Chapter II REVIEW OF LITERATURE

Transcription

1 Chapter II REVIEW OF LITERATURE

2 Chapter 11 REVIEW OF LITERATURE Extensive research on natural dyes in India and other countries during the last two decades have resulted accumulation of a large number of literatures. A comprehensive review of the literatures are presented here. 2.1 Silk and its importance Silk belongs to the group of animal fibres as it is produced by the silkworm. The silk fibre is made up of Fibroin and the silk gum called sericin. The two get hardened as it is secreted and comes in contact with air, thus, forming the basic fibre. The silk worm excretes silk fibre during chrysalis or pupal stage of its life cycle and builds around itself a nest with the silk fibre which is called cocoon. This is basically a protective mechanism for the silkworm. The raw silk fibre is obtained from the silk cocoon by cooking and subsequent reeling process. The raw silk, thus obtained, is then degummed to make it ready for weaving and knitting (Venugopal, 1991). Among the natural fibres, silk occupies a position of prestige (Chowdhury, 1984). Apart from beauty, it possess some extra ordinary qualities, including supreme comfort for the wearer, warmth during wearing without weight, high resistance to wear, strength combined with delicate appearance and insulating properties which keep the wearer warm in winter and cool in summer. It is the queen of fashion from the silk stocking to evening gowns to furnishing fabrics. Everyone is concerned by silk; every one desires silk; everyone has a need to dream about silk, confirmed customers and potential customers (Mouillard, 1988). For more than 4000 years, this luxurious, sensuous and romantic cloth, silk has reigned supreme as the queen of textiles. Even if the silk costs little more than the other textiles, the users always command a better price and silk has a greater value in the long run (Kanna, 1987).

3 Silk - the natural fibres has been an inseparable part of Indian culture and tradition over thousands of years. It is universally accepted as the queen of textiles. Silk has unique combination of properties like high tensile strength, pleasant to handle, excellent draping properties etc. which are not observed in any other fibre. Silk has never lost its luxury appeal and today it is being shown by all houses in their top fashion products (Grover and Gahlot, 2003). Gulrajani et al. (1993) reported that degumming of silk with alkaline solution result in weight loss. Weight loss increases with increase in ph and temperature. The observed weight loss may be due to the hydrolysis of sericin and its solubilization or due to the hydrolysis of fibroin. Mehra et al. (1998) stated that the effect of heat on silk is quite pronounced, it becomes pale yellow at 110 C in 15 min. At 165 C silk disintegrates rapidly. Another drawback of silk fibre is sensitivity to light. On exposure to ultraviolet radiation for 6 hours, raw losses 50 per cent of it s original strength. The silk takes dyes well and seems to have a depth of colour or jewel like tone, not found in the man-made fibres which look like silk (Mullick, 2002). 2.2 Cotton and its importance Cotton from the Arabic word, Qutun has been in use for 5000 years (Mishra, 2000). It is also known as white gold (Mahalingam, 2001) and King of fibres (Lyre, 2000). Cotton is the world s first major textile fibre, which has been used from the pre-historic days (Venkidusamy et al., 1999). According to Ramachandran (2001), cotton was found in India around five millennia years ago. In the 13th century, cotton was considered as material suitable for candle wicks only, then to bedding blankets along with flax, but now the use of cotton has increased triple fold. Cotton fibre is the most important natural vegetable fibre in use for textile purposes. Rebenfeld (2001) and Gokarneshan (2002) described cotton as the only natural cellulosic fibre used world-wide. Cotton has been of service to mankind for so long, that its versatility is almost unlimited (Bernel, 1997). World wide

4 12 production of cotton was 21 million tonnes in (Huber, 2002). Consumption of cotton was 20 million tonnes during 2001 (Narayanan, 2003). Murphy (2000) describes cotton as a fibre that is magnificently and intriguingly assembled by nature. It is a crystalline material, with a dynamic structure which can be readily altered. Cotton is one of the main agro-based cash crops, providing a means of livelihood for millions of people (Bajaj and Sharma, 1999). Cotton, the backbone of world s trade, is described as everyday textile fabric by Rathi et al. (1999). The beauty of cotton is that it is acceptable to all, modern and conservative, men and women from birth to death (Kothari, 2000; Lyer, 1997). Textile Committee in India (1993) reported that cotton fibres are obtained from the cotton plant which belongs to the genus Gossypium. According to Murphy (2000), cotton fibre is composed chiefly of cellulose which constitutes per cent. Bukaye (1984) views that different types of cotton are grown in various parts of the world, some of their basic characteristics differ owing to conditions such as soil, climate, fertilizer and pests. Cotton grows in subtropical climate. This genus comprises about 40 species of which only four are commercially cultivated. These are G. arboreum, G. herbaceum, G. hirsutum and G. barbademe. The first two are popularly known as Desi cotton or old world or Asiatic cotton, because of their origin in Asia. The other species are known as American/Egyptian or New World cotton. India is one of the world s largest reservoirs of cotton (Perhak et al., 1999). Cotton is cultivated in about 9 million hectares to get about 2771 million kg cotton. India produces approximately 160 lakh bales of cotton every year. In India, cotton constitutes 80 per cent of raw material for the textile industry and generates 30 per cent of foreign exchange. According to Narayanan et al. (2002), there is fall in cotton production in recent years. Gill (1999) and Lai and Lyer (2002) also remarked that deficiency in the quality of cotton hamper the healthy growth of the industry. Hence there is consideration to increase the production of high grade cotton in the 10th plan.

