**2. Ultrasound technology**

Sound is transmitted through a medium by inducing vibrational motion of the molecules through which it is traveling. This vibrational motion represents the sound frequency [11]. Ultrasound is sound of a frequency that is above the threshold of human hearing [12]. The lowest audible frequency for humans is about 18Hz and the highest is normally around 18-20 kHz for adults, above which it becomes inaudible and is defined as ultrasound [11]. In recent decades the use of ultrasound technology has established an important place in dif‐ ferent industrial processes such as the medical field, and has started to revolutionize envi‐ ronmental protection. The idea of using ultrasound in textile wet processes is not a new one. On the contrary there are many reports from the 1950s and 1960s describing the beneficial effects of ultrasound in textile wet processes. In spite of encouraging results from laborato‐ ry-scale studies, the ultrasound-assisted wet textile processes have not been implemented on an industrial scale as yet [13].

In practice, three ranges of frequencies (Fig. 1) are reported for three distinct uses of ultra‐ sound: low frequency or conventional power ultrasound (20-100 kHz), medium frequency ultrasound and diagnostic or high frequency ultrasound (2-10 MHz) [13].

As the sound wave passes through water in the form of compression and rarefaction cycles, the average distance between the water molecules varies. If the pressure amplitude of the sound is sufficiently large, then the distance between the adjacent molecules can exceed the critical molecular distance during the rarefaction cycle. At that moment a new liquid surface is created in the form of voids. This phenomenon is called acoustic cavitation [15].

**Figure 1.** Classification of sound according to the frequency [14]

long chain polymer by condensation and polymerization. Silk fiber consists of 97% protein and the others are wax, carbohydrate, pigments, and inorganic compounds. The proteins in silk fiber are 75% fibroin and 25% sericin by weight, approximately. The sericin makes silk fiber to be strong and lackluster; therefore, it must be degummed before dyeing [6]. Silk fi‐ broin, like wool keratin, is formed by the condensation of α-amino acids into polypeptide chains, but the long-chain molecules of silk fibroin are not linked together by disulfide bridges as they are in wool. Chemical treatments can cause modification of main peptide chains, and side chains of amino acids, which in turn influence the fiber's chemical, physical, and mechanical properties [8]. Silk fiber is easily damaged when dyeing at the boil, so lowtemperature dyeing is usualy preferred [7]. Because the brilliancy of dyed and printed silk fabrics is a decisive factor for evaluating the quality of silk fabrics, dyeability of silk fibers is

In recent years, many attempts have been made to improve various aspects of dyeing, and new technologies have been, and are being developed to reduce fiber damage, decrease en‐ ergy consumption and increase productivity [10]. In this chapter, new technologies that im‐ prove the dyeability of proteinous fibers such as ultrasound, ultraviolet, ozone, plasma, gamma irradiation, laser, microwave, e-beam irradiation, ion implantation, and supercritical

Sound is transmitted through a medium by inducing vibrational motion of the molecules through which it is traveling. This vibrational motion represents the sound frequency [11]. Ultrasound is sound of a frequency that is above the threshold of human hearing [12]. The lowest audible frequency for humans is about 18Hz and the highest is normally around 18-20 kHz for adults, above which it becomes inaudible and is defined as ultrasound [11]. In recent decades the use of ultrasound technology has established an important place in dif‐ ferent industrial processes such as the medical field, and has started to revolutionize envi‐ ronmental protection. The idea of using ultrasound in textile wet processes is not a new one. On the contrary there are many reports from the 1950s and 1960s describing the beneficial effects of ultrasound in textile wet processes. In spite of encouraging results from laborato‐ ry-scale studies, the ultrasound-assisted wet textile processes have not been implemented on

In practice, three ranges of frequencies (Fig. 1) are reported for three distinct uses of ultra‐ sound: low frequency or conventional power ultrasound (20-100 kHz), medium frequency

As the sound wave passes through water in the form of compression and rarefaction cycles, the average distance between the water molecules varies. If the pressure amplitude of the sound is sufficiently large, then the distance between the adjacent molecules can exceed the critical molecular distance during the rarefaction cycle. At that moment a new liquid surface

ultrasound and diagnostic or high frequency ultrasound (2-10 MHz) [13].

is created in the form of voids. This phenomenon is called acoustic cavitation [15].

one of the most attractive topics for applied and basic research [9].

carbondioxide will be overviewed.

104 Eco-Friendly Textile Dyeing and Finishing

**2. Ultrasound technology**

an industrial scale as yet [13].

