Newtonian behaviour of sheared aqueous carboxymethylcellulose solution on aging

Abstract

AbstractThe effects of microbiological attack on the rheological properties of sodium carboxymethylcellulose (NaCMC) solutions are described. The effect of aging on the viscosity of aqueous NaCMC solution was studied by means of a Brookfield viscometer. An aqueous NaCMC solution was allowed to age and was subjected to shearing at different time intervals. Dilatant rheological properties were observed in contrast to the usually pseudoplastic behaviour of a normal NaCMC solution. This is attributed to the effect of shear‐induced recombination of NaCMC macromolecular crystallites produced as a result of chain scission of NaCMC molecules during aging. The recombination of the crystallites gives higher values of viscosity at higher shear rates. A five months aged sample when subjected to shearing for a period of 20 h exhibits different behaviour. After prolonged post‐shearing of this sample, the viscosity measured at shear speeds of 10 rpm and 20 rpm at 72 h and 102h approaches a common value for post‐shearing period. The approach to the Newtonian character is attributed to the shear‐stress‐induced breakdown of the crystalline aggregates. These studies reveal that the aging effects on NaCMC solution have a drastic influence on the rheological properties.