Cotton naturally colored

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. 

Berries and leaves of certain plants have been used for centuries to provide the colors necessary to make wool, cotton, flax, silk, and other fabric fibers with an attractive shade differing from the natural colors of the materials. These colors were usually boiled with the formed fabric or yarn to impart color. Additional processes such as cooling the solution and/or the addition of lime, carbonate (chalk), or vinegar was found useful to set the color onto the fabric and impart some degree of fastness. 

Vreeland, J.M., Jr., Naturally colored and organically grown cottons anthropological and historical perspectives. Proceedings of the Beltwide Cotton Conferences, National Cotton Council, Memphis, TN, 1993, pp. 1533-1536. 

The waxes are important in the spinning process but a hindrance to the dyeing operation. Owing to their water-repellent natuie, waxes prevent the proper absorption of the dyestuff. The natural color of cotton and the other impurities also interfere, but to a lesser degree, with the ordinary processes of dyeing, printing and finishing. ... 

Textiles may be colored with natural colorants such as saffron or curcumin. Saffron pigments can be extracted from cotton and wool fibers using a pyridine-water mixture (25/75 v v). This method is, however, not able to extract curcumin from the same fibers (Tsatsaroni et al, 1998). 

Wang B, Sain M (2007) Isolation of nanofibres from soybean source and their reinforcing capability on synthetic polymers. Compos Sci Technol 67 2521-2527 Teixeira EM, Correa AC, Manzoli A, Leite FL, Oliveira CR, Mafioso LHC et al (2010) Cellulose nanofibres from white and naturally colored cotton fibres. Cellulose. doi 10.1007/ si 0570-010-9403-0... 

Fig. 21.12 Suspensions of cellulose nanofibers (on the left) and (a) scanning transmission electron micrographs of nanofibers (at two magnifications), (b) atomic force micrographs of cellulose nanofibers extracted from white and naturally colored cotton fibers by sulfuric acid treatment. Reproduced with permission from Teixeira et al. (2010). Copyright 2010 Springer Science + Business Media B.V.

Teixeira EM, Correa AC, Manzoli A et al (2010) Cellulose nanofibres from white and naturally colored cotton fibres. Cellulose 17 595-606... 

Valcarcel and co-workers proposed in 2003 an automatic system for the determination of riboflavin in lyophilized food products using a solid-phase extraction process that included columns filled with cotton or silica C18 for the sequential retention of synthetic colorants and natural colorants, respectively (Gonzalez et al. 2003). In this case riboflavin was assessed as an authorized natural colorant for total estimation of this class of compounds. The analytical characteristics of this methodology are summarized in Table 18.3. 

C5 ras VP, Manfredi LB, Ton-That M-T, Vazquez A (2008) Physical and mechanical properties of thermoplastic starch/montmorillonite nanocomposite films. Carbohydr Polym 73 55-63 de Morals Teixeira E, Correa A, Manzoli A, de Lima Leite F, de Oliveira C, Mattoso L (2010) Cellulose nanofibers from white and naturally colored cotton fibers. Cellulose 17 595-606 de Moura MR, Aouada FA, Avena-Bustillos RJ, McHugh TH, Krochta JM, Mattoso LHC (2009) Improved barrier and mechanical properties of novel hydrox5q)ropyl methylcellulose edible films with chitosan/tripolyphosphate nanoparticles. J Food Eng 92 448—453 Dean K, Yu L, Wu DY (2007) Preparation and characterization of melt-extruded thermoplastic starch/clay nanocomposites. Compos Sci Technol 67 413 21 Duanmu J, Gamstedt EK, Rosling A (2007) Hygromechanical properties of composites of crosslinked allylglycidyl-ether modified starch reinforced by wood fibres. Compos Sci Technol 67 3090-3097... 

Peracetic acid (Steiner N, 1995, Evaluation of peracetic acid as an environmentally friendly alternative for hypochorite . Textile Chemist Colorist 27 (8), pp. 29-32) as well as a waterless bleaching system that uses oxygen gas (Mowbray J 2008, Light fantastic , Ecotextile News No. 17 Aug/ Sep, pp. 22-24) have been reported as alternate and enviromnent-friendly methods for bleaching cotton. Ozone also can be used as another waterless process to bleach cotton. Bleaching removes residual impiuities and changes the natural color of cotton fabric to clear white rather than the off-white (i.e. various shades of yellow). 

Cellulose nanowhiskers (CNWs) have been obtained from a variety of matrices such as cotton [63], sisal [64], and coconut husk fibers [65]. Other alternative sources of cellulose nanofibrils includes naturally colored cotton, curaua (Ananas erecti-Jblius), and sugarcane bagasse have been successfully used to prepare nanowhiskers [66-69]. 

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). 

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. 

Also, the cost of dyeing cotton with natural vegetable dyes is 31—77/kg compared to a synthetic approach costing 35 cents /kg. In short, the use of natural vegetable dyes to color the world s textiles is both environmentally and logisticaHy impossible (4). 

The yellow dye curcumin, [458-37-7] (Cl Natural Ye//oii> 3 Cl 75300) (41), also known as tumeric, occurs in the roots of the plant Curcuma tinctoria found growing wild in Asia. The dye was well known to the ancient Romans and Greeks who used it to dye wool, cotton, and silk. The dye is an oil-soluble bright yellow material, and is the only natural yellow dye that requires no mordant. It finds use as a colorant for baked goods such as cakes. 

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