Effect of friction between powder and tooling on the die-wall pressure evolution during tableting: Experimental and numerical results for flat and concave punches.

Tablet final properties are mainly determined during the compaction process by the evolution of the stresses applied to the powder. Any process or product parameter that may influence this stress evolution may have a direct impact on the tablet final properties. In this article, we studied the influence of the friction between the tooling and the powder on the evolution of the die-wall pressure during compaction using flat and concave punches. Experimental studies were performed on microcrystalline cellulose as well as numerical studies using finite element method (FEM) simulation. Both methodologies indicate that increasing the friction between the powder and the tooling promotes an increase in the die-wall pressure during tableting. This is in contradiction with results that can be found in the literature. Moreover, the results of this study showed that for flat punches, the stress evolution is mainly driven by the die/powder friction. On the contrary, for concave punches, changing the punches/powder friction have also a consequence in the evolution of the die-wall pressure. This could have practical consequences in sticking situations where, due film formation on the punches, the friction between the punches and the powder may change during tableting.