Textile Chemistry Developments
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Ltd Follow. Probably the oldest known dye is the blue dye indigo, obtained in Europe from the leaves of the dyerswoad herb, Isatis tinctoria , and in Asia from the indigo plant, Indigofera tinctoria. Even by modern standards, both alizarin and indigo have very good dyeing properties, and indigo remains a favoured dye for denim, although synthetic indigo has replaced the natural material.
With a process developed by the Phoenicians, a derivative of indigo, Tyrian purple , was extracted in very small amounts from the glands of a snail, Murex brandaris , indigenous to the Mediterranean Sea. Experiments in yielded 1. Historically, this dye was also called royal purple because kings, emperors, and high priests had the exclusive right to wear garments dyed with it, as is well documented in the Hebrew Bible and illustrated for Roman emperors on mosaics in Ravenna, Italy.
Industrial Dyes (Chemistry Properties Applications) (scattothersign.gqtile…
By the s, with the decline of the Eastern Roman Empire , the Mediterranean purple industry died out. Natural yellow dyes include louting, from the leaves of weld, Reseda luteola , and quercetin, from the bark of the North American oak tree, Quercus tinctoria. These are in the flavonoid family, a group of compounds occurring almost exclusively in higher plants and producing the colours of many flowers. In fact, these compounds can produce all the colours of the rainbow except green.
Luteolin, a yellow crystalline pigment , was used with indigo to produce Lincoln green, the colour associated with Robin Hood and his merry men.
Classification of colorants
Another group of compounds, the carotenoids , present in all green plants, produce yellow to red shades. Lycopene , from which all carotenoids are derived, produces the red colour of tomatoes.
An ancient natural yellow dye, crocetin, was obtained from the stigmas of Crocus sativus ; this dye is undoubtedly derived from lycopene in the plant. Few of the flavonoid and carotenoid colorants would have survived ancient extraction processes. Logwood is the only natural dye used today.
Heartwood extracts of the logwood tree, Haematoxylon campechianum , yield hematoxylin, which oxidizes to hematein during isolation. The latter is red but in combination with chromium gives shades of charcoal, gray, and black; it is used mainly to dye silk and leather.
We are surrounded by colors.
Highly skilled craftsmen with closely guarded secret formulas rendered dyeing a well-protected trade. The formation of different colours by mixing red, blue, and yellow dyes was well known in ancient times, as was the use of metal salts to aid the retention of dyes on the desired material and to vary the resultant colours.
These are adsorbed on the fibre and react with the dye to produce a less soluble form that is held to the fabric. No doubt the secret processes included other ingredients to improve the final results. Mordants also were used to vary the colours produced from a single dye. For example, treatment with aluminum hydroxide, Al OH 3 , before dyeing with alizarin produces Turkey red, the traditional red of British and French army uniforms.
Alizarin gives violet colours with magnesium mordants, purple-red with calcium mordants, blue with barium mordants, and black-violet with ferrous salts. Around , chromium salts, used as mordants, were found to provide superior dye retention and, in time, largely displaced the others; chromium mordants are still widely used for wool and, to some extent, for silk and nylon.
Until the dye industry utilized natural dyes almost exclusively; however, by nearly 90 percent of industrial dyes were synthetic.
Non-textile applications of Dyes
Several factors contributed to the commercial decline of natural dyes. By the Industrial Revolution in Europe led to a burgeoning textile industry, which created increased demand for readily available, inexpensive, and easily applied dyes and revealed the important economic limitations of natural dyes. Since most dyes were imported from distant sources, transportation delays were likely to slow the production of dyed materials. In addition, inefficient processes were often required for optimum results; for example, Turkey red dyeing could involve more than 20 steps to produce the desired bright, fast colour.
Advances in organic chemistry , both practical and theoretical, spurred by studies of the many new compounds found in coal tar , increased interest in finding ways to utilize this by-product of coke production. The dye industry played a major role in the development of structural organic chemistry, which in turn provided a sound scientific foundation for the dye industry. Article Media. Info Print Print.
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