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The Journal of Engineering Research (TJER) Vo. 14, No. 2 (2017) 115-123

DOI: 10.24200/tjer.vol.14iss2pp115-123

Characterization of Mechanical Properties of Aligned Date Palm

Frond Fiber-Reinforced Low Density Polyethylene

K.I. Alzebdeh*,a, M. M. Nassarb, M.A. Al-Hadhramia, O. Al-Aamria, S. Al-Defaaia and S. Al-Shuailya

a Department of Mechanical and Industrial Engineering, College of Engineering, Sultan Qaboos University, Oman.
b Palestine Polytechnic University, Hebron, State of Palestine.

Received 10 March 2017; Accepted 15 August 2017

Abstract: In recent decades, natural fibers have received attention of scientists and researchers due to

their ecofriendly characteristics that qualify them as potential reinforcement in polymer composites in

place of synthetic fibers. In this study, an experimental investigation has been conducted to evaluate

the effect of orientation of fibers on mechanical properties of a newly developed bio-composite in

which date palm fronds (DPF) are embedded as fibers in low-density polyethylene (LDPE) matrix.

Three bio-composite sheets with orientations of 0°, 45° and 90°, respectively have been fabricated after

the date palm fronds were chemically treated. The fabricated composite specimens are tested under

tensile load using Universal Testing Machine (UTM) in accordance with the ASTM D-638 standard.

Then, a comparison of the experimental results against analytical results is made to examine the

accuracy and agreement between the two. An inconsistency in moduli, as was discovered, is

attributed to the adhesion quality between the fibers and surrounding matrix. Output results help to

assess the applicability of such class of bio-composites in real-life applications. The results of tensile

strength, Young’s modulus, and elongation at break revealed that date palm fronds can be used as

reinforcement material in polymer-based composites for low strength applications.

Keywords: Bio-composites; Date palm fronds (DPF); Low density polyethylene (LDPE); Tensile

strength.

البولي إيثيلني منخفض نخيل املصفوف و املقوى اللياف سعف التوصيف اخلواص امليكانيكية ل

الكثافة
أي، سعود الشعيلأرفاعي، شذى الأامري، عثمان العأ، حممد أ. احلضرميبنصار ماجد، حممود *ه,أالزبدابراهيم خالد

الصديقة للبيئة واليت تؤهلها ها: القت األلياف الطبيعية يف العقود األخرية اهتمام العلماء والباحثني بسبب خصائصامللخص

لتكون مقوي حمتمل يف مركبات البوليمر بدال من األلياف االصطناعية. قامت هذه الدراسة بإجراء حبث جترييب لتقييم

حشو سعف النخيل فيه من خالل ،تأثري مدى تكيف األلياف مع اخلواص امليكانيكية للمركب احليوي املطور حديثا

°90و °45, ° .من املركب احليوي بقياسات الواحإثيلني منخفض الكثافة. مت تركيب ثالث كألياف يف نسيج البولي

على التوالي بعد معاجلة سعف النخيل كيميائيا. ومن اختبار عينات املركب املصنعة حتت محل الشد يف آلة االختبار

. بعد ذلك مت مقارنة نتائج التجربة بالنتائج التحليلية من أجل دراسة مدى الدقة ASTM D-638( وفقا ملعايري UTMالعاملية )

إىل جودة االتصاق بني األلياف واألنسجة التضارب يرجع معامل القيمة والتطابق بني االثنني. و تبني أن عدم التطابق يف

النوع من املركبات احليوية يف واقع احلياة. كما احمليطة بها . وتساعد هذه النتائج يف تقييم مدى امكانية تطبيق هذا

أظهرت نتائج قوة محل الشد ومعامل يونغ واستطالة الكسر أنه ميكن استخدام سعف النخيل كمواد حشو يف مركبات

تعتمد على البوليمر يف تطبيقات منخفضة القوة.

