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

Abstract

Mechanical properties of pharmaceutical materials, e.g., Young’s modulus (E), indentation hardness (H), and tensile strength (σ), 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 for a more brittle material.

 

Highlights

  • A systematical investigation of the correlation among Young’s modulus, hardness, and tensile strength of compacts
  • Materials spanning a wide range of mechanical properties were investigated.
  • Young’s modulus is proportional to hardness regardless of the material.
  • More brittle materials require higher Young’s modulus and hardness to attain the same tensile strength.

Conclusions

All three mechanical properties, E, H, and σt, increased exponentially with decreasing porosity for all materials. However, the mechanical strength of more brittle DCPA was more sensitive to changing porosity and exhibited a higher mechanical strength at zero porosity. Because of the interplay between bonding area and intrinsic mechanical strength, the compact

mechanical strength vs. compaction pressure curves between a given pair of materials crossed at a certain pressure. Consequently, more plastic MCC formed compacts that were mechanically stronger at low compaction pressures, but mechanically weaker at higher pressures. In addition, E and H were proportional to each other regardless of the material composition. It is, therefore, possible to infer one from the other. At a given E or H, the σt of a more plastic material is higher.

More

Graphs show the analysis results of plastic MCC and brittle DCPA for their mechanical properties
Analysis mechanical properties of plastic MCC and brittle DCPA

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