Unbleached cellulose from waste corncob for isolation of cellulose nanocrystals

Unbleached cellulose obtained from corncobs was used to synthesize cellulose nanocrystals (CNCs). Corncobs are an agro-industrial residue that has a high cellulose content and can be used as a raw material to obtain CNCs. The cellulose was extracted from the corncobs by means of delignification in two stages. The first stage consisted of a pulping process with ethanol and acetic acid (organosolv method), and in the second stage, the corncob was treated with an organosolv method and potassium hydroxide, followed by sodium hydroxide and boric acid (extraction and purification) to eliminate hemicellulose. The obtained cellulose was not bleached, in order to maintain the groups corresponding to lignin and hemicellulose on their surface. Afterward, the obtained cellulose underwent acid hydrolysis to obtain CNCs, using sulfuric acid at 64%. These nanocrystals were characterized by X-ray diffraction, atomic force microscopy, thermogravimetric analysis and zeta potential. The CNCs obtained from the two types of unbleached cellulose showed lengths from 125.18 to 225.86 nm and diameters from 11.61 to 35.92 nm. The results indicate not only that CNCs can be obtained from unbleached cellulose corncobs but also that their characteristics are similar to those of CNCs obtained by means of bleached cellulose.