Natural Dyes: Dyeing Process and Environmental Impact

What is Natural Dyes?

The word ‘natural dye’ refers to all the dyes derived from the natural sources. Its mainly obtained from different plants, animal and minerals resources. It is mostly non-substantive and must be applied on textiles by the help of mordants.

Ancient humans used root, wood, bark, grass, berries, leaves, nuts, seeds, flowers as natural dye. Throughout civilization, humans gradually invented hand spinning and handloom weaving for making cloths. People were imparted different colours on cloth in order to develop designs and differentiate clothing from one another. Textile clothing and apparel materials are used to be colored for value addition, look, and desire to the customers.

natural dyes
Fig: Natural dyes

Types of Natural Dyes:

There are three types of natural dye which must be applied in fabric with appropriate technique. These are as follow:

  1. Plant dyes: obtained from leaves, flower, skins of fruit, bark, roots, wood etc.
  2. Insect Dyes: obtained from various dried bodies of insects.
  3. Animal Dyes: obtained from created from shellfish Carmine, Cochineal and so on.

Some Common Natural Dyestuffs are as follow:

Part of the Plants Dyestuffs
1. Root Turmeric, Onions, Madder, Beet-root, etc.
2. Bark Purple bark, Sappan wood, Shillicorai, Khair, Sandalwood, etc.
3. Leaf Henna, Indigo, Lemon Grass, Eucalyptus, Tea, Cardamon, Coral Jasmine, etc.
4. Flowers Marigold, Dahlia, Kusum, Tesu, etc.
5. Fruits or Seeds Latkan, Pomegranate rind, Beetle nut, Myrobolan, etc.

Natural Dyeing Process:

For successful commercial use of natural, the appropriate and standardized dyeing techniques have to be adopted for particular fiber. However, the modern natural dyeing process information is very insufficient. That is why an attempt has been made here to give a scientific overview of the dyeing process.

1) Scouring:
Scouring is the first procedure for any dyeing process. Raw fabrics and yarns carry impurities and residues such as: dirt, wax, dust, coatings. If the fiber is not properly scoured, the dye will adhere to the coating of residue, instead of the fiber itself. The colors will not fully penetrate, and the fabric will dye unevenly.

In scouring process, fibers submerging in water along with a scouring agent. Water temperatures, pH and scouring agents vary depending on fiber. Generally, soda ash or neutral soap uses for plant fibers such as cotton, jute, flax, etc. And orvus paste soap used for protein fibers like: silk and wool, etc. Plant fibers will simmer in the bath for a few hours. But protein fibers are sensitive to higher temperatures, so they need to be handled more carefully.

2) Mordanting:
Mordant makes a bond between the fiber and the dyestuff. So this step is very important in the dyeing process. Mordanting is most effective if it’s done before the dyeing process. But some manufacturer prefers to combine the mordants and dyestuff in one bath. While it’s possible to dye fibers without a mordant, but it will not achieve a durable, long-lasting color without a mordant. Mordanting is the process of wetting fibers in hot water with a diluted mordant for at least one hour. But it can, let the fibers cool in the solution overnight to ensure maximum color-fastness.

3) Dyeing:
Powder dyes and extract dyes are concentrated and ready for application in the fabric. But foraged ingredients like fresh plants, insects, flowers, fruits, or roots need some preparation before the dyeing.

After the dye materials are ready to go, it’s time to decide to choose a technique that will apply to the fabric. There are different kinds of traditional techniques available. For solid color, the general-submersion method could be applied. Other techniques including ombre (dip-dyeing), bundle dyeing, shibori dyeing, and the like techniques are available to dye the fabric.

Advantages of Natural Dyes:

  1. Natural dyes shades are lustrous, soft, and soothing to the human eye.
  2. Natural dyestuff can provide a wide range of colours by mix and match system. That is not easily possible with synthetic dyestuffs.
  3. Natural dyestuffs produce rare color ideas which are automatically harmonizing.
  4. Waste in natural dyeing process becomes an ideal fertilizer for use in agricultural fields.
  5. Many natural dyes plants thrive on wastelands. Thus, wasteland utilization is an added merit of the natural dye.
  6. Application of natural dyes has strong potential to reduce the consumption of fossil fuel-based synthetic dyes.
  7. Some of the natural dyes are enhanced with age. But synthetic dyes fade with time.
  8. This is a labor-intensive industry. As a result, these processes providing job opportunities for all those engaged in cultivation, extraction, and application of natural dyes on textiles, food, leather, etc.
  9. Natural dyes are proved that it’s safe for human skin contact and are mostly non-hazardous to human health.
  10. Natural dyes are usually renewable and biodegradable.

