**11. Supercritical carbondioxide technology**

The enhanced solvent properties provided by supercritical fluids (SCFs) are by no means new. In fact, the various phenomena attributed to SCFs have been known for hundreds of years [137]. However, textile dyeing, using supercritical carbon dioxide as dye solvent, has been developed for the last two decades since it potentially overcomes all the economical and ecological disadvantages derived from the conventional water dyeing process [138]. Su‐ percritical fluids are characterized by a very high solute diffusivity and low viscosity. Con‐ sequently, in supercritical fluids all the transport processes are much more rapid. Dyeing in supercritical carbondioxide, for example, entirely avoids the use of water, and consequently there is no possibility of pollution. No auxiliary agents are used and residual dye can be re‐ covered in a reusable form [139].

A supercritical fluid can be defined as a substance above its critical temperature and pres‐ sure. Under this condition the fluid has unique properties, in that it does not condense or evaporate to form a liquid or a gas [140]. Supercritical fluids exhibit gas-like viscosities and diffusivities and liquid-like densities [120]. Although a number of substances are useful as supercritical fluids, carbon dioxide has been the most widely used [140], as the critical tem‐ perature and pressure are easier to achieve than that of other substances [141]. Supercritical CO2 is a dyeing medium which is a potential alternative to water as it is inherently nontoxic, inexpensive, and nonflammable, it can be recycled, it has easily accessible critical conditions [142]. The critical point for carbon dioxide occurs at a pressure of 73.8 bar and a temperature of 31.1°C. ScCO2 represent a potentially unique media for either transporting chemical into or out of a polymeric substrate, because of their thermo-physical and transport properties. The phase diagram of carbon dioxide shown in Fig. 14 represents the interfaces between phases; at the triple point all three phases may coexist. Above the triple point, an increase in temperature drives liquid into the vapor phase, while an increase in pressure drives vapor back to liquid [120]. Above the critical point of carbon dioxide, it retains the free mobility of the gaseous state, but with the increasing pressure its density will increase towards that of a liquid. Solvating power is proportional to density, whilst viscosity remains comparable with that of a normal gas, so the "fluid" has remarkable penetration properties [143].

**Figure 14.** Phase diagram of carbon dioxide [120]

Many techniques have been applied to produce the great potential of ion beam modification technology. It desired surface modifications, ranging from conventional flame treatments, ''wet'' chemical treatments, and electrical treatments (such as corona discharge), to modern plasma treatments and particle beam irradiation (electrons, ions, neutrons and photons) techniques. Among them, particle beam techniques are particularly attractive owing to their flexibility, effectiveness, and environmentally friendly nature compared with conventional techniques. Also, in the domain of particle beam techniques, the ion beam has proven more effective in modifying polymer surfaces than UV-light, c-ray, X-ray and electron beams. This is because energetic ions have a higher cross-section for ionization and larger linear energy transfer (LET, eV nm-1) than these conventional radiation types of comparable energy owing

Numerous papers have appeared in recent years describing surface treatment using ions. Surface modification with ions typically involves fluencies of ~ 109 to 1014 ions/cm2 or in

ly through carbonization. Many different ions have been employed for irradiating poly‐ mers, ranging from hydrogen and helium ions up to ions of heavy elements such as

The enhanced solvent properties provided by supercritical fluids (SCFs) are by no means new. In fact, the various phenomena attributed to SCFs have been known for hundreds of years [137]. However, textile dyeing, using supercritical carbon dioxide as dye solvent, has been developed for the last two decades since it potentially overcomes all the economical and ecological disadvantages derived from the conventional water dyeing process [138]. Su‐ percritical fluids are characterized by a very high solute diffusivity and low viscosity. Con‐ sequently, in supercritical fluids all the transport processes are much more rapid. Dyeing in supercritical carbondioxide, for example, entirely avoids the use of water, and consequently there is no possibility of pollution. No auxiliary agents are used and residual dye can be re‐

A supercritical fluid can be defined as a substance above its critical temperature and pres‐ sure. Under this condition the fluid has unique properties, in that it does not condense or evaporate to form a liquid or a gas [140]. Supercritical fluids exhibit gas-like viscosities and diffusivities and liquid-like densities [120]. Although a number of substances are useful as supercritical fluids, carbon dioxide has been the most widely used [140], as the critical tem‐ perature and pressure are easier to achieve than that of other substances [141]. Supercritical CO2 is a dyeing medium which is a potential alternative to water as it is inherently nontoxic, inexpensive, and nonflammable, it can be recycled, it has easily accessible critical conditions [142]. The critical point for carbon dioxide occurs at a pressure of 73.8 bar and a temperature of 31.1°C. ScCO2 represent a potentially unique media for either transporting chemical into or out of a polymeric substrate, because of their thermo-physical and transport properties.

; higher fluencies may result in destruction of polymer, general‐

to their deeper range [136].

134 Eco-Friendly Textile Dyeing and Finishing

some cases, 1015 ions/cm2

gold or uranium [132].

covered in a reusable form [139].

**11. Supercritical carbondioxide technology**

In the dyeing field, Schollmeyer and co-workers, among others, have demonstrated that both synthetic and natural fibres can be dyed with disperse and reactive disperse dyes in supercritical carbondioxide. However, the dyeing of natural fibres with water soluble dyes in supercritical carbondioxide has not yet been successful, since dyes such as reactive, acid and basic dyes have little solubility in this medium due to their high polarity [144]. One ap‐ proach to this problem was undertaken by Gebert et al. who examined wool and cotton fi‐ bers after attempting to open the fiber surface with a swelling auxiliary so that dye molecules could be readily trapped in the fiber [145].

