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Journal of Composite
http://jcm.sagepub.com/content/39/8/663Theonline version of this article can be foundat:
DOI: 10.1177/0021998305047267
2005 39: 663Journal of Composite MaterialsAbu Bakar A. Hariharan and H. P. S. Abdul Khalil
and Impact Behavior of Oil Palm Fiber-Glass Fiber-reinforced Epoxy ResinLignocellulose-based Hybrid Bilayer Laminate Composite: Part I - Studies on Tensile
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8/9/2019 JourLignocellulose-based Hybrid Bilayer Laminate Compositenal of Composite Materials 2005 Hariharan 663 84
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Lignocellulose-based Hybrid BilayerLaminate Composite: Part I Studies onTensile and Impact Behavior of Oil PalmFiberGlass Fiber-reinforced Epoxy Resin
ABU BAKARA. HARIHARAN*
School of Materials and Mineral Resources
Engineering Campus, Universiti Sains Malaysia14300 Nibong Tebal, Seberang Perai Selatan, Penang, Malaysia
H. P. S. ABDUL KHALIL
School of Industrial Technology, Universiti Sains Malaysia
11800 Penang, Malaysia
(Received January 19, 2004)(Accepted June 28, 2004)
ABSTRACT: The tensile and impact behavior of the oil palm fiberglass fiber
hybrid bilayer laminate composites are studied. The fiber mats are impregnated withepoxy resin and cured at 100C for 1 h followed by post curing at 105C. Thehybridization of the oil palm fibers with glass fibers increases the tensile strength, theYoungs modulus, and also the elongation at break of the hybrid composites. Anegative hybrid effect is observed for the tensile strength and Youngs modulus whilea positive hybrid effect was observed for the elongation at break of the hybridcomposites. The impact strength of the hybrid composite increases with the additionof glass fibers. The hybrid composites which are impacted at the glass fiber layerexhibit a higher impact strength and a positive hybrid effect compared to thoseimpacted at the oil palm fiber layer. The scanning electron micrographs andphotomicrographs of tensile and impact fracture samples are taken to study thefailure mechanism and fibermatrix interface adhesion.
KEY WORDS: hybrid composites, lignocellulose-reinforced composites, laminatecomposites, oil palm fiber composites.
INTRODUCTION
IN RECENT YEARS,the usage of lignocellulosic fibers or plant fibers as a replacement for
synthetic fibers such as carbon, aramid, and glass fibers in composite materials has
*Author to whom correspondence should be addressed. E-mail: [email protected]
Journal ofCOMPOSITE MATERIALS, Vol. 39, No. 8/2005 663
0021-9983/05/08 066322 $10.00/0 DOI: 10.1177/0021998305047267 2005 Sage Publications
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left behind after the removal of oil palm fruits for the oil refining process at the oil
refineries. Based on a report by Tanaka [25], 16 million tons of empty fruit bunches
were discharged per annum from each and every oil palm refinery in the country regularly
in the year 2000. The empty fruit bunches are then used as boiler feedstock in the oil
mill and are also left to mulch and degrade as soil fertilizers in the field, while the majority
of the empty fruit bunches are not utilized, posing a serious environmental threat.
Therefore, by using the oil palm empty fruit bunch fibers, which were extracted from
the empty fruit bunches by Sabutek (M) Sdn. Bhd. (a local company in Malaysia), as
a reinforcement in composite materials, the biomass waste generated by the oil palm
industry can be reduced significantly.
In this work, the mechanical properties of oil palm fiberglass fiber hybrid bilayer
laminate composite are studied. Earlier works done on the lignocellulose fiberglass fiber
hybrid composite basically concentrated on the intermingle fiber system [1517,1921,23].
In addition, the lignocellulose-based sandwich composite system was studied by Mohan
and Kishore [26], and Clark and Ansell [27]. Since studies on a bilayer hybrid composite
based on lignocellulose fibersynthetic fiber have not been reported yet, the opportunitywas taken to evaluate and report the tensile and impact properties of the oil palm fiber
glass fiber hybrid bilayer laminate composite, in this paper. Scanning electron micrograph
and images of tensile and impact fractured samples have been taken in order to study the
fracture mechanism of the hybrid bilayer system. The flexural, moisture absorption, and
flammability properties of the hybrid bilayer composite will be reported in a future
publication.
EXPERIMENTAL
Materials
An epoxy resin based on bisphenol A (Clear Epoxy Resin 331) and a polyamide (Epoxy
Hardener A062) were supplied by Euro Chemo-Pharma Sdn. Bhd. Benzyl alcohol was
supplied by Aldrich Company. Oil Palm Empty Fruit Bunch Fibers (OPEFB) were
obtained from Sabutek (M) Sdn. Bhd. E-glass-chopped strand mat fibers (GF) were
supplied by Euro Chemo-Pharma Sdn. Bhd.
Preparation of Random Oil Palm Fiber Mat
The empty fruit bunch fibers were washed and cleaned of impurities and dried in an
oven at 80C for 24 h [20,21]. The equilibrium moisture content of the fibers was about
11%. The dried fibers were then kept in a sealed polyethylene bag to prevent it from
reabsorbing moisture from the environment. In order to prepare a nonwoven fiber mat,
a weighed quantity of fibers were dispersed in a sieve which was placed in a tub of water.
Once the fibers were evenly dispersed and the mat was formed, the sieve was taken out
from the tub. The excess water from the mat was drained out by pressing the mat against a
flat plate. The random fiber mat was subsequently dried in an oven at 80C for 24 h. The
dried fiber mat was then compacted under pressure at 8000 psi in a compression moldfollowed by trimming of the fiber mat edges in order to obtain a uniform shaped fiber mat.
