel to evaluate and show the effect of the addi-
tion of the talc filler as it affects the tensile strength, percentage elongation at break, flexural strength and modulus. In
order to give additional analysis, the talc filler content effect was presented mathematically to further describe explicitly
the various equations associated with each scatter diagram earlier developed using Microsoft Excel. The mathematical
expression developed shows the actual talc filler content on the fracture mechanical properties of the sample composite.
Keywords: Fracture; Tensile Strength; Talc; Polypropylene; Flexural Strength; Tensile Test
1. Introduction
Polypropylene (PP) composite is one of the most exten-
sively produced polymers, widely used especially as
automotive parts [1]. This is attributed to their high im-
pact strength and toughness when fillers are incorpo-
rated.
Polypropylene is isotactic, notch sensitive and brittle
under severe conditions of deformation, such as low
temperatures or high temperatures. This makes limited its
wider range of usage for manufacturing processes. It is a
versatile material widely used for automotive compo-
nents, home appliances, and industrial applications.
Polypropylene (PP) filled with particulate fillers is of
great interest in both research and industry. It is well
known that polypropylene has good processability and
accepts different types of natural and synthetic filers.
Mica, kaolin, calcium carbonate, and talc are the most
often used fillers to reduce both the production costs and
to improve the properties of the thermoplastics, such as
rigidity, strength, hardness, flexural modulus, dimen-
sional stability, crystallinity, electrical and thermal con-
ductivity. However, fillers have a detrimental effect on
other properties such as the impact property and de-
formability. The filler type, content and size, interfacial
adhesion and bond strength between PP matrix and filler
and surface characteristics of the composite can greatly
influence the filled system.
In a highly filled polymer system, non-uniformity of
properties can exist because of poor dispersion of the
filler in the matrix. A good interfacial adhesion between
matrix and filler may improve the mechanical strength
[1-8]. Due to the high transient temperature and in par-
ticular, at low stress temperatures, notch toughness of
polypropylene is not sufficient and limits its applications.
Introduction of fillers or reinforcements into PP often
alters the crystalline structure and morphology of PP and
consequently results in property changes [5,9]. Although
toughness strength is improved by blending elastomer,
this causes a decrease in strength and stiffness [10]. In
order to overcome these limitations numerous studies
have been performed to improve the toughness, stiffness,
and strength balance. Therefore, polypropylene has been
modified by different fillers and elastomers to produce
ternary composites. The mechanical properties of such
ternary composites are determined not only by their
composition and the characteristics of the components
but also by the phase morphology, and in particular, the
relative dispersion of additive components [11].
To meet demanding engineering and structural speci-
fications, PP is rarely used in its original state and is of-
ten transformed into composites by the inclusion of fill-
ers or reinforcements.
There are a number of inorganic mineral fillers used
with Polypropylene. The most common of these fillers
*Corresponding author.

