The Effect of Compression and Decompression Speed on the Mechanical Strength of Compacts

The purpose of this work was to investigate the effect of punch speed on the compaction properties of pharmaceutical powders; in particular, to separate out differences between the effect of the compression and decompression events. Tablets were prepared using an integrated compaction research system. Various "sawtooth" punch profiles were followed to compare the effects of different punch speeds on the crushing strength of the resulting tablets. The loading and unloading speeds were varied independently of one another. In general, when the compression speed was equal to the decompression speed, the tablet crushing strength was observed to decrease as the punch velocity increased. When the compression speed was greater than or less than the decompression speed, the results varied, depending on the material undergoing compaction. Reduction of the unloading speed from 300 to 10 mm sec for pregelatinized starch and microcrystalline cellulose produced a significant increase in crushing strength, whereas no significant increase in crushing strength was observed until the loading speed was reduced to 10 mm sec. Reduction of the unloading speed had a similar effect on the direct compression (DC) ibuprofen, however, even greater improvement in the crushing strength was observed when the loading speed was reduced. No improvement in the DC acetaminophen tablets was observed when the unloading speed was reduced, however, a significant increase in crushing strength was produced when the rate of loading was reduced. This work showed that the strength of tablets can be improved and some tableting problems such as capping can be minimized or prevented by modifying the rates of loading unloading.