Influence of key parameters on the morphology of ethylcellulose microcapsules prepared via room-temperature spray drying

In this contribution, the morphology of ethylcellulose (EC) microspheres prepared with a room-temperature spray-drying technique is examined as a function of solution concentration, nozzle-to-target distance, and choice of solvent. Additionally, to determine the morphology of EC microspheres in the presence of an aqueous encapsulated material, a series of encapsulation measurements was conducted using hydrogen peroxide solution as the core component. It was observed that highly concentrated EC solutions lead to the formation of tail-like fibers adjacent to the sprayed microcapsules because of the high viscosity of solutions. Furthermore, when the solutions are sprayed from relatively short nozzle-to-target distances, porous EC films are formed on the target surface along with the EC microspheres. Three nozzle-to-target distances were tested (38, 69, and 115 cm), and the optimal one was found to be 115 cm. To determine how and to what extent the solvent used in room-temperature spray-drying experiments affects the morphology of resultant microspheres, EC was dissolved in either acetone or dichloromethane (DCM), and sprayed from the resultant solutions. While microcapsules prepared from the EC-in-DCM system exhibit even, but porous wall surfaces, microspheres prepared from the EC-in-acetone solution display irregular, but cavity-free wall-surfaces. Finally, as opposed to the pure EC capsules, the ones containing H₂O₂ solution exhibit very smooth wall surfaces; this effect was attributed to the plasticizing effect that the aqueous solution has on the ethylcellulose macromolecules.