Magnesium stearate is present as an excipient in more than half of tablet formulations. Most frequently it has a lubricant or antiadherent function, and at the same time it improves flow properties of tableting blends. If magnesium stearate is not used carefully, it can prolong
tablet disintegration time and retard dissolution profile. This is caused by overlubrication effect which means that particles of tableting blend are overly coated with magnesium stearate. Due to its high hydrophobicity, magnesium stearate hinders wettability of tablet surface with water. Magnesium stearate can also have deleterious effects on mechanical strength of tablets, since it prevents the formation of strong bonds during compaction. Lubrication potential of magnesium stearate depends on its physico-chemical properties, its quantity in tableting blend, properties of substrate particles, and mixing conditions of the tableting blend. In this master thesis the physico-chemical properties of two magnesium
stearate batches from different manufacturers were studied. We discovered that they differ in specific surface area, particle size distribution, particle morphology, degree of cristallinity, pseudopolymorphism and in polar component of free surface energy. These properties have a significant impact on the efficacy of lubrication. The results of this master thesis show that the disintegration time extends and the friability
of tablets increases with longer mixing time of magnesium stearate into the tableting blend on laboratory scale. The effect on reduction of tablet hardness was not observed. Furthermore, the mixing of magnesium stearate into the tableting blend occurs also in the force feeder of a rotary tablet press because of the rotating paddles. Longer residence time of tableting blend in a force feeder leads to longer disintegration time of a tablet and slower dissolution profile. Friability of tablets in this case increases.Lastly, we used Design of Experiment to study the effect of force feeder paddles' rotation speed on tablet properties. The disintegration time is significantly longer if the paddles rotate faster. This effect was further confirmed on the industry scale tablet press where higher tableting speeds were used.