Natural dye

Natural Dves Natural dyes and pigments are derived from mineral, animal, or plant sources and generally are complex mixtures of materials. A number of natural dyes can be classified as acid or vat dyes and can be readily mordanted. In general, the natural dyes give more muted tones than synthetic dyes and are useful only on natural or regenerated fibers. 

The above processes are used for application of cfyes to textile substrates in the form of fiber sliver or top, yarn, or fabric by batch (discontinuous) or continuous methods. 

The pad-batch method is a specialized batch technique for application of reactive dyes to cellulosic fibers. hi the pad-batch method, cellulosic fabric is passed through a concentrated solution of reactive dye, followed by storage of the wet fabric in a vapor tight enclosure for 24 to 48 hours 

A number of chemical reagents (auxiliaries) are added to the dyebath to alter in some manner the course of dyeing. Acids or bases may be added to the dyebath to induce charge formation in the fiber in order to increase dye diffusion or to promote reaction of the dye with the fiber as in the case of reactive dyes. In addition, bases may be used to open up the structure of cellulosics to improve dyeing or to aid in dissolving of vat 

The fastness of the dyeing will be dependent on the location of the dye within the fiber, chemical and physical forces holding the dye to the fiber, and the stabil ity of the dye-fiber combination to environmental factors. Dye distributed evenly throughout the fiber in small aggregates is preferred, whereas surface or ring dyeing leads to poor washfastness. 

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The reducing action of sulphurous acid and sulphites in solution leads to their use as mild bleaching agents (for example magenta and some natural dyes, such as indigo, and the yellow dye in wool and straw are bleached). They are also used as a preservative for fruit and other foodstuffs for this reason. Other uses are to remove chlorine from fabrics after bleaching and in photography. 

Dyes for leather Dyes, natural Dyes, reactive Dyes, sensitizing... 

Natural dyes Naturalean process Natural flavorings Natural gas... 

Textile dyes were, until the nineteenth century invention of aniline dyes, derived from biological sources plants or animals, eg, insects or, as in the case of the highly prized classical dyestuff Tyrian purple, a shellfish. Some of these natural dyes are so-caUed vat dyes, eg, indigo and Tyrian purple, in which a chemical modification after binding to the fiber results in the intended color. Some others are direct dyes, eg, walnut sheU and safflower, that can be apphed directly to the fiber. The majority, however, are mordant dyes a metal salt precipitated onto the fiber facUitates the binding of the dyestuff Aluminum, iron, and tin salts ate the most common historical mordants. The color of the dyed textile depends on the mordant used for example, cochineal is crimson when mordanted with aluminum, purple with iron, and scarlet with tin (see Dyes AND DYE INTERMEDIATES). 

Various methods of home-dyeing cotton and wool materials using natural dyes made from hulls of butternut, hickory nut, pecan, eastern black walnut, and Knglish walnut have been described (149). As far back as during the Civil War, butternut hulls have been used to furnish the yellow dye for uniforms of the Confederate troops. More recent attempts have been made to manufacture yellow and brown dyes from filbert shells on a commercial scale. The hulls are treated with copper sulfate and concentrated nitric acid to produce a yellow color, with ferrous sulfate to produce oHve-green, or with ammonia to produce mby-red (150) (see Dyes AND DYE INTERMEDIATES Dyes, natural). 

Organic colors caused by this mechanism are present in most biological colorations and in the triumphs of the dye industry (see Azinedyes Azo dyes Eluorescent whitening agents Cyanine dyes Dye carriers Dyes and dye intert diates Dyes, anthraquinone Dyes, application and evaluation Dyes, natural Dyes, reactive Polymethine dyes Stilbene dyes and Xanthenedyes). Both fluorescence and phosphorescence occur widely and many organic compounds are used in tunable dye lasers such as thodamine B [81-88-9], which operates from 580 to 655 nm. 

Ger. Pat. 927,305 (May 5, 1955), F. Rath. Natural dyes like norbixki, crocetki, and carminic acid are discussed from an appHcations standpokit. 

Mordant dyes have hydroxy groups in their molecular stmcture that are capable of forming complexes with metals. Although a variety of metals such as iron, copper, aluminum, and cobalt have been used, chromium is most preferable as a mordant. Alizarin or Cl Mordant Red 11 [72 8-0] (1) (Cl 58000), the principal component of the natural dye obtained from madder root, is the most typical mordant dye (see Dyes, natural). The aluminum mordant of alizarin is a well-known dye by the name of Turkey Red and was used to dye cotton and wool with excellent fastness. However, as is the case with many other mordant dyes, it gave way to the vat or the azoic dyes, which are applied by much simpler dyeing procedures. 

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. 

