**8. Microwave technology**

Microwaves (MW) which have broad frequency spectrum are electromagnetic waves that are used in radio, TV and radar technology [116]. MWs are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with fre‐ quencies between 300 MHz (0.3 GHz) and 300 GHz [117].

The term "microwave" denotes the techniques and concepts used as well as a range of fre‐ quencies. Microwaves travel in matter in the same manner as light waves: they are reflected by metals, absorbed by some dielectric materials and transmitted without significant losses through other materials. For example, water, carbon, foods with a high water, some organic solvents are good microwave absorbers whereas ceramics, quartz glass and most thermo‐ 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‐ tures of atoms [116].

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‐

Microwaves (MW) which have broad frequency spectrum are electromagnetic waves that are used in radio, TV and radar technology [116]. MWs are radio waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with fre‐

The term "microwave" denotes the techniques and concepts used as well as a range of fre‐ quencies. Microwaves travel in matter in the same manner as light waves: they are reflected by metals, absorbed by some dielectric materials and transmitted without significant losses through other materials. For example, water, carbon, foods with a high water, some organic solvents are good microwave absorbers whereas ceramics, quartz glass and most thermo‐

linity and increase in free amino groups of the fiber.

quencies between 300 MHz (0.3 GHz) and 300 GHz [117].

**8. Microwave technology**

128 Eco-Friendly Textile Dyeing and Finishing

**Figure 12.** Frequency spectrum [118]

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‐ ods [121].

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

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 applicators [116].

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‐ cation area in other industrial processes and these applications are surpassing telecommuni‐ cation applications [116].

[127]. An irradiation can induce chemical reactions at any temperature in the solid, liquid and gas phase without any catalyst; it is a safe method that could protect the environment against pollution; radiation process could reduce curing time and energy saving; it could treat a large and thick three-dimensional fabrics that need not consider of the shape of the

The Use of New Technologies in Dyeing of Proteinous Fibers

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

131

Physical techniques for activating fiber molecules in the absence of solvent for producing functional textiles are becoming increasingly attractive also from an ecological viewpoint. Among them, electron beam processing is particularly interesting as it offers the possibility to treat the materials without solvent, at normal temperature and pressure [129]. Whilst the energy of the electrons in gas discharge plasmas is typically in the range of 1-10 electron volt (eV), electron-beam (E-beam) accelerators generate electrons with a much higher energy, generally 300 keV to 12 MeV. These electrons may be used to modify polymer materials through direct electron-to-electron interactions. These interactions can create active species such as radicals, so there are different possible outcomes from the electron-beam irradiation

The formation of active sites on the polymer backbone can be carried out by several meth‐ ods such as plasma treatment, ultraviolet (UV) light radiation, decomposition of chemical initiator and high-energy radiation [131]. At present, the most common radiation types in industrial use are gamma and e-beam. E-beam machines play a significant role in the proc‐ essing of polymeric materials; a number of different machine designs and different energies are available. Industrial e-beam accelerators with energies in the 150-300 keV range are in use in applications where low penetration is needed, such as curing of surface coatings. Ac‐ celerators operating in the 1.5 MeV range are used where more penetration is needed. Ebeam machines have high-dose rate and therefore short processing times. While they have limited penetration compared with gamma, they conversely have good utilization of energy

New radiation processing applications involving ion-beam treatment of polymers offer ex‐ citing prospects for future commercialization, and are under active investigation in many re‐ search laboratories. Much of the work has involved the irradiation of non-polar polyolefins (PE, PS, PP, etc.) as a means of inducing polar groups at surfaces, in order to enhance such properties as printability, wetability and exc. [132]. Studies related to the e-beam irradiation

*Fatarella et al.(2010)* wanted to clarify whether fiber surface treatments such as plasma and ebeam could affect the effectiveness of a TGase treatment by improving the accessibility of target amino acids in wool to the enzyme or improving the penetration of the enzyme into the wool fiber cortex, thus accessing more sites for reaction. Plasma treatments with differ‐ ent non-polymerizing gases (oxygen, air and nitrogen) and e-beam irradiation in air or nitro‐ gen atmosphere were assessed as possible pretreatments to non-proteolytic enzymatic processes (such as TGase) to improve the accessibility of target groups in the wool proteins to the enzymes. Only limited inhibition and/or inactivation of the transglutaminase enzyme was found after treatment with plasma and e-beam, suggesting such treatments could be used as a preparative treatment prior to the application of the enzyme. In contrast, by in‐

of polymer materials, on the basis of the chosen operating conditions [130].

because it can all be absorbed by the sample irradiated [132].

of proteinous fibers are limited.

samples [128].

In textile processing it is necessary to apply heat as in dye fixation, heat setting or drying the product. Heat can be transferred to the material by radiation, conduction and convection. These three ways of transferring can be used either separately or in combination. The saving of time and energy is of immediate interest to the textile industry. The introduction of new techniques which will allow less energy to be used: is a highly important area of activity to consider. The textile industry has investigated many uses for microwave energy such as heating, drying, dye fixation, printing and curing of resin finished fabrics. In 1966, Ciba-Ge‐ igy obtained one of the earliest patents for using microwave heating in dyeing and printing fibrous material with reactive dyes. Since then many authors have investigated the feasibili‐ ty of using microwaves for a variety of dyeing and finishing processes [123]. Although many studies have focused on investigating the feasibility of using microwaves to dye poly‐ ester fibers with disperse dyes, researches related to the use of microwave heating in dyeing of proteinous fibers are very limited.

*Delaney and Seltzer (1972)* used microwave heating for fixation of pad-dyeings on wool and they demonstrated the feasibility of applying certain reactive dyes to wool in fixation times of 30-60 s [124].

*Zhao and He (2011)* treated the wool fabric with microwave irradiation at different condi‐ tions and then studied for its physical and chemical properties using a variety of techni‐ ques, such as Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron. It was found that microwave irradiation of wool fabric significantly improved its dyeability. It was stated that this could be due to the change in wool surface morpho‐ logical structure under microwave irradiation which implied that the barrier effect in wool dyeing was diminished. Although the breaking strength of the treated wool fabrics also improved with microwave irradiation, the chemical structure and crystallinity did not show any significant change [125].

In literature it was stated that dyeing time of mohair could be drastically reduced from the conventional 90 minutes to 35 minutes using the radio frequency technique, only 5 minutes of the 35 minutes representing actual exposure to the radio frequency field. An estimated saving of some 80% in dyeing energy costs could be achieved. Furthermore, dye fixation im‐ proved slightly from 93% to 96%. *Turpie* quoted unpublished data in which radio-frequency dyeing of tops produced better luster and enabled higher maximum spinning speeds than did conventional dyeing of mohair. *Smith,* claimed advantages of radio-frequency dyeing and bleaching, - for example, reduced chemical damage because of a shorter exposure to 100°C; and reduced energy, water and effluent costs [126].
