Influence of Interfacial Interactions on the Formation of Zein–Ethyl Cellulose Composite Films

In this study, submicrometer zein particle suspensions (ZPS) were prepared by antisolvent precipitation from aqueous ethanol (Eth, 90% w/w) or isopropanol (Iso, 90% w/w) solutions. The resulting ZPS were incorporated into an ethyl cellulose solution (EC, 4% w/w), followed by casting to obtain continuous composite films. The zein particle size distribution was evaluated by laser diffraction, confocal laser scanning microscopy, and atomic force microscopy analyses. The ZPS prepared from 90% aqueous ethanol had zein particles with a smaller average particle size (Dv50 = 0.56 μm) compared to those prepared from 90% aqueous isopropanol (Dv50 = 3.74 μm). Transparent and coherent zein-EC composite films exhibited different scanning electron microscopy features depending on the types of solvent (ethanol = Eth or isopropanol = Iso) and surfactants (Span 85 or Tween 80) used. Atomic force microscopy analysis confirmed the affinity between zein particles and the EC phase when prepared in pure ethanol or in ethanol- or isopropanol-based formulations containing Tween 80. The Hansen Solubility Parameter concept was applied to elucidate how the compatibility of various components affected the microstructures and material properties of the zein-EC films. Overall, results from this study have contributed to increased understanding of the effects of solvents and surfactants on the formation of submicrometer zein particles and zein-EC composite films.