Eco-Friendly Dyes for Textiles
Nikhil Yogesh Upadhye
Department of Textiles (Textile Chemistry)
DKTE’S Textile and Engineering Institute, Ichalkaranji, India
Intern at Textile Learner
Without azo colors are additionally being utilized in the material ventures which are liberated from nitrogen based mixtures that discharge sweet-smelling amines. Also, colors liberated from substantial metals which contain poisonous and cancer-causing substances are utilized to create supportable and eco-friendly fabrics. Today the textile industry which uses on an average 600 dyes and chemicals for the production of consumers textiles, is considered must polluting. With the child of mindfulness and limitation coming in to biology of materials world over the principal thing each material processor need to know period to preparing any materials are the idea of end utilization of the material being handled and the country which being traded. Since each end use model child wear, clothing in direct contact with skin, outfitting textures and so forth. Will have various determinations similarly as every nation will have distinctive enactment. Cotton, rayon and so on fibers can be used for dyeing with eco-friendly dyes. It reduces the problem as water pollution and does not harmful to the environment.
2. Natural Dyes
Natural dyes are classified into three types supported source of origin namely vegetable dyes, animal dyes and mineral dyes. Natural dyes are color substance made up from natural resources. Natural dyes are used for all kids of textile dyeing and printing until central of 19th century. The use of natural dyes were reduced due to the arrival of synthetic dyes, do they wear economical and possesses excellent. However, the growing consumer awareness on harmful impact of synthetic dyes, concern for environment worldwide and stringent environmental laws cause the revival of natural dyes. Besides, natural dyes are the principle sources of eco-friendly dyes.
2.1 Vegetable dyes or plant based:
The most punctual colors were of vegetable beginning, found by unintentionally staining pieces of clothing with juices of organic products or plants. Vegetable colors are gotten from various pieces of plants like leaves, blossoms, organic products, units, bark and so forth these vegetable colors might be applied straightforwardly or with various mordants.
One of the most ancient red dyes, extracted from the roots of a plant, ‘Rubia Tinctorum’. The matured plant is allowed to remain in the earth from 18-24 months in the belief that aging improved the quality of the dye after removal from ground; the roots were washed, dried, and finely milled and stored in casks. The history of the use of madder as a dyestuff is lost in antiquity, although it probably had its origin in India. Because of its beauty, fastness, and range of shades with various mordants, madder was used extensively until 1868, when Alizarin the chief coloring component of madder, was produced synthetically.
Saffron, a bright rich yellow dye obtained from the stigmata of the ‘Crocus Sativus’ plant, was not only used as textile dye but also, as a coloring and flavoring agents for foods and as a medicine. Monks of the middle ages discovered that by combining saffron with an Iron mordant they could produce Inks for their illuminated manuscripts, which resembles Gold. Saffron was the most expensive yellow dyestuff of the ancients due to the fact that 4000 stigmata were required to produce one ounce of dye. The three long stigma of each flower are the saffron of commerce; the red orange tip being first quality dye and then remaining portion being of lesser value. Saffron is still grown in Kashmir in India and is used for dyeing holy men’s robes, as well as for coloring and flavoring of confectionery rice and curry in India and Pakistan.
The Safflower, as a dye producing plant, probably had its origin in south Asia; however, it was cultivated from ancient times in China, India, Persia and Egypt, where it was also used as a foodstuff and as a medicine. In Greece, it was rated as the official color. The yellow dye from safflower is similar to saffron, although the two plants from which the dyes are derived are not related botanically. Safflower dye is obtained from the flowering head of the plant. The florets are harvested by hand when in full bloom. The fugitive soluble yellow dye is removed from the florets by agitating in water. The mass is then pressed, dried, and made ready for market. The coloring matter of the plant is composed of a small percent of insoluble red and a soluble yellow. Depending on whether the dye is mixed with an acid or alkali, various shades of yellow, orange, red and pink are obtained with safflower dye.
