Effect of Radiation on Textile Dyeing

Love for colours is a natural instinct and every individual has his own choice and liking for colour. The icy appearance of Hamaliyan ranges or lush green forests or fields of agriculture or trees laden with colorful fruits or butterflies moving from flower to flower presents the beauty of nature, generation after generations are being attracted. The choice of beautiful fascinating colours reflects the aesthetic sense of humans that varies. Colour is visual perceptual property corresponding in humans to the categories called red, yellow, blue and others. It is a sensation that arises from the activity of retina of the eye and its attached nervous mechanism, and results in a specific response to the radiate energy of certain wavelength and intensity. Thus it is a quality of an object with respect to light (Mizzarini et al., 2002).Colorants may be either pigment or a dye which are characterized by their ability to absorb or emit light in the visible range 400-700nm.They may be organic or inorganic depending upon their structure and method of production. Dyes are the coloured substances which are capable of imparting their colours to the matrix which may be fiber, paper or any object. They must have fixing tendency on a fabric that is impregnated with their solution and the coloured fixed dyes must be fast to light as well as resistant to action of water, dilute acids, alkalies, various organic solvents used in dry cleaning, soap solutions, detergent, etc ( Shukla, 1992 ) . A pigment generally is a substance which is insoluble in the medium in contrast to dye in which it is applied and has to be attached to a substrate by additional compounds e.g. polymer in paints and plastics (Taylor and Nonfiction, 2006) A compound looks coloured because it has absorbed certain electromagnetic radiation from the visible region. The moieties, present in colouring substance, responsible for the absorption of electromagnetic radiation and reflect in the visible region are called chromophores (Younas, 2006).Ultraviolet radiation constitutes to 5% of the total incident sunlight on earth surface (visible light 50% and IR radiation 45%). Even though, its proportion is quite less, it has the highest quantum energy compared to other radiations. Light is electromagnetic in nature. Within the electromagnetic spectrum, human eye captures visible light in the range between about 380 nm and 700 nm (Mizzarini et al., 2002). Dyes absorb electromagnetic radiation of varying wavelength in the visible range of

spectrum. Human eyes detect the visible radiations only for the respective complementary colours. Fig.1 shows the different regions of spectrum with their wavelengths.