؛ محل الشد.(LDPE)الكثافة ثيلني منخفض ؛ البولي إي(DPF): املركبات احليوية. سعف النخيلالكلمات املفتاحية

* Corresponding author’s e-mail: alzebdah@squ.edu.om

mailto:alzebdah@squ.edu.om

K.I. Alzebdeh, M. M. Nasser, M.A. Al-Hadhrami, O. Al-Aamri, S. Al-Defaai and S. Al-Shuaily

116

1. Introduction

The development of advanced renewable

materials to replace the non-renewable and

petroleum-based products has aroused the

interest of researchers in the last few decades.

Although natural fiber reinforced composites

have been successfully used in various non-

critical products, there is still a need to develop

similar materials to broaden their industrial

applications. Two constituents are processed

and mixed together; natural fiber and hosting

matrix, which can be either non-biodegradable

or biodegradable based resin. The mechanical

properties of composite materials are dependent

on the properties of the two constituent phases.

Fibers typically have low density, moderate

specific strength and modulus, but are often

very brittle. Generally, fiber distribution,

concentration, and orientation are the main

factors that influence the overall properties of

the fabricated fiber reinforced composites

(Askeland et al. 2009; Callister et al. 2007).

Besides, the quality of the interface between the

dispersed phases and surrounding matrix is a

highly critical factor in determining the local

and nonlocal behavior of a composite.

Composite materials can be classified into three

main types: particle-reinforced, fiber-reinforced,

and structural composites. Fibers used as

reinforcement make improvements in strength,

stiffness, or high-temperature performance in

case of metals and polymers material, and

improve toughness to ceramics matrix.

Currently, about 40,000 composite products are

in use for an array of applications in diverse

sectors of the industry around the world (Gohil

and Shaikh 2010).

Date palm (Phoenix dactylifera L) is one of

the oldest cultivated and most valuable fruit

trees due to its ritual significance in human

societies, health benefits, productive capacity in

harsh semi-arid and arid environments. It is also

known for the range of subsistence produced

from its fruits, fronds, date seeds and other

parts of the tree. Date palm plantations

worldwide are estimated to have over 150

million trees (Al-Khayri et al. 2015). From each

individual tree, 10 to 15 branches are cut down.

Thus, on average, 35 kg of palm residues are

obtained per tree. However, the bulk of the

material is discarded as waste. Therefore,

efficient utilization of this natural resource in

fabricating natural fiber composite would have

a positive impact on environment and could

improve the economic status of rural areas

(Kocak and Mistik 2015; Mohanty et al. 2014;

Wazzan 2006). Overall, application of the DPF

as reinforcement or filler in polymers is feasible,

especially in case of annual pruning wastes,

noting an abundance of available biomass of

this type (Sbiai et al. 2010).

Natural fibers need to be chemically treated

before mixing with the matrix. Chemical

treatment of fiber helps in removing sticking

dirt and improving its physical and chemical

characteristics. AlMaadeed et al. (2013) and

Shalwan et al. (2016) reported that the use of

high NaOH concentration can cause

deterioration in the fiber strength. Also, Alawar

et al. (2009) concluded that hydrochloric acid

treatment resulted in deterioration in its

mechanical properties. In contrast, some results

revealed that 6% concentration of NaOH is the

optimum solution for treating date palm fiber to

maintain high interfacial adhesion and strength

with epoxy matrix (Alsaeed et al. 2013).

Scanning electron microscopy of the composite

specimens fracture surfaces indicates that the

Maleic Anhydride Grafted Polypropylene

(MAPP) and the treated fibers improved the

interfacial interaction between the fiber and the

matrix (Eslami-Farsani 2014). Based on the

findings, it can be concluded that its physical

and mechanical properties are not directly

related to increased treatment conditions (Taha

et al. 2007). The potential use of extracted date

palm tree fiber has been investigated based on

different aspects and methods (Al-Kaabi et al.

