30/07/2015
Assignment on
“Dyestuff classification and dye selection”
Course title: Wet Processing Technology III
Course code: WPT 401
Submitted to:
Dr. AKM Saiful Islam
Head of the Department
Department of Textile Engineering
City University
Submitted by:
Md. Roman Khandakar
Department of Textile Engineering
ID 121297222
Batch: 2oth
Date of submission: 16/06/2015
Index
Topic Page No
1. Introduction of Dye & Dyes …………………………………………………………………..3
2. Etymology & History of Dyeing ……………………………………………………………….4
3 Dye classification according to origin…….……….…………….………………………… (4-7)
4. Dye classification according to application ……….………………………..…………….. (7-9)
5. Chemical classification of dyes …………………………………….……………….……….10
6. Selection of dyes or dyestuff…………………………………………………………… (10-11)
7. Factors to be considered for selecting dyestuff…………………………………………… (12)
8. Application of dyes……………………………………………………………………..… (12)
9 Conclusion ………………………………………………………………………..….…… (12)
Dye:
Dyeing is the process of adding color to textile products like fibers, yarns, and fabrics. Dyeing is normally done in a special solution containing dyes and particular chemical material. After dyeing, dye molecules have uncut chemical bond with fiber molecules. The temperature and time controlling are two key factors in dyeing. There are mainly two classes of dye, natural and manmade.
The primary source of dye, historically, has generally been nature, with the dyes being extracted from animals or plants. Since the mid-18th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to resist washing and general use. Different classes of dyes are used for different types of fiber and at different stages of the textile production process, from loose fibers through yarn and cloth to completed garments.
Acrylic fibers are dyed with basic dyes, while nylon and protein fibers such as wool and silk are dyed with acid dyes, and polyester yarn is dyed with disperse dyes. Cotton is dyed with a range of dye types, including vat dyes, and modern synthetic reactive and direct dyes.
Dyes: Dyes are used for coloring the fabrics. Dyes are molecules which absorb and reflect light at specific wavelengths to give human eyes the sense of color. There are two major types of dyes - natural and synthetic dyes. The natural dyes are extracted from natural substances such as plants, animals, or minerals. Synthetic dyes are made in a laboratory.
Etymology:
The word dye is from Middle English deie and from Old English dag and dah. The first known use of the word dye was before the 12th century.
History of dyeing:
Archaeologists have found evidence of textile dyeing dating back to the Neolithic period. The earliest surviving evidence of textile dyeing was found at the large Neolithic settlement at Çatalhöyük in southern Anatolia, where traces of red dyes, possibly from ocher, an iron oxide pigment derived from clay), were found. In China, dyeing with plants, barks, and insects has been traced back more than 5,000 years. Early evidence of dyeing comes from Sindh province in Pakistan, where a piece of cotton dyed with a vegetable dye was recovered from the archaeological site at Mohenjo-Daro (3rd millennium BCE). The dye used in this case was madder, which, along with other dyes such as indigo, was introduced to other regions through trade. Natural insect dyes such as Tyrian purple and kermes and plant-based dyes such as wood, indigo and madder were important elements of the economies of Asia and Europe until the discovery of man-made synthetic dyes in the mid-19th century. The first synthetic dye was William Perkin's mauveine in 1856, derived from coal tar. Alizarin, the red dye present in madder, was the first natural pigment to be duplicated synthetically in 1869, a development which led to the collapse of the market for naturally grown madder. The development of new, strongly colored synthetic dyes followed quickly, and by the 1870s commercial dyeing with natural dyestuffs was disappearing.
Classification dyes according to origin:
1. Natural dyes:
The majority of natural dyes are from plant sources – roots, berries, bark, leaves, and wood, fungi, and lichens. Textile dyeing dates back to the Neolithic period. Throughout history, people have dyed their textiles using common, locally available materials. Scarce dyestuffs that produced brilliant and permanent colors such as the natural invertebrate dyes Tyrian purple and crimson kermes were highly prized luxury items in the ancient and medieval world. Plant-based dyes such as woad, indigo, saffron, and madder were raised commercially and were important trade goods in the economies of Asia and Europe. Across Asia and Africa, patterned fabrics were produced using resist dyeing techniques to control the absorption of color in piece-dyed cloth. Dyes from the New World such as cochineal and logwood were brought to Europe by the Spanish treasure fleets, and the dyestuffs of Europe were carried by colonists to America.
