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General Properties of Direct Dyes

Direct dyes are classified according to the dyeing properties. There are three types of dye categories and they are,

Class - A

This type of direct dyes are more and more absorbed by fiber or textile material without leveling agents hence, called self -leveling class.

Class - B

These types of direct dyes are somewhat less absorbent at each place and, it means not self leveling at most time in dye bath. In this process dye exhaustion will decrease. Therefore it is compulsory to use salt to increase dye absorbency etc.    

Class - C

These types of direct dyes are also less absorbent and not self leveling than class A and B. Therefore common salt is needed to be use. And here, dyeing temperature is properly controlled to get better dye exhaustion.

When we are discussing about direct dyes general properties, it is essential to discuss following subtopics. In this answer I wish to describe them in point by point.

Simple application

Dye can be applied in water medium directly with textile materials hence, called direct dyes. In this dyeing process, dyeing assistant chemicals are not compulsory. But to get optimum properties of dyed textiles, some chemical substances are applied.

Range of colour

The large number of colour varieties available under this category of dye. Therefore it is an advantage to colour textile material to get various colour appearance.

Cost effective

Direct dyes are cheap and cost saving dyes hence, colouration cost will be deducted with direct dyes. Therefore textile and garment manufacturing cost will be saved.  

Easy absorbency

Direct dyes are water soluble and can be easily dye with cotton, viscose, silk and woolen materials. Because amorphous region of these textiles available free spaces. When dying process in water medium, direct dye molecules are inserted into the amorphous region. Therefore most fabrics can be easily dyed without dyeing assistant chemicals.

Poor wash fastness properties

Although direct dyes are most absorbent into more textile materials, but their dye stability with textile material is poor. The main reason is water solubility. When washing such coloured garments, then dye molecules are removed with detergent and water. But this can be eliminated by using some mordent. These mordents can be applied before dyeing, in-process of dyeing and after dyeing process hence, called pre-mordanting, post-mordanting and meta-mordanting, etc. For an example can be applied some chemical complex in D- block of periodic table such as CuSO4, K2Cr2O7, SnCl2, FeSO4, etc. But in application process with silk or wool it can be applied some chemicals in S- block of periodic table such as NaCl.       

Good light fastness properties

Direct dyes applied textile materials have good light fastness properties with sun light. It is an advantage to end use of particular textile materials. Therefore direct dyed textiles are used as curtains because rarely washed and good UV and light fastness properties.