Sensing Electrostatic Charge Generation During Granular Flow of Pharmaceutical Powders in a Flow Tester

Abstract

The purpose of this study is to investigate the triboelectrification of pharmaceutical powders during continuous flow in terms of electrostatic charge accumulation and dissipation as the powder tumbles in a rotating cylinder. The intensity of electrostatic signal output, its frequency during particle interactions as the powder flows, and the dependency of particle charge on the shear rate which was captured by varying the rotational speed of the cylinder were studied. Various pharmaceutical blends were run at different rotational speeds in a flow tester and their charge accumulations and dissipations during the powder flow were captured using an electrometer and an oscilloscope. An interesting finding showed that the charge frequency generated during the powder flow was related to the powder flowability. The deterioration of powder flow was found to increase the frequency of voltage spikes. Voltage frequency from charge accumulations during powder flow increased with a corresponding increase in rotational speed of the cylinder. At low shear conditions, cohesive powder exhibited higher voltage peak intensity than the free flowing powder. The voltage charge intensity measured from the powder bed correlated to the powder flow of pure component powders. Voltage peak intensity for cohesive powders was found to decrease with time but remained stable for free flowing powders. Interestingly, voltage peak intensity for cohesive powders decreased with rotational speed but increased in the case of free flowing powders. A stronger correlation between electrostatic charge and powder flow existed in pure component powders than formulations containing additives.