**1. Introduction**

172 Textile Dyeing

[33] Y.-A. Son, G.-T. Lim, J.-P. Hong, and T.-K. Kim, "Indigo adsorption properties to

[34] D. Karst and Y. Yang, "An Explanantion and Prediction of disperse Dye Exhaustion on PLA," *Book of papers - International Conference & Exhibition, AATCC,* p. 184, 2004. [35] D. Karst and Y. Yang, "Using the Solubility Parameter to Explain Disperse Dye Sorption on Polylactide," *Journal of Applied Polymer Science,* vol. 96, p. 416, 2005. [36] R. F. Fedors, "A Method for Estimating Both the Solubility Parameters and Molar Volume of Liquids," *Polymer Engineering Science,* vol. 14, p. 147, 1974.

[37] *Colour Index, III edition* vol. 4: SDC and AATCC, 1971.

2005.

polyester fibers of different levels of fineness," *Dyes and Pigments,* vol. 65, p. 137,

The synthetic fibers are widely used in apparel and home furnishings due to their good physical and chemical properties. The synthetic fiber market is characterized by a trend towards ever-finer fibers. It is very difficult for these finer fibers to obtain very deep colours via the common dyeing processes. The increasing demand of polyester (PES) such as poly(ethylene terephthalate) (PET) in textile market for high performance applications in smart textiles, technical textiles, operation clothing etc. and more recently, for their potential applications as electronic textiles. It indicates that PET has the potential in research in the future due to the wide range of mechanical properties, relative high melting point and glass transition temperature, insensitivity to common solvents and moisture, chemical inertness. PET, an aliphatic-aromatic polymer composition and thermoplastic, shows a rather hydrophobic nature due to its rigid structure,

Fig. 1. Chemical structure of PET

The two carbonyl functions together with the aromatic ring provide the structural rigidity of the macromolecule; little flexibility arises due to the presence of the ethylene group in the repeating unit. The polar ester groups in the PET hold the PES into strong crystals. PET consists of a two-phase structure: crystalline (35 % in vol.) and non-crystalline (65 % in vol.). The most important phase in determining dyeability in the conventional dyeing process is the amorphous region. The PET becomes rubbery and swelling above its glass transition temperature. In this state the dye molecules are able to penetrate into the amorphous region and by cooling down the molecule can be trapped inside the PET macromolecules.

In recent years, consumers have shown an increasing preference for use of synthetic fibers blended with natural fibers to combine advantages of both materials. Due to the hydrophobic nature synthetics such as PES fibers are dyed at high temperatures around 130 °C and high pressure, this needs lot of energy and special equipment (Xu et al. 2002). Moreover, since polyesters are stronger than natural fibers, PES fabric blends containing wool, cotton etc. are very popular, since PES makes the fabrics more resilient and wrinkle free. Similar to PES, low priced polypropylene (PP) is frequently used in the technical

Substrate Independent Dyeing of Synthetic Textiles Treated with Low-Pressure Plasmas 175

Moreover, much research has also been done in the environmentally friendly dyeing of PET with disperse dyes in supercritical CO2 which has the advantage of reducing the need for additional chemicals and waste water (Okuno et al., 1992; Montero et al., 2003; Özcan et al., 2005). The scaling of the supercritical fluid dyeing experiment from laboratory size to industrial scale is far from being a straight-forward procedure because it requires very high pressures (260-300 bar) and high investment cost. At low pressure K/S value is decreased, which yields low dye solubility (Özcan et al., 2005). Moreover, conventional textile dyeing is dependent on the substrate materials due to their specific chemical nature. In a specific dyeing condition, dye molecules chemically and physically bind with the textile fibers and thus, the dyestuff class is also limited to the chemical groups present in the fiber due to dye-fiber interaction. For this reasons, substrate independent dyeing is of particular interest not only for textiles, but also for the materials industries where coloration is needed. Barranco et al. was adding dyestuff molecules downstream in a filmforming plasma in order to obtain dye molecule containing nanocomposite coatings (Barranco et al., 2006). There has been very little attention focused on the application of hydrophilic acid dyes on hydrophobic PET fabrics. Milling acid dyes, which have excellent color brightness and very good wet fastness, can easily be applied to plasmatreated polyester or their blends with natural fibers at low dyeing temperature of 80 °C within an hour dyeing time, where plasma modification is used as an alternative to the

