Mechanical Properties of Iron Ore Tailings Filled-Polypropylene Composites

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Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 671-678

Published Online July 2012 (http://www.SciRP.org/journal/jmmce)

Mechanical Properties of Iron Ore Tailings

Filled-Polypropylene Composites

Segun Mathew Adedayo1, Modupe Adeoye Onitiri2*

1Department of Mechanical Engineering, University of Ilorin, Ilorin, Nigeria

2Department of Mechanical Engineering, University of Lagos, Lagos, Nigeria

Email: *[email protected]

Received February 4, 2012; revised March 20, 2012; accepted April 15, 2012

ABSTRACT

Iron ore tailings filled polypropylene (PP) composites were produced using the compo-indirect squeeze casting (C-ISC)

process. Particle sizes 150, 212 and 300 µm where considered for different volume fractions of 5% to 30% at intervals

of 5%. The tensile and impact behavior of the produced composites were investigated, experimentally, by carrying out

uniaxial tensile and izod impact tests to obtain tensile strength, elongation at break, modulus of elasticity and impact

strength. Empirical data were compared with results obtained from models proposed by Nielsen, Bigg and Einstein. The

experimental results show that elongation at break for iron ore tailings filled PP reduces with increasing 150 µm particle

size. Tensile strength reduces with increasing filler. The Bigg equation exhibited improved predictability with decreas-

ing 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. Izod impact strength decreases with particle size but increases

with increasing volume content of iron ore tailings from 5% to 25% for each particle size considered.

Keywords: Compo-Indirect Squeeze Casting; Iron Ore Tailings; Polypropylene; Izod; Composite

1. Introduction

Particle reinforced plastics composites (PRPCs) are com-

posites to which fillers (discrete particles) have been

added to modify or improve the properties of the matrix

and/or replace some of the matrix volume with a less

expensive material. Common applications of PRPCs in-

clude structural materials in construction, packaging,

automobile tyres, medicine, etc. Determination of effec-

tive properties of composites is an essential problem in

many engineering applications [1,2]. These properties are

influenced by the size, shape, properties and spatial dis-

tributions of the reinforcement [1,3,4].

Among the various studies carried out with particle

filled PP worth mentioning, are works by Maiti and Ma-

hapatro [5,6] on the tensile and impact behavior of nickel-

powder-filled PP and CaCO3 filled PP composites. It was

discovered that the addition of nickel-powder causes de-

crease in tensile modulus, tensile strength and elonga-

tion-at-break with increasing filler. In the case of the

addition of CaCO3, tensile modulus increased while ten-

sile strength and elongation-at-break decreased with in-

creasing filler. Izod impact strength for the composites at

first increased up to a critical filler content, beyond

which the value decreased inappreciably. In a related

work, Tavman [7], performed tensile test on aluminum

powder reinforced high-density polyethylene composites.

The empirical data obtained were compared with theo-

retical findings from the Nielsen’s, Bigg’s and Einstein’s

mathematical models. He discovered that Einstein’s model

explains the experimental results below 12% volume

content of aluminum particles quite well.

This present work intends to investigate, experimen-

tally, the tensile and impact behavior of PP filled with

iron ore tailings. Empirical data obtained from the tensile

test will be compared with the Nielsen’s, Bigg’s and Ein-

stein’s models. The effect of particle size which was not

considered in Tavman’s work will also be considered.

2. Theory

Among the challenges which particle reinforced plastics

composites (PRPCs) present is the complexity of their

mechanical behavior, particularly during plastic defor-

mation. This makes it difficult to predict performance

analytically and hence leads to conservative designs and

extensive test programmes [8].

The tensile behavior of rigid particle reinforced com-

posites is influenced by the particle size, filler concentra-

tion, filler surface treatment, matrix and filler properties,

superimposed pressure and the rate of strain. It is well

established that the fracture of particulate composites is

*Corresponding author.

S. M. ADEDAYO, M. A. ONITIRI

672

associated with interfacial debonding between the matrix

and particles, particle cracking, and the ductile plastic

failure in the matrix depending on the relative stiffness

and strength of the two constituent materials and the in-

terface strength. According to Nie [9], if both constituent

materials have material properties of the same order of

magnitude or if the strength of particle is low, particle

cracking can occur. On the other hand, if the embedded

particles are much stiffer and stronger than the matrix,

matrix cracking (or cavity formation) and particle/matrix

interface debonding become the major damage modes.

Ravichandran and Liu [3] presented a schematic of a

possible damage mode for a two-phase spherical particle

reinforced composite (in perfect adhesion) subjected to

tension. According to them, upon loading at a critical

strain level the matrix deforms more than the filler parti-

cle (interfacial debonding) where formation of cavity for

well bonded particles occurs. Tensile strength and modu-

lus drastically decrease after debonding takes place, and

there is a large increase in volume (dilation) as elonga-

tion continues [4,9].

According to Nielsen [10], the elongation to break of a

system filled with particles of approximately spherical

shaped particles and assuming perfect adhesion can be

predicted by Equation (1) below:



 

 (1)

where c



is the elongation at break of the composite,



is the elongation at break of the unfilled polymer

while



is the percentage volume fraction of the filler.

Bigg [11] proposed a model which states that, for a

case of no adhesion between the polymer matrix and the

filler, the tensile strength of the composite may be ex-

pressed as:









(2)

where c



is the tensile strength of the composite,



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



 (3)

while the second assumes that with poor adhesion be-

tween the filler and the polymer matrix the elastic

modulus can be expressed as:









(4)

where is the elastic modulus for the composite

ile

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)

mat









 



is the weight fraction of particle, mat

where,



is the

density of matrix, and

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,



, was measured at room

temperature based on the Archimedes principle with

water as the immersion medium.



was calculated

from [18]

parwat D











(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-

S. M. ADEDAYO, M. A. ONITIRI

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

S. M. ADEDAYO, M. A. ONITIRI

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)

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].

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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