The effect of ethyl xanthogenate on both the electrokinetic properties and sorption of a cationic dye onto polyester fibers

Abstract

An experimental investigation of the streaming potential and sorption of porous plugs of polyester fibers treated with different amounts of potassium ethyl xanthogenate, at constant temperature, and later dyed with the cationic dye Brilliant Green, is described. The negative zeta potential of polyester fibers pretreated with ethyl xanthogenate/Brilliant Green increases when increasing the amount of ethyl xanthogenate previously taken up the fiber, in the range of dye concentrations in solution between 10 −6 and 2 × 10 −5 M, the reverse trend being observed between 2 × 10 −5 and about 10 −3 M. The sign of the zeta potential changes at high concentrations of cationic dye in the liquid phase. When the amount of ethyl xanthogenate taken up by the fiber increases, a shift of this inversion of sign towards lower concentrations is observed. The sorption of cationic dye increases on increasing the amount of ethyl xanthogenate previously taken up by the fiber. The surface conductance, κ s, predominates in the total electrical conductance of the system, κ at low concentrations of dye in the solution, while it is the bulk component, κ b, that predominates in the higher concentration range. From the experimental results and on the basis of the molecular structures of Brilliant Green and ethyl xanthogenate, it is suggested that the sorption of Brilliant Green on polyester fibers previously treated with ethyl xanthogenate probably takes place by means of electrostatic attraction between the dye cation and the negative charged -S − groups of the ethyl xanthogenate previously taken up by the fibers during their treatment. Given the hydrophobic character of the polyester and the amphiphilic nature of the dye molecules, hydrophobic attractions between the fiber and the hydrophobic part of the dye might account for the interaction explaining the adsorption of Brilliant Green even when it is hindered by electrostatic repulsion.