Dyeing and printing textiles can have a significant impact on the environment from discharge of dyes, pigments, and other chemicals into water systems. Components that contribute to problems include color, salt, acids, and heavy metals. Some materials create problems because of high biological oxygen demand others have high chemical oxygen demand. High BOD and COD materials create environments that are hostile to aquatic plants and animals and may create problems with future use of the water. Color in water creates problems with photosynthesis of aquatic plant life.
Most textiles are colored in one manner or another because consumers demand color. One option to decrease environmental impact is to use fewer dyed or printed textiles. White textiles create problems with the use and disposal of chemical bleaches. Even though consumers purchase beige and off-white goods, they will probably continue to demand a broader range of colors. Another option is to use color-grown textiles, such as the naturally colored cottons and wools. However, a full color spectrum is not available and these natural colors tend to be low in intensity.
Another alternative is to greatly expand the current use of natural dyes in commercially available fabric and products .In order to compete with synthetic dyes and pigments, natural dyes must be economical, consistent in quality, and available in quantity. Mordants used with natural dyes must be restricted to those that have little, if any, impact on the environment. Examples of commercial natural dyes from Caracol and Allegro Natural Dyes include indigo, madder, cochineal, cutch, and osage. Natural dyes are used on cotton, wool, and silk fabrics for apparel and furnishing uses.
Color in water systems in very dilute concentrations can be detected by the unaided eye. Unfortunately, color is very difficult to remove by traditional waste (sludge) treatment facilities. Alternatives for treating color in water systems include use of hyper filtration, electrochemical methods, ozonation, and chemical coagulation. Reconstitution and reuse of textile dyeing water is another possibility being investigated.
Limiting the use of salt and other chemicals is another option. For example, current reactive dyes use large amounts of salt, but some new reactive dyes use significantly less salt and have higher fixation rates. Lower-sulfide sulfur dyes are replacing higher-sulfide sulfur dyes. Use of heavy metals in dyes, catalysts, or after-treatments is restricted. Dye producers are developing dyes that incorporate iron rather than chromium because iron is more environmentally safe. Dyes and pigments with low environmental impact will continue to be a major thrust in preparing goods with consumer appeal.
Liquid carbon dioxide or supercritical carbon dioxide can be used as the carrier rather than water for dyeing polyester and high-performance, fibers. Liquid carbon dioxide dyeing increases dye-fixation rates, decreases energy use, and decreases treatment of waste. In addition, this process does not require use of salt or other dye-bath chemicals, and drying is not needed. The process is quick and efficient, with good leveling. Carbon dioxide can be recycled and is readily available, nontoxic, and economical.