Different Types Of Dyes And Their Properties

In order to grasp the concept of dyeing, one needs to have a clear understanding of the different types of dyes that are currently available on the market. Before getting into that, let’s explore the most obvious question first–

What is Dye?

A dye is a coloring material that is used for imparting color to different substances or altering the color of something. Dyes have chromophores and auxochromes which are responsible for their color and substantivity.

Types of Dyes

Dyes can be classified based on various parameters. However, we’ll take a look at four most pronounces ones –

Based on the Source

Natural dyes
Synthetic dyes

Based on Ionic Nature

Anionic dyes: Reactive dye, acid dye, etc.
Cationic dyes: Basic dye.
Non-ionic dyes: Disperse dye.

Based on Chromophoric Groups

Azo dyes
Anthraquinone dyes
Nitro and nitroso dyes
Triarylmethane dyes
Indigo dyes

Based on Chemical Structure

Ready-made Dyes

Water-soluble dyes: Reactive dye, direct dye, Acid dye, etc.
Water-insoluble dyes: Vat dye, Sulphur dye, etc.

Ingrain Dyes

Mineral colors
Azoic colors
Oxidation colors

Basic Theory of Dyeing

In dyeing, color is transferred to a textile material to make it permanently colored. In the textile industry, generally, it is done by different machines and consists of several steps.

Now coming to the basic dyeing theory, the interaction between dyes and the textile material along with different dyeing auxiliaries consists of 3 general stages.

Dye migration from the solution to the surface of the fiber, which can also be called as adsorption.
Dye diffusion to the interior of the fiber from the surface, which can also be called as absorption.
Dye fixation by different types of bonds or entrapping inside the fiber pores.

Theory of Dyeing — A Simple Representation of How Dye Molecules, Water Molecules, and the Cloth Exists within the Dyebath

Different types of methods are available for textile coloration.

Direct dyeing
Yarn dyeing
Garment dyeing
Stock dyeing
Top dyeing
Piece dyeing
Dope dyeing

Different Dyes with Their Properties

Now, we will discuss different dyes with their primary dyeing mechanism.

Direct Dyes

We can apply these dyes directly on the fiber as they have a strong affinity and so they are called direct dyes. Mainly these dyes are sodium salts of sulphonic acid or carboxylic acid, and their leading chromophoric group is azo. They are also known as substantive dyes.

Properties of Direct Dyes

They are water-soluble and anionic.
The dyeing process requires electrolytes and alkaline conditions.
Generally, cellulosic fiber is dyed, but protein fiber can also be used.
Fastness properties are average; mainly, the wet fastness is poor. For improved fastness, after-treatment is required.
They are attached to the fiber with weak hydrogen bonds and Van der Waals’ force of attraction.
Generally cheap when compared to other dyes.

Primary Mechanism of Direct Dyes

The dyeing involves three steps, adsorption, diffusion, and migration. In water, the cellulosic fiber’s surface becomes anionic. As the dye is also anionic, for neutralizing the surface to remove the repulsion electrolyte is necessary.

Due to swelling in water, the pores of cellulosic fiber’s amorphous region get opened, and the dyes get diffused inside the pores. Dyes are fixed in the fiber with weak H-bond and Van der Waals force. So the fastness properties are not good enough.

Application: Cotton and Viscose.

Reactive Dyes

Reactive dyes have a halogen-containing reactive group present in their structure and become an integral part of the fiber structure by creating a covalent bond. This is the type that is mostly used for dyeing cotton fabrics.

Properties of Reactive Dyes

These are water-soluble and anionic
Exhibit good wash and lightfastness and moderate rubbing fastness
Get fixed into the fiber by a covalent bond
They are found in powder, liquid, and paste form
Dyeing requires alkaline conditions and the use of electrolytes.

Primary Mechanism of Reactive Dyes

the dyeing process that is most used for dyeing cellulose — Mechanism of Reactive Dyeing

The primary dyeing mechanism consists of three stages.