The Spaniards near the bay of Compeche, Mexico, discovered logwood shortly after their conquest of the new world. Quick to see its value as purple dye on wool, blue and black on cotton and wool, and violet and black on silk, the Spaniards introduced logwood dye to dyers of Europe shortly after its discovery. It is still used to some extent as a cloth dye and it is interesting that in labs a black color lake made from logwood was invented for use in the first bleachable ink for printing telephone directories, permitting recovery of millions of pounds of paper pulp each years. Logwood is obtained from a large tree, which is indigenous to sub-tropical and tropical America. The wood in its natural state is colorless. The color is produced by reducing the wood to chips or a paste. This is thoroughly wetted, causing fermentation to take place, in the process of which the color is developed.
2.2 Herbal dyes:
Herbal Textile is dyed entirely with herbal extractions, without using any variety of chemicals. The herbs used are different from vegetable dyes as they’re not only natural but even have medicinal value. These herbs are applied on to the material with the assistance of natural ingredients, so the medicinal value of the herbs are often kept intact. No natural process is adopted while dyeing. Even bleaching of fabric is finished naturally by exposing it to sunlight. The herbs also don’t pollute the environment through contamination of water resources in areas near processing units. Every kind of reminder red, yellow, brown, orange and green etc. are often prepared with the assistance of those herbs.
2.2.1 Tulsi leaves:
Tulsi is mostly used for medicinal purposes and in herbal cosmetics and is widely used in skin preparations due to its antibacterial activity. For centuries, the dried leaves of tulsi have been mixed with stored grains to repel insects. Antimicrobial property of tulsi plant can be used in textile dyeing. If along with natural dyeing some important feature is also added on to the fabric, it will be a real breakthrough. Durable antimicrobial cellulose-containing fabrics have a great deal of demand in a country like ours, where temperate climate conditions especially during rainy season cause immense damage to untreated cotton fabric.
A yellow dye extracted from the roots of the plant, ‘Curcuma Longa’. This dye is still used today in India for Carpet dyeing. Turmeric are often applied on polyester by mordanting and dyeing by the subsequent methods as discussed further. Carrier method consists of galling and mordanting, carrier treatment with dichlorophenol, dyeing and soaping. Heat setting method consists of galling at temperature, mordanting at boil heat setting at 1200C and soaping. The dye uptake within the heat-set method is best than within the carrier method. Copper sulfate confers the simplest fastness properties. Open bath dyeing administered under mild acidic condition shows good dye-uptake. Iron as a mordant gives maximum color value. HTHP method on polyester shows a superb dye uptake with a fluorescent hue and affinity in neutral and acidic medium dyeing. Turmeric exists in additional than two components and therefore the component, which preferentially goes into polyester, shows a really uniform dyeing. Tannin as a mordant gives a high color value.
The wash fastness ratings range from 3 to five. The sunshine fastness ratings are poor and therefore the wash and sublimation fastness ratings are good. The poor fastness to light are often associated to the very fact that fluorescent dyes are more photosensitive and fade sooner because the active life period of their molecules is longer and therefore the chances of collision with oxygen of the air, therefore greater.
Colors produced on the silk, using turmeric in several concentrations and its combination with myrobalan, are yellow based. The wash and lightweight fastness properties range from 2-3 to three the fastness properties of materials dyed with turmeric within the presence of myrobalan increase slightly.
2.3 Dyes derived from fruits:
Dyes are extracted from the following fruits: – pomegranate rind, terminalia bellerica, arecanut, myrobalan, berberry, grape skin, tamarind, and nova red. These can be applied on to various substrates like cotton, wool, silk, and polyester. Some of these examples are described below.
The dye is extracted at 80°C in a basic medium, which gives a high yield of dye and also a clear solution, for two hours. The dye is applied on to silk, cotton, wool and polyester. The colors obtained range from yellow to bluish green and yellowish brown to khakhi with different mordants. The wash fastness ratings range from 3-4 to 4-5 depending on the mordant used and light fastness is 3-4.
