Synthetic Dyes Used in Textile Industry

Synthetic Dyes in Textiles

Nikhil Yogesh Upadhye
Department of Textiles (Textile Chemistry)
DKTE’S Textile and Engineering Institute, Ichalkaranji, India
Intern at Textile Learner
Email: nyupadhye@gmail.com

 

Introduction
Synthetic dyes started with the development of synthetic organic chemistry. The earliest artificial dyes to be prepared were picric acid by Woulfe and aurine by Runge. However, they were not prepared commercially at the time due to high cost of raw material William.H.Perkin is considered as founder of synthetic dyes. In 1865, he prepared the first synthetic dye is called Perkins Mauve or Mauveine. After giving color to the textile substrate it looks attractive. Color is psychological sensation when light particular wavelength reaches to eye. Synthetic dyes are organic compounds used for imparting color to textile, paper, leather, plastic reasonably permanent fashion or permanent manner.

synthetic dyes

Characteristics of True Dye:

  1. It must have stable color.
  2. It must have an attractive color.
  3. It must be able to attract itself to material from solution to capable fix on it.
  4. It is soluble in water or must from stable and good dispersion in water.
  5. When dye is fixed to substrate it does not affect the washing, dry cleaning, perspiration, light fastness and heat etc.

In the synthetic dyes some of are insoluble some of soluble. They are applied on cotton, wool, silk rayon, acetate, polyester, nylon, acrylic, with different dyes as given below.

classification of synthetic dyes
Figure 1. Classification of synthetic dyes

A. Water Soluble Dyes

1. Direct dye:
Direct dyes are normally carried out in neutral or slightly alkaline dye bath, at or near boiling point, with the addition of common salt or sodium sulphate or sodium carbonate. Direct dyes are used on cotton, paper, leather, wool, silk, and nylon. They are also used as pH indicators induce biological stains. This class of dyes derives its name from its property of getting direct affinity for cellulosic fibers when applied from a solution. Chemically, direct dyes are are sodium salts of aromatic sulphonic acids and most of them contain an azo group is the main chromophore. Various manufacturers in the market direct dyes under different trade names.

Some examples of direct dyes are given below:

ManufacturerTrade names
IndokemLncomine
Hindustan cibageigyChlorantine, Solophenyl
ClariantSolar
Atul productsAtul direct
ICIChlorazol

The structure of direct dye is shown below. Note the -N=N- (azo) and the -SO3Na group.

structure of direct dye
Figure 2. Structure of direct dye

Properties of direct dyes:

  1. Direct dyes are soluble in water and have affinity for cellulosic and protein fibers is especially wool.
  2. Chemically the dyes are represented as sodium salt of sulphonic acid (DSO3Na).
  3. Owing to their water solubility, the dyes possess poor wash fastness. Light fastness is poor to moderate even good in some cases.
  4. The fastness properties of these dyes can be improved slightly by means of certain after treatments.
  5. When the days are dissolved in the water the dye molecules get dissociated into ions (DSO3– and Na+). During dying the textile material absorbs the colored anions from the dye solution. This is followed by diffusion of molecules into the fiber where they are finally retained or anchored by means of physical forces.

Disadvantages of direct dyes:

  • Many Direct Dyes are bland and dull in color.
  • Direct Dyes provide duller color than the color provided by the fiber reactive dyes.
  • The wash fastness quality is also low.
  • Few Direct Dyes have low light fastness.

Uses of direct dye:
Direct dyes dye cellulosic fibers. Including viscose rayon, and most of them also dye wool and silk. They do not dye acetate rayon and synthetic fibers. Direct dyes can be applied while at low temperatures and are therefore suitable for dyeing and discharge printing work. Generally these dyes are usually where high wash fastness is not required.

2. Basic dye:
Basic dyes are water soluble cationic dye that are applied to acrylic fibers, but find some used for wool and silk. Usually acetic acid is added to the dye bath to help the uptake of dye onto the fiber. Basic dyes are also used in the coloration of paper.

structure of basic dye
Figure 3. Structure of basic dye

The chemical structures of basic dyes are shown in above Magenta (Geigy).

