Triboelectric charging and dielectric properties of pharmaceutically relevant mixtures

Binary mixtures of pharmaceutically relevant powders were investigated using dielectric spectroscopy over a frequency range of 10(-3) to 300 kHz. Two different binary mixtures were studied as a function of concentration; pseudoephedrine hydrochloride in dicalcium phosphate dihydrate and acetaminophen in microcrystalline cellulose, respectively. Dielectric properties obtained from measurements of these systems are reported and found to follow a trend similar to the observed triboelectric behavior after low-shear tumble blending. Powder samples for charge measurement were mixed using a stainless steel blender and dispensed directly into a Faraday pail. For the two binary mixtures studied, low-frequency conductivity calculated from the imaginary part of the complex permittivity (or loss factor) was observed to be sensitive to water content. Furthermore, the unanticipated trends previously reported in the measured specific charge after blending were observed to correspond with the surface charge density calculated from the capacitance of the composite material. The implications of moisture and the physical and chemical properties of these dielectric mixtures are also discussed with supporting results. (C) 2007 Published by Elsevier B.V.