Exhaustion: With the help of electrolytes.
Fixation: With the help of alkali.
Washing-off: With the help of a soaping agent.

They generally form two types of reaction with cellulose.

Nucleophilic Substitution Reaction

Cell-OH + HO^– ⇒ Cell-O^– + H₂O

Cell-O^–+ Dye-Cl ⇒ Cell-O-Dye + Cl^–

Nucleophilic Addition Reaction

Cell-O^– + Dye-SO₂-CH=CH₂ ⇒ Dye-SO₂-CH=CH₂-O-Cell

Application: Mainly cotton, but protein and polyamide can also be dyed.

Acid Dyes

The application of acid dyes requires an acidic bath. They are mainly carboxylic or sulphuric acid salts. These are the types that are mainly used for dyeing protein fibers.

Properties of Acid Dyes

They are highly water-soluble and anionic.
They have substantivity towards polyamide and protein fibers.
They mainly create ionic bonds, but van der Waals and H-bond also contribute.
The active colored component is the dye anion.
They show poor wash fastness, but lightfastness is excellent.
Acidic medium is required for their application.

Primary Mechanism of Acid Dyes

Wool can be represented as,

H₂N—W—COOH

In water, under a particular condition,

H₂N—W—COOH ⇒ H₃N⁽⁺⁾—W—COO^(–)

When acid is added,

HCl ⇒ H⁺ + Cl^–

H₃N⁺—W—COO^– +H⁺ + Cl^– ⇒ Cl^–+H₃N—W—COOH

After the addition of dyes with wool, the following reaction takes place:

H₃N⁺⁻Cl—W—COOH + R– SO₃⁻⁺Na ⇒ R– SO₃⁻⁺H₃N—W—COOH + NaCl

Wool in Acidic Medium + Acid Dye ⇒ Dyed Wool + Salt

Application: Mainly nylon, silk, and wool.

Basic Dyes

They are mainly salts of organic bases. The cationic part of the dye structure is responsible for color production.

Properties of Basic Dyes

They are cationic dyes.
Soluble in alcohol and methylated spirit but not readily soluble in water.
They exhibit excellent shades but inferior leveling properties.
They are mainly applicable to jute and acrylic.
They show average to good fastness properties.

Primary Mechanism of Basic Dyes

The dyeing of acrylic fiber with these dyes is carried out in a weakly acidic condition where acidic acid and sodium acetate is used with a wetting agent, dispersing agent, and sequestering agent. The temperature and pH should be strictly maintained to prevent unlevel dyeing.

The initial uptake of dyes is very high, so a retarding agent is necessary.

Generally, dyeing is carried out at 98°c, and slow cooling is necessary to prevent the formation of creases. Finally, after-treatment with a non-ionic detergent, acetic acid, and a softening agent is carried out.

Application: Best for dyeing acrylic yarn and fabric; can be used to dye jute also.

Vat Dyes

These dyes generally consist of a keto group in their structure and made water-soluble by vatting. Their application process of vat dyes is quite similar to sulfur dyes. They are mainly used for dyeing denim or jeans.

Properties of Vat Dyes

They are natural coloring substances and not soluble in water.
Vatting is required to convert them into a water-soluble form, and vatting require alkaline conditions.
They produce a wide range of colors and brilliant shades.
They exhibit excellent fastness properties except for the rubbing fastness.
They are found in powder and paste form.
They are very expensive, and their application is limited.

Primary Mechanism of Vat Dyes

The dyeing contains four main stages –

Stages of Vat Dyeing — Mechanism of Dyeing with Vat Dyes

Vatting: The insoluble dyes are converted into soluble leuco forms by reduction.
Diffusion: The soluble leuco dyes get inside the cellulosic fiber.
Oxidation: The soluble dyes converted into insoluble form again.
Washing-off: The unfixed dyes are removed from the surface.

Application: Cotton.

