- 1 Introduction
- 1.1 Properties Of Reactive Dyes
- 1.2 Classification Of Reactive Dyes
- 1.3 Constitutional Characteristics Of Reactive Dyes
- 1.4 Chemistry Of Reactive Dyes
- 1.5 General Factors Affecting The Results Of Reactive Dyeing
- 1.6 Versatility Of Reactive Dyes
- 1.7 Recent Development In Reactive Dyes
- 1.8 Conclusion
- 1.9 Related
This article describes the immense impact of reactive dyes on the textile industry. Their properties, classification, constitutional characteristics, chemistry, mechanism and recent development in reactive dyes have been described.
Reactive dyes are extensively used in textile industry because of their wide variety of color shade high wet fastness, profiles, the simplicity of application, brilliant color and minimum energy consumption. It is evident that this technology offers the colorist many options for producing full bright and tertiary shades on cellulosic and polyamide fibers.In light of above, there is still great scope for further research and development to maximize the benefits of reactive dye systems.
Fiber reactive dyes are colored organic compounds that are capable forming a covalent bond between reactive groups of the dye molecule and nucleophilic groups on the polymer chains within the fibers. They are the highly successful class of modern synthetic dyes due to their wide shade gamut, fibers their flexibility in application and the excellent fastness properties they offer when dyed on wool, silk, cotton and regenerated cellulosic fibers.
Reactive dyes may be loosely defined as chromophores which contain pendant groups capable of forming covalent bonds with nucleophilic sites in fibrous substrates. Providing these covalent bonds are stable to conditions encountered in laundering then the wash fastness properties of the colorations will be outstanding.
Since their introduction in the 1950s reactive dyes has shown rapid growth even today, developments are taking place. The combination of brightness, fastness, and ease of application associated with reactive dyes enables this class of dyes to color cellulosic fibers.
The structure of a reactive dye is shown below:
Properties Of Reactive Dyes
- Reactive dye is anionic in nature.
- Reactive dye is a water soluble dye.
- They have better wash and light fastness properties.
- They have better substantivity.
- They form a strong covalent bond with the cellulosic fiber.
- The alkaline condition is must require for dyeing.
- The electrolyte is the must for exhaustion of dyes in the fiber.
- The wide range of color can be produced.
- Comparatively cheap in price.
Classification Of Reactive Dyes
Low substantivity reactive dyes, often described as Malakai-controllable dyes, addition exhibit rapid washing-off properties. Thier level dyeing properties have to be regulated by slow addition of alkali. This is done in order to encourage migration of dye to the substrate Durin addition and also to prevent the phenomenon of simultaneous exhaustion and fixation.
Medium-high substantivity reactivity dyes often described as salt-controllable dyes, have to exhibit slow washing off characteristics.Their level of dyeing characters to be controlled during the electrolyte addition stage.
These dyes react with cellulose above the boil in the absence of alkali.They can be applied with group 2 dyes, with alkali fixation being done, between 80-100 degree C.These dyes are self-levelling.
Constitutional Characteristics Of Reactive Dyes
The four characteristic feature of a typical reactive dye molecule area a reactive group, a chromophoric group, a bridging group and a solubilizing group.
Reactive dyes owe their covalent bond forming ability to the presence of the reactive groups in their structure.
- Monofunctional Reactive Systems.
These systems can react only once with the nucleophilic groups in the fibre.
- Bifunctional Reactive Systems.
Bifunctional reactive dyes contain two separate reactive centers for reaction with suitable groups in the fibre. They also have the potential to combine with more than one group in the fibre chain molecule.
- Homobifunctional Reactive Dyes.
These dyes consist of two similar reactive groups.e.g. of which are shown in section A & B below.
- Bis-mono-chlorotriazine dyes.
- Bis-mononicotinotriazine dyes.
- Heterobifunctional Reactive Dyes.
These dyes consist of two different types of reactive groups.
- Monochlorotriazine dyes.
- Monofluorotriazine dyes.
Chromophoric groups contribute color to textile fibres. The proper selection of chromophores for commercial reactive dyes is essential to achieving a given shade area. In practice, mono-azo, diazo, metallized mono-azo, metallized disease, formazan, anthraquinone, triphenodioxazine,& phthalocyanine chromophores have been used for the preparation of reactive dyes.
- Azo Reactive Dyes.
- Anthraquinone Reactive Dyes.
- Phthalocyanine Reactive Dyes.
- Triphenodioxazine Reactive Dyes.
- Formazan Reactive Dyes.
