Developments in reactive dyes
- Malik, S Rajput, A Bhargava, S Barhanpurkar
1&4 shri Vaishnav Institute of Technology Indore
2&3 U.P. Textile Technology Institute ,Kanpur
Reactive dyes are well known for their light and pale shades. Several environmental problems are associated with reactive dyeing such as higher alkalinity, colored effluent and large amount of electrolytes. Various efforts had been done to solve this problem such as – (a) modification of the dye to increase the fixation by enhancing the reactivity (Multifunctional reactive dyes-homobifuctional & hetro bifunctional reactive dyes). (b) Modification of the dye to increase the substantives, so that electrolyte requirement is cut down – highly substantive or low salt reactive dyes. (c) Modification of the cellulose substrate- cationisation of cellulosic materials.
Key words- Reactive dyes, Fixation , Electrolyte, Bifunctional
1.Procian T dyes:
ICI introduced the procaine T-dyes, a range of liquid reactive dyes, based on phosphoric acid reactive group. Fixation of these dyes takes under acidic dyeing conditions in the presence of carbodiimide at about 2000C. Acid and neutral fixing reactive dyes are important for polyester cotton blends and their consumption will increase. Studies on the stability of the dye fiber bond of Procian T dyes demonstrated that this class of reactive dyes have dye fiber stabilities in the range as those of other major classes of reactive dyes. However large quantities of fixative are necessary. The rate of fixation agent to the dyes is of the order of 50:1 or more. Procian T dyes do not hydrolyze and at the end of the dyeing process retain their capacity for fixation. The disappointing fixation achieved under even the best conditions recommended is thought to be due to unfavorable competition from the carbodiimide side reaction. It is ironic that the fixation of non hydrolysable reactive dyes should be no better than that of regular reactive dyes due to the same basic problem in the former case relating to the fixation agent and in the latter to the dye itself. High fixation values can be obtained by using solvents and cyanamide at 1600C.
- Reactive cationic dyes:
These dyeing properties of reactive cationic dyes on blended fabrics. Fiber reactive polymethine cationic dyes containing N- chloroacetyl group. After a long silence in this area, reactive cationic dyes have been evaluated on wool and in the context of salt free dyeing of cotton cellulose. In the recent years, in the context of development of a salt free dyeing procedure for cellulose materials, cationic dyes containing a reactive unit have been studied. The principle behind this is that the cationic dyes do not need an electrolyte during exhaustion of the dye as against the anionic dyes.
- Cibacron C dyes,
Mainly produced for pad-batch and continuous dyes are the bifunctional reactive dyes, having monofluorotriazine reactive group linked to the vinyl sulphone group, by an aliphatic bridge between the two groups. While Sum fix Supra bifunctional reactive dyes are mainly for exhaust dyeing, the Cibacron C dyes are designed mainly for pad-batch and continuous dyeing. Due to higher cost and technological constraints to produce the required reactive system, these dyes are not being developed in India.
- Sumafix Supra dyes, marketed by Sumitomo of Japan, are heterobifunctional reactive dyes having a vinyl sulphone and monochlorotriazine groups. These dyes known for their high degree of exhaustion and fixation, good reproducibility and leveling properties. These are also temperature-insensitive between 500-600C. The dyes are distinguished by medium substantively in primary exhaustion phase and high degree of exhaustion and fixation after addition of alkali. These dyes have advantages owing to the vinyl sulphone group, owing to the synergistic effect of the combination of the vinyl sulphone group with a monoclorotriazine group. The main advantages of these dyes are as under-
- High degree of exhaustion and fixation
- Good reproducibility
- Good leveling properties
High fastness to perspiration, light, chlorinated water and peroxide washing etc.
One of the most characteristic dyeing properties of these dyes is its temperature-insensitive dyeing behavior between 500 and 800C, as they show very little change in color yield between this range of temperature. Due to this property, they display an excellent practical performance when the temperature in the dye bath is not completely uniform, particularly in winch dyeing machines.
The various application methods, fastness properties and advantages of these dyes have been described.
These dyes have become popular in USA, Europe, Japan and many of the Asian countries except India. Due to high import duty, it is virtually impossible to import these dyes but a few of the dyestuff manufacturers like Jaysynth, Atlas and Chemiequip have develop and produced in India this type of bifunctional reactive dyes having vinyl sulphone and monoclorotrizine groups.
However so far no manufacturer has been successful to introduce these dyes in the Indian textile market. The main reasons for this can be attributed as follows-
- Higher color cost of these dyes to produce the same color strength, compared to other reactive dyes. However many color combinations shades are also economical when produced from these dyes. Moreover the higher dye cost can well be compensated by high fastness properties and good reproducibility.
- Dyestuff manufacturers have no complete range of these dyes, particularly brilliant blues, to produce a variety of combination shades normally required by the textile processor.
One of the important aspects from the manufacturers point of view is that, though synthetically it is easy to introduce these two reactive groups in one dye molecule, one has to be careful in selecting the dye structure which fulfills the requirement of high fastness which is one of the most important factors in the success of these dyes. Surprisingly it has been found that one of the manufacturers in India has come into market with a wide range of these dyes but many of them have light fastness about 2 to3, and some dyes fade almost completely in sunlight when the goods dyed are in wet conditions. For such reasons textile processors lost their confidence in such new introductions. I feel that the dyestuff manufactures should not just concentrate to increase the number of products/shades by sacrificing important properties of a particular dye range.
- The dyestuff manufacturers in the last few years are preoccupied in fulfilling their commitments and hence they pay less attention to the Nome market to provide technical services and trials normally required for introducing such new dyes.
