Water Absorption and Tensile Strength of Coconut Filter Fiber/Polypropylene Composites.

Volume 702 (2013)
doi: 10.4028/www.scientific.net/AMR.702

Advanced Materials Research

ISSN: 1662-8985

TTP Trans Tech Publications

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Water Absorption and Tensile Strength of Coconut Filter Fibers/Polypropylene
Composites

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Advanced Materials Research Vol. 702 (2013) pp 207-212

© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.702.207

Water Absorption and Tensile Strength of Coconut Filter
Fibers/Polypropylene Composites
NPG.Suardana1,a, IP. Lokantara1,b, YJ. Piao2,c, and JK. Lim2,d
1

Department of Mechanical Engineering, Faculty of Engineering,
Udayana University, Bali Indonesia.

2

Automobile Hi-Technology Research Institute, Faculty of Mechanical & Aerospace System
Engineering, Chonbuk National University, Deokjin 1-664-14, Jeonju, 561-756,
Republic of Korea.
a

npgsuardana@me.unud.ac.id, blokantara_santri@yahoo.com,
c

parkyingjun@hotmail.com,djklim@jbnu.ac.kr

Keywords: Coconut filter fiber, Surface treatment, Polypropylene, Composites, Water absorption,
Tensile properties

Abstract. In this study, we evaluated water absorption and tensile properties of coconut filter fiber
reinforced polypropylene composites. The fibers were subjected to various immersion times for 0.5,
1, and 3 h in 0.5 % acrylic acid solution at room temperature and 0.5 h at 70 oC. The treated fibers
were used as reinforcement of polypropylene composites. Water absorption of treated fiber
composites was lower than those of untreated fiber composite. Boiling in water significantly affect
water absorption rate of the composites. The tensile strength and elastic modulus of treated fiber are
higher than untreated fiber. They show a decrease in tendency when the immersion time increased.
Tensile strength and elastic modulus of composites with AA-treated at 70 oC fiber are the highest.
Introduction
Coconut palm (Cocos nucifera) trees are found in the tropical countries, such as Indonesia,
Malaysia, Philippine, India, Vietnam, Papua New Guinea, South America and so on [1]. One of the
parts of the coconut trees is the coconut filter (Coconut fabric), which is present at the bottom of the
leaves and growing from a young leaves sheath. It is abundantly available and presently wasted [2].
Coconut filter has enough strength, so it can be utilized to make other materials, which are more
useable and profitable, for example, as an alternative for composite reinforcement, replacing glass

fibers with natural fibers in the automobile industry can yield economic, environmental and social
benefits.
Generally, alkalis and acids modify the properties of natural fibers like hemp, sisal, jute, rice
straw, coir and so on. Kim and Lim [3] studied the rice straw fiber treatment by alkali and some
acid solution. They found that the concentration of alkali and acid solution for surface treatment
affect the tensile strength and elongation.
In other study, combining treatment of bagasse can also be achieved by treatment of the fibers
with 1 % NaOH solution for 30 min followed by 1 % acrylic acid for 1 h. This treatment method
showed a better effect on improving mechanical properties in comparison to NaOH-treated of
bagasse fiber-polyester composites [4]. Suardana, et al. [5] studied combining treatment of coir fiber.
They found that 6% alkali treatment at 95oC for 3 h followed by acrylic acid (AA) treatment (0.5 %
AA for 0.5, 1 and 3 h) of fiber reinforced PLA composites resulted in significant improvement of
tensile and flexural strengths and less water sorption than untreated and alkali treated of the
composites.
Though many fibers have been studied, there is a little known on the coconut filter fiber and its
composite. In this study, we have tried to evaluate water absorption and tensile properties of their
composites.

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Advanced Materials Science and Applied Mechanics

The objective of this study is to know the behavior of water absorption and tensile properties of
the coconut filter fiber composites due to AA treatment of their fibers. The expectation of this study
is to give a contribution of the abundant source of a raw material that could be utilized into
profitable and usable products.
Experimental method
Polypropylene (PP) was purchased from Gawall Korea, with density of 0.9 gr/cm 3 and melting
point of 170 oC. Coconut filter (CF) was collected from Bali, Indonesia. It was separated by
combing. Sodium Hydroxide (NaOH) was purchased from Showa Chemical Co. Ltd Japan, and
Acrylic acid (CH2:CHCOOH) was produced by Junsei Chemical Co. Ltd Japan.
The coconut filter fibers were cut into 5-15 mm in length and washed with water to remove dust
and impurities and then boiled in water (ratio fiber and water 1 gr fiber: 40 ml water) at 100 oC for 1
h. Finally, the fibers were rinsed with tap water and then dried in an oven at 70 oC for 12 h [6].
The fibers were subjected to various surface treatments as follows: the CF fibers were treated by
6 % NaOH immersion at 95 oC for 3 h (1 gr fiber in 40 ml solution) [8], and then washed with tap
water to eliminate any NaOH solution remaining on the fibers surface and dried in the oven for 24 h
at 70 oC. Subsequently, they were soaked in 0.5 % acrylic acid (AA) solution (1gr fiber in 40ml
solution) at room temperature for 0.5, 1, 3 h, and at 70 oC for 0.5 h and then washed with distilled
water. Finally, the fibers were dried in the oven at 70 oC for 72 h [6].
The compounded materials were molded from a stack of eight PP films interleaved with CF
fibers (35% volume fraction). The mold and specimen were placed into hot press machine (Carver
#3912) that was used for compression molding. The specimen was heated until 200 oC without
pressure, subsequently the pressure was increased to 1.5 MPa for 15 min at that temperature. It was
cooled down to room temperature with load 40 Kg. The nominal thickness of the specimens was 35 mm.
Water absorption experiments were carried out according to ASTM D570. Before specimens
testing, all specimens were dried at 50 oC for 6 h to reduce the moisture content. First, the
specimens were immersed in water for 6, 18 and 48h, respectively, at room temperature. In the
following step, the specimen’s surface was dried with tissue papers and weighed immediately to
measure their wet weight. Then, the specimens were dried at 50 oC for 6 h and immersed again and
the surface was dried with tissue papers as stated before. Finally, the specimens were dried at 50 oC
for 6 h and repeated immersion in water at 70 oC for 6, 18 and 48 h, respectively. Water absorption
(WA) was calculated by the formula [5]:
WA(%) 

