Materials Sciences and Applicatio n, 2011, 2, 811-817
doi:10.4236/msa.2011.27110 Published Online July 2011 (http://www.SciRP.org/journal/msa)
The Effects of Filler Contents and Particle Sizes on
the Mechanical and End-Use Properties of Snail
Shell Powder Filled Polypropylene
Genevive C. Onuegbu, Isaac Ogbennaya Igwe
Department of Polymer and Textile Engineering, Federal University of Technology, Owerri, Nigeria.
Received February 21th, 2011; revised March 4th, 2011; accepted March 16th, 2011.
ABSTRACT
Polypropylene composites o f snail shell powder were prepared at filler con tents, 0 to 40 wt%. The particle sizes of the
snail shell powder investigated were 0.150, 0.30, and 0.42 µm. Talc, of particle size, 0.150 µm was used as the refer-
ence filler. The polypropylene composites were prepared in an injection moulding machine and the resulting compos-
ites were extruded as sheets. Some mechanical and end-use properties of the prepared composites were determined.
Results showed that the snail shell powder improved the tensile modulus, flexural strength, and impact strength of
polyprop y lene and these properties increased with increases in th e filler content and decreases in the filler particle size.
The elongation at break of the composites was however observed to decrease with increases in the filler content, and
particle size. The elongation at break of talc filled polypropylene was zero, an indication of the brittle nature of poly-
propylene co mposites o f talc. The hardn ess, water sorption (24-hr) and specific gr avity of the composites were found to
increase with increases in the filler content, and decreases in the filler particle size. The level of water absorbed by
snail shell po wder composites of polypropy lene is considerably h igher than that of talc filled polypropylene. The flame
retardant properties of the prepared composites were however found to decrease with increases in the filler content,
and particle size. Generally, snail shell powder was found to show greater property improvement over talc in the pre-
pared composites.
Keywords: Filler, Particle Size, Polypropylene, Snail Shell powder, Composite
1. Introduction
The past decades have witnessed increasing interest in
the use of fillers in the polymer industry. Fillers greatly
enhance the dimensional stability, i mpact resistance, ten-
sile and compressive strength, abrasion resistance and
thermal stability when in corporated into polymers. Fillers
which merely increase the bulk volume, and hence, re-
duce price, are known as extender fillers while those
which improve the mechanical properties particularly
tensile strength are termed as reinforcing fillers [1-4] .
Polypropylene is one of the most important polyole-
fin’s that have wide rage of applications. Presently, there
has been an increase in the use of filled polypropylene in
electrical and automotive engineering. This is mainly due
to the excellent stiffness property which polypropylene
exhibits and which enables it to substitute conventional
materials in demanding engineering applications [5].
Typical fillers for polypropylene are glass fibres, glass
sphere, talc, asbestos, calcium carbonate, silica and mica.
The use of mineral fillers and fibres in making polymer
composites has certain drawbacks. For example, a lot of
energy is required in the processing of glass fibres since
their processing temperatures can exceed 1200˚C. Glass
fibres also tend to abrade processing equipments, and
increase the density of the plastic system [6].There has
been a conbined search for filler materials in compound-
ing polypropylene and which is likely to grow with the
introduction of improved compounding technology, and
new coupling and compatibilizing agents that permit the
use of high filler/reinforcement conten t [7]. As suggested
by Kartz and Milewski [7], fillings up to 75 parts per
hundred(pph) could be common in future.
Different filler materials have been studied for making
polypropy le ne composites. Th es e materials included wo-
od, kenaf and sage fibres [8], saw dust [9], flax [10],
hemp strand [11], green coconut fibre [12], and or-
gano-montmorillonite [13]. Thus, Fan et al. [14] who

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder 812 Filled Polypropylene
studied polypropylene-montmorillonite nanocomposites
reported a decrease in modulus and tensile strength of the
composites with increasing clay conten t. Similarly, Chen
et al. [15] who investigated the properties of polypro-
pylene filled with magnesium hydrox ide reported that the
addition of magnesium hydroxide improved the flame
retardant property of polypropylene/magnesium hydrox-
ide composites, but seriously deteriorated the mechanical
properties. Recently, the use of snail shell powder as a
filler in making polypropylene composite was reported
[16]. Snail shell powder contents of 0 to 5 wt% were
investigated at a powder particle size of 0.30 µm. The
properties of the polypropylene composites determined
were the specific gravity, water sorption (24-hr), flam-
mability, and hardness tests.
