Research/ Review Paper | Textile Articles

Natural dyes –An over view

Published: June 5, 2014

Author: TEXTILE VALUE CHAIN

S Barhanpurkar A Kumar

Assistant Professor ,Department of Textile Technology.

Shri Vaishnav Institute of Technology and Science, INDORE

Director , Uttar Pradesh Textile Technology Institute , Kanpur

ABSTRACT

Dyes can be derived from nature through herbs and plants flowers, seeds, barks and roots. Natural dyes give the subter, rich warm colors that are unique combinations.. Natural dyes can be categorized as either substantive or adjective. Substantive dyes (also known as direct dyes) such as Indigo lichens or Walnut hulls affix to the fiber without the aid of another chemical or additive. Adjective (also known as mordant dyes) require a fixative, generally a metal salt, to present the color from washing or bleaching out.

Keywords: Natural dyes, substantive dyes, adjective dyes

1 Introduction

Today in the world of growing environmental consciousness, natural colorants have attracted in the attention of everyone. The art of dyeing with vegetable dyes has gained attention not only from the safety point of view but it is good for health and environment also having experienced quality of novelty and beauty.(1)(2)

The Importance of color in textile products cannot be under estimated prior to the advent of synthetic dyes in 1856, all coloring matters were extracted from naturally available goods. The Invention of synthetic dyes almost limited the use of vegetable dyes to specific fabric only such as kalamkari, hand printed textiles etc (Katyayini VKLT and Dr. Jacob Mary 1998).(3)(4)(5) The globe has been facing the serious environmental pollution over a long period of time which eventually has turned the social atmosphere back to the mother nature. This entails the need for study and interest in natural dyes performed were the pigment analysis on the old fashioned traditional fabrics dyed in natural agents or the work on natural colorized pigments applicable to dye. The natural dyes have with unique characteristics, viz mild, static deep feel having the capability to express many kinds of hues and chronora according to different mordents and relatively less amount of disposal water, when compared to those of synthetic dyes (Bae, Soon-Ei 2009).(6)(7) Natural dyeing is an age old practice. It was the result of the quest of man for coloring matter from natural sources such as plants and animals. But most of natural dyes do not fix permanently to the fibers and less they are used with chemicals called ‘mordants’. Also with the use of mordants a range of colors can be obtained with the same dye material (Singh Jeet, S.S. Yadav S. & Gaba. G. 2003).

Up to the middle of the 19^th century, only natural dyes were available. In 1856, W.H. Perkins accidentally discovered aniline dye, and synthetic dyes slowly began replacing natural dyes. From Perkin’s discovery of Mauveine in 1856 to the turn of the century, hardly a year passed without the issue of a new patent for a synthetic dye.

Natural dyes are environment-friendly, for example, turmeric the brightest of naturally occurring Yellow dyes is powerful antiseptic which revitalizes the skin, while Indigo gives a cooling sensation, many researches and industrialist have shown that synthetic dye are suspected to release harmful chemicals that are allergic, carcinogenic and detrimental to human health.(12)

2 Importance of Natural Dyes

Color had played a dominant in life of human beings since times immemorial. In the prehistoric times natural colorants were the only source available for imparting color to the life of man. The ancestors of the human activities witnessed unrivalled mastery in innovative application techniques as evident from the works of classical antiquity. Industrial revolution caused chemistry to play a predominant role in offering various synthetic dyestuffs to the textile industry and novel techniques of applying them. The advent of synthetic dyes almost limited the use of vegetable dyes for more than a century in the last decade. The use of synthetic dyestuff during their application has been critized due to the introduction of contaminants into the environment. At present, the textile industry in many developing countries is facing the tremendous impact of famous German ban on 118 specified azo dyes and 20 carcinogenic aryl amides including Benzedine. The need to preserve environment has led to the revival of old practice of coloration with natural dyestuffs due to the carcinogenic nature of some synthetic dyes and their intermediates(13). Natural colorants are more compatible with the environment on account of better biodegradability and can be considered as one of the safe alternative over many hazardous synthetic dyes. The limitation associated with the natural dyes is that the traditional processes for their application on various substrates have been lost in the absence of proper documentation and years of neglect. It becomes therefore necessary to develop new methodology of coloring and also to standardize these techniques with the help of modern scientific inputs so that these dyes can replace the current synthetic dyes.(14)

