Prediction of Air Entrapment in Tableting: An Approximate Solution.

An approximate solution is presented for the prediction of air entrapment during tableting. Assuming weak coupling of the deformation of the solid phase, the flow of interstitial air and a set of reasonable additional geometric assumptions, the general problem is reduced to 1 dimension. Experimental values of air permeability through tablet specimens of commonly used pharmaceutical excipients were obtained using a 3D printed test cell outfitted to a powder rheometer. Using these values, combined with a numerical solution of the governing partial differential equation, parametric studies are presented that demonstrate the importance of permeability, compaction speed, tablet size, and punch-die tolerance on air entrapment. In addition, a first-order approximation of the role of entrapped air on the measured radial tensile strength of formed tablets is presented.