C. O. MGBEMENA, O. A. OKOYE
842
are talc, calcium carbonate and barium sulphate; other
mineral fillers used are calcium silicate (wollastonite)
and mica (aluminosilicates).
Mineral fillers are generally much less expensive than
polypropylene resin itself. Mineral fillers reduce the
costs of the compound formed with polypropylene and
also increase the stiffness. Mineral fillers also provide
reinforcement to the polymer matrix as well. Some min-
eral fillers are surface treated to improve their handling
and performance characteristics. Silanes, glycols, and
stearates are used commercially to improve dispersion,
processing, and also to react with impurities [10].
In this work, the mineral filler used is talc. Hydrated
magnesium silicate [Mg3Si4O10(OH)2], or better known
as talc occurs as the alteration products of magnesium
carbonate rock by the natural action of hydrothermal
solutions. The purer forms are called steatite talc. The
advantages of talc are: Good stiffness, hardness, dimen-
sional stability and reduced creep compared with un-
modified PP [12].
Talc can resist temperatures up to 900˚C. It is unaf-
fected by chemicals and will not harm living tissue. Talc
can be utilized as a medium filler of average whiteness in
thermosetting as well as thermoplastic resins where im-
provements in electrical insulation, heat, and moisture
resistance, chemical inertness and good machinability are
needed. Talc has low absorption rate and because of its
plate like structure, certain grades can improve flexural
properties of mouldings.
In PP, talc gives a good balance of rigidity and impact
strength [13]. Advanced milling technology can be used
to obtain the finest talc without reducing the reinforcing
power of the lamellar structure. Talc filled composites
are also easier to colour with reduced pigment require-
ment due to its whiteness and low yellow index. Al-
though investigations on talc-filled PP have been done
since the 1981, there are still many works that involve
the characterization of talc filled PP, which are still on-
going until today [8].
2. Materials and Methods
2.1. Materials
The grade of Polypropylene used in this work was
SEETEC Homo polymer PP by LG Chem Korea. This
acts as the matrix. The homo polymer PP has a density of
0.90 g/cm3 and a melt flow rate of 14 g/10 minutes (2.16
kg at 230˚C). The nano filler used in this work was Talc
(Zeta talc EW 20) manufactured by Eral, Turkey, with
particle size of around 2 μm. All the materials were pur-
chased from the local chemical market at Ajasa Ose,
Onitsha. The mould release agent used was Petroleum
jelly (Vaseline). The characteristic properties of the ma-
terials are shown in Table 1.
The nanocomposites were prepared by melting the PP
in a mixer and melt compounding it with talc respec-
tively at filler loadings of 0%, 5%, 10%, 15%, 20%, 25%,
30%, 35% and 40% volume fractions. The tensile sam-
ples were cast in an aluminum mould in accordance with
ASTM standard D638 for tensile tests, D790 for flexural
tests and D256 for impact tests.
2.2. Method of Preparation
Manual Mixing and Compounding
The PP was melted from its pelletized form at a tem-
perature exceeding 180˚C in a mixing chamber. Meas-
ured amounts of Talc were added to the melted PP by
volume fractions and stirred continuously for 10 minutes
to ensure a uniform dispersion of the mixture. The com-
pounded mixture was cast in an aluminum mould that has
been treated with a mould releasing agent and dried. The
composite was allowed to cure for 72 hours and was later
de-moulded. The composition of composites taken for
mechanical tests is shown in Table 2.
2.3. Tensile Testing of the Samples
The tensile experiment was performed on ABBA Uni-
versal Testing Machine at a laboratory temperature of
25˚C. The testing machine has rectangular upper and
lower grip equipped with centre marking to facilitate the
correct positioning of the test specimen when mounted
vertically. Tensile testing was performed to determine
elastic modulus, ultimate stress, and ultimate strain for
all samples. The specimen was prepared and tested in
accordance with ASTM D 638.
A minimum of seven samples were tested in each
specimen at their various volume fractions. The speci-
men subjected to tensile test has the dimension 50 × 30 ×
20 mm.
Table 1. Characteristic properties of the materials used for the composites.
Material Trade Name Supplier Melt Flow IndexDensity g/cm3 Melting Temperature ˚C Shape
Polypropylene SEETEC
Homo Polymer
LG Chem
Korea
230˚C,
2.16 kg/10 min 0.90 170 Pellets
Talc Zeta talc EW 20 Eral Turkey - 2.7 - Powder

C. O. MGBEMENA, O. A. OKOYE 843
Table 2. Combination of composites taken for mechanical
tests by volume fractions.
Specimen Code PP % Talc %
PPT-0
PPT-1
PPT-2
PPT-3
PPT-4
PPT-5
PPT-6
PPT-7
PPT-8
100
95
90
85
80
75
70
65
60
0
5
10
15
20
25
30
35
40
In order to analyze the data, load was converted to
stress, σ, from Equation (1)
0
F
A
  (1)
where F is the force applied as reported from the tensile
testing equipment, and A0 is the original cross sectional
area calculated from the average of the sample’s neck
measurements.
Displacement was converted to millimeters and strain,
ε, was calculated using
0
l
l



l
0
l
(2)
where the change in length of the sample as ob-
tained from the extensometer data, and is the original
extensometer gage length.
The natural strain (or True fracture ductility) is ex-
pressed as
0
ln
n
f
A
A
  (3)
where A0 is the original cross sectional area calculated
from the average of the sample’s neck measurements and
Af is the Area of the fractured surface.
The Ultimate strength is expressed as
max
0
u
F
A
 
