Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 825-831
Published Online August 2012 (http://www.SciRP.org/journal/jmmce)
Effects of Palm Kernel Shell on the Microstructure and
Mechanical Properties of Recycled Polyethylene/Palm
Kernel Shell Particulate Composites
Agunsoye J. Olumuyiwa*, Talabi S. Isaac, Obe A. Adewunmi, Adamson I. Ololade
Department of Metallurgical and Materials Engineering, University of Lagos, Lagos, Nigeria
Received May 16, 2012; revised June 30, 2012; accepted July 20, 2012
ABSTRACT
The effect of palm kernel shell on the microstructure and mechanical properties of recycled polyethylene (RLDPE) re-
inforced with palm kernel shell particulate co mposite was evaluated to assess the po ssibility of using it as a new mate-
rial for engineering applications. The composites were produced by compounding and compressive moulding technique
by varying the Palm kernel shell particle from 5 - 25 vol% with particles size of 150, 300 and 400 µm. The microstruc-
ture (SEM/EDS) and the mechanical properties of the composites were investigated. The hardness of the composite
increases with increase in palm kernel shell content and the tensile strength of the composite increased to optimum of 5
vol%. Scanning electron Microscopy (SEM) of the composites surfaces indicates fairly interfacial interaction between
the palm kernel shell particles and the RLDPE matrix. The composites produced with 150 µm particle size have the best
properties of the en tire grade. Hence this grade can be use for interior applications such as car seat, dash board, and car
interior for decorative purposes or other interior parts of automobile where high strength is not considered a critical re-
quirement.
Keywords: Recycled Polyethylene; Palm Kernel Shell; Microstructure and Properties
1. Introduction
Composites are materials that comprise strong load car-
rying material (known as reinforcement) imbedded in
weaker material (known as matrix). Reinforcement pro-
vides strength and rigidity, helping to support structural
load. In re cent years, due to grow ing environmental aw are-
ness, agro-fillers (agro-based waste) have been increas-
ingly used as reinforcing fillers in thermoplastic compos-
ite materials [1-2].
Natural fibers, as reinforcement, have recently attracted
the attention of researchers because of their advantages
over other established materials. They are environmen-
tally friendly, fully biodegradable, abundantly available,
renewable and cheap and have low density. Natural fiber
composites are used in place of glass mostly in non-
structural applications. A number of automotive compo-
nents previously made with glass fiber composites are
now being manufactured using environmentally friendly
composites [2]. This may be attributed to low-weight
ratio of the composites.
Thousands of tons of different crops are produced but
most of their wastes do not have any useful utilization.
Agricultural wastes include wheat husk, rice husk, and
their straw, hemp fiber and shells of various dry fruits
Mechanical properties of plant fibers are much lower
when compared to those of the most widely used com-
peting reinforcing glass fibers. However, because of their
low density, the specific properties (property-to-density
ratio), strength, and stiffness of plant fibers are compara-
ble to the values of glass fibers [3-4]. Plant fi bers are light
compared to glass, carbon and aramid fibers. The biode-
gradability of plant fibers can contribute to a healthy
ecosystem while their low cost and high performance
fulfill the economic interest of industry.
Oil palm fibers have been extensively studied for the
production of various composites, such as thermoplastic
composites, particleboard, medium density fireboard poly-
mer impregnated oil palm trunk and other thermoset
composites [3]. For thermoplastics composites, empty
fruit bunch and oil palm frond has been the focus of
many researchers. This is due mainly to cost, availability
and properties. Oil Palm Fibers has been discovered to
introduce better wear characteristics to polyester com-
pared to glass fiber while it showed lower mechanical
property than Chopp ed strand mat Glass fiber Reinforced
Polyester [4-6]. Treating Oil Palm Fibers has significant
*Corresponding author.

