Mannitol flowability size/stress threshold limit

The flow characteristics of mannitol, a polyol widely used as excipient in pharmaceutical formulations, were analysed using conventional and shear cell methods. The study of these properties is relevant in the understanding of the powders behaviour when they are handled in the production of solid oral dosage forms, especially at some critical steps. The sieved fractions with different particles sizes showed an increase of the Flow Index ( ff c ) as the particle size and major principal consolidation stress ( σ 1) increased with a predominance of the size factor over the shape factor. Above a certain value of σ 1 the fractions with larger particles (F > 63 and F > 90) showed similar flow behaviour (overlap) in Flow Functions and Effective Angle of Internal Friction demonstrating a size limit beyond which there were no differences in the ff c . As the shape factor was similar for all fractions, the ff c depended on the size factor and σ 1 . Thus, the worst ff c was obtained with the smaller particles fraction. • Flow properties of excipients are a critical step in the pharmaceutical development. • The shape and size of the particles may not be additive in the powder flow. • The shear cell method produces more real and reliable results. • Flow index ( ff c ) depends on particle size, shape and major principal consolidation stress ( σ 1 ). • There may be a limit to the particle size beyond which the flow index ( ff c ) does not improve.