Limitations Natural Dyes:

  1. Natural dyeing processing and colour development doesn’t only depend on colour component but also on materials.
  2. It is difficult to reproduce shades by using natural dye.
  3. Natural dyeing requires skilled and experience workmanship which is expensive.
  4. It is difficult to standardize a recipe for the use of natural dye.
  5. Low colour yield of source natural dye thus necessitates the use of more dyestuffs, larger dyeing time and excess cost for mordants and mordanting.
  6. Lack of availability of precise technical knowledge on extraction and natural dyeing techniques.
  7. Natural dyed textile can be changed colour when exposed to the sun, sweat and air.
  8. Natural dyes colour fastness performance ratings are inadequate for modern textile usage.
  9. Science involved in natural dyeing is still need to be explored.

Environmental Impacts of Natural Dyes:

Natural dyes are fascinatedly termed as green chemicals. Its application on textile and apparels has a high demand due to its biodegradability and unique colors. However, during extraction, dyeing, and aftertreatment of natural dyes, textiles face some following important problems. Which pretense an impact on the environment:

  • Pesticides are applied on plants to provide protection against pests. Natural dye extracted from these plants could have traces of pesticides. It may cause problem during eco-testing.
  • All-natural dye could not be extracted by conventional aqueous extraction method. Some natural dyes need acidic or alkaline medium and necessary solvent for efficient extraction.
  • Natural dyes need chemicals other than mordants for their application. It may cause effluent problem.
  • Natural dyeing units are run by small-scale industries. and So, it is economically impossible to set up an effluent treatment plant. As a result, they are disposing the dye effluent to nearby canals or rivers which will further contaminate water sources.
  • Some natural dyes need high amounts of metallic mordants like Cu, Sn, and Fe. Which is eco-friendliness of the process being really questionable.
  • To match the commercial shade 1% the synthetic dye needs. On the contrary, 10 to 25% natural dye is required to match with commercial shade. It may be increased the pollution load in effluent treatment plant.
  • COD and BOD ratio of effluent from natural dye is approximately two. It implied that this effluent is highly biodegradable. Butit’s also indicated the amount of copper, chromium, andiron present in effluent exceeded the acceptable limit.
  • Natural dyeing process consumes more energy and time than conventional dyeing process.

Why Natural Dyeing is Important?

Today global demand for natural dye in the coloration of textiles products is nearly 0.1 million tonnes, which is equivalent to 1% only of the world’s synthetic dye consumption. Almost every synthetic colorant being synthesized from petrochemical sources. As a result, hazardous chemical dye processes pose threat to its eco-friendliness.

Worldwide growing consciousness about organic eco-friendly products has generated renewed interest of consumers towards the use of textiles dyed with eco-friendly natural dyes. Natural dyes are known for its uses in the coloring of food substrate, leather and natural fibers. It was being applicable since pre-historic times. Even after a century, the uses of natural dye never erode completely. Thus, natural dyeing of different textiles has been continued mainly in the decentralized sector for specialty products; besides the use of synthetic dyes in the large-scale sector for general textiles. But natural dye processes are not yet ready for industrial production. We have to make more and more research to make sustainable large production in the textile industry.

References:

  1. Functional Aspects, Ecotesting, and Environmental Impact of Natural Dyes L. Ammayappan and Seiko Jose
  2. Natural Dyes for Textiles: Sources, Chemistry and Applications by Padma Shree Vankar
  3. Colouring Textiles: A History of Natural Dyestuffs in Industrial Europe by Agustí Nieto-Galan
  4. Dyeing of Textiles with Natural Dyes by Ashis Kumar Samanta and Adwaita Konar, Department of Jute and Fibre Technology, Institute of Jute Technology, University of Calcutta India
  5. https://fashionangelwarrior.com/natural-dyeing-methods-that-every-designer-should-know-a-fabric-series/
  6. https://textilelearner.blogspot.com/2011/07/natural-dyes-classification-of-natural_9854.html
  7. https://fashion-history.lovetoknow.com/fashion-clothing-industry/natural-dyes

Author of this Article:
Md. Mahedi Hasan
B.Sc. in Textile Engineering
Textile Engineering College, Noakhali.
Email: mh18.bd@gmail.com

1 thought on “Natural Dyes: Dyeing Process and Environmental Impact”

Leave a Comment