In the present report on further utilization of snail shell
powder in filling polypropylene ,the central objectives
are to (i) investigate fully the properties of polypropylene
composites of snail shell since the work reported above
[16] was considered exploratory and limited in scope, (ii)
determine the effects of snail shell powder particle size
on the properties of polypropylene composites. Snail
shell powder contents of 0 to 40 wt% were used in this
study.
Besides the work reported above [16] ,the use of snail
shell powder in filling polypropylene or any other ther-
moplastic had not been reported in the scientific litera-
ture to our knowledge. Snail shell is a domestic waste.
The waste presently does not have any known domestic
application in our locality, and could be found littering
dust bins in our big cities and farm yards in villages.
2. Materials and Method
2.1. Materials
The polypropylene used in this study was obtained from
Eleme Petrochemical Company Limited, Rivers State,
Nigeria. It has a melt flow index of 2.5 - 3.5 g/min, and
density, 0.926 g/cm3. The snail shell from which snail
shell powder was produced was collected locally within
Owerri metropolis, Imo state, Nigeria .The shell was
properly treated to remove impurities before it was
crushed and sieved to three particle sizes namely, 0.150,
0.30, and 0.42 µm. Talc which was used as a reference
filler was purchased from a Chemical Store at Owerri,
Imo State, Nigeria.
2.2. Preparation of Polypropylene Composites
The polypropylene composites of snail shell powder
were prepared by thoroughly mixing 40 g of polypro-
pylene with appropriate filler quantities (0, 5, 10, 20, 30
and 40 wt%). The polypropylene was melted and ho-
mogenized with the filler in an injection moulding ma-
chine. The resulted composites were extruded as sheets.
The polypropylene composites of talc were prepared only
at filler particle size, 0.150 µm.
2.3. Testing
The tensile strength (ASTM D 638), tensile modulus
(ASTM 1822), flexural strength (ASTM D 790-97), im-
pact strength (ASM D256), rock well hardness, (ASTM
D 785), specific gravity (ASM D 792), and water sorp-
tion (24-hr) (ISO 180) properties of the prepared poly-
propylene composites were determined using standard
methods. A modification of ASTM D 4804 was used to
determine the flammability rate of the composites. Since
polypropylene filled or unfilled is a thermoplast, flame
spread is regarded as the rate of melt-burn, i.e., the rate at
which the original length of the specimen decreases as
flame/heat spreads along the specimen. The flammab ility
rate (FR) is expressed as,
FR (mm/s) = Dp/Pt – It [1]
where Dp = Propagation distance measured in millime-
tre.
Pt = Flame propagation time measured in seconds.
It = Ignition time measured in seconds.
3. Results and Discussion
3.1. Mechanical Properties
The mechanical properties of polypropylene composites
prepared in this study have been determined and the re-
sults are illustrated graphically as shown in Figures 1-5.
Talc was used as the reference filler in this study since it
is one of the standard fillers in use in the plastic indu stry
[13].
3.1.1. Tensile Strength
Figure 1 shows the effect of filler contents, and particle
sizes on the tensile strengths of unfilled, and filled poly-
propylene. The tensile strength of polypropylene com-
posites was observed to increase with increases in with
increases in snail shell powder content and particle size.
From Figure 1, it is clear that the smaller the particle
size of snail shell power, the higher the tensile strength of
the polypropylene composite at any snail shell powder
content and particle size considered .The better disper-
sion and filler-matrix interaction may be the two main
reasons or factors responsible for the observed trend.
Similar observations have been reported by Bigg, [17],
and Fuad et al. [18] for other filled systems. However,
Fan et al. [14] reported decreases in tensile strength of
polypropylene-montmorillonite composites with in-
creases in clay content.

