Evaluation of Electrostatic Drop Making of Concentrated Sodium-Alginate Liquids for Manufacturing of Gel Type Beads
Alginate beads are often used for immobilizing of biocatalysts and are usually produced by dropping in a gelling agent. In this work the application of constant and pulsating DC electric fields is explored to control droplet formation of highly viscous sodium-alginate in the dripping and jet modes. The main aim is to produce mono-sized droplets and consequently mono-sized beads with a specified size after gelation of the droplets in calcium chloride. The effects of electric field strength, frequency and flow rate are investigated to establish the operating boundaries for a single nozzle for two modes of operation, jet mode and dripping mode. In the jet mode employing the pulsating DC potential at an appropriate frequency leads to more uniform size distribution and more spherical beads. Otherwise a constant field would promote the formation of long filament shaped beads. It is shown that in the jet mode and in the absence of any electric field larger beads are produced with lesser uniformity in their size distribution as compared to the pulsating DC field. For the dripping mode it is shown that the use of a constant DC electric field produces uniform droplet sizes. However, in the latter case the maximum possible flow rate is small as compared to the jet mode. In the jet mode, increasing the height of fall of the droplets after jet break up improves the sphericity of the beads because of the increase of time for droplets to relax before gelation