ss="t m4 x14 h13 y6b ff4 fse fc0 sc0 ls0">
is the tensile strength of the composite,
p
is the tensile strength of the polymer matrix while b is a
constant which accounts for the adhesion quality between
the matrix and filler. b = 1.21 implies the extreme case of
poor adhesion, hence, a lower b value e.g. b = 1.1 implies
better adhesion.
Einstein [12] proposed two equations which are valid
only at low concentration. The first assumes that with
perfect adhesion between the filler and the polymer ma-
trix the elastic modulus can be expressed as:

12.5
cp
EE
 (3)
while the second assumes that with poor adhesion be-
tween the filler and the polymer matrix the elastic
modulus can be expressed as:
1
cp
EE

c
E
wh
(4)
where is the elastic modulus for the composite
ile
p
E is the elastic modulus for the polymer matrix.

3. Experimental
3.1. Materials
The matrix used is commercial polypropylene with a
density of 0.91 Mg/m3 in pellet form produced by Lotte
Daesan Petrochemical Corporation under the brand name
“Séetec”. The filler is iron ore tailings in particle form
and approximately irregular in shape with particle sizes
150, 212 and 300 µm from iron ore beneficiation plant in
Itakpe, Kogi State in the Middle belt region of Nigeria.
3.2. Iron Ore Tailings Preparation
The iron ore tailings was dried at room temperature 30˚C
± 2˚C and 50% ± 5% relative humidity for a minimum of
40 hours prior to testing [13,14]. The different particle
sizes were generated using standard ASTM laboratory
sieves [15,16].
3.3. Production of ITR-PPC Tensile Test
Specimens
The dimensions of the ITR-PPC tensile test specimens
are in conformity with BS 18 specimen specification [17].
The ITR-PPC tensile test specimens are dumb-bell shaped
with circular cross section and 64 mm long.
The compo-indirect squeeze casting (C-ISC) process
was used to produce the ITR-PPC tensile test specimens.
Five specimens were produced for each mix ratio 5% to
30% at intervals of 5% for the three particle sizes con-
sidered.
The particle volume fraction was calculated for the
ITR-PPC using the relationship [7]:
(5)
p
ar
mat
1

 
is the weight fraction of particle, mat
where,
is the
density of matrix, and
p
ar is the density of particle.
The weight fraction of particle,
, was determined
using a OHAUS digital scale with an accuracy of 0.01 g.
The density of the particle,
p
ar
, was measured at room
temperature based on the Archimedes principle with
water as the immersion medium.
p
ar
was calculated
from [18]
parwat D
M
S




(6)
where, wat
is the density of water, D is the dry mass of
particle, S is the mass of particle suspended in water, M
is the mass of particle saturated with water.
For the C-ISC process, required quantity of PP was
poured into the crucible and placed on the heating ele-
Copyright © 2012 SciRes. JMMCE
S. M. ADEDAYO, M. A. ONITIRI
Copyright © 2012 SciRes. JMMCE
673
phere [13,14] on an Instrom 3369 testing machine. Prior
to testing, the tensile test specimens were conditioned at
room temperature 30˚C ± 2˚C and 50% ± 5% relative hu-
midity for a minimum of 40 hours [14,15,20].
ment in the melting chamber. The chamber was covered
using the transparent screen (with the stirrer already
fixed to it). The temperature monitoring and control unit
was plugged to the AC mains and switched on. The dial,
initially at zero, was set to 170˚C and the PP melted. This
temperature produces a gelatinous state which is the pre-
ferred condition for further processing in the production
rig. Then appropriate quantity of iron ore tailings was
added to the melt and stirred thoroughly to obtain a good
blend. The melt was stirred to obtain a good mix and
even distribution of heat. Hasty addition of the tailings
could lead to increased melting time which could burn
the PP.
