EFFECT OF SOLUBLE POLYMERS ON THE SHEAR AND EXTENSIONAL VISCOSITY CHARACTERISTICS OF A CONCENTRATED LATEX DISPERSION

The extensional viscosity characteristics of concentrated (45% w/w) la tex dispersions containing various soluble polymers have been determin ed by using an opposing jet rheometer. In all cases, the latex dispers ions were found to exhibit strain thinning behavior. Quantitative comp arison with shear now data, through calculation of the Trouton ratio, indicated the extensional viscosities of the dispersions to be 1-2 ord ers of magnitude greater than their shear flow viscosity at a comparab le deformation rate. For a given added polymer concentration, the late x dispersions containing cellulose ether type thickeners exhibited mor e pronounced shear and strain thinning characteristics and higher Trou ton ratios than those dispersions thickened with associative polyelect rolytes. Mathematical modeling of the shear and extensional viscositie s of the dispersions as a function of deformation rate has been undert aken by modification of the recent model of Barnes and Roberts.(1) The modified model was found to give an excellent fit of the shear viscos ity data and a reasonably good fit of the extensional flow data over s everal decades of deformation rate.