Improved flowability and compactibility of spherically agglomerated crystals of ascorbic acid for direct tableting designed by spherical crystallization process

Spherically agglomerated crystals of ascorbic acid with improved compactibility for direct tableting were successfully engineered by the spherical crystallization technique. In this process, ascorbic acid crystals were precipitated by a solvent change method, followed by their agglomerations with the emulsion solvent diffusion (ESD) or spherical agglomeration (SA) mechanism. The micromeritic properties, such as flowability and packability of the spherically agglomerated crystals were preferably improved for direct tableting. Under static compression, the acceptable compact (tablet) with a sufficient strength was produced successfully without capping, although the capping occurred with the original unagglomerated crystals. The improved compaction properties of the agglomerated crystals were due to their fragmentation and plastic deformation occurred significantly during compression. This mechanism was supported by higher stress relaxation and less elastic recovery of the compact of agglomerated crystals. It was also found that the spherically agglomerated crystals were tableted directly without capping using a single punch machine under dynamic compression, although the tensile strength of resultant tablet decreased in tolerable degree with increasing punch velocity.