In natural textiles, the dye molecules can be fixed by either physical (e.g. Van der Waals) or chemical (e.g. covalent) bonds. Since the dyes used in a ScCO2-dyeing process are non-polar and natural fibres are polar, the affinity between dyes and textiles is low so physical bonds are weak. Therefore, a dyeing process must be developed for dyeing natural textiles in ScCO2 with reactive dyes that create covalent dye-textile bonds. So far, several reactive dyes known from conventional dyeing in water have been investigated in ScCO2:

**•** vinylsulphone dyes have been successfully used for silk and wool,


Jun et al. (2005) investigated the phase behavior of a cationic perfluoropolyether surfactant in supercritical carbon dioxide and its ability to solubilise ionic dyes. This cationic surfactant was found to dissolve satisfactorily in supercritical carbon dioxide and was able to form mi‐ cellar aggregates incorporating a small amount of water in their interior. Conventional anionic dyes such as acid and reactive dyes were solubilised satisfactorily in the cationic sur‐ factant/water/supercritical carbon dioxide system. The surfactant was more effective in this

The Use of New Technologies in Dyeing of Proteinous Fibers

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

137

Schmidt et al. (2007) dyed various fibers, among which wool and silk also exist, with C.I. Disperse Yellow 23 modified with 2-bromoacrylic acid and 1,3,5-trichloro-2,4,6-triazine as reactive groups in supercritical carbon dioxide. It was found that on wool and silk, the color depth was higher than on cotton and the wash, rub and light fastness of all dyeings was be‐

Textile dyeing is the most remarkable process among the wet treatments in textile industry in terms of energy and water consumption and effluent load. In last two decades increased laws related to the environment and competitive market conditions required some new processes to be found in textile dyeing field. This situation increased the interest of the us‐ age of new technologies such as ultrasound, ultraviolet, ozone, plasma, gamma irradiation, laser, microwave, e-beam irradiation, ion implantation, and supercritical carbondioxide in textile industry. These new technologies provide not only decrease in time, energy, and chemical consumption, but also decrease in effluent load. So that all of these new technolo‐ gies considered to be very interesting future oriented processes because of being environ‐ mentally friendly. Although it was proven with many researches that most of these technologies are successful at laboratory scale, there is still need to integrate them into in‐ dustrial applications. There is no doubt that in future these new technologies will find wide range of applications when their disadvantages (to be expensive, not possible to be used for

respect than its anionic analogue [144].

all fiber types and exc.) will be eliminated.

Namık Kemal University, Textile Engineering Department, Turkey

[1] Lewis, D.M., 1992, Wool Dyeing, Society of Dyers and Colorists

tween 4 and 5 [150].

**12. Conclusions**

**Author details**

Rıza Atav

**References**

*Guzel and Akgerman (2000)* dyed the wool fibers with three mordant dyes dissolved in super‐ critical carbon dioxide. Wool fibers were mordanted with five different metal ions (Cr(III), Al(III), Fe(II), Cu(II) and Sn(II)) using conventional techniques and dyed at 333-353°K tem‐ perature and at 150-230 atm pressure. According to the experimental results it was found that dyed materials had excellent wash fastness properties [147].

For water-soluble dyes, attempts were made to dye natural fibers using reverse micelle tech‐ nique (Fig. 15) in which ionic dye, solubilized in the water-pool, passes into the fiber togeth‐ er with a small amount of water immediately after contact with it. Satisfactory results were obtained for proteinous fibers [120].

*Sawada et al. (2002)* has developed a reverse micellar system in supercritical carbon dioxide as a dyeing medium. Water-soluble dyes such as reactive dyes and acid dyes could be suffi‐ ciently solubilised in the interior of a specially constituted reverse micelle. Protein fabrics, silk and wool, were satisfactorily dyed even in deep shades with conventional acid dyes without any special pretreatment. Compared to previously proposed supercritical dyeing methods, dyeing of fabrics with this system could be performed at low temperatures and pressures in a short time [148].

*Jun et al. (2004)* investigated the dyeing of wool fabrics with conventional acid dyes in a su‐ percritical CO2 using a reverse micellar system. A reverse micelle composed of perfluoro 2,5,8,11-tetramethyl-3,6,9,12-tetraoxapentadecanoic acid ammonium salt/CO2/water had a high potential to solubilize conventional acid dyes and to dye wool fabrics in this system. It was found that dyeability of the acid dye on wool in this system take no influence of the density of CO2. On the other hand, variation of dyeing temperature resulted in the remarka‐ ble differences of the dyeability of the acid dye on wool even though the solubility of dye in the system was not varied by the variation of temperature [149]

**Figure 15.** Dyeing of natural fibers using reverse micelle [120]

Jun et al. (2005) investigated the phase behavior of a cationic perfluoropolyether surfactant in supercritical carbon dioxide and its ability to solubilise ionic dyes. This cationic surfactant was found to dissolve satisfactorily in supercritical carbon dioxide and was able to form mi‐ cellar aggregates incorporating a small amount of water in their interior. Conventional anionic dyes such as acid and reactive dyes were solubilised satisfactorily in the cationic sur‐ factant/water/supercritical carbon dioxide system. The surfactant was more effective in this respect than its anionic analogue [144].

Schmidt et al. (2007) dyed various fibers, among which wool and silk also exist, with C.I. Disperse Yellow 23 modified with 2-bromoacrylic acid and 1,3,5-trichloro-2,4,6-triazine as reactive groups in supercritical carbon dioxide. It was found that on wool and silk, the color depth was higher than on cotton and the wash, rub and light fastness of all dyeings was be‐ tween 4 and 5 [150].
