Importance of small pores in microcrystalline cellulose for controlling water distribution during extrusion-spheronization.

The purpose of this research was to investigate the effects of particle size on the wet massing behavior of microcrystalline cellulose (MCC). In this study, a series of six fractionated MCC grades were customized and specially classified to yield different particle size varieties of the standard grade, Comprecel M101. All seven MCC grades were extensively characterized for the physical properties and wet massing behavior using mixer torque rheometry. Effects of MCC physical properties on the maximum torque (Torque(max)) were determined using partial least squares (PLS) analysis. Most physical properties varied systematically with particle size and morphological changes. Marked differences were observed in the small pore volumes (V (highP)) and BET surface areas of the MCC grades. Variables that exerted dominant influences on Torque(max) were identified. In particular, the significance of V (highP) in governing wet mass consistency was established. The role of V (highP) has not been reported in any study because this small but significant variation is likely to be obliterated or compensated by variation in other physical properties from MCC grades from different suppliers. The findings demonstrated the role of small pores in governing the wet mass consistency of MCC and provide a better understanding of MCC's superior performance as a spheronization aid by the ability to fulfill the function as a molecular sponge to facilitate pellet formation during wet granulation processes.