The coefficient of restitution of some pharmaceutical tablets/compacts.

When tablets collide during manufacturing and handling operations they rebound with a force and velocity that is determined by the collision conditions and the properties of the materials. This collision-rebound behavior of solid bodies can be described using a parameter known as the "coefficient of restitution" (CoR). In this work, the CoR of a range of pharmaceutical tablets/compacts is measured using a simple "drop test", and the influences of material properties (elastic modulus, solid fraction, etc.) and collision conditions (substrate, energy/speed, etc.) are investigated. The compacted pharmaceutical materials have CoR values that range from 0.4 to 0.9, and the CoR generally increases with increasing compact solid fraction. The CoR varies with the mechanical properties of both colliding bodies and is lower for more plastic collisions and higher for elastic collisions. This behavior is consistent with theories developed for non-pharmaceutical solids, and can be predicted provided that the elasticity and yield stress of the samples are treated as porosity dependent parameters. In this case, the CoR varies with the impact velocity nearly raised to the fourth root. Having established a simple and reproducible test for the CoR of pharmaceutical compacts and tablets it should be possible to create more accurate engineering models and computer simulations of tablet manufacturing and packaging operations.