SynopsisThe dyeing process for a cellulose membrane-direct dye system is analyzed based on a parallel transport mechanism of surface and pore diffusion with Freundlich isotherm. Numerical solutions were obtained in order to clarify how the surface and pore diffusion resistances affect the uptake curve. The numerical solutions were also compared with an analytical solution for surface diffusion control to establish the range where the analytical solution can be considered as an acceptable approximation. The uptake curves in the cellulose membrane-chromophore (C.I. Direct Yellow 12) system in the presence of inorganic electrolyte were measured. The rate of adsorption and the maximum amount of adsorption increased with a n increase in the concentration of those electrolytes. The rate of adsorption was approximately controlled by the surface diffusion rather than by pore diffusion. The surface diffusivities of the dye were little affected by either the concentration and or nature of the electrolyte.

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The differences in behavior on adsorption of direct dyes with different kinds of counterions on cellulose in the absence of an electrolyte are indicated, and an alternative role for electrolytes on adsorption of the dye on cellulose is proposed. In addition, an interesting effect of urea on the dye adsorption on cellulose at various temperatures is revealed.

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