Structural characterization of coconut tree leaf sheath fiber reinforcement

Abstract

The coconut palm tree leaf sheath fibers were analyzed by FTIR spectral analysis, Chemical, X-ray and thermo gravimetric methods
to assess their suitability as reinforcements in the preparation of green composites. The morphology of the untreated and
alkali treated fibers was studied by scanning electron microscopic method. The FTIR and chemical analyses indicated lowering
of hemi-cellulose content by alkali treatment of the fibers. The X-ray diffraction revealed an increase in crystallinity of
the fibers on alkali treatment. The thermal stability of the fibers was found to increase slightly by alkali treatment. The
tensile properties of these fibers increased on alkali treatment. The mechanical and other physical properties indicated that
these fibers were suitable as reinforcements for making the green composites.

Keywordscoconut leaf sheath fibers-chemical analysis-crystallinity-mechanical properties-scanning electron microscopy

Full text

Journal of Forestry Research (2010) 21(1): 53−58
DOI 10.1007/s11676-010-0008-0
Structural characterization of coconut tree leaf sheath fiber reinforce-
ment
Obi Reddy K. • Sivamohan Reddy G. • Uma Maheswari C. • Varada Rajulu A. • Madhusudhana Rao K.
Received: 2009-06-15; Accepted: 2009-09-29
© Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2010
Abstract: The coconut palm tree leaf sheath fibers were analyzed by
FTIR spectral analysis, Chemical, X-ray and thermo gravimetric methods
to assess their suitability as reinforcements in the preparation of green
composites. The morphology of the untreated and alkali treated fibers
was studied by scanning electron microscopic method. The FTIR and
chemical analyses indicated lowering of hemi-cellulose content by alkali
treatment of the fibers. The X-ray diffraction revealed an increase in
crystallinity of the fibers on alkali treatment. The thermal stability of the
fibers was found to increase slightly by alkali treatment. The tensile
properties of these fibers increased on alkali treatment. The mechanical
and other physical properties indicated that these fibers were suitable as
reinforcements for making the green composites.
Keywords: coconut leaf sheath fibers; chemical analysis; crystallinity;
mechanical properties; scanning electron microscopy
Introduction 
Since the last decade of the 20th century, the usage of natural
products (wood, fibers and agro waste) as reinforcements in
composites has increased dramatically. Environmental concern is
Foundation project: This work was supported by University Grants Com-
mission, India, Major Research Project (No: 33-397/ 2007 (SRF)).
The online version is available at http://www.springerlink.com
Obi Reddy K.• Sivamohan Reddy G. • Uma Maheswari C.•
Varada Rajulu A. ( )
Department of Polymer Science and Technology, Sri Krishnadevaraya
University, Anantapur 515 055, India. Email: avaradarajulu@gmail.com
Madhusudhana Rao K
Ion Exchange Limited, Hyderabad 502319, India
Obi Reddy K.
Email: obireddyk80@gmail.com
Responsible editor: Hu Yanbo
one driving force that led to the consideration of biodegradable
ligno cellulose fibers for this purpose (Mohanty et al. 2000).
Natural fibers have some advantages over the man-made fibers,
including low cost, lightweight, renewable character, high spe-
cific strength and modulus, and availability in a variety of forms
throughout the world (Mohanty et al. 2000; Rajulu et al. 2002;
Maheswari et al. 2008). The reactive surface and the possibility
to generate energy, without residue, after burning at the end of
their life-cycle, motivate their association with organic polymers
in the preparation of green composites. Hence, many efforts are
being made to make natural fiber reinforcement thermoplastic
and thermosetting composites (Taha and Ziegmann 2006; Li et al.
2004; Teramoto et al. 2004; Sydenstricker et al. 2003; Mohanty
and Nayak 2006; Bledzki et al. 1996; Rajulu et al. 2007).
Coconut tree is native to coastal areas of Southeast Asia (Ma-
laysia, Indonesia, and Philippines), tropical Pacific islands (Me-
lanesia, Polynesia, and Micronesia) and westward to coastal
India, Sri Lanka, East Africa, and tropical islands (e.g., Sey-
chelles, Andaman, Mauritius) in the Indian Ocean. Many fibers
are available in different parts of the coconut tree (Satyanarayana
et al. 1982). The sheath is made up of an inner mat which is
sandwiched between two layers of coarse fibers. Only prelimi-
nary studies of coconut leaf sheath fibers were reported in the
literature (Satyanarayana et al. 1982). Though the fibers from
many parts of the coconut trees are put to use, the sheath fibers
are left as huge waste. In the present work, we separated the
coarse fibers from the outer layers and the fine fibers from the
inner mat to study their properties. The effect of alkali treatment
on the properties of these fibers was studied using chemical,
FTIR, WAXRD and TG analyses. Their tensile properties and
morphology were also studied to assess their suitability as rein-
forcements.
Materials and methods
Extracted coconut tree leaf sheath fibers, sodium hydroxide pel-
lets (Merk, India), benzene, sodium chlorite, acetic acid, sodium
bisulphate and ethanol (S.d.fine-Chemicals, India) were used
RESEARCH PAPER

