Impact of Relative Humidity and Powder Filling Level on the Electrostatic Charging Behaviour of Different Capsule Types

Thomas Wutscher^1,2, Sarah Zellnitz¹, Mirjam Kobler³, Francesca Buttini^1,4, Laura Andrade⁵, Veronica Daza⁵, Alberto Mercandelli⁶, Stefano Biserni⁶, Susana Ecenarro Probst⁷, Johannes Khinast^1,2 &
 Amrit Paudel^1,2

¹ Research Center Pharmaceutical Engineering GmbH, Inffeldgasse 13, 8010 Graz, Austria

² Institute of Process and Particle Engineering, Graz University of Technology, Inffeldgasse 13, 8010 Graz, Austria

³ MEGGLE Excipients and Technology, Megglestraße 6-12, 83512 Wasserburg, Germany

⁴ Food and Drug Department, University of Parma, Parco delle Scienze 27, 43121 Parma, Italy

⁵ Laboratorios Liconsa, S.A. C/ El tejido 2, 19200 Guadalajara, Spain

⁶ MG2, Via del Savena 18, 40065 Pianoro, Bologna, Italy

⁷ Qualicaps Avda. Monte Valdelatas 4, 28108 Alcobendas, Madrid, Spain

Summary

Electrostatic charging of powders and solid surfaces (eg. capsule, inhalers) is a complex phenomenon that can negatively impact the performance of inhalation products by particle aggregation or segregation and adherence to surfaces. Besides that, tribo-charging plays a major role during cohesive/ fine powder processing and might undesirably impact certain process steps during DPI manufacturing. For example, excessive charging of capsule may during the capsule filling process may lead to process instability such as jumping and rocking and a higher number of throw out capsules.

The present study aims to understand the charging tendencies of different types of HPMC (thermally and chemically gelled) and gelatin capsules when transported over stainless steel and polyvinylchloride (PVC) surfaces, after storage at the relative humidity (RH) of 22% and 51%. Furthermore, the impact of powder fill level in the capsule on charging propensity was investigated. Results showed that all capsules charge positively, as such and on both steel and PVC surfaces. Charging tendency of capsules was in the range of 0.5 to 2.5 nC/g. Capsules appeared to get charged to the higher extent when passed over the PVC surface as compared to the steel surface. Both HPMC capsules tend to attain the lower extent of charge at 22% RH as compared to that at 51% RH. In contrast, the charge attained by gelatin capsules was independent to the storage RH. Compared to empty capsules, filled capsules show a lower extent of charging. These varying charging tendencies observed for different capsules passing over different surfaces as a function of fill level and storage RH can provide valuable information for the capsule-based DPI product and process development.