5 13 Cotton is the whitest and cleanest natural fibre, with many useful physical and chemical properties (Miller, 1995). Lyle (1982) is of the view that cotton looks like a flat, twisted ribbon. The twists give the fibre an uneven surface. It is more elastic than linen but less elastic than silk and wool. Gaur (1994) says that cotton is a strong, short and fine textile fibre. Length of cotton fibre ranges from 3 mm to 6.5 cm and yarns are of shorter staple are more apt to the linty and fuzzy than those of long staple (Wingate, 1988). According to Mishra (2000) cotton has a staple length of 1 cm to 8 cm, thickness of 3.5 microns to 10 microns, ribbon width of 12 microns to 25 microns, surface area of dry -0.6 to 0.7 sq.m./gm; wet sq.m./gm and density of 1.54 gm/cc. Lyle (1982) remarks that colour of cotton is ordinarily white sometimes it is cream coloured or brown and has very little lustre. Cotton s ability to absorb moisture and perspiration from the human body makes it comfortable to wear. This unique property is not yet been matched by synthetic substitutes and hence it accounts for half of the world market of textile fibre( Munro, 1987). Cotton has natural impurities like pectin, protein, wax and minerals (Alat, 2001). Mayekar (2002) list the properties of cotton as biodegradable, breathable, drapable, insulating and non-allergenic. Joseph (1984) is of the view that cotton is highly resistant to alkalis in fact they are used in finishing and processing the fibre. Strong acids and microorganisms destroy cotton and hot dilute acids will cause disintegration. Cotton is highly resistant to most organic solvents. King (1985) says that the chemical properties of cotton makes vulnerable to acids, yet tolerant to mild alkalis. All bleaches can be safely used on cotton. Cotton has low lustre unless mercerized or resin finished. Generally mercerized cotton fibre under the microscope appears smooth and cylindrical in structure (Gohl and Vilensky, 1983). Tera et al. (1997) remark that cotton is relatively easy to dye and print. Cotton is resistant to moths, yet attacked by mildew. According to Inglesby (2002), cotton has unique combination of properties like durability, low cost, easy washability, dyeability and comfort characteristics.

6 Dyeing of fibres Natural Dyes Natural dyes are described as colorants derived from plant, mineral and animal sources which requires very little chemical processing (Subramanium et al 1997; and Tortora,1982). Dessari (1993), Paul and Pardesh (2001) describe natural dyes as special elements, re- emphasizing nature, environment- friendliness and nonhazardous products. According to Casselman (2002) natural dyes are popular for textile tourism with ramification in global economy. Darwekar et al. (1999) and Akkewar (1999) are of the view that natural dyes are safe dyes, because they do not produce any undesired by- products and at the same time they help in regenerating the environment. Gupta (1999) and Singhal (1997) view that natural dyes are free from sulphur and azo groups. According to Intarachote (1993), natural dyes comprise all those that are obtained from animal, mineral and vegetable matter with no or very little chemical processings. Vatsala and Murugappa (1999) describe natural dyes as biological edible colour, present in plant kingdom. Natural dyes can be obtained from tissue or cell culture technology. Bin (2002), describes natural dyes as biological, traditional and pragmatic dyes. Secrangarajan (1999), Ansari and Thakur (2000) remark natural dyeing as an agro- based rural industry involving activities like cultivation of vegetable dye material, collection and extraction of dyes. Ansari et al. (1999) stated that there are more than 500 varieties of plants yielding natural colours. According to Tiwari and Vankar (2001), every plant will yield some short of colour, either from its root, stem, leave, flower, fruit, seed or wood. Natural dye stuffs have their starting material from flowers, petals, leaves, stems, roots, barks, lichens, mushrooms, dried insects or fresh shell-fishes, kitchen garden or plants along road sides or at construction sites (Kadolph, 2002). According to Namrita (1999) natural dyeing provides opportunity to exploit the forest wealth and identify the various resources.

7 15 Gulrajani and Maulik (2002) points out that most of the importers of textile products are interested in natural dyed products. Swetti (2002) is of the view that natural dyes produce colours unmatched in the knitting world. Ghorpade et al. (2000) and Farooqi (1993) indicated the future of natural dyes as based on competitive costs, simplified procedures and uniform results. The requirements of natural dyes as quoted by Gulrajani et al. (1999) is about 10,000 tones which is equivalent to 1 per cent of world synthetic dye consumption. To replace 1 per cent use of synthetic dyes, a total area of 0.02 per cent land should be used world wide for natural dye cultivation History of natural dyes According to Corbman (1983) primitive people obtained dyes from flowers, nuts, berries and other forms of vegetable and plant materials, as well as from mineral and animal sources. These sources have provided such natural dyes throughout civilization. Senthilkumar et al. (2002) found that the art of dyeing dates back to time immemorial. It was known in India as early as Indus Valley period (3500 BC). In Egypt, indigo dyeing and pomegranate dyeing were used as early as 2500 BC. History of biblical times speaks of materials dyed sky blue, purple and scarlet. Pomegranate was used in Egypt as early as 2000 BC. Henna was said to have been used even before 2500 BC. The list of such dyes is endless. Kernes was the first of the red dyes used by primitive man (Singh, 2000). According to Agarwala and Patel (2000), the practice of applying colour through dyeing and printing techniques has played a significant role in every civilization. Earlier dyestuffs were derived from natural resources, viz. plants, animals and minerals without any chemical processing. Vegetable dyes have been used for thousands of years by mankind. Natural dyes have been an integral part of human life since time immemorial. Egyptian mummies, documents of mughal

