Advancements in Reactive Textile Dyes

Advancements in Reactive Textile Dyes

Classifications, characteristics, developments, and advancements in Reactive Textile Dyes

The market for reactive dyes will continue to increase. This will arise partly from a marginal increase in the production of cellulosic fibres, essentially cotton, and more importantly from the replacement of other classes of cellulose dye, such as azoic and sulphur dyes, by reactive dyes.

Introduction

Throughout the long history of the tinctorial arts, the dyer has been confronted with match the performance of has colourants as closely as possible with the useful life of the fabric.

The dyeing of cotton (cellulosic) with direct, vat or azoic dyes depends on adsorption of dye molecules into the fibre, while vat and azoic dyes, the dyes are first adsorbed on to the fibre followed by reaction to convert them into an insoluble form, thus retained on the fibre. The possibility of attaching dyes to fibres by forming covalent bond has for long been attractive to dyestuff chemists because attachment by physical adsorption and mechanical retention has the disadvantages of either low wet fastness or high cost1.

An event which had far-reaching consequences was the discovery made by Rattee and Stephen (ICI) in 1954, of dyes containing a dichlorotriazinyl group which could be applied from aqueous solution and caused to form a covalent bond with cellulose by increasing the pH. This discovery resulted in first commercial reactive dyes for cellulose.

The appearance of reactive dyes on the market gave a great impulse to the investigation of reactive systems other the s-triazine and within a few years, several other ranges of commercial reactive dyes were available. The impact of reactive dyes in the synthetic dyestuffs scenario has been to such an extent that today reactive dyes constitute the largest group of dyes both on a monetary and bulk basis.

The reason for such rapid increases in demand for reactive dyes is primarily due to the excellent characteristic of reactive dyes. Eg. Their brilliant shades, excellent wet fastness of dying and simple dyeing operations, which have increasingly been accepted within the industry.

Despite the obvious advantage associated with reactive dyes, there are many problems with present qualified by reactive dyes have been raised below:

• In exhaust dye the degree of exhaustion and fixation is low and the colouring
• The degree of wastewater is high.
• The problem occurs in levelness and reproducibility of dying.
• More water, energy and a long time are required for washing off.
• In wearing or washing textile goods of reactive dye or printing, colour change and bleeding to white areas can be done which leads to consumer complaints that for such problem many companies have developed the dyes for dyeing theories.

During the last decade, polyester-cotton blends have emerged as the single largest fabric used. In order to dye polyester-cotton blends, it is necessary to use disperse dye to colour the polyester together with a suitable dye for the cotton component, and it is obviously economical to apply both dyes simultaneously in a single process rather than using them separately.

In the single dyeing process the application temperature is fixed by the need to apply the disperse dye at an elevated temperature, and when the chosen cotton dye is a reactive dye this limits the choice to those dyes designed for the host application. An immediate difficulty arises because the satisfactory applications of disperse dye calls for the dyeing process to be operated either at neutrality or under acidic condition. Since alkaline condition lower dispersion stability, whereas the pressure of alkali is normally required for the application of reactive dye in order to ionize the cellulose and promote the dye-fibre reaction. Many developments have been done in this aspect during the last few years.

The research activity in reactive dyes has been mainly directed towards solving the mentioned deficiencies of reactive dyes. Moreover, the use of some new chromophoric system has been disclosed in the patent literature.

Chemistry of Reactive Dyes

The dyeing principle based on the fibre reactivity involves the reaction of a functional group of the dyestuff with a site on the fibre to form a covalent link between the dye molecules and the substrate.2

The four structural feature of a typical reactive dyes molecule are:

• The chromophoric grouping, contributing the colour much of the substantively for cellulose.
• The reactive system, enabling them to dye to react with the hydroxyl group in cellulose.
• A bridging group that links the reactive system to the chromophore
• One or more solubilising group, usually sulphuric acid substituent attached to the chromophoric group for their colour, although the azo chromophore –N=N- is by far the most important

All reactive dye contain sodium sulphonate group for solubility and dissolve in water to give coloured sulphonate anions and sodium cations. Most reactive dyes have from one to four of these sulphonate group-reactive dye molecules. However, do have several specific structural features of their own.

