What is the dye? Describe different types of dyes with environmental impact.

What is Dye?

Dyes are mainly colored compounds that have two parts, one is chromophore and the other part is auxochrome. The dye is a natural or synthetic substance used to add color or to change the color of something. In other words, a dye is a colored compound that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments that do not chemically bond to the material they color. It is generally applied in an aqueous solution and may require a mordant to improve the fastness of the dye on the fiber. Pigments and pigments are both colored because they only absorb visible light of certain wavelengths. Pigments are usually soluble in water but pigments are soluble. Some colored lakes can be inviolable with the addition of salt to create pigment.

Sources of dyes

Historically, the primary source of dyes has been nature, with the dyes being extracted from animals or plants. Since the mid-19th century, however, humans have produced synthetic dyes to achieve a broader range of colors and to render the dyes more stable to washing and widespread use. Different kinds of dyes are used for different types of fiber and at different stages of the textile production process, from unfastened fibers through yarn and cloth to finish garments.

History of dyes

In history, people have dyed their textiles using common locally available materials. Scarce dyestuffs are produced brilliant and permanent colors such as the natural invertebrate dyes. Tyrian purple and red works were extremely valuable luxury items in the ancient and medieval world. Plant-based dyes such as wind, blue, saffron, and madder were important trade products in the economies of Asia and Europe. Throughout Asia and Africa, patterned fabrics were created using writing techniques to control the color absorption of the dyed fabric. The characters of the New World, such as Cochineal and Logwood, were brought to Europe by the Spanish treasure fleet, and the dyestuffs of Europe were taken to America by colonial colonists. Archaeological evidence suggests that, especially in India and Phoenicia, pigmentation has been widespread for more than 5,000 years. Early dyes were obtained from animal, vegetable, or mineral sources, without very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves, and wood, only a few of which are used on a commercial scale. The discovery of mauveine started a surge in synthetic dyes and inorganic chemistry in general. Other aniline dyes followed, like fuchsine, safranine, and induline. Since then many thousands of synthetic dyes have been prepared.

Properties of dyes

Dyes have many special properties, such as below-

a.    Dyes are colored compounds.

b.    These have ionic nature.

c.    These are soluble in water or can be made soluble in water.

d.    It possesses an affinity for fiber to be dyed.

e.    Penetration of dye in the fiber cross-section under dyeing conditions.

f.    Interact with fiber with suitable dye-fiber interactive forces depending on the nature of fiber and the nature of the dye.

g. The nature of dye-fiber interaction determines the fastness property of dye to external agencies.  

Types of dyes

There are many types of dyes we found. According to solubility and chemical properties as below-

1.    Acid dyes

These are water-soluble anionic dyes that are applied to fibers together with silk, wool, nylon, and modified acrylic fibers using neutral to acid dye baths. Attachment to the fiber is attributed, at the least partly, to salt formation between anionic groups within the dyes and cationic agencies inside the fiber. Acid dyes are not substantive to cellulosic fibers. Most artificial food colorings fall in this category. Examples of acid dye are Alizarine Pure Blue B, Acid purple 88, etc.

2.    Basic dyes

These are water-soluble cationic dyes that are particularly applied to acrylic fibers, however, they discover some use for wool and silk. Usually, acetic acid is brought to the dye bathtub to assist the uptake of the dye onto the fiber. Basic dyes are also used in paper dyeing. Examples of basic dye are Brilliant cresyl blue, Janus Green B, Chrysoidine R, etc.

3.    Direct dyes

The direct dye is generally completed in a neutral or slightly alkaline dyebath, at or near boiling point, with the addition of both sodium chloride (NaCl) or sodium sulfate (Na2SO4) or sodium carbonate (Na2CO3). Direct dyes are used in cotton, paper, leather, wool, silk, and nylon dyeing. They are also used as pH signs and as organic stains. Examples of direct dyes are Congo red, Titan yellow, etc.

4.    Mordant Dyes

It requires a mordant which improves the fastness of the dye against water, light, and perspiration. The preference of mordant is very crucial as specific mordant can trade the very last color significantly. Most natural dyes are mordant dyes and there's, therefore, a massive literature base describing dyeing techniques. The most crucial mordant dyes are the artificial mordant dyes, or chrome dyes, used for wool; these incorporate a few 30% of dyes used for wool and are especially useful for black and navy shades. The mordant potassium dichromates are used as an after-treatment chemical. It is essential to note that many mordant, especially those in the heavy metal category, maybe risky to health, and extreme care ought to be taken in the use of them. Examples of mordant dyes are Alizarin Red S, Alizarin yellow GG, Alizarine Yellow R, etc.

5.    Vat dyes

It is basically insoluble in water and incapable of dyeing fibers directly. However, a reduction in alkaline liquor produces the water-soluble alkali steel salt of the dye. This form is often colorless, in which case it is referred to as a Leuco dye, and has an affinity for the fabric fiber. Subsequent oxidation reforms the authentic insoluble dye. The color of denim is because of indigo, the original vat dye.