With present national and international awareness of environment situation and the use of eco-friendly fibers and natural dyes has been increasing all over the globe. Looking from the angle of national health, it is not possible to ignore the fact that the most synthetic fibers and synthetic dyes are non-biodegradable and many of the chemicals used for their manufacturing are hazardous from health point of view. Because of the drawbacks of using synthetic materials people are reverting back to natural dyes and natural fibers especially for cotton. Most of natural dyes not fix permanently to the fibers without mordants, mordant help in the dye to get absorbed. Also with the use of mordants a range of colors obtained with the same dye materials. A variety of these shades depends on the nature of mordant, its concentration, dye and substrate used. Mordants may or may not be colored, their sole use is due to their capacity to precipitate the coloring matter on the fabric.(15) Natural dyes derived from plant sources on the other hand are non-toxic and biodegradable. These dyes from natural sources do not poses effluent problems. For these reasons, the research investigation carried out throughout the world has steadily increased to identify, and extract natural colorants and use them for dyeing textile fibers. Our interest in the identification of the dye from plant sources have shown that Onion skin (Allium cepa)

Belonging to the family Liliaceae and second source namely Mango Bark (Mangifera Indica), a yellowish brown dye is used for cotton is extracted from the barks so that Mangifera Indica bark and Onion skin were used in dyeing cotton material.(16)

Today natural dyes have become essential need of every person because natural dyes are more relevant worldwide in the context of increasing environment consciousness. However, all the natural dyes are not essentially non-toxic, through most of them are proved to be non-toxic and eco-friendly.

Besides eco-friendliness, natural dyes have many more technical advantages, including their uncommon and soothing shades. In spite of all the present international consumption of natural dyes never shades on cotton material, dyed with extract of natural dye obtained from Onion Skin and Mango Bark combination.

3 Natural Dyes

Different fibers absorb color differently. Protein fibers like wool and silk readily takes dyes. Bast Fibers like linen, rayon, hemp and cotton are more resistant to taking dyes. Proper mordanting, however a sure that the dye will hold part. The basic of any chemical reaction hold true for dyeing. Time, temperature and concentrate and grater concentrations will generally result in more intense colors.

Natural dyes considering the toxic effects of the synthetic dyes there has been a renewed efforts to study and implement the various natural dyes in the dyestuff industry primarily there are three categories of natural dyes firstly that are derived from plants like Indigo, second the ones that are obtained from animal sources called cochineal and those that are got from minerals (ocher).

Natural dyes can provide the much heard alternative to the complex world of chemical dyes. There is a whole variety of plants which can be used to make plant dye. Different parts of plants are used to make dyes: for example the leaves, the skin of fruit, the bark, roots or wood, when you pick a plant for making dye, collect seeds and then plant them, so that more plants will grow.

Natural dyes are non-hazardous and non-toxic.
100% safe for you and the environment, these exciting eco-friendly natural dyes are concerned, inter-mixable and provides all the color possibilities of natural dyes with the ease and convenience of chemical dyes without the hazards.(17)

Natural dyes are a class of colorants extracted from vegetative mater and animal residues.

They can be broken down into the following categories:

Categories of Natural dyes

Natural vegetable dyes have become a part of human life since time immemorial Egyptian mummies, documents of Mughal periods etc. bear testimony to the use of these dyes. These natural dyes obtained from natural resources, are non pollutant, non allergic, shade rich and warm. With the introduction of synthetic dyes in the middle oh the 19^th century, the use of natural dyes was on the wane. But due to several pollution problems posed by synthetic dye the world is once again veering round to natural dyes. In the recent pass, the demand for natural dyes has increased tremendously. Use of natural dyes in coloration of textile materials is just one of the consequences of increased environmental awareness. Natural dyes are being preferred over the synthetic dyes because they exhibit better biodegradability and compatibility with the environment. Also the dyes obtained from natural sources do not posses the danger of allergic reaction and are non-toxic in nature, so this present study is being conducted on natural dyes.

4 Sources of Natural Dyes:

Natural dyes obtained from plants, animals, By-products, and tissue or cell culture. Although some fabrics such as silk and wool can be colored simply by bling in the dye, others such as cotton require a mordant. Natural dyes in the present study belong to Biodegradable pigments.

4.1 Natural dyes obtained from plants:

Many plants and some animals have been identified as potentially rich in natural dye contents and some of them have been used for natural dyeing for quite some time. Various parts of plants like roots, stems, barks, leaves, fruits and seeds may contain coloring matter which can be exploited. Normally natural dyes are extracted from the roots, stems, leaves, flowers, fruits of various plants. Some plants may have more than one color depending upon which part of the plant one uses the shade of the color plant produces will vary according to time of the year the plant is picked, how it was grown, soil conditions etc. The minerals in the water used in a dye bath can also alter the color. Some natural dyes contain natural mordants.

Many natural dyestuff and stains were obtained mainly from plants and dominated as sources of natural dyes. Producing different colors like red, yellow, blue, black, brown and a combination of these. Almost all parts of the plants like root, bark, leaf, fruit, wood, seed and flower etc. produce dyes. It is interesting to note that over2000 pigments are synthesized by various parts of plants, of which only about 150 have been commercially exploited. Nearly 450 taxa are known to yield dyes in India alone, of which 50 are considered to be the most important; ten of these are from roots, four from barks, five from leaves, seven from flowers, seven from fruits, three from seeds, eight from wood and three from gums and resins. (Siva R. 2007).

