Lubricant sensitivity in relation to bulk density for granulations based on starch or cellulose

The study described in this paper was concerned with the susceptibility to lubrication with magnesium stearate of tablets compressed from granulations based on native starches or on modified celluloses. Different properties of the granulations, like particle size, flowability and surface area, were analyzed in relation to the tablet lubricant sensitivity ratio, being the ratio between the decrease in crushing of tablets due to mixing with a lubricant and the crushing strength of tablets prepared without a lubricant. Different linear relationships between the lubricant sensitivity ratio of tablets and the bulk density of the powders were found, for granulations prepared from different starting materials. Flowability proved to be the predominant mechanism in the formation of a lubricant film on the granulations. Poor flow properties, which are characterized by low bulk densities, retard or impede the formation of a lubricant film during mixing.