Influence of parallel nozzle electroencapsulation parameters on microcapsule properties – A case study using the Taguchi robust design method

Abstract

The production of microcapsules by electrospraying two immiscible liquids from oppositely charged parallel nozzles and the subsequent microcapsule collection constitute an electroencapsulation process influenced by numerous parameters. The electroencapsulation parameters include the liquid properties, e.g. bulk liquid conductivity K, viscosity η, density ρ, and surface tension γ; the electric field, gravity field, and the electrospraying and collection geometries; and the atmospheric properties. In the present work, NaI-doped glycerol was used as core liquid, with an optional payload of dispersed thermally carbonized porous silicon nanoparticles (PSi). Chloroform with dissolved Eudragit E 100 cationic copolymer and dispersed talc particles as an anti-tacking agent was used as shell liquid. The influence of varying ten electrospraying parameters (liquid flow rates Qi, electrospraying voltages |Ui| and polarity, solid concentrations, and temperature T) within the cone-jet mode regime on the structure and yield of microcapsules produced by parallel nozzle electroencapsulation was investigated simultaneously using the Taguchi robust design method. Of the investigated parameters, the most important were found to be NaI concentration and T, both influencing the core liquid conductivity; and the liquid flow rates. The Taguchi experiment and additional results suggest that optimally, the parameters affecting liquid conductivities should be set for a coarse atomization current balance when using a maximal shell liquid flow rate. Then, the core liquid flow rate can be adjusted for best process efficiency.