Mixture diffusion of sulfonated dyes into cellulose membrane. III. Application of parallel diffusion model to binary system of direct dyes with different affinity

Mixture diffusion of two dyes (C.I. Direct Blue 15 (DB15) and C.I. Direct Y ellow 12 (DY12)) with different affinity onto the substrate into cellulose membrane from the binary solution was studied at 55 degrees C. Uptake curve s and concentration-distance profiles were measured experimentally in the r atios (DB15:DY12) 1:0.5, 1:1 and 1:2. It was examined whether the diffusion of the dyes could be analyzed based on the parallel diffusion theory of su rface and pore diffusion. It was revealed that the diffusion of DB15 with h igher affinity could be analyzed based on the model in the ratios 1:0.5 and 1:1, although the theoretical value deviated slightly from the data in the concentration - distance profile in the ratio 1:1. On the other hand, the diffusion of DY12 with smaller affinity could not be described by the model , because the diffusivity of the dye changed during the adsorption process against the assumption of the model. (C) 2000 Elsevier Science B.V. All rig hts reserved.