Effects of storage conditions, formulation, and particle size on moisture sorption and flowability of powders: A study of deliquescent ingredient blends

Powder flow characteristics are important for the manufacturability and use of powders. Sticking and agglomeration resulting from exposure to relative humidity (RH) reduce flowability and may be influenced by powder composition and particle size and shape. Deliquescence is an important trait of water-soluble crystalline ingredients; however, few studies address the physical stability of powders relative to their deliquescence behavior. The objective of this study was to determine the impact of formulation, particle size, and storage conditions on the flowability and caking of deliquescent ingredient blends. Sucrose, fructose, sodium chloride, and citric acid were used. Treatment effects of formulation (single ingredient and binary blends at select ratios), particle size (50, 150, similar to 500 mu m), and storage time (0-28 days) on powder flow after storage at 10% and 30% RH below the deliquescence point were examined, and moisture sorption was monitored. Scanning electron microscopy imaging investigated the influence of particle size on the physical state of the solid following RH treatment. Glass spheres were studied to show the effects of particle size and RH on powder flow and moisture sorption isotherms of an insoluble solid with a hydrophilic surface. All treatment conditions affected the flowability of the powders. Interactions between treatments were also present, indicating that there are multiple factors associated with powder flowability and treatments may have synergistic effects. For a given formulation, particle size and the distance between the storage RH and deliquescence RH are particularly important to control in order to maintain powder flowability. (C) 2012 Elsevier Ltd. All rights reserved.