8 16 periods, etc. bear a testimony to the utilization of these dyes. In India, Rajasthan and Kutch still possess a rich tradition in the use of natural dyes for textile dyeing and printing. Dyestuff and dyeing are as old as textile themselves and predate written history. Fabrics dates from 3500 B.C. have been found in thebes that still possess the remains of blue indigo dye. Other fabrics, discovered in the ancient tombs of Egypt, were coloured yellow with dye obtained from the safflower plant. Beautiful colour fabrics dating back several thousand years have been unearthed in China, Asia, minor and sections of Europe (Joseph, 1976). It is believed that dyeing was practised as early as 3500 BC. in China, From the painting on the wall of tombs it can be inferred that as early as 3000 B.C.. the Egyptians were making colour mates which they hung on their walls. By about 1450 B.C., the Egyptians were making textile materials of astonishingly delicate structure and were able to dye them in whole range of different colours. Until the middle of the last century, all dyes were obtained from natural sources. Indigo extracted from the plant Indigofera tinctoria and Alzarin obtained from root of madder have been used in India since the beginning of recorded history (Trotman, 1975). Dyestuffs are evaluated in terms of their colour fastness to a variety of environmental situations. Dyed fabrics may be colourfast to one or two situations but not to all, like laundering with water, detergent, dry-cleaning, wet and dry crocking and sunlight. It is necessary to have all these properties in the same fabric, rather only those which are necessary for the end use of the product (Gulrajani et al., 1993). Early efforts of colouring fabrics were hampered by the fact that few of the natural dyes formed fast colour combination with fibres. Eventually it was found that this defect could be partially overcome by the use of mordants that render the dye insoluble ion the fibre (Joseph, 1984).

9 17 The frescoes of Ajanta, dated 1st century A.D. were painted with natural dyes. Records belonging to the prehistoric Muslim periods were written and illustrated with natural dyes (Goswami, 1988). Natural dyes have been a part and parcel of man s life since time immemorial (Paul and Pardesh, 2000). The first fibre dyes were used in pre-historic times after the last ice age around 1000 B.C. This consisted of fugitive stains from berries, blossoms, barks and roots, points out Gulrajani (1993). According to Casselman (2002), some of the natural dyes were used even during the Bronze Age. Dyeing using natural dyes from plants was a craft practised in Philippines before the influence of the Western civilization in 1500 B.C. Aung (1993) remarks that the robe of Buddhist monks were dyed with the wood o f jack which produced a yellow dye. India s contribution to the field of natural dye has been a long tradition (Kapila, 1999). Aquirre (1993) remarks that the relics of natural dye from the excavations of Harrapan culture serves as evidence of ropes and fabrics dyed with natural dyes. Kumaramangalam (1993), points out that the Moghul period illustrations form ample proof for the indignity of the traditional natural dyes. Venkataswamy (1993) indicated the use of natural dyes in civilization of Mohenjodaro. The use of natural dyes on the caves of Ajanta, dating back to the first century B.C. Miralbes (1993) says that till the last 500 years the use of natural dyes was common. But most of them are unidentified says Salice (2002). Kharbade (1993) points out that the use of natural dyes until the middle of the 19th century was of plant and animal origin belonging to categories of natural products like flavonoids, tannins, terpenoids, quinones and alkaloids. Today the application of natural dyes is gaining popularity, due to German Ban on some of the synthetic azo dyes which are carcinogenic or allergic arylamines (Gianfranco et al., 2002). Gupta (1999) and Pan et al. (2001) remark that natural dyes are unique in the world of fashion and textiles.

10 C lassification and properties of natural dyes Senthilkumar et al. (2002) and Singh (2000) preferred to classify natural dyes into three major groups based on affinity, structure and applications of the dyes. Singh (2000) has given the following classification : I. Classification of natural dyes (affinity based) r (i) Substantive (need no mordant) Indigo, turmeric, orchil, etc. (ii) Adjective (need a mordant) Madder, logwood, cochineal, keremes, fastic etc. (most of the natural dyes) II. Classification of natural dyes ( structure based) (i) (ii) Anthra- (iii) Alpha- (iv) (v) Dihydro- (vi) Antho- (vii) Carote (viii) Poly- Indigenous quinones naptha Flavones pyrans Long cyanidins noids hydric (Blue and (Most of the quinones (Most of the wood, brazil Bigonia, Varrots, phenols purple dyes) important Henna, yellow dyes) wood, etc. chica, Sindur, (Tannins) indigo, red dyes) Walnut, etc. Weld, awobanin, Kesar, etc. (Brown, wood, Madder, lac, Kumkum, etc. Grey and tyrian, cochineal, tesu, onion, black dyes purple, etc. kermes, etc. etc. myrobalan Pomegranat e, etc. III. Classification of natural dyes ( application based) (i) Mordant (ii) Direct dyes (iii) Acid dye (iv) Basic dyes (v) Vat dyes (vi) Disperse dyes (Most of (Many of the saffron, etc. Berberine, etc. Indigo, wood, dyes Henna, the natural natural dyes) tyrian purple, etc. dyes) Madder, turmeric, harar, etc. log wood, pomegranate, cochineal, etc. annatto, safflower, etc. According to Agarwala and Patel (2000), natural dyes can be classified in various ways. The earlier classification was according to alphabetical arrangement of dyes. Later on, numerous other methods of classification were adopted, which are :

