Effects of drying technique on extrusion–spheronisation granules and tablet properties

Extrusion–spheronisation was used to generate smooth, highly spherical granules of a microcrystalline cellulose/propyl gallate/water paste. Freeze-drying retained the shape and size of the granules, whereas oven-drying produced roughened granules due to the uneven shrinkage of the wet powders. Compaction of one size fraction indicated that the granule strength differed noticeably, with the oven-dried samples producing tablets of lower voidage for a given applied compaction pressure. There was a reasonable correlation between tablet crushing strength and voidage. Major differences were observed in tablet dissolution, with the freeze-dried material exhibiting a two-regime behaviour and an initial dissolution rate constant an order of magnitude greater than the oven-dried form. Both the voidage and dissolution characteristics are postulated to be determined by the microstructure established during drying.