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54
as received.
Extraction of the fibers from the trees
The Coconut Palm (Cocos nucifera) is a member of palm family
(Arecaceae ). Coconut leaf sheath fibers occur in mat form. The
leaf sheaths collected from the trees were dipped in water for one
week, thoroughly washed with tap water followed by distilled
water, and dried in the sun for a week. Cleaned leaf sheath was
separated to inner sheath mat and the outer layer fibers. The fi-
bers of the inner mat and outer layers were separately kept in hot
air oven for 24 h at 105−110ºC to remove the moisture. Some of
these fibers were treated with 5% aqueous sodium hydroxide
(NaOH) solution for one hour at room temperature, maintaining
a liquor ratio of 25:1 to remove the hemicellulose and other
greasy materials. These fibers were washed with water repeat-
edly and treated with dilute acetic acid to neutralise them. Finally
the fibers were washed with distilled water before drying in hot
air oven for a period of 24 h.
Morphology
The scanning electron micrographs of the surface of the fibers
were recorded on a JEOL JSM 820 microscope. The micrographs
of the cross section of the fibers were also recorded. These sam-
ples were gold coated before recording the micrographs.
FTIR spectral analysis
The two types of the fibers were cryogenically cooled and pow-
dered separately. These powders were diluted to 1% using potas-
sium bromide (KBr) and pellets were prepared. The FTIR spectra
of the untreated and alkali treated samples were recorded in the
4,000−500 cm-1 region on a Perkin Elmer 16PC FTIR instrument
with 32 scans in each case at a resolution of 4 cm-1.
Chemical analysis
Chemical analysis of the untreated and alkali treated fibers was
carried out as per the standard procedure (Chattopadhyay and
Sarkar 1946; Sarkar et al. 1948; moran et al. 2008). In this analy-
sis, the percents of α- cellulose, hemicellulose and lignin were
determined. In each case, five samples were used and the average
values were reported.
Thermo gravimetric analysis
The thermograms of the leaf sheath fibers were recorded on a
Perkin Elmer TGA-7 instrument in nitrogen atmosphere at a
heating rate of 10ºC/min in the temperature range of 50–500ºC.
X-ray analysis
The wide angle X-ray diffraction spectra of the leaf sheath fibers
were recorded on a Rigaku Dmax 2500 diffractometer. The sys-
tem had a rotating anode generator with a copper target and wide
angle powder goniometer. The generator was operated at 40 KV
and 150 mA. All the experiments were performed in the reflec-
tion mode at a scan speed of 4º/min in steps of 0.05º. All samples
were scanned in 2 range of 5º to 50º.
Tensile properties
The tensile properties such as maximum stress, Young’s mod-
ulus and % elongation at break of the leaf sheath fibers were
determined using INSTRON 3369 Universal Testing Machine
at a crosshead speed of 5 mm/min maintaining a gauge length of
50 mm. In each case, 10 samples were used and the average val-
ues reported.
Results and discussion
The photographs of the coconut tree with leaf sheath (marked
with an arrow), leaf sheath, sheath inner mat and separated
coarse fibers from the outer layers are presented in Fig. 1 a, b, c
and d, respectively. The average dimensions of the outer layer
(coarse) and inner mat (fine) fibers and the corresponding aspect
ratio were presented in Table 1. From this table, it is evident that
the coarse fibers had an average aspect ratio of 478 whereas fine
fibers had a value of 3 322. Scanning electron micrograms of the
surface and cross-section of the untreated and alkali fine and
coarse fibers at different magnifications were shown in Fig. 2.
From these micrographs it is evident that, for both types of fibers,
surface of the fibers became rough on alkali treatment. Further,
the micrographs of cross-section of the fibers indicate that the
fibers had multicellular structure. Each unit cell of fibers was
composed of small particles of cellulose surrounded and ce-
mented together with lignin and hemicellulose. Similar observa-
tion was made in the case of some other ligno-cellulose fibers
also (Rout et al. 2001; Mwaikambo and Ansell 2002; Ouajaj et al.
2004). Alkali treatment tends the fibers to react with the cement-
ing material hemicellulose, and to increase the effective surface
available for wetting by the resin when used in green composites.
Fig. 1 Photographs of (a) coconut tree with leaf sheath; (b) leaf
sheath; (c) leaf sheath inner mat; (d) separated coarse fibers from
outer layers.