Dyed flax fibers have been found in the Republic of Georgia in a prehistoric cave dated to 36,000 BP. Archaeological evidence shows that, particularly in India and Phoenicia, dyeing has been widely carried out for over 5,000 years. The dyes were obtained from animal, vegetable or mineral origin, with none to very little processing. By far the greatest source of dyes has been from the plant kingdom, notably roots, berries, bark, leaves and wood, but only a few have ever been used on a commercial scale.
2. Synthetic dyes:
The first human-made organic aniline dye, mauveine, was discovered serendipitously by William Henry Perkin in 1856, the result of a failed attempt at the total synthesis of quinine. Other aniline dyes followed, such as fuchsine, safranine, and induline. Many thousands of synthetic dyes have since been prepared.
Synthetic dyes quickly replaced the traditional natural dyes. They cost less, they offered a vast range of new colors, and they imparted better properties to the dyed materials. Dyes are now classified according to the process used for their application to the fibers.
Natural dyes have been used since the beginning of organized society, developed so humans could paint their bodies, clothes, houses, weapons and religious icons. The colors were obtained from plants, animals, fruits and earth. In Mexico, they include indigo, cochineal (the bug parasite of the prickly pear cactus paddle), moss, nut shells and leaves, wild flowers, tree bark, and even a sea snail that emits a deep purple ink. Natural dyes are scarce, higher priced, and require a much longer, more complex process to produce.
For example, to make red using cochineal requires one day to grind the grain of the cochineal bug (cultivated on the cactus for three months), one day to prepare the wool, one day to mordant the wool, and one day to dye the wool. This does not factor in the three-to-six months of time required to “grow” the bug on the cactus. To produce a synthetic red dye takes one day. Color variation and intensity is controlled by adding more dye to the solution. It is not the complex chemistry that is involved in the natural dyeing process.
Intensity and Brilliance:
Natural dye color variation and brilliance is achieved by mixing different mordant with one batch of skeins, manipulating the PH of the dye baths, investing hours of time for one color. Colors obtained from natural sources tend to be earthy and subtle. Synthetic dyes often produce garish, stark or muddy colors. Wool rugs prepared with natural dyes are colorfast and will last a lifetime. Colorfastness can be tested by rubbing the surface of the weaving (if the weaver lets you) with a damp cloth. If the dye does not transfer, there is a good chance that the color is permanent.
The Price Difference:
Natural dye materials are scarce and expensive. For example, cochineal is more costly per ounce than gold. Synthetic dyes are readily available at low cost, resulting in a less costly rug to produce. Density of weave also adds to quality and therefore to cost. A low cost rug will likely be woven with synthetic dyes, on brittle; machine spun (not hand-spun) wool, and has a looser weave.
Health and Wellness:
The chemical fumes that are breathed in from the vapors of the dye pot are toxic. Sulfuric acid is potent and can burn the skin. If it splashes into the eye a person can go blind. Because people dye at home and there are not regulations around the use of chemical dyes, most people don’t take necessary precautions to use a face mask. As a result, over time many develop respiratory problems and lung cancer. A movement toward the use of natural dyes is also a good public health step. If you buy a rug dyed with natural materials, even though it may be more expensive, you know you are making a difference for a healthier life.
Natural dyes are far superior to chemical dyes for certain reasons:
- With exposure to light all color fades, but natural dyes fade or mellow leaving lighter tones that are just as beautiful, if not more so, than the original color.
- Natural dyes are more compatible and harmonious with one another. By contrast, chemical colors are easy to use and can produce good results, but have certain drawbacks, in that they can look hard or garish; some fade very quickly, and others fade uneven.
