Physical Form And Handling Of Reactive Dyes

All reactive dyes are prone to hydrolysis in the presence of moisture, especially the highly reactive ranges, and they will deteriorate unless carefully handled and stored. Cool, dry conditions are essential and the lids of packages must be firmly replaced after use. Since reactive dyes in powder form may release dust when disturbed, it is always possible for respiratory allergies to arise with some workers who handle them [1]. For this reason suitable dust-excluding respirators should be used and weighing or dissolving procedures should be carried out in ventilated enclosures.

Conventional dye powders are usually dissolved by one of the following techniques:

1. Pasting with cold water followed by the steady addition, with stirring, of the required amount of water at the correct temperature.
2. Sprinkling a steady stream of dye powder into the vortex formed by the high-speed stirring of water at the correct temperature.

Few ranges of reactive dyes require boiling water, although Remazol (HOE) vinylsulphone dye powders are dissolved in boiling water followed by passing immediately through a fine sieve into the required volume of cold water. Highly reactive dyes, such as dichlorotriazine or chlorodifluoropyrimidine types, require water temperatures no higher than 50°C. Most dyes of lower reactivity, e.g. aminochlorotriazine or trichloropyrimidine systems, require a dissolving temperature of 80°C.

The dusting problem with some reactive dye powder brands can be avoided by working with granulated or liquid formulations. A recent improvement that ensures troublefree weighing and handling of small amounts for batchwise dyeing has been the development of cold-dissolving granular brands such as the Drimarene CDG (S) dyes [2–6]. These are non-dusting, free-flowing grains that dissolve readily in cold water and offer ease of handling in automatic dissolving and metering devices.

The marked tendency of reactive dyes to undergo hydrolysis in solution has delayed the development of liquid formulations until recent years. For continuous dyeing and printing, however, especially where automated metering equipment is installed, liquids are particularly convenient. Liquid brands of the relatively stable types, such as sulphatoethylsulphones, aminochlorotriazines and bifunctional dyes containing both of these systems [44], are well established in commercial use. They are essentially isotropic aqueous solutions of the dyes, often with auxiliaries such as a buffer, a hydrotropic agent such as urea or caprolactam, and often a polymeric stabiliser to inhibit settling out on storage [7].

References:

1. J M Wattie, J.S.D.C., 103 (1987) 304.
2. D Link and E J Moreau, Int. Text. Bull., 34 (1) (1988) 13.
3. D Link and E J Moreau, Tinctoria, 85 (1988) 55.
4. D Link and E J Moreau, Chemiefasern/Textilind., 39/91 (1989) 58.
5. D Link and E J Moreau, Textilveredlung, 24 (1989) 87.
6. C Oschatz, Text. Technol. Int., 194 (1991) 7.
7. A H M Renfrew and J A Taylor, Rev. Prog. Coloration, 20 (1990) 1.