Describe different types of dyes that are used in the textile industry.

Different types of dyes are used in the textile industry

Reactive dyes

Reactive dye is a class of dyes that forms a covalent bond with the fiber and is an integral part of the fiber. A reactive dye chromophore has a layer that reacts with the fiber layer. It has good fastness properties due to the covalent bonding that occurs during dyeing. Reactive dyes are most commonly used as dyeing cellulose such as cotton or flax, but it is also dyed with reactive dyes. Reactive dyeing is the most important method for dyeing cellulosic fibers. Reactive dyes have a lower degree of use than other types of dyestuffs because the functional group bonds to water, creating hydrolysis.

Direct dyes

Direct dye is a type of dyestuff that is applied directly to the substrate for a neutral or alkaline bath. They produce full shades without shading on cotton and linen and can also be applied to rayon, silk, and wool. Direct colors give bright shades but the wash fastness is poor. Used to improve the washing strength of dyes directly after various treatments. Direct dyes are molecules that adhere to fabric molecules without the help of other chemicals. Direct dyes are defined as sufficient amounts of anionic dyes for cellulosic fibers, usually containing sodium chloride (NaCl) or sodium sulfate (Na₂SO₄) from an electrolytic water dye bath.

Acid dyes

Acid dyes are anionic, and water-soluble, and are mainly applied in acidic baths. These dyes contain acid groups like COOH and SO₃H and are applied to wool, silk, and nylon when an ionic bond is formed between the fibers of the protonated – NH₂ group and the acid group of the pigment. Lightfastness is quite good though overall wash fastness is poor. Contrary to the electrical nature of such dyes and fibers, the strike rate and the absorption of acid dyes in these fibers are very fast; Electrolyte retarding at higher concentrations is added to the formation of dye uptake and level shades. The acid forms cations on the fibers and the temperature help to replace the negative part of the acid with the molecules of the anionic dye.

Sulfur dyes

Sulfur dyes are water-insoluble. In the presence of a reducing agent and at a temperature of about 75°C -80°C of the alkali pH, the dye particles disintegrate, which later become water-soluble and can therefore be absorbed by the fabric. Sodium sulfide or sodium hydroxide is a suitable reducing agent. Simple salts facilitate absorption. After removing the fabric from the colored solution, it is allowed to stand in the air after which the dye is dyed by the debris. Dissolved in regenerated parent dye water. Due to the low water solubility, these colored fabrics are the basis of good wash strength. These dyes are all-around fastness good without chlorine bleach. Because the dye is water-insoluble, washing it in water will not cause bleeding or stain other fabrics. It may have poor fastness to rubbing. It may use bleach like hypochlorite bleach.

Vat dyes

Vat dyes are dyes that are applied by the vating method on cellulosic fabric. The original vat dye is indigo which is obtained only from plants but is now often produced synthetically. It has high colorfastness which is uncommon in other dyes. It has poor rubbing fastness, but this can be mitigated with special treatments to the fabric. This means that it is better to dip it multiple times in a weak dye bath than to dip it once in a strong dye bath. Vat dyes need to be characterized by reducing agents. The most common reducing agent is sodium dithionite, which converts dye into its leuco form which is soluble. Once attached to the fabric, the leuco dye is then oxidized to an invisible state that becomes intensely colored. Chemical reactions such as oxidation, reduction, and pH control are often necessary; Adequate amounts of caustic soda and sodium hydrosulfite need to be measured to achieve even a reduction in the dissolution process. The color is soluble only in its reduced form. The fiber is repeatedly immersed in this oxygen-free dyebath, then comes in contact with air, causing the water-soluble reduced form to change color when the oxygen becomes a water-dissolved form. For this reason, vat is less suitable for color amateur use than fiber-reactive dyes.

Disperse dyes

Concerns for polyester and related hydrophobic fibers are a category of dispersed synthetic dyes. Disperse dyes are polar molecules that contain the anthraquinone or azo group. It is estimated that 85% of the scattered colors are azo or anthraquinone. These are non-ionic in nature and partially soluble in water. The interaction of dye molecules and polymers occurs with van der Waals and dipole forces. The higher the temperature like 130°C, the better the spread of the dispersed dyes during boiling.