Natural dyes for textile processing - an opportunity for Sri Lanka

By Dr. (Mrs) Samudrika Wijayapala,
Senior Lecturer, Department of Textile and Clothing Technology,
University of Moratuwa

The fossil fuel era led to the development of and the use of textiles based on petrochemicals. This in turn required different synthetic chemicals as dyeing and fixing agents to enhance consumer appeal.

Today the textile industry is a global industry of significance. However, from a national perspective, becoming greener by using biopolymers and natural dyes at this stage of transition may prove to be quite beneficial and prudent. This article explores such an opportunity.

The ability of natural dyes to colour textiles has been known since ancient times.

The earliest written record of the use of natural dyes was found in China dated 2600 BC. Chemical tests of red fabrics found in the tomb of king Tutankhamen in Egypt show the presence of alizarin , a pigment extracted from madder. In more modern times, Alexander the Great mentions having found purple robes dating 541 BC in the royal treasury when he conquered Susa, the Persian capital. By the 4th century AD, dyes such as woad, madder, weld, Brazilwood, and indigo and a dark reddish purple were known.

Today in Sri Lanka robe dyeing by Buddhist monks still follow this natural route and there are even evidence to show the power of some dyes for having anti-bacterial effects.

There is a rich history which can be looked into with contemporary science and technology to create a strong green industry in Sri Lanka

With the discovery of the first chemical dye in the mid nineteenth century, natural dyestuffs were slowly superseded. Until then both the dyer and the printer had been completely dependent on the natural dyestuffs. The early techniques of dyeing, from the pre historic times, were based on natural colouring substances obtained by boiling the colour yielding parts of plants and insects in water.

The expertise of dyes appears to have developed and been practised independently in almost every region in the world. In all probability the first colouring experiments were earth and mineral pigments being rubbed or painted on cloth, and stains obtained from crushing leaves, fruits and berries.

Although most natural dyes, especially vegetable dyes are now superseded by artificial dyes, such as aniline, alizarin, azo and other products of coal-tar, etc., certain kinds are still of some commercial importance and are generally considered more permanent than the latter.

There are numerous plants, the extracts from which are capable of colouring wool, silk, cotton and linen. Depending on the particular plant, various parts are used, the entire plant, bark, heartwood, leaves, roots or fruits. For various reasons such as dyeing behaviour, fastness properties or their biological availability, only a few have found application as dyeing agents.

Tannin is closely related to dyestuffs and generally occurs in plants as an excretum in the bark and other parts, which may be either employed direct or used for extracting tannin in a concentrated form.

There is no doubt that the use of natural dyes on a commercial scale is gradually increasing.

There is no difficulty in accepting the challenge of a retailer selling merchandise dyed or printed with natural dyes.

There are very few natural dyestuffs, which have a natural affinity to textile fibres and become permanent without a preliminary treatment. Dyes with this property are being described as “substantive”. In the majority of cases the dyestuff will colour the cloth only when assisted by a chemical compound, a mordant. The mordants used in dyeing are metallic salts, although some are acidic.

Although dyeing with natural dyes has not received the due attention of the scientists as well as of the industrialists, recently the textile industry is being confronted more with enquiries on the theme of “dyeing with natural dyes”.

The use of natural colours that would be assumed to have given way to the synthetic dyes over 140 years ago is today once again a matter of topical interest due to the following reasons.

Within the textile manufacturing chain, wet processing is clearly identified as having a potential adverse effect on the environment.

The major problem threatening the textile industry today is the environmental pollution, arising out of the wet processing of the textiles.

The production of synthetic dyes involves many violent reactions, which are conducted at high temperature and pressure, using much hazardous petroleum based primary chemicals as well as the production of hazardous intermediates.

It is high time that the over utilisation of synthetic dyestuffs should be thought about in the context of health of the people and environment. In this regard some European countries have introduced a ban on certain azo dyes, which have been found to be carcinogenic. Many more countries would follow this trend.

It is also note to realize that about 2/3 or more of all synthetic dyes are azo and many more of them may be enlisted as carcinogenic in time to come. In this scenario, the day that the importance of natural dyes as possible alternatives to at least some of the synthetic dyes would not be very far.

Further the recent realization that many intermediates and chemicals used in synthetic dyes are toxic and thus hazardous to human health as well as to the environment, has led to the revival of interest in the non-toxic, biodegradable and eco-friendly natural dyes.

On the other hand, many contemporary synthetic dyes have been derived from naturally occurring pigments such as indigo and alizarin.

The examination of their chemical structures illustrates fundamental resemblance except a few points. At the best, it can be said that the difference between natural and synthetic dyes is blurred, although there will be an argument that claims that a naturally occurring chemical, no matter how potentially dangerous, is more acceptable than a deliberately synthesised chemical.

The lower possibility of allergic reactions by the consumer to textile materials dyed with natural dyes together with its possibility of producing unique and fascinating colours which are not achievable with synthetic dyes are another two important factors for the revival of natural dye usage regardless of its high cost and other disadvantages.

The traditional robe dyeing procedure is an example of using natural dyes in ancient time. Following figure illustrates the traditional robe dyeing procedure practice in Sri Lanka.

To conclude, there is an urgent need for proper collection, documentation, assessment and characterization of dye yielding plants and their dyes, as well as research to

overcome the limitation of natural dyes. There is also a need for a collection of Small and Medium Entrepreneurs (SME's) coming together to carry this out and supports towards that movement.