How do dyes work chemically

Both are used on lower-cost fabrics. Disperse dyes were first developed to dye acetate fibers. Hydrophobic fibers have little affinity for water-soluble dyes. A method to dye hydrophobic fibers by dispersing colored organic substances in water with a surfactant was developed. The finely colored particles are applied in aqueous dispersion and the color dissolves in the hydrophobic fiber. Disperse dyes are the best method for dyeing acetate and polyester. Acrylic, aramid, modacrylic, nylon, olefin, and polyester are dyed by dispersed dyes; colorfastness is good to excellent.

Pigment dyes are not dyes but insoluble coloring particles. Pigments are added to the spinning solution the liquid fiber before extrusion of synthetic fibers and become an integral part of the fiber. Colorfastness is excellent. Pigments are also printed on fabric using resin binders. The adhesive attaches the color to the fabric. Colorfastness is dependent on the binder or adhesive used rather than the pigment. Pigment printing is an economical and simple means of adding color to fabrics.

Reactive fiber-reactive dyes combine with fiber molecules either by addition or substitution. The color cannot be removed if properly applied.

Colors are bright with very good colorfastness but are susceptible to damage by chlorine bleaches. Reactive dyes color cellulosics cotton, flax, and viscose rayon , silk, wool, and nylon.

Reactive dyes are used in conjunction with disperse dyes to dye polyester and cellulosic fiber blends. They were introduced to the industry in Sulfur dyes are insoluble but become soluble in sodium polysulphide. They have excellent colorfastness to water. Another advantage is their low cost and ease of application.

Dark shades-black, brown, navy blue-are typical of sulfur dyes. Newer sulfur dyes are available in brighter colors. They perform well if correctly applied. They are susceptible to damage by chlorine bleaches. Sulfur dyes color primarily cellulosics, such as heavyweight cotton and viscose rayon. Vat dyes are insoluble in water but become soluble when reduced in the presence of an alkali.

Oxidizing the dyed fabric produces a water insoluble dye. The term vat dyes is derived from the large vessels used to apply the dye. The first synthetic indigo dye, introduced to the industry in , belongs to this class. Vat dyes have an incomplete color range but good to excellent colorfastness. They are primarily used to dye cotton work clothes, sportswear, prints, drapery fabrics, and cotton polyester blends.

See also Dyeing ; Natural Dyes. Aspland, J. Textile Dyeing and Coloration. Digital textile printing: Directly printing colors and patterns onto fabric using design software, large-format printers, and specialty inks made with pigments or dyes.

Digital printing is an alternative to standard screen printing, which uses a constrained color palette and requires separate stencils and production steps for each color. Dye: Soluble chemicals that contain chromophores, or color-containing compounds. Dyes are mixed with other additives in a color solution. They can be derived from natural sources, such as plants, but are more commonly human made.

Different classes of dyes are used for different fibers and stages of the textile production process. Direct dye: A class of dye that can be applied directly to cotton or other cellulosic fabrics such as rayon, silk, and wool.

Direct dyes are applied in a neutral or alkaline bath of hot water. They do not require mordant or fixatives for fastness; instead, they attach with hydrogen bonds and van der Waals forces.

Direct dyes are soluble salts of complex sulfonic acids, including diazo or polyazo chemicals. Disperse dye: A category of nonionic dyes used to color synthetic yarns and fabrics such as polyester. These organic chemicals, mostly monoazo dyes, are nonsoluble and rely on dispersing agents to spread the color molecules in water. Reactive dye: A class of colored synthetic organic chemicals that attach to textile fibers via a chemical reaction that forms a covalent bond.

Reactive dyes are the most permanent of all dye types and are the most common type of dye used on cotton and other cellulose fibers. They are categorized by their functional group, such as dichlorotriazine or vinyl sulfone. Dye exhaustion or dye fixation: The mass of dye taken up by the yarn or fabric divided by the total initial mass of dye in the water bath. Once the dyeing process reaches equilibrium, a portion of the dye remains in the dye bath and becomes part of the dye process wastewater.

The exhaustion ratio depends on the quality of the dye and the characteristics of the fiber. Leveling agent: Used in disperse dyeing to regulate or slow the uptake of dye onto synthetic fibers to ensure that the color level is uniform.

Leveling agents are often nonionic surfactants that increase the solubility of the dye and slow adsorption. Mordant: Also called a dye fixative, a substance used to chemically bond a dye to natural fibers to ensure fastness. Mordant chemicals include alum, caustic soda, and metal salts. The mordant forms a coordination complex with the dye, increasing its molecular weight and making it insoluble. Pigment: Insoluble materials, usually in powder form, that add color to inks, paints, plastics, cosmetics, and foods.

