Long Way Education

By Eman Abdallah Kamel

Eman is a writer and textile engineer. She obtained a bachelor’s degree in textile sciences from the College of Applied Arts in Egypt.

This article covers reactive dye chemical structure, types, classifications based on types of reactions, and some tips when using reactive dyes.

Reactive Dyes

Reactive dyes are a very successful class of modern synthetic dyes due to their wide shade range, flexibility of application, and excellent fastness properties when dyed on wool, silk, cotton, linen, and renewable cellulosic fibers such as rayon and bamboo fibers.

These dyes are chromophores with pendant groups that attach to the fiber substrate’s nucleophilic sites to form covalent bonds. Provided that these covalent bonds are stable under the conditions encountered during washing, the colorfastness properties of the wash will be outstanding.

Reactive dyes have become more widely used on polyamide materials to produce dyeings and prints of excellent wash-fastness.

Polyamides are synthetically or naturally. Naturally, polyamides are proteins, such as wool and silk. Artificial polyamides such as nylons, aramids, and sodium polyaspartate.

China, Germany, and the US ranked as the top exporters of paints, pigments, and varnishes globally in 2021. Asia-Pacific was the largest region in the reactive dyes market in 2023.

Did You Know?

The CHT Group unveiled its line of reactive dyes, BEZAKTIV ONE, in June 2023. These dyes are meant to be used in dyeing procedures that use less energy and water and require shorter processing times. BEZAKTIV ONE dye is suitable for cotton and other cellulosic fibers.

Chemical Structure

Reactive dyes are those whose chemically active radical groups react chemically with fibers. The British company Imperial Chemical Industries invented reactive dye in 1956. Most of the reactive dyes dissolve in water. We can use W-D-B-Re to represent the general structure, where:

• D is a chromogen.
• B is an active group and a chromogenic coupling group.
• (Re) It is an active group.
• W is an aqueous solution.

Azo, anthraquinone, phthalocyanine, and trimethoprim are examples of parent dyes. Examples of active groups include vinyl sulfone, quinoxaline, pyrimidine, and acrylamide.

Reactive dyes are applied either from a high-pH solution or neutral solutions that are subsequently alkaline through a separate process. Sometimes, different shades are obtained by applying heat to the dyed fabric.

Classification of Reactive Dyes

Reactive dyes are primarily classified into two classes based on the type of reaction they undergo:

1. Dyes react through the nucleophilic substitution reaction.
2. Dyes react through the nucleophilic addition reaction.

Types of Reactive Dyes

There is a wide range of reactive dyes, including:

• Vinyl Sulfone Dyes
• Cyanuric Chloride Dyes
• Bi-functional Dyes
• Monochlorotriazine Dyes
• Dichlorotriazine Dyes
• Cold Brand Dyes
• Hot Brand Dyes
• Higher-Reactive dyes
• Dyes with Moderate Reactivity
• Lower Reactive Dyes
• Azo Reactive Dyes
• Anthraquinone Reactive Dyes
• Phthalocyanine Reactive Dyes
• Triphenodioxazine Reactive Dye
• Formazan Reactive Dyes

The first photo is Vinylsulfon-Gruppe (R=Alkyl- oder Arylrest). The second photo is of a vinyl sulfone parabase ester (2-[(4-Aminophenyl)sulfonyl]ethyl hydrogen sulfate). Image source: wikimedia.org

1. Vinyl Sulfone Dyes

Vinyl sulfone dyes are monofunctional reactive dyes. They are applied to wool, silk, cotton, hemp, and linen. These reactive dyes can be applied using the exhaust and padding methods.

Usually, an aromatic or aliphatic amine is used to introduce the vinyl sulfone reactive anchor into the reactive dye. The oldest and most popular intermediate is vinyl sulfone parabase ester, an aniline substituted with a [2-(Sulfooxy)ethyl]sulfonyl group.

This dye, even in the presence of alkali, has excellent solubility. Fastness properties are good. Possess less affinity, and leveling is good.

Monofunctional reactive dyes contain reactive groups of one or more reactive species at individual sites in the dye molecule.

2. Cyanuric Chloride Dye

Cyanuric chloride (C₃Cl₃N) is an organic compound; this white solid is the chlorinated derivative of 1,3,5-triazine.

Cyanuric chloride appears as a colorless, crystalline solid with a pungent odor. Melting point: 146° C. Density: 1.32 g/cm³. Very slightly soluble in water. Toxic by ingestion and inhalation of vapors. It irritates the skin and eyes.

