Civil Engineering Reference
In-Depth Information
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Figure 11.6
Schematic of ultrasonic setup, (1) Power, (2) Piezoelectric converter, (3) Ultrasonic probe,
(4) Sample suspension, (5) Double-walled glass beaker, (6) Ice water inlet and (7) outlet [74].
diameters around 10-20 nm, 10-40 nm and 15-35 nm, respectively, can be easily dis-
tinguished. While because of the high cellulose content in l ax i ber which leads to
strong H-bond and dii culty in the i brillation process, non-uniform NFC with a 15
to 100 nm width is produced (Figure 11.5d). h e schematic of ultrasonic setup can be
seen in Figure 11.6 [74].
h e ei ciency of dei brillation in the ultrasonic process is dependent on power, con-
centration, temperature, size of i bers, time and distance from probe tip to collector [77].
In some cases, researchers have been used a combination of ultrasonication with other
methods to increase i brillation of nanoscale cellulose. For example, Li
et al.
[78] pre-
pared nanocrystalline cellulose by ultrasonication and acid hydrolysis with H
2
SO
4
from
bleached sot wood pulp. h ey found that ultrasonication led to folding and erosion
of the cellulose surface, and thus provided more reactive site to penetrate acid and
prepare high-crystalline and small-size nanocellulose. Furthermore, Wang and Chen
[77] reported that a combination of ultrasonication and homogenization boosts unifor-
mity and i brillation of cellulose nanoi ber in comparison to ultrasonication solely. In
addition, when compared to mechanical blender, ultrasonic bath and ultrasonic probe,
Mishra
et al.
[79] concluded that TEMPO-oxidized i ber treatment with ultrasonic
probe was more ei cient for nanocellulose production than the other three methods.
11.3.3
Electrospinning
Electrospinning is a versatile and simple process for formation of nanoi bers by electri-
cal force from various sources such as cellulose. In 1930, Formhal patented this method
[80] . h e basic parts of the electrospinning instrument include high voltage supply,
a syringe to carry polymer solution and a target to collect nanoi bers [81] . Figure 11.7
shows the basic electrospinning apparatus [82]. In this process, nanoi bers form from
polymer solution between two electrodes with opposite polarity, one electrode con-
nected to a syringe and the other one to a collector [83]. At a critical voltage, a conical
shape droplet known as “Taylor cone” is held at the capillary tip due to surface tension
[84, 85]. When the electric force which is created at the surface of polymer solution
