Production and Characterization of Kenyan Sisal
Josphat Igadwa Mwasiagi,
Zheng Fan Li
Sisal is one of the fibers that have lately recorded a rapid increase in demand. This can be attributed to an increasing awareness of the need to use eco-friendly materials. An increase in demand invariably leads to improved commodity prices, therefore making sisal production a very profitable venture. Kenya is among the largest producers of sisal. However, 80% of the sisal grown in Kenya is exported as raw materials. This is a major concern and therefore, needs to be addressed urgently. According to vision 2030, Kenya lays emphasize on the value addition of Kenyan agricultural products. This implies that agricultural products like sisal should be processed and then exported as high valued products. The value addition of Kenyan sisal can be enhanced if research into the production of sisal is done. Fiber characterization will also equip scientists and investors with the much needed information about the nature and potential of the Kenyan sisal. The aim of this research work concentrated on the production and characterization of the Kenyan sisal. The results of this research work show that Kenyan sisal production and yield has been declining in the last four decades. This is the trend in the other sisal producing nations, except Brazil whose production has been rising and China whose yield has been rising. The characterization of the Kenyan sisal indicated that the Kenyan sisal has a higher percentage of lignin and hemicellulose. The tensile strength of the Kenyan sisal was comparable to the lower spectrum of sisal tensile strength for sisal from other regions (countries).
March 13, 2012; Accepted: April 14, 2012;
Published: July 09, 2012
Sisal is a natural vegetable fiber which can be obtained from the leaves of
Agave (Agave sisalana) plant and is considered as an economic fibers
in several countries which include Kenya, Tanzania, China and Brazil. In Kenya
sisal is the sixth most important cash crop coming after tea, coffee, sugar,
pyrethrum and cotton. The sisal growing and processing industry in Kenya can
be traced back to 1914, when the first sisal growing firm was established in
Thika. The industry grew by leaps and bounds in the first 50 years characterized
by a rapid increase in acreage and quantity of sisal exported. The increase
in sisal production lead to the establishment of a spinning factory in Juja
and a sisal research station in Thika. The invention of cheaper synthetic fibers
in the 1940s, can be marked as a major drawback for the world sisal production,
since, it lead to reduced sisal demand. In Kenya the industry enjoyed some government
protection mainly in the 1960s and 1970s (Odhiambo
et al., 2004). The government subsidies were however, removed in
the 1980s dealing a major blow to the once thriving Kenyan sisal industry.
This phenomenon was not limited to Kenya. Other major sisal producing countries
such as Tanzania experienced a similar decline in sisal production, characterized
by a big decline in acreage and fiber yields. This was attributed to decreasing
fiber prices and poor crop husbandry (Hartemink and Wienk,
1995; Shamtu, 2000). The introduction of new applications
for sisal fibers coupled with the push for eco-friendly fibers has however reversed
the aforementioned trend.
Traditionally Sisal fibers can be classified into a variety of grades which
include; the lower, medium and higher fibers, which are used for paper, rope
and carpet making, respectively. Sisal has however found new applications in
a variety of industries which include; the medical field (Thatoi
et al., 2008), the automotive and Building industry (Salazar
et al., 2011; Filho et al., 2009).
Apart from the sisal fiber which constitutes 4% of the sisal leaf, the sisal
industry generates a lot of biomass commonly referred to as sisal waste. The
biomass obtained during sisal decortication has for a long time been a nuisance
to the sisal factories. While the factories were struggling to cope with the
sisal waste another event seemingly unrelated came to the rescue of the sisal
factories. The high rate of depilation of natural resources has compelled man
to optimize the use of resources. Terms like eco-friendly or green
processes are now common words in many government and industrial circles. While
Kotchoni and Gachomo (2008), paints a picture of bio-fuel
as a promising concept, Ramachandra (2008) assumed that
green fuel is here with us and he goes ahead to design a model which can be
used to assess the need for biogas for a given region. Green energy is here
to stay, since the fossil fuels are getting depilated at a high rate. In Tanzania
sisal biomass, which was a nuisance 20 years ago is being used to generate electricity
hence, improving the profitability of the sisal industry. It is hoped that other
sisal producing countries like Kenya will soon implement such eco-friendly activities.
