Quantifying effects of moisture content on flow properties of microcrystalline cellulose using a ring shear tester

In this work, we have quantified effects of moisture content, over the relative humidity (RH) range of 5-92% corresponding to 1.6-10.9% of water content, on flow properties of a grade of microcrystalline cellulose (Avicel PH102) using a ring shear cell. Several key powder flow parameters, including cohesion (τ_c), unconfined yield strength (f_c), powder bulk density (ρ_b), flowability (ffc), and effective angle of internal friction (ϕ_e), were assessed. Powder flow properties deteriorated continuously with increasing RH, as shown by the higher f_c and τ_c as well as lower ffc, under all stress conditions. With increasing RH, ρ_b increased and then decreased with a maximum at 20% RH. The ϕ_e initially increased, from 41 to 43 degrees, and then remained approximately constant from 20% to 92% RH. The deterioration in powder flow properties is caused by surface modification by moisture, which enhances particle-particle interaction strength. The knowledge obtained in this study is useful to achieving consistent properties of this important tablet excipient and formulations containing it.