An analysis of a simple test device for tribo-charging of bulk powders

A simple device for characterisation of the tribo-charging propensity of powders has been developed at the University of Leeds, where a small amount of powder is placed inside a 10 ml container, which is shaken by reciprocal strokes in a horizontal direction. Several containers with different materials have been made: stainless steel, polytetrafluoroethylene (PTFE) and glass. The charge on the powder is measured using a Faraday cup connected to an electrometer. The charge is measured before and after the shaking process.

The main objective of this work is to analyse the operation of this simple test device by investigating the behaviour of α-lactose monohydrate, hydroxy propyl cellulose (HPC) and a 50:50 binary mixture (by mass) of these two powders with various surfaces that are most commonly used in the pharmaceutical industry. The experiments are carried out in controlled environmental conditions and using different shaking times together with different shaking frequencies of 10, 20 and 30 Hz.

The experimental results show that -lactose monohydrate and HPC particles have the highest magnitude of charge at 20 Hz frequency against all surfaces tested. This is surprising, as it is intuitively expected that higher charges should be produced at 30 Hz, given other conditions. The dynamic movement of particles within a shaking container vary with frequency. This results in a varied amount of particle-wall contacts which affects particle charging.