PURPOSE: As an effect of their plastic deformation behavior, ductile materials create a large surface for bonding during compaction. However, a serious drawback is their high lubricant sensitivity, preventing the formation of strong bonds. The purpose of this study was both an increase in compactibility and a reduction of the lubricant sensitivity of ductile filler-binders by using hollow particles. This was illustrated for inulin.
METHODS: Both solid and hollow inulin particles were prepared by spray-drying. Unlubricated tablets and tablets containing 0.5% magnesium stearate were compressed in a compaction simulator, operating at 300 mm/s. The tablet crushing strength was determined with a Schleuniger apparatus.
RESULTS: The compaction of unlubricated, solid inulin particles showed that the product had good compatibility. This was caused by plastic deformation of the ductile, amorphous material under load, creating a large surface for bonding. After lubrication, however, the bonding properties decreased significantly, which was caused by the presence of a lubricant film. Hollow inulin particles have an increased compactibility as compared with solid particles and a strongly reduced lubricant sensitivity. Scanning electron micrographs show that hollow particles fragment before they start plastic deformation. This fragmentation behavior is supported by tablet surface area measurements and calculation of the buckling strength. This effect was responsible for both a higher crushing strength and a lower lubricant sensitivity as compared with solid inulin particles.
CONCLUSIONS: Compactibility of inulin particles can be increased, and lubricant sensitivity can be decreased by using hollow instead of solid particles.