Isolation of Cellulose Nanowhiskers from Kenaf Fiber - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 193

Finally, the absorbance peaks in range of 1,0281,161 cm -1 were due to C-O stretch-
ing and C-H rocking vibration of pyranose ring skeletal (Alemdar and Sain, 2008).
The differences in the FTIR spectrum between raw kenaf fiber and CNW illustrates
that CNW has been extracted successfully from kenaf fiber by hydrolysis treatment.
No obvious changes were observed in the FTIR spectrum of the CNW at different time
of hydrolysis.
morphological analysis
Figure 4 shows the FESEM micrograph and surface morphology of kenaf fibers after
chemical treatments. It is clearly seen in Figure 4(a) that raw kenaf fiber bundles are
composed of individual fibers linked together by massive cement material. Figure 4(b)
reveals the morphology of alkali treated fiber. At high temperature alkali treatment, the
hemicelluloses were hydrolyzed and became water soluble and lignin was depolymer-
ized. It can be seen that all impurities around the fibers was removed and causes the
fiber bundles to separate into individual fibers. Figure 4(c) illustrates the micrograph
of bleached kenaf fiber. Bleaching process helps to remove most of the lignin present
in the kenaf fiber, which helps in further defibrillation. Sodium chlorite and sodium
acetate buffer allow the removal of lignin. Lignin is rapidly oxidized by chlorine.
Lignin oxidation leads to lignin degradation and to the formation of hydroxylcarbonyl
and carboxylic groups, which facilitate the lignin solubilization in an alkaline medium
(Bibin Mathew Cerian et al., 2010).
Figure 4. FESEM images from raw kenaf fiber (a), Alkali treated fiber (b), Bleached fiber (c).
Furthermore, the image analysis demonstrated a significant reduction in the diam-
eter of fiber from between 40170 to 2060 μm and 512 μm in raw fiber, alkali treated
and bleached fiber, respectively.
Acid hydrolysis of kenaf fibers after bleaching, not only helps to disintegrate the
fibers, but also helps in defibrillating the fibers diameter to nano range. Figure 5 shows
the TEM micrograph of obtained cellulose whiskers. The cellulose whiskers displayed
diameter between 6 and 22 nm. Moreover, the length of nanofibers was in 90150 nm
range whereas for the raw fiber, the length was around 12.5 mm. The aspect ratio
is one of the most important parameters in determining reinforcing capability of the
nanofibers. Aspect ratio for obtained cellulose whiskers based on the average diameter
and length was calculated to be around 13.