- One of the key reasons why natural colors look better than chemical colors because they are not 'pure' color: a natural red, for example, will include blue and yellow, whereas a chemical red will only contain red pigment. The impurities of natural dyes, which may comprise from five to 25 percent of the dye, consist of other hues that are similar to the main one, and it is these mixtures that make natural dyes so beautiful and create their harmony with neighboring natural colors. Where one person will see some purple in a hank of gray yarn, another may see some blue in it. To be able to see the difference is partly genetic, like the ability to curl one's tongue lengthwise, and partly a matter of experience. On the other hand, evenness of a synthetically dyed carpet is flat and uninteresting. Natural dye, precisely because of its unevenness, makes color vibrate or sparkle. And for some people this "imperfection," a sign of the artist's hand working natural substances from the garden or fields, has spiritual overtones.
- Natural dyes make different shades at the different time of the day. When these natural dyes expose to the light, they leave lighter tones, which makes them to look beautiful in different way than their original colors.
- Natural-dye enthusiasts see "mellow" hues that sparkle and glow which give esthetically comfortable feeling. But to be able to see these features one needs, perhaps, a passion for color.
- Natural dyes are substantially less destructive to the environment than the chemical dyes widely in use. Synthetic dyes used in textile dyeing generally cause environmental pollution and health problems in humans.
- Each plant provides an amazing diversity of shades. From one plant one may obtain between 5-15 varying colors and shades. These colors and shades are subtle and tend to harmonize with one another. The resulting fabrics or fibers are now original pieces - it is extremely difficult for anyone to duplicate exactly (even the dyer).
- Natural color is inherently more muted than chemical color, which looks very stark, and so if chemical colors are used while the desired effect is for the 'natural' look, it will be necessary to mix a variety of colors in imitation of nature.
- Color created from natural elements lasts much longer than chemical dyes.
Classification of dye according to application:
Reactive Dyes
Acid Dyes
Pre-metalized Dyes
Direct Dyes
Azoic Dyes
Disperse Dyes
Vat Dyes
Sulfur Dyes
Basic Dyes
Mordant Dyes
1. Reactive Dyes:Reactive dyes are the most recent of dyes. These are the most popular in the world among fiber and fabric artists, used at first only by surface designers, but recently by weavers as well. There are now reactive dyes for a wide range of fibers, e.g. cotton (PROCION), silk and wool (PROCILAN). The dye actually reacts with the fiber molecules to form color and is, as a result, extremely fast to both light and washing. There are hot and cold water reactive dyes, in fact there is a dye for almost every need. They can be most successfully used for silk painting, with a much better color fastness than the traditional basic dyes, and are already used by batik artists. We can identify a reactive dye by the alkali used to set off the fixation process, which requires time to take place (silk and wool reactive uses acetic acid). Assistants used are salt, soda ash and resist salt, and sometimes bicarbonate of soda and urea. Reactive dyes are equally suited to screen printing polychromatic printing, fabric painting yarn and piece dyeing. 2. Acid Dyes:Acid dyes are water-soluble anionic dyes that are applied to fibers such as silk, wool, nylon and modified acrylic fibers using neutral to acid dye baths. Attachment to the fiber is attributed, at least partly, to salt formation between anionic groups in the dyes and cationic groups in the fiber. Acid dyes are not substantive to cellulosic fibers. Most synthetic food colors fall in this category.
3. Pre-metalized Dyes:These are an acid dyes with the addition of one or two molecules of chromium. The dyes give mutetonings, not unlike those of natural dyes. They are the synthetic dyes mostly used by weavers who dye their own yarns. 4. Direct Dyes: Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dyebath, at or near boiling point, with the addition of either sodium chloride (NaCl) or sodium sulfate (Na2SO4) or sodium carbonate (Na2CO3). Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.
5. Azoic (Napthol) Dyes: These are another sort of direct dye, but ones that are extremely fast to washing, bleach and light. They are intended for cellulose fibers and can be used successfully on protein fibers, although the colors are different. These dyes are widely used all over Asia and Australia for batik and direct application. They can be used to give interesting texture color effects on fabric, thread or paper. Their use for straight silk painting is minimal because of the difficulty in achieving evenness of painted color. Azoic dyeing is a technique in which an insoluble azo dye is produced directly onto or within the fibre. This is achieved by treating a fibre with both diazoic and coupling components. With suitable adjustment of dyebath conditions the two components react to produce the required insoluble azo dye. This technique of dyeing is unique, in that the final color is controlled by the choice of the diazoic and coupling components. This method of dyeing cotton is declining in importance due to the toxic nature of the chemicals used.
