Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 774-779
Published Online August 2012 (http://www.SciRP.org/journal/jmmce)
Study of Mechanical Behaviour of Coconut Shell
Reinforced Polymer Matrix Composite
J. Olumuyiwa Agunsoye*, Talabi S. Isaac, Sanni O. Samuel
Department of Metallurgical and Materials Engineering, University of Lagos, Lagos, Nigeria
Received February 21, 2012; revised March 30, 2012; accepted April 22, 2012
ABSTRACT
The morphology and mechanical prop erties of coconut shell reinforced polyethylene composite have been evaluated to
establish the possibility of using it as a new material for engineering applications. Coconut shell reinforced composite
was prepared by compacting low density polyethylene matrix with 5% - 25% volume fraction coconut shell particles
and the effect of the particles on the mechanical properties of the composite produced was investigated. The result
shows that the hardness of the composite increases with increase in coconut shell content though the tensile strength,
modulus of elasticity, impact energy and ductility of the composite decreases with increase in the particle content.
Scanning Electron Microscopy (SEM) of the composites (with 0% - 25% particles) surfaces indicates poor interfacial
interaction between the co conut shell particle an d the low density polyeth ylene matrix. This study therefore exploits the
potential of agro-based waste fiber in Nigeria as an alternative particulate material for the development of a new com-
posite.
Keywords: Coconut Shell Particles; Mechanical Pro perties; Composite; Morphology; Polyethylene Matrix
1. Introduction
Over the last thirty years, composite materials, plastics
and ceramics have been the dominant emerging engi-
neering materials. The volume and number of applica-
tions of composite materials have grown steadily, pene-
trating and conquering new markets relentlessly [1].
Agricultural wastes which include shell of various dry
fruits, rice husks, wheat husk, straws and hemp fiber can
be used to prepare fiber reinforced polymer composite
for commercial use. There is great opportunity in devel-
oping new bio-based products. Natural fibers are basic
interest due to their many advantages from the point of
weight and fiber matrix adhesion. Existing polymers are
mainly blended with different materials with the aim of
cost reduction and tailor the product for specific applica-
tions.
Environmental regulations and ethical concerns have
triggered the search for materials that are environmen-
tally friendly. A pressing issue in Nigeria today, is the
recycling of waste products and other agricultural
by-products suitable for the invention and characteriza-
tion of new materials. Annually, approximately 33 billio n
coconuts are harvested worldwide with only 15% of
these coconuts being utilized for fibers and chips [2,3].
This suggests that there is considerable room to reduce
this kind of environmental pollution and enhance the
efficiency of using natural resources.
Natural lignocellulosics such as coconut shell powder
(cocosnucifera) has outstanding potentials as reinforce-
ment in plastic. Coconut shell is important filler for the
development of new composites as a result of its inherent
properties such as high strength and high modulus [4].
Increased in coconut shell content increases the tensile
strength, Young’s modulus and water absorption rate but
reduces the elongation at break of coconut shell filled
polyester composites [5]. Incorporating coconut shell
powder reduces the damping property of Pu/Ps biocom-
posite with a significant improvement in the tensile
strength and tensile modulus [6]. Surface modification of
coconut fiber by plasma treatment to enhance the interfa-
cial adhesion between the coconut fibers and polylactic
acid (PLA) matrix improves the mechanical properties,
such as tensile strength and Young’s modulus of a coco-
nut fibers/PLA green composites fabricated using com-
mingled yarn method [7]. Coconut shell reinforced com-
posites showed 80% better elongation at break and 20%
better Charpy impact strength than soft wood composites
[8]. The natural waxy surface layer of coconut fiber pro-
vided a strong interfacial bonding between the fiber and
polyethylene matrix [9]. Tensile modulus and tensile
strength values increases with the increase of coconut
shell particles content in a coco nut sh ell reinfo rced epo x y
*Corresponding author.

J. O. AGUNSOYE ET AL. 775
resin composite, while the impact strength slightly de-
creased, compared to pure epoxy resin [10].
An attempt is made in this work to use the agro-based
coconut shell particles as reinforcement of polyethylene
matrix.
In the current study, coconut shell particle and poly-
ethylene were used to fabricate the composites with the
aim of exploring the potential of coconut shell as rein-
forcement for polyethylene matrix composite.
2. Materials and Method
The coconut shell was dried in open air and grinded into
powder using a pulverizing machine, the powder was
sieved in accordance with BS 1377:1990 standard. The
result of the chemical analysis of the coconut shell pow-
der is shown in Table 1. The chemical analysis of the
coconut shell was done with Absorption Spectrometer
(AAS)-Peckinhelma 2006 model. The particle size used
was 100 µm .
The pelletised polyethylene waste was sun-dried and
shredded in a plastic crusher machine. The coconut shell
powder and the grinded pelletised (polyethylene) were
blended together using a two-roll rheomixer at 50˚C and
a rotor speed of 60 rpm. The percentage of the filler in
the matrix was varied from 5% to 25% to produce five
different compositions. Compression of the composites
was carried out with a hydraulic pressing machine for 7
minutes under controlled pressure (30 tons) at 150˚C.
Each of the samples was cooled to room temperature
under sustained pressure before it was removed from the
press. Prior to testing, all samples were conditioned for
72 hours at a temperature of 23˚C ± 2˚C and a relative
humidity of 50% ± 5%. Densities of th e compacted sam-
ples of known weight were determined from Equation (1).
In other to determine the rate of water absorption of the
samples, initially weighed dried samples were placed in a
beaker with water and reweighed at an interval of 24 hrs
for 7 days (168 hrs). The water absorption rate was then
determined using Equation (2).
The hardness property of samples produced was de-
termined using Rockwell hardness tester on scale B with
a 1.56 mm steel ball under a minor load of 3 kg and a
major load of 60 kg. A charpy impact machine was used
to determine the impact energy of the samples. Tensile
test of the composites was carried out using the Houns-
field Tensometer Tensile Machine and the morphologies
of the composites observed by a Scanning Electron Mi-
croscope (S EM).
m
v
ρ = (1)
where
ρ
= density, m = mass, v = volume of sample.
final weightinitial weight
%Weight gained100
initial weight
−
=× (2)
3. Result and Discussion
3.1. Physical Properties of Coconut Shell Powder
Reinforced Polymer Matrix Composite
From Figure 1, it can be seen that the sample with the
highest volume of coconut shell particles (25%) has the
most consistent rate of absorption in water. When com-
pared with the control sample containing 0% coconut
shell particles has a lower rate of absorption in water
after 120 hou rs.
From Figure 2, as the filler increases, the porosity of
the composites decreases. The water absorption is due to
the hydrophilic nature of the coconut shell.
Table 1. Chemical composition of coconut shell powder in
(mg/L).
Metal Ca Fe Si Al Mn
Composition28.8841.882 - - -
Figure 1. Effect of coconut shell particles addition on the
rate of absorption of particulate coconut shell reinforced
polyethylene.
Figure 2. Effect of coconut shell particles addition on the
density of particulate coconut shell reinforced polyethylene
composite.

