**6. Gamma irradiation technology**

Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denot‐ ed as γ, is electromagnetic radiation of high frequency and therefore energy. Gamma rays typically have frequencies above 10 exahertz (or >10<sup>19</sup> Hz), and therefore have ener‐ gies above 100 keV and wavelengths less than 10 picometers (less than the diameter of an atom) [98]. Gamma rays are identical in nature to other electromagnetic radiations such as light or microwaves but are of much higher energy. Examples of gamma emit‐ ters are cobalt-60, zinc-65, cesium-137, and radium-226. Like all forms of electromagnetic radiation, gamma rays have no mass or charge and interact less intensively with matter than ionizing particles [99].

**Figure 11.** Gamma ray radiation [99]

*Naebe et al. (2010)* treated the wool fabric with atmospheric-pressure plasma with helium gas for 30 seconds. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry confirmed removal of the covalently-bound fatty acid layer (F-layer) from the surface of the wool fibers, resulting in exposure of the underlying, hydrophilic protein material. Dye uptake experiments were carried out at 50°C to evaluate the effects of plasma on the rate of dye uptake by the fiber surface, as well as give an indication of the adsorption characteristics in the early stages of a typical dyeing cycle. The dyes used were typical, sulfonated wool dyes with a range of hydrophobic characteristics, as deter‐ mined by their partitioning behavior between water and n-butanol. No significant effects of plasma on the rate of dye adsorption were observed with relatively hydrophobic dyes. In contrast, the relatively hydrophilic dyes were adsorbed more rapidly (and uniformly)

*Demir (2010)* treated the mohair fibers by air and argon plasma for modifying their some properties such as hydrophilicity, grease content, fiber to fiber friction, shrinkage, dyeing, and color fastness. The results showed that the atmospheric plasma has an etching effect and increases the functionality of a fiber surface. The hydrophilicity, dyeability, fiber friction coefficient, and shrinkage properties of mohair fibers were improved by atmospheric plas‐

*Atav and Yurdakul (2011)* investigated the use of plasma treatment for the modification of fi‐ ber surfaces to achieve dyeing of mohair fibers at lower temperatures without decreasing dye uptake. The study was carried out by using different gases under various powers and times. The effect was assessed in terms of color. Test samples were also evaluated using scanning electron microscopy (SEM). The optimum conditions of plasma treatment for im‐ proving mohair fiber dyeability, is treatments carried out by using Ar gas at 140 W for 60''. According to the experimental results it can be concluded that plasma treated mohair fibers can be dyed at lower temperatures (90°C) shorter times (1 h instead of 1.5 h) with reactive dyes without decreasing color yield. Dyeing kinetics was also searched in the study and it was demonstrated that the rate constant and the standard affinity of plasma treated sample

Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denot‐ ed as γ, is electromagnetic radiation of high frequency and therefore energy. Gamma rays typically have frequencies above 10 exahertz (or >10<sup>19</sup> Hz), and therefore have ener‐ gies above 100 keV and wavelengths less than 10 picometers (less than the diameter of an atom) [98]. Gamma rays are identical in nature to other electromagnetic radiations such as light or microwaves but are of much higher energy. Examples of gamma emit‐ ters are cobalt-60, zinc-65, cesium-137, and radium-226. Like all forms of electromagnetic radiation, gamma rays have no mass or charge and interact less intensively with matter

by the plasma-treated fabric [95].

124 Eco-Friendly Textile Dyeing and Finishing

ma treatment [96].

was increased [97].

**6. Gamma irradiation technology**

than ionizing particles [99].

Studies on the interaction of high energy radiation with polymers have attracted the atten‐ tion of many researchers. This is due to the fact that high-energy radiation can induce both chain scission and/or crosslinking [100]. The efficiency of these two types of reactions de‐ pends mainly on polymer structure and irradiation atmosphere. However, dose rate, types of radiation source and temperature during irradiation can influence the reaction rates [101]. For some applications radiation degradation can be controlled and devoted to achieve a spe‐ cific property [100]. Degradation, in broad terms, usually involves chemical modification of the polymer by its environment; modification that is often (but not always) detrimental to the performance of the polymeric material. Although the chemical change of a polymer is frequently destructive, for some applications degradation can be controlled and encouraged to achieve a specific property. In this regard, different vinyl monomers have been grafted onto gamma irradiated wool fabric to improve some favorable properties such as dyeability, and moisture regain. These studies have been based on the formation of stable peroxides on wool, upon irradiation, which are thermally decomposed to initiate polymerization [102].

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 reac‐ tive, and they will combine with the material in their vicinity. The irradiated modified fab‐ rics can allow: more dye or pigment to be fixed, producing deeper shades and more rapid fixation of dyes at low temperature [32]. In literature it is stated that two kinds of effects might occur in parallel in wool during the irradiation. The first effect as manifests as an evi‐ dent decrease in dye accessibility at lower doses may not be altogether independent of crosslinking. On the other hand, the remarkable increase in the uptake at higher doses seems to be associated with strong structural damage of fibers. It is interesting to note that the increase in accessibility to dyes of the highly irradiated fibers is so great that the bilateral structure is hardly visualized by the partial staining. Thus the cross-sections of fibers irradi‐ ated with a dose of 108 roentgens are stained uniformly in dark tone even under the condi‐ tion which does not give rise to the staining of unirradiated fibers [103]. In literature there are limited studies related to the effect of gamma irradiation treatment on dyeability of pro‐ teinous fibers. Some of them are summarized below.

