ADHESION AND AUTOADHESION MEASUREMENTS OF MICRONIZED PARTICLES OF PHARMACEUTICAL POWDERS TO COMPACTED POWDER SURFACES

Micronized samples of lactose monohydrate and salmeterol xinafoate hav e been used to study the adhesion of micronized particles to compacted powder surfaces, After an initial increase in median adhesion force w ith increased press-on force no further increase in median adhesion fo rce can be achieved, Thus application of larger press-on forces eventu ally appears to result in a maximum plastic deformation of the microni zed particles, This is in contrast to previous experiments using parti cles of the same materials in a size range between 20 and 120 mu m, wh ere an increase in press-on force always led to an increase in median adhesion force. The adhesion of micronized lactose monohydrate particl es to salmeterol xinafoate surfaces is numerically higher than the adh esion of micronized salmeterol xinafoate particles to lactose monohydr ate surfaces, although theoretically the same two materials are adhere d to each other, This effect could be due to differences in the surfac e roughness of the compacted surfaces, Hence, if a true estimate of ad hesion is required from adhesion studies of any two materials, either material should be used as particulate and as compacted powder materia l. Otherwise a careful consideration of the practical conditions which are to be modelled has to be made to choose the most appropriate syst em. The relative autoadhesion force of micronized lactose monohydrate particles could have been predicted from the results obtained using la rger particles, This is valid with small limitations also for the rela tive autoadhesion force of salmeterol xinafoate. The relative adhesion force of salmeterol xinafoate particles to compacted lactose monohydr ate surfaces appears independent of particles size even into micronize d size range if particles with similar morphology are compared.