**Figure 2.** Formation of a cavitation buble [16]

Power ultrasound can enhance a wide variety of chemical and physical processes, mainly due to the phenomenon known as cavitation in a liquid medium that is the growth and ex‐ plosive collapse of microscopic bubbles. Sudden and explosive collapse of these bubbles can generate ''hot spots'', i.e., localized high temperature, high pressure, shock waves and se‐ vere shear force capable of breaking chemical bonds [17]. High temperature and pressures resulting from the collapse of the transient cavitation bubbles are responsible for all the ob‐ served effects of ultrasound [18]. Parameters which affect cavitation and bubble collapse are:

**•** energy savings by dyeing at lower temperatures and reduced processing times, **•** environmental improvements by reduced consumption of auxiliary chemicals,

creasing industry competitiveness [21]

3 main phenomenons,

dispersions in the dye bath,

tween dye and fiber [11].

**•** lower overall processing costs (due to less energy and chemical consumption), thereby in‐

The Use of New Technologies in Dyeing of Proteinous Fibers

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

107

Improvements observed in ultrasound-assisted dyeing processes are generally attributed to

**•** Dispersion: breaking up of micelles and high molecular weight aggregates into uniform

**•** Degassing: expulsion of dissolved or entrapped gas or air molecules from fiber into liquid

**•** Diffusion: accelerating the rate of dye diffusion inside the fiber by piercing the insulating layer covering the fiber and accelerating the interaction or chemical reaction, if any, be‐

A good wool dyeing process must provide a satisfactory uptake of dye bath and an ade‐ quate penetration of dye into the fiber, with the practical advantages of good wet fastness and uniform coloration. The conventional methods for wool dyeing are based on long times at temperature close to the boiling point, in order to ensure good results of dye penetration and leveling. These conditions can damage the fibers, with negative effects on the character‐ istics of the finished material. Such damage can be minimized by reducing the operation time or, better yet, by reducing the dyeing temperature. Recently, ultrasound assisted wool dyeing was studied with the aim to reduce temperature or dyeing time with respect to the conventional dyeing technique [22]. Some literature related to the use of ultrasound technol‐

*Shukla and Mathur (1995)* studied the dyeing process of silk using cationic, acid and metalcomplex dyes at low temperatures, assisted by a low frequency ultrasound of 26 kHz and compared the results of dye uptake with those obtained by conventional processes. Their re‐ sults show that silk dyeing in the presence of ultrasound increases the dye uptake for all classes of dyes at lower dyeing temperatures (45°C and 50°C) and a shorter dyeing time (15 min.), as compared with conventional dyeing at 85°C for 60 min. Furthermore, there was no

*Kamel et al. (2005)* have investigated the dyeing of wool fabrics with lac as a natural dye in both conventional and ultrasonic techniques. The extractability of lac dye from natural ori‐ gin using power ultrasonic was also evaluated in comparison with conventional heating. The results of dye extraction indicate that power ultrasonic is rather effective than conven‐ tional heating at low temperature and short time. Color strength values obtained were found to be higher with ultrasonic than with conventional heating. The results of fastness

*Vankar and Shanker (2008)* have extracted coloring pigment from Hollyhock (Alcea rosea) flower and used for dyeing wool yarn, silk and cotton fabrics. It is observed that the dyeing

and removal by cavitation, thus facilitating dye-fiber contact, and

ogy in dyeing of proteinous fibers is summarized below.

apparent fiber damage caused by cavitation [23].

properties of the dyed fabrics were fair to good [17].


Cavitation induced by ultrasound will allow accelerating processes and obtaining the same results as existing techniques but with a lower temperature and low dye and chemical con‐ centrations [20]. For this reason textile wet processes assisted by ultrasound are of high in‐ terest for the textile industry. A review of earlier studies using ultrasound in textile wet processes was compiled by Thakore et al. Ultrasound-assisted textile dyeing was first re‐ ported by Sokolov and Tumansky in 1941 [13]. Some of the benefits of using of ultrasonics in dyeing can be listed as below;

