The effect of moisture on the properties of ibuprofen tablets

The crushing strengths of ibuprofen tablets produced at compression speeds ranging from 15 to 240 mm/s with varying moisture contents 24 h after ejection have been investigated. Increasing moisture content up to about 2.5% progressively increased compact strength probably due to the hydrodynamic lubrication effects of moisture promoting optimum transmission and utilisation of compaction force and the formation of a moisture film around the drug. This moisture film, which was tightly bound, could be regarded as a part of the surface molecular structure of the particles and facilitated the formation of inter particle hydrogen bonding. This bonding produced an increase in the van der Waals forces and so smoothed out the surface microirregularities and reduced interparticle separation. At higher moisture contents beyond 3.5% w/w, a decrease in tablet strength was observed attributed to hydrostatic resistance of the excess moisture in the void spaces producing force transmission which in turn reduces particle-particle contact areas, surface energy and adhesive forces. It was found that compressibility of ibuprofen powder was strongly determined by the level of moisture present during consolidation and that a moisture content of 1-3.5% w/w at the slowest compression speed of 15 mm/s and a compression force of 10 kN produced tablets with optimal crushing strength and minimum capping.