International Journal of Mechanical Engineering and Technology (IJMET)
Volume 10, Issue 03, March 2019, pp. 473-479. Article ID: IJMET_10_03_049
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication
Scopus Indexed
Edith Egbimhanlu Alagbe
Department of Chemical Engineering, Covenant University, Ota. Ogun State, Nigeria
Ezekiel Sunday Bassey
Department of Chemical, Fibre and Environment Technology, Federal Institute of Industrial
Research, Oshodi. Lagos State. Nigeria
Olusegun Adegboyega Alagbe
Lagos State Ministry of Physical Planning and Urban Development, Ikeja, Lagos State.
Vincent Enontiemonria Efeovbokhan
Department of Chemical Engineering, Covenant University, Ota. Ogun State, Nigeria
Daniel Temitayo Oyekunle
Department of Chemical Engineering, Covenant University, Ota. Ogun State, Nigeria
Kamilu F. Oyedeko
Department of Chemical and Polymer Engineering, Lagos State University, Epe, Lagos State.
In this study, the chemical compositions of waste okra stalks and rice husks were
investigated and their use, evaluated as raw materials for the Kraft pulping process.
Pulp yield, Consistency and 1% NaOH solubility were determined. Both raw materials
were dried, and the chemical compositions obtained prior to cooking/digestion in a 15
L autoclave. While properties such as moisture content, 1% NaOH solubility,
extractives and hot water solubility seem to favour raw rice husk, the pulp yield was
very low (25.7%) as against the pulp yield from okra (41.2%). The high ash content
and Silicates/Silica in rice husk (6.1 – 45.82% and 20480ppm respectively) will pose
problems in the liquor recovery stage in the process. Therefore, the okra stalk is a
better raw material for pulp and paper making than the rice husk. From this study,
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Comparative Evaluation of The Effect of Chemical Composition of Waste Okra Stalk And Rice
Husk On Pulp Yield
waste okra stalk is found to possess some economic value and can no longer be left to
become a nuisance to the environment.
Keywords: NaOH solubility, pulp yield, pulp consistency, okra stalk, rice husk.
Cite this Article: Edith Egbimhanlu Alagbe, Ezekiel Sunday Bassey, Olusegun
Adegboyega Alagbe, Vincent Enontiemonria Efeovbokhan, Daniel Temitayo
Oyekunle and Kamilu F. Oyedeko, Comparative Evaluation of The Effect of Chemical
Composition of Waste Okra Stalk and Rice Husk on Pulp Yield, International Journal
of Mechanical Engineering and Technology, 10(3), 2019, pp. 473-479.
Paper is made up of an array of pulp fibres obtained from wood or non-wood sources, from
which lignin (the binder) and other non-cellulose parts have been separated by cooking at
high temperature. Pulp and paper manufacture began when non-wood sources like papyrus
was used to make paper on which early civilization inscribed the events and commands of
their time. Later, wood sources became attractive because they gave stronger and whiter fibres
since they can withstand the harshness of the chemicals used in the cooking (separation of the
lignin from the cellulose). In the late 1990s, sugar cane bagasse, straw and bamboo became
the choice of non-wood raw material for pulp and paper production [1; 2] as it became more
difficult to get wood sources.
The use of paper is so versatile that it can be said that no human race can do without it. It
finds usefulness as writing materials, packaging materials and ceiling boards, to mention but a
few. Therefore, it is expected that the consumption of paper will continually be on the
increase [3], with increase in population, irrespective of the adoption of a paper-less
operation, especially in the offices. With recent concerns on the green environment,
hardwoods have suddenly become ‘endangered’. Therefore, it is imperative to look inwards
and fall back on the readily available annual crops whose stalks are usually made of long
cellulose fibres. Although, Okra stalks are short, they contain long fibre bast, close to that of
jute plant [4].
In Nigeria, okra is a commonly consumed vegetable by all tribes. It is an annual crop that
is cultivated between the months of March and July - which happens to be within the rainy
season. At maturity, the fruits (okra pods) are harvested and the stalks with the leaves are
disposed of in the farmlands and allowed to rot. Usually, farmers prefer to dump the wastes
outside their farmlands – to create space for the next crop planting which follows almost
immediately after. This destroys the aesthetics and beauty of the environment and portends a
befitting breeding ground for disease-causing organisms to fester [5] and endanger the lives of
plants and animals (6). In addition, the decayed matter finds themselves in the underground
water as leachates, which contaminates the water and renders it unfit for consumption. During
the putrefaction of the waste, greenhouse gases, typically, CO2, NO2 and CH4, are released
into the atmosphere which contributes to global warming [7, 8].
Nigeria is currently in a drive to produce rice for her growing population and minimise her
importation. While we rejoice that we can now produce rice for ourselves, we must also be
concerned with the growing waste generated from rice cultivation.
