Abstract
The application of terahertz pulsed imaging (TPI) in an in-line configuration to monitor the coating thickness distribution of pharmaceutical tablets has the potential to improve the performance and quality of the spray coating process. In this study, an in-line TPI method is used to measure coating thickness distributions on pre-coated tablets during mixing in a rotating pan, and compared with results obtained numerically using the discrete element method (DEM) combined with a ray-tracing technique. The hit rates (i.e. the number of successful coating thickness measurements per minute) obtained from both terahertz in-line experiments and the DEM/ray-tracing simulations are in good agreement, and both increase with the number of baffles in the mixing pan. We demonstrate that the coating thickness variability as determined from the ray-traced data and the terahertz in-line measurements represents mainly the intra-tablet variability due to relatively uniform mean coating thickness across tablets. The mean coating thickness of the ray-traced data from the numerical simulations agrees well with the mean coating thickness as determined by the off-line TPI measurements. The mean coating thickness of in-line TPI measurements is slightly higher than that of the off-line measurements. This discrepancy can be corrected based on the cap-to-band surface area ratio of the tablet and the cap-to-band sampling ratio obtained from ray-tracing simulations: the corrected mean coating thickness of the in-line TPI measurements shows a better agreement with that of the off-line measurements.
Original language | English |
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Pages (from-to) | 34-45 |
Number of pages | 12 |
Journal | Chemical Engineering Science |
Volume | 192 |
Early online date | 18 Jun 2018 |
DOIs | |
Publication status | Published - 31 Dec 2018 |
Keywords
- coating thickness variability
- discrete element method
- pharmaceutical coating
- terahertz in-line sensing
- terahertz pulsed imaging
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Profiles
-
Daniel Markl
- Strathclyde Institute Of Pharmacy And Biomedical Sciences - Senior Lecturer
Person: Academic