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Preparation of Bilayer Laminate Hybrid Composite
The laminate composite was prepared by following a prepreg route as described by Hill
and Abdul Khalil [10]. A high-density polyethylene (HDPE) liner was used for the fiber
mat impregnation process. A schematic diagram of the laminate impregnation process is
shown in Figure 1. One end of the liner was sealed with a tape while the other end was left
open so that the resin could be poured into the liner. A cardboard was placed at the sealed
end of the liner and was connected to a vacuum pump. The cardboard was used to prevent
excess resin from entering the vacuum pump during the impregnation process. The glass
fiber (GF) and the oil palm fiber mats (EFB) were stacked (one on top of the other) and
were placed in the liner. The middle section of the liner was sealed with clips as shown in
Figure 1.
A fixed amount of resin was stirred manually for 10 min in a plastic container using a
glass rod. Table 1 shows the resin formulation used for the impregnation process. The
mixture was then warmed in an oven at 70C for about 10 min in order to further reduce
the viscosity of the resin. While vacuum was applied to the liner containing the fiber mat,the resin was poured into the open end of the liner (Figure 1). The clips in the center were
removed and the open end of the liner was closed with the clips thus allowing the resin to
flow and impregnate the mat. Once the mat was completely impregnated, the vacuum
connection was removed and the liner was cut open. The impregnated mat was then
transferred onto a 2-mm thick aluminum plate which was subsequently placed on a hot
press. Spacer bars of 10 mm thickness were placed beside the mat and the mat was
compressed at a constant pressure of 6000 psi while squeezing out the excess resin. The
laminate composite was left to cure at 100C for 1 h. An open leaky mold method was used
Resin flow
Middle section
Sealed end Cardboard Fiber matOpen end
Vacuum pump Clips HDPE liner
Figure 1. A schematic diagram of the laminate impregnation process.
Table 1. Resin formulation used for the impregration process.
Amount
Epoxy resin 100 phr
Polyamide 30 phr
Benzyl alcohol 10 wt.% of totalepoxypolyamide mixture
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in this research. Once the laminate was cured, the laminate composite was removed from
the plate followed by post curing in an oven at 105C for 30 min. Finally, the laminate
composite was cooled in a cold press under a constant pressure of 500 psi for 15 min in
order to prevent warpage of the laminate composite. Table 2 shows the formulation for the
hybrid bilayer laminate composite while Figure 2 shows the schematic diagram of the
bilayer hybrid laminate composite. The physical and mechanical properties of epoxy, oil
palm fiber, and glass fiber are given in Table 3.
Mechanical Testings
Tensile testing was performed according to ASTM D638-76. Rectangular strips
(120 20 10mm3) were cut from the laminate composite followed by milling of the
strips into a dumbbell shape with dimensions of 120 10 10mm3. The tensile test was
conducted on a Universal Testing Machine Model 1114 at a crosshead speed of 5 mm/min
and gauge length of 60 mm. A minimum of five samples were tested and an average valuewas recorded. Unnotched Izod impact test samples with dimensions of 70 15 10mm3
were cut from the laminate composites. The testing was conducted according to ASTM
D256 on a Zwick model 5101 with a pendulum weight of 25 J. The samples were impacted
Glass fiber plies
Oil palm fiber ply
Figure 2. The schematic diagram of the hybrid bilayer laminate composite.
Table 3. The physical and mechanical properties of epoxy, oil palm fiber, and glass fiber.
Properties Epoxy Oil palm fiber Glass fiber
Density (g/cm3) 1.15 0.71.55 2.56
Tensile strength (MPa) 20 100400 17003500
Youngs modulus (GPa) 7.97 19 6672
Elongation at break (%) 7.35 818 3
Impact strength (kJ/m2) 10.89
Flexural strength (MPa) 78 Flexural modulus (GPa) 2.13
Table 2. Hybrid bilayer laminate composite formulation.
Oil palm fiberglass fiber (wt.%)
Bilayer laminate 100/0 90/10 70/30 50/50 30/70 10/90 0/100
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at the glass fiber layer and at the oil palm fiber layer. Five samples were tested (at each
layer) at room temperature and the average value was taken as the Izod impact strength.
The Izod impact strength was calculated using the formula given below :
Impact strength kJ=m
2
Impact energy J=Crosssectional area 10
3
1
Fracture Sample Analysis
A scanning electron microscope (SEM), Model Leica Cambridge S-360 was used to
study the fracture surface of the tensile and impact specimens. The specimen was coated
with a thin goldpalladium layer using Sputter Coater Polaron SC 515 to avoid electrical
charge accumulation during examination. The basic shapes of the fiber and the fiber
matrix adhesion were also studied using the SEM. Images of fractured samples from
impact test were also taken using a digital video camera JVC 3-CCD, which was connectedto a computer and was analyzed using an Image Analysis Pro software.
RESULTS AND DISCUSSION
Tensile Properties
Figure 3 shows the stressstrain diagram of the glass fiber composite, oil palm fiber
composite, and hybrid composites. From the stressstrain curve, the deformation behavior
of the composites can be well understood.
0
20
40
60
80
100
120
0 1 2 3 4 5 6 7
Strain (%)
Stress(MPa)
GF composite90 wt% GF
10 wt% GFEFB composite
Figure 3. The tensile stressstrain behavior of glass fiber composite, oil palm fiber composite, and hybridcomposites.