Classification of dyes: Natural & synthetic dyes
All colourants obtained from animals, plants and minerals without any chemical processing are called natural dyes.e.g.Alizarin a pigment extracted from madder, tyrian purple from snail and ochre which is a mineral of Fe 2 O 3 (Gulrajani, 1992). Natural dyes may be vat dyes, substantive or mordant dyes as they require the inclusions of one or more metallic salts of tin, chromium, iron, copper, aluminum and other for ensuring reasonable fastness of the colours to sun light and washing. The natural dyes have several advantages such as: these dyes need no special care , wonderful and rich in tones , act as health cure, have no disposal problems, have no carcinogenic effect ,easily biodegradable, require simple dye house to apply on matrix and mild reactions conditions are involved in their extraction and application (Sachan and Kapoor,2004).There are some limitations of natural dyes which includes, lesser availability of colours, poor colour yield, complex dyeing processing, poor fastness properties and difficulty in blending dyes (Pan et al., 2003). Table 1 given below, shows the classification of dyes based upon both colours and structures.
Commercialization of natural dyes can be done successfully by a systematic and scientific approach to extraction, purification and use. Optimization of extraction condition is a must to minimize the investment cost and to avoid discrepancy in the dye shade quality. Natural dyes occur in many plant parts in small quantities and as complex mixtures with many chemical compounds of similar or different structures. These compounds vary considerably with change in general, same genus but different species and ecological conditions of the plant source. So when natural dyes extracted from these sources are used for dyeing and printing, variation in shade, depth and tone, among others, may arise. Further, chemical components of plants change with age and maturity of the parts. Extraction may include drying, pounding, soaking, skimming, crystallizing, condensing, caking and liquidifying, among others, depending on the quality and species of the dye yielding plant, mineral and insect (Shrivastava and Dedhia, 2006;Vankar et al., 2000). Synthetic dyes are a class of highly coloured organic substances, primarily utilized tinting textiles that attach themselves through chemical bonding between the molecules of dye and that of fiber. The use of natural dyes in textiles was eliminated since synthetic dyes give variety of reproducible shades and colours (Deo and Desai, 1999). Synthetic dyes are classified on the basis of chemical structure or on the basis of methods of application to the material. Dyes are synthesized in many ways by using different chemicals. On the basis of methods of application dyes are categorized as:-Acid dyes: These dyes are anionic and form ionic bonds with fibers that are cationic in acid solutions. These dyes are applied onto the acrylic, wool, nylon and nylon/cotton blends. These are called acidic because they are normally applied to nitrogenous fibers in inorganic or organic acid solutions. Azoic dyes: These dyes contain azo component (-N=N-), used for dyeing of cotton fabrics. In the dyeing process fiber is first treated with coupler followed by application of azo dye. This type of dye is extremely fast to light. Basic dye: These dyes are cationic and form ionic bonds with anionic fibers such as acrylic, cationic dyeable polyester and cationic dyeable nylon. These are amino derivatives used mainly used for application on paper Disperse dyes: These dyes are colloidal and are soluble in hydrophobic fibers. Mostly these dyes are used for coloring polyester, nylon, and acetate and triacetate fibers. They are usually applied from a dye bath as dispersion by direct colloidal absorption method Direct dyes: These are also azo dyes applied generally on cotton-silk combination from neutral or slightly alkaline baths containing additional electrolyte. These dyes predominantly interact and attach themselves with the Matrix ( wool , polyamide fabric) through electrostatic interactions. These dyes are used to color cellulose, wool, nylon, silk etc.
Reactive dyes: Reactive dyes are the best choice and other cellulose fiber at home or in the art studio. Fixation of dye occur onto the fiber under alkaline conditions by forming a covalent bond between reactive group of dye molecule and OH, NH, SH etc groups present in the fibers (Cotton , wool , silk , nylon etc). Mordant dyes: Applied in conjunction with chelating salts of Al, Cr and Fe. Metallic salts or lake formed directly on the fiber by the use Al, Cr or Fe salts which cause precipitation in situ. Sulfur dyes: These dyes are used for dyeing cotton and rayon. The application of this dye requires careful process due to its water-soluble reduced form and insoluble oxidized form. These dyes are fast to washing but poorly fast to chlorine and give dark and dull colors. Vat dyes: These dyes are insoluble in water and cannot be directly applied to textiles. These dyes require oxidation as well as reduction step for its application onto matrix. Acetate rayon dyes: Developed for cellulose acetate and some synthetic fibers (Kim et al., 2005;Shenai, 1992). Dyes are synthesized in a reactor, filtered, dried, and blended with other additives to produce the final product. The synthesis step involves reactions such as sulfonation, halogenation, amination, diazotization, and coupling, followed by separation processes that may include distillation, precipitation, and crystallization. In general, organic compounds such as naphthalene are reacted with an acid or an alkali along with an intermediate (a nitrating or a sulfonation compound) and a solvent to form a dye mixture. The dye is then separated from the mixture and purified. On completion of the manufacture of actual colour, finishing operations, including drying, grinding, and standardization, are performed. These steps are important for maintaining consistent product quality.

