Mechanics of tablet formation: a comparative evaluation of percolation theory with classical concepts

The present study is based on the fundamentals of percolation theory and its application in understanding compression and compaction of powder materials. Four materials, i.e. carbamazepine, microcrystalline cellulose, crospovidone and croscarmellose sodium, with dissimilar deformation and compaction behavior were selected to validate the hypotheses of percolation phenomenon. The values of two percolation thresholds, i.e. bond and site, corresponding to the lower and intermediate compression pressures, were determined using Heckel equation. The compactibility of powder materials was evaluated using classical models as well as the power law equation. The values of percolation thresholds were found to better assess the deformation behavior of powder materials compared to the values of mean yield pressure. The power law equation demonstrated better prediction of compactibility of powder materials compared to the classical models. The value of the critical exponent, q, determined using power law equation by plotting tensile strength vs. normalized relative density of powder compacts was found to be closer to the theoretical value of 2.70. Furthermore, the theoretical knowledge of percolation thresholds of individual powder components in the binary mixture was found to be helpful in improving compaction properties of the poorly compactible material, i.e. carbamazepine. Thus percolation theory can be helpful in predicting compression and compaction behavior of powder materials and serve as a potent tool for the successful design of tablet formulations.