The general form of the reactive dye is as follows.

S——R——B—-X

Where,

• S = Water solubility group
• R = Chromophore
• X = Reactive system
• B = Bond between reactive system and Chromophore

Chromophore (R):?It is the colour producing part. The Chromophore absorbs a certain wavelength of incident white light and reflects the rest, which incident on the eye retina giving colour vision.

Reactive system (X):?Reactive system reacts with fibres forming XF dye covalent bond. It influences the fastness property.

Bridging group (B):?Bridging group links R and X which determines stability and reactivity of the dye particle. In some, the reactive group is directly attached to the Chromophore and most reactive system contains a heterocyclic ring that contributes some substantivity for cellulose. The sulphatoethyl sulphone precursor of the vinyl sulphone reactive group contributes significantly to the aqueous solubility of reactive dyes.

Water solubility:?This group imparts water to dye. Generally, it is sodium salt of sulphuric acid. One should always keep in mind that the easier is the application of the dye on the fibres the easier is the removal from fibres.

Classification of Reactive Dyes

Monofunctional Type

The most important reactive system contains an only possible reactive centre, such as the halogen substituent in the aminohalotriaz the dye or the activated terminal carbon atom in vinylsulphone system.3

In the other two equivalent replaceable halogen substituent dichlorotriazine, diflouropyrimidine hetrocyclic ring system. The reactivity of the remaining halogen substituent is greatly decreased by the presence of the new hydroxyl or cellulose substituent.

The different monofunctional reactive dyes are as follows.

No.REACTIVE DYEBRANDNAME1Dichlorotrazine dyeProcion MXZeneca2Aminochlorotriazine dyeProcion HZeneca3Aminoflurotriazine dyeCibacionCGY4Trichloropyridine dyeDrimarine XS5Dichloroquinoxaline dyeLevafixBAY6Sulphatoethyl-sulphone dyeRamazolHDE

Bifunctional Type

It is a high value of Cuprammonium fluidity observed for dyeing of many reactive dyes full depths, although tests of tensile strength demonstrated that the cellulose remained undamaged. Investigation showed that these anomalous results were associated with those dye capable of forming cross-links between neighbouring cellulose chains.3

The degree of cross-linking was relatively insignificant for the typical pad-batch dyeing at ambient temperature, but thermal fixation by pad-dry steam method resulted in a much higher proportion of cross-linked dye molecules.

The different bifunctional dyes are as follows.

NoREACTIVE DYEBRANDNAME1Bis(aminochlorotriazine)Procion HEZeneca2Bis(aminonicotionotriazine)Kayaceton reactKYK3Aminichlorotriazine-Sulphatoethyl-sulphone

Sumifix supraNSK4Aminiflurotrizine-Sulphatoethyl-sulphone

Cebracin CCGY

Conclusion

The market for reactive dyes will continue to increase. This will arise partly from a marginal increase in the production of cellulosic fibres, essentially cotton, and more importantly from the replacement of other classes of cellulose dye, such as azoic and sulphur dyes, by reactive dyes.

The major driving force of reactive dye research and product development over the past decade falls into three broad categories: the need for products with greater economy, better environmental performance and improved technical properties. These have been achieved by a variety of means. The greater economy has been gained by using more efficient dye manufacturing processes, shortening dyeing cycles, increasing the percentage of right-first-time dye house production the use of more fixation efficient dyes and the use of stronger chromophores.

Often these requirements overlap. These are likely to remain the key drivers over the next decade. Much effort has been expended on achieving complete fixation of dye to cotton. To date, no satisfactory way of achieving this has been commercialized but recent patent claims suggest that fixation yields of greater than 99% are possible. If these claims are verified it might appear that there are few further improvements to be made in reactive dye technology.