DEFORMATION KINETICS OF POTASSIUM-BROMIDE CRYSTALS PREDICT TABLET STRESS-RELAXATION

A model relating the interparticulate contact stress within a tablet m atrix with the compaction stress was developed previously to permit th e nonlinear deformation kinetic analysis of the viscoelastic behavior of pharmaceutical tablets with the known properties of the tablet cons tituents. The present research was undertaken to determine whether the inverse operation (i.e., using tablet stress relaxation to determine single crystal properties) was possible. The stress relaxation of pota ssium bromide (KBr) compacts was evaluated as a function of temperatur e and relative density, and an attempt was made to calculate the defor mation kinetic parameters. The stress relaxation of KBr did not fit th e model under ambient conditions for two reasons: ( I) KBr has two sli p systems with approximately the same shear stress at room temperature ; and (2) KBr strain-hardens. When these complications were taken into consideration, the stress relaxation behavior could be explained. The refore, whereas single crystal tests are capable of yielding parameter s that can be used to predict compact behavior, the inverse process of quantifying fundamental material parameters from compact behavior is problematic due to the difficulty of determining, a priori, all the pr ocesses that operate simultaneously.