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The stressstrain curve of the composites show a linear elastic behavior until about
0.16% strain followed by a deviation from linearity which is maintained until complete
failure of the composites. The nonlinear behavior of a natural fibersynthetic fiber hybrid
composite was also reported by Thwe et al. [17], Sreekala et al. [21], and Clark and Ansell
[27]. When the load is applied to a fiber-reinforced composite, the difference in stiffness
properties between the fiber and the matrix results in the development of high local stress
and strain concentrations in the matrix [28]. Therefore, in order to prevent the local stress
and strain concentrations from inducing failures in the composite, the stresses are
redistributed in the composite through plastic deformation and microcrack initiation of
the matrix [21,29]. According to Hull and Clyne [30], these phenomena result in the
nonlinear behavior of the composite and are also related to the initiation of composite
failure. The plastic deformation though is caused by the shearing of fibers in the matrix
and also by the inherent ductility of the fiber, especially the oil palm fibers [27].
Besides this, at higher strain levels, the drop in the stressstrain curves indicates
progressive failure of the fibers and propagation of cracks through the matrix while the
end of the curve indicates the ultimate strength of the composite which is due to fiberpullout and fiber fracture. Extensive fiber pullout was observed not only in the oil palm
fiber composite but also in the oil palm fiber layer of the hybrid composites while fiber
fractures were observed in the glass fiber composite and in the glass fiber layer of the
hybrid composites (Figure 4(a)(e)). The weak interfacial adhesion between the oil palm
fibers and epoxy resin leads to the pullout of fibers from the matrix while the better
adhesion between the glass fibers and epoxy matrix resulted in fiber fracture. Existence of
epoxy matrix adhered on the surface of the glass fibers indicates a perfect adhesion as
shown in the scanning electron micrographs of the tensile fractured surfaces of the
composites (Figure 4(c)).
Tensile Strength
The tensile strength of the oil palm fiberglass fiber hybrid bilayer laminate composite
as a function of glass fiber loading is shown in Figure 5. As observed from the graph, the
tensile strength of the oil palm fiber composite, which is about 24 MPa, is very much
inferior compared to the glass fiber-reinforced composite which has a tensile strength of
111 MPa.
This is mainly due to the nature of oil palm fibers, which are irregular in shape and size
as seen in the scanning electron micrograph in Figure 6. Furthermore, oil palm fibers also
exist in the form of fiber bundles as shown in Figure 7 [22]. The fiber bundles are
composed of several individual fibers, which are bundled together by a strong pectin
interphase [31].
According to Oksman et al. [2], the load distribution in fiber bundles is not homo-
geneous because the individual fibers are not loaded uniformly as some individual fibers
are not loaded at all. Therefore, the oil palm fibers are unable to support the stress
transferred from the epoxy matrix successfully. Furthermore, the poor adhesion between
the epoxy matrix and the oil palm fibers, which is evident by the extensive fiber pullout of
the oil palm fibers as shown in Figure 4(a), leads to a weak interfacial bond, resulting in an
inefficient stress transfer between the epoxy matrix and the oil palm fibers. As a result, the
oil palm fiber composite fails at a lower load compared to the glass fiber-reinforcedcomposite.
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However, with the addition of glass fibers into the oil palm fiber composite, the tensile
strength of the hybrid composites increased significantly as seen from the graph in Figure 5.
A similar trend was reported by Kalaprasad et al. [16,32], Pavithran et al. [20], and Mishra
et al. [15] with the addition of glass fibers into a natural fiber composite. At 0.8 volume
fraction of glass fibers, the tensile strength of the hybrid composite increased by about
(a)
(c)
(b)
Fiber pull out
Matrix cracking
Fiber pull out
Matrix cracking
Fiber fracture
Epoxy matrix
Figure 4. Scanning electron micrographs of the tensile-fractured surface of the oil palm fiber-reinforced
composite. The clean surface of oil palm fibers indicates weak adhesion between the fibers and matrix:
(a) magnification 50and (b) magnification 500; (c) Scanning electron micrograph of the tensile-fractured
surface of the glass fiber-reinforced composite. Epoxy matrix adhered on the surface of glass fibers indicates a
good adhesion between the fibers and matrix (magnification 500); (d) Scanning electron micrograph of the
tensile-fractured surface of the hybrid composite at 90 wt.% loading of glass fibers. The fracture surface of an
oil palm fiber layer (magnification 500); (e) Scanning electron micrograph of the tensile-fractured surface of
the hybrid composite at 90 wt.% loading of glass fibers. The fracture surface of a glass fiber layer(magnification 500).
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263% and exhibited a tensile strength of 87 MPa, which is comparable to the tensile
strength of the glass fiber-reinforced composite.
In a hybrid composite, the mechanical properties are governed by the fiber content,
fiber length, fiber orientation, arrangement of individual fibers, extent of intermingling of
the fibers, and the interfacial adhesion between the fiber and matrix [21,29]. The tensile
failure of a hybrid composite though, is mainly dependent on the breaking strain and
modulus of the individual reinforcing fibers [15,21,33]. Glass fibers are low elongationfibers with a high modulus whereas oil palm fibers are high elongation fibers with a low
Matrix cracking
Fiber pull-out
Matrix cracking
Fiber fracture
(d)
(e)
Figure 4. Continued.
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modulus (Table 1). When the oil palm fiberglass fiber hybrid composite is subjected to a
tensile load, the glass fibers and the oil palm fibers are uniformly strained and a strain level
is reached corresponding to the failure strain of the glass fibers (smallest failure strain).A further increase in the strain level results in an early failure of glass fiber plies.
0
20
40
60
80
100
120
140
0 0.2 0.4 0.6 0.8 1
Relative volume fraction (Vf) of glass fiber
Tensilestrength(MPa)
Rule of mixture
Figure 5. The effect of glass fiber loading on the tensile strength of the oil palm fiberglass fiber hybrid bilayer
laminate composite.
Figure 6. The scanning electron micrograph of the cross section of the oil palm fiber composite. Arrows
indicate irregular size and shape of the oil palm fibers (magnification 101).