11 19 Classification based on chemical structure Classification based on their origin of the sources from which they are obtained. Classification based on their methods of application Classification based on their colour. The natural organic dyes and pigments, constitute a wide range of chemical classes such as indigoids, anthraquinoids, naphthaquinones, polymethines, ketones, imines, quinones, flavones, flavonoids, flavonones and chlorophyll. Some of the important chemical classes are represented in Table 2.1. Depending on the origin of sources from where they are produced, the natural dyes can be grouped into three distinct classes based on the dyes derived from vegetable resources, insects as well as animal and mineral resources. Natural dyes can be grouped into different classes based on chemical structures, botanical names, colour index and hues (Paul and Pardesh, 2000). Sekar (1999) quotes the classification of Bancroft given in his Treaties of permanent colours as substantive and adjective dyes, direct and mordant dyes and monogenetic and polygenetic dyes. Substantive dyes need no pretreatment to the fabric, but adjective dyes can dye the fabric which are mordanted with metallic salts or with the addition of metallic salt to the dye bath. Kannan and Gayathri (1996) divide substantive dyes as : Direct (for cotton e.g. : turmeric, sunflower and myrobalan), Acid (for silk and wool, e.g.: saffron) and basic (for silk and wool, e.g.. Berberine). Mishra et al. (2001), names substantive and adjective dyes as non- mordant dyes and mordant dyes. Gupta et al. (1998) classified natural dyes based upon the mordants used. The monogenetic type of dyes produce only one colour irrespective of the mordant applied along with the dye present on the fibre whereas the polygenetic dyes produce different colours according to the mordant employed. Jacob (1999) and Secrangarajan (1999) classify natural dyes as natural organic dyes and mineral inorganic dyes. Nalankilli (1997) classifies natural dyes based on chemical nature as : Diaryol methane (turmeric), carotenoid (saffron, harsingher, Indian mahogany,

12 Table 2.1. Important chemical classes of natural dyes Chemical class Natural dyes source Substrate Colour produced Indigoids Indigo (Indigofera tinctoria) Cotton, wool, silk Blue Wood (Isatis tinctoria) Cotton, wool, silk Blue Tyrian purple (Purple hoemastroma/murex brandaris) Cotton, wool, silk Blue purple/reddish purple Anthraquinones Maddar (Riiba cordifolia) Wool and silk Pink, red, crimson orange, brown and maroon* Manjith (Rubia cordifolia) Lac (Luccifer lacca) Wool, silk Red, scarlet, crimson and brown* Kermes (Kermer vermillo) Wool Red and purple* Cochineal (Coccus cacti) Wool, silk, cotton Crimson, scarlet and (printing) pink Alphanaphthaqui nones Henna or lowsome (Lowsomia inermis) Wool and silk Yellow to brown Juglone (Juglans regia) Wool and silk Brown Flavones Weld (Reseda luteola) Wool, silk and Yellow, orange and Dihydropyrans Logwood (compeachy wood - Haematoxylin campechianum) Brazil wood (red wood species, Caesalpinia echinate) Sappan wood (red wood species, Caesalpinia sappan) cotton Wool, silk, cotton and leather Wool, silk and cotton olive Black Crimson, black and purple* Anthocyanins Carajurin (leaves of Bigonia chica) Cotton, silk Orange Acobanin (flowers of Tsuykusa cammellia communis) Silk Blue Carotenoids Annatto (Bixa orelluna) Wool and silk Yellow and orange Saffron (Crocus sativus) Wool and silk Yellow and orange * Indicate different colours with different mordants

13 21 annatto), alkaloids (barberry), quinonoid (dol, henna), flavonoid (french, marigold, jackfruit, flame of forest, kamela, kaiphal, onion, hemp yellow larn spur, sandal) benzoquinone (sunflower) and anthraquinone (manjit, chay root, airoor, moyam, patrang). Shanghir (2002) says that natural dyes can be applied in the yam stage, or on the loom stage or at the post loom stage, depending upon the end products. Natural dyes produce depth and complexity of colours (Urbanek, 2002). According to Dedhia (1998) and Mohanty (1997) natural dyes are non- allergic and non- toxic. Natural dyes yield lustre, rich colour, aromatic smell, light shades and bring smoothing effect to human eyes, says Mukherjee (1999). Mohanty et al. (1997) and Vankar et al. (2000) remark that natural dyes can produce rare colours and gives scope to generate unlimited shades. Rathi et al. (1999) states that the use of natural dyes amongst craftsmen is increasing due to its unique characteristics to produce individuality in colour and shade. Designers of modern days create novel apparel using naturally dyed fabrics. Denton and Brown (2002) used multi-layers of natural dyed materials to produce complex art cloth. The natural dye art is still seen on Kalamkari works (Humayun, 1993). Natural dyes are an important ingredient for handloom industry and handloom products dyed with natural dyes are widely marketed (Aquirre, 1993; Gopal, 1999; Miralbes, 1993). Paige (2002) strongly advocates that all hand made crafts can be developed as value added products by using ecofriendly natural resources and natural dyes. According to Wirtz (2002) natural dyes can make an interesting and exciting alternative for water based point on paper. Natural dyes are known for-their medicinal values also as some of them shows antibacterial, insecticidal (Casselman, 2002; Seong-it Ecom and Kyu Bong Rhu, 1999) Environmental aspects of natural dyes Naturally dyed textiles are one of the most sought after, environmental friendly products (Meyer, 2002). Natural dyes are obtained from renewable resources

