Effect of surface compositional difference on powder flow properties

Surface composition plays an important role in the cohesion/adhesion behavior of powders. Yet, the quantification of the major factors that affect powder kinematics is a challenge because of the surface composition heterogeneity of granular materials. This study aims to understand the mechanisms that drive cohesiveness in dry powders by evaluating the bulk flow performance of uniform size glass beads coated with distinct chemical components. Silica beads of 125, 180, and 250 pm were coated with corn starch, molasses, butter, or wheat gluten to reproduce the surface composition of food powders. Particle size and shape distributions, dynamic flow properties, shear flow properties, and compressibility profile of the coated materials were evaluated and compared with uncoated silica beads. The stability index, a dynamic flow property, ranged from 0.9 to 1.1 for all samples, which indicated a stable flow. Surface modified powders showed increasing bulk cohesion and higher compressibility indexes in comparison with the control samples. Specifically, butter and molasses coated powders had the highest specific energy, cohesion, and compressibility indexes, primarily, due to the higher magnitude of inter-particle interactions, lower bulk densities, and poor bed dilatancy. This study provides quantitative understanding on powder flow that will be important for smoother powder processing operations in which the surface compositional difference is of major interest such as hopper discharge, high shear mixing, and tablet compaction processes. (C) 2018 Elsevier B.V. All rights reserved.