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Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.6, pp.569-582, 2010
jmmce.org Printed in the USA. All rights reserved
Investigating the Effect of Chemical Treatment on the Constituents and
Tensile Properties of Sisal Fibre
I.O. Oladele*, J.A. Omotoyinbo and J.O.T. Adewara
Metallurgical and Materials Engineering Department,
Federal University of Technology, Akure.
Ondo State, Nigeria.
Affiliated to African Materials Science and Engineering Network (AMSEN).
*Corresponding Author: firstname.lastname@example.org
This work was carried out to investigate the effect of chemical treatment on the constituents
and tensile properties of sisal fibre (Agave Sisalana). Sisal leaves were cut and buried
underground close to the stream and were wetted with water regularly in order to ensure
proper fermentation for about 15 days. The fermented leaves were washed and sun dried. The
dried sisal fibre obtained was treated mechanically with chemicals after which the
percentages of their constituents were characterized and, their tensile properties determined
with Instron universal tensile testing machine. The results show that the ch emical treatments
enhance the removal of lignin and hemicelluloses which are detrimental to the bonding
strength of composite produced from natural fibres except that of sample treated with
alkaline peroxide. The results of the tensile test revealed that sample treated sequentially with
KOH, acetic acid, NaCl and HCl has the best tensile properties followed by the sample
treated with alkaline peroxid e.
Keywords: Investigate chemical treatment, constituents, tensile properties, and sisal fibre.
There is a growing interest in the use of natura l fibres as reinforcement for thin sheet cement
composites  and thermoplastic matrix composites . Natural fibres generally have poor
mechanical properties compared with synthetic fibres but their use as reinforcement material
has been adopted since the beginning of mankind to make straw reinforced huts and other
570 I.O. Oladele, J.A. Omotoyinbo and J.O.T. Adewara Vol.9, No.6
articles . However, the main advantages of these fibres are their availability in large
quantities in many countries, low density, low cost and ease of manufacture.
In the last decade, extensive research work has been carried out on the natural fibre
reinforced composite materials. Natural fibres can be used to reinforce polymers to obtain
light and strong materials. Natural fibres from plants are beginning to find their way into
commercial applications such as in automotive industries and household applications, .
Due to the relatively high cost of synthetic fibres such as, glass, plastic, carbon and Kevlar
used in fibre reinforced composites, and the health hazards of asbestos fibres, it has become
necessary to explore natural fibres. Natural fibres are produced from renewable resources, are
biodegradable and relatively inexpensive compared to the traditionally used synthetic fibres.
Fibres of this type, for instance, hemp and flax, are successfully used as packaging material,
interior panels in vehicles, and building components, among others. Also, natural fibres like
banana, sisal, hemp and flax, jute, coconut, local fibres and oil palm [5-11] have attracted
scientists and technologists for applications in consumer goods, low-cost housing and other
The fibre/matrix interface has an important role in the micromechanical behaviour of
composites. One difficulty that has prevented the use of natural fibres is the lack of good
adhesion with the polymeric matrix. In particular, the large moisture sorption of natural fibres
adversely affects adhesion with hydrophobic matrix material leading to premature ageing by
degradation and loss of strength. To prevent this phenomenon, fibre surface properties have
been modified in order to promote adhesion . To reinforce therm oplastic composites, blue
agave fibres were modified via esterification reaction . The mechanical properties
characterization of these fibres showed a change in the elastic modulus and an improvement
in the impact resistance . There are, however, several separation of fibre processing
techniques such as mechanical or chemical pulping, whereby the lignin is degraded and
dissolved, leaving most of the cellulose and hemicelluloses in the form of fibres. This
generally has an important effect on both mechanical and chemical properties of the fibres.
Resently, natural fibres have proved to be effective reinforcement as simple fillers in
thermoplastic and thermoset matrix composites for automotive sectors . A number of
investigations have been conducted on several types of natural fibres such as kenaf, hemp,
flax, bamboo, and jute to study the effect of these fibres on the mechanical properties of
composite materi als. This work was carried out to invest ig ate the effect of chemical tre atment
on the chemical constituents and the tensile properties of sisal fibre (Agave Sisalana).
2. MATERIALS AND METHOD
The materials that were used are sisal leaves, distilled water, hydrogen chloride, hydrogen
peroxide, potassium hydroxide and acetic acid.
