Development of drying-induced stresses in pharmaceutical granules prepared in continuous production line

The phenomenon of development of drying-induced stresses has been given a through consideration in the literature on drying of many products. At the same time, to the best of our knowledge, the open published sources contain no information on drying stresses in pharmaceutical granules prepared by continuous manufacturing methods. To study the appearance and evolution of drying-induced stresses in pharmaceutical granules during their production, in this work a theoretical model of drying of single wet pharmaceutical granule has been developed and successively validated by published experimental data obtained on ConsiGma™ continuous from-powder-to-tablet production line (GEA Pharma Systems). The results demonstrate that elevated temperatures of drying air result in faster drying process (which reduces the specific cost of the final product), but, on the other hand, quick drying leads to substantial drying-induced stresses which may damage the granule microstructure, resulting in cracking or even breakage of granules. The drying-induced stresses increase with drying temperature, porosity and size of dense non-hollow granules. The negative effects promoted by the drying-induced stresses should be taken into consideration when choosing operating conditions of continuous production lines including drying of pharmaceutical granules.