The flow curves of three kinds of cellulose materials such as purified cotton and wood pulps in cupriethylenediamine solution (CED) and cuprammonium solution (CAM) have been measured over a wide range of the velocity gradients. The viscosity measurements were carried out by employing a capillary viscometer with continuously varying pressure head, which is a modification of the viscometer described by Maron, Krieger and Sisko.
The solvents themselves behave as Newtonian liquids, whereas the cellulose solutions manifest non-Newtonian behavior unless the concentration is extremely low. For concentrations less than 3/[η], the wood pulps in CED behave practically as Newtonian liquid, and therefore it seems that the one-point method can be applied satisfactorily for determining the intrinsic viscosity. In the case of the cellulose having higher molecular weights, such as cotton, much more dilute solution must be used in order to apply the one-point method. Although the concentrated solutions exhibit remarkable non-Newtonian behavior, the apparent viscosities become constant at low velocity gradients. Hence it may be concluded that the measurement of the intrinsic viscosity by means of the one-point method will be desirably performed with dilute solution at as low a velocity gradient as possible.
Even the most dilute solution of a dissolving pulp for viscose in CAM (0.522g/100ml) in the present work exhibits non-Newtonian behavior, suggesting that the current method (JIS P 8101) must be employed carefully for determining the relative viscosity of cellulose having a higher degree of polymerization.
