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Applied Mechanics and Materials Vols. 754-755 (2015) pp 955-959
© (2015) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMM.754-755.955
Submitted: 06.01.2015
Accepted: 06.01.2015
Mercerization Effect on Morphology and Tensile Properties of roselle
fibre
R. Nadlene1,4a,S.M. Sapuan1,3 b,M. Jawaid3, cand M.R. Ishak2,3,5 d
1
Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, 43400
UPM Serdang, Selangor, Malaysia
2
Department of Aerospace Engineering, Universiti Putra Malaysia, 43400
Selangor, Malaysia
UPM Serdang,
3
Laboratory of Biocomposite Technology, Institute of Tropical Forestry and Forest Products
(INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
4
Department of Material and Structure, UniversitiTeknikal Malaysia Melaka, 76100 Durian Tunggal,
Melaka, Malaysia
5
Aerospace Manufacturing Research Centre, Universiti Putra Malaysia, 43400 UPM Serdang,
Selangor, Malaysia
a
[email protected], [email protected], [email protected],
d
[email protected]
Keyword: Roselle Fibre, Tensile, morphology, Mercerization
Abstract. Natural fibres are preferred compared to synthetic fibres because of several advantages
such as biodegradable, lightweight, low cost and good mechanical properties. Roselle is one of the
plants found to be suitable to be used to produce natural fibres. Although natural fiber reinforced
composites are becoming widely used, several weaknesses such as lack of good interfacial
adhesion, low melting point and poor resistance to moisture absorption are harmful to its further
acceptance. Chemical treatment is a method that can improve the interfacial bonding, stop water
absorption, clean the fibre and increase surface roughness. In this study, roselle fibres were
immersed in Sodium hydroxide (NaOH) with 3 different concentration (3, 6, and 9%). The results
before and after treatment were compared. Scanning electron microscope was used to examine the
surface morphology. Tensile properties of roselle fibre were performed to study the tensile
properties. Results shows that the higher concentration of NaOH will increase the surface roughness
and have higher ability to clean the fibre. For tensile properties, 6% of NaOH give the highest
tensile strength. It can be concluded that, 6% of NaOH is the most suitable concentration to clean
roselle fibre and while maintaining good tensile properties.
1.0 Introduction
Recently, in line with raising environmental concerns, scientists and researchers are now
replacing synthetic fibres with natural fibres as the main component in composites. Several reasons
have attracted material engineers to use natural fibres to reinforce polymer composites such as
reduction of timber usage and degradation of the unused natural fibres. Other advantages include
low cost, good mechanical properties, abundantly available, material renewability, biodegradability
and abrasive in nature for ease of recycling[1]–[3]. These natural fibres can be processed into
composite boards or other forms suitable for various applications while preserving the environment.
Natural fibres can be found in southeast Asian countries such as Malaysia, Indonesia and
Thailand[4]. Natural fibre such as Roselle (Hibiscus sabdariffa) are found in abundance in nature
and cultivated in Borneo, Guyana, Malaysia, Sri Lanka, Togo, Indonesia and Tanzania. Roselle is
one of the plants found to be suitable to be used to produce natural fibres.The scientific name for
Roselle is Hibiscus sabdariffaL. and it is from Malvacea family. Roselle belongs to the hibiscus
family and is found abundantly in tropical area. They are commonly used as an infusion and to
produce bast fibre. There are various use of roselle. The fruit is commonly used in medical [5][6]
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Advanced Materials Engineering and Technology III
and food industry [7][8] while the fibre is used as a textile [9] and reinforcement material for
polymer composites [10]. However, very limited studies have been done on the application of
Roselle fibres and its composites[11].Roselle stem is red in colour as illustrated in Figure 1 in water
retting process. In Malaysia, after a year, Roselle plant will be cut, and it will become a waste. This
is because the quality of roselle fruit is not good after a year. In order to use this plant efficiently,
the fibre can be used as a reinforcement material for polymer composite.
