Moistening liquid-dependent de-aggregation of microcrystalline cellulose and its impact on pellet formation by extrusion-spheronization.

The wet-state particle size of microcrystalline cellulose (MCC) dispersed in different moistening liquids was characterized to elucidate the effect of moistening liquid type on the extent of MCC particle de-aggregation. Cohesive strength of moistened MCC masses was also assessed and pellet production by extrusion-spheronization attempted. MCC dispersed in alcohol or water-alcohol mixtures with higher alcohol proportions generally had larger particle sizes. Moistened mass cohesive strength decreased and poorer quality pellets were obtained when water-alcohol mixtures with higher alcohol proportions were used as the moistening liquid. MCC comprise aggregates of small sub-units held together by hydrogen bonds. As MCC particle de-aggregation involves hydrogen bond breaking, moistening liquids with lower polarity, such as water-alcohol mixtures with higher alcohol proportions, induced lesser de-aggregation and yielded MCC with larger particle sizes. When such water-alcohol mixtures were employed during extrusion-spheronization with MCC, the larger particle size of MCC and lower surface tension of the moistening liquid gave rise to moistened masses with lower cohesive strength. During pelletization, agglomerate growth by coalescence and closer packing of components by particle rearrangement would be limited. Thus, weaker, less spherical pellets with smaller size and wider size distribution were produced.