Journal of Forestry Research (2010) 21(1): 53−58
55
Table 1. Average dimensions of the outer layer and inner mat fibers
of coconut leaf sheath.
Fiber Length (L)
(cm)
Diameter (D)
(cm)
L/D Ratio
Inner mat fine fiber 47.5 0.014 3322
Outer layer coarse fiber 47.5 0.099 478
Fig. 2 Scanning electron micrographs of untreated and alkali treated
coconut leaf sheath fibers. (a) Untreated leaf sheath inner mat fiber (20 X);
(b) Alkali treated leaf sheath inner mat fiber (20 X); (c) Cross-section of
untreated leaf sheath inner mat fiber (600 X); (d) Cross-section of alkali
treated leaf sheath inner mat fiber (600 X); (e) Untreated leaf sheath coarse
fiber from outer layer (200 X); (f) Alkali treated leaf sheath coarse fiber from
outer layer (200 X); (g) Cross-section of untreated leaf sheath coarse fiber
from outer layer (2000 X); (h) Cross-section of alkali treated leaf sheath
coarse fiber from outer layer (2000 X).
The composition of both types of fibers was estimated by
chemical analysis as per the method reported in recent literature
(Moran et al. 2008). The chemical analysis of untreated and al-
kali treated fibers (Table 2) indicated the presence of α-cellulose,
hemicellulose and lignin. Other compositions, usually regarded
as surface impurities, were the pectin and wax. For comparison,
the chemical compositions of some natural fibers are also pre-
sented in Table 2. From this table, it is also evident that the he-
micellulose content of the fibers decreased on alkali treatment
for all the fibers. Further, it can also be observed that chemical
composition of coir sheath fibers was comparable with that of
Borassus fruit fibers.
FTIR technique was employed to confirm the changes in the
composition on alkali treatment of the coarse and fine fibers. The
FTIR spectra of the untreated and alkali treated leaf sheath fibers
are presented in Fig. 3. It can be observed that for alkali treated
and untreated fibers, well defined bands corresponding to
α-cellulose, hemicellulose and lignin were present in the spectra.
But in the case of untreated leaf sheath fibers, additional bands at
around 1 734 cm-1 and 1 248 cm-1 were also present correspond-
ing to hemicellulose (Pandey 1999). On alkali treatment, these
bands were found to be almost absent, indicating the elimination
of the hemicellulose to larger extent. The bands at around 3 435
cm-1 and 2 930 cm-1 corresponded to α-cellulose whereas the
remaining bands belonged to lignin. Thus, the FT-IR studies
suggested the reduction of the hemicellulose content upon alkali
treatment of the leaf sheath fibers. This was supported by the
chemical analysis data of the alkali treated fibers as shown in
Table 2. Almost similar trends were noticed for both the fine
inner mat and coarse outer layer fibers.
Table 2. Chemical composition of some various natural fibers
Chemical component
α - Cellulose Hemicellulose Lignin α - Cellulose Hemicellulose Lignin
Fiber
Untreated Alkali treated
Ridge gourd
a) Top layer 57.2 14 27.7 73 12.5 14.4
b) Bottom layer 60 14.1 25.9 72.7 12.3 14.96
(Rajulu et al. 2006)
Tamarind 59 22 19 64.5 16 19.5
(Maheswari et al. 2008)
Sterculia urens 62.9 24.3 12 81.5 7.5 10.8
(Jayaramudu et al. 2009)
Polyalthia cerasoides 10.7 64.5 22.7 12.6 70.5 18.5
(Jayaramudu et al. 2009)
Borassus
a) Coarse 45.67 32.76 21.53 48.24 25.42 26.33
b) Fine 53.4 29.6 17 60.02 22 17.98
(Obi Reddy et al. 2009)
*Coir sheath
a) Inner mat 34.3 29.1 36.4 40.2 16.8 42.9
b) Coarse 53.6 22.3 24 60.5 12.5 26.9
The wide angle X-ray diffraction patterns of fine and coarse fibers are shown in Fig. 4. The diffractograms show two reflec-

