The Effect of Moisture on the Mechanical and Powder Flow Properties of Microcrystalline Cellulose

Abstract

Purpose. This study determined the effects of moisture on the mechanical and powder flow properties of microcrystalline cellulose. Methods. A variety of mechanical properties were determined as a function of solid fraction at moisture levels ranging from 0 to 12.2% and included: compaction pressure required to form a compact, dynamic indentation hardness, quasi-static indentation hardness, tensile strength, best case and worst case Bonding Index, Brittle Fracture Index, Strain Index, Compressibility Index and shear cell index. Results. Significant changes were observed as the moisture level of microcrystalline cellulose increased. The compaction pressure required to produce a compact at a solid fraction of 0.6 decreased with increasing moisture content. The permanent deformation pressure and tensile strength of compacts were observed to be relatively independent of moisture content below about 5% moisture and then decrease as the moisture content increased further. The “best case” Bonding Index was also observed to be independent of moisture content below 5% and then increase with increasing moisture. The Brittle Fracture Index and “worst case” Bonding Index, however, did not appear to be affected by changes in moisture content. Powder flow was shown to decrease with increasing moisture content. Conclusions. These mechanical property data are consistent with the hypothesis that water acts as a plasticizer and influences the mechanical properties of microcrystalline cellulose. At moisture levels above about 5%, the material exhibits significant changes consistent with a transition from the glassy state to the rubbery state.