(22c) Assessment of Powder Cohesion Strength Using Shear Cell and Warren Spring Cohesion Testers

The characterization of powders and bulk solid materials is extremely important to ensure uniform product quality. The flow obstructions in both large and small scales lead to process down time, bin collapse, compromised aerolisation of dry-powder inhalers (DPIs), etc. Many shear cell instruments have been designed to characterize the flow behaviour of particulate materials. However, most of these devices are limited to work at linear boundary of the yield locus, i.e., at higher normal stress loads. The cohesion index values are obtained by extrapolation of the yield locus. This limitation compromises the characterization of cohesiveness at low normal stresses (< 100 Pa). This study compares the cohesion index of common food and pharmaceutical powder materials obtained from a shear cell and Warren Springs cohesion (WSC) instrument. The powders analysed were starches (from wheat, potato and corn), microcrystalline cellulose (MCC) and wheat gluten. Volume mean diameter (D_4,3) of the particles ranged from 118.47 ± 5.26 µm for gluten to 27.71 ± 1.41 µm for corn starch. For MCC, the cohesion index using WSC at 0.1 kPa was 6.55 ± 0.02, approximately, four times the value for wheat starch (1.59 ± 0.28). Intermediate values were found for corn starch samples (0.84 ± 0.02) and gluten samples (0.53 ± 0.18), whereas potato starch samples presented the lowest cohesion index (0.38 ± 5x10^-3). The WSC values will be compared with the shear cell values to characterize the difference in cohesion index due to different measurement techniques. At completion of this study, the cohesion index values of common powder materials, at low stress levels, will be established.