Journal of Forestry Research (2010) 21(1): 53−58
56
tions, corresponding to 2θ values of around 16º and 22º, respec-
tively. Among these, the low angle reflection (16º) was broad
whereas the (22º) reflection was sharp and intense. These reflec-
tions were attributed to amorphous (Iam) and crystalline compo-
nents (I002) arising from hemicellulose and α-cellulose, respec-
tively. The crystallinity index of the fibers was determined
(Mwaikambo and Ansell. 2002) by using the following equation
(1).
100*
)002(
)()002(
I
II
Ic am
−
= (1)
Where, I(002) (2θ=22º) represents the intensity of crystalline peak
while I(am) (2θ=16º) denotes intensity of the amorphous peak in
the diffractograms. Accordingly, the computed index values for
untreated and alkali treated fine fibers from inner mat were
37.1% and 44.2%, respectively. These values for untreated and
alkali treated coarse fibers were 39% and 41.5%, respectively.
The increase in crystallinity of treated fibers might be due to loss
of amorphous hemicelluloses as indicated in chemical and FTIR
analyses.
Fig. 3 FT-IR spectra of untreated and Alkali treated Coconut leaf
sheath fibers. (a) Untreated leaf sheath inner mat fibers; (b) Alkali treated
leaf sheath inner mat fibers; (c) Untreated leaf sheath coarse fibers from outer
layer; (d) Alkali treated leaf sheath coarse fibers from outer layer.
Fig. 4 X-Ray diffractograms of untreated and alkali treated coconut
leaf sheath fibers. (a) Untreated leaf sheath inner mat fibers; (b) Alkali
treated leaf sheath inner mat fibers; (c) Untreated leaf sheath coarse fibers
from outer layer; (d) Alkali treated leaf sheath coarse fibers from outer layer.
The primary thermograms of both coarse and fine fibers be-
fore and after alkali treatment were presented in Fig. 5. Using
these thermograms, the initial degradation temperature, 25% and
50% degradation temperatures, refractoriness (T*), inflection
point (where the degradation rate was maximum) and integral
procedural degradation temperature (IPDT) were calculated us-
ing the Doyle (1985) method. As shown in Table 3 in both cases,
the initial and final degradation temperatures of the alkali treated
fibers were slightly higher than those of the untreated fibers.
However, for fine fibers, the IPDT and refractoriness of the fi-
bers increased to a higher extent on alkali treatment. The inflec-
tion point was found to be unchanged for coarse fibers on alkali
treatment. In the case of the fine inner mat fibers, the residue at
500ºC for untreated and alkali treated fibers were found to be
9.2% and 16.4%, respectively. Similarly, these values for coarse
untreated and alkali treated fibers were 26.7% and 28.2%, re-
spectively. Using the thermograms, the moisture content (%) was
also calculated and these values are also presented in Table 3.
For both coarse and fine fibers, the moisture contents were found
to be slightly decreased on alkali treatment. The increase in
thermal stability and decrease in moisture content of the fibers
might be attributed to the increased crystallinity on alkali treat-
ment as in crystalline polymers, the molecular are closely packed
which lowers the permeation of water into them. Further, these
results indicated that alkali treated fibers were suitable as rein-
forcement even in thermoplastic matrix materials with process-
ing temperatures below 275ºC.
Table 3. Thermal degradation parameters of untreated and alkali
treated coconut leaf sheath inner mat fibers and coarse fibers from
outer layers
Degradation sheath inner mat fibers sheath separated coarse fibers
Parameter Untreated Alkali treated Untreated Alkali treated
IDT 280.1 284.6 274.5 275
25%DT 305.7 323.2 313.8 314.6
50% DT 344.8 353.5 356.4 356
IP 352.6 342.1 352.7 352.3
IPDT 155.1 200 234 237.7
RF 184 266.6 371.5 3.9
MC 4.7 4.4 4.6 392.5
IDT: Initial degradation temperature; 25% DT: 25% degradation temperature;
50% DT: 50% degradation temperature; IP: Inflection point; IPDT: Integral
procedure degradation temperature; RF: Refractoriness; MC: moisture con-
tent.
Fig. 5 Primary thermo-
grams of untreated and
alkali treated coconut leaf
sheath fibers. (a) Untreated
leaf sheath inner mat fibers;
(b) Alkali treated leaf sheath
inner mat fibers; (c) Untreated
leaf sheath coarse fibers from
outer layer; (d) Alkali treated
leaf sheath coarse fiber from
outer layer.

