Technologyof Denim Production: Part- II (Warping & Indigo Dyeing Techniques for Denim)
Indigo dyestuff originally extracted from the varieties ofplants, including wood plants. Indigo belongs to the legume family and overthree hundred species have been identified. Most natural indigo is extractedthroughout the ancient world from the genus Indigofera. In Asia, the primarycommercial indigo species was Indigofera tinctoria (true Indigo) which was alsoknown as Indigofera sumatrana. In Central and South America the commercialindigo species were Indigofera suffructicosa and Indigofera arrecta (Natal indigo).
Indigo is popular from the ancient time due to its brilliantblue hue to fabric. Indigo partially penetrates into the fibers and impartunique surface color. The inner layers remain uncolored when it is indigo dyed.The indigo having the unique characteristic of fading during rubbing or dailyusage of wear and repeated washing. This gives a worn look and for this reasonit is commonly used to color denim.
Until about 1900, natural indigo was the only source of thedye. As the demand for indigo increased during the industrial revolution, thenatural extraction process of indigo could not fulfill the huge demand ofindigo. Hence there is a need of alternate source of indigo. All over theworld, chemists began researching for synthetic methods of producing the dye.
In 1883 Adolf von Baeyer (of Baeyer aspirin fame) developedthe chemical structure of indigo. He found that oxindole can be produced bytreating omega-bromoacetanilide with an alkali (a substance that is high inpH). Based on his observation, K. Heumann identified a synthesis pathway toproduce indigo.
Indigo is a crystalline powder that melts at 390392°C. Itis dark blue in colour, insoluble in water, alcohol, or ether but soluble inchloroform, nitrobenzene, or concentrated sulfuric acid. Its chemical structureof indigo corresponds to the formula
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Theauthor is Manager (TQM) at Shri Lakshmi Cotsyn Limited, UPSIDC Industrial Area,Malwan, Dist. Fatehpur, UP
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