Celluloses in an Ionic Liquid: the Rheological Properties of the Solutions Spanning the Dilute and Semidilute Regimes

Abstract

The ionic liquid of 1-allyl-3-methylimidazolium chloride ([amim]Cl) was used as the good solvent to dissolve celluloses. Cellulose concentration covers the range of 0.1-3.0 wt %, spanning both the dilute and semidilute regimes. The rheological properties of the cellulose ionic liquid solutions have been investigated by steady shear and oscillatory shear measurements in this study. In the steady shear measurements, all the cellulose solutions show a shear thinning behavior at high shear rates; however, the dilute cellulose solutions show another shear thinning region at low shear rates, which may reflect the characteristics of the [amim]Cl solvent. In the oscillatory shear measurements, for the dilute regime, the reduced dimensionless moduli are obtained by extrapolation of the viscoelastic measurements for the dilute solutions to infinite dilution. The frequency dependences of the reduced dimensionless moduli are intermediate between the predictions from the Zimm model and elongated rodlike model theories, while the fitting by using a hybrid model combining these two model theories agrees well with the experimental results. For the semidilute regime, the frequency dependences of moduli change from the Zimm-like behavior to the Rouse-like behavior with increasing cellulose concentration. In the studied concentration range, the effects of molecular weight and temperature on solution viscoelasticities and the relationship between steady shear viscosity and dynamic shear viscosity are presented. Results show that the solution viscoelasticity greatly depends on the molecular weight of cellulose; the empirical time-temperature superposition principle holds true at the experimental temperatures, while the Cox-Merz rule fails for the solutions investigated in this study.