Journal of Forestry Research (2010) 21(1): 53−58
57
The tensile properties of the fine and coarse fibers are presented
in Table 4. The data supported that for these fibers, the maxi-
mum stress, Young’s moduli and %elongation at break increased
on alkali treatment. As hemicellulose remained dispersed in the
inter-fibrillar region separating the cellulose chains from one
another for the untreated fibers, the cellulose chains were in a
state of strain. When the hemicellulose was removed by the ac-
tion of alkali, the internal strain was released and the fibrils be-
came more capable of rearranging themselves in a more compact
manner and resulted in a close packing of the fibers which led to
improved tensile properties. The tensile properties of the coir
sheath fibers are compared with those of some natural fibers in
Table 4. From this table, it is evident that the tensile properties of
coir sheath mat fibers were superior to those of some natural
fibers.
Table 4. Tensile properties of some various natural fibers
Tensile properties
Maximum stress
(MPa)
Young’s modulus
(GPa)
Elongation
(%) at break
Maximum
stress
(MPa)
Young’ smodulus
(GPa)
Elongation
(%) at break
Fiber
Untreated Alkali treated
Hildegardia 46.4 2.3 2.84 57 3 3.3
Jagadeesh et al. 2008)
Tamarind 61.16 2.1 6.22 66.26 3 7.97
(Maheswari et al. 2008)
Sterculia urens 10.03 0.6 2 18.92 2 2.47
(Jayaramudu et al. 2009)
Polyalthia cerasoides 44.3 3.4 2.5 51.6 2.7 5.7
(Jayaramudu et al. 2009)
Borassus
a) Coarse 50.9 1.2 41.2 53.5 1.6 41.9
b) Fine 65.2 4.9 47.2 90.7 9.8 58.5
(Obi Reddy et al. 2009)
*Coir sheath
a) Inner mat 119.8 18 5.5 128.6 6.8 8.7
b) Coarse 94.3 4.4 6.3 196.8 5.2 5.7
* Present work
Conclusions
The fine fibers from inner mat and the coarse fibers from outer
layers of coconut leaf sheath were analyzed by SEM, FTIR,
XRD and TGA techniques. The amorphous hemicellulose was
found to be eliminated to large extent on alkali treatment. Due to
this, the crystallinity of the alkali treated fibers was found to
increase. Based on the thermal stability, the renewable and envi-
ronment friendly natures, coconut leaf sheath fibers were found
to be suitable materials as reinforcement in green composites.
Acknowledgments
This work was carried out under the UGC, India Major Research
Project (No׃ 33-397/ 2007 (SRF)). We thank Dr B. Nagarjuna
Reddy, Assistant Director (A.H), CSCC, and Anantapur, India
for his help in cryogenically cooling the samples with liquid
nitrogen.
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