Chemistry of fibers
Cotton the most abundant of all naturally occurring substrates and is widely used. For the fabric strength, absorbency quality, capacity to be washed and dyed, cotton has become the principal clothing fabric of the world. The materials characteristically exhibit excellent physical and chemical properties in terms of water absorbency, dye ability and stability and can not be entirely substituted by artificial polymer fibers (Jun et al., 2001). The cellulose consists of glucose units linked together through oxygen atoms, 30 to several hundred chains from micro fibrils (Foldvary et al., 2003). By dry weight 94% of cotton is made up of cellulose. The remaining constituents include 1.3% protein, 1.2% pectic substances, 0.6% waxes, 1.2% ash, and 4% of other components. Of three hydroxyl groups on the cellulose ring, two are secondary, and one is primary. Most of the reactions with cellulose occur at the primary hydroxyl groups.
When cellulose is chemically modified with the compounds containing cationic and anionic groups, the molecular chains are modified. In the modified fiber surface, the chemical and physical properties of cellulose fiber are changed. Through chemical modification, the reactivity of the cellulose fiber is enhanced. And several classes of dyes such as direct, azo, reactive etc can be successfully applied. The application of the cationic dyes has not gained widespread success. Our study comprises of the treatment method such as high energy radiation treatment which may create the anionic centre in the fabric to transfer the cationic dye onto the physically or chemically modified fabric. The reports of modified cellulose with the compounds containing multifiber cationic and anionic groups are scarce (Kim et al., 2005). Wool is different to other fibers because of its chemical structure that influences its texture, elasticity, staple and crimp formation. It is composed of keratin-type protein having more than 20 amino acids and very small amount of fat, calcium and sodium. The amino acids in wool linked together in ladder-like polypeptide chain to form a protein/polymer type structure. Wool polymer contains some important chemical groups that able to form inter-polymer forces of attraction. These groups are: the polar peptide groups (i.e. -CO-NH-) and the carbonyl groups (-CO-), which forms hydrogen bonds with the slightly positively charged hydrogen of the amino groups (-NH-) of another peptide groups. There are also carboxylate groups (-COO-), and amino groups (-NH3+) present in wool as side groups, between these two groups salt linkages or ionic bonds may be formed. Finally, the existence of the above mentioned inter-polymer forces tends to make the van der Waals` forces rather significant (Tamada, 2004).

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Wool is easy to dye since the surface of the wool fiber diffuses light giving less reflection and a softer colour. The proteins in the core of the fiber absorb and combine with a wide variety of dyes and allow the wool to hold its colour (Michael and El-Zaher, 2005). Silk is an insect fiber comes from the silkworm that spins around itself to form its cocoon. A single filament from a cocoon can be as long as 1600 meters. It is considered an animal fiber because it has a protein structure. Like other animal fibers silk does not conduct heat, and acts as an excellent insulator to keep our bodies warm in the cold weather and cool in the hot weather. The flat surfaces of the fibrils reflect light at many angles, giving silk a natural shine. Natural and synthetic silk is known to manifest piezoelectric properties in proteins, probably due to its molecular structure. Silk emitted by the silkworm consists of two main proteins, sericin and fibroin, fibroin being the structural center of the silk, and sericin being the sticky material surrounding it. Fibroin is made up of the amino acids Gly-Ser-Gly-Ala-Gly-Ala and forms beta pleated sheets. Hydrogen bonds form between chains, and side chains form above and below the plane of the hydrogen bond network (Ellison, 2003).
Silk polymer is composed of sixteen different amino acids where as wool polymer contains twenty amino acids of wool polymer. Three of these sixteen amino acids namely, alanine, glycine and serine, make up about four-fifth of the complete polymer chain The important chemical groupings of the silk polymer are the peptide groups which give rise to hydrogen bonds, the carboxyl and amine groups give rise to the salt linkages. The high proportion (50%) of glycine, which is a small amino acid, allows tight packing and the fibers are strong and resistant to breaking. The tensile strength is due to the many interceded hydrogen bonds, and when stretched the force is applied to these numerous bonds and they do not break (Jun and Chen, 2006) Polyester was first introduced to the American public in 1951by W.H. Carothers Laboratory. It was advertised as a miracle fiber that could be worn for 68 days without ironing and still look presentable. Polyester was once hailed as a magic fiber capable of being washed, scrunched and pulled on without showing any signs of water or wrinkles.

