Pre-formulation studies on moisture absorption in microcrystalline cellulose using differential thermo-gravimetric analysis

Abstract

A study on the differential thermo-gravimetric (DTG) measurements of microcrystalline cellulose (MCC) containing moisture indicated that particle size affected the amount of bound water and the flow indices. Thermal analysis of 6 commercial grades of MCC powders and MCC/water blends were performed using a thermogravimetric analyzer. These MCCs were differentiated by their particle size, bulk and tapped densities, crystallinity and micromeritic properties. From the DTG curves, it was observed that water loss from the MCC/water blends occurred in 3 phases which corresponded to the different states of water associated with the solid particles. Area under the third phase, or the falling rate phase, can be associated with the release of water that was physically shielded or bound to the solid. This water may be referred to as "structured" water. The large particle size grades of MCC-Avicel PH 102, PH 302 and Pharmacel 102 were found to possess smaller quantities of structured water. Water vapor sorption results revealed the monolayer capacities for the respective MCC grades. The amount of structured water appeared to correspond to the existence of bilayers on the surface of the small particle size MCC grades. Using the avalanche flow assessment method, flow properties of small particle size grades of MCC were found to be poorer as indicated by the significant correlation between their flow indices and size, in addition to the longer mean times to avalanche. © 2004 Pharmaceutical Society of Japan.