The anthraquinone stmcture occurs in both the plant and animal kingdom. Those natural dyes having this stmcture surpass all other natural dyes in fastness properties (see Dyes, anthraquinone). 

Turkey, for centuries, has been known for the beauty of its handwoven mgs dyed with natural dyes. Nowadays Turkish peasants prefer to dye machine-made mgs with synthetic dyes since these are more readily available and easier to apply. However, there is a growing demand by collectors and connoisseurs connoisseurs for handmade mgs dyed with natural dyes, especially alizarin, and they command premium prices (22). Also, there is a small demand for natural alizarin by artists and home dyers who claim that natural alizarin produces subde shades not obtainable with synthetic alizarin. Just as synthetic alizarin forced natural alizarin out of the market, synthetic alizarin has been replaced by azoic dyes since they are easier to apply. 

Logwood [8005-32-2] (Cl Natural Black 1 Cl 75290) is a modified ben2opyrone, and was the last of the natural dyes to survive after the appearance of synthetic dyes because of the desirable bluish-black hue it produced on chromemordanted fibers. However, for economic reasons and because it requires a mordant, it too is no longer used commercially. 

Health, Safety, and Environmental Factors of Natural Dyes... 

Natural dyes processed for the market do not undergo any chemical operations. Those operations iavolved are purely physical, such as grinding, spray or vacuum dryiag, and water or solvent extractions. None of these operations create any great environmental problems. 

The use of natural dyes as food colorants evolved over a period spanning thousands of years. During that period, by trial and error, some dyes were found to be safe while others were not. By comparison, the development of synthetic dyes as food colorants has taken place over a comparatively short time. During that period, some synthetic dyes considered safe by existing health standards were used as food colors. Later, with iacreased knowledge, these were found to create health problems and were removed from the marketplace. The manufacture of synthetic dyes for use on foods creates more of a health and environmental problem than natural dyes, but offers greater variety and stabiUty of color (see Dyes, environmental chemistry). 

R. J. Adrosko, Natural Dyes and Home Dyeing, Dover Pubhcations, Inc., New York, 1971, p. 21. 

R. Buchanan, M Weaver s Garden, Interweave Press, Loveland, Colo., 1987, p. 97 R. J. Adrosko, Natural Dyes in the United States, Smithsonian Institution Press, Washington, D.C., 1968, p. 39. 

Salvador, R, The use of ultrasonication in the extraction of natural dyes, presented at 2nd International Congress on Pigments in Food, Portugal. 

Nishizawa, M. et al.. Analysis of natural dyes (III). Analysis of cochineal dye and lac dye in foods and dyes, Hokk. Eisei Kenyush., 35, 7, 1985. 

This noble but naive attempt - bearing in mind that only the molecular formula of C20H24N2O2 was known at the time - was doomed to fail. In subsequent experiments with aniline, which was fortunately contaminated with toluidines, Perkin obtained a purple product in low yield. Perkin was quick to recognize the commercial potential of his findings the natural dye, Tyrian purple, which was extracted from a species of Mediterranean snail, cost more per kilogram than gold in 1856. Within a few years the first commercial plant for the production of mauveine was in operation. 

This serendipitous discovery marked the beginning of the synthetic dyestuffs industry, based on coal tar as its main raw material, which is, incidentally, a waste product from another industry, steel manufacture. The development of mauveine was followed by efficient syntheses of natural dyes such as alizarin in 1869 (Graebe and Liebermann, 1869), and indigo in 1878 (Bayer, 1878 Heumann, 1890). The synthetic production of these dyes marked the demise of the agricultural production of these materials and the advent of a science-based, predominantly German chemical industry. The present-day fine chemicals and specialties, e.g. pharmaceuticals, industries developed largely as spin-offs of this coal tar-based dyestuffs industry. 

Fillers e.g. calcium carbonate, kaolin, titanium dioxide Sizing agents, starches Natural dyes, brighteners Retention aids... 

Indigo (57), the parent system of this group of colorants, is one of the oldest known natural dyes (see Chapter 1). The naturally occurring... 

Even elder buds have been used as a natural dye. They give a yellow color. 

William Henry Perkin, an 18-year-old working in the back room and outdoor shed of his London home, had discovered in black coal tar a beautiful purple dye that would change the world. For the first time in history, color could be democratized. William Henry Perkin and his purple, later known as mauve, rescued the poor and middle classes from their age-old austerity of hues. Natural dyes were expensive and, before Perkin s synthetic mauve, millions of poor people lived their lives in untreated drab and dingy fibers. Even for the middle class, pieces of brilliantly dyed cloth were treasures to be reused from garment to garment and from year to year. It was the schoolboy William Henry Perkin and his successors who would give the world the ample abundance of tints that only the rich had previously enjoyed. 

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