A new theoretical model to characterize the densification behavior of tableting materials

The purpose of the study was to develop a new three-dimensional model using force, time and displacement to characterize the densification behavior of tableting materials. Normalized time (x), displacement converted to ln(1/1 - D(rel)) according to Heckel (y) and force presented as pressure (z) were used to plot a graph. A twisted plane was fitted to this three-dimensional plot. This plane was characterized by three parameters d, the slope over time called 'time plasticity', e, the slope over pressure called 'pressure plasticity' and omega, the angle of rotation called 'fast elastic decompression'. These parameters were used to characterize the densification behavior of the well-known materials microcrystalline cellulose, dicalcium phosphate dihydrate, theophylline monohydrate, cellulose acetate and hydroxypropyl methylcellulose at different rho(rel, max). It could be shown that brittle, elastic and plastic compression properties could be very well distinguished and differentiated. Further on, it could be shown whether these properties were due to pressure or time. Thus this model has the prevailing advantage to characterize tableting materials in one step according to time and pressure and it is a useful tool to develop tablet formulations or new excipients.