Properties of basic dye:

  1. Outstanding characteristics of basic dyes are the brilliance and intensity of their color.
  2. Basic dyes process high tinctorial value.
  3. They have poor percentage to light and poor to moderate washing fastness.
  4. An important property of basic dyes is that they will combine with tannic acid and to form an insoluble compound, provided that mineral acid is absent.
  5. The wet fastness basic dyes on protein fibers can be improved by ‘back tanning’. This consists of after treating the dyed material with tannic acid in order to form an insurable complex and thereby reduce the tendency of the dye to migrate.
  6. Basic dyes are used to dye woollen goods especially when particularly bright shades that cannot be obtained with acid dyes are required basic dyes are also largely used for dyeing silk.
  7. The so called ‘cationic dyes’ developed synthetically, are made specially for dyeing acrylic fibers as they exhibit excellent all round on these fibers.

Advantages of basic dye:

  • Relatively economical
  • Shows good brightness
  • High tinctorial

Limitations of basic dye:

  • Poor shade stability
  • Very poor light fastness

Applications of basic dye:
These dyes are applied to wool, silk and acrylic fiber, usually acetic acid is added to dye bath to help the take up of the dye onto the fiber. These dyes are also used in coloration of paper.

3. Acid dye:
Most acid dyes are sodium salts of organic sulphonic acids. The consists of an aromatic structure containing chromogen and solubilizing groups, which is almost always sulphonic acid salt (D-SO3Na). The acid dyes soluble ionic compounds where the color is contained in the anionic portion.  Initially acid dyes are called so because of the presence of an acid was required in their application. The term acid dye is also consistent with their chemical structure since they are salts of organic acids. Often, dies are also referred to as anionic dyes. Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dye baths.

acid dye structure
Figure 4. Acid dye structure

Properties of acid dyes:

  1. Acid dyes produce a wide range of brilliant shades.
  2. They do not have affinity to cellulosic fibers.
  3. They have good affinity for protein and polyamide fibers and are the main class of dyes used for wool, silk and nylon dyeing.
  4. Individual days of this class vary in terms of their fastness properties and hence care should be taken while dying mixture shades.
  5. The rate of dyeing of acid dyes is function of temperature and each member has a specific temperature at which it rate of dyeing and exhaustion are maximum.
  6. Chemically, acid dyes resemble the direct dyes in the sense that after dissolution they produce a colored anion (DSO3-) and colorless cation (Na+). They are generally represented as D-SO3Na, where the ‘D’ represents the chromogen part of the dye molecule.

Advantages of acid dyes:

  • They are water soluble
  • They have affinity towards the protein fibers
  • Many bright shades are found.

Disadvantages of acid dyes:

  • They do not have affinity to cellulosic fibers.
  • Poorwashing fatness.

Uses of acid dyes:
Acid dye is a dye that is typically applied to a textile at low pH. They are mainly used to dye wool, not cotton fabrics. Some acid dyes are used as food colorants and some can also be used to stain organelles in the medical field.

4. Reactive dye:
Reactive dyes utilize chromophore attached to a substituente that is capable of directly reacting with the fiber of substrate. The covalent bonds that attached reactive dye two natural fibers make them among the most permanent of dyes. Cold brand reactive dyes, such as Procion MX, Cibacron F, and Drimarene K, are very easy to use because the dye can be applied at room temperature. Even at high temperature also they can be applied. The structure of a reactive dye is shown below.

reactive dye structure
Figure 5. Reactive dye structure

Properties of reactive dyes:

  1. Reactive dyes, on account of the sulphonic acid groups in their molecules are readily soluble in water.
  2. Unlike direct dyes, the reactive dye molecules tend to be much less substantive to cotton and require much larger quantities of salt for exhaustion.
  3. These dyes, unlike any other class of dyestuff, react and combine chemically (covalently) with cellulose. It is this characteristic that gives them the name reactive dyes.
  4. The reactivity of the dyestuffs can be reduced when describe by blocking one of the reactive chlorine atoms giving the hot brand type of reactive dye.
  5. Reactive dye molecules are not as long as those of direct dyes. Short molecules have two advantages namely, (a) clarity and brightness of hue and (b) easy penetration and therefore good levelling.
  6. Textile materials colored with reactive dyes have moderate to good light fastness and washing fastness.
  7. Reactive dyes can be applied to cellulosic fibers by the exhaust dyeing (batch dyeing), semi-continuous dyeing (pad batch) and continuous dyeing techniques.

