Fluid bed coating of minitablets and pellets with optimization of the process based on Taguchi method
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Small particles like pellets are coated in fluid bed systems. This method can be also feasible for minitablets but selection of optimal process parameters is complicated. The aim of the research was to optimize the coating process for minitablets and to compare the conditions with required for pellets. Minimum fluidization velocities (umf) for 2.0 and 2.5mm minitablets and for 0.7-0.8mm or 1.0-1.25mm pellets were determined experimentally. Additionally, the results were verified using the Ergun equation. The smallest relative differences between the calculated and experimental values of umf were obtained for P0.7 (4.6%), while the largest for MT2.5 (11.8%). To simplify optimization of the coating process, Design of Experiment (DoE) based on Taguchi method was employed. Selection of the best process parameters was based on the film thickness measurements for minitablets, while the sieve analysis was used for pellets to detect agglomeration. The best combination of process parameters resulted in uniform film thickness in minitablets, with RSD less than 15%, and the pellets batch containing only 0.25% of bonded particles. It was found that the largest impact on the uniform film deposition on minitablets had a spraying pressure, responsible for the size of coating mixture droplets. In case of pellets the most critical was the inlet air temperature. The presented research demonstrated that it was possible to achieve the best parameters of the coating process for minitablets and pellets by combining calculations of minimum fluidization velocity and Design of Experiment based on Taguchi method.
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