2005a, 2005b; AlRawahi et al. 2015; Kocak and

Mistik 2015; Mohanty et al. 2014; Taha et al. 2007;

Wazzan 2006). In general, date palm fibers can

be extracted from the stem mesh, midribs, bark

and leaves or fronds. Also, the particulate or

powder can be produced by milling the date

palm fruit seeds. Studies have shown that date

palm fibers provide a viable alternative for

exploitation in composite material fabrication

and they can serve as a replacement for glass

fiber, thus solving associated environmental

problems.

Polymer matrix in natural fiber composites is

divided into two main categories; bio-based and

Characterization of Mechanical Properties of Aligned Date Palm Frond Fiber-Reinforced Low Density Polyethylene

117

petroleum based. LDPE is a petroleum

thermoplastic matrix widely used in packaging

applications due to its chemical and corrosion

resistance, light weight, good impact resistance,

high stiffness and good process ability.

However, the usage of LDPE, as a polymer

matrix for reinforced composites, contributes to

a serious environmental problem due to LDPE

non-biodegradable properties. Also, LDPE is

soft, flexible and inert, thus resists reacting with

any other elements. Additionally, it possesses a

low static charge, so it does not attract dust and

dirt. Hence, it has a huge potential in fabrication

of polymer based composites (Al-Nasir 2013;

Fahim et al. 2012; Rahman et al. 2012; Sarifuddin

and Ismail 2013). An enhancement in the

mechanical properties of the developed bio-

composites compared to the virgin LDPE has

been observed (Fahim et al. 2012; Nur et al. 2010;

Rahman et al. 2012). Sarifuddin and Ismail

(2013) stated that the optimum tensile strength

was obtained when 10 wt.% of kenaf fiber

loaded into the LDPE. In the case of

Cannabis/LDPE, it has been found that the best

fibers ratio is 5 wt.% to improve the mechanical

properties of the developed bio-composites (Al-

Nasir 2013). Moreover, lower elongation of

break compared to pure LDPE occurs. In

another study conducted by Prasad et al. (2016),

the potential use of Banana fiber in LDPE matrix

was explored. It showed that a composite with

composition of 25 wt.% banana fiber is the

optimal rate on the basis of biodegradability

and mechanical properties.

In this study, alkali treated aligned date palm

fronds are used as reinforcing fibers in low-

density polyethylene bio-composites.

Mechanical properties (modulus of elasticity,

tensile strength, and strain at break) were

determined via experimental testing at different

fiber orientations (0o, 45o, and 90o) at ambient

temperature. In addition, analytical calculations

of mechanical properties based on

micromechanics are presented.

2. Methodology

2.1 Composite Fabrication and Physical

Testing
The date palm fronds were manually

extracted from Khusab palm tree of a local farm.

Chemical analysis showed the detailed

composition of all constituents (Table 1).

Firstly, fronds, as shown in Fig. 1 (a), were
dried under the sun for a month, and cleaned to
remove any contaminants. The extracted fronds
were cut into 1250 mm in length. A second-
hand treatment was applied using tap water as
a preliminary step of the cleaning process. In
order to improve morphology structure of
fibers, alkali treatment using 1 wt.% of NaOH
for 2 hours (Alawar et al. 2009; Taha et al. 2007)
was applied. Then, 20 wt.% volume of fibers
was aligned based on the specified direction in
the mold (200mm×200mm×5 mm) using a hand
lay-up method. Care was taken to achieve a
uniform distribution of fibers while being
layered in the LDPE matrix. Secondly, an
electrical oven was used to mix the composite
constituents at 300˚C (AlMaadeed et al. 2013)
until the matrix fully encapsulated the fibers as
shown in Fig.1(b). Sheets were manually
pressed under 25 kg load for 15 minutes to
eliminate any porosity or void formation and
maintain a uniform thickness as specified.
Lastly, the composite sheets were pressed
manually again for a day prior to cutting. Then,
specimens were cut according to the ASTM D
638 using CNC machine in order to characterize
their mechanical properties as shown in Fig. 2.
The prepared specimens were tested using
Universal Testing Machine (UTM) at a fixed
cross head speed of 5 mm/min, at room
temperature 23˚C and humidity 50%. For each
direction, three samples were tested at a fixed
gage length of 57 mm and average response
value was recorded.