Advantages of reactive dyes:

  • Reactive dyes are one of the best alternatives to banned dyes and other types of cellulose dyes such as sulphur dyes, azoic dyes and vat dyes.
  • Dyed materials having excellent properties, particularly good wet fastness, can be obtained by dyeing with reactive dyes through an economical and simple dyeing process.
  • The reactive dyes have wide chromatogram, bright color, excellent performance and strong applicability, and their properties can satisfy the requirements of the market for fibers and fabrics.
  • Reactive dyes are suitable for dyeing of new type of cellulose fiber products such as Lyocell fiber.

Disadvantages of reactive dyes:

  • The utilization rate is not high enough (generally 60%~70%). The dyeing process produces a large amount of colored sewage, and its COD value is generally between 0.8 and 30,000 ppm, and the COD value of concentrated wastewater is more than 50,000 ppm.
  • In order to suppress the charge on the surface of the fiber, a large amount of electrolyte is consumed when using the reactive dye, which not only increases the labor intensity, but also raises the concentration of chloride ions in the wastewater to more than 100,000 ppm, thereby greatly increasing the difficulty level of the treatment of dyeing wastewater.
  • Some reactive dyes cannot meet the requirements of the market, such as their light fastness to wetness, wet rubbing fastness, and the light fastness of azo red dyes and azo blue dyes in light colors.
  • There are few dark varieties of reactive dyes that can replace sulfur dyes and vat dyes.

Uses of reactive dyes:

  1. Cold water fiber reactive dyes, suitable for dyeing on cotton, silk, jute, rayon and hessian.
  2. Reactive dyes are used where bright dyeing with high light and wash fastness is required.
  3. Cold dyeing is used extensively in batik work.
  4. Although some reactive dyestuffs have been specially modified to dye wool, their main usage is in dyeing cotton linen and viscose rayon.

5. Metal complex dye:
Metal complex dyes are also called pre-metallized acid dyes. This is because a metal, usually chromium, is incorporated in the dye molecule during its manufacture. The in Corporation of metal in the dye molecule enables the dye to be more readily applied to the fiber and therefore facilitates a dyeing process that is relatively short.

metal complex dye structure
Figure 6. Metal complex dye structure

Properties of metal complex dyes:

  1. The light fastness rating of metal Complex bi is around 5.
  2. There washing process rating is 4-5. The great number of van der Waals forces occurring between the relatively large dye molecules and the macromolecules of the fiber makes it difficult for dye molecules to be removed during laundering. Other Inter molecular dye-fiber bonds such as ionic bonds, hydrogen bonds and coordinate bonds also play a major role in this respect.
  3. The presence of mainly chromium in these dyes provides only a limited range of rather dull colors.

Advantages and disadvantages of metal complex dyes:

  • Excellent, light‐fastness.
  • Medium washing fastness.
  • Shows very good level dyeing and penetration characteristics.
  • Can cover up for the irregularities in the substrates.
  • They are water soluble dye.

Uses of metal complex dyes:

  1. Metal Complex Dyes is using fora variety of applications like wood stains, leather finishing,
  2. Stationery printing inks, inks, coloring for metals, plastic etc.
  3. These are suitable for wool, silk, polyamides.
  4. The metal used are copper, chromium and cobalt and nickel.
  5. Fastness properties of the fabric dyed by metal complex dyes show good light fastness.
  6. However wet fastness is moderate, particularly when darker shades are to be considered.
  7. However the fastness also is dependent on the choice of fiber and type of dye category.
  8. These dyes are either dyed at neutral pH to weakly acidic to even sometimes strongly acidic pH.

B. Water Insoluble Dyes

1. Vat dye:
Vat dyes are essentially insoluble in water and incapable of dyeing fibers directly. However, reduction in alkaline liquor produces the water soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fiber. Vat dyes owe their name to the fact that the foremost member in this series, indigo, was applied to textiles by means of a fermentation process in wooden vessels commonly known as ‘vat’. The dyes are amongst the oldest natural coloring matter derived from origins like vegetable (plants, stems, etc.), insects and animals. Vat dyes provide textile materials with the best color fastness of all the dyes in common use. The fibers most readily colored by them are the natural and man-made cellulosic fibers. Like cotton, viscose rayon, etc.

vat dye structure
Figure 7. Vat dye structure

Properties of vat dyes:

  1. A Vat dyes are insoluble in water.
  2. They are generally converted to their soluble “leuco” state by means of sodium hydrosulphite (reducing agent) in the presence of caustic soda.
  3. Vat dyes have excellent washing and light fastness.
  4. Vat dyes are very expensive compared with the other classes of dye.
  5. They are available commercially in different forms such as powder fine, micro fine ultra disperse highly concentrated, supra paste and double-paste.