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Sreekala et al. [21] and Mishra et al. [15] who worked on oil palm fiberglass fiber
hybrid and sisalglass fiber hybrid composites respectively, cited that once the glass fibers
fail, the sudden transfer of load to the weak natural fibers would result in the failure of the
natural fibers eventually leading to a catastrophic failure of the hybrid composites.
Nevertheless, in this study which is a hybrid bilayer system, the load from the failed
glass fiber plies is not directly transferred to the oil palm fibers. The failed glass fiber plies
though, are able to continue to carry the load in the laminate and are also capable of
undergoing multiple failures throughout the loading process. This may be due to the
presence of the strong interlaminar bond, which enables the adjoining oil palm fiber ply to
restrain and localize the failure of the glass fiber plies [34]. As the failed glass fiber plies are
still able to carry the load, the oil palm fibers can effectively transfer the load from the
glass fibers without failing catastrophically. As the volume fraction of glass fiber increases
in the hybrid composites, the number of glass fiber plies also increases (Table 4), thus they
are able to withstand a higher load while redistributing a lesser load to the oil palm fibers
resulting in an improved tensile strength of the hybrid composites with the addition of
glass fibers. The increase in the tensile strength of the hybrid composites is also due to the
higher tensile strength of glass fiber than the oil palm fiber (Table 3) [32]. Therefore, it is
well understood that the hybridization of the oil palm fiber composites with glass fibers
enhances the tensile strength of the hybrid composite.
Figure 5 also shows a negative hybrid effect exhibited by the oil palm fiberglass fiber
hybrid bilayer laminate composites. Marom et al. [35] defined a positive or negative hybrideffect as a positive or negative deviation from the rule of mixture behavior. The condition
Oil palm fiber
bundle
Individual fibers
Figure 7. Scanning electron micrograph of the cross section of the oil palm fiber bundle in epoxy matrix
(magnification 201).
Table 4. Relationship between the relative volume fraction of glass fibers and the numberof glass fiber plies in the bilayer hybrid laminate composite.
Relative volume fraction of glass fibers 0 0.1 0.2 0.4 0.5 0.8 1
Number of plies of glass fibers 0 2 3 5 7 9 10
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for positive or negative hybrid effect is mainly influenced by the relative volume fractions
of the individual fibers, the construction of the layers in the hybrid, and the loading
configuration (e.g., translaminar or interlaminar). The rule of mixture predictions is based
upon the weighted average of the characteristic properties of the individual composites[35,36]. Wagner et al. [36] later stressed that the weighting is proportional to the volume
fraction of the constituents without taking into consideration the internal geometry of the
composite. Furthermore, the rule of mixture predictions as explained by Sreekala et al. [21]
expects a complete intermingling of both the individual fibers in the matrix. Therefore, the
negative deviation from the rule of mixture predictions shown by the bilayer hybrid
laminate composite may be due to the presence of distinct and segregated layers of the oil
palm fibers and glass fibers. This is evident from the cross section of the hybrid composite
shown in Figure 8.
Elongation at Break
Figure 9 shows the effect of elongation at break with the addition of glass fibers in oil
palmglass fiber hybrid bilayer laminate composite. Referring to the graph in the figure, it
is noted that the elongation at break of the oil palm fiber composite is slightly lower than
the glass fiber-reinforced composite.
As the oil palm fibers are high elongation fibers compared to the low elongation glass
fibers, one would expect the oil palm fiber composite to have a higher elongation at break
than the glass fiber composite. However, owing to the low strength nature of the oil palm
fibers and its inability to withstand the load transferred from the epoxy matrix (as
explained in the previous section), the oil palm fiber composite fails catastrophically evenbefore reaching its actual extensible strain.
Glass fibers
Oil palm fibers
Figure 8. Scanning electron micrograph of the cross section of the hybrid composite at 0.8 volume fraction of
glass fibers. The distinct layering of the glass fibers and oil palm fibers can be observed in the cross section of
the hybrid composite (magnification 17).
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As observed from the graph, the hybrid composites exhibited a positive elongation at
break effect with the addition of glass fibers. The positive hybrid effect of the elongation at
break in hybrid composites was also observed by Hayashi [37], Bunsell and Harris [38],Zweben [33], Sreekala et al. [21], and Krestsis [39]. Zweben [33] concluded that in a hybrid
composite, the addition of high elongation fibers with low elongation fibers often
increased the elongation at break of the hybrid composite than the composite made from
low elongation fibers.
On the other hand, in this bilayer hybrid laminate system, with the addition of glass
fibers the elongation at break of the hybrid composites increased beyond the elongation at
break of the individual composites. This exceptional behavior of the hybrid composites is
due to the existence of a load sharing mechanism between the glass fiber plies and the oil
palm fiber ply. This is because the failed glass fiber plies are able to continue to carry the
load while redistributing the remaining load to the oil palm fiber ply. As the number of
glass fiber plies increases with the increase in the volume fraction of glass fibers, they are
able to withstand a higher applied load while redistributing a lesser load to oil palm fibers.
Thus the oil palm fibers do not fail catastrophically and are able to reach its actual
extensible strain successfully with the addition of glass fibers. As a result, the oil palm
fibers are able to restrain the crack propagation upon fracture of the glass fibers leading to
an increase in the strain level required to propagate the fiber breakage. Zweben [33],
Sreekala et al. [21], Jones and Di Benedetto [40], and Peijs et al. [41], concluded that in a
hybrid fiber composite, fibers with a low modulus and high elongation are able to stop and
deflect the crack at a micromechanical level. Furthermore, the fiber cell arrangement in a
cellulosic fiber is able to divert the crack route by blunting it. This is because when the
crack approaches the fiber cells, it surrounds the cells unable to propagate, and it finallystops [42]. Therefore, the existence of a synergistic effect between the glass fibers and oil
0
2
4
6
8
10
0 0.2 0.4 0.6 0.8 1
Relative volume fraction(Vf) of glass fiber
Elongationatbreak(%
)
Rule of mixture
Figure 9. The effect of glass fiber loading on the elongation at break of the oil palm fiberglass fiber hybrid
bilayer laminate composite.