2.2. Analytical Modeling
A connection with the classical micromechanics

may be established here. Our experimental testing

Table 1. Chemical composition of DPL fiber
(Mohanty et al. 2013).

Constitutes Percentage (%)

Cellulose 54.75
Lignin 15.3

Hemi-Cellulose 20.00
Pectin 1.2

Moisture 6.5
Ash 1.75
Wax 0.50

K.I. Alzebdeh, M. M. Nasser, M.A. Al-Hadhrami, O. Al-Aamri, S. Al-Defaai and S. Al-Shuaily

118

(a) (b)

Figure 1. Manually extracted date palm fronds fibers; (a) raw, and (b) encapsulated.

(a) (b)

Figure 2. Tensile testing procedure (θ = 90˚); (a) specimen, and (b) testing setup.

results can be compared with Voigt (rule of mixture)

and Reuss bounds. For instance, Voigt bound as

given by Eqn. (1), assumes a constant strain and

therefore gives upper bound on effective elastic

modulus of a composite (E
c
).

m
EmV

f
EfV

V
c
uE 





 (1)

While Reuss bound assumes a constant
stress and gives lower bound on effective elastic
modulus as given in Eqn. (2).

R
c
l

E 





 (2)

Where Ef, Em are the Young’s moduli of fiber

and matrix, respectively and Vf and Vm are the

volume fractions of fiber and matrix,

respectively. However, it is well known that the

Hashin-Strikman bounds (H-S) (Hashim 1963)

give more accurate and rigorous values as

compared to those of Voigt and Reuss bounds.

Characterization of Mechanical Properties of Aligned Date Palm Frond Fiber-Reinforced Low Density Polyethylene

119

Such bounds are given in Eqns. (3) & (4) for

isotropic elastic modulus of elasticity.

(𝐸𝑢
𝑐 )𝐻−𝑆 = 𝐸𝑓 +

𝑉𝑚
1

(𝐸𝑚−𝐸𝑓)
+

𝑉𝑓

2𝐸𝑓

(3)

(𝐸𝑙
𝑐 )𝐻−𝑆 = 𝐸𝑚 +

𝑉𝑓
1

(𝐸𝑓−𝐸𝑚)
+

𝑉𝑚
2𝐸𝑚

(4)

Where (Eu
c )H−S and (El

c)H−Sare the upper and
lower H-S bounds on effective elastic modulus

of a composite. It is important to mention that
all these bounds assume prefect bonding
between fibers and surrounding matrix.

3. Results and Discussion

The mechanical properties of both fiber and

matrix used in this study are given in Table 2.

One observation on the tensile properties of

both fiber (frond) and matrix (LDPE) is a

noticeable mismatch between the two ingredi-

Table 2. Mechanical properties of fibers and matrix used.

Tensile Strength

(MPa)
Tensile Strain

(%)
Young's Modulus

(GPa)
Specific Gravity

Khusab frond 19 4.7 5.4 1.17
Neat LDPE 9.6 100 0.4 1.08

Figure 3. Tensile strength (left) and Tensile Modulus (right) of the tested bio-composites sheets.

Figure 4. Strain at break of the tested bio-composites sheets.

Neat LDPE 0 45 90

K.I. Alzebdeh, M. M. Nasser, M.A. Al-Hadhrami, O. Al-Aamri, S. Al-Defaai and S. Al-Shuaily

120

-ents can be detected. This may affect the

interfacial properties of the interface region and

can lead to a degradation in tensile properties of

the composites.

