Physical characterization of powder blends with a focus on electrostatic properties
Blending and segregation are two opposite processes in bulk material handling. Therefore, we can say that these are two sides of the same coin. The triboelectric charges are produced during blending and segregation process at the contacts between the grains and as well as between the grains and the container. Unfortunately, this triboelectric effect is not fully understood, even at the fundamental level. The approach to solve practical problems is mostly empirical. Moreover, reproducible electrostatic measurements are difficult to perform. In the present study, the tribo-electrification of a set of excipients and active pharmaceutical ingredients (APIs) has been analyzed during the flow in contact with different materials. This behaviour is analyzed with a recently developed instrument called GranuCharge. The obtained charge density is found to depend on the material in contact. While different excipients have almost the same triboelectric behavior and a low chargability, APIs show complex triboelectric properties. Some APIs charge a lot while other APIs charge less. Afterward, the electrostatic behavior of API/ excipient blends is considered. It is found that the net charge of the blend is a complex function of the relative quantity of API in the mixture and the hygrometric conditions of the air. Moreover, both the quantity and the sign of the charge are found to depend on the material in contact with the powder during the flow. Finally, a relation between electrostatic charges, flowing (GranuDrum measurement) and packing (GranuPack measurement) properties will be discussed.