14 22 and prevent environment pollution and do not release harmful amines which irritate the skin (Vankar et ah, 2001; Gharia, 1999). According to Dayal and Dobhal (1999) and Bhattacharya (1971) natural dyes provide an opportunity to explore natural resources occurring in abundance Fastness properties of natural dyes Colour fastness to one of the major factors affecting the selection of any fabric (Mahale et ah, 2002). Colour fastness of a coloured textile is defined as its resistance to changes when subjected to a particular set of conditions. Colour fastness must be specified in terms of these changes and expressed in terms of their magnitude (Gupta et ah, 1998). AATCC (1995) defines colour fastness as the resistance of a material to change in colour characteristics, transfer its colourant(s) to adjacent materials or both, as a result of an exposure of the material to any environment that might be encountered during the processing, testing, storage or use of the material. According to Saito et ah (1988), the various environmental factors controlling, the colour fading of dyes are light, oxygen, water and heat. Colour fastness of textile materials is of considerable importance to the consumers. The fastness depends not only upon the nature and depth of shade of the dyestuff used but also upon the nature of the fibre and the method of dyeing or printing employed; the same colouring matter, when used in dyeing Ur printing different fibres or when applied by different methods upon the same fibre, may give vastly different results. Colour fastness means the resistance of the colour of textiles to different agencies such as washing, sunlight, perspiration, crocking etc. to which textiles may be exposed during manufacture and subsequent use. According to Agarwal and Patel (2000), generally most fabrics dyed with natural dyes do not posses excellent fastness properties as exhibited by present day natural dyes. Although mordanting and after treatment improved fastness, the

15 23 intrinsic susceptibility of the chromophore of the natural colouring matters to photochemical degradation resulted in low fastness to washing and light. However Sekar (1999) realized that light fastness is a complicated phenomenon and can not be related to the invariable effect of subsitituent groups in a dye molecule. Several other factor which effect the fastness to light of natural dyed materials are : Chemical structure of the colourant. Concentration of the dyestuff. Nature of fibre. Nature of incident light. Composition of surrounding atmosphere. Effect of mordants. Presence of foreign materials. The poor washing fastness of many natural dyes is mainly due to- Weak dye-fibre bond between natural dyes and fibre Change in hue due to the breaking of the metal complex during washing and Ionization of natural dyes during alkaline washing. Yellow dye Vegetable yellow dyes generally have low line torial value and the shades are pale. Hence, their fading is quicker which is also greatly influenced by the mordant f used during their application. Aluminium and tin mordants cause more light fading than chrome, iron or copper mordants as in the case of onion tesu and others. Flavonoids constitute a major class of yellow natural dyes. The basic flavonoids chromophore is susceptible to photochemical attack and probably leads

16 24 to the formation of quinones. Due to this reasons, the yellow colour becomes a dull brown as commonly seen in the old museum textiles. The nature and position of the subsitituent group on the chromophore as well as their number also affect the intensity and light fastness. For example, flavonic pigments presents in weld, sandal wood and plumes exhibit a light fastness rating much higher than flavonol pigments, such as those present in quercitron, Persian berries and onion skin. This is due to highly photosensitive hydroxyl group in position 3 present in flavonic pigments. Turmeric is the most brilliant natural dye available to date. Despite being fugitive to light, it continues to be used for its brilliance. Berberis is a basic dyes and being fugitive to light exhibit a light fastness grade of 1. In this case, the ammonium group, which impart the basic dyeing property is probably responsible for the photosensitivity, which is further increased by fluorescence. Anthraquinoid based yellow and orange mordants dyes, such as rhubarb, manjith, morinda, madder, chayroot etc. exhibit very good fastness to light. These colours are quite resistant to photofading due to the presence of anthraquinone chromophore which in intrinsically fast to light fading. The wash fastness properties of yellow dyes range from fair to excellent. Brown dye Browns dyes are generally quinone based dyes. Napthaquinones have only moderate fastness. While anthraquinones based browns have excellent fastness due to the stability of dye chromophore-copper and iron salts, sometimes referred to as saddening agent since they tend to turn the colours to dull and deep shades, particularly browns. Both these mordants enhance the light fastness of dyes. Some yellow dyes, viz., dolu give deep rich browns when mordanted with copper salts. Tannins combine with ferrous salts to form complexes which give a range of greybrown shades.

17 25 Red dye : Natural red dyes are commonly based on anthraquinone and its derivatives. The light stability of this chromophore has been well established in synthetic dyes. It has also been observed with synthetic anthraquinone that the nature of substrate and substituents have little effect on their fastness to light. Blue : Blue colours is obtained only from indigo. An unusual facet of the photochemical behaviour of indigo is the fact that its light fastness on protein fibre is generally much higher that cellulose fibre. The indigoid chromophore which is resistant to photo reduction shows high fastness on protein fibre. It also exhibit excellent fastness to washing Limitation of natural dyes Natural dying is laborious, costly and time consuming process without proper dyeing procedural standards (Vankar et al., 2001). According to Gulrajani (2001) and Sumant (1999), the major disadvantages of natural dyes are lack of standardization and inadequate degree of fixation. Agarwal (1999) and Paul et al. (1996) describe natural dyes as dyes which can not produce wide range, brilliance of shades and fastness in colour. They lack reproducibility. Teli et al. (2000) and Sewekov (1998) list the limitations of natural dyes as, non- availability, complexity of dying process, non- reproducibility of shade, limited number of suitable dyes, great difficulty in blending dyes and water pollution by having metal mordants. Natural dyes deteriorate because of exposure to light, air and extreme temperature resulting in fading, or darkeing hues (Khanna, 1993; Vankar, 2002). One of the major criticisms of natural dyes is that large amount of plant material is needed and thus the corresponding amount of land that would be removed from food production or may result in deforestation because of harvesting of dyeyielding wild plants (Vijayakumar and Krishnakumar, 1999).

