(259a) Electrostatic Charge Generation Due to Shear Deformation of Pharmaceutical Powders

In powder handling operations, such as pneumatic conveying, sieving and milling, particles make frequent contacts between themselves and the walls of the processing equipment. During these interactions, electrification of particles takes place, commonly known as tribocharging.

Electrostatic particle charging is a common nuisance, as it is a contributor to many undesirable effects such as segregation, adhesion deposition or the blockage of pipelines and explosion. An important manifestation of this problem in the pharmaceutical industry is a susceptibility to agglomeration in various processes such as tabletting and encapsulation. Pharmaceutical powders are usually semiconductors or insulators of a small particle sizes and low bulk densities which provide ideal conditions for electrostatic effects.

Tribocharging due to impact has been investigated extensively. However for a number of cases associated with powder flow the powder bed is sheared and this can also cause tribocharging, but little work has been reported in the literature on this topic. This paper focuses on investigating tribocharging of bulk powders under shear deformation. Electrostatic charge generation is quantified by applying a shear strain to a bed of pharmaceutical powders using an annular shear cell. The shear cell has been electrically isolated and the electric current through the earth is measured by an electrometer. The ongoing work on the analysis of current as a function of the applied normal load and shear strain will be presented.