Cyanuric chloride is a key raw material for producing numerous reactive dyes. Reactive dyes form a chemical bond with cellulose, the main component of plant fibers. Other fibers that have nucleophilic groups can also enter into a covalent bond with the triazine substituents. Cyanuric chloride dye is a high-grade, non-fading, colorfast dye.

Did You Know?

Investigation into the antimicrobial mechanism indicated that the phenol-like structures on dyed cellulose caused microbial degradation and leakage of intracellular components. The antimicrobial functions were durable upon repeated washing, and the dyed cellulose showed remarkable biocompatibility with mammalian cells.

3. Bi-functional Dyes

Bifunctional reactive dyes contain more than one reactive moiety per molecule or group capable of forming covalent bonds between the carbon atoms of dye ions or molecules and the functional groups of the substrate. Bifunctional dyes have excellent dyeing efficiency and overall fastness properties.

Bifunctional dyes that contain two similar functional groups are known as homo-bifunctional group pigments. Dyes that contain two separate functional groups are known as heterobifunctional group dyes. Dyes are of the common dichlorotriazine type, with a final condensation of ethyl sulfone containing various reactive groups in a single molecule. Improved repeatability is provided by reactive dyes, especially for medium to light tones. Due to the triazine ring structure, it has excellent dyeing capabilities even for non-critical substrates. Dyeing variables such as temperature, heating rate, alkali dosage, etc., rarely affect this dyeing.

Did You Know?

Bifunctional reactive dyes can react more easily with viscose, showing better dye exhaustion and fixation than monofunctional types, resulting in improved dye fixation yields.

4. Monochlorotriazine Dyes

Monochlorotriazine dyes are monofunctional reactive dyes. These dyes have weak reactivity. To make these colors water-soluble, pour 80–85°C of hot water over the powder and mix well. Monochloromonohydroxy-S-triazine colors can bond effectively to wool when used in moderately acidic conditions because the keto form of the hydroxy-S-triazine ring is dominant in these conditions.

5. Dichlorotriazine Dyes

Dichlorotriazine dyes belong to the category of monofunctional reactive dyes. This dye can be easily attached to cellulosic fabrics by pad batch dyeing at room temperature or batch-wise dyeing at 30–40°C. To ensure adequate dye movement on the fiber during the fatigue phase, small chromogenics are preferred. This need makes these pigments ideal for brilliant dyeing but less suitable for deep tertiary colors. The larger chromogenics used for this purpose sometimes fail to provide sufficient performance under low-temperature conditions.

Because of their low pH, some dichlorotriazine dyes break the bond between the dyed fibers through acid-catalyzed hydrolysis, which lessens wash fastness or acid/alkaline sweating. This defect is more pronounced in red dyes containing acid H as the coupling element. When the dye partially hydrolyzes to form 2-chloro-4-hydroxy-S-triazynylamino species, it loses the opportunity to stabilize with the remaining chlorine atom. Ionization of the acidic 4-hydroxy substituent in the stabilization step produces strong negative feedback in the triazine ring, deactivating the remaining 2-chloro substituent entirely under alkaline conditions.

Two more classes of monofunctional dyes are 2-amino-4-chloro and 2-alkoxy-4-chloro-triazine, which are produced when dichloro-triazine dyes react with alcohols or amines in a regulated manner. The bulky isopropoxy group was chosen to disrupt the planarity of the substituted triazine system, making it easier to wash the unfixed dye from the printed fabric.

6. Cold Brand

Cold-brand dyes have a highly reactive group as a component, which makes them highly reactive. Therefore, these pigments can be colored at low temperatures, such as 30 to 40 °C. Several examples include Portion MX, Drimarenc K, and Levafix EA. Cold branding is dyed at a lower temperature than medium branding. These dyes contain a reactive group with a moderate level of reactivity. 40 to 60 degrees Celsius are typical temperatures in this region. Among them are the dyes Remazol RR and Cibacron F.

Did You Know?

Bis-azo reactive dyes were prepared by coupling 4,4′-bis-methylene-bis anthranilic acid diazotide with different coupling components containing o-toluidino, and their dyeing performances were evaluated on wool, silk, and viscous rayon. The dyes give a wide range of shades, from yellow to maroon, with good depth and evenness over every fiber. The rate of the dye extraction bath and fixation on the fibers was good and acceptable. The dyed fibers showed acceptable and good fastness to light, washing, and rubbing.

7. Hot Brand

Since hot branding dyes contain fewer reactive groups, high temperatures, such as 60–90 °C, are required for dyeing. The dye is fixed at 100–150 degrees Celsius by steaming. Some examples include Procion H, Levafix E, and Drimarene X.

