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### Theory:

Dye Chemistry:

Colours have always fascinated humans because we live in a colourful world. We could see a wide range of colours in plants and their flowers. We eat coloured foodstuff and use a variety of coloured materials in our daily life.

Do you know how do they get their colours?
Because they contain some chemicals known as colourants.
Dye preparation

1. Humans' uses of colourants for painting and dyeing dates back to the dawn of progress. Until the mid $$19th$$ century, all colourants applied were of natural origin. As colourants, inorganic pigments such as soot, manganese oxide, and hematite were used.

2. Organic natural colourants have a long history of use, particularly for colouring textiles.
The organic compounds that are used as colourants are called dyes. These dyes are all aromatic compounds arising from plants and also from insects, fungi and lichens.
After the development of modern organic chemistry, various synthetic dyes were developed and used by humankind.

Dye chemistry is the study of such types of dyes. It gives us information on the theory, structure, synthesis and applications of synthetic dyes.

Characteristics of Dyes:
Not all coloured compounds are dyes. Dyes are coloured compounds that can be chemically or physically bonded to fabrics.
As a result, a dye should have the following properties:
• First, it should have a proper colour.
• It should be able to set itself or be capable of being a fix to the fabric.
• It should be quick to light.
• It should be not affected by the action of water, dilute acids and alkalies.
Classification of Dyes:

Coal tar dyes:
Nowadays, almost all the dyes are synthetic and are prepared from aromatic compounds obtained from coal tar. Hence, such dyes are sometimes called coal tar dyes. But, they may vary in their basic structure and their way of application.
Coal tar dyeing

Therefore, dyes are divided in two ways based on the application and their parent structure.