**2. 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 Fe2O3 (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.


Table 1.

2 Textile Dyeing

spectrum. Human eyes detect the visible radiations only for the respective complementary

Fig.1 shows the different regions of spectrum with their wavelengths.

Fig. 1. Regions of electromagnetic spectrum

**2. Classification of dyes: Natural & synthetic dyes** 

shows the classification of dyes based upon both colours and structures.

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 Fe2O3 (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,

colours.

*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.

2005).

structure.

(Tamada, 2004).

Effect of Radiation on Textile Dyeing 5

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.*,

*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

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

*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.

#### **3. 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

*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

*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

*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

*Acetate rayon dyes:* Developed for cellulose acetate and some synthetic fibers (Kim *et al.*, 2005;

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

*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

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

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

dyes require oxidation as well as reduction step for its application onto matrix.

performed. These steps are important for maintaining consistent product quality.

can not be entirely substituted by artificial polymer fibers (Jun *et al.,* 2001).

cellulose occur at the primary hydroxyl groups.

fibers (Cotton , wool , silk , nylon etc).

situ.

Shenai, 1992).

**3. Chemistry of fibers** 

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).

Effect of Radiation on Textile Dyeing 7

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

*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

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.

**4.1 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

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

alcohol and a terephthalic acid (Kiran, 2009).

(Hunger, 2003).

**4. Irradiation in textiles** 

impart yellow colour with dark shades.

showed the dull redder shades.

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.

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

*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

*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.

break (Jun and Chen, 2006)

variety of dyes and allow the wool to hold its colour (Michael and El-Zaher, 2005).

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).
