Powder rheology is essential in the pharmaceutical industry for the characterization of excipients and the optimization of drug formulations. It involves the study of the flow behavior and deformation of powders, which directly impacts manufacturing processes and the quality of the final product. Flowability, compressibility, and cohesion can be measured, providing a complete picture of powder flow behavior and particle interactions. Lactose monohydrate and carboxymethyl cellulose (CMC), popular excipients in the pharmaceutical industry, have rheological properties such as flowability, cohesion, and compressibility. Their flow, compressibility, and cohesion are quantified to optimize formulations before scale-up. In this study, lactose exhibited over three times higher compression and cohesion values compared to CMC. Both powders showed rate-dependency, with flow energy decreasing as tip speed increases. Their rheological properties were also examined at 45 °C, simulating exposure to sunlight, and at 4 °C, simulating refrigeration. At 4 °C, the flow function of lactose monohydrate shifted towards cohesive flow. It can be concluded that under high stress, CMC flows better, while under moderate to relatively low stress, lactose monohydrate flows better. Under very low to no stress, both have similar flowability. Lactose monohydrate demonstrates easy flow, relatively low confined flow energy, moderate cohesion, and excellent compressibility. CMC exhibits lower cohesion but higher confined flow energy, which should be taken into account when considering CMC as a filler.
