Particle Packing and Shape Effects on the Rheological Characteristics of Paper Coating Pigments, 1991 Coating Conference Proceedings

A method is described and used to infer particle packing and aspect ratio from viscosity measurements. Of three semiempirical equations compared, Eiler’s equation was found to give the most reliable information on particle packing and shape. The maximum packing fractions of clay slurries were found to be 0.5 volume fraction, while ground calcium carbonate slurries were close to 0.6. With more spherically-shaped ground calcium carbonate, the intrinsic viscosity in Eiler’s equation was measured close to 3, which is comparable to the theoretical value of 2.5 for nonrotating spheres. With high aspect ratio delaminated clays, the intrinsic viscosity was nearly 10. Polystyrene-butadiene latex binder is small in size compared with pigment particles, so the increase in viscosity with binder addition was found to be less than for an equivalent additional volume of solids pigment particles. When the effect of latex addition was calculated considering it part of the continuous phase, the maximum packing fraction was reduced with increasing binder content; however, the difference in the maximum packing fraction of one slurry to another is insensitive to binder addition.