Improving Powder Flow Properties of Citric Acid by Crystal Hydration

A batch of poorly flowing citric acid anhydrate was exposed to 69.9% relative humidity to prepare pure monohydrate with nearly identical particle size and morphology but different surface properties. Flow properties of the powders were tested using a ring shear cell. Results show the hydration can significantly improve flow properties of anhydrous citric acid. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:1744-1749, 2009