On the Structural Integrity of Bilayer Tablets Upon Ejection

Using a model system (microcrystalline cellulose, dicalcium phosphate) we explore the origins of processing difficulties of bilayer tablets. Differences in the mechanical behavior during compaction result in differential expansion in the two layers which in combination with the stress singularity of bimaterial interfaces and the geometrical characteristics of the interface may lead to cracking or splitting of bilayer tablets during ejection. The effect of tamping is reviewed and a process robustness map is presented. Preliminary results on the effect of differential moisture absorption in the long term structural integrity of bilayer tablets will also be presented.