MOVEMENT OF LIQUIDS THROUGH POWDER BEDS

The movement of hydrophilic fluids into and out of beds of two grades of lactose, microcrystalline cellulose (MCC) and mixtures of the two materials has been assessed by a pressure membrane technique. While water was an appropriate fluid to use with MCC, because of its solvent properties, it proved unsuitable for use with lactose and the binary mixtures with MCC. In these cases, a 50:50% mixture of ethanol and water proved acceptable. The method clearly illustrated the differences in the movement of fluid in the two grades of lactose, which differed in particle size, and between lactose and MCC. These differences could be quantified in terms of limiting saturation pressures, irreducible saturation and 'apparent' pore distributions. The MCC introduces absorptive and adsorptive influences into the binary mixtures with lactose which are absent or minimal in the lactose systems. Such effects are undoubtedly involved in ensuring that these binary mixtures can be used to produce spherical granules by extrusion/spheronisation whereas the process is not successful for lactose alone.