Advantages of vat dyes:

  • The vat dye have high color fastness, which is uncommon in other dye classes.
  • The poor rubbing fastness.
  • Indigo dye is a type of vat dye that uses light rather than oxygen to fix the dye.
  • Mostly used in garments industry.

Disadvantages of vat dyes:

  • Limited shade range (bright shade).
  • Sensitive to abrasion.
  • Complicated application procedure.
  • Time consuming.
  • Slow process.
  • Not more suitable for wool.

Uses of vat dyes:

  1. Vat dyes are used in cotton dyeing where high wash & boil fastness required.
  2. Because of the high alkali concentration in the dye bath, pure vat dyes cannot be used on animal fibers, (wool, natural silk, & various hairs). Bright red is absent in vat dye range.
  3. Solubilized vat dyes, not requiring the presence of alkali, can be used for dyeing on animal fibers.
  4. Because they are dyed at low temperatures, they are used in Indonesian batik dyeing for green shades.

2. Disperse dye:
Disperse dyes are dyes with extremely low solubility in water which is in finely dispersed state. The size of a disperse dye particles is in the region of approximately 0.5-1 micrometer. Disperse dyes are applied in the form of fine aqueous dispersion. The fibers most readily colored by disperse dyes are cellulose acetate, polyester, acrylic and nylon Chemically, the disperse dyes belong to various classes such as azo, anthraquinone, methylene, and diphenylamine The dyes usually have -OH, -NO, -CN, haloger and amine groups, but never any polar groups The chemical structures of two disperse dyes.

disperse dye structure
Figure 8. Disperse dye structure

Properties of disperse dyes:

  1. Generally, these dyes are insoluble in water. However, they are soluble in hot water to some extent, the solubility increasing with temperature.
  2. A feature of disperse dye molecules is their lack of polar groups. This is why they are not readily soluble in water.
  3. Textile materials colored with disperse dyes have fair to good light fastness the average light fastness rating is 4-5.
  4. Disperse dyed textile materials have moderate so good wash fastness, being 3-4 on the average. This is due partly to the insolubility of the dye and partly to the hydrophobic nature of the fibers to which they are usually applied.
  5. Excessive hot pressing or ironing of disperse dyed or printed textiles may result in color loss.
  6. The dyes have low molecular weight.
  7. They are available in the form of powder, liquid and micro-dispersed granules.

Advantages of disperse dyes:

  • Short dyeing time
  • Stable color light
  • Complete chromatography

Disadvantages of disperse dyes:

  • The structure of disperse dyes contains ester groups,
  • Which are easy to hydrolyze the dyes under alkaline conditions,
  • Leading to the change of light and dye loss during dyeing

3. Sulphur dye:
Sulphur dyes being relatively inexpensive are widely used for dyeing of cellulosic fibers and their blends especially with polyester/cotton yarn is dyed in a package or hank dyeing machine. Sulphur dyes are widely used for black, blue, maroon, olive and green colors in medium to heavy depths. Fastness properties of sulphur dyes vary markedly throughout the range, e.g. light fastness of yellow dyes is almost 3 where as black is about 7. Wash fastness is generally good. Fastness to bleaching is poor except in the case of a few dyes. These dyes are available in powder, pre-reduced powder, grains, paste and liquid form.

sulphur dye structure
Figure 9. Sulphur dye structure

Properties of sulphur dyes:

  1. Sulphur dyes are insoluble in water.
  2. They are soluble in a solution of sodium sulphide to which sodium carbonate mayor may not be added.
  3. The sodium sulphide acts as a reducing agent, severing the sulphur linkage and breaking down the molecules into simpler components, which are soluble in water.
  4. The wash fastness is good (3-5) and the light-fastness is satisfactory (3-7). These dyes have poor fastness to chlorine.

Advantages of sulphur dyes:
The main advantage of using sulphur dye lies in their cheapness, even when producing deep shades on cotton with good wash and light fastness, compared against other classes of cotton dye. Consumption of costlier indigo in dyeing denim can be reduced by topping or bottoming with sulphur dye. In topping, denim dyed with indigo to a lighter shade is re-dyed with sulphur dye to develop the desired shade. The bottoming process is just the opposite: denim dyed with sulphur dye is then re-dyed with indigo, with the sulphur dye remaining at the bottom of the indigo layer. The top or bottom can be accomplished by applying sulphur dye in the pre-wash, final indigo bath, or in the after-treatment section.

