Lamination of pharmaceutical tablets due to air entrapment: direct visualization and influence of the compact thickness.

Capping and lamination are two problems that are often faced during the industrial manufacturing of pharmaceutical tablets. Several reasons have been proposed to explain these phenomena. Among them, air entrapment is supposed to play a role in some cases. Nevertheless, no direct proof were given to prove that air entrapment can promote lamination or capping and various publications have questioned this hypothesis. In this article, using a model product compacted on a compression simulator, a direct proof of the implication of air entrapment during lamination was given. In fact, at the surface of the compact, defects with a spherical shape, clearly linked with an entrapped bubble of air, began to appear on the surface of the compact just below the pressure level to which lamination was observed. Moreover it was also observed that, when the compact thickness increased, the lamination pressure decreased, meaning that the compact thickness can promote lamination. As a conclusion, contrary to what is said in some publications, air entrapment can be involved when problems of lamination occur, and, in this case, powder desaeration should be considered.