Viscoelastic properties of concentrated cellulose acetate solutions

Abstract

Steady-shear and dynamic viscoelastic properties of cellulose acetate (CA) solutions were measured for concentrations up to 20 wt. % in dimethyl formamide, dimethyl sulfoxide, N-methyl-2-pyrrolidinone, and triethyl phosphate. For each solvent system, the specific viscosity showed a transition in concentration dependence from approximately c1 to c5 at about 3.4 g/dl while the steady-state compliance of the solutions was inversely dependent on concentration for CA content above 10 wt. %. Master curves of the concentration-reduced viscoelastic parameters were obtained by using a concentration-dependent function equal to c. Over the entire experimental frequency range, the dynamic storage and loss moduli of the 20 wt. % solutions did not exhibit any rubbery plateaus. Results suggest that the observed transition in concentration dependence of the specific viscosity was due to the chain rigidity of CA rather than the typical polymer chain entanglement effect. The solvent nature strongly influenced the specific viscosity but not the steady-state compliance. Negative primary normal forces, due to inertia, were observed for relatively dilute CA solutions at high shear rates.