2.2. Preparation of cellulose nanocrystals
2.2.1. Purification
Initially the untreated corncob (CC) was milled with a blender to
pass through a 35-mesh screen. After that, the CC was treated with
a sodium hydroxide aqueous solution of 2% (w/w) for 4 h at 100 ◦C
under mechanical stirring and then washed several times with distilled
water until the alkali was completely removed, and finally
dried at 40 ◦C for 24 h in an air-circulating oven. After this treatment,
the fibers were bleached with a solution made up of equal
parts (v:v) of acetate buffer (27 g NaOH and 75 mL glacial acetic
acid, diluted to 1 L of distilled water) and aqueous chlorite (1.7 wt.%
NaClO2 in water). This bleaching treatment was performed at 80 ◦C
for 6 h. The bleached fibers were washed repeatedly in distilled
water until the pH of the fibers became neutral and subsequently
dried at 40 ◦C for 24 h in an air-circulating oven (de Rodriguez et al.,
2006; Siqueira et al., 2010a). The fiber content throughout these
chemical treatments was about 4–6% (w/w). The material which
resulted after the purification was the treated corncob (TCC).