Technology
of Denim Production: Part- II (Warping & Indigo Dyeing Techniques for Denim)
Indigo dyestuff originally extracted from the varieties of
plants, including wood plants. Indigo belongs to the legume family and over
three hundred species have been identified. Most natural indigo is extracted
throughout the ancient world from the genus Indigofera. In Asia, the primary
commercial indigo species was Indigofera tinctoria (true Indigo) which was also
known as Indigofera sumatrana. In Central and South America the commercial
indigo species were Indigofera suffructicosa and Indigofera arrecta (Natal indigo).
Indigo is popular from the ancient time due to its brilliant
blue hue to fabric. Indigo partially penetrates into the fibers and impart
unique surface color. The inner layers remain uncolored when it is indigo dyed.
The indigo having the unique characteristic of fading during rubbing or daily
usage of wear and repeated washing. This gives a worn look and for this reason
it is commonly used to color denim.
Until about 1900, natural indigo was the only source of the
dye. As the demand for indigo increased during the industrial revolution, the
natural extraction process of indigo could not fulfill the huge demand of
indigo. Hence there is a need of alternate source of indigo. All over the
world, chemists began researching for synthetic methods of producing the dye.
In 1883 Adolf von Baeyer (of Baeyer aspirin fame) developed
the chemical structure of indigo. He found that oxindole can be produced by
treating omega-bromoacetanilide with an alkali (a substance that is high in
pH). Based on his observation, K. Heumann identified a synthesis pathway to
produce indigo.
Indigo is a crystalline powder that melts at 390392°C. It
is dark blue in colour, insoluble in water, alcohol, or ether but soluble in
chloroform, nitrobenzene, or concentrated sulfuric acid. Its chemical structure
of indigo corresponds to the formula C16H10N2O2.
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The
author is Manager (TQM) at Shri Lakshmi Cotsyn Limited, UPSIDC Industrial Area,
Malwan, Dist. Fatehpur, UP
