Influence of particle wall adhesion on particle electrification in mixers

In this work, particle electrification in the Turbula and horizontally oscillating mixers were investigated for adipic acid, microcrystalline cellulose (MCC), and glycine particles. MCC and glycine particles acquired positive electrostatic charges, while adipic acid particles attained negative charges in both mixers. Adipic acid (of sieved size larger than 500 μm), MCC, and glycine particles were monotonically charged to saturated values, and had negligible wall adhesion. On the contrary, the adipic acid particles, both unsieved and sieved but of smaller sieved size fraction, exhibited very different charging kinetics in the horizontally oscillating mixer. These adipic acid particles firstly acquired charges up to a maximum value, and then the charges slowly reduced to a lower saturated value with increasing mixing time. Furthermore, these particles were found to adhere to the inner wall of the mixer, and the adhesion increased with mixing time. Surface specific charge densities for adipic acid particles were estimated based on particle size distribution, and were found to increase with particle mean diameters under the conditions investigated. The results obtained from the current work suggested that electrostatic force enhanced particle–wall adhesion, and the adhered particles can have a significant impact on particle electrification.