Basic Dyes: Types, Properties, Process on Cotton Fabric

By Eman Abdallah Kamel

Eman is a writer and engineer. She obtained her bachelor’s degree in textile science from the Faculty of Applied Arts.

A basic dye is a cationic dye. Here, you will learn about basic dye chemistry, common types, properties, facts, and the process of dyeing cotton fabric.

Image source: istockphotos.com

Basic Dyes

Basic dyes are positively charged and therefore react with negatively charged substances. They are usually synthetic and act as a base. They are insoluble in water but can be made soluble by converting the base to a salt. Basic dyes are characterized by high tinting strength and brightness, but they are not generally photoresistant.

Mauveine, also known as aniline violet, was the first synthetic basic dye discovered in 1856, but its composition was not determined until 1994. Basic dyes are widely used for dyeing jute, silk, acrylic, cotton, and wool fibers, among others.

Most major manufacturers of basic dyes are based in China and India, focusing on cationic dyes used in papermaking, acrylic fibers, leather, and specialty inks. Leading global and regional manufacturers include the Dystar Group, Arcromma, and Indian companies such as the Navjevan Group and Darshan Industries.

Chemistry

Chemically, basic dyes are cationic, or positively charged. They contain cationic functional groups such as -NR₃⁺ or =NR₂⁺. Because they are positively charged, basic dyes react readily with negatively charged (anionic) substances. Basic dyes contain amino groups or alkylamino groups as auxiliaries.

Example of basic dyes,

Crystal violet.

An example of a basic dye that has amino groups as its
auxochrome,

Basic red 9.

An example of alkylamino groups,

Methylene blue (basic blue 9).

Chemical structure of methylene blue or basic blue 9. Image source: https://cameo.mfa.org/wiki/File

Popular Basic Dyes

The most common types of basic dyes are the following:

Crystal Violet: Widely used in textile dyeing, its ability to produce deep, vibrant purple hues makes it a sought-after color in the fashion and design industries.
Methylene Blue: Known for its rich blue color, this dye is widely used in dyeing wool and silk, as well as in many industrial applications.
Rhodamine B: With its striking pink to red color, Rhodamine B is a versatile dye used in various textiles, including cotton, wool, and silk.
Auramine O: This bright yellow dye is known for its fluorescent properties. Auramine O is used not only in textiles but also in paper coloring and as a biological dye.

Did You Know?

Methylene blue is an oxidizing-reducing agent. The US Food and Drug Administration (FDA) has approved its use for intravenous administration in the treatment of acquired methemoglobinemia in children and adults. Historically, it was widely used in Africa to treat malaria. Its potential use as a urinary tract antiseptic has also been investigated. Methylene blue is an experimental drug under development by the University of Aberdeen and Tawerx Therapeutics, and initial clinical trials have shown it to be an inhibitor of tau protein aggregation. This drug shows promise for the treatment of Alzheimer’s disease.

Properties

Luster: Basic dyes are characterized by their luster and color intensity.
Solubility: Many basic dyes are poorly soluble in water. Adding glacial acetic acid speeds up the dissolution of the basic dye in water.
Lightfastness: Basic dyes have poor lightfastness.
Wash fastness: Their wash fastness varies from poor to moderate.
Stability: The fastness of basic dyes on protein fibers while wet can be improved by reverse tanning. This process involves treating the dyed material with tannic acid to form an insoluble compound, which reduces its tendency to migrate.
Affinity to cellulosic fibers: Basic dyes do not readily bond to cellulosic fibers such as cotton. The cellulose fibers need to be treated with a mordant before dyeing.

Dyeing of Cotton Fabric

Dyeing of cotton fabric includes two stages:

Pretreatment of Cotton.
Dyeing Method

1. Pretreatment of Cotton

Cotton fabric is cleaned and bleached according to the following recipe:

Sodium hydroxide: 5 g/L
Hydrogen peroxide: 8 g/L
Stabilizer: 1 g/L
Detergent: 1 g/L
Duration: 50 minutes
Temperature: 100°C

The fabric is then washed and dried.

2. Dyeing Method

Before beginning the dyeing process, cotton must be treated with a color-fixing agent.

What are mordants?

Mordants are chemical substances that can bind to both the fibers and the dye.

Tannic acid has been used as a mordant. A 4% tannic acid solution is boiled, and then the cotton fabric is immersed in this solution. The temperature is then reduced to 60°C for two hours. The material is then removed from the bath and squeezed.

Mordant dyeing recipe:

Tannic acid: 4%
M:L: 1:40
Temperature: 100°C lowered to 60°C
Time: 2 hours

The cotton treated with the fixative is then dipped into a solution of tartaric emetic acid, where it is worked on for 30 minutes at room temperature, during which the tannic acid is fixed to the cotton fibers.

Recipe for fixing:

Tartar emetic acid: 2%
M:L: 1:20
Temperature: Room Temperature
Time: 30 minutes

The dye is mixed with an equal amount of acetic acid. The dye solution is then prepared with the required amount of hot water. The cotton is then dyed in a basic dyebath at 70°C for 90 minutes. The dyed fabric is then rinsed and dried.

Recipe for dyeing:

Basic dye: 2%
Acetic acid: 1-3 g/L
Water: 20 times
Leveling Agent: gm/l
pH: 4
Temperature: 70°C
Time: 90 minutes

Sources

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