APPLICATION AND EVALUATION

Physical and organic chemistry of dyes and the dyeing process, Dyeing of ceUulosic fibers. 

Dyes can be classified according to chemistry, shade, apphcation conditions, fastness, etc (see Dyes and dye intermediates). In this article the traditional classification by apphcation method is used. 

The first synthetic dyestuff, mauveine, was discovered by Perkin in 1856 in the UK and led to many investigations of the derivatives of coal tar as potential coloring matters. The first dia2onium salt derived from picramic acid was prepared in 1858 and is still the basic chemistry behind coundess commercial products. Despite these inventions, in 1900 the vast majority of dyestuffs were still of natural origin. Now at the end of the century the situation has changed dramatically synthetic dyes dominate. 

With the increased awareness of environmental and green issues there has been an increased interest in natural dyes accompanied by a lobby for natural fibers in favor of synthetic fibers. However, studies have shown (3) that if 1990 s volume of cotton were colored with natural dyes, at least 31% of the available world s agricultural land would be needed to cultivate the requisite plants. The estimate is based on it taking, on average, 440 g of fresh dye plant to achieve the same tinctorial effect as 1 g of synthetic dye. 

Contrary to proponents assumptions, natural dyes are not necessarily environmentally friendly. First, large amounts of plant waste would be produced because of the low dye content in plants, eg, 170 million t of waste to color the cotton volume. Also, in order to dye fabric with natural dyes, mordants, which are usually based on heavy metals, have to be used. For example, madder is appHed with tin (Sn) or aluminum (Al). Weld is appHed with tin salts. Salts based on copper and iron can also be used. 

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ACRYLIC ESTERPOLYTffiRS - 2-CYANOACRYLIC ESTpRpOLYTffiRS] (Vol 1) -dyeing of pYES, APPLICATION AND EVALUATION] (Vol 8)... 

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