Rheologic properties of semi‐rigid polymers for the example of cellulose nitrate, 2. Influence of molecular weight distribution on the flow curves of semi‐dilute solutions

Abstract

AbstractThe apparent viscosity η of semi‐dilute solutions of cellulose nitrate in ethyl acetate was measured as a function of shear rate at 20°C by rotational viscometry. The mass concentration c of the solutions was chosen such that the product between c and the intrinsic viscosity was 8 < c · [η] < 22, lying in the range of viscosity‐average degrees of polymerization covered by the employed samples 550 < DPη < 7600. The experimental flow curves were interpreted in terms of Graessley's theory for non‐Newtonian flow of polydisperse polymers. The polydispersities derived for five individual samples according to the theory of Graessley were used for calculating the resulting theoretical curves belonging to four binary mixtures each between two of them. The reasonable good agreement between calculated and experimental reduced flow curves of blends indicates consistency of the theory when applied to the present system of a semi‐rigid polymer. This and other results point to a flow behaviour of semi‐rigid cellulose nitrate being similar to that of linear flexible polymers.