EFFECTS OF AIR ENTRAINMENT ON THE RHEOLOGY OF CONCENTRATED SUSPENSIONS DURING CONTINUOUS PROCESSING

Samples of a concentrated suspension were systematically collected from the mixing volume of a continuous processor. The large amplitude oscillatory shear behavior of the samples was found to be significantly affected by the screw configuration employed and the location. Microstructural analyses employing nuclear magnetic resonance imaging, wide-angle X-ray diffraction and X-ray radioscopy revealed substantial entrainment of air into the suspension during continuous processing. The volume fraction of the entrained air increased with geometries and operating conditions leading to partially full channels. Overall, air entrainment is identified as a dominant factor in the development of the microstructure and the rheology of concentrated suspensions and should be considered in their optimum processing.