(13c) Single Drop Impact on Heterogeneous Powder Beds through Granule Formation Mechanisms, Drop Penetration Time, and Granule Morphology and Structure

Authors: 
Gao, T., Arizona State University
Singaravelu, A. S. S., Arizona State University
Chawla, N., Arizona State University
Emady, H. N., Arizona State University
Wet granulation is a process by which agglomerates are formed using liquid to bind particles together. It is important in particulate applications like pharmaceuticals, detergents, agricultural chemicals and catalysts, with the purpose to achieve particle size enlargement, create dosage uniformity and improve the powder's flow properties. Specifically, the interaction between liquid and heterogeneous mixtures, where the powders have different wettabilities, has a lot of relevance in the pharmaceutical industry, where active ingredients are often relatively hydrophobic. Within granulation, single drop granule formation is of large interest, by revealing the fundamentals of the interaction between liquid and powders. Parameters like drop penetration time and granule formation mechanisms have been studied in single drop granulation to better quantify the drop impact and subsequent granule formation process. Studying the granule morphology and content uniformity can also help understanding the structure and property of granules, thus improving their quality. Therefore, it is novel to combine drop penetration time, granule formation mechanism, and granule characterization together to achieve a comprehensive map of the granulation process.

In this work, single drop impact of liquid on a static powder bed was studied to investigate the granule formation mechanism, droplet penetration time, granule content uniformity, as well as the characterization of granules (morphology and internal structure). Water was used as the liquid binder and two pharmaceutical powders, microcrystalline cellulose (MCC) and acetaminophen (APAP), were mixed to make heterogeneous powder beds of varying compositions. The complete drop impact and penetration was recorded with a high-speed camera. Three granule formation mechanisms identified previously [1] have occurred: Spreading, Tunneling, and Crater formation. At a low impact height, Spreading occurred for mixtures with an APAP amount of less than 25%, while there is a transitional regime from Spreading to Tunneling when the APAP amount increased from 25% to 50%. Tunneling dominates from 50% to 100% of APAP proportion. Crater formation occurred at a high impact height for the materials that exhibit Spreading at low impact height. The granule morphology and the internal structure were characterized by a prism method with image analysis [1] and micro-CT, respectively. The content uniformity was characterized via UV-vis spectrometry by measuring the UV absorbance of the APAP dissolved in ethanol. It is believed that the mean particle size of the powder bed is the predominant factor in influencing the granule formation mechanism, drop penetration time, and granule properties.

[1] Emady, H. N., Kayrak-Talay, D., Schwerin, W. C., & Litster, J. D. (2011). Granule formation mechanisms and morphology from single drop impact on powder beds. Powder technology, 212(1), 69-79