Changes in small-angle X-ray scattering during powder compaction — An explanation based on granule deformation

Empirical relationships between compaction conditions and changes in small-angle X-ray scattering (SAXS) patterns were reported previously, suggesting a novel method for studying powder compaction [1,2]. In the present work, a more quantitative model was developed to explain the changes in SAXS patterns observed for pre-gelatinised starch and microcrystalline cellulose. Analysis of SAXS data suggested (approximately) power-law scattering behaviour for these materials, which was consistent with their hierarchical intragranular morphologies, including nanoscale porosity, as described elsewhere [3]. Observations using XµT suggested affine deformation of granular shapes during compaction. Based on the assumption that the sub-granular morphology also deformed affinely, a description of the azimuthal variations in scattering intensity was developed, which gave very close agreement with experimental observations. Based on this model, it appeared that SAXS could be used to obtain quantitative estimates of granule deformation specifically, isolating this component from the other mechanisms operating during powder compaction.