**•** energy savings by dyeing at lower temperatures and reduced processing times,

plosive collapse of microscopic bubbles. Sudden and explosive collapse of these bubbles can generate ''hot spots'', i.e., localized high temperature, high pressure, shock waves and se‐ vere shear force capable of breaking chemical bonds [17]. High temperature and pressures resulting from the collapse of the transient cavitation bubbles are responsible for all the ob‐ served effects of ultrasound [18]. Parameters which affect cavitation and bubble collapse are: **•** Properties of the solvent: The solvent used to perform sample treatment with ultrasonica‐ tion must be carefully chosen. As a general rule, most applications are performed in wa‐ ter. However, other less polar liquids, such as some organics, can be also used, depending on the intended purpose [19]. Cavities are more readily formed when using a solvent with high vapor pressure, low viscosity and low surface tension. But at high vapor pres‐ sure more vapor enters the cavitation bubble during its formation and the bubble collapse

**•** Properties of gases: Soluble gases should result in the formation of a larger number of cavitation nuclei, but the greater the solubility of the gas is the more gas molecules should penetrate the cavity. Therefore, a less violent and intense shock wave is created on bubble

**•** External pressure: With increasing external pressure, the vapor pressure of the liquid de‐ creases and higher intensity is necessary to induce cavitation [13]. In addition, there is an increment in the intensity of the cavitational bubble collapse and, consequently, an en‐ hancement in sonochemical effects is obtained. For a specific frequency there is a particu‐

**•** External temperature: Higher external temperature reduces the intensity necessary to in‐ duce cavitation due to the increased vapor pressure of the liquid. At higher external tem‐ peratures more vapor diffuses into the cavity, and the cavity collapse is cushioned and

**•** Frequency of the sound wave: At high sonic frequencies, on the order of the MHz, the production of cavitation bubbles becomes more difficult than at low sonic frequencies, of the order of the kHz. To achieve cavitation, as the sonic frequency increases, so the inten‐ sity of the applied sound must be increased, to ensure that the cohesive forces of the liq‐ uid media are overcome and voids are created [19]. Lower frequency produces more violent cavitation and, as a consequence, higher localized temperatures and pressures. At very high frequency, the expansion part of the sound wave is too short to permit mole‐

Cavitation induced by ultrasound will allow accelerating processes and obtaining the same results as existing techniques but with a lower temperature and low dye and chemical con‐ centrations [20]. For this reason textile wet processes assisted by ultrasound are of high in‐ terest for the textile industry. A review of earlier studies using ultrasound in textile wet processes was compiled by Thakore et al. Ultrasound-assisted textile dyeing was first re‐ ported by Sokolov and Tumansky in 1941 [13]. Some of the benefits of using of ultrasonics in

lar external pressure that will provide an optimum sonochemical reaction [19].

cules to be pulled apart sufficiently to generate a bubble [13].

is cushioned and less violent [13].

106 Eco-Friendly Textile Dyeing and Finishing

collapse [13].

less violent [13].

dyeing can be listed as below;


Improvements observed in ultrasound-assisted dyeing processes are generally attributed to 3 main phenomenons,


A good wool dyeing process must provide a satisfactory uptake of dye bath and an ade‐ quate penetration of dye into the fiber, with the practical advantages of good wet fastness and uniform coloration. The conventional methods for wool dyeing are based on long times at temperature close to the boiling point, in order to ensure good results of dye penetration and leveling. These conditions can damage the fibers, with negative effects on the character‐ istics of the finished material. Such damage can be minimized by reducing the operation time or, better yet, by reducing the dyeing temperature. Recently, ultrasound assisted wool dyeing was studied with the aim to reduce temperature or dyeing time with respect to the conventional dyeing technique [22]. Some literature related to the use of ultrasound technol‐ ogy in dyeing of proteinous fibers is summarized below.

*Shukla and Mathur (1995)* studied the dyeing process of silk using cationic, acid and metalcomplex dyes at low temperatures, assisted by a low frequency ultrasound of 26 kHz and compared the results of dye uptake with those obtained by conventional processes. Their re‐ sults show that silk dyeing in the presence of ultrasound increases the dye uptake for all classes of dyes at lower dyeing temperatures (45°C and 50°C) and a shorter dyeing time (15 min.), as compared with conventional dyeing at 85°C for 60 min. Furthermore, there was no apparent fiber damage caused by cavitation [23].

*Kamel et al. (2005)* have investigated the dyeing of wool fabrics with lac as a natural dye in both conventional and ultrasonic techniques. The extractability of lac dye from natural ori‐ gin using power ultrasonic was also evaluated in comparison with conventional heating. The results of dye extraction indicate that power ultrasonic is rather effective than conven‐ tional heating at low temperature and short time. Color strength values obtained were found to be higher with ultrasonic than with conventional heating. The results of fastness properties of the dyed fabrics were fair to good [17].