4.Kayacelon React dyes, Introduced by Nippon Kayaku of Japan, react with cellulose at 1300C at nentral pH. This has made them most suitable for one-bath, one –stage dyeing of polyester/cellulosic blends where polyester portion can be dyed with disperse dyes while the cellulose portion with these new dyes in one stage at 1300C and neutral pH. The leaving group in the reaction with cellulose is 3-carboxypyridine in this class of dyes. These are best known for reduction in processing time, simplified dyeing process and increased productivity.34
The ease and the simplicity of the dyeing method for one bath dyeing of polyster/cellulose blends has made possible the dyeing of various blended textiles like nylon/cellulose, wool/cellulose, acrylic/cellulose etc. with these reactive dyes along with other dyes in one bath.
These kinds of dyes have been developed in India by Chemiquip Ltd., Jaysynth Dyechem Ltd, Atlas Dyechem industries etc. but so far, like bifunctional dyes no one has been successful to introduce these dyes in the Indian textile market. The reasons are given hereunder-
- Higher color cost of these dyes to produce the same color strength, compared to other reactive dyes. However when the total cost are taken into account, like reduction in fixed expenses, utilities, labour cost etc, and particularly dyeing medium and pale shades where the amount of the dye used is less, this may result in overall cost saving.
- Dyestuff manufacturers have no complete range and hence have not been able to produce the required varieties of combination shades, normally demanded by textile processors.
- The dyestuff manufacturers in last few years are preoccupied in fulfilling their export commitments and hence pay less attention to the home market to provide technical services and trials normally required for introducing new dyes.
It will be worthwhile to point out that ICI, as early as in 1977, introduced reactive blue 187 (Procian Brilliant Blue HEG) which contained Bis 3 carboxy-pyridinium group.
4.Procilence N dyes introduced by ICI (now Zeneca) are the combinations of Dispersol PC disperse dyes and Procion T reactive dyes for the one-stage printing of polyester/cellulosic blends. Procilene N dye range is a combination of matched shades from Dispersol PC dyes and selected Procion T monochlorotriazinyl reactive dyes. These dyes are fixed to the polyester/Cellulose blends under approximately neutral conditions.
5.Daystar has introduced Remazol Carbon RGB, a new high strength reactive black dye, said to be economical and to exhibit excellent build up, thereby reducing the amounts needed to achieve deep shades that cannot be achieved with conventional process. DyStar says the new product also has good wash-off properties and meets high wet fastness and chlorine fastness requirements. Remazol Carbon RGB is suitable for exhaust and pad-dry pad- steam dyeing of cellulosic fiber blends. Properties include very good reserving of polyamides fibers and a virtually constant shade under different light sources. Any fading caused by exposure to light and perspiration is on-tone. Remazol Carbon RGB has only a very slight tendency to bronzing. Therefore, it has been claimed by Dystar that a full neutral black is obtained, even in very deep shade.37
6.Bifunctional reactive dye:
An inadequate degree of fixation has been regarded as one of the problems of dyeing and to improve it, an idea of introducing two or more reactive systems into a dye molecule was introduced. If a dye molecule contains two separate reactive groups, it is statistically self evident that higher percentages of chemical bond formation may be obtainable. In other words, if one of the two reactive groups reacts with water, there is still the second that may react with cellulose. This advantage may outweigh the definite disadvantage of higher cost of producing a dye with two reactive groups.
The earliest commercial dye based on this approach is Remazol Black B by Hoechst (CI Reactive Black 5).
It is characterized by two vinyl sulphone groups. They are masked as sulphuric acid esters of β-hydroxy ethyl sulphone.
This approach was again utilized by ICI when they launched their range of Procian Supra dyes and Procian HE dyes. These dyes are termed as homo-bifunctional dyes. Every reactive system has some inherent deficiency e.g. Dyes based on s-triazine do not have good fastness properties in acedic media and due to their high substantivity they have poor wash off properties.
Similarly, dyes having a vinylsulphone (VS) reactive system have poor alkaline fastness and have synthetic disadvantage. The VS group must usually be synthesized as a substituent on an intermediate, which is then used in dye preparation. Attempts to introduce it directly into a particular position of a chromogen have been unsuccessful, owing to unsatisfactory selectivity and unavoidable side reactions and decompositions.
7.Homobifunctional (2MCT) type (HE Brand) reactive dye:
These dyes (HE Brand) containing two triazinyl groups, each containing one reactive group is characterized by low affinity (like M Brand reactive dyes) and high exhaustion and fixation efficiency( unlike M-brand reactive dyes). Due to high fixation and hence good build up, washing-off of the dyed good is easier, since the dyed fabrics contain less hydrolyzed dye to be removed. This leads to less effluent problems. Since there are monochloro-s-triazine groups, which are less reactive as in H-Brand reactive dyes, their storage stability is good. Another advantage of these dyes is that even if one of the reactive chloro groups react with water and get hydrolyzed during dyeing under alkaline condition , there is still another reactive chloro groups available in the dyestuff molecule for reaction with cellulose ; hence the higher shade build-up on the fiber, leaving less hydrolyzed dye. Where the reactive chloro groups react with water, in dye bath at the end of dyeing cross-linking of cellulose may take place.
Some of the useful features of HE-type are:
- Excellent build-up in high or low liquor ratios.
- The high fixation is of particular important while dyeing polyester/cellulose blend fabrics, where the liquor ratio (with respect to cellulose component only) is quite high.
Conclusion – The conclusion of this article is that , in the dyeing method of the reactive dye the process consume various amount of water and chemical like alkali ,electrolyte, various types of fixing agents and acids also. So improvements in the reactive dyeing research are going on very fastly for maintaining ecological and environmental solutions. As well as importance has also been given to save the energy and water level, which is used for Reactive dyeing.
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4.www.sdc.org.uk.Recent development in reactive dye