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The Influence of Tribo-Electrification on Bulk Powder Rheology

Researcher: Charley Jones

Principal Invesigator: Prof. Mojtaba Ghadiri

Co-Investigator(s): Dr Xiaodong Jia

Industrial Supervisor(s): Dr Steve Ward-Smith, Dr Paul Kippax, Dr Richard Storey

Project Sponsor(s): Malvern Panalytical, AstraZeneca, EPSRC

Status: Ongoing (2019 - )

 

Abstract

Triboelectric charging is the term given to the non-equilibrium based, surface phenomena of contact charging of particles, when accompanied by frictional tractions (rubbing, sliding, etc.). These particles can obtain electrostatic charges during transportation, due to either particle-particle or particle-wall interactions. Electrostatic charging can then lead to a number of undesirable processes due to adhesion, such as agglomeration, segregation and deposition on surfaces of powders, which in turn adversely affects their flowability. These issues commonly arise in process operation procedures such as: pneumatic conveying, comminution and mixing. Contact charging has been known for thousands of years, dating back to the ancient Greeks charging amber against wool, but despite its longevity, it is a remarkably poorly understood phenomenon. The objectives of this project are two-fold: to initially assess the charging behaviour of a number of model systems, followed by a variety of other materials. This will be addressed by using a method known as ‘Tribo-electric charging via aerodynamic dispersion’, developed inhouse. The second core objective of this project is to identify and establish a relationship between the surface charge and the flowability properties of the powders.

The outcomes of this project are particularly applicable to the pharmaceutical industry, as the majority of API’s are organic solids with very high surface resistivity values, and consequently very slow charge decay, leading to the charges remaining on the powder surfaces for a significant period of time. Naturally, this means that these materials will suffer the adverse effects of triboelectric charging during manufacture, handling and transportation.

Publications

  • Zafar U., Alfano F., Ghadiri M. (2018). Evaluation of a new dispersion technique for assessing triboelectric charging of powders. International Journal of Pharmaceutics, Volume 543, Issues 1–2, 30 Pages 151-159, https://doi.org/10.1016/j.ijpharm.2018.03.049
  • Ali M., Ghadiri M. (2017). Analysis of triboelectric charging of particles due to aerodynamic dispersion by a pulse of pressurised air jet. Advanced Powder Technology, Volume 28, Issue 10, Pages 2735-2740, https://doi.org/10.1016/j.apt.2017.07.026