Isolation of Cellulose Nanowhiskers from Kenaf Fiber - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 191

samples were heated from room temperature up to 500°C at a heating rate of 10°C/
min under a nitrogen atmosphere.

Transmission Electron Microscopy (TEM)
A Transmission Electron Microscope (TEM) observation was performed using a Phil-
ips CM30 to study the morphology of cellulose nanowhiskers. One droplet of 1% sus-
pension was put on a Cu-Grid covered with a thin carbon film. To enhance contrast in
TEM, the nano-saized whiskers were negatively stained in a 2 wt% solution of uranyl
acetate (a heavy metal salt) in de-ionized water for one min.

results aNd disCussioN
Chemical Composition
The chemical compositions of kenaf fiber at different stages of alkali and bleaching
treatments are presented in Table 1. It is clear that raw kenaf fiber has the highest
percentage of hemicelluloses and lignin and the lowest percentage of α-cellulose.
When, the fiber is subjected to alkali and bleaching treatments, the percentage
of hemicellulose and lignin decrease, whereas, the percentage of α-cellulose in-
creased. The NaOH was found to be efficient in removing hemicellulose from
kenaf fibers with the reduction of less than half of raw kenaf from 34.7 to 13.3
wt% after alkali treatment while the amount of lignin was reduced from 11.5 to
9.3 wt%.

table 1. Chemical composition of kenaf fibre after each stage of treatment.

Materials Cellulose (%) Hemicelluloses (%) Lignin (%)

Raw kenaf fiber 43.7±1.2 34.7±1.2 11.5±0.5

Alkali treated kenaf fiber 65.7±0.3 13.3±0.3 9.3±0.5

Bleached kenaf fiber 91±0.2 6±0.2 0

The bleaching process helps to remove the majority of the lignin component. As
shown in Table 1, a further reduction in the percentage of hemicellulose and lignin
contents is observed. Nevertheless, the percentage of α-cellulose content increased
from 43 to 91%. The final fibers obtained after bleaching process is found to have the
highest percentage of cellulose content.
Therefore, the reinforcement ability of these fibers is expected to be much higher
than other fibers, which have less percentage of cellulose content. Figure 2, shows
the optical micrographs of kenaf fibers after each stage. It is clear that the color of
raw kenaf fiber turns to be lighter after alkali treatment and completely white after
bleaching treatments. This indicates that there is still a significant amount of lignin
after alkali treatment and removal of most of the hemicelluloses and lignin is by
bleaching.