Rheological characterization of cellulose solutions in N-methyl morpholine N-oxide monohydrate

Abstract

Three different modes of rheological properties were measured on 11 and 13 wt% solutions of cellulose in N-methyl morpholine N-oxide (NMMO) monohydrate, in which concentration range lyocell fibers of much reduced fibrillation are preferably produced. The dynamic rheological responses revealed that the Cox-Merz rule did not hold for these cellulose solutions. Both cellulose solutions showed a shear thinning behavior over the shear rate measured at 85, 95, 105, and 115°C. However, 13wt% solution gave rise to yield behavior at 85°C. The power law index ranged from 0.36 to 0.58. First normal stress difference (N1) was increased with lowering temperature and with increasing concentration as expected. Plotting N1 vs shear stress (τω) gave almost a master curve independent of temperature and concentration, whose slope was about 0.93 for both cellulose solutions over the shear rate range observed (τω > 500 Pa). In addition, the cellulose solutions gave high values of recoverable shear strain (SR), ranging from 60 to 100.