Chemical And Synthetic Dyes On Fabric

by Ozza Konveksi Business Owner

Synthetic dyes are made from organic molecules. Before synthetic dyes were discovered in 1856, dyes were made from natural products such as flowers, roots, vegetables, insects, minerals, wood, and mollusks. Natural dyes have the disadvantage of never being the same in hue and intensity, whereas synthetic dyes can be produced consistently.

This is because computer use and computer color matching produce identical colors from one group to another.

Accidental Discovery

William Henry Perkin, an 18-year-old British chemist, was looking for a cure for malaria and stumbled across the first synthetic dye. He found that the oxidation of aniline could dye silk.

From a coal tar derivative he made a reddish purple dye. The brilliant purple color is called light purple. The dye is unstable to sunlight or water and fades easily into what is now called light lilac, a pale lilac.

This discovery resulted in additional research with coal tar derivatives and other organic compounds and a new synthetic dye industry was born.

In the twenty-first century, synthetic dyes were cheaper, had better color resistance, and completely dominated the industry compared to natural dyes. Thousands of very different synthetic dyes are produced in the world.

Classification

Dyes are classified according to their chemical composition, type of usable fiber, color, or method of application. The dye molecules can stick to the surface of the fiber, be absorbed by the fiber, or interact with fiber molecules. Each fiber reacts differently to dyes. Fiber modifications will also react differently to the same dye. In the classification of dyes, different hues will have different color resistance.

The Society of Dyers and Colourists (SDC) and the American Association of Textile Chemists and Colorists (AATCC) classify dyes based on their chemical composition. In the publication, The Color Index International, dyes are listed according to their generic name, which indicates the class of application, and by a Color Index constitution number (CI number) indicating their chemical structure.

Acid Dyes

Acidic (anionic) dyes are water-soluble dyes applied to wool, silk, nylon, modified rayon, certain modified acrylics, and polyester fibers. Fibers that will be damaged by acids, such as cellulose, cannot be colored with this dye family.

Dyes in this class vary in their chemical composition but all use an acid bath. These dyes produce bright colors and have a complete color range but varying color resistance.

Basic Dyes

Cationic dyes are very bright but have poor color resistance. These dyes have limited use in cellulose fibers and proteins. Wool and silk can be dyed with a basic dye in an acidic dye bath. Cotton fibers can be colored with basic dyes but only in the presence of mordants, generally metal salts.

The colored part of the dye molecule carries a positive charge. Base dyes are relatively resistant to the color of acrylic fibers. Nylon and polyester fibers that have been modified to accept basic dyes will exhibit excellent color resistance. The first synthetic dye, mauveine, belongs to this class.

Direct Dyes

Direct (substantive) dyes are soluble and have an affinity for cellulose fibers. Electrolytes, salts, are added to the dye bath to control the absorption rate of the dye by the fibers. The dye is absorbed by the fiber; fastness to light is good, but fastness to washing is not. Direct dyes are best used when wet cleaning is limited.

Direct dyes developed are dyes that are developed on the fabric after dyeing. This type of dye produces insoluble dyes that form chemical bonds with fiber molecules. The developed direct dyes have better washing resistance but poorer light fastness compared to the direct dyes. Both are used in low-cost fabrics.

Dispersion Dyes

Dispersion dyes were first developed to dye acetate fibers. Hydrophobic fibers have little affinity for water-soluble dyes. A method for dyeing hydrophobic fibers by dispersing colored organic substances in water with surfactants was developed. The fine colored particles are applied in water dispersion and the color dissolves in hydrophobic fibers.

Dispersion dyes are the best method for dyeing acetates and polyesters. Acrylic, aramid, modacrylic, nylon, olefin, and polyester are colored with dispersed dyes; color absorption is pretty good.

Pigment Dyes

Pigment dyes are not dyes but insoluble dye particles. Pigments are added to the spinning solution (liquid fiber before extrusion) of synthetic fibers and become an integral part of the fibers. Very good absorption.

Pigments are also printed on the fabric using a resin binder. The glue attaches the color to the fabric. Color resistance depends on the binder or adhesive used, not the pigment. Pigment printing is an economical and simple way to add color to fabrics.

Reactive Dyes

Reactive (fiber-reactive) dyes combine with fiber molecules either by addition or substitution. Color cannot be removed if applied properly. Bright color with excellent color resistance but susceptible to damage by chlorine bleach.

Color cellulose reactive dyes (cotton, hemp, and viscose rayon), silk, wool, and nylon. Reactive dyes are used together with dispersion dyes for polyester dyes and cellulose fiber blends. They were introduced to the industry in 1956.

Sulfur Dyes (Sulfur)

Sulfur dye does not dissolve but becomes soluble in sodium polysulfide. Sulfur has excellent color resistance to water. Other advantages are low cost and ease of application. Dark shades-black, brown, dark blue are characteristic features of sulfur dyes.

The newer sulfur dyes are available in lighter colors. Can work well if applied properly. However, this dye is very susceptible to damage due to chlorine bleach. Sulfur dyes mainly color cellulose, such as heavyweight cotton and viscose rayon.

Coloring Tank

Vat dyes are insoluble in water but become soluble when reduced in the presence of alkalis. The term vat dye comes from the large vessel used to apply dye. The first synthetic indigo dyes, introduced to the industry in 1896, belong to this class.

Vat dyes have an incomplete color range, but have excellent color resistance. This type of dye is used primarily for dyeing work clothes, sportswear, screen printing shirts, curtain fabrics, and cotton polyester blends.

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