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Now it is remembered for its bright double knit fabrics and comfortable texture. The name "polyester" refers to the linkage of several monomers (esters) within the fiber. Polyester is long chain polymer chemically composed of at leas 85% by weight of an ester and a dihydric alcohol and a terephthalic acid (Kiran, 2009). Polyester Cotton(PC) is a blend of polyester and cotton in varied proportions. This particular fabric is well received by customers around the world. The yarn is available in single and twisted form. The polyester cotton (PC) fabric yarn commonly has a blend ratio of 50% polyester to 50% cotton. In polyester cotton fabric (PC), polyester provides wrinkle resistance and shape retention while cotton provides absorbency and consequent comfort (Hunger, 2003).

Irradiation in textiles
Irradiation processes have several commercial applications, in the coating of metals, plastics and glass, in printing, wood finishing, film and plastic cross linking and in the fields of adhesive and electrical insulations. The advantages of this technology are well known energy saving (low-temperature process), low environmental impact, simple, economical and high treatment speed. Despite these advantages, there have been few applications of radiation curing in the textile industry, such as non woven fabric bonding, fabric coating and pigment printing (Ferrero and Monica, 2011). Radiation treatment on fabric and garments can add value in colouration. Modification of the surface fiber can allow more dye uptake; its fixation at low temperature and increase wettability. Cotton knitwear pilling can be eliminated from the surface of the fabric by radiation treatment without affecting the strength of the fiber (Kim et al., 2005).Effect of UV radiation in natural as well as synthetic dyeing using irradiated cotton fabric has given significant results.