Katri Saijonkari-Pahkala [9] opined that suitable replacement for wood sources in the
production of fine printing paper is the use of herbaceous field crops, especially in the nonavailability of wood sources as raw materials. To this effect, this research is poised to evaluate
the possibility of using the waste from the okra and rice farmlands for pulp and paper
[email protected]
Edith Egbimhanlu Alagbe, Ezekiel Sunday Bassey, Olusegun Adegboyega Alagbe, Vincent
Enontiemonria Efeovbokhan, Daniel Temitayo Oyekunle and Kamilu F. Oyedeko
manufacture by evaluating and comparing the chemical composition of the waste okra stalk
and rice husk. Hence, converting these farm wastes to wealth and consequently, providing an
agricultural system that is sustainable in Nigeria. Inevitably, this conversion to pulp and
paper will also help ameliorate the waste disposal problem [10]. The obtained fibre properties
would be used to determine its usefulness in paper making and for what purpose the paper
would be most suitable for.
Harvested mature waste okra stalk and rice husks were obtained from farms in Ota, Ogun
State, Nigeria.
2.1. Raw materials preparation and pulping
The samples of okra stem and rice husk were dried at room temperature for 3 days. Part of the
samples were further dried in an oven at a temperature of 70 0C for 1 hour and hammer-milled
into powder, according to prescribed standard preparation procedure [11], for the purpose of
determining the desired properties of the raw sample before cooking. The part of the air-dried
sample was then cut into pieces of 0.5 – 1cm in length, using knives.
The Kraft cooking process was used with a raw sample: liquor ratio of 1:5. 200g of
chipped raw materials was charged into a well labelled conical flask. 7% active alkali (NaOH
and Na2S), calculated based on the moisture content of the raw samples was added to the
content of the conical flask. Cooking was affected in an autoclave at a temperature of 125 0C
and a pressure of 0.15 Pa for 45 mins (including the time to achieve the desired temperature)
in addition to a 20 minutes gas down period which was allowed before removing and
washing. The pulp was disintegrated and washed with de-ionized water on a standard size
1mm x 1mm netted sieve and defiberized with a blender.
2.2. Parameter Determination
Moisture content: The TAPPI Standard Method T208 om-94 [11] was followed in preparing
the samples for moisture content determination. The moisture content was then carried out
digitally using a moisture analyser domiciled in the Federal Institute of Industrial Research,
Oshodi. Lagos, Nigeria.
Ash content: Empty porcelain was cleaned and ignited in a furnace at a temperature of 525
C for 40 minutes. It was then cooled in a desiccator and weighed. After weighing, 3g of the
raw sample was put in the porcelain, placed in the oven and gradually heated to 525 0C and
left in the furnace for complete carbonization. It was thereafter cooled in a desiccator and
weighed. The ash content was calculated as:
Where A = weight of ash in the porcelain after carbonization, g
B = initial weight of sample, g = 3g
1. Lignin –The acid insoluble lignin was determined using TAPPI standard methods
T 222 om-02 [12]
2. 1% NaOH solubility:
3. About 1 gram of accurately weighed sample was placed in 100ml flask and 1%
NaoH solution, based on the moisture content of the sample, was added .The flask
was placed in a boiling water bath with intermittent shaking for 1hour.Thereafter,
the sample was filtered by suction on a tarred frithed- glass crucible, washed
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Comparative Evaluation of The Effect of Chemical Composition of Waste Okra Stalk And Rice
Husk On Pulp Yield
thoroughly with hot water and the crucible and contents were dried at 105°C for 10
minutes, cooled and weighed.
Where A = intial weight of sample, g
B = final sample weight, g
1. Hot water solubility and cold-water solubility were determined using the TAPPI
Standard Method, T207 cm-99 [13]
2. Silica/Silicate: 100 ml of concentrated HNO3 was added to 10 g of sample in a
beaker and warmed until a viscous solution resulted. The solution was the
evaporated to about 40 ml, cooled and 20 ml of concentrated H2SO4 was then
added. This was heated until white fumes of SO3 evolved. 20 ml of concentrated
HNO3 was quickly added. It was cooled and 20 ml of concentrated H2SO4 was readded and heated again to emit more white fumes until no fumes were evolved
again. The solution was then cooled to room temperature and 250 ml of distilled
water was carefully added, using a squirt bottle. It was boiled for a few minutes,
filtered using a filter paper, washed with distilled water, dried and weighed. The
silica/Silicate in solution is calculated from:
Where: X = Silicates and silica as SiO2, ppm
a = weight of insoluble residue, mg
m = weight of oven dry pulp, g
Where: a = weight of insoluble residue, mg
m = weight of oven-dry pulp, g
x = Silicates and Silica as SiO2, ppm
1. Yield: Standard procedure was employed in determining the sample yield and
calculated from:
Where: Wi = initial weight of sample (before pulping)
Wf = final weight of sample (after pulping)
1. Consistency of pulp suspension: Sampling cup was used to withdraw 5 portions of
100 ml each and then the entire content was deposited in a 1000 ml beaker. The
sample weight was then determined using a digital weigh balance.