While some efforts have been devoted to study dyeability of PES by plasma treatments, very few articles have been reported about the application of acid dyes to PES. In this research, an attempt was made to solve some limitations of PET dyeing using hydrophilic acid dye by modifying the surface with a novel nanoporous plasma polymer coating. Since the dyeing becomes independent from the substrate material, this approach enables the dyeing of all kinds of synthetic fibers or blend fabrics. Surface modification of fabrics induced by ammonia/acetylene and ammonia/ethylene plasmas was carried out in order to incorporate amine end-functional groups into the hydrocarbon plasma polymer and consequently, provide accessible functional groups for the diffusion of hydrophilic acid dye molecules into

Nitrogenated amorphous hydrocarbon films (a-C:H:N films) were deposited on PET fabrics by cold plasma using a pilot-plant plasma reactor. Tightly woven and washed polyethylene terephthalate (PET) fabric (76 ends/in, 76 picks/in, 43.5 g/m2) from Sefar AG (Switzerland) was used in this study. The deposited-hydrophilic a-C:H:N films were characterized by contact angles (CAs). The mechanical stability of the plasma coating was examined by Abrasion & Pilling Tester. Dyeing of the plasma coating was examined by Datacolor Spectraflash, and the results of dyeing were compared for both plasmas (ammonia/acetylene and ammonia/ethylene), while a study was investigated to observe the influences of energy input in terms of power input per unit of gas flow W/F (J/cm3),

A gas discharge allows the acceleration of free electrons when driven by an external source (e.g. RF generator). As a consequence, highly reactive and activated molecular species such as chemical radicals, ions, metastables, electrons etc. can be created by ionization, fragmentation (dissociation), excitation, UV radiation, etching reactions etc. These species

required pre-treatment of PET textiles (Hossain et al., 2007a).

the nanoporous structure of the plasma polymer.

film thickness, and gas ratio.

**2. Plasma treatments** 

textiles, home textiles, the automobile industry and to lesser extent in apparel textiles due to their special characteristics such as resistance to chemicals, low density etc. The dyeing of PP is difficult and the fastness properties are not good due to the highly crystalline molecular structure. However, dyeing of PES blends is a problem due to damage/reduction in the strength of natural fibers (cellulose degradation etc.) at high dyeing temperatures. Due to the hydrophobic nature of PES, its compact structure and cristallinity dyeing is limited to water-insoluble dyes such as disperse dyes, vat dyes etc. (De Girogi et al., 2000). The low and finite water solubility of these dyes is also a critical factor in determining levelling properties and dyeing rate (Kulkarni et al., 1986). Conventional polyester dyeing processes additionally require dispersing agent, dye carriers, and surfactants to obtain dye solubility in water. Due to dye reduction and migration, the fastness to washing was found to be on the satisfactory level when dyeing with these dyes (Son et al., 2004). The rate of diffusion of these dyestuffs in the fiber is relatively low. Therefore, the rate of diffusion in the conventional PES dyeing commercially may be raised either by working at higher temperature in the region of 130 °C and/ or in the super atmospheric pressure in the presence of accelerating agent or carrier or surfactants or dyeing auxiliaries.

