Effect of addition of water on the rheological and mechanical properties of microcrystalline celluloses

Abstract

A study was conducted to examine the effect of addition of water on the compactibility of two commercially available microcrystalline celluloses, Avicel PH-101 and Emcocel. The cohesiveness of the two samples when measured by a shear test was found to be different. Addition of water caused an increase in cohesiveness to about 20-30 wt.% for both samples although the change in shear force with water content was different. There was no difference on further increase in amount of water added. These changes in cohesiveness were reflected in the properties of granules formed and the strength of tablets compressed from such granules. For example, while both the microcrystalline cellulose powder samples had identical compressibilities, equivalent amounts of water used for granulation (37 wt.%) formed larger granules with Avicel than Emcocel but the latter formed stronger tablets and the compressibility of these granules was far less than that of the original powder samples. "Normalized work of failure" and "apparent failure viscosity" determinations were carried out to quantify tablet mechanical properties and results suggested that less plastic deformation occurred during compaction of granules in comparison with compaction of powder particles. This indicated that a large proportion of compaction energy was probably utilized in breaking up primary granule structures. Thus they contributed less to increasing contact areas through particle deformation and therefore produced tablets of lower strengths than for powder particles compressed at comparable forces, where relatively more energy was used in causing deformation at particle interfaces. © 1988.