Wt  Wo
Wo

x100

(1)

where Wt is the weight of the sample after immersion at each time and Wo is the weight of the
dry sample.
The composites tensile tests were performed using an Instron Universal Testing Instrument
model 4206 and carried out in accordance with ASTM D3039.
Results and discussions
Water Absorption of Composites. Water Absorption of the untreated and treated coconut filter
fiber composites were monitored at room temperature and at 70 oC. The results are shown in Figs.
1(a-c) where water absorption is plotted against soaking time. These figures show that water-uptake
for all specimens increased when the soaking time are increased. Water absorption of untreated
fiber composite was the highest in all cases. This may be attributed to the lignocelluloses absorbing
water by forming hydrogen bonding between water and hydroxyl groups of cellulose,
hemicelluloses in the cell wall [5.7]. The cellulose and hemicelluloses in the untreated fiber are
more than 50 % [8,9], leading to the poor wettability and weak adhesion between untreated fiber
and PP, therefore, the fiber can behave like capillary flow of the water along the fiber-matrix

Advanced Materials Research Vol. 702

209

interface. For surface modified CF fiber composites, the alkali treatment of natural fiber can reduce
the hydroxyl group from surface fiber [4], and also the fibers get masked with the polypropylene
which is hydrophobic and strong adhesion each other, hence water absorption is less than untreated
fiber composites.
The effect of AA-treated fibers reinforced PP composites on water absorption was better than
those of the untreated fiber composites. This is due to AA coating on the fiber surface, resulting in
decrease of the water absorption of composites [10].
The initial water absorption rate is the lowest for 3h-AA-treated fiber composites followed by
alkali-treated fiber composites for all cases. Similar trends were observed in water absorption rate
value between Fig. 1a and Fig. 1b, but water absorption rate with immersion in boiling water at 70
o
C significantly increased for all specimens (Fig. 1c). From this Figure, it is evident that initial
water absorption rate increased to about 100 % for all composites. Similar results are observed by
Sreekala et al. [11] and Patel et al. [12]. Temperature is one of the parameters to give effect of water
uptake in fibrous composite besides of the presence of hydrophilic groups, fiber loading, orientation
of fiber, permeability of fiber, etc. Water absorption increases with increasing temperature, because
of the deterioration of adhesive bonding.

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Advanced Materials Science and Applied Mechanics

Fig. 1. Water absorption of CF/PP composites of: (a) the first time at room temperature; (b) the second time
after re-drying and immersing at room temperature; (c) the third time after re-drying and immersing at 70oC.

Tensile Properties of Composites. Tensile strength (σt) and modulus of elasticity (Et) of the CF/PP
composites with different fiber treatment are presented in Fig. 2. The σt and Et of untreated fiber
composites are the lowest as in comparison to those of treated fiber/PP composites. Fig. 3a shows
the tensile fracture surface of this composite. It can also be seen that CF fibers debonded easily and
pullout from PP when stress is applied, so some holes are created in the fracture surface, which
indicates poor adhesion at the interface between fibers and PP. Therefore, the σt and Et become low.
Fig. 2 exhibits that the tensile strengths of the treated CF fiber composites increase 36.14, 44.03,
32.7, 35.98 and 45.66 % in comparison to those of untreated CF fiber composite when the fibers
being treated with alkali, alkali followed with 0.5 % AA-treated for 0.5 h, 1 h, 3 h at room
temperature and 0.5 h at 70 oC, respectively. Fig. 2 also shows that the elastic modulus increases by
20.42, 26.88, 11.42, 17.78 and 38.33 % in comparison to those of untreated CF fiber composite
when the same treatment was for them, respectively. SEM photographs that are shown in Fig. 3b-3d
supported those results. These Figures show that are good interface bonding between fibers and
matrix without any debonding and pullout.
The trend of composites tensile properties has a little difference with their single fibers [6].
These may be due to the reinforcing ability of the fibers not just depending upon the mechanical
strength of the fibers but some factors affect the interfacial interaction between the matrix and the
fibers surface like polarity of the fiber, surface characteristics and the presence of reactive centers of
functional groups [13,14].
The enhancement of σt and Et of composite with AA at 70 oC indicates the effectiveness of the
reinforcement because of heating as an initiator system to induce any chemical changes.

Advanced Materials Research Vol. 702

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Fig. 2. Graph of Tensile strength and Elastic modulus of the untreated and treated fiber composites.

Fig. 3. SEM of tensile fractured surface of: (a) untreated; (b) alkali-treated; (c) and (d) alkali followed by
0.5%AA for 0.5h at room temperature and at 70oC treated fiber composites, respectively.

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Advanced Materials Science and Applied Mechanics

Conclusions
Based on this study, the following conclusions are drawn:
Treated fiber composites have lower water absorption than those of untreated fiber composite.
Boiling in water significantly affect water absorption rate of coconut filter/polypropylene
composites.
3. Tensile strength and elastic modulus of treated fiber composites are higher than those of
untreated fiber composite.
4. Tensile strength and elastic modulus of composites with AA-treated at 70 oC fiber are the
highest in this study. This indicates that heating as an initiator system to induce any chemical
changes.
1.
2.

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