Developments in reactive dyeing

8/7/2019 Developments in reactive dyeing

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DEVELOPMENTS IN REACTIVE DYEING

Reactive dyes for cellulosic materials were invented in 1954 and ICI in England introduced thefirst range of reactive dye popularly known as Procion dye in the year 1956. Invention of these

dyes in textile industry has brought sea changes in the history of dyes. Reactive dyes are the most

predominant class of dyes for cellulosics today and 50% of cellulosics are dyed with these dyes.

They are also increasingly gaining importance for wool and polyamide fibres. Share of reactive

dyes among all textile dyes is 29%, which is next to disperse dyes consumption (32.5%).

Easy application and choice of different kinds of application techniques like exhaust, semi-

continuous & continuous, suitability to dye on any conventional or modern machines, presence

of wide range of gamut of shades from dull to bright and pastel to dark, compatibility, possibility

of getting acceptable allround fastness properties and cost effectiveness are the major key factors

which are responsible for the growth of reactive dyes.

It is estimated that reactive dyes represent the only range of cellulosic dyes that is expected to

increase in sales volume in the early part of the next century. Reactive dyes are expected to take

share from other cellulosic dyes like sulphurs and azoics on environmental ground, vats on cost

and application, directs on fastness. On the other hand, these dyes are also facing criticism on the

ground of being highly polluting either during their manufacturing or their application on textile

substrate.


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Reactive dyes in general require high usage of salt (especially in exhaust method of application),

alkali for fixation and high usage of urea (CDR and printing), which adds more load during

treatment of effluent. Besides these, reactive dyes are facing issues like presence of AOX within

the dye molecule, more water consumption, presence of heavy metal ion in dye molecules (Cu,

Br, Cr, Co), relatively low fixation levels, difficulty in removing hydrolysed reactive dyes and

removal of colour from effluent stream to meet legal limits.

Therefore, all research in dye chemistry is being directed towards the new generation reactive

dyes that can meet all environmental norms as well as can satisfy the needs of the customer (ie,

fastness requirements). Hence, it is a need to invent new generation reactive dyes with

environmental & technical satisfaction.

Current trends in reactive dyes & their application

* Warm dyeing application offers many advantages on the ground of utilisation of energy. So,

there is a perceptible shift from hot dyeing application to warm dyeing.

* The chlorotriazine group together with vinyl sulphone has dominated on both technical &

commercial grounds.

* Vat dyes are being replaced more & more with reactive dyes due to availability of new

generation reactive dyes.

* The demand for Right-First Dyeing is increasing.

* The pressure on environmental issues & cost economics is increasing due to stiff competition

in the global market.


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Future trends in reactive dyes

Research is being carried out for:

* Increasing the robustness of individual dyes and dye combinations in trichromatic systems.

* Enhancing reproducibility of trichromatic combinations used in most commonly applied

dyeing processes.

* Reducing salt consumption and/or unused dye in the effluent. (Dyes with no salt, low alkali

addition & 100% fixation).

* Improving fastness properties (eg, light fastness, fastness to repeated laundering).

* Polyfunctional dye chemistry to improve reactivity, fixation levels & reproducibility.

* Reactive dyes exclusively for printings, which are different from low- molecular weight MCT

dyes.

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Developments in reactive dyeing