Source: Textile Review

Colouring matters, which may be classified as dyes and pigments, have been exploited by man for their aesthetic values and used to embellish various articles and the environment in which man lived over the centuries. Starting with Indigo, the oldest known dye, originating from India; the royal Phoenician's dye, Tyrian purple (or Royal Purple), of the ancient city of Tyre; Alizarin, among the Turkey people and Cochineal, of the European and Mexican dyers, indigenous dye-yielding plants have been discovered in almost every region of the world.

Synthetic dyes were first discovered at the early century. It is only in the 1930's that parenteral route of administration was actually developed: methylene blues, methyl violet are some examples that were used for leprosy and filariasis, respectively. After the 2nd world war, one can observe a rapid decrease of the therapeutic use of dyes by intravenous route. Only a few dyes are still used today, such as patent blue V or fluorescein, as drugs for diagnostic use.

General Dye Chemistry Classified

Dyes that are used by the textile industry are now mostly synthetic. They are mostly derived from two sources namely, coal tar and petroleum-based intermediates. These dyes are marketed as powders, granules, pastes or liquid dispersions. The concentrations of active ingredients typically range from 20 to 80 percent. The textile dye segment is characterized by new dyes. These new dyes are regularly developed for meeting the demands of new technology, new kinds of fabrics, detergents, advances in dyeing machineries, along with overcoming the serious environmental concerns posed by some existing dyes.

With the fast changing of the product profile of the textile industry, from high-cost cotton textiles to the durable and versatile synthetic fibers, the pattern of consumption of these dyes is also going through rapid changes. Nowadays, Polyesters account for a major part of dye consumption. Accordingly, disperse dyes that are used in Polyesters, are also projected to grow at a faster rate.

If we take general dye chemistry as one of the basis for classification, textile dyestuffs can be grouped into the following categories for an easier understanding.

• Acid Dyes • Direct Dyes • Azoic Dyes • Disperse Dyes • Sulphur Dyes • Reactive Dyes • Basic Dyes • Oxidation Dyes • Mordant Dyes (Chrome Dyes) • Vat Dyes • Optical / Fluorescent Brightener • Solvent Dyes

For convenience all the above dyes can be clubbed together into three categories namely:

  • Dyes for Cellulose Fibers
  • Dyes for Protein Fibers
  • Dyes for Synthetic Fibers (All the dyes are not fixed to the fiber during the process of dyeing.)