KINETICS OF RELEASE OF A MODEL DISPERSE DYE FROM SUPERSATURATED CELLULOSE-ACETATE MATRICES

A study has been made of the kinetics of release into water of a model disperse dye (4-aminoazobenzene) from supersaturated solvent-cast cel lulose acetate films at room temperature. Excess dye was introduced in to the polymer matrix by: (i) sorption from aqueous solution at 100 de grees C; (ii) sorption from the vapour phase at 110 degrees C; or (iii ) prior dissolution in the casting solvent. The effect of the method o f introduction of the dye, the degree of supersaturation and the rate of agitation of the bath were investigated. Under conditions of strong agitation, the release kinetics from films dyed by method (i) or (iii ) were in general accord with the theoretical model which assumes solu te in the film in excess of the saturation limit to be in the form of immobile aggregates at equilibrium with mobile dye; although the value of the diffusion coefficient of the solute in the film was found to b e substantially higher than that in the unsaturated film. On the other hand, when dyeing had been effected from the vapour phase, Fickian ki netics was followed and the diffusion coefficient was found to be equa l to that observed in unsaturated film. It was concluded that under th ese conditions, the excess dye in the film tends to remain molecularly dispersed. Under conditions of slow agitation, the root t kinetics wa s not attained in many instances. General and early-time approximate e xpressions based on the Roseman-Higuchi model proved useful for the in terpretation of the results in such cases; while the said model was ex tended to include the effect of significant variation of the partition coefficient of the solute with concentration. (C) 1998 Elsevier Scien ce B.V. All rights reserved.