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palm fibers and the load sharing mechanism between the glass fiber plies and oil palm fiber
ply enhance the elongation at break of the hybrid bilayer composites.
Youngs Modulus
The incorporation of glass fibers into the oil palm fiber composite increased the stiffness
of the hybrid composites as seen in Figure 10. This behavior agrees well with the work
done by Pavithran et al. [20] and Kalaprasad et al. [16,32] who worked on coirglass fiber
hybrid and sisalglass hybrid composites, respectively. Owing to the weak interfacial
adhesion between the oil palm fibers and epoxy matrix and the weak nature of the oil palm
fibers, the oil palm fiber composite is unable to withstand the applied load transferred
from the epoxy matrix resulting in an inferior stiffness property of oil palm fiber
composite compared to the glass fiber composite [43].
The enhancement in the stiffness of the hybrid composites with the addition of glass
fibers is attributed to the higher tensile modulus of glass fibers which is about 6672 GPathan that of oil palm fiber which has a tensile modulus of about 19 GPa. Furthermore,
the addition of glass fibers into the oil palm fiber composites increases the load bearing
capability of the hybrid composites resulting in an improved stiffness. This is due to the
efficient stress transfer between the glass fiber plies and oil palm fiber ply, which enables
the hybrid composites to carry a higher tensile load [18,44].
The hybrid composite exhibited a large deviation from the rule of mixture behavior as
observed from the graph in Figure 10. This may be due to the distinct layering of the oil
palm fibers and glass fibers in the epoxy matrix. The effect of layering on the negative
hybrid effect of the Youngs modulus was also observed by Sreekala et al. [21] in oil palm
0.0
0.2 0.4 0.6 0.8 10
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Relative volume fraction (Vf) of glass fiber
Young
'smodulus(GPa)
Rule of mixture
Figure 10. The effect of glass fiber loading on the stiffness of the oil palm fiberglass fiber hybrid bilayercomposite.
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fibersglass fiber-reinforced phenolformaldehyde hybrid composites. As the fibers are
not homogenously dispersed in the matrix, the fibers are unable to effectively restrict
the mobility and deformability of the matrix resulting in a negative hybrid effect of the
Youngs modulus. Furthermore, the Youngs modulus of the hybrid composites would
follow the rule of mixture if the fibers act in the same direction with the applied stress and
also if the interphase of the fibermatrix is perfect.
Impact Properties
Figure 11 shows the effect of glass fiber loading on the impact strength of the hybrid
composite. Based on the graph, it is noted that the oil palm fiber composite has a lower
impact strength (18 kJ/m2) than the glass fiber composite (107 kJ/m2).
According to Joseph et al. [8], the impact properties of a fiber-reinforced composite is
influenced by the nature of the constituent materials, interface properties, construction
and geometry of the composite, and also the test conditions. The mode of fracture of theoil palm fiber composite and the glass fiber composite is shown in Figures 12 and 13. As
the interfacial bonding between the oil palm fibers and the epoxy matrix is weak, fiber
pullout would be expected in the composite [10]. However, scanning electron micrograph
observation of the fractured surface of the oil palm fiber composite showed fiber fracture
as the predominant failure mechanism (Figure 14). As the oil palm fiber composite is
subjected to a high speed impact load, the sudden stress transferred from the matrix to the
fiber exceeds the fiber strength resulting in the fracture of the oil palm fibers at the crack
plane without any fiber pullout. Owing to its low strength nature, irregular cross section,
and the presence of fiber bundles, the oil palm fibers are unable to withstand the high
0
20
40
60
80
100
120
140
0 0.1 0.2 0.4 0.5 0.8 1
Relative volume fraction (Vf) of glass fiber
Impacts
trength(KJ/m2)
Oil palm fiber layer
Glass fiber layer
Rule of mixture
Figure 11. The effect of glass fiber loading on the impact strength of the oil palm fiberglass fiber hybridbilayer composite.
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transverse load and therefore fractures before reaching its fracture strain. Furthermore, as
the oil palm fibers used are long, they would have flaws distributed along its length. The
flaws would act as stress concentrators resulting in the fracture of the fibers when the load
is transferred onto the fibers [45].
The glass fiber-reinforced composite exhibited extensive delamination between the glass
fiber plies as shown in Figure 13. Glass fibers are capable of absorbing high impact energy
and are also resistant to propagation of microcracks [19,27]. Therefore, as the crack
propagates through a ply in a laminate and reaches the adjacent ply it gets arrested andbranches off and propagates at the fibermatrix interface parallel to the plane of the plies.
Impact load direction
Figure 12. Photomicrograph of the impact fracture sample of the oil palm fiber composite.
Impact load direction
Delamination
Figure 13. Photomicrograph of the impact fracture sample of the glass fiber composite.
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The crack branching produces a large surface area resulting in an increase in the fracture
energy [34].
Agarwal and Broutman [34] also cited that fiber breakages only account for a small
portion of the total energy absorbed in a composite. Park and Jang [46] later stressed that
compared to fiber fracture, delamination failure significantly increases the impact energy
absorption characteristic of the composite. As a result, the glass fiber composite exhibiteda higher impact strength than the oil palm fiber composite.