A. J. OLUMUYIWA ET AL.
826
effect on the wear and frictional performance of Oil Palm
Fiber Reinforced Polyesters composites. It enhanced the
wear properties of polyester by about 35 to 52 and 65 to
75 percent in the case of the pin-on-disc and block-on-
ring techniques respectively. An investigation was con-
ducted to enhance and predict the modulus of elasticity
(MOE) of palm kernel shell concrete (PKSC), a highest
value of 11 kN/mm2 was recorded and an equation which
predict the MOE close to the experimental values was
also devel o ped [1].
The disposable component of harvested agricultural
product (palm kernel) and pelletized pure-water nylon
are becoming increasingly problematic in Nigeria, litter-
ing the rural and urban areas of the country, and consti-
tuting a serious threat to environmental health of the na-
tion. The purpose of the research is to explore the poten-
tial of using palm kernel shell (powder) as reinforcement
in polymer matrix composite for the development o f new
engineering material for the car interior.
2. Experimental Procedure
The palm kernel shell was dried and grind ed into powder
using a pulverizing machine, the powder was sieved in
accordance with BS1377:1990 standard [7-8]. The recy-
cled polyethylene was sun-dried and shredded in a plastic
crusher machine. The palm kernel shell powder and the
grinded pelletized recycled polyethylene were blend to-
gether using a two-roll rheomixer at 165˚C and a rotor
speed of 60 rpm. The percentage of the kernel shell par-
ticles in the matrix was varied from 5% - 25% and five
samples each were compacted using 150 µm, 300 µm,
400 µm. Compression of the composites was carried out
in a Wabash V200 hot press for 5 minutes under con-
trolled pressure 30 tons at 175˚C. Each of the samples
was cooled to room temperature under pressure before it
was removed from the press. Prior to testing, all samples
were conditioned for 72 hou rs at a temperature of 23˚C ±
2˚C and a relative humidity of 50% ± 5%.
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 10 kg, major
load of 100 kg, and a standard block o f 101.2 HRB.
A charpy impact machine was used to determine the
impact energy of the samples. Tensile test of the compos-
ites was carried out using the Hounsfield tensometer and
the scanning electron microscope (SEM) JEOL JSM-
6480LV wer e used to identify the surface morp hology of
the composite samples. The rate of water abso rption of the
samples was determined by initially weighed dried sam-
ples and placed in a beaker with water and reweighed at
an interval of 24 hrs for 168 hrs. The water absorption
rate was then determined using Equ ation (1) [9].
final weightinitial weight
%weight gained100
initial weight

 (1)
3. Result and Discussion
The morphology of the developed composites are shown
in Plates 1-7. From the morphology it, can be seen from
the Scanning Electron Microscope results that homoge-
neity between the kernel shell particles and the matrix
decreases with increase in the kernel shell particles con-
tent. The mwicrostructure clearly shows that when the
kernel shells particle was added to the recycled polyeth-
ylene (RLDPE) morphological change in the structure
take place. The microstructure of the RLDPE matrix re-
veals chain of lamellae and interlammeller amorphous
structure with linear boundaries between adjacent spher-
ulites boundaries (see Plate 1). From the EDS spectrum
it can be clearly see that the functional group of the RLDPE
were revealed.
Plate 1. EDS/SEM morpholo gy of the r ecycled polye t hy le ne.

A. J. OLUMUYIWA ET AL. 827
Plate 2. EDS/SEM morpholo gy of the r ecycled poly ethylene reinforced with 10 vol% at 150 µm size.
Plate 3. EDS/SEM morpholo gy of the r ecycled polyethylene reinforced with 25 vol%, 150 µm size.
Plate 4. EDS/SEM morpholo gy of the r ecycled polyethylene reinforced with 5 vol%, 300 µm size.

A. J. OLUMUYIWA ET AL.
828
Plate 5. EDS/SEM morpholo gy of the r ecycled polyethylene reinforced with 20 vol%, 300 µm size.
Plate 6. EDS/SEM morpholo gy of the r ecycled polyethylene reinforced with 15 vol%, 400 µm size.
Plate 7. EDS/SEM morpholo gy of the r ecycled polyethylene reinforced with 25 vol%, 400 µm size.