Sisal biomass can also be used to manufacture bio-fertilizers, since crop residue
have proven potential for the manufacture of fertilizers (Taiwo,
2011). The Kenyan government is carrying out research to use sisal waste
for bio-energy generation, livestock feed as well as organic fertilizer. This
enhanced interest and investment in research and development will improve production
and hopefully the profitability of the sisal industry.
The increasing use of sisal in a variety of industries demands a thorough understanding
of the properties of the fiber. According to De Andrade
Silva and Filho (2007) the sisal plant leaf is a composite structure that
is made up of three types of fibers: structural, arch and xylem fibers. Every
sisal fiber contains numerous elongated individual fibers (fiber-cells). Each
individual fiber-cell is made up of four main parts, namely the primary wall,
the thick secondary wall, the tertiary wall and the lumen. Sisal leaves can
be harvested from the age of 2 years. Harvesting can continue for 9 to 12 more
years, producing over 200 leaves in its lifespan. This research concentrated
on the study of the characteristics of the sisal fiber. Previous works indicated
that the mechanical and chemical characteristics of sisal may vary depending
on growing and processing conditions. The mechanical properties of the fiber
have for example been shown to be dependent on the age of the fiber (Chand
and Hashmi, 1993). A regression model designed by Mukherjee
and Satyanarayana (1996) to study sisal fiber revealed that the structure
and properties of sisal are affected by cellulose content, microfibrillar angle
and other structural parameters which include cell dimensions and defects. Therefore,
characterization of the Kenyan sisal will be important, since it will shed light
on the quality of the sisal and hence encourage its appropriate application.
The use of sisal in a wide range of application has lead to an increase in
sisal demand. This has been accompanied by an improvement of the prices of sisal,
hence making sisal production a very profitable venture. The Kenyan government
through the Kenya sisal board has embarked on a program to increase the acreage
of sisal to meet the rising demand. There is however a major concern for economist
in Kenyan due to the fact that over 80% of the sisal grown in Kenya is exported
as raw fiber. According to the Kenyan Vision 2030, which lays emphasize on the
value addition of Kenyan agricultural products, the value addition of Kenyan
sisal should be considered. While the Kenyan vision 2030 may be considered as
utopian like the Nigerian Vision 20:2020 which promises a lot and is likely
to deliver little (Eneh, 2011), public university which
includes Moi University are duty bound to demonstrate their commitment to the
fulfillment of the vision. It was in this spirit that a research on the study
of the Kenyan sisal was envisaged. The whole process of value addition of the
Kenyan sisal will benefit a great deal if the Kenyan sisal is characterized.
This will enable the Kenyan farmer to bargain for a competitive price for his
sisal fiber. The characterization of the Kenyan sisal will also enable researchers
to optimize its usage in various industrial applications. This study reported
the production of sisal in Kenya in comparison with other major sisal producing
nation (Brazil, Tanzania). China has also been considered due to the high sisal
yields recorded in the last decade. The other part of the paper concentrates
on the characterization of the Kenyan sisal fiber.
MATERIALS AND METHODS
Sisal production and yield: The production of sisal in Kenya, Tanzania,
Brazil and China were studied from 1961 to 2009 from the commodity data website
which records the production and export of products worldwide. Sisal fiber production
and yield were considered.
Characterization of Kenyan sisal fiber: Sisal fiber samples were collected from Kenyan sisal factories and characterized. The fiber characteristics considered included the physical, mechanical and chemical properties of the fiber.
Chemical ingredients of Kenyan sisal: The chemical composition of the Kenyan sisal fiber was investigated using Chinese standards for the determination of the chemical ingredients of bast fibers (GB 5889-1986, P. R. of China).
Tensile properties: The mechanical properties were measured using a single fiber tensile machine, which had a speed of 5 mm min-1 and a gauge length of 10 cm.
