Arising of electrostatic charge in the mixing process and its influencing factors

The aim of this work is to improve the understanding of how triboelectric charge arises on pharmaceutical powders and of how it can be influenced and controlled especially with respect to dry powder inhaler development. In the present work the triboelectric properties of mannitol are examined because very few literature treating this new alternative carrier material for dry powder inhalers is available. To study the very complex triboelectric charging process in a simple and controlled way mixing studies are carried out. The powder samples are blended in polypropylene and stainless steel mixing containers for defined durations using a tumble blender (T2F Turbula®, Willy A. Bachofen AG — Maschinenfabrik, Switzerland) and then poured into a Faraday cup where charge measurement is performed. Several influencing factors like mixing time, particle size, mixing container size and the addition of a fines fraction to the powder are studied. In contrast to other published literature the present work focuses on the new alternative carrier material mannitol and uses statistical tools like design of experiments (DOE) to check the significance of the influence of factors and also the interactions between the influencing factors. The study reveals a direct relationship between the arising charge and the container size as well as the fines fraction and an indirect relationship between the arising charge and the particle size. Further also three different charge dissipation scenarios are investigated. It is shown that charge dissipation to the atmosphere is negligible within an hour. Keeping the powder inside the mixing container allowing charge dissipation via the container walls is more effective. Additional grounding of the mixing container does not result in a significant enhancement of the dissipation process. This is because charge transport from the powder bulk to the mixing container walls is limited.