Rheology of synthetic latex. I. Test of some flow equations

Abstract

Measurements made with both concentric cylinder and capillary viscometers show that type III synthetic latex is Newtonian at concentrations below ca. 25% solids, and non-Newtonian above. Analysis of the data demonstrates the absence of either a yield point at low shearing stresses or a limiting viscosity at high, ruling out Bingham body behavior. The linearity of logarithmic plots of the data indicates the applicability of the exponential flow equation of Farrow, Lowe, and Neale for the conversion of experimental observables to rate of shear—shearing stress values. However, above ca. 45% solids, separate exponential flow equations must be used at high and low shearing stresses. A composite rate of shear—shearing stress plot, including values obtained from three capillaries and the concentric cylinder viscometer, yields a single smooth curve, confirming the validity of the conversion procedure. Comparison of values of the two constants of the exponential equation, as determined independently using the capillary and concentric cylinder instruments, shows agreement between the two types of viscometer. Similar results have been observed for other latices, both synthetic and natural.