Biomedical Engineering Reference
In-Depth Information
2.2 Sample preparation
Nanocellulose was isolated from MCC by means of cation-exchange resin hydrolysis. 3 g
dried MCC and 30 g ion exchange resin were put into 250 ml distilled deionized water. The
suspension was stirred and sonicated at 40-60°C for 150-210min. Then the ion exchange
resin was separated from cellulose suspension. The resulting suspension was centrifuged
several times at 12000 rpm and washed with distilled deionized water until the supernatant
became turbid, and then the nanocellulose was collected.
2.3 Experimental design and statistical analysis
The Box-Behnken experimental design method was used to determine the effects of major
operating variables on the yield of nanocellulose and to find the combination of variables in
order to produce maximum nanocellulose yields. The advantage of Box-Behnken design is
that it has only three levels, coded -1, 0, and +1 for low, middle and high concentrations,
respectively. This experimental design reduced the number of experiments, so it is more
efficient and easier to arrange and to interpret in comparison to others (Majumder et al.,
2009). Therefore, this statistical technique was adopted in this study.
The experiments at ratio of NKC-9 to MCC (5: 1, 10: 1 and 15: 1), temperature (40, 50 and
60°C), time (150, 180 and 210min) were employed simultaneously covering the spectrum of
variables for the percentage of nanocellulose yield in the Box-Behnken Design. As presented
in Table 1, the experimental design involved three parameters (X
1
, X
2
and X
3
), each at three
levels, coded -1, 0, and +1 for low, middle and high concentrations, respectively. A second-
order polynomial equation was used to express the responses as a function of the
independent variables as follows:
n
n
YB
iXi
B jXiXj
(1)
0
i
1
i
j
1
Where
Y
represents the measured response variables, three variables are involved and hence
n takes the value 3.
B
0
is the constant coefficient,
B
i
s are the linear coefficients,
B
ij
s are the
interaction coefficients.
Symbols & level
b
-1
Factor
0
+1
ratio of resin X
1
5
10
15
temperature X
２
(°C)
40
50
60
time X
3
(min)
150
180
210
b
x
1
=( X
1
－
10)/5; x
2
=( X
2
－
50)/10; x
3
=( X
3
－
180)/30.
Table 1. Code and level of factors chosen for the trials.
2.4 Characterization of nanocellulose
Electron microscopy was conducted to observe the surface of MCC and nanocellulose.
Samples were mounted on metal stubs by double side adhesive tape and examined with FEI
XL30 ESEM-FEG field emission scanning electron microscopy (FESEM). The nanostructure
of nanocellulose was examined in a transmission electron microscope (TEM), Tecnai G2F20
FETEM (FEI Co. Ltd., USA) at an acceleration voltage of 200 kV. The X-ray diffraction