Recently, research on the use of different surface modification techniques such as low pressure plasma (LPP) and atmospheric pressure plasma (APP) in order to improve the dyeability of polyesters has grown in interest, since they are environmentally efficient. An increase in hydrophilicity and dyeability of knitted PES textiles after the plasma modification in an O2/CF4 mixture was obtained, as reported by Aubrecht et al. (2006). The dyeability with basic dye is enhanced on PET/cotton blends by in situ polymerization of acrylic acid and water (Öktem et al., 2002). Sarmadi et al., 1993 observed that the dyeability with basic dye (dye bath temperature 100 °C and 2 hours dyeing time) can further be improved by an increase in the time it is exposed to CF4 cold plasma, and found K/S values between 0.50-1.51 for a 2% owf (on the weight of fabric) dark shade dyeing with hydrophobic basic dye. A higher color yield was obtained on acrylic acid grafted PET fiber induced by Ar plasma. Barani et al. (2010) compared the dyeability of PES microfiber fabrics using various pre- and post-treatments. They reported that alkali, sol-gel and oxygen plasma treatments are able to enhance the color strength. Continuous modification of PES was carried out using DBD (dielectric barrier discharge) plasma at atmospheric pressure with a Ar/O2 ratio of 10:1 (Zhongfu et al., 2007). It was reported that the spectral value (K/S) dyed with blue disperse dyes was found to be increased by 50% in comparison with that of untreated samples due to the formation of –COOH groups during plasma treatment. The work of Ferrero et al. (2004) has shown that the fastness to washing with basic dye on PET by in situ polymerization of acrylic acid using low temperature plasma was found to be unsatisfactory probably because of an unstable bond between grafted acrylic acid and dye molecules. Anti-reflecting coating layers have been deposited with organo-silicon compounds using APP plasma, which enhanced the color intensity on PET surfaces as explained by Lee et al. (2001). Okuno et at. (1992) studied the correlation between the crystallinity and dyeability of PET fibers using non-film-forming gases by cold plasma. They found that plasma-treated samples significantly reduced the dyeability due to the etching of macromolecules in the dyeable amorphous phase. Recently, Addamo et al. (2006) reported that the color depth of air LPP plasma treated PET fibers is related to their topographical characteristics and to their chemical surface composition. They observed that the color strength with disperse dye at a dyeing temperature of 100 °C can be increased by decreasing the fraction of light reflected from the treated surfaces.

Moreover, much research has also been done in the environmentally friendly dyeing of PET with disperse dyes in supercritical CO2 which has the advantage of reducing the need for additional chemicals and waste water (Okuno et al., 1992; Montero et al., 2003; Özcan et al., 2005). The scaling of the supercritical fluid dyeing experiment from laboratory size to industrial scale is far from being a straight-forward procedure because it requires very high pressures (260-300 bar) and high investment cost. At low pressure K/S value is decreased, which yields low dye solubility (Özcan et al., 2005). Moreover, conventional textile dyeing is dependent on the substrate materials due to their specific chemical nature. In a specific dyeing condition, dye molecules chemically and physically bind with the textile fibers and thus, the dyestuff class is also limited to the chemical groups present in the fiber due to dye-fiber interaction. For this reasons, substrate independent dyeing is of particular interest not only for textiles, but also for the materials industries where coloration is needed. Barranco et al. was adding dyestuff molecules downstream in a filmforming plasma in order to obtain dye molecule containing nanocomposite coatings (Barranco et al., 2006). There has been very little attention focused on the application of hydrophilic acid dyes on hydrophobic PET fabrics. Milling acid dyes, which have excellent color brightness and very good wet fastness, can easily be applied to plasmatreated polyester or their blends with natural fibers at low dyeing temperature of 80 °C within an hour dyeing time, where plasma modification is used as an alternative to the required pre-treatment of PET textiles (Hossain et al., 2007a).

While some efforts have been devoted to study dyeability of PES by plasma treatments, very few articles have been reported about the application of acid dyes to PES. In this research, an attempt was made to solve some limitations of PET dyeing using hydrophilic acid dye by modifying the surface with a novel nanoporous plasma polymer coating. Since the dyeing becomes independent from the substrate material, this approach enables the dyeing of all kinds of synthetic fibers or blend fabrics. Surface modification of fabrics induced by ammonia/acetylene and ammonia/ethylene plasmas was carried out in order to incorporate amine end-functional groups into the hydrocarbon plasma polymer and consequently, provide accessible functional groups for the diffusion of hydrophilic acid dye molecules into the nanoporous structure of the plasma polymer.

Nitrogenated amorphous hydrocarbon films (a-C:H:N films) were deposited on PET fabrics by cold plasma using a pilot-plant plasma reactor. Tightly woven and washed polyethylene terephthalate (PET) fabric (76 ends/in, 76 picks/in, 43.5 g/m2) from Sefar AG (Switzerland) was used in this study. The deposited-hydrophilic a-C:H:N films were characterized by contact angles (CAs). The mechanical stability of the plasma coating was examined by Abrasion & Pilling Tester. Dyeing of the plasma coating was examined by Datacolor Spectraflash, and the results of dyeing were compared for both plasmas (ammonia/acetylene and ammonia/ethylene), while a study was investigated to observe the influences of energy input in terms of power input per unit of gas flow W/F (J/cm3), film thickness, and gas ratio.