b
E
(4)
where Fmax is the maximum applied force to break the
specimen.
Ultimate stress and strain were taken as the maximum
values at the sample fracture point, as determined in the
data. Results from multiple tests were averaged for each
system.
2.4. Flexural Testing of the Samples
Flexural modulus and strength were measured according
to ASTM D790 test method with three point bending and
was carried out using Instron Universal testing Machine
Series XI and support span length was adjusted to 50
mm.
The Flexural Modulus values () were calculated
using the following equation:
3
3
4
b
Lm
Ebd  (5)
where, m is the slope of the tangent to the initial straight
line portion of the load-deflection curve.
The Flexural strength (S) in the units of MPa was cal-
culated using the following equation:
2
3
2
PL
Sbd  (6)
where P is the applied load at the deflection point, L is
the span length, d and b are the thickness and width of
the specimen respectively.
3. Results and Discussion
From the results of the tensile and flexural tests con-
ducted on the composite, scatter diagrams were made
using Microsoft Excel to evaluate/show the effect of the
addition of the talc filler as it affects the tensile strength,
percentage elongation at break, flexural strength and
modulus. In order to give additional analysis, the talc
filler content effect was presented mathematically to fur-
ther describe explicitly the various equations associated
with each scatter diagram earlier developed using Mi-
crosoft Excel. This mathematical expression shows the
actual talc filler content on the fracture mechanical prop-
erties of the sample composite.
Furthermore, the experimental data was used to search
for a relationship amongst the fracture mechanical prop-
erties in order to predict the point of convergence of the
product material properties in terms of its fracture me-
chanical properties.
3.1. Tensile Test Results
Figure 1 depicts the linearity of the stress-strain proper-
ties obtained from the tensile tests. It explains ductile to
brittle transition of the PP matrix as talc filler particles
are incorporated. At lower talc filler concentrations of
5% - 20%, extensive plastic deformations (molecular
chain breakage) took place before fracture of the Talc/PP
composite when the tensile test was performed. The line-
arity of the initial part is consistent with the Principles of
Hooke’s Law for elastic deformation and the Young’s
Modulus of Elasticity can be obtained from the straight
line. Also, at filler concentration higher than 20%, the
Talc/PP composite exhibited little and no plastic defor-
mation before fracture. This is because the Talc/PP com-
posite displays less ductile characteristics and miniature

C. O. MGBEMENA, O. A. OKOYE
844
(visible) signs of brittle characteristics such as restriction
of the polymer chains.
Equation describing the curve is
1042 18.75

 
8.75 1042
(7)
1

  (8)
1042
118.75 18.75







(9)

18.75 155.573

  (10)
where 0

is the ultimate strength at zero strain and is
equal to 18.75 MPa and Equation (10) is in the form of
equation developed by [14]. This becomes
0

1 55.573



55.573
(11)

From Equation (11), the talc filler content can be
mathematically represented as
(12)
3.2. Flexural Test Results
Figure 2 shows the effect of talc filler on the flexural
force applied on the nanocomposite. The highest applied
force is at 10% talc filler concentration because of the
high ductility characteristics exhibited by the PP matrix
and at higher concentrations, the flexural force applied
declines. The ductile characteristics start to reduce at
higher concentrations till the brittleness starts taking ef-
fect on the composite.
Equation describing the curve is
23
7277 184.19.3090.108F (13)


23
184.1 9.3090.108
7277 17277 72777277 F



  




253
7277 10.02530.00121.4810F
(14)



(15)


Figure 1. Plot of ultimate stress on tensile strain.
Figure 2. Plot of flexural force on volume fraction.

