PREPARATION OF FIXING AGENTS FOR ANIONIC DYES

Abstract

The selection of dyes and dyeing auxiliaries is a crucial factor in optimising dyeing processes. Dyeings often show unsatisfactory wet fastness properties. This is usually encountered with direct dyes and to a lesser extent with reactive dyes also. Different cationic fixing agents have been used as pretreatment or aftertreatment to improve the wet fastness properties of these dyes but none has proved to be totally satisfactory. Therefore, there is still a need for novel dyeing processes that improve properties in respect of application and fastness properties of the dyeings. The present work is therefore concerned with the synthesis of new cationic fixing agents and their evaluation as fixing agents in improving the wet fastness properties of anionic dyes on cellulose fibres. Eight mono-reactive (28a-d and 29a-d) and four bis-reactive (30a-b and 31a-b) 2,3-epoxy / 3- chloro-2-hydroxy propyl derivatives of quaternary ammonium chloride have been synthesised and their structures have been characterised using IR and 1H- NMR spectroscopy. Purity of these compounds has been checked by thin layer chromatography (TLC). One mono-reactive (28c) and two bis-reactive (30a and 30b) 2,3- epoxypropyl derivatives have been used for the cationisation of cellulosic iv fabrics under different pretreatment conditions. Pretreated fabrics were then dyed with a variety of direct, reactive and acid dyes under neutral and alkaline conditions in the absence of salt. A bis-reactive derivative compound 30b was also applied as an aftertreatment to the conventional direct dyeings under neutral and alkaline conditions. The reflectance values and the corresponding CIE L*, a*, b*, C* and ho colour coordinates of the samples were measured. From the reflectance values at the λ max. of the dyeings, colour strength (K/S) values of the dyeings were calculated using Kubelka-Munk equation. Fastness properties of the dyeings have been determined by following standard methods for the determination of colour fastness of textiles and leather. Pretreatment with mono- and bis-reactive cationic fixing agents (30a, 30b, 28c) has enabled the dyeing of cotton fabrics with anionic (direct, reactive and acid) dyes under neutral conditions in the absence of salt. Higher colour strength (K/S) and good wash fastness properties were obtained with the pretreated fabrics as compared to the untreated fabrics dyed with the same direct and reactive dyes. Bis-reactive derivatives showed better wet fastness properties as compared to the mono-reactive derivative. In addition, pretreatment has significantly reduced the dyeing time, thus becoming a more environmentally friendly method for the direct and reactive dyeing of cotton fabrics. Aftertreatment with cationic agents has shown a slight change in the colour of the direct dyeings but has beneficial effects on the wash fastness results.