18 Mordants, their classification, function and application Mordants are the substances capable of binding a dye to a textile fibre (Nalankilli, 1997). Natural dyes require chemical in the from of metal salts to produce an affinity between the fibre and the pigments : such chemicals are known as mordants. The word mordanting has been derived from Latin word modere which means to bite the surface of fibre so that the dye can sink in. It forms a link between dye and fibre which otherwise has no affinity. It forms with dye a complex, which is insoluble in water and thus gives a fast colour. The main objective of the mordant is to open up the pores and renders the fibres more suitable for the entrance and penetration of the colouring matter, there by helping in the fixation of dyestuffs on the substrate in case of objective dyes. However the mordants can also be used in case of dyes which are capable of being applied directly, where they form an insoluble compound with the dyestuff within the fibre itself, there by improving the fastness properties of the dyed material (Gohl and Vilensky, 1983; Gupta et al., 1998; Singh, 2000; Senthilkumar et al., 2002). Generally, there are three types of mordants viz, metal salt or metallic mordants, tannins and tannic acid and oil mordants (Gupta et al., 1998; Singh, 2000 and Agarwal and Patel, 2000). Originally only naturally occurring metal salts were used as mordants. Now a days metal salts of aluminium, iron, copper and tin are used. Some of the common mordants are alum, potassium dichromate, ferrous sulphate, copper sulphate, stannous chloride and stannic chloride. Tannins are primarily used in the preservation of leather. They are also used in glues, stains and mordants. Vegetable tannins are bitter and astringent substances in plants, often occurring as excretion in the bark and other parts (especially leaves, fruits and galls). For tanning purpose, the extractions are either employed directly or used in concentrated form. A number of tanning containing

19 27 substances are employed as mordants in the dyeing of textiles fibre. Some of these are used on account of their lower price as a substitute for tannic acid in mordanting. Among the tannins myrobalans and sumach are most important. Oil mordants are used mainly in the dyeing of Turkey red colour from madder. The main function of the oil mordant in form a complex with alum used as the main mordant. Since alum is soluble in water and does not have affinity for cotton, it is easily washed out from the treated fabric. The naturally occurring oils contain fatty acid such as palmitic, stearic, oleic, ricinoleic etc. and their glycerides. The -COOH groups of fatty acids react with metal salts and get converted into - COOM, where M denotes the metal. It was found that the treatment of oils with concentrated sulphuric acid produces sulphonated oils which possess better metal binding capacity than the natural oils due to introduction of sulphonic acid group, - S03H. The sulphonic acid can react with metal salts to produce -SOv The bound metal can then from a complex with the mordant dye such as madder to give Turkey red colour of superior fastness and hue. Agarwal and Patel (2000) also mentioned that most of the natural dyes are capable of forming metal complexes and there by produce different shades (hues). However, some restrictions have been put by the famous German ban to the use of metal salts. The maximum permissible amounts of different metals in the final products are As (1 ppm), Cd (2 ppm), Co (4 ppm), Cr (2 ppm), Pb (1 ppm), Cu (50 ppm), Ni (4 ppm), Zn (20 ppm). However, the upper limit of the presence of metals is variable for different products and it also depends invariable on the eco-standard chosen. Fortunately, there is no upper limit on aluminium, iron and tin and that on copper is fairly high. So, these salts can be safely used for complexing and mordanting. Egyptian history dated in the first century A.D. records a method by which white cloth was smeared with a series of colourless Drugs and then plunged the whole in to boiling dye bath, producing multicoloured cloth. The variation in hue,

20 28 varied on where each drug has been placed and the type of drug used (Nalankilli, 1997). This technique was later called as mordanting. In the eighteenth century iron mordants were commonly used for fixation of colours like blue, green and violet and alum mordants for red colour, reveal Mohanty et al. (1997). Today the most effective ones are alum, copper, chrome, iron and tin. Copper and chrome are considered unsafe (Teli et al., 2001; Gulrajani etal., 1999). Alum, harda (commercial vegetable mordant) and babool (anar) are the most eco-friendly natural mordants. In olden days urine, saliva, egg-albumin and tannins were widely used (Venugopal, 1993) Application of mordant on silk Suneetha and Mahale (2003) used alum, potassium dichromate, copper sulphate, ferrous sulphate for their study on dyeing of silk with natural dyes. Potash alum, potassium dichromate, copper sulphate and ferrous sulphate shows excellent colour fastness for parthenium dyed silk yarn. The chemicals commonly used for fixing colour on silk fabrics were copper sulphate, Ferrous sulphate, potassium dichromate and a combination of the two mordants stannous chloride and magnesium chloride (Radhika and Jacob, 1999). Silk is highly receptive towards natural dyes and mordants. On account of its amphoteric nature it can absorb acids and bases with equal effectiveness. However silk does not have thiol groups (-SH) of cool (present in cystine amino acid), which act as a reducing agent and reduce haxavalent chromium or potassium dichromate to trivalent form. The trivalent chromium forms a complex with the fibre and the dye. Hence, potassium dichromate cannot be effectively used as a mordant for silk. Stannic chloride in the most important mordant for mordanting of silk, which is also weighed by it, resulting in lowering of strength. Iron salts are also often used both for mordanting and weighting of silk, which give excellent black colours on tannic acid treated silk (Singh, 2000).

