Effect of pH and electrolyte concentration on sol–gel state of semi-dilute aqueous cellulose nanofiber suspension: an interpretation based on angle-dependent DLVO theory.

Understanding rheological properties of dispersions of cellulose nanomaterials such as cellulose nanofiber (CNF) and cellulose nanocrystal (CNC) has received tremendous attentions from scientific and industrial viewpoints. To gain insight into the effect of aggregation-dispersion of CNF on the sol–gel state of aqueous CNF suspensions, simple turnover tests were performed for semi-dilute CNF suspensions as a function of pH and potassium chloride (KCl) concentration. Experimental results revealed that the gel state was confirmed around 20–100 mM KCl depending on pH, and the sol state was observed at higher or lower KCl concentrations. The upper and lower boundaries between gel and sol states were 20 and 80 mM around pH 4, and 50 and 120 mM around pH 7. These boundaries were discussed using the angle-dependent Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for cylindrical particles. From the discussion, we presume that the gel of semi-dilute CNF suspension can be formed when the aggregation is allowed at the orientation angle between 45 and 90°. Aggregation at orientation angles below 30° can occur at high KCl concentration and might result in sol state due to the formation of aggregate with compact structure, which cannot allow the network structure in the whole suspension. [ABSTRACT FROM AUTHOR]