Compaction properties of L-lysine salts

Purpose. To examine the effects of salt form, i.e., different anions with a common cation (L-lysinium), on compaction properties and to identify the factors that determine the tensile strength of tablets. Methods. L-Lysine salts with the following anions were compressed at various pressures: acetate, monochloride, dichloride, L-aspartate, L-glutamate (dihydrate), and L-lysine (zwitterionic monohydrate). The yield strength of each salt was evaluated from the "out-of-die" Heckel plot. Results. At low compaction pressures, the tensile strength of the compacts increases linearly with increasing compaction pressure. Simultaneously, the compact tensile strength decreases exponentially with increasing yield strength of the salt. However, at high compaction pressures, the compact tensile strength is determined by the interparticulate bonding strength and not by the yield strength. The compact tensile strength, extrapolated to zero porosity, increases linearly with increasing melting temperature of the salts. Conclusions. The counterion affects the tableting properties of L-lysine salts. The tensile strength is controlled by both the yield strength and the interparticulate interaction strength with the former predominant at low compaction pressures and the latter predominant at high compaction pressures. The melting temperature of each L-lysine salt is a good indicator of the tensile strength of its compacts at zero porosity.