In this study, we characterize the shear and extensionalrheologyof dilute to semidilute solutions of cellulose in the ionic liquid1-ethyl-3-methylimidazolium acetate (EMIAc). In steady shear flow,the semidilute solutions exhibit shear thinning, and the high-frequencycomplex modulus measured in small amplitude oscillatory shear flowexhibits the characteristic scaling expected for solutions of semiflexiblechains. Flow curves of the steady shear viscosity plotted againstshear rate closely follow the frequency dependence of the complexviscosity acquired using oscillatory shear, thus satisfying the empiricalCox–Merz rule. We use capillary thinning rheometry (CaBER)to characterize the relaxation times and apparent extensional viscositiesof the semidilute cellulose solutions in a uniaxial extensional flowthat mimics the dynamics encountered in the spin-line during fiberspinning processes. The apparent extensional viscosity and characteristicrelaxation times of the semidilute cellulose/EMIAc solutions increasedramatically as the solutions enter the entangled concentration regimeat which fiber spinning becomes viable. [ABSTRACT FROM AUTHOR]