The relationship among tensile strength, Young's modulus, and indentation hardness of pharmaceutical compacts

Mechanical properties of pharmaceutical materials, e.g., Young's modulus (E), indentation hardness (H), and tensile strength (σ_t), play an important role in powder compaction process. However, few studies investigated the relationship among these parameters and consequence for tablet compression. Using microcrystalline cellulose, a plastic material, and dibasic calcium phosphate anhydrate, a brittle material, as well as their binary mixtures, we systematically examined the relationship among the three properties. It was found that Young's modulus was proportional to indentation hardness (H/E ≈ 0.036) regardless of the composition and compaction pressure. For a given material, tensile strength was also proportional to E and H but the relationship varied with materials. Higher E and H were required to attain the same σ_t for a more brittle material.