Segregation of Formulated Bulk Powders due to Electrostatic Effects

Particle electrification is a common phenomenon that occurs in many powder handling industries such as pharmaceuticals and detergents etc. The unit operations involved in the manufacture of pharmaceutical formulations frequently subject particles to frictional sliding and impact against processing surfaces, giving rise to tribo-electric charging. Pharmaceutical materials, in particular, are susceptible to electrostatic charging due to their low bulk density, small particle size and often irregular shape and electrically insulating nature. The electrostatic charge may cause particles to adhere to container surfaces leading to a loss of powder through deposition; however the problem often extends further and affects the end products’ quality. Segregation can also occur when powders have been subjected to tribo-electrification. In this paper we investigate whether such adhesion resulting from the electrostatic charging could give rise to the segregation of components within a binary mixture. Binary mixtures comprising of α-lactose monohydrate (α-LM) and hydroxypropyl cellulose (HPC) were firstly tribo-charged and then the wall adhered particles were separated by a selective dissolution of one component and the filtration of the non-dissolving component, followed by a gravimetric analysis. The findings reveal that a considerable level of segregation can take place on the wall-adhered particles.