21 Application of mordant on cotton Cotton fibre has very low affinity for most of the natural dyes and can loosely hold metallic mordant. Hence these mordant have to be precipitated on the cotton fabrics by converting them into insoluble form, or by first treating the cotton fabrics with tannic acid, subsequently impregnating the treated fabrics with the solution of a mordant. The metallic mordant is then held on cotton fibres via oil or tannic acid (Singh, 2000; Agarwal and Patel, 2000; Devi et al., 2002). A variety of mordants are used in the process of dying of cotton fibres. The commonly used ones are - copper sulphate, potassium dichromate, ferrous sulphate, cobalt sulphate and alum (Kalyani and Jacob, 1998; Saxena et al., 1997; Paul et al., 2003, Devi et al., 2002). Treatment of the fabrics with tannic acid before mordanting is a common practice to get the desired results from natural dyes (Saxena et al., 1997). Pretreatment of cotton yarn Pretreatment of cotton fibre with extract of myrobalan fruit before dying is an excellent method for dying cotton fabrics with natural dyes. Myrobalan treated fabric has more affinity to dyes and imparts better fastness properties to the treated fabrics (Senthilkumar et al., 2002; Kalyani and Jacob, 1998; Radhika and Jacob, 1999; Paul et al., 2003). Extract of myrobalan makes pores on the surface of cotton fibres and the dye is easily fixed in the pores (Senthilkumar et al., 2002; Devi et al., 2002) Mechanism of mordant dyeing with different methods of mordanting There are mainly three methods of application of mordant dyes to the textile materials namely pre - mordanting, simultaneous mordanting and'-post mordanting. Pre mordanting method is the oldest method among the three methods of mordanting involving two stages, In the first stage, the mordant is applied to the textile material and in the second stage, the mordanted material is treated in the dye liquor. The mordant is applied to textile material by boiling it in the aqueous solution

22 30 containing the mordant and an acid for about three quarters of an hour to one hour. Then the mordanted textile is transferred to aqueous solution of the mordant dye and boiled for an hour to one and half hours in order to obtain a level of dying and achieve adequate exhaustion of the dye. During this stage, the dye molecule attaches itself to the mordant which is already in the fibre polymer system and form complexes which are called lakes. The dye is thought to be held in the fibre polymer system by forming a link with the mordant which has formed a link with the fibre polymer. This complex formed within the fibre polymer is large and provides dyeing with good washing fastness which is due to the presence of Vander wall s forces. The latter binds the larger molecules and the presence of hydrogen bonds within the polymer system prevents the removal of the dye molecules during laundering. This method gives the most results and is suitable for dyeing light and medium shades. Simultaneous mordanting method, also known as stuffing, is one stage process in which the dye and the mordant are applied to the fibre at the same time in the same bath. In this method, the mordant and dye can form the complex in the dye liquor itself before entries the polymer system of the fibre. To minimize the formation of this complex in the dye liquor, firstly, the mordant dye is added and the textile material is treated in this dye liquor and the temperature is raised to 50 C. At this point the mordant is added and the temperature is slowly raised to 100 C in about 45 minutes and dyeing is continued at the boiling point for one hour. The method of attachment of the dye to fibre is the same as that for the pre mordanting method. Since, it is a single bath process, the simultaneous mordanting method is very simple to apply. The colour produced are usually bright but not always fast. Post mordanting method known as saddening, involves a two stage process which is the reverse of the pre mordanting method. As the name implies, the post mordanting method first involves the application of the dye on textile material followed by the treatment with the mordant. In the first stage, the textile material is treated in the aqueous solution containing dye and sodium sulphate by raising the temperature of the bath to the boil where it is kept for an hour. At this

23 31 stage, only penetration of the dye molecules in to the fibre polymer system takes place and no lake is formed. Subsequently, in the second stage, the mordant is added either in the completely exhausted dye bath or the dyed material is treated in a separate mordant bath with temperature maintained at boil for another 45 minutes to an hour. This results in the formation of the dye complex or lake within the fibre polymer system and hence fixing the dye. The mode of attachment of the dye to the fibre is same as that for the pre mordanting method (Gohl and Vilensky, 1983, Shenai, 1995). Senthilkumar et al. (2002) tried four different methods viz. alkali, acid, aqueous and alcoholic method for extraction of the dye and pre, simultaneous and post mordanting methods for mordanting with alum, chrome, copper sulphate and stannous chloride. They found that dyeing of cotton fabric with cabbage leaves gave uniform and good shades under different mordanting techniques. Devi et al. (2002) found that annatto produces very bright orange shades on cotton. The important parameters for dyeing with annatto on cotton were alkali concentration, dye material concentration and dye extraction time. By observing the fastness properties of mordanted annatto dyed cottons they observed that the dye was having moderate fastness properties. Copper sulphate mordanted cotton had good colour fastness in terms of washing, crocking and light Application of natural dyes on different fibres Natural dyes for cellulosic fibres Bhattacharya (1996) investigated dyeing of cotton fabric with the naturally occurring dyestuff Katha (Acacia catechu) which has been done in an automatic jigger. The resulting brown fabrics, when assessed for colour strength, wash fastness, acidic and alkaline perspiration fastness and light and rubbing fastness found that it was good with respect to the ISO standards. A study on printing of cotton fabric with Manjishta was carried out by Goel and Chauhan (1996). The fabric was printed with mordant and thickener paste. It was observed that best results were obtained