A bridging group is a group that links the reactive system to the chromophore.These groups are necessary for synthetic reasons, they also influence the reactivity, degree of fixation, stability of reactive dyeing & other dyeing characteristics such as substantivity & migration, significantly.
Solubilising groups provide characteristics such as water solubility, substantivity, migration & wash off.The dominant solubilising group in reactive dyes is the sulphonic substituent.
Chemistry Of Reactive Dyes
Chemical Reactions Between Reactive Dyes And Fibres
- Nucleophilic Substitution
Triazynil reactive dyes react with cellulose by a process called nucleophilic substitution. Nucleophilic substitution characterizes dye fibre fixation that occurs when a leaving group in the reactive system is displaced as a result of an interaction with a nucleophilic group on the polymer chain. The reaction of a mono-chlorotriazine reactive dye with a hydroxyl group of cellulose & or an amino group of keratin is typical of this process. The same process accounts for the competitive hydrolysis reaction between the dyes & water during dye application.
- Nucleophilic Addition
Nucleophilic addition characterizes the dye fibre reaction in which a nucleophilic group in the fibre adds across an activated C-C double bond in the reactive group.
Structurally related dyes containing a beta-sulfamoyl group probably form a cyclic compound capable of reacting with cellulose to give a cellulose ether.
General Factors Affecting The Results Of Reactive Dyeing
Affinity Of The Dye
The affinity of a dye for a textile fibre is determined by its molecular structure and therefore is not under the control of the dyer except that he can select dyes from among the available dyes, those most suited to his particular process of dyeing.
Material To Liquor Ratio
The liquor ratio has a powerful effect in determining exhaustion, and this is particularly significant with low-affinity reactive dyes.
Concentration Of Electrolyte
In the first phase of dyeing, the reactive dyes behave like direct dyes and therefore electrolytes are used for improving the exhaustion percentages.
PH Of Dye Bath
The ph of fixation of reactive dyes on cotton and viscose actually depends on individual dyes and the temperature and time of dyeing.
Time Of Dyeing
The dye is generally added to the bath into the portions. The salt may also be added in two lots. Exhaustion normally takes place in 20-30 minutes.There is no specific advantage in extending the exhaustion phase beyond 30 minutes. The alkali is then added also in two lots, and the dyeing continued for 30-90 minutes.
Nature Of Fibre
There are marked differences in the degree of exhaustion obtained with reacting to dyes on different cellulosic fibers.Viscose rayon gives the highest exhaustion and cotton the lowest with mercerized cotton occupying an intermediate position.
Versatility Of Reactive Dyes
Use Of Reactive Dye In Thermal Transfer Printing Process
A formulation and a method of printing anion or meltable in a layer having a reactive dyes or mixtures of reactive dyes and disperse dyes as colorants.The melt layer also includes an alkaline substance, a binder and optionally, a heat activated printing additive.Permanently bonded color images are provided by the reaction between the reactive dye and the final substrate,wh ich may be any cellulosic, protein, or polyamide fibre material.
New Reactive Dye Ink Set Added Dupont Artistry Ink
Dupont digital printing a leading supplier of inkjet inks announced the addition of a new reactive dye in the set to their portfolio of digital textile inks at the drupa 2008 trade show in Dusseldorf Germany.
The inks can be fixed by the various methods of fixation typically used in conventional printing with reactive dyes and provide high wash fastness and perspiration tolerance making them ideal for apparel application.
Recent Development In Reactive Dyes
Reactive dyes occupy an important position for dyeing cellulosic fibers but this is not the case in the dyeing of natural and synthetic polyamide fibres however it is likely that environmental pressures will increase the usage of reactive dyes in the latter area. Cellulosic fiber reactive dye systems pose environmental question due to their current high salt requirements and colored effluent discharge.In the case of polyamide fibres such as wool, reactive dyes give good uptake and fixation efficiencies and their use are expected to grow since they offer the possibility to replace chrome dyes.
This article on “Chemistry of Reactive Dyes” reveals the overview of properties, classification, constitutional characteristics, mechanism and the recent development of Reactive dyes.
Reactive dyes and other systems which form covalent dye-fibre bonds have been described.
Reactive dyes are extensively used in textile industry because of their wide variety of color shade high wet fastness, profiles, the simplicity of application, brilliant color and minimum energy consumption.
It is evident that this technology offers the colorist many options for producing full bright and tertiary shades on cellulosic and polyamide fibers.
In light of above there is still great scope for further research and development to maximize the benefits of reactive dye systems; even so, the development and use of reactive dyes, has to rate as one of the most important achievements of the color chemist.
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