The effect of moisture content on the energies involved in the compaction of ibuprofen

The influence of moisture content and compression speed on the ejection force, plastic and elastic energies of ibuprofen was measured. It was found that moisture can significantly reduce the force required to initiate ejection by the breaking of tablet/die-wall adhesions. At all compression speeds, an increase in moisture content resulted in a marked reduction in the ejection force of ibuprofen compacts. The plastic energy was found to increase with moisture content up to 2.5% w/w, ascribed to an increase in particle-particle interactions. Subsequent decrease in plastic energy at higher moisture contents was probably due to a decrease in particle interaction due to the moisture separation of the particles of ibuprofen. The elastic energy was found to decrease with increasing moisture content up to about 2.5% w/w. This is believed to be due to the strong bonding of particles, brought about by moisture facilitating the formation of interparticle hydrogen bonding and so reducing the interparticle separation. Subsequent increase of elastic energy with increasing amount of moisture beyond 2.5% w/w was thought to be due to the formation of multilayers of water at the surfaces of the particles. This excess moisture increased the elastic energy, by decreasing particle-particle interaction.