Comparison of Methods for Determining Intrinsic Viscosities from Non-Newtonian Viscosities

Abstract

Absolute flow curves for solutions of two samples of cotton cellulose at concentra tions of 0.1. 0.2. and 0.3 g. 100 ml. in 0.5 M cupriethylenediamine were determined over a shear stress range of 0.01-1000 dynes sq. cm. Both rotational and capillary viscome ters were employed. All three solutions behaved as Newtonian fluids below a shear stress of 1.0 dyne sq. cm. Various methods of calculating intrinsic viscosities were investigated. Values based on zero shear rate viscosities are required to avoid dependence on the viscometric proce dure. Where determination of intrinsic viscosities is not the primary objective, the best method for precise differentiation among closely similar samples appears to be compari son of apparent viscosities using a single high concentration and as low a standard shear stress as practicable. Intrinsic viscosity determinations, based on non-Newtonian vis cosities, are less satisfactory.