Cross-sectional and longitudinal morphology: In order to evaluate the surface morphology of the fiber the sisal fibers were investigated using a Scanning Electron Microscopy (SEM), Hitachi TM1000. The excitation energy for the general procedure was 15 Kev. The fiber samples were sputtered with gold before examination to ensure good conductivity. The cross-sectional and longitudinal morphology were investigated.
Chemical groups in sisal: The chemical groups in sisal fiber were investigated using Fourier transform infrared spectrophotometry (FT-IR) Nicolet 8700. FT-IR spectra of each sample studied using a range of 4000 to 400 cm-1. Spectra outputs were recorded in the absorbance mode as a function of wave number.
Crystallinity of sisal: The sisal fiber crystalline index was obtained
from an X-ray Diffraction (XRD) patterns of the sisal fiber obtained from a
D/MAX-2550PC X-ray detector diffraction system. The machine was set at voltage
of 18 kW, current of 30 mA and scan rate of 2° min-1.
RESULTS AND DISCUSSION
The trend of sisal production and yield: The production and yield of sisal in Kenya and other selected countries (Brazil, Tanzania and China) is given in Fig. 1 and 2. Corresponding values for three other countries (Brazil, Tanzania and China) have been included for comparison purposes. The figures indicated that the production of sisal in Kenya exhibited a declining trend in the last four decade. The production of sisal in Tanzania has shown a drastic decrease while Brazil has experienced an erratic production howbeit with marginal increase.
The Kenyan agricultural sector enjoyed government protection up to 1982, when
agricultural subsidies were removed. During the years of government protection,
sisal production was robust, with higher production level being realized in
1970. The major decline in production recorded in the late 1970s can be
attributed to high level of corruption in government departments. When the government
liberalized the agricultural sector, the small scale farmers were unable to
grow sisal, due to low sisal prices and high cost of inputs. In 2008, for example
eight large scale companies produced over 90% of the Kenyan sisal (Kiome,
2010). The production from small scale farmers was a merge 420 tons. The
Kenyan government needs to look into ways and means of encouraging the small
scale sisal farmers to boast sisal production. In Brazil, the bulk of the sisal
is produced by the small scale farmers. It is a high time, Kenya tried to study
the Brazilian sisal growing industry with an aim of encouraging small scale
sisal farmers. Going by reported findings available in the public domain, the
decline in sisal production in Tanzania was caused by poor husbandry, propagation
of the wrong varieties and a decrease in the length of sisal leaves (Hartemink
and Wienk, 1995). Similar factors could also be responsible for the decrease
of sisal yield in Kenya, since the two are neighboring countries. The phenomena
increase in sisal yield in China is hereby noted and should be considered a
research subject by the Kenyan sisal industry.
The characterization of the sisal fiber
Cross-sectional and longitudinal morphology of sisal: The morphology
of the Kenyan sisal fiber for the longitudinal and cross-section views obtained
using the SEM are given in Fig. 3. These SEM images are similar
to those obtained by Mukherjee and Satyanarayana (1984)
for Indian sisal and Martins et al. (2004) for
Brazilian sisal. The surface irregularities appearing on the surface of the
fiber will lead to variations of sisal fiber properties.
|| Sisal production from 1961 to 2009
|| Sisal yield from 1961 to 2009
||The SEM of the Kenyan sisal fiber, (a) Longitudinal view and
(b) Cross sectional view
The cross-section view attest to the fact that sisal fiber is made up of several
fiber cells (Filho et al., 2009). These fiber
cells are held together by resin like material called lignin.
The chemical composition of Kenyan sisal: As stated earlier the chemical
contents of sisal fiber were determined using Chinese standards for bast fibers.
The composition of the Kenyan sisal fiber was 63-69% cellulose, 10-13% lignin,
18% hemicellulose, 0.8-1.6% pectin, 1.5% wax and 0.6-1% water soluble matter.
As stated earlier the chemical contents of a bast fiber has been proven to affect
the mechanical properties of the fiber (Mukherjee and Satyanarayana,
1984). Sisal fiber like other bast fibers is considered to be a natural
composite material where cellulose is the main weight bearing component and
cellulose and lignin are the matrix (the joining gum). Typically a fiber cell
will consist of fibrillae in a matrix of lignin (De Andrade
Silva and Filho, 2007). The fibrillae is also another composite consisting
of cellulose in a matrix of hemicelluloses. As shown in Table
1 and 2 different researchers have reported varying values.
