The individualization process consists of chemical pretreatment
and high-intensity ultrasonication (Fig. 1). In the chemical pretreatment
stage, the wood fibers were purified to prepare the cellulose
fibers according to general methods (Abe&Yano, 2009). First, lignin
was removed from the samples using acidified sodium chlorite
solution at 75 ◦C for an hour; this process was repeated five times
until the product became white. Next, the samples were treated
in 3 wt% potassium hydroxide at 80 ◦C for 2 h, and then in 6 wt%
potassium hydroxide at 80 ◦C for 2 h in order to leach hemicellulose,
residual starch, and pectin. After a series of chemical treatments,
the samples were filtered and rinsed with distilled water until
the residues were neutralized. To avoid generating strong hydrogen
bonding among nanofibers after matrix removal, the samples
were kept in awater-swollen state during the whole chemical process.