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
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:

12
1
cp
   (1)
where c

is the elongation at break of the composite,
p

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:
 
23
1b  
cp
 (2)
where c

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-

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 f

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)
(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].

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.
REFERENCES
[1] B. M. Love, “Multiscale Analysis of Failure in Hetero-
geneous Solids under Dynamic Loading,” Ph.D. Thesis,
Virginia Polytechnic Institute and State University, Blacks-
burg, 2004.
[2] J. A. W. Van Dommelen, W. A. M. Brekelmans and F. P.
T. Baaijens, “A Numerical Investigation of the Potential
of Rubber and Mineral Particles for Toughening of Semi-
crystalline Polymers,” Computational Materials Science,
Vol. 27, No. 4, 2003, pp. 480-492.
doi:10.1016/S0927-0256(03)00050-8
[3] G. Ravichandran and C. T. Liu, “Modeling Constitutive
Behavior of Particulate Composites Undergoing Dam-
age,” International Journal of Solids and Structures, Vol.
32, No. 6-7, 1995, pp. 979-990.
doi:10.1016/0020-7683(94)00172-S
[4] Y. W. Kwon, J. H. Lee and C. T. Liu, “Study of Damage
and Crack in Particulate Composites,” Composites Part B:
Engineering, Vol. 29, No. 4, 1998, pp. 443-450.
doi:10.1016/S1359-8368(98)80002-4
[5] S. N. Maiti and P. K. Mahapatro, “Mechanical Properties
of i-PP/CaCO3,” Journal of Applied Polymer Science, Vol.
42, No. 12, 2011, pp. 3077-3273.
[6] S. N. Maiti and P. K. Mahapatro, “Mechanical Properties
of Nickel-Powder-Filled Polypropylene Composites,” Poly-
mer Composites, Vol. 13, No. 1, 1992, pp. 47-52.
doi:10.1002/pc.750130107
[7] I. H. Tavman, “Thermal and Mechanical Properties of
Aluminum Powder-Filled High-Density Polyethylene Com-
posites,” Journal of Applied Polymer Science, Vol. 62,
No. 12, 1996, pp. 2161-2167.
doi:10.1002/(SICI)1097-4628(19961219)62:12<2161::AI
D-APP19>3.0.CO;2-8
[8] M. A. McCarthy and J. F. M. Wiggeraad, “Numerical
Investigation of a Crash Test of a Composite Helicopter
Subfloor Structure,” Composite Structures, Vol. 51, No. 4,
2001, pp. 345-359. doi:10.1016/S0263-8223(00)00150-1
[9] S. Nie, “A Micromechanical Study of the Damage Me-
chanics of Acrylic Particulate Composites under Ther-
momechanical Loading,” Ph.D. Thesis, State University
of New York, Buffalo, 2005.
[10] L. E. Nielsen, “Simple Theory of Stress-Strain Properties
of Filled Polymers,” Journal of Applied Polymer Science,
Vol. 10, No. 1, 1996, pp. 97-103.
doi:10.1002/app.1966.070100107
[11] D. M. Bigg, “Mechanical, Thermal, and Electrical Prop-
erties of Metal Fiber-Filled Polymer Composites,” Poly-
mer Engineering & Science, Vol. 19, No. 16, 1979, pp.
1188-1192. doi:10.1002/pen.760191610
[12] A. Einstein, “On the Movement of Small Particles Sus-
pended in Stationary Liquids Required by the Molecu-
lar-Kinetic Theory of Heat,” Annale n de r Phy sik, Vol. 17,
1905, pp. 549-560.
[13] R. P. Lukens, “ASTM E 171: Standard Specification for
Standard Atmospheres for Conditioning and Testing Ma-
terials,” Annual ASTM Standards, Vol. 41, 1981, pp.
190-193.
[14] R. P. Lukens, “ASTM E 41: Standard Definitions of
Terms Relating to Conditioning,” Annual ASTM Stan-
dards, Vol. 41, 1981, pp. 56-58.
[15] S. O. Adepoju and B. M. Olaleye, “Gravity Concentration
of Silica Sand from Itakpe Iron-Ore Tailings by Tabling
Operation,” Nigerian Journal of Engineering Manage-
ment, Vol. 2, No. 2, 2001, pp. 51-55.
[16] P. A. Olubambi and J. H. Potgieter, “Effectiveness of
Gravity Concentration for the Beneficiation of Itakpe
(Nigeria) Iron Ore Achieved through Jigging Operation.”
Journal of Mineral & Materials Characterization & En-
gineering, Vol. 4, No. 1, 2005, pp. 21-30.
[17] V. John, “Testing of Materials,” Macmillan, London,
1992.
[18] J. Wang, “High-Temperature Deformation of Al2O3/Y-
TZP Particle Composites and Particulate Laminates,”
Ph.D. Thesis, University of Texas, Austin, 2003.
[19] R. A. Priemon-Storer, “ASTM D 638: Standard Test
Methods for Tensile Properties of Plastics,” Annual Book
of ASTM Standards, Vol. 08.01, 1985, pp. 227-253.
[20] R. A. Priemon-Storer, “ASTM D 618: Standard Methods
of Conditioning Plastics and Electrical Insulating Mate-

S. M. ADEDAYO, M. A. ONITIRI
678
rials for Testing,” Annual Book of ASTM Standards, Vol.
1, 1985, pp. 208-213.
[21] R. A. Priemon-Storer, “ASTM D 256: Standard Test Me-
thods for Impact Resistance of Plastics and Electrical In-
sulating Materials,” Annual Book of ASTM Standards,
Vol. 1, 1985, pp. 99-120.