Dyeing of nylon with reactive dyes. Part 1. The effect of changes in dye structure on the dyeing of nylon with reactive dyes

Abstract

The dyeing behaviour of seven red commercial cellulosic reactive dyes, all based on the same chromophore and possessing one or more reactive group, and one to three chromophore units, were evaluated on nylon. Fixation levels appeared to be independent of the number of either reactive groups or chromophore units. Also, the degree of sulphonation, per se, appeared to have little effect on fixation, whereas the type of reactive group was important. The major determinant of dye fixation appeared to be associated with the shape of the molecule and the type, not the number, of reactive groups.

Introduction

The presence of terminal amino end groups in nylon fibres imparts substantivity towards anionic dyes, specifically acid dyes, direct dyes and reactive dyes. Acid dyes are commonly used on nylon, with 1:2 pre-metallised acid dyes generally being used when reasonable levels of wet fastness [1] are required. However, even these dyeings can cause some staining of adjacent fabrics during laundering. Whilst an after-treatment of the dyed nylon can result in somewhat improved wet-fastness, repeated washing can still result in loss of colour and there remains much scope for improvement.

Reactive dyes for cellulose resemble acid dyes in their basic structure, but additionally possess one or more fibre reactive group, their name being derived from their ability to react chemically with groups on the fibre. In the mid-fifties Rattee and Stephen [2], [3], [4], [5] showed that dyes containing a dichlorotriazinyl reactive group are capable of reacting with cellulosic fibres, in the presence of alkali, to form covalent dye to fibre bonds. Subsequently, research into the chemistry and the application of reactive dyes focused overwhelmingly on cellulosic fibres [6], [7]. In contrast, considerably less attention has centred on reactive dyes for polyamide fibres. Thus, compared with the vast number of reactive dyes for cellulose [8], relatively few reactive dyes have been introduced specifically for polyamide fibres. It is known that some reactive dyes, which were developed for cellulosic fibres, can be covalently fixed at the boil, to nylon at slightly acidic pH. Under these conditions, covalent bonds form between the dye and the amino groups of nylon, without the need for an alkaline fixation step [9], [10]. Of the reactive dyes which have been developed specifically for application to nylon the Stanalan [11] and Eriofast [12] ranges are probably the best known. Eriofast dyes are metal-free, sulphonated reactive dyes, developed for application to nylon in order to achieve outstanding wet fastness properties. Water soluble dyes possessing electrophilic reactive groups such as chlorodifluoropyrimidines [13], bromoacrylamides [14], chlorotriazines and vinylsulphones [15], [16], as well as some disperse types [17] have been evaluated on nylon.

As a first step towards the design of novel reactive dyes for nylon, and before embarking on a synthetic programme, an attempt was made to identify the structural features associated with good reactive dyeing performance on nylon. Therefore the effect, on dyeing properties, of changes in dye structure, including molecular size, number of reactive groups, type of reactive groups and also the degree of sulphonation were evaluated.