Micro-scale measurement of the mechanical properties of compressed pharmaceutical powders. 2: The dynamic moduli of microcrystalline cellulose.

The use of two 'micro-scale' dynamic mechanical testing techniques for determining the viscoelastic properties of very small microcrystalline cellulose compacts ( approximately 20 mg) is reported. The first method is a simple tensile 'stretching' test, and the second is a dynamic version of the three-point beam-bending technique. For both approaches the storage (elastic) and loss (viscous) moduli could be readily determined for compacts of a wide range of porosities. The experimentally determined storage moduli were consistently one order of magnitude greater than the corresponding loss moduli indicating a dominating elastic response for the microcrystalline cellulose compacts. The moduli determined using the oscillating three-point beam-bending technique were slightly lower than expected and this was attributed to sample anisotropy and imperfect sample alignment/friction during testing. The moduli obtained using the simple dynamic tension tests were practically identical to complex moduli values reported for much larger specimens, and it appears that this technique is well suited to measuring the dynamic mechanical properties of very small pharmaceutical powder compacts.