Bonding characteristics by scanning electron microscopy of powders mixed with magnesium stearate

The effect of degree of mixing on the bonding properties of blends of magnesium stearate and tablet excipients is shown to be dependent upon the compression behaviour and bonding mechanism of the excipient studied. Magnesium stearate exercises a maximum effect on excipients such as the starch derivative Amylose V, which undergoes complete plastic deformation without any fragmentation and is bonded by cohesion. The effect on excipients bonded by cold-bonding mechanisms after plastic flow of the crystals, as demonstrated for sodium chloride, is dependent on the extent to which clean, lubricant-free surfaces are formed during compression. The bonding properties of excipients such as dicalcium phosphate dihydrate, which undergo complete fragmentation under pressure, are practically uninfluenced by mixing with magnesium stearate.