*Vankar and Shanker (2008)* have extracted coloring pigment from Hollyhock (Alcea rosea) flower and used for dyeing wool yarn, silk and cotton fabrics. It is observed that the dyeing with hollyhock gives fair to good fastness properties in sonicator in 1 hour and shows good dye uptake as compared with conventional dyeing [24].

tion. The "electromagnetic spectrum" of an object is the characteristic distribution of electro‐ magnetic radiation emitted or absorbed by that particular object. The electromagnetic spectrum extends from low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom [30]. UV energy is found in

The Use of New Technologies in Dyeing of Proteinous Fibers

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

109

Ultraviolet or UV radiation is part of the electromagnetic (light) spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye [31]. 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 [32]. Scientists classify UV ra‐ diation into three types or bands: UVA, UVB, and UVC (Fig. 4). The ozone layer absorbs

**•** UVA: Long-wavelength UVA covers the range 315-400 nm. Not significantly filtered by the atmosphere. Approximately 90% of UV radiation reaching the Earth's surface. UVA is

**•** UVB: Medium-wavelength UVB covers the range 280-315 nm. Approximately 10% of UV

**•** UVC: Short-wavelength UVC covers the range 100-280 nm [34]. They are the most dan‐ gerous among all the rays. However, these rays do not reach the earth's surface as they

The deleterious effects of solar irradiation are perceived as changes in texture and color, dry‐ ness, etc., and can be evaluated in terms of reduced elasticity, increased porosity or swelling

again divided into UVA-I (340 nm - 400 nm) and UVA-II (315 nm - 340 nm) [34].

the electromagnetic spectrum between visible light and x-rays [29].

**Figure 3.** A diagram of the electromagnetic spectrum [30]

some, but not all, of these types of UV radiation [33].

radiation reaching the Earth's surface [34].

properties, altered

are completely absorbed by the ozone layer [31].

*Battu et al. (2010)* observed that in wool dyeing at 85°C with acid dyes, ultrasound caused an improvement of the dye uptake as much as 25%, or dyeing time would be nearly 20% short‐ er than conventional dyeing [25].

*Yukseloğlu and Bolat (2010)* stated that the wool fabrics have presented similar color yield (K/S) and acceptable color differences (ΔE) with the use of ultrasonic energy. Ultrasonic en‐ ergy was found to be advantageous to be used for wool dyeing at lower temperatures (such as 80°C and 90°C) and lower dyeing times (i.e. 80 min. or 90 min.) as an alternative process for conventional dyeing (100°C and 144 min) [26].

*McNeil and McCall (2011)* investigated the effects of ultrasound at 35-39 kHz on several wool dyeing and finishing processes. Ultrasound pre-treatment increased the effectiveness of sub‐ sequent oxidative-reductive bleaching, but had no effect on the uptake of acid leveling and acid milling dyes. The pre-treatment retarded the uptake of reactive dye, possibly by in‐ creasing the crystallinity of the fiber or removing surface bound lipids. Ultrasound did not improve dyeing under conditions that are currently used in industry, but did show potential to reduce the chemical and energy requirements of dyeing wool with reactive and acid mill‐ ing dyes, but not acid leveling dyes [27].

*Atav and Yurdakul (2011)* investigated the effect of ultrasound usage on the color yield in dyeing of mohair fibers. They found that dyeing in the presence of ultrasound energy in‐ creases the dye-uptake of mohair fibers and hence higher color yield values are obtained. The difference between the samples dyed in the presence and absence of ultrasound, was greater for darker shades and for dyeing carried out in acidic medium (pH 5), and also for shorter dyeing periods. Furthermore there is no important difference between washing fast‐ ness and alkali solubility values of fibers dyed in the presence and absence of ultrasound [28].

*Ferrero and Periolatto (2012)* studied the possibility of reducing the temperature of conven‐ tional wool dyeing with an acid leveling dye using ultrasound in order to reach dye uptake values comparable to those obtained with the standard procedure at 98°C. Dyeings of wool fabrics were carried out in the temperature range between 60°C and 80°C using either me‐ chanical or ultrasound agitation of the bath and coupling the two methods to compare the results. For each dyeing, the dye uptake curves of the dye bath were determined and the better results of dyeing kinetics were obtained with ultrasound coupled with mechanical stirring. Finally, fastness tests to rubbing and domestic laundering yielded good values for samples dyed in ultrasound assisted process even at the lower temperature [22].