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder
Filled Polypropylene
813
3.1.2. Tensile Modulus
Figure 2 illustrates the effects of snail sh ell powder con-
tent, and particle size on the tensile modulus of prepared
polypropylene composites. Like was observed on the
effect of filler content and particle size on the tensile
strength of filled polypropylene, the modulus of the
composites increased with increases in filler content and
filler particle size. This observation highlights the fact
that the incorporation of fillers into polymer matrix im-
proves the stiffness of the composites [19]. The snail
0
20
40
60
80
100
120
140
0 1020304050
Filler content (wt. %)
Tensi le Str engt h (M Pa)
0.15 µm
0.30 µm
0.42 µm
0.15 µm(talc)
(wt%)
Figure 1. Tensile strength versus filler content for polypropylene composites at different filler particle size.
0
2
4
6
8
10
12
14
16
0 1020304050
Filler content (wt.%)
Tensile Modulus (MPa)
0.15 µm
0.30 µm
0.42 µm
0.15 µm(talc)
Figure 2. Tensile modulus versus filler content for polypropylene composites at different filler particle size.
0
20
40
60
80
100
120
140
160
180
0 1020304050
Filler content (wt.%)
FlexuralStrength (MPa)
0.15 µm
0.30 µm
0.42 µm
0.15 µm(talc)
(wt%)
Figure 3. Flexural strength versus filler content for polypropylene composites at different filler particle size.
(wt%)

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder 814 Filled Polypropylene
0
2
4
6
8
10
12
14
0 1020304050
Fill e r content ( wt.%)
El o ng ation at break a ge (%)
0.15 µm
0.30 µm
0.42 µm
0.15 µ m (t alc)
(wt%)
Figure 4. Elongation at breakage versus filler content for polypropylene composites at different filler particle size.
0
20
40
60
80
100
120
140
160
0 1020304050
Filler content (wt.%)
Impa ct Strength (J / m)
0.15 µm
0.30 µm
0.42 µm
0.15 µm(talc)
(wt%)
Figure 5. Impact strength versus filler content for polypropylene composites at different filler particle size.
shell powder exhibited higher tensile modulus on the
composites than talc, the reference filler.
3.1.3. Flexural Strength
From Figure 3, the flexural strength of polypropylene
composites is observed to increase with increases in filler
content, and decreases in filler particle size.
Embu et al. [20] who studied the effect of mica con-
tent on the mechanical properties of polypropylene
composites reported increases in the flexural strength of
the composites with increases in mica content. The pre-
sent study shows that snail shell powder is superior to
talc in improving the flexural stren gth o f polypropylene .
3.1.4. Elongation at Break
Figure 4 shows that the elongation at break for snail
shell powder-polypropylene composites decreases with
increases in filler content at any given filler particle size
considered.
Fillers can be considered as structural elements em-
bedded in the polymer matrix, and at the concentrations
of the filler used (0 - 40 wt%), the contents might not be
high enough to significantly restrain the polypropylene
molecules. Consequently, highly localized strains might
have occurred at the concentrations investigated, cau sing
dewetting between polypropylen e and the filler, and thus,
leaving essentially a matrix that is not ductile. Such a
reduction in elongation at break of a composite with in-
creases in filler content, irrespective of filler particle size
has been reported by Ismail et al. [21]. Figure 4 shows
that the elongation at break of the polypropylene com-
posites decreases with increases in the filler particle size.
It is very interesting to note that in the presen t investiga-
tion, talc filled polypropylen e did not exhibit any elonga-
tion at break, an indication that talc filled polypropylene
is brittle and would no t be suitable for some of the appli-
cations of polypropylene composites.
3.1.5. Impact Strength
The impact strength of polypr opylene composites of snail
shell powder at a particular filler particle size was ob-
served to increase with increases in snail shell powder
content (Figure 5).

