Yield strength of microcrystalline cellulose: experimental evidence by dielectric spectroscopy

The water-induced ionic charge transport in compacted microcrystalline cellulose (MCC) has been reported to be governed by the densification behaviour. Hence, mechanical properties were expected to correlate with conductivity behaviour of MCC compacts. Both in-die and out-of-die compaction behaviour of MCC powder was investigated using a fully instrumented rotary tablet press. The dielectric measurements were carried out using a Novocontrol Concept 40 broadband dielectric spectrometer and dc conductivity (σdc) was extracted from the low frequency conductivity data at room temperature. As postulated, compaction pressure corresponding to maximum conductivity (σdc max) was observed to correlate with yield strength of MCC, determined using in-die and out-of-die Heckel analysis. Although Heckel transformation is most commonly used in pharmaceutical technology, its general use to characterise the mechanical properties of organic pharmaceutical materials has been criticized. The present study has provided experimental evidence that Heckel equation is practically useful to describe plastic deformation of organic pharmaceutical powders.