Effect of hydrolysis time, pH and surfactant type on stability of hydrochloric acid hydrolyzed nanocellulose.

Nanocelluloses are the subject of much interest on the account of their mechanical properties, high surface area, porosity, etc. Typically, sulfuric acid is used to produce cellulose nanocrystals with high aspect ratio and dispersibility in water suspensions. However, hydrolysis in sulfuric acid leads to cellulose esterification, which has some drawbacks such as lower thermal stability of nanocellulose. Hydrochloric acid does not cause functionalization of the nanocellulose surface, yet yields in poor colloidal stability in aqueous solutions due to the lack of ionic interactions between CNC/CNF and water molecules. Therefore, it should be possible to tune the colloidal stability of nanocellulose aqueous suspensions by modifying the properties of the solution (such as pH and/or the presence of surfactants). In this work, we attempted to obtain stable aqueous CNF suspensions via hydrochloric acid hydrolysis. Hydrolysis was performed at three time intervals, at 60 °C temperature and 6 mol/dm3 of hydrochloric acid. To find the optimum stabilizing conditions, the effect of different pH values and various surfactants on CNF stability was explored. The best stabilizing effect was observed at pH range 5-9 and in nonionic surfactant. The obtained products were characterized by using spectroscopic (FTIR), microscopic (AFM), thermogravimetric and X-ray diffraction techniques.