C. O. MGBEMENA, O. A. OKOYE 845
where 0
F
is the ultimate flexural force at zero volume
fractions and is equal to 7277N and Equation (15) is in
the form of equation developed by [14]. This becomes
253
1.48 10  
253
1.48 10  
0.663 0.009
0
1 0.02530.0012
F
F   (16)
From Equation (16), the talc filler content can be
mathematically represented as
0.0253 0.0012  (17)
Figure 3 shows the effect of talc filler on the deflec-
tion of the sample composite when the flexural tests were
conducted. The deflection displays a steady reduction or
decline in response to increasing talc filler concentrations
and as such, describing the flexural characteristics of the
sample composite at each volume fraction.
Equation describing the curve is

 (18)
0.009
10.663





0.663
 (19)


0.663  1 0.0136
(20)
where δ0 is the ultimate defection at zero volume frac-
tions and is equal to 0.663 and Equation (20) is in the
form of equation developed by [14]. This becomes
0


1 0.0136 
0.0136
2
46.91 0.5340.017S
(21)
From Equation (21), the talc filler content can be
mathematically represented as
(22)
From Figure 4, it was found that the flexural strength
of the neat PP is 46 MPa and for talc filler concentrations
of 10% to 15%, there was a steady increase in the flex-
ural strength as shown above. The maximum flexural
strength was obtained for talc concentration of 10%. Also,
talc concentration of 20% and more led to the increase of
brittleness which caused the decline of the flexural
strength of the PP/Talc composite [15].
Equation describing the curve is

 (23)
2
0.534 0.017
46.91 146.91 46.91
S








42
46.91 10.0113.6210S
(24)



 (25)


S
where 0 is the ultimate flexural strength at zero vol-
ume fractions and is 46.91 MPa and Equation (25) is in
the form of equation developed by [14]. This becomes
42
0
10.0113.62 10
S
S



42
0.0113.62 10
(26)
From Equation (26), the talc filler content can be
mathematically represented as


23
1381 69.841.9030.025
b
E
(27)
Figure 5 shows that the addition of talc greatly in-
creased the flexural modulus at all levels of the composite.
This continuous increase is as a result of the Talc filler
particles mixed into the polypropylene matrix making the
composite more brittle. The most significant increase is
seen in talc filler concentrations of 10% - 30%.
Equation describing the curve is

 (28)
23
69.84 1.9030.025
1381 11381 13811381
b
E








253
1381 10.0510.00141.8110
b
E
(29)



 (30)


where Εb0 is the ultimate flexural modulus at zero vol-
ume fractions and is 1381 MPa and Equation (30) is in
the form of equation developed by [14]. This becomes
253
0
10.0510.00141.81 10
b
b
E
E


  (31)
Figure 3. Plot of deflec tion on volume fraction.

C. O. MGBEMENA, O. A. OKOYE
846
Figure 4. Effect of filler concentrations on flexural strength of the composite.
Figure 5. Effect of filler concentrations on flexural modulus of the composite.
From Equation (31), the talc filler content can be
mathematically represented as
253
1.81 10  0.051 0.0014  (32)
4. Conclusions
The results of the study showed that the addition of talc
nano-filler has resulted in some improvement in the ten-
sile mechanical properties of the Homo Polypropylene.
The flexural modulus increases with increase in the talc
filler concentrations of 0% to 20%. From the result of the
experiments conducted, it was observed that 10% of talc
filler concentration led to an optimum value of the flex-
ural strength. The tensile strength showed no consider-
able change up till nano-filler concentration of 10%.
According to Liang et al., the strength of particulate-
filled polymer composites depends, to a great extent, on
the interfacial adhesion between the matrix and the filler
which will facilitate the transfer of a small section of
stress to the filler particle during deformation. Tensile
mechanical properties seem to be affected by the disper-
sion/distribution of the nanoparticles.
Fracture represents one of the major problems associ-
ated with the selection and use of engineering materials
for high temperature applications. The fracture toughness
is of special relevance on the design of components. It is
one of the mechanical characteristics that have more dif-
ficulty in its determination and analysis as there are nu-
merous factors affecting it such as: Temperature, Strain
rate, Specimen dimension and the testing geometry.
The fracture behavior/toughness of polymers is
strongly affected by the addition of rigid particles [16-
18]. Several features of the particles have a decisive in-
fluence on the values of the fracture toughness: shape
and size, chemical nature, surface nature, concentration
by volume, and orientation. Among those of thermoplas-
tic matrix, polypropylene (PP) composites are the most
industrially employed for many different application
fields.
From the foregoing, it is clear that the strength of a
nano-filled composite depends to a great extent on the
interfacial adhesion between the polymer matrix and the

C. O. MGBEMENA, O. A. OKOYE 847
nano-filler which aids the transfer of a small section of
stress to the filler particle during deformation.
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