The increasing market demand for dyes and the dwindling number of dye-yielding plants forced the emergence of synthetic dyes like aniline and coal-tar, which threatened total replacement of natural dyes. Even today, some dyes continue to be derived from natural sources, for example- dyes for lipstick are still obtained from Bixa Orellana L. and Lithospermum erthrorhizon sieb and Zucc and those for eye shadow from Indigo.(18)

4.2 Natural dyes obtained from animals:

Cochineal is a brilliant red dye produced from insects living on cactus plants. The properties of the cochineal bug were discovered by pre-columbian Indians, who dried the female insects under the sun, and then ground the dried bodies to produce a rich red powder. When mixed with water, the powder produced a deep, vibrant red color. Cochineal is still harvested today on the Canary Islands. In fact, most cherries today have a bright red appearance through the artificial color ‘carmine’ which is obtained from the cochineal insect.

4.3 By-products (especially lac dye):

The lac industry gives lac dye as a by-product, which is extracted from the effluent similarly, from Cassia Tora, used in gum manufacturing; a brown dye is obtained as a by-product.

4.4 Tissue or cell culture by DNA transfers biotechnology:

Certain fungi such as Drechslera and Trichoderma produce anthraquinone derivatives as secondary metabolites. As anthraquinones are a very important class of dyes, exploiting the fungi would be advantageous over their chemical synthesis, if genetic modifications can be achieved, it is possible to develop fungi that produce substituted anthraquinones.

5 Eco-friendly Natural Dye:

In recent years, s lot of awareness and concern has developed over the environmental issues of textiles wet processing. The pollution control board has become more strict on the implementation of the pollution control act. This has brought a lot of environmental pressure on the textile industry.

Environmental awareness throughout the world now seems to rescue the total ‘Fall’ of natural dyes. Hazards of chemical industries and dyes in particular have forced environmentalists to think in terms of natural products. Trend of greater uses of synthetic substitutes of natural substances have been reserved. This actually started when people throughout the world in general and west in particular preferred pure cotton clothes and dress material in place of clothes made from synthetic yarn.

Worldwide growing consciousness for use of eco-friendly products in daily life has generated renewed interest of consumers towards use of textiles from natural fibers dyed with eco-friendly natural dyes. However, all the natural dyes are not essentially non-toxic, though most of them are proved to be non-toxic and eco-friendly. (EM Dedhia 1998).

Besides eco-friendliness, natural dyes have many more technical advantages, including their uncommon and soothing shades. The ancient art of natural dyeing was nearly lost when synthetic dyes were introduced to the global market. Natural dyes are being received with the increase of environmental awareness. Eco-friendly natural dyes are non-hazardous and non-toxic, hundred percent safe for the people and the environment, these exciting eco-friendly natural dyes with the ease and inter-mixable and provides all the color possibilities of natural dyes with the ease and convenience of chemical dyes without the hazardous.(17)(18)(19)

The so-called ‘green’ textiles have become elite products in the developed world, with the organic cotton industry as a major leader in the process. However, more and more dyeing and tannery units are being forced to stop their activities, due to their polluting production process. The colors of natural concentrates on that aspects of vegetable dyeing which is environmentally friendly for instance, the water coming from the dyeing is first before being returned to nature-treated via an effluent treatment and plant moreover, the unit uses a fermentation process which is the most environmentally sound process for Indigo dyeing. It consumes less water than other Indigo dyeing methods: No fixing agents are required and the process doesn’t use hydrosulphite.

By reviewing this method, the colors of nature shows that environmentally friendly Indigo dyeing for industrial purposes (Medium bulk) is possible.

Characterization / Chemistry of Natural Dyes:

A dye can be defined as a highly colored substance used to import color to an infinite variety of materials like textiles, paper, wood, varnishes, leather, ink, fur, foodstuff, cosmetics, medicine, toothpaste etc. As far as the chemistry of dyes is concerned a dye molecule has two principle chemical groups, viz. chromophores and auxochromes. The chromophore, usually an aromatic ring, is associated with the coloring property, it has unsaturated bonds such as –C=C, =C=O, -C-S, -C-NH, -CH=N-, -N=N- and –N=O, whose number decides the intensity of the color. The auxochrome helps the dye molecule to combine with the substrate, thus imparting color to the latter.(18)(20)

7 Bonding of Natural dyes with natural fibers:

Natural dyes work best with natural fibers such as cotton, linen, wool, silk, jute, ramie and sisal. Among these wool takes up dyes most easily followed by cotton, linen, silk and then the coarse fibers such as sisal and jute. Nearly all of them require some sort of a mordant. The trick is to choose the right dye from the right source that gives not only beautiful tones, but colorfast shade as well.