Cellulose sulfates (CS) were prepared by heterogeneous sulfation esterification of α-cellulose, using chlorosulfonic acid in dimethylformamide as the sulfation agent. The degree of substitution (DS) of sulfate groups in CS was approximately 2.0, as determined by elemental analysis. Carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy data suggested that the sulfation pattern of CS included complete C-6 substitution as well as complete or partial C-2 substitution. CS showed good solubility in deionized water. Upon using a series of CS solutions with similar DS and fitting with Mark-Houwink equation, the sugar chains of CS showed a relatively compact conformation in dilute solution, based on the relationship between molecular weight and intrinsic viscosity. At high concentration, the dynamic viscosity of CS increased with an increase in CS concentration. The addition of salt promoted charge repulsion within the polyelectrolyte in CS, resulting in an increase in dynamic viscosity of CS. The addition of Ca2+ triggered complexation between CS and Ca2+ and significantly enhanced the dynamic viscosity of CS. The pH value of the solution was one of the main factors influencing the dynamic viscosity of CS, which was highest at neutral pH and decreased at acidic or alkaline pH values.
