Inclusion of azo disperse dyes by cyclodextrins at dyeing temperature

Abstract

Changes in the sorption isotherms of six azo disperse dyes(4-amino-4-′-nitroazobenzene derivatives) on a hydrophobic fibre from water on addition of α, β and γ CD ḿeasured at 70–90° C. Formation constants and the stoichiometry of the complex formation of the azo dyes with CD's were obtained by analyzing the changes in the isotherms. Most of dyes form 1:1 complex with CD's when their maximum cross section of β-phenyl ring is comparable to, or smaller than, the cavity diameter of CD's. Azo dyes with electron withdrawing bulky groups at the 2′ or 2′ and 6′-position form 2:2 complexes with γ CD. The nature of the complex formations is discussed in terms of the thermodynamic parameters for the complex formations and of the changes in the absorption spectra of the dyes on complex formation. The retarding action of β CD on the dyeing rate of an azo disperse dye on secondary acetate fibres at 90° C was assessed by a computer simulation.