Effect of UV and gamma radiation on the fabric dyed with natural dyes
There is a remarkable difference in colour strength when different extracts of irradiated and un-irradiated turmeric powder were used to dye the irradiated and un-irradiated fabric (Afifah et al., 2011). The methanol solubilized extract gave more colour strength than aqueous (heat) solubilized and alkali solubilized extract as displayed in Fig. 2. The low colour strength using alkali solubilized extract is due to alkaline degradation of curcumin into products like vaniline, vanilic acid, feruloylmethane, ferulic acid and other fission products, which sorb on the fabric along with colourant and impart dull redder shades (Tonnesen and Karlsen,1985a). While using (heat) aqueous solubilized extract, the colourant being insoluble in water may undergo hydrolytic degradation and the actual colourant concentration becomes low onto the fabric as a result low colour strength is observed (Tonnesen and Karlsen, 1985 b). By using methanol solubilized extract, the actual colourant get significant chance to sorb onto fabric and impart yellow colour with dark shades. The irradiation of fabric is also another factor which affects the colour strength of the fabric. Previous studies show that UV irradiation adds value to colouration and also increases the dye uptake ability of the cotton fabrics through oxidation of surface fibers of cellulose (Millington , 2000;Javed et al ., 2008). The colourants from Methanol solubilized extract reach the vicinities of fibres and upon investigation of colour strength using spectraflash SF 650, dark yellow shade was observed. In the case of un-irradiated fabric, the insoluble impurities get significant chance to sorb on the matrix along with colourant which showed the dull redder shades. Gamma rays are ionizing radiations that interact with the material by colliding with the electrons in the shells of atoms. They lose their energy slowly in material being able to travel through significant distances before stopping. The free radicals formed are extremely reactive, and they will combine with the material in their vicinity. Upon irradiation the cross linking changes the crystal structure of the cellulose, which can add value in colouration process and causes photo modification of surface fibers. The irradiated modified fabrics can allow: more dye or pigment to become fixed, producing deeper shades, more rapid fixation of dyes at low temperature and increases wet ability of hydrophobic fibers to improve depth of shade in printing and dyeing (Millington, 2000). The influence of gamma radiation on the colour strength values of the fabric dyed with natural dyes extracted from eucalyptus bark has been shown in Fig. 3. High colour strengths and dark brown shades of the fabric dyed in ethanolic extract were obtained as compared to aqueous extracts. The low colour strength and un-evenness in shade in aqueous extract is due to presence of insoluble impurities that might come on the fabric along with colourant. (Vankar et al., 2000) The results shown in Fig. 3. demonstrate that irradiated fabric dyed using alcoholic extract gave more colour strength than un-irradiated fabric. Previous studies showed that gamma irradiation causes dislocation and fragmentation of fabric fibers (Foldvary et al., 2003) however, only soluble colourant free from impurities get maximum chances to sorb on the fabric. But un-irradiated fabric contained less dye and yielded greener shade. The colour strength changes significantly in aqueous than in alkaline media. The fabrics dyed in aqueous extract of turmeric powder were darker yellow in shades than that of www.intechopen.com fabrics dyed in alkaline extract. The low colour strength was due to alkaline degradation of curcumin into water-soluble products like vaniline, vanilic acid, feruloylmethane, ferulic acid and other fission products, which gave dull redder shades (Tonessen and Karlsen, 1985a). Tonessen and Karlsen reported that below pH 7, curcumin existed in yellow colour and is insoluble in water (Tonessen and Karlsen, 1985b). Due to insolubility, the colourant might have tendency to get absorbed completely on the fabric without passing through the medium and shows darker yellow shades. Hence irradiated fabrics dyed in aqueous media gave more colour strength than un-irradiated fabrics due to oxidative degradation of cellulose fibres. Treatment of fabric by high-energy radiation causes either dislocation and fragmentation or slight loss in mass of fabric (Foldvary et al., 2003;Takacs et al., 2000). However, only colourants get maximum chance to sorb on fabric than insoluble impurities. So more colour strength is obtained in case of irradiated fabric dyed using aqueous extract of irradiated turmeric powder. Thus it is found that if irradiated fabric dyed with aqueous extract of irradiated turmeric powder, maximum colour strength and darker yellow shade was obtained. The data displayed in Fig 5. shows that irradiated fabric for 120 min. gave maximum colour strength as compared to un-irradiated fabric. The fabric irradiated for 120 min. showed even shade with better colour strength. The reason might be the oxidation of cellulose upon exposure to UV radiation. Michael and EL-Zaher in 2005 reported that the UV treatment of cellulose fibre created spaces between fibres which imbibed more dye and as a result the interaction between dye and cellulose fabric becomes more significant. The dye molecules rush rapidly onto the fabric and as a result darker shades were obtained (Tayyba, 2010). The above Fig. 6. shows that the fabric irradiated for 90 min. has maximum affinity for dye substrate to attach. The fabric irradiated for 30 and 60 minutes show even shades having good colour strength. This improvement might be due to the oxidation of cellulose in to carboxylic acid group upon exposure of cellulose to UV radiation which interacts more towards the dye material to form covalent bond. The un-irradiated and irradiated cotton fabric for the period of 30, 60 and 90 min was dyed, the results of fabrics have been shown in Figure 7. (a,b) shows that irradiated fabric and irradiated dyes for 90 min has maximum affinity for dye to attach on it. Oxidation of cellulose upon UV radiation significantly increases the dye uptake in the substrate due to the interstices available in the case of irradiated fabric surface (Michael and EL-Zaher, 2005).

