Electrostatic charging during a melt agglomeration process.

Lactose monohydrate was melt agglomerated in an 8-l high shear mixer using stearic acid, polyethylene glycol (PEG) 3000, and a mixture of stearic acid and glycerol monostearate as meltable binders. Electrostatic charging during processing at relative air humidities of 35 and 75%, respectively, was estimated from the voltage of a monitoring probe inserted into the mixer. Stearic acid produced a high level of electrostatic charges, whereas PEG 3000 gave rise to a markedly lower level. Addition of glycerol monostearate to the stearic acid reduced the level of electrostatic charges. A correlation was found between the resistivity of the binder and the level of electrostatic charges in the material. With the stearic acid and the binder mixture, the level of electrostatic charges was higher at a low air humidity. The amount of adhesion to the bowl was found to depend on the level of electrostatic charges.