3.5. Izod Impact Test
The impact test was carried out as specified in ASTM D
256 under standard laboratory atmosphere on an Avery-
Denison 6705/U series impact testing machine [21]. Prior
to testing, the impact test specimens were conditioned at
room temperature 30˚C ± 2˚C and 50% ± 5% relative hu-
midity for a minimum of 40 hours [14,15].
Prior to melting the PP and adding the iron ore tailings,
the metal mould and barrel were preheated to tempera-
tures of 100˚C - 120˚C and 170˚C, respectively. The
temperature of the barrel was kept at the same tempera-
ture as the melt to allow for easy flow of the molten mix.
Mould temperature above 120˚C produced specimens
that were brittle and flaky with irregular geometry. After
the required mix had been achieved, the plunger is pulled
out of the barrel and the mix poured into the barrel
through the funnel at a steady continuous rate to prevent
turbulence which could lead to air pockets developing in
the cast. The plunger is then pushed into the barrel at a
steady rate of approximately 3.75 mm/s and pressure of
27 kN/mm2. After two hours the mould was dismantled
to remove the cast. This procedure was carried out for
different particle sizes and corresponding volume content
of iron ore tailings.
4. Results and Discussion
Tables 1-3 and Figures 1-3 and 5 were obtained from
the uniaxial tensile test carried out on the produced com-
posites. Tables 1-3 show the tensile stress-strain results
for 150, 212 and 300 µm particle size iron ore tailings
reinforced polypropylene composites (ITR-PPC) while
Figure 1 shows the stress-strain curves for pure poly-
propylene (PP) and PP reinforced with 5% and 15% iron
ore tailings.
It can be seen in Table 1 that inclusion of 150 µm par-
ticle size in PP causes reduction in yield, ultimate and
fracture stress and strain compared with pure PP (see
Figure 1). 15% ITR-PPC exhibited the highest strain
value at ultimate and fracture point while 5% ITR-PPC
has the highest stress at ultimate and fracture point for all
mix ratio considered. Table 2 shows that the addition of
212 µm particle size in PP leads to drop in tensile prop-
erties of the composites when compared with pure PP.
ITR-PPC exhibited the highest rigidity and plastic de-
formation with the addition of 5% iron ore tailings. Ta-
ble 3 shows that ITR-PPC experiences reduced yield
3.4. Tensile Test
The tensile test was carried out as specified in ASTM D
638 at a test speed was 1.30 mm/min [19]. The tensile
test was carried out under standard laboratory atmos-
Figure 1. Stress-strain curves of pure PP and ITR-PP composites with particle sizes 150 µm, 212 µm and 300 µm at volume
content 5% and 15% of iron ore tailings.
S. M. ADEDAYO, M. A. ONITIRI
674
Table 1. Stress-strain results (tensile) for 150 µm particle size ITR-PPC.
Volume ratio of iron ore tailings (%)
0 5 10 15 20 25 30
Min. Mean Max.S.D
Stress at
yield (MPa) 3.40 +0.10
0.10 2.60 +1.20
1.41 2.42 +0.58
1.12 2.59 +0.91
0.32 3.63 +0.87
0.23 2.95 +0.5
0.23 2.95 +1.55
1.55 2.42 3.42 3.63 0.69
Stress at
ultimate
point (MPa)
12.05 +1.05
1.05 7.38 +1.38
1.38 6.84 +0.96
0.84 5.33 +0.17
0.13 5.92 +1.08
1.08 5.05 +3.51
1.29 5.25 +0.75
0.75 5.05 7.97 12.502.08
Stress at
fracture
(MPa)
12.05 +1.05
1.05 7.30 +0.00
0.00 5.70 +4.30
4.30 3.87 +0.37
0.37 5.92 +0.00
0.00 2.56 +0.13
0.13 2.55 +0.25
0.25 2.55 6.66 12.502.45
Strain at
yield (%) 1.00 0.51 0.50 0.50 0.80 1.00 0.60 0.50 0.82 1.000.25
Strain at
ultimate
point (%)
7.00 4.50 4.00 5.50 5.00 3.70 3.60 3.60 5.55 7.001.08
Strain at
fracture (%) 7.00 4.50 4.50 6.10 5.00 5.00 5.00 4.50 6.18 7.001.06
Table 2. Stress-strain results (tensile) for 212 µm particle size ITR-PPC.
