Drying is one of the standard unit operations in the pharmaceutical industry and it is important to become aware of the circumstances that dominate during the process. The purpose of this study was to test microcapsulated thermochromic pigments as heat indicators in a fluid bed drying process. The indicator powders were manually granulated with α-lactose monohydrate resulting in three particle-size groups. Also, pellets were coated with the indicator powders. The granules and pellets were fluidized in fluid bed dryer to observe the progress of the heat flow in the material and to study the heat indicator properties of the indicator materials. A tristimulus colorimeter was used to measure CIELAB color values. Color indicator for heat detection can be utilized to test if the heat-sensitive API would go through physical changes during the pharmaceutical drying process. Both the prepared granules and pellets can be used as heat indicator in fluid bed drying process. The colored heat indicators give an opportunity to learn new aspects of the process at real time and could be exploded, for example, for scaling-up studies.
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Niina Kivikero is acknowledged for advising with fluid bed dryer. Outi Pajunen is thanked for her assistance with the coating equipment. The authors also thank Henri Salokangas for language consulting.
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Lakio, S., Heinämäki, J. & Yliruusi, J. Colorful Drying. AAPS PharmSciTech 11, 46–53 (2010). https://doi.org/10.1208/s12249-009-9351-x
- colored heat indicator
- fluid bed drying
- tristimulus colorimetry