The hybridization of the glass fibers with the oil palm fiber composite increased the
impact strength of the bilayer hybrid composites significantly as shown in the graph in
Figure 11. At 0.1 volume fraction of glass fibers, the impact strength of the bilayer hybrid
composite increased about 24% when impacted at the oil palm fiber layer while an
increase of 110% was noted when the hybrid was impacted at the glass fiber layer. This is
mainly due to the superior damage tolerance capability and efficient crack resisting
characteristics of the glass fibers compared to the oil palm fibers. Furthermore, with the
increasing number of glass fiber plies as the volume fraction of glass fiber increases in
the hybrid composites, additional impact absorption energy occurs between the glass
fiber plies through extensive delamination, hence increasing the impact resistance of
the hybrid composites. Figure 15(a)(d) shows the impact fractured samples of the hybrid
composites.
The bilayer hybrid composites, which were impacted at the glass fiber layer, exhibited a
positive hybrid effect and also a higher impact strength than those impacted at the oil
palm fiber layer. The impact strength of the hybrid composite at 0.8 volume fraction of
glass fibers is comparable to the impact strength of the glass fiber composite.
Park and Jang [46], who worked on the impact performance of aramid fiber
polyethylene fiber hybrid composite, concluded that in a laminated fiber composite, the
position and volume ratio of each individual fiber in the hybrid composite determine
the impact strength of the composite. When the bilayer hybrid composite was impacted atthe glass fiber layer, the glass fibers were able to resist the high impact load and were also
Fiber fracture
Figure 14. Scanning electron micrograph of the impact-fractured surface of the oil palm fiber composite
(magnification 101).
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able to absorb a significant amount of impact energy through extensive delamination
between the glass fiber plies as shown in Figure 15(a) and (c). Thus the energy needed to
initiate and propagate the crack increases. Moreover, the delamination at the glass fiber
oil palm fiber layer interface further contributes to the additional impact energy
absorption characteristic of the hybrid composite [46,47]. The absorbed impact energy is
then dissipated to the overall laminate through the fiber breakages in the oil palm fiber ply
(Figure 16(a) and (b)).
However, when the bilayer hybrid composite was impacted at the oil palm fiber layer,
the weak oil palm fibers were unable to withstand and absorb the high impact load
resulting in fiber breakages as shown in Figure 15(b) and (d). The initiated crack
then easily propagates from the impacted surface to the back surface of the hybrid
composite. A further propagation of the crack is restricted by the glass fiber plies. Theglass fiber plies at the back surface of the laminate are unable to delaminate completely
(a) Impacted at glass fiber layer (b) Impacted at oil palm fiber layer
(c) Impacted at glass fiber layer (d) Impacted at oil palm fiber layer
Glass fiber
Oil palm fiberGlass fiber
Oil palm fiber
Delamination
Glass fiber
Oil palm fiber
Glass fiber Oil palm fiber
Restricted delamination
Figure 15. Photomicrographs of impact-fractured samples of hybrid bilayer composites: (a) and (b) 0.1
volume fraction of glass fibers; (c) and (d) 0.8 volume fraction of glass fibers. Dotted arrow indicates the
impact load direction.
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(as clearly seen in Figure 15(d)) owing to the restraint of the adjacent oil palm fiber ply.
Hence, the applied impact load is not dispersed effectively into the overall laminate and
the stresses are localized in the laminate leading to a low impact strength of the hybrid
composite [48].
CONCLUSIONS
From this research it can be concluded that :
. Hybridization of oil palm fibers with glass fibers had improved the tensile and impactproperties of the oil palm fiber composite.
(a)
(b)
Fiber fracture
Fiber fracture
Figure 16. Scanning electron micrographs of the impact fracture surface of the oil palm fiber layer when
impacted at the glass fiber layer. (a) 0.1 volume fraction of glass fiber and (b) 0.8 volume fraction of glass fiber
(magnification 101).
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. Addition of a high volume fraction of glass fibers of about 0.8 enhanced the tensile and
impact properties of the hybrid bilayer laminate composites.
. A negative hybrid effect was observed for the tensile strength and tensile modulus of the
hybrid composite. However, a positive hybrid effect was observed for the elongation at
break of the hybrid composite.
. Glass fibers when placed at the front surface (impacted surface) of the hybrid bilayer
laminate composites offered a better impact resistance compared to oil palm fibers at
the front surface. A positive hybrid effect was also observed when the hybrid
composites were impacted at the glass fiber surface.
The oil palm fiberglass fiber hybrid bilayer composite offered encouraging and
comparable mechanical properties when compared to the glass fiber-reinforced compo-
sites. Therefore, through hybridization, the oil palm fiber composite may find applications
as structural materials where higher strength and cost considerations are important
factors.
REFERENCES
1. Joseph, K., Varghese, S., Kalaprasad, G., Thomas, S., Prasannakumari, L., Koshy, P. andPavithran, C. (1996). Influence of Interfacial Adhesion on the Mechanical Properties andFracture Behaviour of Short Sisal Fibre Reinforced Polymer Composites,Eur. Polym. J.,32(10):12431250.
2. Oksman, K., Wallstrom, Lennart, Berglund, L.A. and Filho, R.D.T. (2002). Morphology andMechanical Properties of Unidirectional Sisal-Epoxy Composites, J. Appl. Polym. Sci., 84:23582365.
3. Pal, S.K., Mukhopadhyay, D., Sanyal, S.K. and Mukherjea, R.N. (1988). Studies on ProcessVariables for Natural Fiber Composites Effect of Polyesteramide Polyol as Interfacial Agent,J. Appl. Poly. Sci., 35: 973985.
