Investigation of the Polyamide 6,6 dyeing process with Acid Blue 45 dye.: Part II.: Surface free energy, zeta potential and dye/polyamide interactions

Synthetic fibres are now of great importance for textile production. In Part I of this study, the kinetic and thermodynamic functions of the sorption process for Acid Blue 45 on Polyamide 6,6 (Nylon 6,6) were studied; in Part II, the surface free energy components for the polymer and the dye were investigated. If van Oss et al.'s approach to the surface free energy components is used, the results obtained show that the surface of Polyamide 6,6 is a monopolar electron-donor surface. Also, the dye, when compressed as pellets, shows practically only electron-donor character. But these values are debatable, as both acidic and basic sites are present on the polyamide surface. The isoelectric point for the polyamide appears at pH 3, while for the dye in its saturated aqueous solution it is at pH 2. Therefore both surfaces are negatively charged in a broad pH range. Nevertheless, the adsorption takes place, which means that the attractive forces are higher than the electrostatic repulsive forces. As the adsorption takes place in spite of the mostly electron-donor character of both surfaces and the same sign of the electrical charge, this places doubt on the validity of such determined components, But on the other hand, it may be concluded that the adsorption process on the bare polyamide surface is of a chemical nature. For example, interactions may occur between the -COOH end-groups of the polyamide and the -OH groups of the dye, as well as between the -NH2 end-groups of the polyamide and -SO3Na of the dye, which are much stronger than electrostatic repulsive forces. The two electron-donor sites do not interact repulsively. The increase in sorption with increasing temperature (Part 1) and practically no desorption of the dye from the polyamide surface for lower coverages (when dyed from a solution of concentration up to 10(-3) M) support the above conclusion.