Yielding of cellulose nanocrystal suspensions in the presence of electrolytes

Abstract

The rheological properties and yielding behavior of 1 wt. % aqueous sulfonated cellulose nanocrystals (CNCs) in the presence of monovalent (Na+) ions have been investigated. The introduction of more than 20 mM NaCl to the system causes aggregation of neutralized CNCs and leads to the formation of self-similar clusters, which grow in size until they form a three-dimensional network. In the present work, we report a comprehensive study of nonlinear rheology and yielding behavior of CNC/salt gels in steady shear and oscillatory experiments. Two yield stresses have been determined. The first yield stress at low shear rates is attributed to the disconnected CNC clusters as a result of bond breakage. The second yield point occurs at higher shear rates, and it is related to the deformation of clusters, where individual nanorods are nearly separated and dispersed. The existence of these two yield stresses has been identified in both steady-shear scans (high to low and low to high) as well as oscillatory experiments, resulting in consistent results.