Vol.9, No.6 Investigating the Effect of Chemical Treatment 571
Weighing balance, shaker water bath, beakers, furnace, crucible, instron universal tensile
2.3.1 Preparation of Materials
The sisal fibre used was obtained from the plant leaves. The leaves were cut and buried under
ground for 15 days so as to allow fermentation to take place. For the reaction to take place
normally, the leaves were buried close to stream of water and are watered daily. The
fermented leaves were washed after which they were sun dried.
2.3.2 Chemical Treatment
Cellulose micro fibrils were prepared using different combinations of chemical and
mechanical treatments. Three different treatments were carried out on different samples while
some was left as control. The treatment was carried out as follows:
Mass of Fibre used: 120g sisal fibre was divided into four equal mass of 30g each.
188.8.131.52 Sample A
The sample was treated with 0.5M NaOH solution (450ml) inside shaker water bath at 40ºC
for 10 hours. The insoluble residue was treated with 0.5M NaOH and 3wt% H2O2 solution
(400ml) at 45ºC for 8hours and was finally treated with 2M NaOH solution (400ml) at 55ºC
184.108.40.206 Sample B
The sample was treated with 0.5M NaOH solution (450ml) inside shaker water bath at 40ºC
for 10 hours. The insoluble residue was treated with 0.5M NaOH and 3wt% H2O2 solution
(400ml) at 45ºC for 8hours and finally treated with 2M HCl (400ml) at 70ºC for 2hours in
order to remove mineral traces.
220.127.116.11 Sample C
This sample was treated with 5wt% KOH solution (450ml) inside shaker water bath at 40ºC
for 10hours. The insoluble residue was delignified with 1% NaCl solution (400ml) at pH 3,
and adjusted with 10wt% acetic acid at 70ºC for 1hour. Another treatment with KOH solution
(250ml) under the same conditions as the first step was used. Finally, a 1wt% HCl solution
(300ml) at 80ºC for 2hours was used to remove mineral traces.
572 I.O. Oladele, J.A. Omotoyinbo and J.O.T. Adewara Vol.9, No.6
2.3.3 Control Sample
The untreated sample was used as the control.
2.4 Determination of Chemical Constituents
2.4.1 Determination of Lignin Content by Gravimetric Method
1.5g of the sample was weighed and 72% H2SO4 was added and soaked for 2hours. 8%
H2SO4 was later added and the solution reflux for 4hours. The residue was filtered with
purpling cloth and washes severally with hot water. The crucible to be used was weighed and
the sample was scraped into it. The sample was oven dried at 105ºC for 2hours and was
cooled inside desiccators after which the weight was taken. The sample was later ashed in the
furnace at 550ºC for 3hours after which it was cooled inside the desiccators and finally
weighed. The % Lignin was later calculated as follows;
% Lignin= W2 – W1 X 100
W1=weight of the ash sample + crucible
W2=weight of the oven dried sample +crucible
Ws =initial weight of the dried extractive free sample.
2.4.2 Determination of Cellulose Content
1g of the sample was weighed and place inside a beaker where 25ml of 80% acetic acid, 1ml
of concentrated nitric acid and 4 glass beads was added and reflux for 20minutes on cellulose
refluxing apparatus. The fibre was washed into 50ml centrifuge tube with hot 95% ethanol
and centrifuge at 18000r.m.p for 5minutes. The liquid is decanted, 95% ethanol is added,
stirred and centrifuge for another 5minutes. Liquid is decanted; sample washed with hot 95%
ethanol and filter by suction. Sample is washed three times with hot benzene, two times with
95% ethanol and once with ether. The sample was placed inside a weighed crucible that was
later placed in the oven maintained at 105ºC for 1hour. The crucible was latter cool in
desiccators and weighed. The crucible was placed inside the furnace that was maintained at
550ºC for 4hours; cool in desiccators and weigh for ash weight. The percentage cellulose was
calculated as follows;
%Cellulose= W2 – W1 X 100
W1=weight of crucible + sample after ashing.
