Solution rheology of cellulose in 1-butyl-3-methyl imidazolium chloride

Abstract

Solution rheology of cellulose in 1-butyl-3-methyl imidazolium chloride([BMIm]Cl) is reported using oscillatory and steady shear for celluloseconcentrations from 0.1 to 10 wt %, spanning the dilute, semidiluteunentangled, and entangled regimes. Although pure [BMIm]Cl is a crystallinesolid at room temperature with a melting temperature of 65 degreesC, all solutions prepared at 75 degrees C are transparent and visuallyhomogenous at 25 degrees C, and these supercooled solutions, withof order 0.1 wt % water, show no sign of crystallizing for monthsin either calorimetry or rheology measurements, allowing the potentialfor room temperature solution processing of native cellulose, suchas fiber spinning. The overlap concentration of our cellulose in([BMIm]Cl) is 0.5 wt % and the entanglement concentration is a factorof 4 larger (2 wt%). For semidilute unentangled solutions (between0.5 and 2 wt %), the specific viscosity, relaxation time, and terminalmodulus exhibit concentration dependences eta(sp) similar to c(2),tau similar to c, and G similar to c, respectively, while for entangledsolutions (between 2 and 10 wt %) we find eta(sp) similar to c(14/3), tau similar to c(2.3), and G similar to c(2.3), consistent withscaling predictions for neutral polymers in a theta solvent. However,failure of the Cox-Merz rule with steady shear viscosity larger thancomplex viscosity and the observed internal mode structure of diluteand semidilute unentangled solutions suggest that cellulose in ([BMIm]Cl)is not simply a flexible polymer in a theta solvent. (C) 2011 TheSociety of Rheology. [DOI: 10.1122/1.3553032]