Laser technology has been widely used in surface modification of polymers [109]. Since the late 90s, different types of commercial lasers are available for surface modification of materi‐ als [110]. While most of the efforts in developing surface treatments have been made using UV laser, infra-red lasers, like CO2 appear to be less concerning [109]. Adequate power lev‐ els for a specific application are very important in surface modification processes, because an excessive amount of energy can damage the polymers. Infra-red lasers like CO2 are the most powerful lasers; with no suitable power level, severe thermal damage can be resulted. However, this short coming can be overcome by the use of pulsed-mode CO2 lasers, which are easier to control than lasers operating in the continuous wave mode [110]. Excimer la‐ sers, which are a form of ultraviolet lasers [111], are a special sort of gas laser powered by an electric discharge in which the lasing medium is an excimer, or more precisely an exciplex in existing designs. These are molecules which can only exist with one atom in an excited elec‐ tronic state. Once the molecule transfers its excitation energy to a photon, therefore, its atoms are no longer bound to each other and the molecule disintegrates. This drastically re‐ duces the population of the lower energy state thus greatly facilitating a population inver‐ sion. Excimers currently used are all noble gas compounds; noble gasses are chemically inert and can only form compounds while in an excited state. Excimer lasers typically operate at

The Use of New Technologies in Dyeing of Proteinous Fibers

http://dx.doi.org/10.5772/53912

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It has been shown that materials like polymers, woods, metals, semiconductors, dielectrics and quartz modified by laser irradiation often exhibit physical and chemical changes in the material's surface [106]. Physical modifications occur in the form of a certain, regular surface structure of the irradiated sites. The high energy input of the excimer radiation into the pol‐ ymer might also give rise to chemical changes of the surface [112]. In the case of polymers, some well-oriented structure of grooves or ripple structures with dimensions in the range of micrometer are developed on surface with irradiation fluence above the so-called ablation threshold. The laser irradiation of highly absorbing polymers can generate characteristic modifications of the surface morphology. The physical and chemical properties are also af‐ fected after laser irradiation. Hence, it is reasonable to believe that such surface modification

The possible applications of laser technology in the textile industry include removal of indi‐ go dye of denim, heating threads, creating patterns on textiles to change their dyeability, producing surface roughness, welding, cutting textile webs. Laser irradiation on polymer surface is used to generate a modified surface morphology. The smooth surface of polymers is modified by this technique to a regular, roll-like structure that can cause adhesion of parti‐

Laser technology can also be used for improving dyeability since it is well known that the UV output from excimer lasers can modify the surface of synthetic fibers. But the use of la‐ ser energy in textile treatment is still uncommon and is generally limited with denim gar‐ ment finishing [114]. Although there are many studies in the literature related to the investigation of the effect of laser treatment on dyeability of many fiber types, there is still no study carried out on wool. But, by taking into consideration that the chemical structure and dyeing property of proteinous fibers is similar to polyamide, in the light of the studies

of a polymer may have an important impact on its textile properties [106].

cles and coating, wetting properties and optical appearance [113].

ultraviolet wavelengths [107].

*Horio et al. (1962)* investigated the effect of irradiation on dyeing property of wool fiber. It was found that the dyeing property of wool fiber was greatly affected by irradiation even at low doses where any changes in mechanical properties were not noticeable. The rate of dye absorption was strongly depressed by irradiation with Co-60 gamma radiation of low doses from 103 to 105 roentgens. Two dyestuffs, C.I. Acid Red 44 and C. I. Acid Green 28 were used. The dye absorption was strikingly suppressed at the range of doses from 103 to 105 roentgens, but fibers regain dye accessibility at higher doses [103].

*Beevers and McLaren (1974)* have been found that small doses of gamma radiation (0.5-10 Mrad) produce marked effects on some physical properties of wool. The results indicate that even small doses of gamma radiation break sufficient covalent bonds to make the cross‐ linked peptide chain structure more susceptible to the action of swelling and disordering agents. These small radiation-induced changes can be expected to affect properties of wool significantly in absorption and penetration processes, such as those involved in dyeing, chemical modification, and grafting treatments of wool [104].

*Millington(2000)* investigated the effects of γ-radiation (60Co) on some chemical and physical properties of wool keratin and compared and contrasted with the effects of ultraviolet radia‐ tion in the UVC (200-280 nm) region. The effect of UVC doses up to 25 J/cm2 on fabric strength was found to be small (5%), whereas γ-irradiated wool experienced strength reduc‐ tions of 15% at doses over 100 kGy. Color changes following UVC and γ-irradiation were quite different: UVC wool was initially green changing to yellow under ambient conditions, γ-treated wool became pink-red at doses 25-250 kGy, and yellow at higher doses. The chro‐ mophores produced by UVC were easily removed by oxidative bleaching with hydrogen peroxide, whereas γ-treated wool remained yellow even at relatively low doses (25–50 kGy). This has implications for the use of γ-radiation as a means of sterilising wool for compliance with quarantine regulations. The effects of the two forms of radiation on the natural fluores‐ cence of wool, permanent setting, printing properties and the epicuticle layer were also de‐ scribed [105].
