Interparticle van der Waals force in powder flowability and compactibility.

Particle flowability and compactibility are the two critical process parameters tested when a pharmaceutical material is formulated for a tabletting process. These behavioral descriptions are strongly affected by geometrical, physical, chemical and mechanical particle properties, as well as operational conditions. The property influences are broadly known in a qualitative sense, but have largely escaped fundamental quantitative description. Various measurement methods have been separately developed for each of these properties which provide comparative indices to assist in process and formulation design. This paper seeks to establish the connections between interparticle van der Waals force and both flowability and compactibility, and therefore also the inter-relations between the two apparently distinct properties. Paracetamol and the excipients often associated with it for tabletting are used as test materials to provide an initial validation of the theoretical development. These powders are well-characterized and known to be particularly difficult with respect to flowability and compactibility.