W2=weight of crucible + sample after drying
WS=weight of sample
Vol.9, No.6 Investigating the Effect of Chemical Treatment 573
2.4.3 Determination of Hemicelluloses
0.5g of sample were weighted into two different beakers denoted as A and B. 5%KOH was
added to the sample in flask A while 24% KOH was added to the sample in flask B and both
samples were allowed to stand for 2hours. The mixtures were filter with purpling cloth,
washed with additional KOH solution of their respective percentages and the filtrate is
received into two different beakers (A and B). The hemicelluloses are then quantitatively
precipitated by the addition of alcohol (ethanol). The precipitated hemicelluloses were
isolated by centrifuging for 10minutes. The isolated hemicellulose was washed with alcohol
(ethanol) and ether and finally transfers into two different crucibles (A and B). The samples
were dried in oven for 2hours at 105ºC. After this, they were transferred into desiccators and
allowed to cool for 30minutes after which their weights were taken. The samples were also
placed inside the furnace maintained at 550ºC for 3hours after which they were cooled inside
the desiccators and weighed. The weight of the precipitate A was calculated (WA) while the
weight of the precipitate B was also calculated (WB). Hence the percentage hemicelluloses
compositions of the samples were calculated as follows;
%Hemicelluloses (A) = WA X 100
WA =dried weight of hemicelluloses precipitate A
W2=dried weight of the hemicelluloses sample
% Hemicelluloses (B) = WB X 100
WB =dried weight of hemicelluloses precipitate B
W2 =dried weight of the hemicelluloses sample
2.4.4 Determination of the Tensile Properties of the Fibre
The tensile properties were determined from the instron universal tensile testing machine.
This was carried out by fixing the sample on the grips of the machine after which it was
operated automatically. As the extension proceeds, the graph and some readings were
displayed on the computer.
3. RESULTS AND DISCUSSION
3.1 Variation of the Constituents with Chemical Treatments of the Sisal Fiber
The results of the constituents of the different fibres were as shown in table1and Figure1
574 I.O. Oladele, J.A. Omotoyinbo and J.O.T. Adewara Vol.9, No.6
Table1: Constituents of the Sisal Fibres and their pH Values.
Fibre Cel lulose (%) Ash (%) Lignin (%) Hemicellulo ses
Control 42.85 2.34 18.65 25.28 5.86
A 31.40 2.10 20.24 30.04 8.52
B 17.61 1.16 5.87 9.80 3.43
C 15.93 1.02 8.92 11.26 4.69
Figure1: Plots of the Sisal Constituents and PH Values for both Treated and
Untreated Sisal Fibres.
During chemical treatments, constituent like hemicelluloses was hydrolyzed by the action of
alkaline solutions, whereas lignin was removed during additional steps using sodium chloride
or hydrogen peroxide. To improve and achieve an acceptable dispersion level in the solution,
mechanical homogenization with shaker water bath was also used for all samples.
The treatments with the exception of alkaline peroxide (AP), sample A, contributed to the
removal of hemicelluloses and lignin contents as shown in Table1 and Figure 1. The
resistance to extraction with alkaline of the sugars that are the main constituents of
hemicelluloses is due to the association between xyloglucan and cellulose that is very strong.
Xyloglucan probably binds not only to the surface of cellulose microfibrils, but it can also be
entrapped within the microfibrils . Xylans, xyloglucans and glucomannans are all able to
bind onto cellulose fibrils in a manner similar to the interchain bonding of cellulose itself.
Vol.9, No.6 Investigating the Effect of Chemical Treatment 575
 demonstrated that the method with the sodium chlorite was more efficient than that with
hydrogen peroxide to remove lignin.
From the results, it was observed that the lignin and hemicelluloses constituents as well as
their pH values have the same response to the chemical treatments. The results show higher
percentages of lignin and hemicelluloses in sample A that was treated with alkaline peroxide
more than that of the control sample while samples B treated with HCl in addition to the
alkaline peroxide and C treated with HCl in addition to KOH, acetic acid and NaCl have
lower values. However, it was observed that sample B has the least values for both
constituents. This result was in agreement with the results from the above mentioned
Also, the results revealed the response of the cellulose and the ash contents as well as the pH
values of the fibres to the chemical treatments. It was observed that, the percentages of the
constituents as well as their pH values reduce in the same order from Control down to C for
both constituents as shown in Table1 and Figure1.
The bonding nature between the fibre and the matrix depends on the atomic arrangement,
chemical properties of the fibre and the chemical constitution of polymeric matrix. However,
in the natural fibre composite, cellulose is the principal coupling agent in the polymer/fibre
bonding. On the other hand, lignin acts as an obstruction to the coupling agent diffusion,
preventing good adhesion .
3.2.1 Variation of Tensile Properties with Chemical Treatments of the Sisal Fiber
The results of the tensile properties obtained were shown in Figures 2-9.
Figure 2: Plot of Stress against Strain for the Untreated Sample.
576 I.O. Oladele, J.A. Omotoyinbo and J.O.T. Adewara Vol.9, No.6
Figure 3: Plot of Stress against Strain for Treated Sample A (NaOH).
Figure 4: Plot of Stress against Strain for Treated Sample B (HCl).
