Viscoelastic Behavior of Aqueous Hydroxypropyl Cellulose Solutions Due to Entanglements

Hydroxypropyl cellulose (HpC) forms a liquid crystalline phase and is thought to have a rod-like shape in aqueous solution. The viscoelastic behaviors of aqueous solutions of HpC samples with average molar substitution numbers (MS ∼ 3.8) and weight-average molar masses (M_w = 36-740 kg mol^-1) were examined over a wide concentration (c) range, and the results were discussed based on a concept of rod particle suspension rheology. The c and M_w dependencies of viscoelastic parameters determined in the frequency range showing flow behavior, such as the zero-shear viscosity, the average relaxation time, and the steady-state compliance in the c range for HpC molecules to fully entangle, were considered by using the number density (ν = cN_A/M_w, where N_A is the Avogadro constant), the intrinsic viscosity, and the average rod particle length of HpC molecules determined via dilute solution properties. The obtained relationships were successfully understood with the rod particle suspension rheology.