8. Higher-Reactive dyes

These dyes have a high reactivity, which makes fixation simple and allows for less alkaline solution use. The pH of the dye bath is maintained at 10–11 by adding NaHCO3. Examples are Procion MX, Drimarene K, and Levafix E-A.

Did You Know?

Procion MX dye causes skin irritation and serious eye irritation. If inhaled, it may result in symptoms of allergies, asthma, or trouble breathing and irritate the respiratory tract.

9. Dyes with Moderate Reactivity

These dyes have an average level of reactivity. The pH of the dye bath is maintained at 11–12 by adding Na2CO3. Examples are Cibacron F and Remazol RR dyes.

Remazole is a dye that reacts with heat and forms a strong chemical bond with fibers such as cotton and wool. It requires a dyeing temperature of about 60°C. Lightfastness varies by color, with lighter shades fading more. Appropriate pre-washing and testing of unfamiliar materials is recommended. Remazole can be used in dyeing, coating, and printing.

10. Lower Reactive Dyes

These dyes have a low reactivity, so an extremely alkaline environment is required to fix them to the substrate. The pH of the dye bath is maintained between 12.5 and 12.5 by combining NaOH with Na2CO3. Examples include Procion H, Levafix E, Drimarene X, and Cibacron.

11. Azo Dyes

Numerous dyes can be produced from the azo chromophore by adjusting couplers, diazo components, and reactive systems. Greenish-yellow reactive dyes, such as C.I. Reactive Yellow 1, are usually mono-azo dyes based on heterocyclic couplers. Reddish-yellow reactive dyes usually have mono-azo structures from aniline or naphthylamine couplers.

Proper selection of chromophores for commercial reactive dyes is essential to achieving a specific shade zone. Market data also shows that reactive dyes are increasingly selected based on shade.

12. Anthraquinone-Reactive Dyes

Until the end of the 1970s, anthraquinone reactive dyes dominated the brilliant blue dye market, despite their relatively low color strength and high cost. However, anthraquinone dyes have good fastness properties. The most widely used reactive anthraquinone dyes are derived from promaminic acid and a variation of ring substituents, giving colors from bluish-violet to bluish-green. Bright reddish to medium blue colors are most important.

13. Phthalocyanine Dyes

Phthalocyanine-reactive dyes are used for turquoise colors when azo or anthraquinone dyes are insufficient. The main ingredients in turquoise-blue dyes are phthalocyanine derivatives of copper and nickel. The most often used chromophore is copper phthalocyanine, used to make dyes like C.I. Reactive Blue 7.

14. Triphenodioxazine Reactive Dye

Triphenodioxazine dyes are used to produce deep, bright blue shades on cotton. ICI introduced the first triphenodioxazine reactive dye to the market in the middle of the 1970s. The gradual replacement of the anthraquinone chromophore by the triphenodioxazine chromophore is today a well-established trend. Triphenodioxazine dyes have gained an important share of the blue shade area because of their high color strength and low production cost.

15. Formazan Reactive Dyes

Copper complexes of formazan dyes are capable of producing red to greenish-blue shades. Research activity in the formazan reactive dye area has increased since these dyes exhibit high color strength. To learn more about formazan blue reactive dye, visit patents.google.com

Tips when using Reactive Dyes

1. Avoid breathing gas, fumes, dust, mist, vapors, or spray.
2. Wash the skin thoroughly after handling.
3. Use only outdoors or in a well-ventilated area.
4. Contaminated work clothing should not be allowed out of the workplace.
5. Wear protective gloves, eye protection, and face protection.
6. If the dye touches your hands or eyes, wash it with soap and water.
7. Before reusing contaminated clothing, remove it and wash it.
8. Keep dyes in an area with good ventilation. Keep the container closed tightly.

Sources

• Reactive Dyes Global Market Report 2024.
• chemicalbook.com/Product Catalog.
• Vinyl Sulfone Fiber Reactive Dyes.
• Vinyl Sulfone Dyes
• Cyanuric Chloride-Based Reactive Dyes for Use in the Antimicrobial Treatments of Polymeric Materials.
• pubchem.ncbi.nlm.nih.gov/compound Cyanuric chloride.
• Optimization of Enzymatic Treatment and Reactive Dyeing of Viscose Fabric in One-bath Process.
• Studies on the Synthesis of Some Bisazo Reactive Dyes and Their Application on Various Fibers.
• Chemistry Classification and Application of Reactive Dye to Cotton.
• A Concise Theoretical Aspect of Reactive Dyeing and Solvent Dyeing.
• Procion MX Dyes: Assorted Colors

©Eman Abdallah Kamel, 2024

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