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder 815
Filled Polypropylene
The increase in impact strength of the prepared com-
posites was very remarkable for snail shell powder com-
posites of polypropylene than was for talc. This remark-
able performance indicates that snail shell powder was
more effective in distributing the applied stress over a
large volume at the base of the notch, and which helped
to prevent propagation of cracks by carrying large part of
the load in the area under the crack. The increase in im-
pact strength of a polymer composite with increase in
filler content has been reported in the literature [17 ] .The
impact strength of the prepared composites for particular
filler and at a given filler content was observed to de-
crease with increase in filler particle size. Thus, increas-
ing the particle size of snail sh ell powder at a given filler
content probably increased the level of stress concentra-
tion in the composites with the resultant decrease in im-
pact strength.
3.1.6. Hardness
At a given filler particle size, the hardness of polypro-
pylene composites was observed to increase with in-
crease in the amount of filler incorporated into polypro-
pylene (Figure 6).
This result indicates enhancement of abrasion and im-
pact strength of the composites. Generally, the hardness
of the composites could be observed to decrease with
increase in the particle size of the filler at a given filler
content. Such a decrease in the hardness of polypropyl-
ene composites with increases in filler particle size was
reported by Kokta et al. [22].
3.1.7. Water Sorption (24-hr)
The water sorption (24-hr) indices of polypropylene
composites are shown in Figure 7. All the composites
showed increases in water absorption with increase in
filler content at all the filler particle sizes investigated.
Unlike all the other property parameters of the pre-
pared composites discussed, the variation of water ab-
sorption with snail shell powd er content and particle size
is not much, an indication that water absorption by snail
shell powder composites of polypropylene does not de-
pend strongly on the filler content or particle size. All the
prepared snail shell powder compos ites of polypropylene
sorbed more water than that of talc, the reference filler.
Generally, the level of water absorption observed for
snail shell powder composites of polypropylene is con-
siderably higher than those for other mineral filled sys-
tems. Although, water absorption could lead to a de-
crease in the end-use applications of these composites,
there is reason to believe that by understanding the limi-
tations and benefits of these composites, snail shell
powder is not likely to be igno red by the plastic industry
for use in formulat i ng pl ast i c products.
3.1.8. Specific Gravity
Figure 8 shows a gener al increase in the spec ific gravity
of the composites with increases in filler content at any
given filler particle size considered.
However, there was a general decrease in the specific
gravity of the composites with increase in snail shell
powder particle size at any given sn ail shell powder con-
tent considered. The increase in the specific gravity of
snail shell powder composites of polypropylene with a
reduction in filler particle size could be attributed to the
greater uniform distribu tion of the small sized filler in the
matrix. It is interesting to note that the specific gravity of
glass, talc, and mica filled polypropylene are 1.23, 1.27,
and 1.26 respectively [23], values which are less than
those of sn ail shell powder filled polypropylene.
3.1.9. Flame Propagation
The rate of burning of the prepared composites of poly-
propylene at any given particle size of the snail shell
powder considered was generally observed to decrease
with increase in snail shell powder contents (Figure 9).
The above result indicates that the flame retardant
property of polypropylene is enhanced by snail shell
powder. Snail shell powder filled polypropylene was
observed to reduce the rate of burning of polypropylene
more than talc. The present flame retardant property of
the snail shell powder investigated could be attributed to
the following factors. Snail shell powd er, like most other
shells consists mostly of calcium carbonate [24]. On
heating/application of flame, calcium carbonate decom-
poses according to the equation,
32
CaCOCaO+CO


with the evolution of carbon dioxide (CO2) which does
not support combustion. The more snail shell powder is
incorporated into po lypropylen e, the more the qu antity of
calcium carbonate (CaCO3) in the composites, and the
less, the tendency of th e comp osite to bu rn since CO2 is a
good fire extinguisher. Further more, as a filler, the snail
shell powder particles interact with the resin macro-
molecules. The adsorption of the macromolecules on the
filler surfaces which would result in better chain align-
ment, also contributes significantly to the filler’s flame
retardant property .The net result o f all these would be an
intimate union between the filler particle and the binder.
This is expected to raise the thermomechanical properties
such as Tm of the composite as against the unfilled poly-
propylene.
