Page 364 - Basic Principles of Textile Coloration

REACTIVE DYES FOR WOOL 353

variations of this type of process and it is also incorporated into the continuous
dyeing of cotton/polyester materials using disperse and reactive dyes (Sections
10.5.3 and 23.7.3)

16.5.6 Application of reactive dyes and finishing chemicals
Reactive dyes may be applied to undyed cellulosic materials at the same time as
the usual crease-resist and durable press resin finishes, thus combining dyeing and
finishing into one step. During curing, when the methylolamino groups
(–NHCH2OH) of the polyfunctional finishing chemicals react with hydroxyl
groups in the cellulose (Section 25.3.1), the dye reacts with free amino groups in
these agents rather than with the fibre. Since the dye is fixed to the finishing
agent, the fastness properties of the final dyeing depend on the permanence of the
finish.

16.6 REACTIVE DYES FOR WOOL [2]

16.6.1 Introduction
The somewhat late development of fibre-reactive dyes was partly caused by a lack
of appreciation of the considerable reactivity of fibres made of cellulose or
proteins. A number of dyes developed for wool with 2-sulphatoethylsulphone or
chloroacetylamino groups were not immediately recognised as reactive dyes. In
fact, the development of reactive dyes really started with the introduction of the
Procion dyes for cotton by ICI in 1955.

Despite the many possible reactive groups in dyes capable of covalent bond
formation with nucleophilic groups in wool, only a limited number of types of
reactive dye have been commercially successful. Figure 16.7 shows the major types
of reactive groups. The dye chromophores are essentially those used for cotton
reactive dyes.

The most important reactive groups in wool are all nucleophilic and are found
mainly in the side-chains of amino acid residues. They are, in order of decreasing
reactivity, thiol (the –SH of cysteine), amino (–NH– and –NH2 of say histidine
and lysine) and hydroxyl groups (–OH of serine or tyrosine). Difluoro-
chloropyrimidines undergo aromatic nucleophilic substitution of one or both
fluorine atoms, the fluorine between the two nitrogen atoms being the most
reactive. Bromoacrylamido groups are stable in boiling water at pH 7 and react by