The Guide To Cotton Dye: The Best Dye And Practices

Abstract

As the most common fabric, cotton can be made from light and transparent voile to thick canvas and thick velveteen, and is suitable for making all kinds of clothes, furniture fabrics and industrial fabrics.

Different dyes are selected when dyeing different fabrics. Due to its characteristics, cotton can be dyed with reactive, direct, and sulfur dyes. After the dyeing process of distribution, washing, bleaching, dyeing and post-treatment, colorful fabrics are finally produced.

Common Dyes for Cotton

Cotton is a highly absorbent natural fiber that is easily dyed and is currently a very popular fabric. Its commonly used dyes include direct dyes, reactive dyes, and sulfur dyes.r

Direct dyes are dyes that can be heated and boiled in neutral and weakly alkaline media without the help of mordants. Direct dyes are formed by hydrogen bonds and van der Waals forces between direct dyes and cotton fibers. According to their application classification, they mainly include ordinary direct dyes, direct lightfast dyes and direct azo dyes.

Reactive dyes, also known as reaction dyes, are new water-soluble dyes. The dye molecules contain reactive groups that can react with hydroxyl groups in cellulose and amino groups in protein fibers. During dyeing, covalent bonds are formed with fibers to form "dye-fiber" compounds. Reactive dyes have the characteristics of bright colors, good dyeing properties, simple dyeing methods, high dye fastness, complete chromatography and low cost.

Sulfur dyes are dyes dissolved in sulfide alkali and are mainly used for dyeing cotton fibers. The cost is low, and the dyes are generally washable and light-resistant.

Conventional Dyeing Process

1 Distribution

original fabric inspection, turning (batching, cartoning, printing) and seaming. The purpose is to check the quality of gray cloth.

2 Singeing

The fabric is quickly passed through a high-temperature flame or rubbed against a red-hot metal surface. At this time, the fluff on the cloth surface heats up quickly and burns, while the cloth body is relatively tight and heats up slowly. When it reaches the ignition point, it has left the flame or red-hot metal surface, thereby achieving the purpose of burning off the fluff without operating the fabric. The purpose is to burn off the fluff on the cloth surface to make the cloth surface smooth and beautiful, and to prevent uneven dyeing and printing defects caused by the presence of fluff during dyeing and printing.

3 Desizing

Textile mills will size warp yarns to improve strength and wear resistance. The slurry on the gray fabric will affect the water absorption performance of the fabric and increase the consumption of dyeing chemicals. The slurry should be removed before scouring. The sizing on cotton fabrics can be removed from the fabric using methods such as alkali desizing, enzyme desizing, acid desizing and oxidant desizing.

4 Scouring

When cotton fiber grows, there are natural impurities accompanying it. After desizing, a small amount of sizing and natural impurities still remain on the fabric. Scouring is the use of caustic soda and other scouring aids to react chemically with natural impurities, and then remove the impurities from the fabric after washing.

5 Bleaching

After scouring cotton fabrics, due to the presence of natural pigments on the fibers, their appearance is not white enough. When used for dyeing or printing, the brightness of the color will be affected. The purpose of bleaching is to remove pigments and give the fabric the necessary and stable whiteness without causing significant damage to the fiber itself. Commonly used bleaching methods for cotton fabrics include sodium nitrite, hydrogen peroxide and sodium chlorite.

6 Dyeing

A process in which dyes are physically or chemically combined with fibers, or chemical methods are used to generate pigments on fibers, so that the entire textile has a certain color. Dyeing is carried out under certain conditions such as temperature, time, pH value and required dyeing auxiliaries.

7 Mercerization

A process in which cotton fabrics are treated with concentrated caustic soda solution at room temperature or low temperature, under tension in both the warp and weft directions, to improve the performance of the fabric. After mercerization, the alkali must be fully removed by flushing and absorbing, steaming, or flat washing until the fabric becomes neutral.

7 Finishing

A textile technology project that gives clothing fabrics wearability and beauty.

Dye Types for Different Fabrics

Different fabrics use different dyes. What dyes are used in other common fabrics are listed below.

Acid dyes refer to dye molecules containing acidic groups, also known as anionic dyes. They are mainly used for dyeing wool, silk and nylon.

Disperse dyes are a type of dye with relatively small molecules and no water-soluble groups in their structure. They are mainly used to dye polyester fiber (polyester), acetate fiber (diacetate, triacetate) and polyamide fiber (polyamide fiber) in chemical fibers. Nylon) is dyed, and polyacrylonitrile (acrylic fiber) is also used in a small amount.

Direct dyes are used in natural fibers such as cotton, linen, and cellulose.

Cationic dyes are in a cationic state, soluble in water, and ionize in aqueous solution to generate dyes with positively charged colored ions. Special dyes for dyeing acrylic fibers have the advantages of high strength, bright color, and good light fastness.

Conclusion

When dyeing fabrics, you need to choose appropriate dyes according to different fabric types. Cotton fabrics have more dye options than other fabrics due to their characteristics. Pay attention to process specifications during the dyeing process.

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