Effect of geometric structure and surface wettability of glidant on tablet hardness

The aim of this study is to investigate the effect of geometric structure and surface wettability of glidant on tablet hardness. Geometric structure is defined, in this work, as three-dimensional structure such as porosity, particle size and specific surface area. A variety of silica was incorporated in direct compressive fillers as glidant and mixed powder was compressed in single punch tablet machine with and without 0.5 wt.% magnesium stearate. Flowability of mixed powder was evaluated with Carr's index measurement. In the case of unlubricated compression, tablet hardness decreased as a function of additional concentration of silica. Reduction rate directly depended on surface coverage of silica over filler surface and hydrophobicity. Since surface coverage is related to geometric structure, it can be concluded that structural influence plays an important role to determine tablet hardness. While, in the case of lubricated compression, either water adsorption amount or geometric structure effects on tablet hardness. Increase of tablet hardness was observed only when hydrophilic porous and small size nonporous silica were added. All the other silica had deleterious effect on tablet hardness and in particular hydrophobicity strongly reduced tablet hardness.