Tensile strength of tablets containing two materials with a different compaction behaviour

The tensile strength of tablets compressed from binary mixtures is in gener al not linearly related to the strength of tablets prepared from single mat erials; in many cases it shows a decreased tensile strength relative to int erpolation. The materials used in this study, sodium chloride and pregelati nised starch, are both plastically deforming materials, but have a differen t densification and relaxation behaviour. The yield pressure of the binary mixtures shows an almost linear relationship. As an effect of their lower y ield pressure, starch particles yield earlier than sodium chloride particle s. The following enclosure prevents some sodium chloride particles to yield or crack. The relaxation of the tablets is higher than the relaxation calc ulated by linear interpolation of the relaxation behaviour of the two pure materials. The difference between the measured porosity expansion and the d ata obtained by linear interpolation can be considered as a measure for the reduced interparticle bonding. SEM-photographs indicate that the reduced i nterparticle bonding is caused by the low adhesive forces. The measured dec rease of the tensile strength of the tablets is also considered to be the r esult of reduced interparticle bonding. In this paper it is shown that ther e exists a similar relationship between the tensile strength reduction and the percentage of starch on the one hand and the extra porosity expansion a nd the starch percentage on the other hand. (C) 2000 Elsevier Science B.V. All rights reserved.