Measuring the water retention capacities (MRC) of different microcrystalline cellulose grades

The ability of various types of microcrystalline cellulose (MCC) to hold wa ter when subjected to an applied force has been assessed by a centrifuge te chnique. By considering the final percent of water retained after a standar d centrifugation, as a function of the initial water content, a moisture re tention capacity (MRC) can be determined. Statistical analysis of the resul ts identified that it was possible to divide the nine samples of MCC into s ix sub-sets in terms of final moisture content retained. Those types which contained added polymer had by far the highest water level remaining. In te rms of the MRC value, statistical analysis again sub-divided the celluloses into six sub-sets, although different from those for the final water conte nt. Again those types containing added polymer gave much higher MRC values. As experiments were carried out with initial water/MCC ratios of different levels, statistical analysis of the influence of initial water content on the MRC values was undertaken with each type of MCC. The results showed a v arying dependence on initial water level with the different types of cellul ose. To provide a value of MRC which characterised the cellulose, the maxim um value of MRC at the lowest initial water level was identified. Samples o f MCC with low values of MRC have been shown previously to require less wat er for processing by extrusion/spheronization, while celluloses with a high MRC value appear better for the limitation of water movement during the pr ocess of extrusion/spheronization. The water retention must, however, also be considered in association with the rheological properties of the wet pow der mass. Thus, while the Avicel RC591 had the highest MRC value, its rheol ogical properties are so that the production of pellets with such a type ca n be less effective than with other types of MCC. (C) 2001 Elsevier Science B.V. All rights reserved.