00.020.040.060.08 0.1 0.12
00.01 0.02 0.03 0.04 0.05 0.06 0.07
Vol.9, No.6 Investigating the Effect of Chemical Treatment 577
Figure 5: Plot of Stress against Strain for Treated Sample C (KOH).
Figure 6: Plot of UTS against Fibres for both Treated and Untreated Samples.
00.02 0.04 0.06 0.080.1
578 I.O. Oladele, J.A. Omotoyinbo and J.O.T. Adewara Vol.9, No.6
Figure 7: Plot of Young’s Modulus against Fibres for both Treated and Untreated
Figure 8: Plot of Extension against Fibres for both Treated and Untreated Samples.
Vol.9, No.6 Investigating the Effect of Chemical Treatment 579
Figure 9: Plot of Energy against Fibres for both Treated and Untreated Samples.
3.2.2 Response of the Fibers to Tensile Stress and UTS
The results revealed the response of the fibres to tensile stress and UTS in Figures 2-6. It was
observed that sample treated with combination of KOH, CH3COOH, NaCl and HCl that was
coded as C-KOH has the highest UTS of 0.96N/mm2 followed by sample treated with
combination of NaOH and H2O2 that was coded as A-NaOH with a value of 0.73 N/mm2.
However the untreated sample has higher UTS of 0.5N/mm2 than sample treated with
combination of NaOH, H2O2 and wash with HCl which was coded as B-HCl, its UTS was 0.3
3.2.3 Young’s Modulus of the Fibres
The results of the Young’s modulus of elasticity of the fibres were shown in Figure 7. The
untreated sample has the best modulus of 23.89 N/mm2 followed by sample A-NaOH with a
close value of 23.089N/mm2 Sample C-KOH was next with a value 17.852 N/mm2. Again,
sample B-HCl has the least value of 13.486 N/mm2. Young’s modulus is the slope of the
stress-strain curve within the range of proportionality before yield. Yield stress is defined as
the stress at which materials experience a major micro structural deformation while the
breaking stress is the stress at which materials failed. At the yield stress, a large amount of
deformation takes place at constant stress .
3.2.4 Response of the Fibers to Extension and Tensile Strain.
The response of fibers to the extension at yield and at break was shown in Figure 8. The
results showed that sample C-KOH has the best extension of 7.5048mm before it yield
followed by sample A-NaOH with a value of 6.1597mm. Yielding Point is defined as the
point at which materials experience a major deformation at the microstructural level. It is a
point where additional strain occurs without any increase in stress load on the material,
.However, the extension at break revealed that the untreated sample that was refer to as
580 I.O. Oladele, J.A. Omotoyinbo and J.O.T. Adewara Vol.9, No.6
the control has the highest value of extension (20.4089mm) before breaking followed by
sample A-NaOH with a value of 14.0959mm. This shows that these samples can withstand
the load generating the stress that will cause the materials to fail for longer period after
yielding than sample C-KOH with the highest extension before yielding and UTS
respectively. The breaking load is the load that brings about material failure, .
3.2.5 Response of the Fibers to Energy
Figure 9 shows the response of the materials to the absorbed energy before yield and failure.
The energy parameter denotes the resilience of the materials. From the results, it was
observed that sample C-KOH posses the highest energy of 0.0306J before yielding followed
by sample A-NaOH which has a value of 0.0182J. However at break, it was observed that
sample A-NaOH posses the highest value of 0.0539J while sample C-KOH followed with a
value of 0.0388J.
The results of the research have shown that;
• Chemical treatment has been found to improve the tensile properties of the sisal fiber.
• Chemical treatment has been found to be effective in this respect by removing the
deleterious constituents such as lignin, hemicelluloses and ashes which affect the
bonding strength between the sisal fiber and the polyester matrix.
• The chemicals applied in this work are combinations of NaOH, H2O2 KOH,
CH3COOH, NaCl and HCl as follows:
Combination I: NaOH and H2O2 with NaOH wash
Combination II: NaOH, H2O2 with HCl wash
Combination III: KOH, CH3COOH, NaCl with HCl wash
• Samples treated with Combination III gave the best tensile strength properties
followed by the samples treated with Combination I.
• However, the untreated fiber produced the best extension before fracture.
I wish to acknowledge the following organisations for their support. They are Regional
Initiative in Science Education (RISE), Science Initiative Group (SIG) and African Materials
Science and Engineering Network (AMSEN).
Vol.9, No.6 Investigating the Effect of Chemical Treatment 581
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