Facile and rapid one-step extraction of carboxylated cellulose nanocrystals by H2SO4/HNO3 mixed acid hydrolysis

A facile and rapid approach was designed to extract carboxylated cellulose nanocrystals (CCNCs) through a one-step hydrolysis process by using mixed acid system of sulfuric acid and nitric acid (H2SO4/HNO3). It is found that the surface hydroxyl groups on CNCs could be converted into carboxyl groups efficiently after 0.5 h treatment by introducing HNO3 as oxidant. The degree of oxidation could reach a maximum value of 0.11 at the reaction temperature of 80 degrees C, which was consistent with those prepared by the conventional TEMPO or APS oxidation method. Meanwhile, the as-prepared CCNCs presented a rod-like morphology with the length and diameter of 186 +/- 13 and 9 +/- 3 nm, respectively. More importantly, the CCNCs showed excellent dispersibility in water and some organic solvents due to the existence of negative carboxyl groups, which was benefit for their reinforcing applications and developing new applications by further surface functionalization.