6. Disperse Dyes: Disperse dyes were originally developed for the dyeing of cellulose acetate, and are water-insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste, or spray-dried and sold as a powder. Their main use is to dye polyester but they can also be used to dye nylon, cellulose triacetate, and acrylic fibres. In some cases, a dyeing temperature of 130 °C (266 °F) is required, and a pressurised dyebath is used. The very fine particle size gives a large surface area that aids dissolution to allow uptake by the fibre. The dyeing rate can be significantly influenced by the choice of dispersing agent used during the grinding.
7. Vat Dyes: Vat dyes are essentially insoluble in water and incapable of dyeing fibres directly. However, reduction in alkaline liquor produces the water-soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fibre. Subsequent oxidation reforms the original insoluble dye. The color of denim is due to indigo, the original vat dye.
8. Sulfur Dyes:
Sulfur dyes are inexpensive dyes used to dye cotton with dark colors. Dyeing is effected by hearing 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 form dark colors that adhere to the fabric. Sulfur Black 1, the largest selling dye by volume, does not have a well defined chemical structure. They are cheap, generally have good wash-fastness, and are easy to apply. Sulfur dyes are predominantly black, brown, and dark blue. Red sulfur dyes are unknown, although a pink or lighter scarlet color is available.
9. Basic Dyes:
Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibers, but find some use for wool and silk. Usually acetic acid is added to the dyebath to help the uptake of the dye onto the fiber. Basic dyes are also used in the coloration of paper. The colors are very bright, but not very fast to light, washing, perspiration. Fastness is improved if they are given an after-treatment or steaming, e.g. French Silk dyes are basic dyes and should be steamed to fix.
10. Mordant Dyes:
Mordant dyes require a mordant, which improves the fastness of the dye against water, light and perspiration. The choice of mordant is very important as different mordants can change the final color significantly. Most natural dyes are mordant dyes and there is therefore a large literature base describing dyeing techniques. The most important mordant dyes are the synthetic mordant dyes, or chrome dyes, used for wool; these comprise some 30% of dyes used for wool, and are especially useful for black and navy shades. The mordant, potassium dichromate, is applied as an after-treatment. It is important to note that many mordants, particularly those in the heavy metal category, can be hazardous to health and extreme care must be taken in using them.
Food dyes:
One other class that describes the role of dyes, rather than their mode of use, is the food dye. Because food dyes are classed as food additives, they are manufactured to a higher standard than some industrial dyes. Food dyes can be direct, mordant and vat dyes, and their use is strictly controlled by legislation. Many are azo dyes, although anthraquinone and triphenylmethane compounds are used for colors such as green and blue. Some naturally-occurring dyes are also used.
Other important dyes:
A number of other classes have also been established, including:
Oxidation bases, for mainly hair and fur
Laser dyes: see, for example, rhodamine 6G and coumarin dyes.
Leather dyes, for leather
Fluorescent brighteners, for textile fibres and paper
Solvent dyes, for wood staining and producing colored lacquers, solvent inks, coloring oils, waxes.
Contrast dyes, injected for magnetic resonance imaging, are essentially the same as clothing dye except they are coupled to an agent that has strong paramagnetic properties.
Mayhem's dye, used in water cooling for looks, often rebranded RIT dye
Chemical classification:
By the nature of their chromophore, dyes are divided into
Category: Acridine dyes, derivates of acridine
Category: Anthraquinone dyes, derivates of anthraquinone
Arylmethane dyes
Category: Diarylmethane dyes, based on diphenyl methane
Category: Triarylmethane dyes, derivates of triphenylmethane
Category: Azo dyes, based on -N=N- azo structure
Diazonium dyes, based on diazonium salts
Nitro dyes, based on a -NO2 nitro functional group
Nitroso dyes, based on a -N=O nitroso functional group
Phthalocyanine dyes, derivatives of phthalocyanine
Quinone-imine dyes, derivatives of quinone
Category:Azin dyes
Category:Eurhodin dyes
Category:Safranin dyes, derivates of safranin
Indamins
Category: Indophenol dyes, derivates of indophenol
Category: Oxazin dyes, derivates of oxazin
Oxazone dyes, derivates of oxazone
Category: Thiazine dyes, derivatives of thiazine
Category: Thiazole dyes, derivatives of thiazole
Xanthene dyes, derived from xanthene
Fluorene dyes, derivatives of fluorene
Pyronin dyes
Category: Fluorone dyes, based on fluorone
Category: Rhodamine dyes, derivatives of rhodamine
Selection of dyes or dyestuffs:
With the enormous host of dyes available to today’s textile industry, the choices are significant. Aside from each coloring agent’s ability to impregnate fibres and fabrics with different color intensities, each has specific functional characteristics that may make it more suitable for one project than for another.
