The influence of punch curvature on the mechanical properties of compactedpowders

The influence of changing the overall thickness and face curvature of compa cted microcrystalline cellulose powder (a direct compression excipient used extensively in the pharmaceutical industry) prepared at different compacti on pressures has been assessed by the diametral compression test. For speci mens that failed in tension, the tensile strength of the compacts was calcu lated from formulae derived from stress analysis. The values for tensile st rength indicated that for equivalent compaction pressures, compacts with di fferent thicknesses and face curvatures, strengths were not equivalent. Thi s could be due to differences in the internal structure of the compacts due to different stress distributions during the formation process. The result s, however, clearly show that the maximisation of the tensile strength can be achieved for different thicknesses and face curvature. In general, a com pact diameter to face curvature ratio of 0.67 corresponding to what are ter med "normal" concave tablets, gave the maximum value for the tensile streng th. (C) 2000 Elsevier Science S.A. All rights reserved.