Modeling and Validation of the Cohesion Reduction of Fine Powders via Surface Modification

Flow and handling of fine powders is a topic of great interest to industry. High cohesion relative to their weight of fine powders leads to problems such as, agglomeration, poor flowability, electrostatic charging and low bulk density. In this talk, powders of interest to pharmaceutical industry are considered where poor flow problems lead to downstream problems such as poor content uniformity and marginal improvement in dissolution rate of fine API powders. To encounter these problems, nano-particle dry coating is shown to be a more rigorous approach. Surface modified pharmaceutical powders are produced using several devices, both based on batch and scalable continuous operation. Results illustrate the improvement in flow, fluidization, dispersion, lack of agglomeration, bulk density, and electrostatic tendency, all leading to potentially significant cost benefits in industrial processing, handling, storage and transportation. In order to understand the cause of cohesion reduction, contact modeling based on our multi-asperity advanced models where the influence of material properties, surface area coverage and spatial and size distribution of guest particles is presented. Models are qualitatively validated by bulk and particle scale experimental results, including detailed surface energy measurements that explain cohesion of pharmaceutical powders based on two major tuning parameters, surface roughness and surface energy. Issues of linking particle to bulk scale are discussed along with selected results from Discrete Element Modeling of cohesive powders.