Dyeing of Anionically-Modified Polyamide Fibers with Cationic Dyestuffs

Abstract

The diffusion from the fiber surface into the interior is the rate-determining step in the cationic dyeing of anionically-modified polyamide fibers. The diffusion coefficients for the diffusion of an oxazonium dyestuff (Astrazon Blue BG, C.I. 51004) and a thiazonium dyestuff (Methylene Blue, C.I. 52015) into two polyamides modified with the monosodium salt of 5-sulphoisophthalic acid at pH 4.5 and 1.8 have been determined by the steady-state method and have been compared with the diffusion coefficients for diffusion into the corresponding unmodified polyamides. In the case of the anionically-modified polyamides, active cooperation of the sulpho groups in the diffusion of the dyestuff cations into the interior of the fiber must be assumed, of a type in which the dyestuff cations are first bound to outer sulpho groups and then, in movements of the segments of the polymer chain, are transferred from the outer sulpho groups to free inner sulpho groups. The activation energies for the diffusion process have been determined by means of the Arrhenius equation from the temperature dependence of the diffusion coefficients.