Rheology of Plastisols of Poly(Vinyl Chloride)

Abstract

Abstract The viscosity of PVC plastisols is seen to be affected by numerous variables. Increase in concentration of the resin causes the viscosity to rise, with the increase being more abrupt at the higher concentrations. Deviation from Newtonian behavior also increases with concentration. Decrease in the size of particles results in an increase in viscosity, the effect being more pronounced at low shear rates. Broadening the distribution of particle sizes results in a decrease in viscosity. Porous particles yield plastisols with higher viscosity as compared to nonporous compact particles. The type of plasticizer also affects the viscosity. A plasticizer which is a better solvent for PVC (low value of polymer-solvent interaction parameter, χ) results in a higher viscosity due to an increase in the amount of dissolved polymer. Additives such as alcohols and soaps affect the viscosity in an, as yet, unknown way. Fillers, heat stabilizers, and pigments also increase the viscosity. With increasing temperature, the viscosity first decreases, passes through a minimum and then increases until gelation. With further rise in temperature the viscosity again decreases and then levels out before degradation occurs. In future work, particular emphasis needs to be given to the understanding of the basic mechanism involved in the effect of additives on the flow behavior. Systematic experiments with a range of well-defined particle sizes and over a wide range of shear rates are also needed. A better understanding of the factors affecting the behavior of plastisols will go a long way in changing the art of plastisol formulation to a science.