24 32 when dye material was immersed in water and strained. Pre-mordanting method was best. The washing fastness was determined by ordinary method and revealed that washing made colour faster and brighter. Saxena et al. (1997) standardized the method of application of lac dye on cotton using chitosan (a naturally occurring polymer) pretreatment. Alum, ferrous sulphate and tannic acid were used as mordants. The dyed fabric had medium light fastness, good rubbing and perspiration fastness but poor wash fastness. Dyeing of jute fibres with natural dyes was investigated by Bhattacharya et al. (1998). Bleached jute fibres were dyed with Acacia catechu, Ornosmas echiodes, Indigofer a tinctoria, Artocarpus integrifolia, Adenanthera pavonina, Rubia cardiofolia, Terminilia chebula, etc. The dyeing procedure was standardized without using any mordant except in the case of Rubia cardifolia, where aluminium sulphate was used, while in the case of Artocarphus integrifolia copper sulphate and potassium dichromate were used in small amounts. The fastness properties viz. light, water and perspiration were found to be good. Kalyani and Jacob (1998), studied the tapping dye from gulmohor for cotton. Out of four methods of extraction tested, i. e. aqueous, alkaline, acidic and alcoholic, aqueous and alkaline methods gave best results. Copper sulphate, potassium dichromate, ferrous sulphate, cobalt sulphate were used to get colours like olive green, green, brownish black and biscuit. Samples have fair to excellent fastness to dry rubbing. Wet rubbing exhibited poor to good fastness. Samples exhibited poor to good washing fastness. To alkaline perspiration test, the samples showed poor to excellent and good to excellent fastness was shown with acidic perspiration. Sunlight fastness show poor to fair fastness after 40 h of exposure. Kumar and Bharti (1998) investigated dye obtained from Eucalyptus plant. Aqueous extract of the hybrid Eucalyptus bark yield bright brown dye and light fastness on cotton. The wash and light fastness can be increased by the use of metal salts or tannic acid. A wide range of shades were obtained by the use of metal salts as mordants. From the study of Padmaja and Jacob (1998), dyeing with red hibiscus

25 33 flowers and its performance on cotton, it was observed that acidic media of dye extraction was found to be the best and among the three mordanting methods, post mordanting method gave best result. Biscuit colour had good fastness to rubbing, showed fair to poor fastness to colour change, good resistance to colour staining during washing and good fastness to both acidic and alkaline perspiration. Sunlight fastness was also found to be good. Dyeing with African marigold on cotton was studied by Prabhu and Raja (1998). In the slightly acidic media it gave dull yellow colour on cotton. The cotton dyed in this condition showed poor fastness properties. A noticeable change was that, during the washing fastness determining test of the sample, first the colour of the fabric intensified to slightly greenish yellow and there after the colour striped from the fabric. In the slightly alkaline media, a deep yellow coloured fabric was produced with moderate fastness properties. Bisht and Goel (1999) studied dyeing of natural fiber- Bhimal with natural dye- Kilmora. General appearance, lustre and evenness of colour was found better for unbleached Bhimal fibres mordanted with chemical mordant. For bleached samples general appearance had mixed results for natural and chemical mordanted dyed samples, for visual inspection on lustre and evenness of colour, alum mordanted samples were best rated. The light fastness ratings were best for pomegranate and katha mordanted samples, while the washing and staining fastness were best rated for the dyed samples mordanted with chrome and alum Mesta calyx dye produces different colours on cotton fabrics such as pink, pinkish brown and violet with alum, copper sulphate and stannous chloride respectively (Katyayini and Jacob, 1999). When these samples were rinsed in water, the colours turned to grey, greyish green and violet. The colour range of vegetable dyes are thus being increased, thereby adding variety and interest to the existing products. The coloured materials were then subjected to different colour fastness tests like rubbing, washing, perspiration and sunlight. The results revealed that all six colours had poor to good fastness to different colour fastness tests. Radhika and Jacob (1999) extracted dye from Jatropha seed to give a range of bright, even and

26 34 soft colours on cotton fabric. Different shades of colours were dark khaki, black, biscuit colour and greenish yellowish khaki with copper sulphate, ferrous sulphate, cobalt sulphate and potassium dichromate plus lead acetate respectively. Colour fastness properties of some dyes like golden rods, marigold, onion skins on cotton fabrics were studied by Vastad et al. (1999). From the results, it was concluded that tin is the mordant which imparts good wash fastness to samples dyed with golden rods; chrome for marigold dyeing and alum and tin for dyeing with onion skins. Irrespective of the dyeing material, alum showed good fastness to dry crocking and perspiration. According to Waikhom et al. (1999) the effects of selected metallic salts on cotton fabric dyed with turmeric (Curcuma longa) dye were found to be good colour fast to sunlight, washing, crocking and pressing. The tested samples were found to be good, fair and poor in appearance with untreated and treated with alum and ferrous sulphate mordant respectively.ghorpade et al. (2000) studied the dyeing of cotton fabric with Canna flower extracts using ecofriendly mordants. The samples dyed with canna have good fastness properties. The colour range obtained is from pinkish purple to dark purple by pre-mordanting in stannic chloride, sap green with alum, dark green with ferrous sulphate and mustard yellow by post mordanting with ferrous sulphate. The study on dyeing of terrycot and cotton fabric with lac dye in sonicator was carried by Ghorpade et al. (2000). Lac dye has good fastness to light and excellent fastness to rubbing as well as to alkaline and acidic perspiration. Alum mordanting has slight stone wash effect on the fabric. Stannic chloride gave a very uniform peach colour and ferrous sulphate gave a grey colour. The advantage of using sonicator is, firstly, it minimizes the heat consumption needed during dyeing and secondly, the dye uptake by the fabric in the sonicator method is faster. Ghorpade et al. (2000) also studied ultrasound energized dyeing and durable antimicrobial finish to cotton fabric with Tulsi5 leaves. The dyeing and the anti-microbial treatment was achieved, by methanolic extract in one bath. Use of sonicator shows very effective dyeing as could be evaluated by the fabrics fastness properties. Similarly the antimicrobial activity evaluated by soil burial test of both treated and untreated fabric showed the resistance