The dye is eco-friendly because the concentration of toxic heavy metals is much below stipulated limits in the extracted dye. There are only traces of pesticides and banned aryl amines are absent since the dye is not based on azo-linkage.
2.3.2 Terminalia bellerica:
Coloring matter: The chemical composition of T.b. includes gums, green fixed oil, tannins, organic acids and sugars.
The fruits are dried and powdered. The dye is extracted as described in the general process. The dyeing is carried out on premordanted wool. The dye yields a yellow color. The mordants used for wool are chromic chloride+ lactic acid, potassium dichromate + lactic acid, copper sulphate, ferrous sulphate giving colors ranging from yellow, beige, brown to moss green depending on mordant concentration.
2.4 Indigo dyes:
For 4000 years, Indigo was regarded as the most important of all natural dyestuffs. The blue dye producing plant, ‘Indigo era Tinctoria’, probably originated in India, as this country was its chief exporter. The color intermediate is obtained mainly from the leaves of the Indigo plant and is soluble, colorless glucoside known as Indican. The leaves are steeped and allowed to ferment, and clear yellow liquid is formed which contains the White Indican. The Indican being soluble in water in an alkaline is readily absorbed on fibers. Upon agitation, the indigo white oxidizes to insoluble Indigo blue. This process of coloring is known as Vat Dyeing.
2.4.1 Indigoid dyes:
Indigo and Tyrian purple are the oldest dyes known to mankind. This is perhaps the most important group of natural dye. Indigo is extracted from ‘Indigo era Tinctoria’, a bush of pea family. The dye was used prehistorically in India, where it probably originated. The dyestuff is extracted from the leaves of the plant, which grows three feet in height and has a maximum dye content of 0.4%. The coloring matter is present in the form of soluble glucoside known as Indican. Woad is a blue dye similar to indigo and can be obtained from fleshy leaves of the plant ‘Isatis Tinctoria’. Tyrian Purple was probably the most expensive dyestuff in history. Extracted from a tiny gland in the body of the mollusks, murex brandaris and murex tranculus. This dye has excellent fastness properties and very brilliant purple shade.
2.4.2 Advances in dyeing with indigo:
Implementation of new technological advances in indigo dyeing can result in improved quality control in both dyeing of denim yarn and laundering of denim garments, lower dyeing and laundering costs and reduced pollution. Advances that are made possible by control of ionic form of indigo dye and cotton substrate in dyebath are shown to provide both the denim dyer and the garment manufacturer benefits that previously were not attainable by the use of conventional indigo dyeing techniques.
2.5 Natural dyes-techniques of extractions:
Natural dyes cannot be used directly from their renewable sources. Using raw materials for dyeing has many limitations. Safe and cheap extraction of main coloring component is most important without affecting the extraction conditions and avoiding any contamination in various extraction techniques. Several Extraction Methodologies for natural dye that comply with both consumer preference and regulatory control and that are cost effective are becoming more popular.
Techniques of extractions of natural dyes involve:
- Simple Aqueous Methods
- Complicated Solvent Systems
- Ultrasonic Extraction in Sonicator
- Supercritical Fluid Extraction Techniques
2.5.1 Simple aqueous methods:
Natural dyes are mixed with required amount of water and boiling for optimum time (found out by optimization of parameters) which is 60 minutes in most cases. The content is cooled to Room Temperature and filtered. The filtrate is used as a dye for dyeing.
Extraction of Onion Dye: The outermost dry papery skins of onion were removed and boiled with water for 1 hour. The content was cooled to a R.T. and filtered. The filtrate was used as the dye solution.
2.5.2 Complicated solvent systems:
The dried material (leaves, roots, barks, wood, resinous secretion of insects etc.) are ground to very fine particles. The crude dried powder is weighed and solvent extracted using Soxhlet Apparatus, Steam Heated Extractor. Different solvents (such as Acetone, chloroform, ether, n-hexane, alcohol, soda ash, etc.) are used for Extraction. The process is carried out for 4 hours. The dye extract is evaporated in an evaporating dish over a water bath. After evaporating to dryness, the solute is weighed and the percentage yield is calculated.
