International Journal of Pharmaceutics 369 (2009) 2–4 Contents lists available at ScienceDirect International Journal of Pharmaceutics journal homepage: www.elsevier.com/locate/ijpharm Rapid communication Use of a static eliminator to improve powder flow Kalyana C. Pingali a , Stephen V. Hammond c , Fernando J. Muzzio a , Troy Shinbrot b,∗ a Department of Chemical and Biochemical Engineering, Rutgers University, 98 Brett Road, Piscataway, NJ 08854, United States b Department of Biomedical Engineering, Rutgers University, 98 Brett Road, Piscataway, NJ 08854, United States c Pfizer Inc., 182 Tabor Road Morris Plains, NJ 07950, United States article info Article history: Received 2 October 2008 Received in revised form 6 December 2008 Accepted 18 December 2008 Available online 20 January 2009 Keywords: Static Flow Eliminator Additives Electrostatics abstract Glidants and lubricants have long been used to improve the flow and processing of pharmaceutical and other powder blends. In this letter, we find that similar improvements can be attained, without additives, by using a simple static eliminator. These results indicate, first, that electrostatic effects on powder blends may be a significant cause of powder aggregation and flow instabilities, and second, that common addi- tives such as magnesium stearate, colloidal silica, and talc may have as their chief effect the reduction of static. This suggests both that intelligent placement of static eliminators can eliminate the need for some of these additives and that judicious engineering of ionic and cationic additives may be effective in improving flow of “clingy” materials. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Problems with electrostatic charge accumulation range from catastrophic events such as dust explosions and fires (Palmer, 1973), to more mundane, but nonetheless serious, problems including jamming (Eilbeck et al., 2000; Nishiyama et al., 1998; Rowley, 2001; Mullarney and Hancock, 2004), agglomeration (Shinbrot et al., 2006), spontaneous segregation (Mehrotra et al., 2007), flow instabilities (Al-Adel et al., 2002; Liang et al., 1996), and mate- rial degradation (Vinod et al., 1997; Alebi-Jureti et al., 2000). Longstanding efforts to mitigate the effects of static charges in powder beds (Taillet, 2003; Matsusaka and Masuda, 2003) have included both the use of antistatic agents (Orband and Geldart, 1995) and the direct elimination of charges using passive, active, or radioactive static eliminators (Revel et al., 2003; Kodama et al., 2002). Although there remains some uncertainty concern- ing the level of efficiency of different static control alternatives, these approaches have been shown to significantly address charge accumulation problems, most recently including improving pow- der flow (Orband and Geldart, 1995). In the present study, we focus on the specific issue of how well static elimination alone improves powder flow, as compared with additives such as gli- dants that have traditionally been believed to mechanically reduce friction and cohesion between grains (Egermann and Frank, 1990; Kornchankul et al., 2002; Otsuka et al., 1993). We find, surprisingly, ∗ Corresponding author. Tel.: +1 732 445 6710. E-mail address: shinbrot@soemail.rutgers.edu (T. Shinbrot). that static elimination alone provides as great an improvement to flow as do a variety of glidants, lubricants and other addi- tives. This suggests that powder flow and electrostatics may be more intimately related than has been previously appreciated. In this brief paper, we first describe experiments performed using 10 blends of excipients, active pharmaceutical ingredients, and flow additives. Next, we evaluate the flow behavior of the blends with and without static elimination, and finally we draw conclu- sions. 2. Materials and methods Nine different blends of pharmaceutical powders were prepared by mixing the blends for 30 min in a V-blender with an intensi- fier bar. A detailed discussion of the mixing equipment appears in a previous study (Pingali et al., 2009), and the compositions of ingredients in each blend are as shown in Table 1. Pure ingredients (blends #1–5) are taken directly from the supplier bin without tum- bling. In each experiment, a sample of 5 lb blend was prepared for testing, and the sample was tumbled in an acrylic drum, 20 cm in diameter and 42 cm in length as shown in the schematic of Fig. 1(a). The drum was tumbled at 14 rpm for all experimental runs. Concen- tric holes were drilled at either end of the drum so that ions from an active static eliminator (model: 7901; manufacturer: EXAIR Corp.; location: Cincinnati, OH) could be introduced while the drum was tumbled. Compressed air was used to inject ions produced by the static eliminator into the rotating cylinder. To evaluate flow behavior, we make use of a result documented elsewhere (Faqih et al., 2006a,b): that the “Flow Index” of a powder 0378-5173/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpharm.2008.12.041