THE EFFECT OF PRECOMPACTION PROCESSING AND STORAGE-CONDITIONS ON POWDER AND COMPACTION PROPERTIES OF SOME CRYSTALLINE MATERIALS

The effect of humidity during the pre-compaction storage of milled act ivated materials on the powder and compact properties was studied. Tes t materials were sodium chloride, sucrose, dicalcium hydrogen phosphat e (CHP) and acetylsalicylic acid (ASA). Storage of the milled powders at 0% RH before compaction affected neither the powder characteristics nor the tablet strength of the materials. Storage at high RH before c ompaction affected the powder and tablet surface areas as well as redu cing the tablet strength for sodium chloride. Crystallisation of the s olid materials' activated surfaces occurred before compaction, i.e., a deactivation of the milled material, mediated by the presence of wate r vapour at the particle surfaces. For sucrose, a reduction in powder surface area on pre-compaction storage at high RH did not lead to chan ges in tablet strength. This was attributed to its fragmenting behavio ur during compaction creating new bonding surfaces. Storage of sodium chloride and sucrose compacts increased the tablet strength except at 0% RH, suggesting the existence of a lower critical RH, below which th e compacts appeared to be physically stable. The pre-compaction powder storage at high RH, reduced the post-compaction strength increase for sodium chloride compacts. ASA and CHP being less water soluble were n ot affected by RH on pre-compaction storage of the milled powders.