Dyeing cotton with reactive dyes under neutral conditions

This paper describes a new method to dye cotton with selected reactive dyes by long-liquor – or so-called 'exhaustion'– processes under neutral conditions. Particularly promising results were obtained with reactive dyes containing free vinyl sulphone residues. Although there are dyes on the market that contain free vinyl sulphone groups, for example, the Novacron C (Huntsman) range of dyes, many of this class contain 'blocked' vinyl sulphone residues; examples include sulphatoethylsulphone or chloroethylsulphone precursor groups, and these may be preactivated to the highly reactive vinyl sulphone form simply by a mild alkali treatment. After this activation, neutral, long-liquor dyeings can be carried out at the boil in the presence of electrolyte. This new dyeing method gave very good results in terms of overall fixation efficiency values, without the need for alkali additions.