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 dis-persibility 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 function-alization 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 degrees C temperature and 6 mol/dm3 of hy-drochloric acid. To find the optimum stabilizing conditions, the effect of different pH values and various sur-factants 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), ther-mogravimetric and X-ray diffraction techniques.

Automated summary

Nanocelluloses have attracted much attention due to their mechanical properties, high surface area, and porosity. Sulfuric acid is commonly used for the production of cellulose nanocrystals, but it leads to cellulose esterification and lower thermal stability. Hydrochloric acid hydrolysis does not result in functionalization of the nanocellulose surface, but it lacks ionic interactions and causes poor colloidal stability. This study aimed to obtain stable aqueous suspensions of cellulose nanofibrils (CNF) through hydrochloric acid hydrolysis. The best stabilizing effect was achieved at pH 5-9 and with nonionic surfactants.