Extraction of Henna (lele) using solvent: The dried leaves were ground to very fine particles. 40gm of the crude dried powder was weighed and solvent extracted using a Soxhlet apparatus. Three different solvents acetone, chloroform and water were used for the extraction. 250 ml of each solvent was used. The process was carried out for four hrs. The dye extract was evaporated in an evaporating dish over a water bath. After evaporating to dryness, the solute was weighed and the percentage yield is calculated.
2.6 Advantages of natural dyes:
a) Health and safety aspects of natural dyes: Synthetic colorants have been cited as causing skin complaints, illnesses and cancer. The people in general are at risk from skin sensitization through coming into contact with certain reactive dyes, azo dyes and triphenylmethine derivatives. Close skin contact with colored textiles (e.g. leggings heavily dyed with azo and anthraquinone disperse dyes) has been a concern, and in some cases dermatitis results. Respiratory sensitivity to synthetic dyes is also reported. The carcinogenity of synthetic dyes is a major issue. The worst culprits are dyes from benzidine. Although these are no longer manufactured in Europe, many other parts of the world are a safe haven to these dye manufacturing industries. These mainly present a risk for factory workers rather than to the consumers of the dyed textiles. Some azo dyes, the largest and most important group of textile dyes, are also implicated because many of them cleave to yield an aromatic amine, which is carcinogenic.
Though all natural dyes are not 100% safe they are less toxic than their synthetic counterparts. Many of the natural dyes like turmeric, annatto and saffron are permitted as food additives. Many natural dyes have pharmacological effects and possible health benefits. But these benefits are often hard to quantify on scientific grounds. For example, the people of Arabia perceive that wearing natural indigo dyed clothing next to their skin has a positive effect on their health and lowers the incidence of illnesses.
b) They are obtained from renewable sources.
c) Natural dyes cause no disposal problems, as they are biodegradable.
d) Practically no or mild reactions are involved in their preparation.
e) They are unsophisticated and harmonized with nature.
f) Many natural dyes have the advantage that even though they have poor wash fastness ratings, they do not stain the adjacent fabrics in the washing process because of the non-substantive nature of the dye towards the fabric. An exception to this is turmeric, which shows substantively for cotton.
g) Natural dyes are cost effective
h) It is possible to obtain a full range of colors using various mordants.
2.7 Limitations of natural dyes:
The limitations / disadvantages of natural dyes that are responsible for their decline are:
- Color yield
- Complexity of dying process
- Reproducibility of shade
Besides these there are other technical drawbacks of natural dyes:
- Limited number of suitable dyes
- Great difficulty in blending dyes
- Inadequate degree of fixation
- Inadequate fastness properties
- Water pollution by heavy metals and large amounts of organic substances.
3. Reactive Dyes
Late 1920s: Investigations were carried out by Haller and Heckendorn in which cellulose was treated with conc. NaOH (6%) and then reacted with cyanuric chloride. The product ‘immunised cellulose’ (a cellulose-triazine adduct) could then link to a dye molecule via displacement of one of the two chlorine atoms and resulted in dyed fabric with good wet fastness, albeit degraded strength. However, the harsh alkaline conditions led to this method falling out of use. Mid 1950s changing the sequence of the original Haller and Heckendorn procedure was the first step to a successful procedure for dyeing cellulose. The next breakthrough came when it was realized that concentrated alkali treatment was not required in the condensation step.
