In rotary tablet presses, the powder flow into the dies is typically facilitated by paddle feeder. For internally lubricated formulations, the shear forces exerted by the paddle rotation can result in a considerable decrease in tablet strength due to the dispersion of lubricant agglomerates. Available models to describe the lubricant dispersion in paddle feeder allow only a limited quantitative description and transferability of the process. This study introduces an empirical dispersion kinetic which is able to precisely describe the reduction of compactibility due to the shear stresses inside the paddle feeder, even for inhomogeneously flowing material. Additionally, by blending different grades of magnesium stearate at three levels of lubricant concentration with two different grades of microcrystalline cellulose, the impact of bulk properties on the lubrication dispersion in the feed frame was investigated. It was shown, that for a given formulation, the kinetics of compactibility reduction are comparable for different magnesium stearate concentrations. Additionally, the bulk properties of the applied magnesium stearate grade critically affect the dispersion kinetics as well as the maximum compactibility reduction inside the feed frame. In summary, the developed model represents a meaningful extension of the currently available process models for pharmaceutical tablet lubrication.
Keywords: Modeling; Overlubrication; Particle dispersion; Tableting.
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