Modelling of the void space of tablets compacted over a range of pressures

A previously developed computer model, named Pore-Cor, has been used to simulate the changes in the void-space dimensions which occur during the compaction of tablets over a range of pressures. The tablets were made by mixing pharmaceutical grade crystalline lactose and an anti-inflammatory compound in the proportion 4:1. Compacts were made by placing a weighed amount of the mixed powder into a stainless-steel die and applying pressure with a hand-operated calibrated hydraulic press. Compacts were prepared at eight pressures over the hydraulic pressure range 1 to 8 ton in-2 (15.4-123.2 MPa) in 1 ton in-2 increments. Mercury-intrusion curves were measured for the eight samples by use of a porosimeter and the Pore-Cor package was then used to simulate the mercury-intrusion curves and generate void-space models of the correct porosity. The experimental and simulated characteristic throat diameter, the experimental and simulated porosity, and the simulated permeability of the tablets have all been shown to follow expected trends. The successful modelling of void-structure parameters, which are difficult or impossible to measure experimentally, opens the way to an improved understanding of the strength of compacts.