**7. Laser technology**

In the last decade, considerable effort has been made in developing surface treatments such as UV irradiation, plasma, electron beam and ion beam to modify the properties of textile materials. Laser modification on material surface is one of the most studied technologies [106]. A laser is a device that emits light (electromagnetic radiation) through a process of op‐ tical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for "Light Amplification by Stimulated Emission of Radiation" [107]. Laser processing as a new processing method, with its processing of accurate, fast, easy, automa‐ tization, in leather, textile and garment industry increasingly widely used [108].

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 ultraviolet wavelengths [107].

are limited studies related to the effect of gamma irradiation treatment on dyeability of pro‐

*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

*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,

*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‐

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‐

In the last decade, considerable effort has been made in developing surface treatments such as UV irradiation, plasma, electron beam and ion beam to modify the properties of textile materials. Laser modification on material surface is one of the most studied technologies [106]. A laser is a device that emits light (electromagnetic radiation) through a process of op‐ tical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for "Light Amplification by Stimulated Emission of Radiation" [107]. Laser processing as a new processing method, with its processing of accurate, fast, easy, automa‐

tization, in leather, textile and garment industry increasingly widely used [108].

tion in the UVC (200-280 nm) region. The effect of UVC doses up to 25 J/cm2

used. The dye absorption was strikingly suppressed at the range of doses from 103

roentgens, but fibers regain dye accessibility at higher doses [103].

chemical modification, and grafting treatments of wool [104].

roentgens. Two dyestuffs, C.I. Acid Red 44 and C. I. Acid Green 28 were

to 105

on fabric

teinous fibers. Some of them are summarized below.

from 103

scribed [105].

**7. Laser technology**

to 105

126 Eco-Friendly Textile Dyeing and Finishing

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

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

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 carried out on polyamide [114, 115], it can be said that dyeability of proteinous fibers with anionic dyes such as acid and reactive dyes may increase due to the decrease in the crystal‐ linity and increase in free amino groups of the fiber.

plastic materials absorb microwaves slightly [119]. Electromagnetic waves can be absorbed and be left as energy units called photon. The energy carried by photon is depended on the wavelength and the frequency of radiation. Energy of MW photons is 0.125 kJ/mol. This val‐ ue is very low considering the necessary energy for chemical bonds. Therefore MW rays can not affect the molecular structure of the material directly and change the electronic struc‐

The Use of New Technologies in Dyeing of Proteinous Fibers

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

129

Microwave-promoted organic reactions are known as environmentally benign methods that can accelerate a great number of chemical processes. In particular, the reaction time and en‐ ergy input are supposed to be mostly reduced in the reactions that are run for a long time at high temperatures under conventional conditions [120]. Reactions conducted through mi‐ crowaves are cleaner and more environmentally friendly than conventional heating meth‐

The use of microwave radiation as a method of heating is over five decades old. Microwave technology originated in 1946, when Dr. Percy Le Baron Spencer, while conducting laborato‐ ry tests for a new vacuum tube called a magnetron, accidentally discovered that a candy bar in his pocket melted on exposure to microwave radiation. Dr. Spencer developed the idea further and established that microwaves could be used as a method of heating. Subsequent‐ ly, he designed the first microwave oven for domestic use in 1947. Since then, the develop‐

Microwave heating occurs on a molecular level as opposed to relying on convection currents and thermal conductivity when using conventional heating methods. This offers an explana‐ tion as to why microwave reactions are so much faster [122]. The fundamental mechanism of microwave heating involves agitation of polar molecules or ions that oscillate under the effect of an oscillating electric or magnetic field. In the presence of an oscillating field, parti‐ cles try to orient themselves or be in phase with the field. However, the motion of these par‐ ticles is restricted by resisting forces (inter-particle interaction and electric resistance), which restrict the motion of particles and generate random motion, producing heat [121]. Micro‐ wave (MW) heat systems consists of three main units; magnetron, waveguide and applica‐ tor. Magnetron is used as a microwave energy source in industrial and domestic type of microwave ovens. One of the oscillator tube, magnetron consists of two main parts as anode - cathode, and it converts the continuous current - electrical energy to MW energy. Circula‐ tor transmits approximately all of the waves that are sent from magnetron and shunts trans‐ mitted waves to water burden. Thus magnetron is protected. Electromagnetic waves are transmitting to the applicator by waveguides. Applicators are parts of the matter MW ap‐ plied on. MW energy produced in generator is affected directly on the material in applica‐ tors in MW heating systems. Type of applicators used in practice can be divided into three groups as multi-mode (using 80% of the industrial systems), single-mode and near field MW

Since the beginning of the twentieth century MW technology has made significant contribu‐ tions to scientific and technological developments. Also due to its initial intend to be used in telecommunications, very important progresses have been made in this area. Nevertheless from the second half of twentieth century, MW energy is finding increased number of appli‐

ment of microwave radiation as a source of heating has been very gradual [121].

tures of atoms [116].

ods [121].

applicators [116].
