A combined experimental and numerical approach to explore tribocharging of pharmaceutical excipients in a hopper chute assembly.

Electrostatic charging via contact electrification or tribocharging refers to the process of charge transfer between two solid surfaces when they are brought into contact with each other and separated. Charging of continuous particulate flows on solid surfaces is poorly understood and has often been empirical. This study aims toward understanding the tribocharging of pharmaceutical excipients using a simplified geometry of unidirectional flow in a hopper-chute assembly. Assuming electron transfer to be the dominant mechanism of electrification, a triboelectric series was generated using work functions estimated from quantum chemical calculations. A 3D-DEM model has been developed employing charge transfer and electrostatic forces. Using numerical simulations, the charge accumulation for an assemblage of particles during flow was determined under different conditions. To theoretically analyze the process of charging, parametric studies affecting powder flow have been investigated. A higher specific charge was observed at larger friction coefficients and lower restitution coefficients. The results obtained from the simulation model reinforce the collisional nature of triboelectrification. The simulation results revealed similar trends to experimental observations. However, to enable a priori prediction the model needs to be tested for additional materials or extended to other process operations.