4. Rozman, H.D., Tay, G.S., Kumar, R.N., AbuBakar, A., Ismail, H. and Ishak, Z.A.M. (1999).Polypropylene Hybrid Composites: A Preliminary Study on the Use of Glass and CoconutFiber as Reinforcements in Polypropylene Composites, Polym. Plast. Technol. Eng., 38(5):9971011.
5. Albuquerque, A.C.de., Joseph, K., Carvalho, L.H.de. and Morais d Almeida, J.R. (2000).Effect of Wettability and Ageing Conditions on the Physical and Mechanical Properties ofUniaxially Oriented Jute-Roving Reinforced Polyester Composites, Comp. Sci. Tech., 60:833844.
6. George, J., Bhagawan, S.S. and Thomas, S. (1998). Effects of Environment on the Properties ofLow-Density Polyethylene Composites Reinforced with Pineapple-Leaf Fibre,Comp. Sci. Tech.,58: 14711485.
7. Devi, L.U., Bhagawan, S.S. and Thomas, S. (1997). Mechanical Properties of Pineapple LeafFiber Reinforced Polyester Composites, J. Appl. Poly. Sci., 63: 17391748.
8. Joseph, S., Sreekala, M.S., Oommen, Z., Koshy, P. and Thomas, S. (2002). A Comparison ofthe Mechanical Properties of Phenol Formaldehyde Composites Reinforced with Banana Fibresand Glass Fibres, Comp. Sci. Tech., 62: 18571868.
9. Sreekala, M.S., George, J., Kumaran, M.G. and Thomas, S. (2002). The MechanicalPerformance of Hybrid Phenol-formaldehyde Based Composites Reinforced with Glass andOil Palm Fibres, Comp. Sci. Tech., 62: 339353.
10. Hill, C.A.S. and Abdul Khalil, H.P.S. (2000). Effect of Fiber Treatments on Mechanical
Properties of Coir or Oil Palm Fiber Reinforced Polyester Composites, J. Appl. Polym. Sci.,78:16851697.
682 A. B. A. HARIHARAN ANDH. P. S. A. KHALIL
by NAGARJUNA KONDURU on November 20, 2012jcm.sagepub.comDownloaded from
http://jcm.sagepub.com/http://jcm.sagepub.com/http://jcm.sagepub.com/http://jcm.sagepub.com/ -
8/9/2019 JourLignocellulose-based Hybrid Bilayer Laminate Compositenal of Composite Materials 2005 Hariharan 663 84
22/23
11. Abdul Khalil, H.P.S., Ismail, H., Ahmad, M.N., Ariffin, A. and Hassan, K. (2001). The Effectof Various Anhydride Modifications on Mechanical Properties and Water Absorption of OilPalm Empty Fruit Bunches Reinforced Polyester Composites, Polym. Int., 50: 395402.
12. Rozman, H.D., Ismail, H., Jaffri, R.M., Aminullah, A. and Ishak, Z.A.M. (1998). MechanicalProperties of Polyethylene-oil Palm Empty Fruit Bunch Composites, Polym. Plast. Technol.
Eng., 37(4): 495507.13. Deem, S. (2003). A Class Coconuts: The Quest for Greener Takes DaimlerChrysler to the
Rain Forest, http://popularmechanics.com/popmech/auto3/0107AUTKWFBM.html
14. Sherman, L.M. (2003). Natural Fibers, http://www.plasticstechnology.com/articles/199910fa1.html
15. Mishra, S., Mohanty, A.K, Drzal, L.T., Misra, M., Parija, S., Nayak, S.K. and Tripathy, S.S.(2003). Studies on Mechanical Performance of Biofibre/Glass Reinforced Polyester HybridComposites, Comp. Sci. Tech., 63(10): 13771385.
16. Kalaprasad, G., Joseph, K. and Thomas, S. (1997). Influence of Short Glass Fiber Addition onthe Mechanical Properties of Sisal Reinforced Low Density Polyethylene Composites, J. Comp.Mater., 31(5): 509527.
17. Thwe, M.M. and Liao, K. (2002). Effects of Environmental Aging on the Mechanical Properties
of Bamboo-Glass Fiber Reinforced Polymer Matrix Hybrid Composites, Composites: Part A,33: 4352.
18. Thwe, M.M. and Liao, K. (2003). Durability of Bamboo-Glass Fiber Reinforced PolymerMatrix Hybrid Composites, Comp. Sci. Tech., 63(34): 375387.
19. Rozman, H.D., Tay, G.S., Kumar, R.N., AbuBakar, A., Ismail, H. and Ishak, Z.A.M. (1999).Polypropylene Hybrid Composites: A Preliminary Study on the Use of Glass and Coconut Fiberas Reinforcements in Polypropylene Composites, Polym. Plast. Technol. Eng., 38(5): 9971011.
20. Pavithran, C., Mukherjee. P.S. and Brahmakumar, M. (1991). Coir-Glass Intermingled FibreHybrid Composites, J. Reinf. Plast. Comp., 10: 91101.
21. Sreekala, M.S., George, J., Kumaran, M.G. and Thomas, S. (2002). The MechanicalPerformance of Hybrid Phenol-Formaldehyde Based Composites Reinforced with Glass and
Oil Palm Fibres, Comp. Sci. Tech., 62: 339353.22. Rozman, H.D., Tay, G.S., Kumar, R.N., AbuBakar, A., Ismail, H. and Ishak, Z.A.M. (2001).Polypropylene-Oil Palm Empty Fruit Bunch-Glass Fibre Hybrid Composites: A PreliminaryStudy on the Flexural and Tensile Properties, Eur. Polym. J., 37: 12831291.
