Molecular Characterization on the Anomalous Viscosity Behavior of Cellulose Solutions in N,N-Dimethyl Acetamide and Lithium Chloride
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The physical properties of dilute cellulose solutions in N,N-dimethyl acetamide (DMAc) including 9 wt% lithium chloride (LiCl) were investigated in terms of concentration, temperature and molecular weight of cellulose. Over the concentration range of 0.01 to 2.5 g/dL, the viscosity of the cellulose solutions exhibited a lower critical solution temperature (LCST) behavior which proved thermoreversible between 30 and 60 °C. The LCST behavior was further supported by dynamic light scattering measurement. In the extremely dilute concentration range, 0.01 to 0.08 g/dL, the reduced viscosity (η red ) of cellulose solutions was increased with decreasing concentration. The anomalous coil expansion with decreasing concentration could be explained by the increase of the conductivity of cellulose solutions with decreasing concentration, which was also verified by dynamic light scattering experiment. In the concentration range of 0.1 and 2.5 g/dL, both cellulose solutions gave a drastic increase of η red in the vicinity of the critical concentration (C*), 0.9 g/dL. The slope of the curve of η red vs. concentration was higher for the cellulose of higher molecular weight, but it did not change with temperature between 30 and 60 °C.
Keywordscellulose N,N-dimethylacetamide/LiCl LCST behavior thermoreversibility polyelectrolyte effects
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