Fig. 1Water retting process
Although roselle fibres have some advantages over synthetic fibre especially in term of material
cost, is still weakness on the fibre matrix interface. Crucial issues in using natural fibres includes
poor adhesion between fibre and matrix, water absorption and high moisture content which leads to
dimension instability of the fibers that can cause micro cracking of the composite and degradation
of mechanical properties. The performance and quality of the composites product highly depends on
fibre matrix adhesion and stress from the matrix to the fiber. Mechanical performances of natural
fibers such as kenaf, jute and hemp have been improved by several methods in the past.
Mwaikambo and Ansell [12] found that 6% was the optimum concentration in terms of cleaning the
fiber bundle surfaces and retaining a high index of crystallinity. The same method has been
conducted by Edeerozey et. al. and they found that 9% of NaOH showed the cleanest surface and
6% treated by NaOH provide highest tensile properties. In this research, mercerization method have
been used due to the low price and it’s efficiency. Different percentages of concentration of NaOH
(3%, 6%, 9%) have been conducted to study the effect on the morphology and tensile properties of
the fibre.
2.0 Material and Method
2.1 Materials
Roselle plants have been collected from Johor, Malaysia. Roselle fibres were extracted by using
water retting process for 7 days. The retted stem of the roselle plant was washed in running water
and fibres were removed manually. Next, fibres were cleaned, and dried in the sunlight. The roselle
fibres were then prepared for several tests to study on their potential as reinforcement materials in
polymer composites. Fig. 1 is the roselle plant taken from farm.
2.2 Chemical treatment
Roselle fibres were immersed in the three different concentrations of NaOH for 2 hours at room
temperature in a basin. 3%, 6% and 9% of concentration have been chosen for the chemical
treatment. After the chemical treatment of roselle fibre, the fibre were thoroughly washed with
running water and dried in oven at 104 0C to eliminate the moisture effect of the fibres for 48 hours.
Fig. 2 is the roselle fibre treatment in NaOH solution.
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Fig. 2 Chemical treatment of roselle fibre in NaOH
2.3 Scanning electron microscopy (SEM)
The morphology of roselle fibre on the effect of chemical modification have been observed under
scanning electron microscope (SEM), model Hitachi S-3400N. The fibres were gold coated in order
to obtain a good quality of results. The structural change upon treatment can be observed through
microscopic analysis.
2.4 Tensile test
Tensile test is a simple method in order to know the mechanical properties of natural fibre. Several
significant mechanical properties can be obtained from tensile test such as Young’s modulus, tensile
stress, maximum elongation, tensile strain and yield stress. The tensile properties of roselle fibre
were determined using Universal Testing Machine, model Instron 5556. ASTM D3379 standard was
used for single fibre tensile test[13]. Gauge length of the roselle fibre samples was 20mm and the
cross-head speed was 1mm/min with a 5kN load cell. The fibre was properly selected under optical
microscope before being tested to ensure that the specimen yields accurate result. The fibre was
glued on the sample holder. Before testing was commenced, the sample holder needs to be cut at the
middle. Fifteen samples of roselle fibre were prepared to perform tensile test.
3.0 Results and discussion
3.1 Fibre surface morphology
In this study 4 samples of roselle fibres with and without treatment have been examined their
surface morphology by using scanning electron microscopy. Scanning electron microscopy is one of
the methods that provide a good result to study the morphology of natural fibre. As expected as
published literature review, there was a different between the treated fibre and untreated fibre in
term of their surface (smoothness and roughness) and properties. This concludes that surface
topography studies provide important information on the level of interfacial adhesion that would
exist between the fiber and the matrix later when used [14]. Figure 4 (a,b,c,d) shows the SEM
results of treated and untreated roselle fibre and it was taken by using 800 to 1000k magnification.