When used on textiles, they require binders or other additives to attach to the fibers. Pigments can be derived from minerals but can also be made synthetically. Because they are not soluble in water, they can last longer than dyes. To reduce this burden, Huntsman has developed a line of dyes for cotton called Avitera that bonds to the fiber more readily.

According to the company, the colors require one-quarter to one-third less water and one-third less energy. Thanks to these extra reactive groups, the dye step lasts about four hours, compared with seven hours for conventional dyes. Still, it takes a lot of legwork to sell customers on a new suite of dyes. Different regions and countries have different cost structures, he says. Another way to improve the bond between dyes and cotton fibers is a process called cationization.

In North Carolina, textile industry veteran Tony Leonard is taking that approach. Leonard is the inventor and technical director behind ColorZen, a start-up that has developed a cotton pretreatment step.

ColorZen treats raw cotton fiber right from the field after the seeds are removed. After treatment, cotton is spun into yarn at customer facilities. It also cuts out almost half the dye compared with processes that call for salts in the dye bath. The company has a partnership with the manufacturing technology firm Jabil to help it scale up its plant in Mebane, N. It is also in a program run by the apparel start-up incubator Fashion for Good. Hohenstein developed Oeko-Tex, a series of standards and tools for certifying nontoxic textiles.

The first version of the standard was called Oeko-Tex for the number of chemicals it tracked. Oeko-Tex certification is now up to more than chemicals. Synthetic indigo, used to make blue jeans blue, is an example of a dye that can release unreacted chemicals downstream of manufacturing. Indigo is unlike most dyes in that in its unreduced form it is not soluble.

So companies like Archroma upgrade it into easier-to-use, prereduced solutions that are more water soluble. The company became concerned after seeing published reports that about metric tons of aniline per year escapes the dyeing process from 70, metric tons of indigo. Archroma developed a technology for prereducing indigo to prevent aniline from carrying through as a contaminant. Finished textiles colored with the dye contain a nondetectable amount of aniline, whereas competitor dyes can contain up to 2, ppm of the chemical, according to Archroma.

Carnahan acknowledges differing views about how big a problem aniline is in the textile industry. It has a better reputation than the category 1 carcinogenic amines that cleave off of azo dyes and were an early target for elimination by clothing brands.

Of course, in the beginning, indigo came from a plant, not a factory. The very first pair of modern-style blue jeans, made by Levi Strauss, debuted in That was about 25 years before chemists developed the synthetic route to indigo dye—with its unappetizing starting materials of aniline, formaldehyde, and hydrogen cyanide.

The ambition at Stony Creek Colors is to return to those early days. Founder Sarah Bellos says a complete life-cycle review of the production and use of synthetic indigo provides plenty of reasons to look again at indigo from plants.

Dyeing : Warm temperature, long process time, requires addition of large amounts of salt and alkali fixatives. Washing : Long, energy- and water-intensive process using multiple baths, with at least one at boiling temperature.

Washing : Shorter process requiring less energy, water, and chemicals than cotton. Uses alkali and chemical reducing agent. Washing : Similar to cotton but shorter process, possibly due to less unfixed dye to be removed. Stony Creek is developing varieties of leguminous indigo plants that can provide a high-yield, high-profit crop for Tennessee farmers looking for an alternative to tobacco.

The company is selling all the dye it can make; its goal is to expand U. These Cs are carbon atoms, like you see in charcoal. The Os are oxygen, like in the air you breathe, and these Cls are chlorine, like in bleach.

This model shows you what the blue molecules in this bottle are shaped like. All other atoms are spelled out with their own one- or two-letter abbreviation, Cl for Chlorine, O for Oxygen, etc. Some dyes, such as the kind you can buy in the grocery store here in the US, really just stain clothes, so the dye washes out a little every time you wash it.

A really good dye actually chemically attaches to the molecules of the fabric and can never be washed out. Here is a model of another dye molecule. Each different shape of dye molecule absorbs light differently. That's what makes the different colors! The fabric your clothing is made out of is also made of molecules.

Cotton, which grows on a cotton plant, is made of long strands of cellulose molecules, all twisted together. Cellulose is the same thing that wood is made of. Here is a model of a cellulose molecule : [model showing rope with -OH groups sticking out] If you put these two molecules, the dye and the cotton, together, nothing will happen, unless you can get some of the atoms on the surfaces to come unstuck.