Steady Shear Rheological Behavior of PVC Plastisols

The rheological behavior of PVC emulsion resin plastisols was investigated in steady shear flow. The shear rate dependence of the plastisol viscosity was influenced by (1) Brownian diffusion, (2) partial dissolution of the suspended resin, and (3) particle-particle interactions. Partial dissolution of polymer from the resin particle surface resulted in a particle-size-dependent increase in the continuous phase viscosity. At a disperse phase volume fraction of O = 0.2 a non-Newtonian master curve was obtained for the relative viscosity of several plastisol systems as a function of Peclet number, independent of plasticizer or particle radius. These plastisols behaved (at O = 0.20) as suspensions of rigid spheres subject to Brownian motion. The magnitude of the deviation from Newtonian behavior appeared to be influenced also by the strength of particle—particle interactions. Viscoelastic response was observed in concentrated plastisols. At O = 0.54 relaxation time versus shear rate was found to be independent of plasticizer and of resin particle size. Large discontinuous increases in shear and normal stresses were observed in a critical shear rate range.