Textile materials and clothing are known to be susceptible to microbial attack, as these provide large surface area and absorb moisture required for microbial growth. Natural fibers have protein (keratin) and cellulose, etc., which provide basic requirements such as moisture, oxygen, nutrients and temperature for bacterial growth and multiplication. This leads to objectionable odor, dermal infection, product deterioration, allergic responses and related diseases. This necessitates the development of clothing that could provide a desired antimicrobial effect. Antimicrobial treatment for textile materials is necessary to avoid cross infection by pathogenic microorganisms, control the infestation, arrest metabolism in microbes in order to reduce the formation odour and safeguard the textile products from staining, discolouration and quality deterioration.
Dyes are coloured molecules used widely as colourants, especially in textile industries. Today, however, practically all dyes in use are synthetic and are prepared from aromatic compounds. For industrial application, dyes used are such that they should be resistant to light, water, dilute acids, alkalis, organic solvents used in dry cleaning etc. these characteristics make dyes not only durable, but also recalcitrant. According to the chemical structure, dyes can be classified into azo, anthraquinone, triarylmethane, nitro, azoic, indigoid dyes etc. According to the application method, dyes can be classified into acid, basic, mordant, vat, reactive, disperse, metal complex dyes etc. out of these, azo dyes represent the most widely used class of dyes. They have azo bond linking two aromatic rings as chromophore, while common auxochromes are -NH2, -NR2 and -OH. These dyes are highly resistant to commonly used removal methods at effluent treatment plants. The presence of dyes in textile discharge raises aesthetic concerns due to the colour imparted by them. Secondly, many dyes or their cleavage products are known to be toxic or even carcinogenic and has created serious threat to public health and environment. Dye wastewater treatment still remains a topic of intense research for economically feasible way to tackle the problem.
Herbal technology circumscribes all the advancing technical frontiers (except genes) meant to tap myriads of modes of manipulating plants around us. A large number of technologies have been developed to harvest the bountiful products that the plants manufacture, including natural dyes, biopesticides, growth regulator as well as biofuel. The chemical, biological and medicinal properties of these plants were worked out only in the last three decades. The protective properties of natural dyes have been recognized only in the recent past. Many of the plants used for dye extraction are classified as medicinal, and some of these have recently been shown to possess remarkable antimicrobial activity. Several plant dyes are rich in naphthoquinones such as lawsone from henna, juglone from walnut and lapachol from alkannet are reported to exhibit antibacterial and antifungal activity.
Natural Dyes are the colors extracted from plants, insects & minerals (table). Natural Dyes along with natural fabrics are protective to skin. These can improve human body's aura along with the inhibition of the bacterial growth due to sweat and other reasons. In simple words to explain the beneficial aspects of the natural dye (most of them have medicinal properties) in comparison to any of the synthetic dyes, helps in removing the toxic effect of the human body sweat. However the synthetic dyes are in majority toxic in nature and increase the toxicity of the sweat manifold, which results in various kinds of allergies.
Curcumin, a common natural dye used for fabric and food colorations, was used as an antimicrobial finish due to its bactericidal properties on dyed textiles. Mushrooms are also used for dye production. The dyes produced from mushroom have antimicrobial properties working against human pathogenic bacteria, and fungi, hence these are natural and ecofriendly dyes. Monascus, a new source of natural dye used for wool dyeing and also has the antimicrobial activity. Lithospermum erythrorhizonIt can be used as a natural colour having an anti-inflammatory and calming effect too. From clover or Trifolium pratense one can obtain a natural colourant called pratol, which is a dull, golden yellow and have anti-bacterial property on fabric. There are a number of flavonoids that can be used from plant sources. Clover has been traditionally used for eczematous skin conditions, especially where the skin is pruritic. It is also useful for boils and pimples. Some of the natural finishing agents used for the colouration of the fabric also show antimicrobial activity e.g. clove oil shows the excellent anti-bacterial property on cotton fabric.
Although many of the plants used for dye extraction also show the medicinal properties and have recently been shown to possess remarkable antimicrobial activity. Dyes commonly used in textile are seldom screened for use as antimicrobial agents for textile finishing. Human beings are commonly exposed to the microbes in household or hospital environments. Common pathogenic bacteria are Escherichia coli, Bacillus subtilis, Klebsiella pneumoniae, Proteus vulgaris and Pseudomonas aeruginosa as per the ASTM (American Society for Testing and Materials Standards) specifications. The textiles dyed with the natural dyes can be very useful in developing clothing for infants, elderly and infirm people to protect them against common infections. They will be equally useful in bed linen, carpets and other home textiles, which are major propagators of common infections.
Table : Categories of Natural Dyes
Colors | Chemical | Classifications | Common Names
• Blue | Indigoid | Dyes | Indigo
• Brown and Purple-Grey | Naphthoquinone | Dyes | Henna, Walnut, Alkanet, Pitti
• Orange-Yellow | Chromene | Dyes | Kamala
• Neutrals | Vegetable | Tannins: gallotannins, ellagitannins and catechol tannins | Wattle, Myrobalan, Pomegranate, Sumach, Chestnut, Eucalyptus
• Purple and Black | Benzophyrone | Dyes | Logwood
• Red | Anthraquinone | Dyes | Lac, Cochineal, Madder (Majithro)
• Yellow | Iso-quinoline | Dyes | Barberry
• Yellow and Brown | Flavone | Dyes | Weld, Quercitron, Fustic, Osage, Chamomile, Tesu, Dolu, Marigold, Cutch
In conclusion, natural diversity can be exploited only through ecofriendly techniques for obtaining useful byproducts. In India we have diversify flora and fauna, which can be exploited to obtain various types of dyes for odorless and hygienic cloths.
About Author / Additional Info:
Dr. Rajni Singh, Additional Director in Amity Institute of Microbial Biotechnology, Noida, U.P., India. Working on formulation of microbial consortium for biodegradation of organic wastes, production & purification of enzymes, their molecular characterization, biological formation of nanoparticles.