RHEOLOGICAL PROPERTIES OF CELLULOSE-NaOH COMPLEX SOLUTIONS: FROM DILUTE TO CONCENTRATED STATES

Steady-state shear flow of cotton cellulose dissolved in a NaOH complex solution (8% NaOH/6.5% thiourea/8% urea aqueous solution) was studied over a large range of concentrations (0-6.2%) and temperatures (0-20 oC), to guide the spinning conditions. The formation of cellulose aggregates was favored when either the cellulose content or temperature was increased. The solution flow curves exhibited a Newtonian zero-shear viscosity (o) region and a two-shear rate dependent apparent viscosity (app) region. The rheological properties of the cellulose solution, especially at a high shear rate (according to the actual spinning process), were investigated systematically, including the dependence of zero-shear viscosity, activation energy, non-Newtonian index and structural viscosity index on cellulose concentration and temperature. On the basis of steady-shear flow test data, two critical overlaps (C and C) of the cellulose solution were determined, respectively, of 2.1 and 5.0%. The critical concentrations C and C delimitate three different states of the cellulose solution: semi-diluted entangled network, semi-diluted tangled network and concentrated solutions. The results are favorable for predicting the spinnability of the cellulose-NaOH complex spinning solution, being particularly important before using this effective solvent system in the spinning process.