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Although the interparticulate forces can be qualitatively estimated using a mathematical model, it is practically impossible to predict the actual force of particulate interaction on a quantitative basis since many factors are involved in this process. Thus, great caution must be exercised when attempting to extrapolate findings derived from hypothetical models to real systems encountered in pharmaceutical and other processes. G. (1984) Electrostatic phenomena during powder handling. Powder Technol.

1986) since the drugs and excipients will exist in this form at the beginning, throughout and, often, at the end of the manufacturing process. Not surprisingly, the physicochemical properties of powders have attracted considerable attention but this usually addressed a collection of discrete particles with dimensions less than 100 ␮m. Pharmaceutical powders are composed of either fine drug particles (those Ͻ200 ␮m) or mixtures of drug particles together with excipient(s). Due to the intrinsic nature of small particles, interparticulate forces within a pharmaceutical powder are often one of the primary determinants of its behaviour, influencing such properties as flow, mixing and agglomeration.

Then, a beam of small thickness and width in comparison with its length is subjected to transverse loads and its central deflection caused by bending is measured. Young’s modulus for a specific porosity can be calculated from the applied load and the deflection of the mid-point of the beam. If Young’s modulus is plotted against the porosity then the true modulus of the material can be obtained by extrapolation to zero porosity. g. g. 1). For example, tabletting excipients can be placed in the following increasing order of rigidity: starch Ͻ microcrystalline celluloses Ͻ sugars Ͻ inorganic fillers.