Natural Dyeing of Cotton Fabric Using Terminalia Chebula and Turmeric Part-3

Textile Chemistry, SSM College of Engineering,
Komarapalayam, Namakkal, India.
Textile Chemistry, SSM College of Engineering,
Komarapalayam, Namakkal, India.

Previous Part

Most of the natural dyes have no substantively on cellulose or other textile fibers without the use of a mordant. The majority of natural dyes need a mordanting chemical (preferably metal salt or suitably coordinating complex forming agents) to create an affinity between the fibre and dye or the pigment molecules of natural dyes. Aluminium sulphate or other metallic mordant anchored to any fibre; chemically combine with certain mordant able functional groups present in the natural dyes and bound by coordinated/covalent bonds or hydrogen bonds and other interactional forces. Thus, for proper fixation of natural dyes on any textile fibre, mordanting is essential in most of the cases.
Natural Dyeing
Natural Dyeing
Natural dyes can be classified in a number of ways. The earliest classification was according to alphabetical order or according to the botanical names. Later, it was classified in various ways, e.g. on the basis of hue, chemical constitution, application class etc.
  • In “treatise on permanent colours” by Bancroft, natural dyes are classified into two groups: ‘Substantive Dyes’ such as indigo, turmeric etc. which dye the fibres directly and ‘Adjective Dyes’ such as logwood, madder etc. which are mordant with a metallic salt. 
  • Humme classify the colouring matter as ‘Monogenetic Dyes’, those produce only one colour irrespective of the mordant present on the fibre or applied along with the dye and ‘Polygenetic Dyes’, those produce different colour with different mordant applied, e.g., alizarin (Dedhia, 1998) 
  • In the colour index the natural dyes are classified according to the hue (Predominating colour).
  • The shades produced by natural dyes/colorants are usually soft, lustrous and soothing to the human eye. 
  • Natural dyestuff can produce a wide range of colours by mix and match system. A small variation in the dyeing technique or the use of different mordant with the same dye (polygenetic type natural dye) can shift the colours to a wide range or create totally new colours, which are not easily possible with synthetic dyestuffs. 
  • Natural dyestuffs produce rare colour ideas and are automatically harmonizing. 
  • Unlike non-renewable basic raw materials for synthetic dyes, the natural dyes are usually renewable, being agro-renewable/vegetable based and at the same time biodegradable. 
  • In some cases like hard a, indigo etc.,the waste in the process becomes an ideal fertilizer for use in agricultural fields. Therefore, no disposal problem of this natural waste. 
  • Many plants thrive on wastelands. Thus, wasteland utilization is an added merit of the natural dyes. Dyes like madder grow as host in tea gardens. So there is no additional cost or effort required to grow it. 
  • This is a labour intensive industry, thereby providing job opportunities for all those engaged in cultivation, extraction and application of these dyes on textile/food/leather etc. 
  • Application of natural dyes has potential to earn carbon credit by reducing consumption of fossil fuel (petroleum) based synthetic dyes. 
  • Some of its constituents are anti-allergens, hence prove safe for skin contact and are mostly non-hazardous to human health. 
  • Some of the natural dyes are enhanced with age, while synthetic dyes fade with time. 
  • Natural dyes bleed but do not stain other fabrics, turmeric being an exception. 
  • Natural dyes are usually moth proof and can replace synthetic dyes in kid’s garments and food-stuffs for safety. Despite these advantages, natural dyes do carry some inherent disadvantages, which are responsible for the decline of this ancient art of dyeing textiles.
  • It is difficult to reproduce shades by using natural dyes/colorants, as these agro products vary from one crop season to another crop season, place to place and species to species, maturity period etc. 
  • It is difficult to standardize a recipe for the use of natural dyes, as the natural dyeing process and its colour development depends not only on colour component but also on Materials. 
  • Natural dyeing requires skilled workmanship and is therefore expensive. Low colour yield of source natural dyes thus necessitates the use of more dyestuffs, larger dyeing time and excess cost for mordant and mordanting. 
  • Scientific backup of a large part of the science involved in natural dyeing is still need to be explored. 
  • Lack of availability of precise technical knowledge on extraction and dyeing techniques. 
  • The dyed textile may change colour when exposed to the sun, sweat and air. 
  • Nearly all-natural dyes with a few exceptions require the use of mordant to fix them on to the textile substrate. While dyeing, a substantial portion of the mordant remains unexhausted in the residual dye bath and may pose serious effluent disposal problem. 
  • With a few exceptions, most of the natural dyes are fugitive even when applied in conjunction with a mordant. Therefore, sometimes their colour fastness performance ratings are inadequate for modern textile usage. 
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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