Impact of Electrolytes on the Rheology of TEMPO-oxidized Cellulose Nanofibril

Cellulose nanofibril (CNF) gels are interesting natural materials that have various potential applications, but some applications require specific gel properties: producing stiffer/strong gels. In this study, CNFs were prepared by TEMPO-mediated oxidation pre-treatment under three conditions (CNF-1, CNF-2, CNF-3). Gelation of CNFs was initiated by the addition of various concentrations of monovalent (Na+) and divalent (CaSUP2+/SUP) ions (500, 1,000, 5000, 10,000 ppm) in order to improve the mechanical strength of the gels. CNF gels were analyzed and characterized in terms of shear viscosity, storage moduli, and loss moduli using a rheometer at the temperature of 25℃. The results showed that the amount of carboxyl content on the surface charge of CNF strongly affected the rheological properties of CNF gels. Increasing the carboxyl content contributes to enhancing the mechanical strength of CNF gel. Similar effect to the addition of cations in which the viscosity and storage moduli of CNF gels significantly increased as the concentration of added cation increased from 500 to 10,000 ppm. However, CNF gels with calcium showed higher strength than those with sodium, this may due to the different charge and ionic radii of both sodium and calcium. Ionic radii, a charge of cation, and concentration of cation used, carboxyl group contents as well, played an important role in influencing the mechanical properties of CNF gels. However, further analysis is required related to a concentration of cation used to form a maximum strength of CNF gel.