Low Solid-Loaded Formulation Homogenization Using Dual-Asymmetric Centrifugation

Abstract

Dual-asymmetric centrifugation (DAC) has emerged as an attractive processing technology across industries that process solid-filled formulations, and it shows great potential to safely and rapidly combine formulation constituents. Legacy processing of such formulations often utilizes high-shear bladed mixers. However, these mixers are prone to issues such as inhomogeneous mixing due to vessel dead spots, end-of-mix viscosity restrictions (requiring materials to be sufficiently inviscid for blades to move through the material), safety concerns arising from the impact and frictional insults among mixer components, and extended mix times. To bypass inherent drawbacks in bladed mixers, the present study has undertaken the development of a mixing protocol using a DAC mixer yielding the most repeatable and safe formulation homogenization of a binder comprised of a 9:1 mass ratio of cellulose acetate butyrate (CAB) to triacetin, with a balance of diethyl ketone (DEK) solvent, filled with 15 wt.% granulated sugar. Six mixing protocols were investigated to identify the protocol yielding the best result in terms of minimal heat generation, most uniform solids dispersion, and the most repeatable mixing evolution in terms of evolved torque, final mixture viscosity, and visual consistency during mixing. After assessing the viability of the protocols explored, a protocol was selected to guide future mixing, and an outlook for developing additional DAC mixing protocols for other materials was proposed. These DAC mixing protocol development principles could be applied to a broader range of formulated products, opening new horizons for future DAC mixing applications.