Preparation and Characterization of Emulsifier-free, Submicron-sized Monodisperse Rice Bran Wax Particles and their Applicability

The development of an optimal material design is crucial for rice bran wax (RBW) to achieve significant advancements in value-added byproducts. In this study, emulsifier-free, submicron-sized, monodisperse RBW particles were prepared via melt emulsification using a combination of a high-HLB emulsifier-decaglycerin stearate or Tween 20-and a low-HLB emulsifier-glyceryl stearate or Span 20. High dispersibility was achieved due to the zeta-potential generated by the surrounding surfactants, resulting in monodispersed submicron-sized RBW particles. Surface cleaning with ethanol effectively removed surface-adsorbed emulsifiers, yielding emulsion-free RBW particles. Due to the hydrophobic nature of the wax particles, high solvent repellencies were observed, along with the formation of colloidal assemblies such as liquid marbles and W/O Pickering emulsions using cosmetics-applicable liquids. Based on X-ray diffraction analysis and differential scanning calorimetry, RBW was identified as a promising candidate for emulsifier-free submicron-sized particles due to its high crystallinity, which facilitates the effective elimination of emulsifiers.