World Journal of Engineering
OPTIMIZATION OF CELLULOSE FIBER ISOLATION FROM RICE STRAW
AND ITS APPLICATION FOR THERMOPLASTIC COMPOSITE FORMATION
Siritorn Narkchamnan1 and Chularat Krongtaew1*
Department of Chemical Engineering, Faculty of Engineering, Mahidol University,
Nakhon Pathom, 73170, Thailand. *E-mail: egchularat@mahidol.ac.th
Isolation of natural fibers
Rice straw (Oryza sativa) was cut into 2-mm pieces
before pre-treatment. The cut rice straw was treated
in three consecutive steps: 1) soaking in concentrated
alkaline solution at NaOH concentration based on
straw dry weight and then washed with 1-L distilled
water, 2) hydrolysis by dilute HCl and then washed
with 1-L distilled water, and 3) treatment in dilute
alkaline solution containing 2%w/w NaOH. Finally,
isolated fibers were homogenized to micro-nano
scale.
The central composite design (CCD)
For the central composite design (CCD), variation of
soaking time, solvent and NaOH concentrations was
in a range of -1 and +1; soaking time (8 to 24h),
solvent concentration (10 to 50%v/v) and NaOH
concentration (15 to 25%w/w). Regression
coefficients of the quadratic model of each response
for isolated cellulose fibers from CCD are showed in
Table.1.
Processing of the biocomposite
Starch thermoplastic composite was prepared by
mixing of rice straw fibers, glycerol and cassava
starch. Isolated cellulose rice straw fibers were added
into a proportion of starch-to-glycerol of 50 : 6
%w/w. Composite was formed using compression
molding technique at 210C for 6 min. The influence
of cellulose fibers in composite was studied by
varying the fiber content at 0%, 5%, 10% and
15%w/w.
Analyses of fibers and biocomposite
Thermogravimetric analysis (TGA) of the starch
composite containing 0%, 5%, 10% and 15%w/w
cellulose fibers was performed by thermogravimetric
analyzer (Pyris Diamond TG/DTA, PerkinElmer)
with a heating rate of 10°C/min in nitrogen
atmosphere and temperature ranging between 30 and
500°C. Mechanical properties of the composite
specimens were determined by using a universal
testing machine (Instron 4467, USA) and 3-point
bend fixture with a load cell of 0.5 kN. The flexural
modulus and strength strain of the composite
specimen were then calculated.
Introduction
Rice is the most export agricultural product of
Thailand. Side products from rice processing can be
utilized as precursors for alternative energy
production, bioplastic formation, natural fertilizer
manufacturing, etc [1]. At present, most of plastic
industries depend greatly on petroleum sources
which are non-degradable. They produce a large
amount of plastic waste that has detrimental effect to
environment concerning a global warming. Thus,
utilization of environmentally friendly resources for
biodegradable plastic application has become
interesting topic throughout the world [2].
Rice straw, one of the most plentiful agro-residues in
Thailand, composed mainly of holo-cellulose, alphacellulose and lignin. Alpha-cellulose in rice straw has
crystalline structure that makes it suitable to use for
increasing tensile strength and young modulus of
plastic [3]. From the earlier work [7], the authors
previously published a research work on cellulose
isolation from rice straw and the crucial factors
influencing alpha-cellulose yield and fiber
morphology were reported. In the present work,
experimental optimization study on cellulose
isolation from rice straw at moderate condition at
atmospheric pressure was conducted by using a
central composite design (CCD). Isolated cellulose
fiber was used for light weight starch thermoplastic
formation.
Experimental
Materials
Rice straw (Oryza sativa) was obtained from a local
source (Nakhon Chaisee, Nakhon Pathom, Thailand).
Chemicals for the experiments on chemical treatment
of rice straw and the analyses were analytical grade
and purchased from Sigma, Fluka and Ajax
Finechem. Cassava starch, glycerol and magnesium
stearate used for thermoplastic formation were from
Erawan Co., Ltd., Ajax Finechem and Sigma.
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World Journal of Engineering
Table 1 Regression coefficients of the quadratic models for holo-cellulose, alpha-cellulose, lignin contents and
weight loss of isolated cellulose fibers from the CCD.
Equation Z=a+bX1+cX2+dX3+eX12+fX22+gX32+hX1X2+iX1X3+jX2X3
Regression
Holo-cellulose
Alpha-cellulose
Lignin
Weight loss
coefficients of the
eq (3)
eq (4)
eq (5)
eq (6)
equation (eq)
a
-8.82
74.04
108.82
101.40
b
3.38
0.26
-3.38
-3.69
c
0.02
-0.02
-1.31
d
7.01
-7.01
e
-0.03
0.04
0.03
0.05
f
0.03
0.01
-0.01
g
-0.08
0.08
-0.07
h
0.02
0.03
-0.02
0.02
i
-0.14
0.01
0.14
0.11
j
0.03
0.03
0.05
R2
0.95
0.51
0.95
0.55
2
R (adj)
0.85
0.24
0.85
0.11
P-value
0.0214
0.3316
0.1195
0.1903
design (CCD). Three factors influencing an increase
of alpha-cellulose content and lignin removal
including 1) soaking time, 2) solvent and 3) NaOH
concentration were used for the experimental design.
It was found that the optimum condition for the
isolation of the natural fibers was at 24-h soaking
time, 10%v/v solvent, and 25%w/w NaOH. From
this condition, the alpha-cellulose content was
88.38%w/w and the weight loss was 58.43%.
As shown in Fig.1, TGA analysis of starch/glycerol
thermoplastic when adding 0%, 5%, 10% and 15%
cellulose rice straw fibers demonstrated that an
increase of cellulose rice straw fibers in the
thermoplastic composite proportion (starch : glycerol
of 50 : 6) decreased its degradation temperature. A
significant increase of flexural strength and modulus
was obtained after adding fibers into the starch
thermoplastic composite as illutstrated in Table 2.
References
120
100
Weight loss (%)
80
60
40
20
0
0
100
200
300
400
500
600
Temperature (°C)
nofiber
10%fiber
chemically treated
5%fiber
15%fiber
Fig. 1 TGA thermograms of starch thermoplastic
composite with different fiber contents (0 –
15%w/w) and chemically treated rice straw fibers.
Table 2 Mechanical properties of the composites
Strengtha
Modulusa
(kPa)
(MPa)
TPS-0% fibers
0.21±0.1
4.65±4.9
TPS-5% fibers
0.34±0.2
11.66±10.2
TPS-10% fibers
0.41±0.1
17.08±6.5
TPS-15% fibers
0.43±0.2
32.83±20.8
a
All values are reported as mean ± s.d. (N≥3)
TPS = thermoplastic starch
Sample
1.
William, J. O., Shey, J., Syed, H. I., Grgory, M.,
Glenn, M. E. and Jean, F. R. (2005). “Application of
cellulose microfibrils in polymer nanocomposites”,
Journal of Polymers and the Environment, 13, 301-306.
2.
Wittaya, T. (2009). “Microcomposites of rice
starch film reinforced with microcrystalline cellulose from
palm pressed fiber”, International Food Research Journal,
16 493-500.
3.
Sain,
M.
and
Alemdar,
A.
(2008).
“Biocomposites
from
wheat
straw
nanofibers:
Morphology, thermal and mechanical properties”,
Composites Science and Technology, 68, 557-565.
Results and Discussion
The optimization of cellulose isolation from rice
straw was carried out by using the central composite
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