ξ-POTENTIAL AND SURFACE DYEABILITY OF GRAFTED POLYESTER FIBER IN AQUEOUS SOLUTION OF METHYLENE BLUE

Abstract

To study interfacial electrical properties of the polyester fibers ungrafted and grafted with acrylic and methacrylic acid and surface dyeability by cationic dye on these fibers, the ξ-potential of the fibers was measured in aqueous solution of Methylene Blue.
The negative ξ-potential of the ungrafted and grafted polyester fibers increased with increasing pH, and it's value reached equilibrium value above pH 8. The ξ-potential of the fibers decreased with increase in the degree of grafting because the position of slipping plane in electrical double layer moved into diffused layer according to the hydrogel layers formed by grafted polymer chains.
The amount of Methylene Blue adsorbed per unit area of the fiber surface was calculated from the ξ-potential values. With increasing concentration of the dye, the sign of the ξ-potential changed from negative to positive and the amount of the dye adsorbed on the fiber surface increased. These results suggest that electrostatic interaction and van der Waals force act between the fibers and the dye. The amount of the dye adsorbed decreased with increase in the degree of grafing.
The free energy of adsorption (Δ_??_) for Methylene Blue on the fibers was calculated from the slope of the ξ-log C_d (C_d: the concentration of dye) curve etc.. The negative value of Δ_??_ decreased with increasing the degree of grafting. The heat of adsorption (Δ_??_) was negative and the entropy of adsorption (Δ_??_) was positive. The positive value of Δ_??_ suggests the importance of entropic interaction (the formation of hydrophobic bond) as a driving force of adsorption for the dye on the fiber surface. It is concluded that the surface dyeability of Methylene Blue on the grafted polyester fibers is less than that on the ungrafted polyester fiber since the hydrogel layer is formed at the fiber surface by grafted polymer chains.