In this study, the effect of filler particle size on the
flame retardant property of snail shell powder is not very
apparent since all the particle sizes investigated exhibited
similar flame retardant property.

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder 816 Filled Polypropylene
4. Conclusions
The mechanical and end-use properties of snail shell
powder filled polypropylene have been determined in
this study. Snail shell powder has sh own greater property
improvement over talc in the prepared composites. The
specific gravity and hardness of snail shell powder filled
polypropylene were observed to increase with increases
in filler content, and decreases in filler particle size. The
flame retardant property of polypropylene is greatly en-
hanced at high filler content, an d filler particle size. With
the exception of talc filled polypropylene, all the pre-
pared composites investigated showed significant water
absorption in a 24-hr water sorption test. The present
study has highlighted the benefits of using snail shell
powder as a filler for polypropylene. The results obtained
suggest that the scope of application of polypropylene
can be greatly broadened with the use of snail shell
powder as a filler.
5. Acknowledgements
The authors express their gratitude to the staff of the
Eleme Petrochemicals Ltd, Port Harcourt, Nigeria for
their support in the preparation of polypropylene com-
posites used in this study.
REFERENCES
[1] B. English, P. Chow and D. S. Bajwaz, “Processing
Composites,” CRC Press, New York, 1997.
[2] K. Oksman and J. F. Selin, “Plastics and Composites
from Polylactic Acid,” Kluwer Academic Press, Berlin,
2004.
[3] A. K. Bledzki and J. Gassan, “Composite Reinforced with
Cellulose-based Fibres,” Progress in Polymer Science,
Vol. 24, No. 5, 1999, pp. 221-274.
doi:10.1016/S0079-6700(98)00018-5
[4] D. Plackett, L. A. Logstrup, P. W. Batsberg and L. Niel-
sen, “Biodegradable Composites based on 1-Polylactide
and Jute Fibres,” Composites Science and Technology,
Vol. 63, No. 9, 2003, pp. 1287-1296.
doi:10.1016/S0266-3538(03)00100-3
[5] L. Sun, M. Xiao, P. Xiao, J. Song, W. Wang, Y. Zhang
and K. Gong, “Electrical Properties of Metal Filled Poly-
propylene Composite,” Society of Plastics Engineers,
Annual Technical Conference, 1986, pp. 2230-2234.
[6] A. R. Sanadi, D. F. Caulfield, R. E. Jacobson and R. M.
Rowell, “In: Kenaf properties, Processing and Products,”
Mississipi State University, Ag and Bio Engineering,
Chapter 32, 1999, pp. 381-392.
[7] H. S. Katz and J. V. Milewski, “Handbook of Fillers for
Plastic,” Van Nostrand Reinhold, New York, 1987.
[8] M. Gahleitner, B. Kretzschmar, D. Pospiech, E. Ingolic, E.
Reichelt N. Reichelt and K. Bernreitner, “Morphology
and Mechanical Properties of Polypropylene/Polyamide 6
Nanocomposites Prepared by a two-step Melt Com-
pounding Process,” Journal of Applied Polymer Science,
Vol. 100, No. 1, 2006, pp. 283-291.
doi:10.1002/app.23102
[9] S. K. Najafi, E. Hamidinia and M. Tajvidi, “Mechanical
Properties of Composites from Sawdust and Recycled
Plastics,” Journal of Applied Polymer Science, Vol. 100,
2006, pp. 3641-3645. doi:10.1002/app.23159
[10] J. Moran, V. Alvarex, R. Petrucci, J. Kenny and A.
Vazquez, “Mechanical Properties of Polypropylene
Composites Based on Natural Fibres subjected to Multi-
ple Extrusion Cycles,” Journal of Applied Polymer Sci-
ence, Vol. 103, No. 1, 2007, pp. 227-237.
doi:10.1002/app.251739
[11] P. Mutje, M. E. Vallejos, J. Girones, F. Vilaseca, A. Lo-
pez, J. P. Lopez and J. A. Mendez, “Effect of Maleated
Polypropylene as Coupling Agent for Propylene Compos-
ites Reinforced with Hemp Strands,” Journal of Applied
Polymer Science, Vol. 102, No. 1, 2006, pp. 833-840.
doi:10.1002/app.24315
[12] J. L. Leblanc, C. R. G. Furtado, M. C. A. M. Leite, L. L.