2. Moisture filter paper was placed, and suction was applied to the flask and filter.
For cloudy filtrate, it should be re-filtered until it is clear. The filter paper was then
removed and placed in a drier until steaming stopped. The residue was weighed,
and successive readings were carried out until constant weight was attained. The
percent consistency of the specimen was calculated from:
Where, w = weight of the moisture-free pad and filter paper, grams
f = weight of the moisture-free filter paper, grams
g = net weight of the original specimen in the 1000 ml Beaker, grams
[email protected]
Edith Egbimhanlu Alagbe, Ezekiel Sunday Bassey, Olusegun Adegboyega Alagbe, Vincent
Enontiemonria Efeovbokhan, Daniel Temitayo Oyekunle and Kamilu F. Oyedeko
3.1. Chemical composition of raw samples of okra and rice husk
Table 1 Chemical composition of raw samples
Moisture content, %
Ash content, %
Extractives, %
Lignin, %
1% NaOH solubility, %
Hot water solubility, %
Cold water solubility, %
None detected
3.2. Chemical composition:
Results from Table (1) show lower moisture content for the rice husk and this lower moisture
content of the rice husk is expected to favour a higher pulp yield than the okra stalk because
more solid content is presumed to be present in the rice husk.
Low ash contents are desirable in the pulping process, as high as contents are problematic
in the chemical recovery steps. Despite appearing low in value compared with other measured
properties (from Table 1), neither of the raw materials (okra stalk and rice husk) fairs well
when compared to the ash contents of okra from Bangladesh [4], rice straw and mature aspen
[14, 15].
Higher extractives value in the raw material for pulp and paper making predispose the
paper from the process to be stained by the extracts. Therefore, relatively whiter pulp is
expected from the rice husk when the results in Table (1) are considered..
The 1% NaOH solubility is an indication of the ease with which the cellulose can be
separated out from the raw material using NaOH. Pre-treatment using 1% NaOH helps to
reduce the fines produced during pulping and gives better drainage resistance [16]. Higher
values are expected to give better pulp yield. It is therefore, expected that the okra stalk
(54.1%) will give better pulp yield than either the rice husk used (14.3%) or H. cannabinus
with a 1% NaOH value of 34.2% [17].
For hot water pre-treatment prior to the Kraft pulping process, the rice husk with a hot
water solubility value of 17.36% (Table 1) is also expected to require fewer cooking
chemicals than the okra stalk and also, most likely, give a better pulp yield.
The presence of silica/Silicates, no matter how small it is in quantity, in pulping raw
material, poses a threat on the liquor recovery of the process. Silica was only detected in the
rice husk and its content was found to be higher than that of rapeseed [18].
3.3. Pulp characteristics
Table 2 Results obtained from the pulp analysis
Yield, %
Consistency, %
1% NaOH solubility, %
[email protected]
Comparative Evaluation of The Effect of Chemical Composition of Waste Okra Stalk And Rice
Husk On Pulp Yield
Pulp yield, consistency and 1% NaOH solubility were used to evaluate the pulp quality, in
this work. Table 2 shows a higher yield for okra (41.2%) than rice husk (25.7%). This may be
attributed to the better ease of separating the cellulose from the lignin as indicated by a higher
1% NaOH solubility (54.1%) of the raw okra sample.
Unfortunately, the paper sheets from the okra stem may easily be degraded, as suggested
by the higher 1% NaOH solubility of the pulp at 17.5% when compared to 9.31% for the rice
From the results obtained in this work, the okra stalk is a better pulp and paper raw material
than the rice husk. In conclusion, the chemical compositions of the raw materials seem to
have a visible impact on the pulp yield. The part of the rice plant used may be a determining
factor in its performance as a pulp and paper raw material because the chemical composition
of each plant part is different from one other.
Also, soil type and planting season/condition could be responsible for the variations of
some properties of okra stalk when compared to previous works done in other countries.
Waste okra stalk is a better alternative raw material for the pulp and paper industry than
rice husk. For further work, a blend of the pulps from the two raw material sources may be
considered and the paper properties compared with paper from 100% of either pulp.
The authors would like to thank the management of Covenant University, Ota, Ogun State,
Nigeria and the Federal Institute of Industrial Research, Oshodi, Lagos State, for their
support, in creating an enabling environment for this research.
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