23. Abdul Khalil, H.P.S., Hariharan and Abu Bakar, A. (2002). Agro Hybrid Composites:Combination of Oil Palm Fibres and Glass Fibres Reinforced Polyester Composites, In: Proc.Regional Symposium on Chemical Engineering 2002 in conjuction with 16th Symposium ofMalaysian Chemical Engineers, Department of Chemical Engineering, University of Malaya,Malaysia, Vol. 1, pp. 945951.
24. Sabutek (M) Sdn. Bhd. (2003). www.sabutek.com.
25. Tanaka, R. (2003). Utilization of Oil Palm Residues as a Raw Material for Pulp and Paper,http://ss.jircas.affrc.go.jp/kanko/newsletter/nl2000/No.23/04Tanaka.htm
26. Mohan, R. and Kishore (1985). Jute Glass Sandwich Composites, J. Reinf. Plast. Comp., 4:186194.
27. Clark, R.A. and Ansell, M.P. (1986). Jute and Glass Fibre Hybrid Laminates,J. Mater. Sci.,21:269279.
28. Adams, D.F. (1974). Elastoplastic Behavior of Composites, In: Sendeckyj, G.P. (ed.),Mechanics of Composite Materials (Composite Materials, V.2), pp. 170207, Academic Press,Inc., New York.
29. Gowda, T.M., Naidu, A.C.B. and Chhaya, R. (1999). Some Mechanical Properties of UntreatedJute Fabric-Reinforced Polyester Composites, Composites: Part A, 30: 277284.
30. Hull, D. and Clyne, T.W. (1996). An Introduction to Composite Materials, 2nd edn, UniversityPress, Cambridge.
31. Singleton, A.C.N., Baillie, C.A., Beaumont, P.W.R. and Peijs, T. (2003). Composites: Part B,34: 519526.
Lignocellulose-based Laminate Composite: Part I 683
by NAGARJUNA KONDURU on November 20, 2012jcm.sagepub.comDownloaded from
http://jcm.sagepub.com/http://jcm.sagepub.com/http://jcm.sagepub.com/http://jcm.sagepub.com/ -
8/9/2019 JourLignocellulose-based Hybrid Bilayer Laminate Compositenal of Composite Materials 2005 Hariharan 663 84
23/23
32. Kalaprasad, G., Thomas, S., Pavithran, C., Neelakantan, N.R. and Balakrishnan, S. (1996).Hybrid Effect in the Mechanical Properties of Short Sisal/Glass Hybrid Fiber Reinforced LowDensity Polyethylene Composites, J. Reinf. Plast. Comp., 15: 4973.
33. Zweben, C. (1977). Tensile Strength of Hybrid Composites, J. Mater. Sci., 12: 13251337.
34. Agarwal, B.D. and Broutman, L.J. (1980). Analysis and Performance of Fiber Composites,
Wiley Interscience Publications, New York.35. Marom, G., Fisher, S., Tuler, F.R. and Wagner, H.D. (1978). Hybrid Effects in Composites:
Conditions for Positive or Negative Effects Versus Rule of Mixtures Behaviour, J. Mater. Sci.,13: 14191426.
36. Wagner, H.D., Roman, I. and Marom, G. (1982). Hybrid Effect in the Bending Stiffness ofGraphite/Glass-Reinforced Composites, J. Mater. Sci., 17: 13591363.
37. Hayashi, T. (1972). On the Improvement of Mechanical Properties of Composites by HybridComposition, In:Proc. 8th International Reinforced Plastics Conference, Brighton (UK): BritishPlastics Federation, Paper 22, pp. 149152.
38. Bunsell, A.R. and Harris, B. (1974). Hybrid Carbon and Glass Fibre Composites,Composites,5(4): 157164.
39. Kretsis, G. (1987). A Review of the Tensile, Compressive, Flexural and Shear Properties ofHybrid Fibre-Reinforced Plastics, Composites, 18: 1323.
40. Jones, K.D. and DiBenedetto, A.T. (1994). Fiber Fracture in Hybrid Composite Systems,Comp. Sci. Tech., 51: 5362.
41. Peijs, A.A.J.M. and De Kok, J.M.M. (1993). Hybrid Composites Based on Polyethylene andCarbon Fibres, Part 6: Tensile and Fatigue Bahaviour, Composites, 24(1): 1932.
42. Paiva, J.M.F. and Frollini, E. (2002). Sugarcane Bagasse Reinforced Phenolic andLignophenolic Composites, J. Appl. Polym. Sci., 83: 880888.
43. Luo, S. and Netravali, A.N. (1999). Mechanical and Thermal Properties of EnvironmentFriendly Green Composites Made from Pineapple Leaf Fibers and Poly(hydroxybutyrate-co-valerate) Resin, Polym. Comp., 20(3): 367378.
44. Khatri, S.C. and Koczak, M.J. (1996). Thick Section AS4 Graphite/E-Glass/PPS Hybrid
Composites: Part 1. Tensile Behavior, Comp. Sci. Tech., 56: 181192.45. Chawla, K.K. (1942). Composite Materials. (Materials Research and Engineering), Springer-
Verlag, New York.
46. Park, R. and Jang, Jyongsyik (2000). Effect of Laminate Geometry on Impact Performance ofAramid Fiber/Polyethylene Fiber Hybrid Composites, J. Appl. Polym. Sci., 75: 952959.
47. Park, R. and Jang, Jyongsyik (1998). Impact Behavior of Carbon Fiber/Polyethylene FiberHybrid Composite: The Effect of Surface Treatment of Polyethylene Fiber,Polym. Comp.,19(5):600607.
48. Nielsen, L.E. (1974).Mechanical Properties of Polymers and Composites, Vol. 2, Marcel Dekker,Inc., New York.
684 A. B. A. HARIHARAN ANDH. P. S. A. KHALIL