Plasma surface modification of powders for pharmaceutical applications

The surfaces of lactose particles are coated with SiO(x) nanostructures in a plasma downstream reactor to increase the surface roughness and thus, to reduce the prevailing van der Waals forces between the substrate particles. As a consequence of the smaller interparticle friction, both the bulk density and the flowability of plasma modified powders are increased. In this study different powder fractions with mean particle sizes between Sand 40 mu m are processed separately to investigate the influence of the particle size on the process. The measured bulk densities and flow factors become larger with increasing mean particle size for both untreated and plasma treated powders. The bulk density of all powder fractions is increased by 40 to 50% and all originally cohesive powders reach an easy flowing regime through the short low-temperature plasma treatment. Scanning electron microscope images are presented to appraise the particle size and distribution of the deposited spacer structures on the lactose surface. This estimation leads to the conclusion that the spacer structures have typical diameters between 15 and 60 nm and cover the surface with approximately 5 to 15%. Comparative studies investigating the influence of admixed glidants on the powder flowability show that this range is desirable for a maximal reduction of attractive van der Waals forces. (C) 2010 Elsevier BM. All rights reserved.