In 1954, Dr. Ian Rattee patented a procedure in which cotton was treated with triazine-derived dye using only 3% NaOH, resulting in a dyed fabric with excellent wet fastness. The original discovery of “Covalent Dyeing” is attributed to Dr.Ian Rattee and Steven. In 1954, they found that dichlorotriazine containing monoazo acid dyes reacted with the hydroxyl group of cellulosic fibers, when the neutral dyebath is rendered alkaline, because at higher pH, a larger percentage of the cellulosic –OH groups are dissociated and thus more nucleophilic. ICI introduced commercial reactive dye in 1956 exactly after 100 years of first synthetic dye Mauveine Hoechst commercialized the dyeing of wool with reactive Ramaln dyes containing (SO2CH2CH2OSO3H) groups already in 1949; and Ciba had introduced in 1954 Cibalan Brilliant dyes which contain reactive chloroacetyl amino groups (NHCOCH2Cl). Soon after ICI’s procion dyes are known, Ciba and Hoechst realized that their dyes can also render reactivity on fiber by alkaline after treatment and this led to Cibacron and Remazol dyes.
3.1 Low-salt reactive dyes:
Reactive dyes that require less salt upon application have been developed. The Cibacron LS range (LS = low salt) is the most prominent of them, as it employs a variety of reactive groups in a variety of configurations. The majority of the dyes are bi-functional, with bismonofluorotriazines being the most common.
MFT and MCT in combination with VS, as well as trifunctional (MCT/bis VS) dye, are among the other groups or combinations used. These dyes’ ability to work in the presence of decreased salt is due to their high affinity for cellulose, which is partly attributable to their huge molecular size. The affinity for the substrate is increased by flat dye molecules with hydrogen bonding sites. Hoechst introduced the Remazol EF line of low-salt reactive dyes. These are most likely dyes from the standard VS range.
Improved cellulose substantivity towards anionic dyes reduces the demand for electrolyte in the dyebath and improves dyebath exhaustion, resulting in less residual dye in the dyehouse effluent. Several cellulose chemical changes have been described. Amino groups are introduced into the cellulose structure, resulting in a fiber that resembles wool. Wool, unlike cellulose, has a natural substantivity toward anionic dyes, which is especially important in acidic environments.
During the modification of reactive dyes, the following observations were made:
- The number of sulphonic groups in the chromophore has been adjusted to provide the requisite solubility while maintaining good substantivity.
- The presence of bridging groups between the chromophore and the reactive group allows for molecular flexibility, allowing for facile diffusion.
- Reactivity control: Two fluorine groups with extremely high reactivity were introduced. (Fluorine takes the role of chlorine.)
Cibacron LS dye onditions is an example of this sort of dye,
In recent years, an interest in eco-friendly dyes has been mainly manifested as Conservation and Restoration of old Textiles with replacement of synthetic dyes (which uses violent technology) by natural dyes for textiles, food, safety and so forth by using Mild Chemistry.
The buyers from European Economic Community (EEC) Countries especially from Germany insist on a certificate for eco-friendliness of the commodities and therefore, Identification and Testing of natural dyes and natural dyed substrates as per Eco-standards as well as their authenticity has become imperative.
The Research and Development work in Standardization of natural dyes are least or negligible. Very few serious attempts have been made to generate new information on the use of natural dyes. Most of the researches in this area are carried away by the empirical information reported in the literature that does not have any scientific reasoning or basis. Using raw materials for dyeing has many limitations. Besides its being of unknown composition, it generates considerable amount of biomass that is cumbersome to handle in the dye-house. Non-availability of natural dyes, especially in the standardized form, which may be powder, paste or solution form.
If there had been significant research on the use of natural dyes, it would be probable that they would be already being much more widely used than they currently are. As there is much catching up to do after 150 years of neglect, there is rapid scope for developments. This applies to the techniques of agricultural production and processing as well as to dyeing itself. A medium-to-long-term view of research and development is needed. It is unlikely that the total cost of R and D required to make natural dyes a profitable commercial reality need be very great when compared with many industrial products.
Only small portion of a huge icebergs of standardization of natural dyes are only achieved. The contributions for standardization of natural dyes are made by some companies like Alps Industries Ltd. that uses Supercritical CO2 plant for extraction of dyes for a step towards standardization. The standardized natural extracts are very much useful for Textiles, food, pharmaceuticals and cosmetics.
It is a challenge for any enlightened dyer for working out suitable standardized applications of natural dyes on Textiles with eco-friendliness.
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