Monday, March 28, 2011

Informative articles on Dye reactivity, Application and Storage of Reactive dyes

Dye reactivity is very important terms for dyeing cellulose fibre. Shed of dyed textile fabric directly depend on the reactivity of reactive group. Highly reactive group of reactive dyes makes strong covalent bond with cotton fibre structure. The reactive groups of different types of reactive dyes have different chemical structures and show a wide range of reactivities. They were originally divided into cold- and hot-dyeing types but many current ranges would be better called warm dyeing. The most reactive types, such as DCT reactive dyes, are applied at lower temperatures (20–40 °C) and for dyeing process only require a weak alkali such as NaHCO3 or Na2CO3 for fixation. The less reactive types, such as MCT dyes required higher temperatures (80–90 °C) and stronger alkalis such as Na2CO3 plus NaOH. Many reactive dyes manufacturers now market several ranges of reactive dyes for cotton fibre , each with its own particular recommended dyeing procedure.

Gives some typical examples of reactive dyes based on the type of reactive grouping.
Reactive group
Commercial name of reactive dyes
Exhaust dyeing
temperature (°C)
Procion MX (BASF)

Procion H (BASF) Basilen (BASF)
Cibacron (Ciba)
Cibacron F (Ciba)
Levafix E (DyStar)
Drimarene K (Clariant)
Levafix E-A (DyStar)
moderate to high

Remazol (DyStar)
Drimarene X (Clariant)

Kayacelon React
(Nippon Kayaku)
moderate to high

Because most reactive dyes are prone to hydrolysis, their handling and use requires care. Most of the reactive dyes are readily water-soluble dye and the dye solution in dye bath is prepared in the usual way by pasting with water and then adding more water. The temperature of the water used depends upon the ease of solution and the reactivity of the dye. Hot water is not recommended for dissolving dyes of high reactivity, because of the risk of hydrolysis of the reactive group, but is suitable for the less reactive types.
 Special care must be taken for storing reactive dyes. Highly reactive dyes could be react with air. Once the dye solution of reactive dye has been prepared, it cannot be stored for later use without some risk of hydrolysis of the reactive group of reactive dyes. This decreases its fixation ability after dyeing and is a particular problem with the most reactive types of dye. Dyes containing a 2 sulphatoethylsulphone group, however, can be dissolved in neutral water at the boil without risk of hydrolysis. Formation of the reactive vinyl sulphone group requires the addition of alkali. Reactive dyes for printing are usually dyes of low reactivity so that the print paste can be stored for some time at room temperature without deterioration from hydrolysis of the reactive group. Reactive dyes of low reactivity and relatively high substantivity are valuable for dyeing using long (high) liquor ratios, using a winch machine for knitted fabric and twill tape dyeing. Exhaust dyeing method with low reactivity of reactive dyes at the higher temperatures required for fixation allows better penetration of the dyes into the cotton fibres. For continuous dyeing with reactive dyes stabilised liquid forms are available. Although these contain special pH buffers and stabilisers to minimise the hydrolysis reaction, they only have a limited shelf life. Many commercial reactive dyes are dusty powders but all physical forms must be handled with care. These dyes react with the amino groups in proteins in the skin and on mucous surfaces. Inhalation of the dust is dangerous and a dust mask is obligatory during handling. Reactive dye powders and grains are sometimes hygroscopic and drums must be carefully re-sealed. Most reactive dyes have a limited storage period, after which some deterioration can be expected. Standardisation and comparison of reactive dye powders or liquids cannot be done by the usual spectrophotometric procedure involving absorbance measurements of standard solutions. Both the reactive dye and its hydrolysed form are evenly coloured, but only the former is capable of reaction with the cellulose fibre during dyeing. Therefore, dyeing must be prepared and their colors compared with standard dyeings. Chromatographic techniques usually allow separation and quantitative measurement of the relative amounts of a reactive dye and its hydrolysis product in a given dye.
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