One of the most important decisions that must be made in dye selection is influenced by the products final use. Colorfastness, the degree to which the dye can withstand fading, is crucial in many cases. Washables, for example, must be colorfast so bleeding, the running of color, will not take place when the garment is laundered or used for swimming. Fading is another factor that must be considered, especially when exposed to sunlight, as in the case of active sportswear.
Fabrics that are improperly colored cause numerous problems for mills, manufacturers, retailers, and consumers. One wrong dyeing decision can generate displeasure for every part of the distribution cycle. The consumer returns the damaged product to the merchant, often causing a refund of the purchase price; the retailer, in turn, returns the product to the manufacturer, requesting credit for returned goods; the producer finally becomes embattled with the mill and requests and adjustment. An in-depth study of the various dye classes and their properties is appropriate for anyone wishing to enter the textile industry – and, for that matter, anyone interested in a career in any aspect of the fashion world. Some of the general classifications are offered to give an indication of their important characteristics to the apparel, accessories, and home furnishings industries.
Acid:
Excellent to achieve bright colors; not fast to washing, but able to withstand the chemicals used in dry cleaning
Chrome:
Excellent colorfastness to light and washing; however, the resulting colors are dull.
Basic:
Bright shades are easily achieved; generally colorfastness to washing and light. Fabrics colored with this dye are usually resistant to crocking; the color will not rub off from friction.
Direct:
Poor colorfastness to laundering as well as to light pe*******on; dry cleanable in most cases
Disperse:
Their potential for colorfastness varies according to the fibers being colored; colorfastness to crocking, perspiration, and dry cleaning is generally good.
Reactive:
Perfect for bright colors; good overall colorfastness, except to chlorine, which eliminates it as a useful agent in the dyeing of swimsuit fabrics
Napthol:
Bright colors; colorfastness to light varies, depending on the specific makeup of the dye; colorfast to washing
Vat:
Excellent colorfastness to sunlight, washing and perspiration
Factors to be considered for selecting dyestuff:
1. Nature of the shade
2. Nature of the material
3. Availability of the dyes
4. Fastness of the dyed material
5. Chemistry between dye & fiber
Application of Dyes:
There are different types of dyes for dyeing textile goods. These dyes have different nature in fiber. It depends on fiber characteristics. Application of dyes in different fibers is given below:
Name of DyesApplicationAcid dyeManmade fiber (Nylon),
Natural fiber (Silk, Wool)Direct DyeManmade fiber (Viscose),
Natural fiber (Cotton)Vat dyeManmade fiber (Viscose),
Natural fiber (Cotton, Silk, Wool)Disperse dyeNylon, Polyester, Acrylic, Tri-acetate, Di-acetateBasic dyeJute, AcrylicReactive dyeCotton, Wool, Silk, Viscose, NylonSulfur dyeCotton, ViscoseMordant dyeCotton, Wool, SilkPigmentCotton, Manmade fiberMineralCotton, Wool, SilkAzoic dyeCotton, ViscoseAniline BlackCottonRapid and Rapidson dyeCottonOnium dyeCotton, Jute
Conclusion:
From the above discussion it’s clear that different dyestuffs are compatible for different textile materials. In order to achieve a better dyeing performance it’s necessary to select suitable dyestuff for the respective textiles. Though now a day’s synthetic dyes are broadly used to fulfill our daily necessaries but we should keep in mind that it’s also harmful for our environment which the gift from nature. In this regard comparatively natural dyes are eco-friendly as well as better in individual performance. Before using dyestuff we should be conscious about our environment and the others related factors also.
THE END