Volume ratio of iron ore tailings (%)
0 5 10 15 20 25 30
Min. Mean Max.S.D
Stress at
yield (MPa) 3.40 +0.10
0.10 2.90 +1.10
1.10 1.50 +0.57
1.73 1.37 +1.33
0.27 2.20 +0.80
0.70 0.76 +0.01
0.01 0.98 +1.02
0.73 0.76 2.18 3.40 0.92
Stress at
ultimate
point (MPa)
12.05 +1.05
1.05 4.30 +1.33
1.33 4.13 +0.13
0.13 5.23 +0.97
0.98 4.13 +0.27
0.13 4.40 +0.60
1.40 3.77 +0.27
0.63 3.77 6.33 12.501.85
Stress at
fracture
(MPa)
12.05 +1.05
1.05 4.50 +1.33
1.33 1.70 +0.00
0.00 4.48 +0.25
0.25 1.49 +0.41
0.33 2.10 +0.40
0.40 2.75 +0.05
0.05 1.48 4.85 12.502.13
Strain at
yield (%) 1.00 0.80 0.10 0.55 0.60 0.45 0.50 0.10 0.67 1.000.27
Strain at
ultimate
point (%)
7.00 4.30 7.00 3.00 3.00 2.00 2.00 2.00 4.72 7.001.92
Strain at
fracture (%) 7.00 4.50 4.00 4.30 4.00 4.60 3.00 3.00 5.23 7.001.02
Table 3. Stress-strain results (tensile) for 300 µm particle size ITR-PPC.
Volume ratio of iron ore tailings (%)
0 5 10 15 20 25 30
Min. Mean Max.S.D
Stress at
yield (MPa) 3.40 +0.10
0.10 3.45 +0.15
0.15 2.30 +0.49
0.50 1.75 +0.90
0.75 2.07 +0.43
0.28 1.60 +1.00
0.50 1.25 +0.25
0.25 1.25 2.64 3.45 0.90
Stress at
ultimate
point (MPa)
12.05 +1.05
1.05 3.42 +0.98
0.92 5.30 +0.30
0.30 3.25 +0.25
0.25 3.04 +0.41
0.41 4.66 +0.21
0.21 2.80 +0.10
0.10 2.80 5.75 12.502.05
Stress at
fracture
(MPa)
12.05 +1.05
1.05 2.84 +0.98
0.92 5.30 +0.30
0.30 2.98 +0.38
0.38 3.04 +0.41
0.41 3.50 +0.00
0.00 2.80 +0.10
0.10 2.80 5.42 12.502.02
Strain at
yield (%) 1.00 0.67 0.01 0.50 0.50 0.50 0.30 0.01 0.58 1.000.27
Strain at
ultimate
point (%)
7.00 5.00 6.00 3.10 4.50 6.00 1.21 1.21 5.47 7.002.05
Strain at
racture (%) 7.00 5.45 6.00 5.00 4.50 7.00 1.21 1.21 6.03 7.001.98
f
Copyright © 2012 SciRes. JMMCE
S. M. ADEDAYO, M. A. ONITIRI
Copyright © 2012 SciRes. JMMCE
675
strength for all particle sizes. The relationship between
experimental tensile strength and the Bigg’s model seem
to improve with decreasing particle size. This could be
attributed to the fact that perfect adhesion, in the absence
of binding agents, improves with decreasing particle size.
Large particle size creates greater filler surface area to be
covered by the matrix and thinner inter particle space to
occupy with increasing volume concentration of fillers
(see Fi g u r e 4).
stress with increasing percentage volume of iron ore tail-
ings at a standard deviation of 0.9.
