Water distribution studies within microcrystalline cellulose and chitosan using differential scanning calorimetry and dynamic vapor sorption analysis

The objective of the study was to assess and compare the interaction and distribution of water within microcrystalline cellulose (MCC) and chitosan by differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water in hydrated samples were determined from melting endotherms obtained by DSC. After accounting for the percent crystallinity of MCC and chitosan, no statistically significant difference was observed in their ability to bind water molecules per repeating unit at the minimum water content at which freezing water is evident. Exposure of chitosan to water for 30 min was sufficient to achieve equilibration at 61% w/w actual water content. The moisture sorption profiles were analyzed according to the GAB and Young and Nelson equations. The adsorbed monolayer, externally adsorbed moisture, and internally absorbed moisture were not statistically different for MCC and chitosan after accounting for the amorphous content of the polymers. These studies suggest that chitosan can act as a molecular sponge,'and thus aid in the production of beads by extrusion and spheronization. (C) 2004 Wiley-Liss, Inc. and the American Pharmacists Association.