Y. Visconte and M. H. Ishizaki, “Investigating Polypro-
pylene-Green Coconut Fibre Composites in the Molten
and Solid States through Various Techniques,” Journal of
Applied Polymer Science, Vol. 102, No. 2, 2006, pp.
1922-1936. doi:10.1002/app.24239
[13] W. W. Yi, Z. X. Fei, W. G. Guan and C. J. Feng, “Prepa-
ration and Properties of Polypropylene Filled with Or-
gano-Montmorillonite Nanocomposites,” Journal of Ap-
plied Polymer Science, Vol. 100, No. 4, 2006, pp. 2875-
2880. doi:10.1002/app.23396
[14] Y. Fan, J. Lou and D. M. Shinozaki, “Microstructure
Dependent Properties of Polypropylene-Clay Nanocom-
posites,” Applied Polymer science, Vol, 103, No. 1, 2007,
pp. 204-210.
[15] X. Chen, J. Yu and S. Guo, “Structure and Properties of
Polypropylene Composites Filled with Magnesium Hy-
drixide,” Applied Polymer science, Vol. 102, No. 5, 2006,
pp. 4943-4951.
[16] I. O. Igwe, “Studies on the Properties of Polypropylene
filled with Agricultural and Domestic Wastes,” Journal of
Research in Engineering, Vol. 4, No. 2, 2007, pp. 8-12.
[17] D. M. Bigg, “Mechanical Properties of Particulate filled
Polymers, ” Polymer Composites, Vol. 8, No. 2, 1987, pp.
115-122. doi:10.1002/pc.750080208
[18] M. Y. A. Fuad, Z. Ismail, Z. A. M. Ishak and A. K. M
Omar, “Application of Rice Husk Ash as Fillers in Poly-
propylene: Effect of Titanate, Zirconate and Silane Cou-
pling Agents,” European Polymer Journal, Vol. 31, No. 9,
1995, pp. 885-893. doi:10.1016/0014-3057(95)00041-0
[19] S. N. Das, T. K. Khastgir and D. K. Chakraborty, “Effect
of Filler Blend Composition on the Electrical and Me-
chanical Properties of Conductive AVE Composite,”
Project Euclid, Vol. 8, 2002, pp. 457-634.
[20] Y. E. Embu, C. C. Briggs and R. J. Heath, “The Effect of

The Effects of Filler Contents and Particle Sizes on the Mechanical and End-Use Properties of Snail Shell Powder
Filled Polypropylene
817
Mica Reinforcement on the Mechanical Properties of
Polypropylene,” Nigerian Journal of Polymer Science,
Vol. 1, No. 1, 2000, pp. 40-45.
[21] H. Ismail, H. D. Rozman, R. M. Jaffri and Z. A. Mohd
Ishak, “Oil Palm Wood Flour Reinforced Epoxidized
Natural Rubber Composites: The Effect of Filler Content
and Size,” European Polymer Journal, Vol. 33, No.
10-12, 1997, pp. 1627-1632.
doi:10.1016/S0014-3057(97)00020-7
[22] B. V. Kokta, R. G. Raj and C. Daneault, “Use of Wood
Flour as Filler in Polypropylene: Studies on Mechanical
Properties,” Polymer Plastic Technology and Engineering,
Vol. 28, 1989, p. 247.
[23] R. M. Rowell, A. Sanadi, R. Jacobson and D. Caulfield,
“Properties of Kenalf/Polypropylene Composites,” Mis-
sissipi State University, Ag and Bio Engineering, Chapter
32, 1999, pp. 381-392.
[24] A. S. M. Salenddin and K. M. Wilbur, “Chemical Com-
position of Snail Shell,” Journal of Zoology, Vol. 47,
1969, pp. 51-55.