Preparation of thermally stable and surface-functionalized cellulose nanocrystals via mixed H2SO4/Oxalic acid hydrolysis

A mild and efficient approach for the preparation of cellulose nanocrystals (CNCs) was developed by using mixed H2SO4/Oxalic acid hydrolysis. In this process, the mixed acid of sulfuric acid, oxalic acid and H2O in an optimal mass ratio of 1:5:4 was used to produce CNCs from bleached eucalyptus kraft pulp (BEKP) at 80 °C for 2-5 h. The CNCs with a diameter range of 5-20 nm and a length range of 150-400 nm were obtained at a high yield (>70%) and showed excellent dispersion stability in water and good thermal stability. Moreover, the dosage of sulfuric acid can reduce to 2.4 g/g CNCs in this mixed acid hydrolysis, which is far lower than that of the typical 64% sulfuric acid hydrolysis (55 g/g CNCs, tested in this work). In addition, 91±2% of oxalic acid could be recovered by a simple recrystallization operation.