STUDIES ON DIRECT COMPRESSION OF TABLETS 22 INVESTIGATION OF STRENGTH INCREASE UPON AGING AND BONDING MECHANISMS FOR SOME PLASTICALLY DEFORMING MATERIALS

Strength increase as a function of time has been measured for tablets of five plastically deforming materials. The addition of small amounts of magnesium stearate was also tested for all materials in this context. The effect of ageing was evaluated by measuring the radial tensile strength immediately after compression and again after 2 days storage. The contribution of bonding with intermolecular forces as compared to bonding with solid bridges capable of penetrating the lubricant film was evaluated. Stress relaxation resulting in increased areas of interparticulate attraction was suggested to be a common denominator for strength increase in the unlubricated compacts. Solid bridges contributed to the strength increase upon ageing only for sodium chloride. Bonding with intermolecular forces seems in general to be the dominating bonding mechanism for the investigated materials. © 1990.