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The solubilization process of sorbitan monooleate (Span 80) niosomes, formed by sonication, by addition of the anionic surfactant sodium dodecyl sulfate (SDS) was studied in this work. The main parameters studied were the optical density at 350 nm wavelength, particle size distribution, ζ-potential, and the concentration of SDS monomers in the dispersions. Results allowed us to differentiate the stages of the solubilization process for each formulation, as well as to identify critical points of saturation by the SDS adsorbed in the bilayer, and the total niosome solubilization. The composition of these critical points turned out to be independent from time, thus allowing the construction of the pseudophase equilibrium diagram, where the lines of saturation and total solubilization of niosomes follow a linear behavior. Monomeric SDS concentration measurement corroborates the composition of the critical point of total solubilization and confirms that the niosome solubilization is a micellization process in which any amount of SDS added above critical values of total solubilization will increase the mixed micelle concentration, keeping constant the concentration of SDS monomers in solution. The results of this study shed light on further research of this biodegradable system regarding its possible use in multiple sustainable applications.

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The ultrafiltration process for separation of sodium lactate from sorbitan monooleate (Span 80) and sodium dodecyl sulfate (SDS) surfactants using ZrO 2 flat-disc ultrafiltration membranes was studied in this work. The study is focused on the influence of the nominal molecular weight limit of the membrane (NMWL), the transmembrane pressure (TMP), and initial lactic acid concentration (C A) on the permeate flux (J p) and rejections observed to ion lactate (R A) and SDS (R S) using a full central composite experimental design and response surface methodology. Experiments were conducted in four stages: a first stage of lactic acid extraction with niosomes formulated with Span 80 (20 mol/m 3) and SDS (4 mol/m 3), a second backextraction stage conducted by NaOH addition until pH > 12 for niosomes breaking and sodium lactate releasing, and a third and fourth ultrafiltration stages at 25 o C to separate the lactate ions from the mixed surfactants. Membrane NMWL, TMP and their interactions presented statistically significant influence on the permeate flux. Rejections to lactate ion and SDS were lower than 4.5% and higher than 86%, respectively, whereas Span 80 rejection was 100% in all range of experimental conditions tested. The optimal conditions were established for maximum values of permeate flux, and they were obtained for a 2 bar TMP and 15 kDa NMWL membrane. Under these conditions, the rejections of SDS surfactant and lactate ion were 87.3% and 4.31%, respectively, with a permeate flux of 42.63 L/m 2 h. The antagonistic effect between permeate flux and SDS rejection is also proved.