Figure 4 a shows roselle fibre without treatment under 800 magnifications. It can be seen that, there
is still impurities even after the fibre have been washed with fresh water. It can be concluded that
fresh water cannot remove all the bur and impurities. In contrast with Fig 3. (b), treated roselle with
3% NaOH, the impurities still exist but less than untreated fibre. 3% NaOH is still not enough to
modify the surface and remove all the impurities. Fig. 4 (c) shows roselle fibre with 6% NaOH
treatment. It can be observed that, the surface of roselle fibre was smoother and almost all of the
impurities were removed. The surface is rougher than without and 3% treatment of NaOH. Figure 4
(d) shows the roselle fibre treated with 9% NaOH. Clearly that roselle fibre treated by 9% NaOH
has ability to remove all the impurities as seen in the figure. Even the fibre surface is clean but it
looks jagged and the surface is rougher. From the surface morphology examination, 9% NaOH
treatment of roselle fibre is the cleanest and roughest than the others. From the published literature,
the rougher surface of natural fibre is most desired surface because it will increase the interfacial
bonding between fibre and matrix. Physically, presence of rough surface giving the mechanical
lock between the fibre surface and matrix and it may enhance the interfacial bonding between them
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Advanced Materials Engineering and Technology III
[15].Fibre cleanliness is one of the important factor that effect the interfacial bonding. This is
because impurities can weaken the interfacial bonding between fibre and matrix and create weaken
point which leads to micro cracking.
(a)
(b)
(c)
(d)
Fig.3 SEM Micrograph of (a) untreated roselle fibre, (b) 3% of NaOH treated of roselle fibre, (c)
6% of NaOH treated of roselle fibre, (d) 9% of NaOH treated of roselle fibre
Tensile Strength, (MPa)
3.2 Tensile properties
Fifteen from each group of treated and non-treated sample have been tested with gauge length of all
samples is 20mm with 1mm/min cross-head speed. The average tensile strength was measured.
From the obtained results, there are different tensile properties between with and without treatment
sample as shown in Fig. 4. From fig. 4 it can be seen that tensile strength of roselle fibre without
treatment give the lowest value compared to treated fibre. The tensile strength of roselle fibre
increase 5.47% from non-treated to 3% treated by NaOH and 49% for 6% of NaOH treated which
the tensile strength is 340.63 MPa. The removal of impurities increases uniformity which in turn
contributes to the increase in strength. However, the tensile strength of 9% treated by NaOH
suddenly drop to 242.52 MPa. This is due to the high concentration of NaOH damages the cellulose
content of roselle fibre [12]. The value recorded was even lower than that of the non- treated fibers.
Alkali treatment has an effect on the chemical composition of the fibers which can reduce the water
absorption and at a certain concentration it will increase the tensile properties of the fibre. However,
if exceed too much concentration of NaOH the chemical composition will effect badly and might
decrease the tensile properties. This might be due to removal of lignin, cellulose and hemicelluloses
component, wax and oil of fiber during alkali treatment(Jannah et al. 2008; D. Sampathkumar et al.
2012; Mwaikambo 2002)
400
300
200
100
0
Without 3 NaOH 6 NaOH
treatment
Roselle fibre
9 NaOH
Fig. 4 Tensile properties of roselle fibre
4.0 Conclusions
Roselle fibre has been treated by using different concentration of NaOH (3, 6, and 9%). From the
scanning electron examination results, it can be concluded that, increase concentration of NaOH
will increase the ability to remove all the impurities and the surface become smoother. For 3%
NaOH improves the roselle fibre surface but it is not sufficient enough to remove all impurities. 9%
of NaOH treatment results is the cleanest, and the surface of roselle fibre become smooth and
rougher when it is touched. Increased concentration of NaOH solution affects the tensile properties
of roselle fibre. From the obtained results, it can be seen that 6% of NaOH treatment give the
Applied Mechanics and Materials Vols. 754-755
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highest tensile strength and the results dramatically drop after treated with 9% of NaOH. It is
believed that, higher concentration of NaOH will change the chemical content and damage the
structure of roselle fibre.
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