The difference in the results could be attributed to the fact that sisal is
a natural fiber and its properties are bound to be affected by the growing conditions.
Referring to Table 2, which is a summary of the chemical contents
of sisal as reported by several researchers, the cellulosic contents of the
Kenyan sisal can be adjudged as average.
|| Ingredients of sisal
|| Mechanical characteristics of sisal
Apart from the reports of Favaro et al. (2010),
Rowell et al. (2000) and Salazar
et al. (2011), the cellulose contents for the Kenyan sisal can be
adjudged to be low. The lower percentage of cellulose, accompanied by higher
percentage of hemicellulose may lead to some changes in the physical and mechanical
characteristics of the fiber. Hemicellulose has lower degree of polymerization,
is attacked by both acids and alkalis, while cellulose has very high resistance
to alkali attacks, but is attacked by acids. Lignin binds the cellulose and
hemicellulose together. Levels of 4-8% should be optimum. Higher percentages
of lignin will have adverse effect on the mechanical strength.
Chemical groups in Kenyan sisal: The FT-IR spectroscopy was used to
study the functional groups present in the sisal fiber. Fig. 4
gives the graph of the absorbency. The peaks at 3340.8 and 1035 cm-1
could be attributed to the O-H stretching and bending groups, respectively.
There are a series of peaks in the 1720 to 1610 cm-1 range which
could be attributed to the carbonyl stretching (C = O) for acetyl groups in
hemicelluloses and for aldehydic groups present in lignin (Favaro
et al., 2010; Abdul Khalil et al., 2010)
which is one of the ingredients found in bast fibers. The presence of an aldehyde
could be confirmed by a peak that occurs at 2840 cm-1. The vibration
peak at 1244.4 cm-1 could be attributed to C-O stretching vibrations.
Other minor peaks at 2922.9 and 1426.5 cm-1, could be attributed
to C-H2 stretching and bending vibrations, respectively.
Crystallinity of sisal: The XRD diffraction curve for the Kenyan sisal
fiber is given in Fig. 5. There are two main peaks; one sharp
peak at 22.1° and a broad peak at around 15°. Other minors peaks
were noticed at 34.8 and 44.5°. The Crystallinity of the sisal fiber was
51.15%. These results are comparable to the values reported by Yi
et al. (2010) for Chinese sisal, albeit on the lower side. As noted
earlier the lower percentage of cellulose, coupled with a higher percentage
of hemicellulose and lignin could have lead to lower crystallinity.
|| The FT-IR for Kenyan sisal fiber
Tensile properties: The tensile strength for the Kenyan sisal was 450
MPA (410 -570) while the elongation was 4.76% (3.9 to 5.17%). A summary of the
mechanical properties of sisal given in Table 2, indicated
that the tensile properties of the Kenyan sisal was comparative lower than those
reported by other researchers. Considering reports from Joseph
et al. (1999), Mohanty et al. (2000)
and Taj et al. (2007), higher cellulose contents
accompanied with lower lignin contents gives higher tensile strength. This could
be attributed to the fact that cellulose is the main strength bearing element
in the sisal fiber structure and lignin and hemicellulose are the matrix member
of the component.
The lower tensile strength reported for the Kenyan sisal could therefore be attributed to the lower percentage of cellulose coupled with higher percentages of lignin.
A study of the production and characterization of the Kenyan sisal was undertaken. According to the data obtained, it can be concluded that Kenyan sisal production and yield has been declining in the last four decades. This is the trend in the other sisal producing nations, except Brazil whose production has been rising and China whose yield has been increasing. The Characterization of the Kenyan sisal indicated that the Kenyan sisal has a higher percentage of lignin and hemicellulose. The tensile strength of the Kenyan sisal was comparable to the lower spectrum of sisal tensile strength for sisal from other regions (countries).
We wish to thank the Chinese government which supported the project through the Sino-Africa 20+20 program and the China Scholarship Council.
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