Moisture sorption profiles and tensile strength of tableted phenobarbitone formulations

The tensile strength of tablets made from phenobarbitone and sodium phenobarbitone formulations after storage at increasing ambient relative humidity has been investigated. The moisture sorption and desorption profiles of the formulations were analysed for three locations of moisture: monolayer adsorbed moisture, normally condensed moisture and absorbed moisture. Maxima in tensile strength occur at moisture distributions determined by the disintegrant used. The changes in tensile strength have been explained in terms of changes produced in the interparticle separation, the range of the interparticle forces and changes in the ratio of the binding to diffusional forces, acting on the water molecules which are on the particles' surface.