On the links between elastic constants and effective elastic behavior of pharmaceutical compacts: importance of poisson's ratio and use of bulk modulus.

The elastic properties of pharmaceutical powders and compacts are of great interest to understand the complex phenomena that occur during and after the tableting process. The elastic recovery after compression is known to be linked with adverse phenomena such as capping or delamination of tablets. Classically, the elastic behavior is modeled using linear elasticity and is characterized using only Young's modulus (E), often by using a value extrapolated at zero porosity. In this work, four pharmaceutical products were studied. The elastic behavior of compacts obtained using a large range of applied pressure was characterized. First, it was found more suitable to use apparent elastic moduli than extrapolations at zero porosity. Then, the results indicate that there was not always a good correlation between the values of Young's modulus and the actual elastic recovery of the compacts. Poisson's ratio (v), which differs from one product to another and is porosity-dependent, must be taken into account. Finally, the bulk modulus (K), which combines E and v, was shown to be well correlated with the elastic recovery of the compacts and can be considered as a relevant parameter to characterize the elastic behavior of pharmaceutical compacts.