Compactibility of binary mixtures of pharmaceutical powders

In order to understand and predict the behaviour of mixtures of pharmaceutical powders during tabletting, 3 different substances were selected: microcrystalline cellulose (CM), dicalcium phosphate dihydrate (FC) and sodium laurylsulfate (LSS) which were compressed in a range up to 980 MPa, alone and as binary mixtures. The tablet hardness was measured as the dependant variable. The compactibility of each mixture was defined through the maximal tablet hardness reached (D(max)) and the slope and intercept of the curves. Each system showed different interactions and bond strengths between the components of the mixtures. Mixtures of CM and FC showed a maximum in their maximal tablet hardness at a CM proportion of 82% (w/w), while in the case of the CM-LSS system, D(max) decreases as the LSS proportion increases. The LSS-FC system presents a maximum, in the maximal tablet hardness, at a LSS concentration of 1.2% (w/w). The type and strength of the bonds between particles of different materials was also dependant on the compaction pressure. At high compaction pressures the compactibility curves showed more clearly the characteristics of the bonds between different particles, whereas at low compaction pressures the tablet hardness seemed to represent just an arithmetic addition of the bonds between particles of the same material.