A study of the charging characteristics of selected pharmaceutical dry powders: Applications to improve mixture formulation and fugitive dust control
This study aims to gain a better understanding of the pharmaceutical powder-charging processes by contact or friction (triboelectrification) and by unipolar ions. To study the first process, an instrument for measuring the capability of dry powders to develop electrostatic charge (chargeability) has been developed. A 0.5 cc volume of eleven excipients and five active ingredients pneumatically conveyed in a stainless steel pipe develops a charge that is measured as the slug of powder passes through an inductive, non-contact sensor ring located in a Faraday cage. Powder charge ranged from +131.2 mV/0.5cc to -598.3 mV/0.5cc. Following these single component tests, we study binary mixtures of spray dried lactose (95% w/w) with five compounds and different grades of two excipients. We found that the standard deviation of the binary mixture chargeability increased in direct relationship with its chargeability. This implies both that the chargeability of the mixture can be used as an indicator of the blend uniformity of the mixture, and that chargeability needs to be minimized in order to improve blend uniformity. To this effect, we found that compounds such as colloidal silicon dioxide (Cab-O-Sil®) can be used as mixture charge control agents. The second process studied was the charging of air-entrained particles (fugitive emissions) in order to enhance their particle number decay rate by unipolar ions generated by corona discharge. This portion of the study was completed using a control system called open-path precipitation at the source, in which the source of emissions and the source of ions are in the same space. An optical particle counter was used to monitor the particle concentration in six different size ranges (0.3 to >25 μm). A pilot study was followed by a larger scale study, where three compounds were tested in a conditioned 8.35 m3 room under zero-net-flow conditions, the average (n=3) percent reduction in the steady state for the total particle concentration was in the range of 20% to 43%. The repeatability of the protocol to conduct these tests in terms of the coefficient of variation presented an average value of 22.3% ± 19.5% (S.D.). This study verified that the open-path unipolar ion system has the potential to enhance the control at the source of pharmaceutical fugitive emissions. ^
Major Professor: Robert B. Jacko, Purdue University.