J. O. AGUNSOYE ET AL.
776
3.2. Mechanical Properties of Coconut Shell
Powder Reinforced Polymer Matrix
Composite
The coconut shell particles have significant effect on the
strength, hardness, and impact energy of the composite.
From Figure 3, it can be seen that the tensile strength of
the composites decrease with increase in the volume
percent of the coconut sh ell particles within the matrix of
the composite. The polyethylene composite with the
highest volume fraction of filler (25%) has the lowest
strength (6.59 MPa). This may be due to imperfect inter-
facial bonding between the coconut shell coconut shell
particles and polyethylen e matrix.
As expected, the yield strength values of the composite
samples decrease with increase in the volume of the co-
conut shell particles (See Figure 4).
From Figure 5, the ductility of the composites de-
creases with an increase in volume fraction of the coco-
nut shell particles within the sa mples. Samples with 20%
and 25% volume fraction of coconut shell particles have
the same strain valu e (0.9021), extrapolated fro m Figure
5.
Figure 3. Effect of coconut shell particles addition on the
tensile strength of coconut shell reinforced polyethylene
composite.
Figure 4. Effect of coconut shell particles addition on the yield
strength of coconut shell reinforced polyethylene composite.
From Figure 6, it can be seen that there was a sharp
decrease in the rigidity of the sample with 5% coconut
shell particles within the matrix of the composite. But, as
the volume fraction of the coconut shell particles in-
creases from 5% to 25%, the modulus of elasticity of the
samples increases with 69.5 MPa obtained for the com-
posite which has 25% volume fraction of coconut shell
particles. This value (69.5 MPa) is high er than that of the
sample without any reinforcement (i.e. 0% filler).
From Figure 7, it can be seen that the hardness of the
composite increases with increase in the coconut shell
Figure 5. Effect of coconut shell particles addition on the
strain of coconut shell reinforced polyethylene composite.
Figure 6. Effect of coconut shell particles addition on the
modulus of coconut shell reinforced polyethylene composite.
Figure 7. Effect of coconut shell particles addition on the
hardness of coconut shell reinforced p olyethylen e compos ite.

J. O. AGUNSOYE ET AL.
777
de
olyethylene matrix
of the composite. The appearance of the gold as seen in
the EDS results is indicative of the composition of the Al
foil used as a laminatio n material to prevent the compo s-
ite from sticking to the die mould surface during and
after compaction and hot pressing using a two-roll rheo-
mixer.
particles content within the matrix of the compos ite. The
sample having the highest coconut shell coconut shell
particles shows the highest har dness value of 11.4 HRB.
From Figure 8, the impact energy of the composite
creases with an increase in coconut shell particles con-
tent within the matrix of the polyethylene coconut shell
reinforced composite. The sample with 25% volume
fraction coconut shell particles in the matrix h as the low-
est impact energy of 1.76 J.
3.3. Microstructural Analysis
The control sample represents the p
sample without coconut shell particles (particulate coco-
nut shell) additions (See Plate 1). From Plates 2-6, it can
be seen from the Scanning Electron Microscope results
that homogeneity between the coconut sh ell particles and
the matrix decreases with increase in the coconut shell
particles content. This explains the decrease in strength
with increased in the coconut shell particles content
within the matrix structure of the composite. The in-
crease in hardness is as a result of the increase in the
volume percent o f the coconut shell particles within matrix Figure 8. Effect of coconut shell particles addition on the
impact of coconut shell reinforced polyethylene composite.
Plate 1. SEM & EDS microanalysis of polyethyle composite without coconut shell particles additions.
ne matrix
Plate 2. SEM & EDS microanalysis of polyethylenmposite with 5% coconut shell particles addition. e matrix co

J. O. AGUNSOYE ET AL.
778
Plate 3. SEM & EDS microanalysis of polyethylene mposite with 10% coconut shell particles addition. matrix co
Plate 4. SEM & EDS microanalysis of polyethylene mmposite with 15% coconut shell particles addition. atrix co
Plate 5. SEM & EDS microanalysis of polyethylene mmposite with 20% coconut shell particles addition. atrix co

J. O. AGUNSOYE ET AL.
779
Plate 6. SEM & EDS microanalysis of polyethylene mposite with 25% coconut shell particles addition.
. Conclusions
the investigations and discussio
oconut shell parti-
cl
percentage of coconut shell particles in
cr
rove the hardness
er
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1) The non-uniform distribution of c
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2) As the-
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