Limitation of sulphur dyes:
Inadequate tinctorial ability limits production of light shades. Limited hue range – true red, orange and yellow cannot be produced.  Shades lack brightness (though this can be manageably).  Improved by topping with basic dyes.  Bronzing due to heavy dyeing. Tendering of cotton on storage in a humid atmosphere not applicable on swimming costumes for fear of discoloration. Not applicable on protein fibres due to the high alkalinity of the bath.

4. Ingrain dye:
The colored pigment formed by the chemical combination of the two colorless components is insoluble in water and therefore exhibits extremely good fastness to wet treatments. The insoluble dye is a product of a reaction between water-soluble components in an aqueous medium, this contributes to the occurrence of the reaction in the solution phase also. The pigment formed in the bath is loosely deposited on the surface of the material and leads to poor rubbing fastness. However, the dyeing process aims at the production of the insoluble azoic pigment within the fiber structure. It is for this reason that azoic dyes are classified as “ingrain dyes”.

5. Azoic dye:
Azoic dyes are not ready-made dyes but are produced within the substrate using two different components i.e. napluhok and bases, which are also referred to as “coupling components” and “diazo components respectively. Owing to the requirement of very Tow temperatures requiring the use of ice in the application of azoic dyes, this group of dyes is also known as “ice colors”.

azo dye structure
Figure 10. Azo dye structure

Properties of azoic dyes:

  1. They are insoluble in water.
  2. They are not ready-made dyes the color is formed in the fiber by two components usually referred to as naphthols and bases.
  3. The dyed goods have very good to excellent light fastness.
  4. The dyed goods have good washing fastness.
  5. The dyed goods suffer from poor rubbing fastness and this can be overcome by proper soaping treatment

Advantages of azoic dyes:

  • It has wide color range.
  • It has good color fastness.
  • It has ability to absorb light.
  • The environmental impact is low here.

Disadvantages of azoic dyes:

  • Color range/ gamut is limited – only orange, red, yellow, blue, brown & blacks produced
  • Poor rubbing fastness,carcinogenic in nature.

Application of azoic dyes:

  • Impregnation with a solution of naphthol. This step is called ‘naphtholation’.
  • Development of the chromophore (azo group). This is the ‘diazotisation’ step.
  • Development of colored pigment. This is the ‘coupling’ step.
  • Removal of the surface color from the dyed fiber. This step is called ‘soaping’.

Conclusion

  1. The dyeing process is one of the key factors in the successful trading of textile products.
  2. Dyeing methods have not changed much with time.
  3. Basically water is used to clean, dye and apply chemicals to the fabrics, and also to rinse the treated fibers or fabrics.
  4. The changing technology, from hand power, to water power to steam and then to electricity, fundamentally changed the textile industry, its product marketability and its profitability.
  5. Now it’s time for another change! Plasma technology is poised to change the concept of textile wet processing, as we all know Innovation never ends.

References

[1] Handbook of textile and industrial dyeing (Volume 1) by M. Clark Woodhead Publication

[2] Handbook of textile and industrial dyeing (Volume 2) by M. Clark Woodhead Publication

[3] Synthetic Dyes by Gurdeep R. Chatwal

[4] The chemistry of synthetic dyes (volume viii) by K. Venkataraman

[5] Industrial dyes by Klaus Hunger

[6] https://www.slideshare.net/amirhamza1234/presentation-on-dye.

[7] https://www.researchgate.net/publication/279891046_Direct_dyes.

You may also like:

  1. Methods of Dyeing | Different Types of Dyeing Methods
  2. Basic Dyes: Properties, Classification, Application, Advantages and Limitations
  3. Why So Called Vat Dye | Properties, Classification and Application of Vat Dyes
  4. Classification and Characteristics of Dyes | Commercial Name of Dyes
  5. Classification, Application and Aftertreatment of Direct Dyes
  6. Requirements of Dyes and Pigments and Their Differences
  7. Pigment Types, Properties, Trade Name, Uses, Advantages and Disadvantages
  8. Reactive Dyes: Classification, Dyeing Mechanism, Application & Stripping
  9. Disperse Dyes: Properties, Classification, Dyeing and Printing Method
  10. Sulphur Dyes: Properties, Classification, Mechanism, Stripping & Defects
  11. Different Types of Dyes with Chemical Structure

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