Effect of UV and gamma radiation on the fabric dyed with synthetic dyes
The dye molecules rush rapidly on to the fabric and as a result darker shades were obtained (Sajida Parveen, 2009, Afifah Kausar, 2009Afifah et al., 2011). Previous study carried out by K.R. Millington suggested that photo modification of surface fiber may attain more dye or pigment to become fixed producing deeper shades. UV radiation causes more rapid fixation of dyes increases wettability of hydrophobic fibers to improve depth and shade in printing. For knitted wool and cotton fabrics, the problem of pilling can be eliminated.  Fig. 8. (a & b).At this time, oxidation of cellulose generates carboxylic acid group which helps in significant interaction of dye with oxidized a surface and show darker shades. Irradiation for less time does not activate the surface to interact with dye molecules to such an extent. While irradiation for long time may either facilitate insoluble impurities to rush onto modified fabric due to availability of wide interstices /gaps among the fibers which may cause dull and uneven shades having low colour strength (Saddique, 2008). Gamma radiation shows a promising influence in textile dyeing since irradiated fabric dyed with synthetic dye gave a prominent difference The result shown in Fig. 9. indicate that colour strength values change remarkably using irradiated fabric which results in darker colour strength and more bluer shades than that of un-irradiated fabrics. This low colour strength is due the stuffing of insoluble impurities present in the dye solution on to the fabric. Results given in Fig. 9. show that the dyeing performed using irradiated fabric treated with 300Gy absorbed dose gave maximum colour strength with darker bluer shades. At higher doses, low colour strength is obtained, which may be due to the degradation or dislocation of crystal moieties on cellulosic material (Foldvary et al. 2003;Takacs et al.2000). While at low dose, fabric surface does not activate enough to fix dye onto it and does not able to make firm interaction with dye material. The result displayed in Fig. 10. reveal that colour strength values decrease with increase in absorbed doses. The more colour strength is because of photo modified surface of cellulose which may have more affinity for dye substrate (Mughal et al., 2007). The results show that the dyeing performed using 200Gy dose gives maximum colour strength with darker shades. At sufficient higher dose insoluble impurities along with dye molecule become fixed and causes uneven shades, while below optimum dose, surface of cellulose do not stimulate much to interact significantly with dye material. Thus dyeing performed using cotton fabric irradiated to an absorbed dose of 200Gy gave better colour strength (Toheed Asghar, 2009 Fig. 10. Effect of gamma irradiation on the colour strength of irradiated cotton fabric dyed with Irradiated reactive black dye powder

Effect of UV and gamma radiation on wool and silk and polyester
Studies on wool keratin have been previously performed in order to evaluate the effect of UV radiation. Chemical changes induced by short term UV radiation are confined to fibers at surface where as it is unable to penetrate into the fabric. The colour changes i.e. green followed by yellow in wool keratin due to UV radiation have been observed also (Millington, 2000).There are several processes to reduce the pilling yet no process can guarantee the zero pilling in wear. But Millington reported that it is only UV radiation which can reduce the pilling through siro flash technology followed by oxidation with hydrogen peroxide in germicidal UV Tubes. After using such techniques and then dyeing with UV irradiated wool fabric, the characterization of wool fabric meets standard marks by ISO. Thus the continuous UV reduction of the fabric followed by batch oxidation is of great commercial value. (Millington, 1998a;Millington, 1998b;Millington, 1997). When wool fabric is exposed to UV radiation, it exhibits some physical and chemical changes on its surface. This interaction not only modifies the fabric of wool but also improve the shades particularly grey and black. It also helps in even dyeing, deeper shades, chlorine free printing and improve the photo bleaching of wool (Millington, 1998c). Now a days, UV curing technology is being used for the modification of wool surface that helps in finishing as well as deepening the shades of wool when dyed using reactive dyes. By using UV curing technology, there are no risks involved to any loss of fabrics fibers in weight as well as in its physical appearance. This technology also do not cause any hazardous use of chemicals, smoothness of surface, unpilling as well as deep hues (Ferrero and Periolatto, 2011;Abdul Fattah et al., 2010).

Conclusion
Radiation processes has several commercial applications starting from curing of fabrics, finishing, improvement of shades and characterization of dyed fabrics. The advantage of this technology are well known such as improvement in shades , enhanciong colour fastness , colour stregnth , low cost effective and reduction of the concentration of the dye. All these results have been seen from our above experiments. Radiation curing of silk, wool and cotton fabric to reduce pilling , their finishing and mercerization processes has also been improved. Thus both UV and gamma radiation has improved the textile sttuff according to standards of ISO , EPA and FAO. The use of eco-friendly technnology giving eco-label products under the influence of high energy radiations that may give new orientation for other dyes such as vat, reactrive azo and other brands. Similarly improvement of fibers of wool , silk , nylonn , Polyester cotton (P.C). etc., for dyeing to get good shades, even and lavelled dyeing, accepatable fastness properties yet are underway.So the dyers and colourists should try such techniques inorder to get better results and alternating methods for any risks related to human health.