Effects of electrostatic charging on pharmaceutical powder blending homogeneity.

During the pharmaceutical powder blending process, electrostatic charges generate and accumulate unavoidably due to particle-particle and particle-wall collision. The effect of electrostatic charging on pharmaceutical powder blending homogeneity was investigated on two binary blending systems: (1) lactose as an excipient with caffeine as an Active Pharmaceutical Ingredient (API) and (2) Micro-crystalline Cellulose (MCC) with caffeine. Three different blending procedures were conducted: (1) conventional blending without any charge control, (2) blending with simultaneous charge neutralization, and (3) blending combined with a corona charging process. It was found that the average API concentration variation increases with the increase of charge-to-mass ratio of final blend samples. In other words, the presence of uncontrolled electrostatic charges has an adverse effect on powder blend uniformity. Elimination or minimization of electrostatic charges also appears to have a negative impact on powder blend uniformity. In contrast, blending of positively charged excipient material and negatively charged API material leads to a better blend uniformity. The controlled electrostatic charging opens an opportunity for improving uniformity of the pharmaceutical blending process.