INVESTIGATIONS INTO THE DEFORMABILITY AND TENSILE-STRENGTH OF PELLETS

The fracture and deformation properties of soft and hard pellets, whic h were prepared as described by Lundqvist et al. (1997), have been stu died by measuring individual pellets and groups of pellets subjected t o compaction in a punch and die system. Uncompacted, hard pellets were found to be less brittle and less deformable than soft pellets. Howev er, the soft pellets were found to fracture under the influence of low tabletting pressures, and laser light reflection measurements have sh own that they are able to form a coherent network of deformable materi al in tablets at higher tabletting pressures. Hard pellets were more r esistant to crack propagation, but cracks and flaws were formed if a t hreshold tabletting pressure of about 9 MPa was reached. A change in t he surface and internal pellet structure appears therefore certain. Ho wever, even under the influence of high loads the pellets were unable to deform to such an extent that a coherent network of material was fo rmed in the tablets. Hard pellets differed from soft pellets by a fact or of about 5 in their tensile strength, whereas they differed by a fa ctor of 2 in their shear strength. Tested in tension, hard pellets had a higher strength value than the soft pellets, while when tested in s hear they were characterized by the lower strength value. While compac ts made from soft pellets were found to reduce their volume considerab ly under load, compacts made from hard pellets decreased in volume onl y slightly by deformation, but initially by particle rearrangement. Th is is a further sign of the larger deformability of the soft pellets i n comparison to the hard pellets studied. (C) 1998 Elsevier Science B. V. All rights reserved.