Effect of magnesium stearate on bonding and porosity expansion of tablets produced from materials with different consolidation properties

The negative effect of magnesium stearate on tablet strength is widely know n. This strength reduction is always considered to be the result of reducti on of interparticle bonding. It is also known that interparticle bonding af fects relaxation of tablets. Relaxation increases with decreasing bonding. Microcrystalline cellulose is an example of a material with a high lubrican t sensitivity, which effect is caused by its plastic deformation behavior d uring compression. This paper shows for microcrystalline cellulose that the porosity under pressure was equal for unlubricated tablets and for tablets containing 0.5% magnesium stearate. This points to equal densification pro perties. The lubricated tablets show, however, a much larger relaxation tha n the tablets without magnesium stearate, This difference can be ascribed t o the reduction of interparticle bonding by the lubricant, because a strong interparticle bonding counteracts tablet relaxation. In contrast to microc rystalline cellulose, aggregated gamma-sorbitol (Karion Instant) has a low lubricant sensitivity. Both porosity under pressure and tablet relaxation w ere found to be equal for lubricated and unlubricated sorbitol tablets. Thi s phenomenon is caused by the particle structure of gamma-sorbitol. During compression, a lubricant film will be destroyed by fragmentation of the sor bitol aggregates. For this reason, magnesium stearate will hardly affect th e interparticle bonding between sorbitol particles and hence have only a sm all or no effect on tablet relaxation. (C) 1999 Elsevier Science B.V. All r ights reserved.