Indices of tableting performance

Abstract

Indentation hardness P and tensile strength σ T measurements are used to formulate three dimensionless parameters, indices, that characterize the relative tableting performance of individual components and mixtures. The Strain Index P/E′ is obtained from the dynamic indentation hardness experiment. E′ is the reduced Young's Modulus. P/E′ may be interpreted as indicating the relative strain during the elastic recovery that follows plastic deformation or as the relative potential for strain energy to develop at the tip of a defect. The Bonding Index σ T/p is interpreted as indicating the relative survival during decompression of the areas of true contact that formed at maximum compression. The Brittle Fracture Index is obtained by comparing the tensile strength of tablets with and without a hole at their center. The rationale for all three indices is given. This includes a discussion of processes at the ‘isthmus’ regions between contacting particles. It is concluded that plastic deformation in these regions during decompression is necessary to produce significant bond strength. The use of the indices as formulation guides is discussed.