Bifunctional Systems of Reactive Dyes

In the early years of the commercial exploitation of reactive dyes, it was soon noted that anomalously high values of cuprammonium fluidity were observed for dyeings of many reactive dyes in full depths, although tests of tensile strength demonstrated that the cellulose remained undamaged. Investigation showed that these anomalous results were associated with those dyes capable of forming crosslinks between neighbouring cellulose chains, such as the bis(sulphatoethylsulphone) dye CI Reactive Black 5 (Figure 1) or the dichlorotriazine dyes with two chloro substituents capable of attack by cellulosate segments of the polymer chains, such as CI Reactive Red 1 (Scheme 1).

Figure-1

Scheme-1

These phenomena attracted further interest when ICI introduced the ProcionH-E dyes, a full range of high-fixation dyes containing two aminochlorotriazine groups per molecule. A detailed study of representative members of this range, as well as other potentially crosslinking reactive systems (dichlorotriazine, chloromethoxytriazine, dichloroquinoxaline, trichloropyrimidine and chlorodifluoropyrimidine) provided convincing evidence of the extent of crosslinking that could take place. The degree of crosslinking was non-existent or relatively insignificant for typical pad–batch dyeings at ambient temperature, but thermal fixation by the pad–dry–steam method resulted in a much higher proportion of crosslinked dye molecules.

Recently attention has turned to the more difficult problem of analysing the mode of fixation to cellulose of a bifunctional reactive dye of the Sumifix Supra (NSK) range that contains two dissimilar reactive systems (vinylsulphone and chlorotriazine). Controlled enzymatic degradation of a mechanically milled cotton fabric that had been batchwise dyed at 60°C yielded interesting results.

1. About 80% of the vinylsulphone groups had reacted with the cellulose.
2. About 50% of the chlorotriazine groups had not reacted with cellulose and only half of these had hydrolysed to OH groups.
3. A considerable proportion of the dye molecules had formed crosslinks by reacting via both mechanisms.