ξ-potential and surface dye-ability of poly(vinyl alcohol) fiber with different degree of formalization in a cationic dye solution

Abstract

The surface dyeability of the poly(vinyl alcohol) fiber with different degree of formalization was studied by measuring ξ-potential of the fiber in alkaline aqueous solutions (pH 10) of a cationic dye Methylene Blue. With the increase in the dye concentration, the sign of the ξ-potential of the fiber changed from negative to positive and thereafter the positive value approximated to saturated value, and the amount of dye adsorbed (expressed in mol/cm2-fiber) increased also. These results may possibly be attributed to the formation of the electrostatic bond between the fiber and the dye. The linear relations were found between ξ and logC d and its slope did not change with rise of temperature. The free energy of dyeing ΔG (negative) calculated from the slope of the ξ-logC id curve, etc. increased with increasing the degree of formalization of the fiber. This fact corresponds to the increase in the surface dye adsorption with increasing the degree of formalization. With increasing the degree of formalization, the heat of dyeing ΔH (negative) increased and the entropy of dyeing ΔS (positive) decreased. The positive value of ΔS for each fiber, suggests the formation of hydrophobic bond as a driving force to the dyeing of Methylene blue on the fiber surface in addition to the electrostatic bond.