BINDER HARDNESS AND PLASTICITY IN GRANULE COMPACTION.

The effect of binder hardness on compaction reproducibility was studied by measuring dimensional variability, springback, and granule deformation of three spray-dried powders with polyvinyl alcohol (PVA), polyethylene glycol (PEG), plasticized polyvinyl alcohol, or acrylic wax binder systems. The last two binder systems with glass transition temperatures (T//g) of 25 and minus 17 degree C, respectively, were soft, whereas the PVA was hard when pressed at room temperature. It is demonstrated that the softer and more deformable binders result in more reproducible pressing with less springback. This is attributed to enhanced stress relaxation of the softer systems during pressing. Some pressing differences could not be solely attributed to T//g differences but are probably a result of mechanical property differences of the organic systems.