THE INFLUENCE OF CHEMICAL-STRUCTURE ON THE FRICTION PROPERTIES BETWEEN PARTICLES AND COMPACTED POWDER SURFACES

Friction measurements on particles adhered to compacted powder surface s have been undertaken by the centrifuge technique to investigate the influence of the variations in the chemical structure of a series of s alts of salmeterol. Two mathematical models have been used to evaluate the experiments, and the coefficient of static friction, the friction force and the theoretical shear force on compacted powder surfaces of lactose monohydrate and salmeterol xinafoate have been derived. The r esults show differences in the mechanism of friction and also divide t he five compounds into comparatively hard (salmeterol base and sulfate ) and soft (salmeterol 4-chlorobenzoate, salicylate and xinafoate) mat erials. The hydrophilic nature of the particulate material was found t o be indicative of its friction properties on a hydrophobic surface, a nd vice versa. The ability of a material to adsorb water is reflected in the relative hydrogen bonding coefficient (Hansen-solubility parame ter), and a linear relationship was found between this coefficient and the friction force obtained. Water can act as a lubricant reducing th e friction between two surfaces. The friction between like materials i n contact was found to be minimal. The results also imply that no gene ral descriptor of the chemical structure of related compounds, which w ould allow the prediction of friction properties, exists. Instead, the descriptor needs to be chosen according to the properties of the surf aces in contact, or friction experiments have to be performed.