The dye which have strong affinity towards the fiber which can be applied directly on the fabric and which do not need any assistance, such type of dye is called direct dye.This dye posses a great affinity towards the cellulosic fibers. Any fiber except synthetic fiber and tri-acetate fiber can be dyed by this dye. Since synthetic fibers cant be dyed by this dye so now a days, it is known as cotton dye.
Congo-Red was the first direct dye discovered by Mottiger in 1884.
Property of Direct Dye
- Direct dye consist of sodium salt of sulphonic acid or carboxylic acid, so it is easily and readily soluble in water.
- Cellulose fibers have strong affinity for direct dyes, specially cotton and viscous rayon, protein fibers also can be dyed by this dye.
- This dye can easily penetrate into the fiber
- Washing fastness is low but can be increased by after treatment.
- This dye can applied both in alkaline or natural medium.
- Different types of shades can be produced by the help of this dye.
- It is low cost dye than other.
- The dye is simple and common in the practical point of view.
Chemical Classification of Direct Dye
There are mainly four groups of derivatives
1. Azo derivatives.
2. Stilbene Derivatives.
3. Primuline Derivatives.
4. Phthalocyanine Derivatives.