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The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostatic interaction among the charged headgroup of the surfactant and the charged fiber surface.

In the present work, we studied the role of an anionic surfactant, sodium dodecyl sulfate, and a cationic surfactant, dodecyltrimethylammonium chloride, in the sorption of 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers. Fluorescence spectroscopy was used to quantify the amount of sorbed Tinopal CBS on the fiber surface. Differences in the spectral properties and the efficiency of sorption of the whitener/surfactant/fiber system are explained in terms of electrostatic interactions. Our results also show that the sorption efficiency is greater for solutions containing cationic surfactants only below the critical micelle concentration, while anionic surfactants show a smooth influence on the sorption process.

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