Abstract
The effect of type and amount of thickener on the shear and extensional rheological properties of paper coating colors was studied. A coarse delaminated kaolin clay was used as pigment and either a carboxy methylcellulose (CMC) or an associative gum was used as thickener. The shear properties were evaluated with a stress controlled rheometer and the extensional properties were obtained at high strain rates using an orifice flow meter. The apparent extensional viscosity was compared to the shear viscosity in terms of the Trouton ratio, which was shown to exceed considerably the theoretical value of 3 expected for Newtonian fluids. Suspensions formulated with the associative gum exhibited more pronounced strain hardening at high strain rates than those prepared with CMC.
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