Sulfur Dyes

Sulfur dyes are quite similar to vat dyes. They are hugely used for producing black and brown shades in cotton. They have a disulfide linkage in their structure.

Properties of Sulfur Dyes

They are water-insoluble, and the use of reducing agents is required for making them soluble.
Applied in alkaline condition and oxidation is required for color production.
Electrolytes can improve the exhaustion.
They show average fastness properties.
Range of shades are limited, and generally dull shades are produced.
They are cheap.

Primary Mechanism of Sulfur Dyes

In order to dye with sulfur dyes, you have to follow the following route –

best types of dyes for dyeing black shades — Mechanism of Sulfur Dyeing on Cellulose

Application: Cotton and viscose.

Disperse Dyes

Disperse dyes are sparingly water-soluble dyes used for dyeing hydrophobic thermoplastic fibers. These synthetic fabric dyes are mainly substituted azo, anthraquinone, or diphenylamine compounds.

Properties of Disperse Dyes

They have low molecular weight, are non-ionic, and sparingly water-soluble.
The dispersing agent is required for making dispersed in water.
They sublime without decomposition and show gas fume fading.
They are found in powder and liquid forms.
They have no strong solubilizing group present in their structurer.
They do not have an affinity towards any fiber.
They are physically trapped inside the pores of polyester.

Primary Mechanism of Disperse Dyes

The dyeing of Man-Made Fiber (MMF) with disperse dyes follows these steps –

best types of dyes for dyeing polyester — Dyeing Man-Made Fiber (MMF) with Disperse Dyes

Dissolution or dispersion of the dye molecules in water
Adsorption
Diffusion of the dye molecules in the fiber interior.

Application: Acetate, triacetate, nylon, polyester, acrylic.

Azoic Dyes

They are mainly mono or bis azo water-insoluble coloring compounds. They require coupling components for producing colors. The most exciting thing is that they are not ready-made colors like other dyes.

Properties of Azoic Dyes

They have an insoluble azo group present in their structure and are not water-soluble.
Two baths, a developing bath, and an impregnation bath are required.
They produce intense and bright orange, red and scarlet shades.
They exhibit excellent washing and lightfastness.
Their actual color depends on diazonium and coupling compounds.
They are cheap.

Primary Mechanism of Azoic Dyes

They require two main components.

Coupling component (Naphthol)
Diazonium salt

Magic Color — Mechanism of Dyeing with Azoic Color

The necessary steps of dyeing are,

Naphtholation: The insoluble naphthol is made water-soluble by alkali.
Diazotization: Sodium nitrate reacts with a base containing an amino group that produces diazonium chloride of the base.
Coupling: The material impregnated in the naphthol solution is added to the diazonium bath to produce color.

Application: Cotton, nylon, polyester.

Mordant Dyes

These dyes have no substantivity towards textile material. Chemical binding agents called mordants help them to get attached to the fiber. They are also called chrome dyes, as they are mainly inorganic chromium.

Properties of Mordant Dyes

They do not have an affinity for textile material.
They can produce dark shades.
They exhibit good fastness properties and leveling properties.
Dye fiber bond is strong ionic bonds.
They have a metal ion present in their structure.
They are soluble in cold water.

Primary Mechanism of Mordant Dyes

A complex is formed with the dyes by the chromium ion when potassium dichromate is added to the solution of acid mordant dyes in the presence of H₂SO₄. The complex is water-insoluble and gets precipitated in the fiber.

Three processes can be followed.

Pre-mordanting also known as Chrome
Meta mordanting also known as Metachrome
Post mordanting also known as Afterchrome

Application: Natural protein fibers, nylon, and modacrylic fibers.