The elongation at break versus volume fraction of 150,
212 and 300 µm iron ore tailings at varying volume con-
tent in PP curves are presented in Figure 2. It can be
seen that the Nielsen model gives poor representation
with increasing percentage volume of iron ore tailings
from 15% in the case of 212 µm fillers. This shows that
the weak adhesion between particles and matrix of ITR-
PPC, due to absence of binding agents, becomes signifi-
cant at high volume concentration of fillers for Neilsen
model which assumes perfect adhesion.
The modulus of elasticity versus volume of 150, 212
and 300 µm iron ore tailings at varying volume content
in PP curves are presented in Figure 5. The experimental
results are compared with values calculated from the
Einstein equations. Einstein equation which assumes
perfect adhesion between fillers and the polymer shows
Figure 3 shows the tensile strength versus volume of
150, 212 and 300 µm iron ore tailings in PP curves.
Bigg’s model gives poor representation of the tensile
(a) (a)
(b) (b)
(c) (c)
Figure 2. Elongation at break versus volume of (a) 150 µm;
(b) 212 µm; (c) 300 µm iron ore tailings in PP. Figure 3. Tensile strength versus volume of (a) 150 µm; (b)
212 µm; (c) 300 µm iron ore tailings in PP.
S. M. ADEDAYO, M. A. ONITIRI
676
(a)
(b)
(c)
(d)
Figure 4. (a) Pure polypropylene; 25% volume content of (b)
150 µm; (c) 212 µm and (c) 300 µm iron ore tailings in
polypropylene (×100).
good match for volume fractions below 5% for all the
particle sizes. Einstein equation which assumes poor ad-
hesion exhibits an improved predictability with increas-
ing particle size. This trend confirm the fact that the
composite produced, as earlier stated, is expected to ex-
hibit poor adhesion with increasing volume content of
filler or particle size due to the absence of binding agent.
Figure 6 shows the average impact energy versus vol-
ume content of iron ore tailings particle sizes 150 µm,
212 µm and 300 µm in PP. The entire specimens experi-
enced complete break when impacted. Izod impact
strength increased with increasing volume of 150 µm
iron ore tailings except at 10% where average impact
energy of 4.393 J was recorded compared with 4.501 J
(a)
(b)
(c)
Figure 5. Modulus of elasticity versus volume of (a) 150 µm;
(b) 212 µm; (c) 300 µm iron ore tailings in PP.
for polypropylene. Addition of 212 µm iron ore tailings
causes improved impact strength for volume ratio con-
sidered; with the highest value of 4.867 J recorded at 5%.
After the initial drop at 5%, addition of 300 µm iron ore
tailings causes increase in impact strength with increas-
ing filler content contrary to the trend highlighted in
Maiti and Mahapatro’s work on nickel-powder-filled PP
and CaCO3 filled PP [5,6].
Copyright © 2012 SciRes. JMMCE
S. M. ADEDAYO, M. A. ONITIRI 677
Figure 6. Average impact energy versus volume content of
iron ore tailings curves for PP-filled with 150 µm, 212 µm
and 300 µm iron ore tailings particle sizes at volume content
0% to 30%.
5. Conclusion
Nielson’s model shows better predictive capability with
the smallest particle size and decreasing volume ratio for
ITR-PP. The predictability of the Nielsen’s model can be
enhanced by addition of binding agents to improve inter-
facial adhesion. The Bigg equation shows improved pre-
dictability with decreasing particle size of filler in PP
while the Einstein equation which assumes poor adhesion
gives the best prediction of modulus of elasticity with
increasing particle size in PP. The least volume content
of iron ore tailings that can be predicted by the Einstein
equation which assumes perfect adhesion is 5%. Izod
impact strength increased with increasing volume of 150
µm iron ore tailings except at 10% volume content of
iron ore tailings.
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