A. J. OLUMUYIWA ET AL.
Copyrig JMMCE
829
The microstructure reveals that there are small discon-
tinuities and a reasonably uniform distribution of parti-
cles and the RLDPE. The particles phase is shown as
white phase, while the resin phase is dark. The kernel
shell particles are embedded within the amorphous ma-
trix composed of randomly distributed in the matrix pla-
nar boundaries. The surface of the agro-waste particles is
fairly smooth indicating that the compatibility between
particles and the RLDPE was not so good. It can be seen
that the agro-waste particles are not detached from the
RLDPE surface as the volume fraction of kernel shell
particles increased in the RLDPE, from the microstruc-
ture it was observed the smallest particles size has good
interfacial bonding them the biggest particle size.
The particle size of the reinforced (palm kernel shell
particles) has significant effect on the strength, hardness,
and impact energy of the composite. From Figure 1, it can
be seen that the tensile streng th of the composite in creases
upto a maximum of 5 vol% of palm kernel shell particles
within the matrix of the recycled polyethylene. The ten-
sile strength of composites with 150 µm size palm kernel
shell particles showed higher value, this is because of
increasing in the surface area. This may also account for
the good distribution and dispersion of the palm kernel
shell particles in the RLDPE matrix resulting in strong-
particles-RLDPE matrix interaction. This good particles
dispersion will improve the particles-RLDPE matrix in-
teraction and consequently increases the ability of the
particles to restrain gross deformation of the RLDPE
matrix. Nevertheless the tensile strength obtain in this
study remained within acceptable levels for car interiors
[8-10].
As expected, the yield strength varies directly with the
tensile strength of the samples (See Figure 2). The yield
strength slightly decreased as the vol% of palm kernel
shell particles increased in the RLDPE matrix.
Figure 1. Effect of filler addition on the tensile strength of particulate palm kernel reinforced polyethylene composite.
Figure 2. Effect of filler addition on the yield strength of particulate palm kernel reinforced polyethylene composite.
ht © 2012 SciRes.

A. J. OLUMUYIWA ET AL.
830
From Figure 3, it can be seen that the hardness of the
composite increases with increase in the kernel shell par-
ticles content within the matrix of the composite. This is
due to increase in the percentage of the hard and brittle
phase of the ceramics body in the polymer matrix. In
comparison with the unreinforced RLDPE matrix, a sub-
stantial improvement in hardness values was obtained in
the reinforced polymer matrix. This is in line with the
earlier researches of [10].
The sample with palm kernel shell particles having the
smallest particle size shows the highest hardness. A
maximum hardness value of 15.4 HRB was obtained for
the sample with 25 vol% at 150 µm particle size.
From Figure 4, the impact energy of the composite
decreases with an increase in kernel shell particles con-
tent within the matrix of the recycled polyethylene com-
posite. The sample with 25 vol% at 400 µm particle size
has the lowest impact energy. High strain rates or impact
loads may be expected in many engineering applications
of polymer composite materials. The suitability of a
polymer composite for such applications should th erefore
be determined not only by usual design parameters, but
by its impact or energy absorbing. These results are in
agreement with the work of ot he r re se archers [ 8-10].
The rate of water absorption of the composite over a
period of 168 hours at an interval of 24 hours increased
with increased in kernel shell particles content in the
composite. This may be due to imperfect interfacial
bonding between th e palm kernel shell particle and recy-
cled polyethylene matrix. Also the water absorption is
due to the hydrophilic nature of the palm kernel shell
(See Figure 5). The swelling that occurs during the water
absorption is the sum of two components, namely, swell-
ing by hygroscopic particles and the release of compres-
sion stresses imparted to the composites during the
pressing of mat in the hot press. The release of compres-
sion stresses, known as spring back, is not recovered
when the composites is in a dry state.
Figure 3. Effect of filler addition on the hardness of par-
ticulate palm kernel reinforced polyethylene composite.
Figure 4. Effect of filler addition on the impact strength of
particulate palm kernel reinforced polyethylene composite.
Figure 5. Effect of filler addition on the rate of absorption
of particulate palm kernel reinforced polyethylene compos-
ite.
4. Conclusions
From the result of the investigations and discussion, the
following co nclusion has been made.
1) This work successfully shows that the fabrication of
RLDPE and the palm kernel shell particles composite by
compounding and compression moulding is feasible.
2) The uniform distribution of palm kernel shell particle
in the microstructure of the composite is the major factor
responsible for the increase in strength.
3) Palm kernel shell improves the hardness property of
the recycled polyethylene matrix composite.
4) The tensile strength increased up to an optimum of
5 vol% and the composite produced with 150 µm particle
size has the best properties of the entire grade. Hence this
grade can be use for interior applications such as car seat,
dash board, and car interior for decorative purposes or
other interior parts of automobile where high strength is
not considered a critical requirement.

A. J. OLUMUYIWA ET AL. 831
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