6.    Reactive dyes

These dyes make use of a chromophore attached to a substituent this is able to without delay reacting with the fiber substrate. The covalent bonds that connect the reactive dye to natural fibers make them amongst the maximum permanent of dyes. "Cold" reactive dyes, inclusive of Procion MX, Cibacron F, and Drimarene K, are very smooth to use due to the fact the dye can be implemented at room temperature. Reactive dyes are by far the best choice for dyeing cotton and other cellulose fibers at domestic or within the artwork studio.

7.    Disperse dyes

Disperse dye has low solubility in water, typically less than 1 mg/L. It became originally developed for the dyeing of cellulose acetate and is water-insoluble. The dyes are finely ground inside the presence of a dispersing agent and bought as a paste, or spray-dried and sold as a powder. Their main use for dyeing polyester, but they can also be used to dye nylon, cellulose triacetate, and acrylic fibers. In a few cases, a dyeing temperature of 130 °C (266 °F) is required, and a pressurized dyebath is used. The very fine particle size gives a large surface place that aids dissolution to allow uptake by using the fiber. The dyeing rate may be appreciably influenced by way of the selection of dispersing agent used for the duration of the grinding. Examples of reactive dyes are dispersed red 11, disperse yellow 42, disperse orange 1, etc.

8.    Azoic dyes

Azoic dyes are sometimes called magic dye or naphthol dye. It is a method wherein an insoluble Azo dye is produced directly onto or within the fiber. This is performed by way of treating a fiber with each di-azoic and coupling additives. With appropriate adjustment of dyebath conditions, the two additives react to produce the required insoluble azo dye. This method of dyeing is unique, in that the final color is controlled via the selection of the di-azoic and coupling components. This technique of dyeing cotton is declining in importance due to the poisonous nature of the chemical substances used.

9.    Sulfur dyes

These are inexpensive dyes that are used to dye cotton with dark colors. Dyeing is affected through heating the fabric in a solution of an organic compound, typically a nitrophenol derivative, and sulfide or polysulfide. The organic compound reacts with the sulfide source to shape dark colorings that adhere to the fabric. Sulfur Black 1, the largest selling dye by means of volume, does no longer has a well-defined chemical structure.

10.  Solvent dyes

The solvent dye is a dye, soluble in organic solvents. It is commonly used as a solution in a natural/organic solvent. It is used to color natural/organic solvents, hydrocarbon fuels, waxes, lubricants, plastics, and other hydrocarbon-based totally nonpolar materials. Fuel dyes are one use of solvent dyes. Their molecules are normally nonpolar or little polar, and they do not go through ionization. They are insoluble in water. They have poor to good lightfastness. Solvent dyes are used for gold imitation of metalized polyester films. Also utilized in marking inks, inkjet inks, glass coloration, and so on. Red and yellow solvent dyes are regularly azo dyes, inexperienced and blue ones have a tendency to be anthraquinone dyes. The names of solvent dyes are Solvent Red 24, Solvent Red 26, Solvent Red 164, Solvent Yellow 124, Solvent Blue 35, etc.

Environmental Impacts of dyes

Today’s fashion depends on the color. For coloring fiber, yarn, fabric or garment need water. After coloring or dyeing wastewater is drained out to the river, canal, or others with a treat or without a treat. All colors contain different chemicals. So river or canal water is polluted by this wastewater, which causes aquatic environment damage. The main pollutants are recalcitrant organic, toxicant, surfactant, colored, and chlorinated compounds and salts in the textile run-offs. Drinking water, irrigation, and recreation water are limited for use because of the oxygen deficiency from highly toxic and mutagenic dyes that causes light penetration and photosynthesis to decrease. Our DNA could also get damaged when a so-called N-hydroxylamines are formed. Dyes are created to keep their color and not degrade so they stay in our environment for a very long time. An example is, at pH 7 and 25°C, it is about 46 years for the half-life of a hydrolyzed dye Reactive Blue 19. It is confirmed by mutagenic activity that our river and drinking water contain C.I- Disperse Violet 93 (DV93), C.I- Disperse Orange 37 (DO37) and C.I- Disperse Blue 373 which means that flotation, coagulation, flocculation, and pre-chlorination (effluent treatment) do not work as much as everyone would want to remove the dyes from water.

Conclusion

Looking at our surroundings, there are colors everywhere. Everything that exists has color and we will manage the colors to our liking. We can see specific colorations because each conjunction can soak up a specific amount of radiation, they have distinctive lengths, and feature a one-of-a-kind quantity of chromophore and auxochrome. The chromophore is the most responsible for the given color paint or ink has. These coloration giving chemical substances doesn’t only give coloration in our lives but in addition, they cause harm to fitness and homes. They create harmful chemical substances that contaminate the water bodies that we use for everyday cleaning or drinking. We can now understand how colors are implemented in dyes, how they're created, and what the cons of the usage of them are?