Granule deformation and densification during compression of binary mixtures of granules.

The purpose of this study was to investigate whether the deformation and densification during compression of one type of granules are affected by adjacent granules of a different porosity, corresponding to different mechanical strength. Three mixtures were prepared, each consisting of two types of microcrystalline cellulose pellets (intermediate porosity study pellets plus low, intermediate or high porosity surrounding pellets) in the proportion 1:7. The mixtures were compressed and the study pellets were retrieved and analysed in terms of porosity, thickness, surface area and shape. It was shown that the study pellets were compressed by deformation and densification. The degree of densification (decrease in porosity) of the study pellets was independent of the porosity of the surrounding pellets but the deformability (changes in the thickness, surface area and shape) of the study pellets was linked with the porosity of the surrounding pellets. It is concluded that the mode of deformation of the study pellets was regulated by the porosity of the surrounding granules; in a mixture containing granules with a low porosity, compression resulted in irregular study granules with regularly positioned indentations caused by the surrounding granules. The compression properties of the surrounding granules affected the flattening of the study granules to a lesser degree.