Rheology in dispersion testing and mill base formulation optimization

Abstract

Rheology offers only slight advantages in terms of mill base formulation, because of the comparatively low shear rates available on existing viscometers and the considerable changes in mill base rheology which occur during the milling cycle. These changes can however be utilised as a means of dispersion testing and satisfactory and reproducible “milling isotherms” can be obtained for a wide variety of dispersion and size reduction operations. It would seem possible to characterise grinding and dispersion by changes in mill base rheology in that grinding shows an increase in non-Newtonian characteristics whereas dispersion shows a decrease in these characteristics. Care must be taken to ensure that controlled pretreatment of the samples is adopted be ore satisfactory results can be ensured, but extensive storage periods tend to magnify differences between samples.