For all the tested composite specimens,

mechanical properties were degraded in

relation to those of neat LDPE. For tensile

strength, around 14% drop was observed in case

of θ = 0o (Fig. 3), which is considered to be

reasonable as there were several limitations in

the fabrication process that contributed to a

poor adhesion between fiber and surrounding

matrix. At θ = 45o, a slight stronger composite

was obtained. As expected, the weakest

composite occurred at θ = 90o. Young’s modulus

follows a similar behavior (Fig. 3). A drop of

15% in strain at failure was obtained for

composite at θ = 0o. It is almost an equal strain

at failure for both specimens at θ = 0o and θ =

45o (Fig. 4). Recently, Alzebdeh et al. (2016)

studied the mechanical properties of chopped

date palm fronds reinforced LDPE. At 20%

volume of date palm fronds, a tensile strength

in the range of 5.81 to 7.2 MPa was obtained.

Therefore, continuous date palm frond

reinforcement composites showed slightly

higher strength.

The recorded stress-strain curves under

uniaxial tensile loading are shown in Fig. 5. As

reflected in the approximate linear region of

these curves, Young’s moduli are similar in both

cases θ = 0o and θ = 45o with the weakest value

at θ = 90o. Yield for the first two cases occurred

at strain equal to 0.3 while for the third case, it

occurred at strain around 0.6. Ultimate tensile

strength of 8.4 MPa was achieved at θ = 45o with

higher toughness.

Analytical modeling results in the whole

range of volume fraction of fibers are depicted

in Fig. 6. Again, it is worthwhile to emphasize

that these bounds assume perfect bonding

between fiber and hosting matrix. With

admitted limitations on hand-lay-up method of

fabrication, it is clear that this assumption is not

well satisfied here.

Figure 5. Stress-Strain curves in tension of tested specimens.

Characterization of Mechanical Properties of Aligned Date Palm Frond Fiber-Reinforced Low Density Polyethylene

121

Figure 6. Bounds on effective Young’s modulus.

Table 3. Young’s modulus (GPa) as obtained experimentally and analytically.

Experiment Voigt Reuss
H-S
(upper)

H-S
(lower)

0.25 1.4 0.49 0.99 0.56

At 20% volume fraction and 0o orientation,

Young’s modulus of 0.25 GPa is obtained, which

is less than the corresponding analytical values

(Table 3).

A better controlled fabrication process that

ensures a strong adhesion between fibers and

hosting matrix will result in a closer matching of

experimental values of Young’s modulus to

those estimated analytically.

4. Conclusion

The increasing awareness toward the

biodegradable natural fibers, as an alternative to

synthetic fibers, has generated an interest to

develop eco-friendly polymer composite

materials. In this study, three sheets of LDPE

were fabricated using hand lay-up method in

which continuous palm tree fronds were

aligned as fibers. Based on experimental testing

for mechanical properties, a few observations

can be highlighted:

 In general, mechanical properties have been

degraded with a drop of 16% in tensile

strength, 37% in tensile modulus and 15% in

strain at failure.

 This degradation in mechanical properties is

attributed to the poor adhesion between

fibers and matrix.

 45˚ orientation of fiber resulted in higher

tensile strength.

 A mismatch between the experimental and

analytical results occurred due to lack of

perfect bond between fiber and matrix.

Regardless of such drop in mechanical

properties of the new developed DPF/LDPE

composites, preliminary results indicate that

using date palm fronds as fillers in plastics and

other types of polymers is promising as these

biodegradable fronds are priceless, have

abundant source, which is considered as waste.

Finally, it can be concluded that date palm

fronds fibers can be used as “reinforcing”

material for low strength applications with cost

effectiveness and environmental awareness.

Conflict of Interest

The authors declare no conflicts of interest.

0 0.2 0.4 0.6 0.8 1

E
c
(

M
P

a
)

Voigt Reuss HS-U HS-L

K.I. Alzebdeh, M. M. Nasser, M.A. Al-Hadhrami, O. Al-Aamri, S. Al-Defaai and S. Al-Shuaily

122

Funding

No funding was received for this research.

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