Summary of the Property & Uses of Dyes

Before finishing this article let’s summarize the most important attributes of these dyes –

Soluble Dyes
Types of Dyes	Ionic Nature	Dyeing pH (Working Condition)	Means of Fixation	Solubilizing/Reactive Group	Uses of Dyes
Direct (Substantive)	Anionic	Neutral	H-bonds & Van Der Waals forces (Physical Bonding)	Sodium Sulphonate (NaSO₃–), Carboxylic Group	Cellulose, Protein Fibers (Especially Wool)
Acid	Anionic	Acidic	Salt Linkage	Sodium Sulphonate (NaSO₃–), Carboxylic Group	Protein Fibers (Wool, Silk, Nylon etc.)
Basic	Cationic	Acidic	Salt Linkage	Amino Group	Acrylic & Modacrylic
Reactive	Anionic	Alkaline	Covalent Bond	Sodium Sulphonate (NaSO₃–)	Cellulosic (mostly), Wool, Silk
Insoluble Dyes
Vat	Anionic	Alkaline	Mechanically Trapped	Carbonyl group	Cellulose
Sulfur	Anionic	Alkaline	Mechanically Trapped	Sulfur Linkage	Cellulose
Disperse	Non-ionic	Acidic	Mechanically Trapped	N/A (May Contain Weak Solubilizing Group Like –NH₂,–NHR, –OH)	Polyester, Nylon, Cellulose Acetate, Cellulose Tri-acetate

Direct Dye vs Reactive Dye

Here’s the difference between direct dye and reactive dye –

Property	Direct Dye	Reactive Dye
Type of Bond	No chemical bonds, just Van der Waals force	Covalent bond
Dyeing Condition	Basic	Acidic
Colorfastness to Wash	Very poor	Excellent
Mostly Used for	Cotton & Viscose	Cotton & Polyamides (sometimes)
Example	Direct Black E	CI Reactive Blue 19

Vat Dye vs Reactive Dye

Here are the most obvious differences between vat dye and reactive dye –

Properties	Reactive Dyes	Vat Dyes
Preparatory Process	Reactive dyes don’t require any sort of extra preparatory processes.	Vat dyes require vatting.
Dyeing Container Condition	Doesn’t require to be dyed in air-tight conditions	Requires to be dyed in air-tight conditions
Possibility of Hydrolysis	Prone to hydrolysis, thus huge amount of dye wastage	Prone to over-reduction, needs ORP value monitoring
Fastness to Cross-staining	Cross-staining fastness isn’t as good as vat dyes.	Excellent fastness to cross-staining
Cost	Comparatively less expensive than vat dyes	One of the most expensive dyestuff
Example	CI Reactive Blue 19	CI Vat Red 10

Reactive Dye vs Disperse Dye

The difference between reactive and disperse dyes is that –

Properties	Reactive Dyes	Disperse Dyes
Solubility	Water-soluble dyes	Initially insoluble, have to make soluble using a dispersing agent
Dye-Fiber Bond Type	Covalent Bond	Mechanically trapped inside the fiber
Dyeing Container Temperature	Commercially, mostly dyed at 60°C or around boil	High-Temp-High-Pressure (HTHP) machines are required to reach 135°C
Possibility of Hydrolysis	Prone to hydrolysis, thus huge amount of dye wastage	No hydrolysis, lesser dye wastage
Fastness to Wash	Excellent	Excellent
Mostly Used for	Natural fabrics	Synthetic fabrics
Example	CI Reactive Blue 19	Disperse Blue 6

Frequently Asked Questions

1. Which types of colorants have the best wash fastness?

It varies depending on the material. For example, both are reactive dyes, and vat dyes have excellent wash fasteners on cellulosic fibers as well as cotton and tetron. However, their dyeing procedure is very different.

2. What is the most suitable kind of dyes for dyeing cotton?

That would be fiber reactive dyes. They give a wide variety of shades, possess excellent wash fastness and comes at a cheaper price too.

3. What are the best types of dyes for dyeing polyester?

When it comes to polyester, disperse dyes should be your go-to choice. They require a higher dyeing temperature, though. We have a detailed article on it. Give it a read to know more.

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