**4. Commercialization**

186 Textile Dyeing

Fig. 13. Effect of dye bath pH on dyeability (dyeing time 60 min and dyeing temperature 80 °C)

Table 2 shows summarized results of plasma-dyed PES that were assessed using an ISO test method (ISO 105-X12 for color fastness to rubbing and EN ISO 105-C06 for color fastness to washing). Under D65 illumination color changes, staining and rub were evaluated using grey scales: ISO-105-A02 grey scale for assessing change in color; ISO-105-A03 grey scale for staining and rub. All plasmas show almost comparable fastness properties after washing at 60 °C for ammonia/acetylene and ammonia/ethylene plasmas dyed PET. The acid dyeing

NH3/C2H2 = 1.00 3 5 4 4-5 4-5

NH3/C2H2 = 1.25 3 5 4 4 4

NH3/C2H2 = 1.50 3 5 4 4 4-5

NH3/C2H4 = 0.71 3 5 3-4 4 4-5

NH3/C2H4 = 1.00 3 5 3-4 4 4-5

NH3/C2H4 = 1.25 3 5 3-4 4 4-5

Table 2. Wash (at 60 °C) and rub fastness of a-C:H:N films deposited on PET fabrics

Wash fastness Rub fastness

Color change Staining (PET) Staining (wool) Dry Wet

(600 W, NH3/C2H4 = 0.84, 20 min) and light-shade dyed PET (0.5% owf).

**3.1.3 Fastness properties** 

Gas ratio (vol.)

A considerable amount of basic research has been devoted mostly in laboratory scales to incorporate functional groups on the textile surfaces by plasma modification. Besides plasma parameters, the reactor geometry complicates the process scaling-up (Hegemann et al., 2007). Another fundamental problem at this moment is the lack of adapted plasma systems and the transfer of the laboratory findings into textile industry. Textilveredelung Grabher GmbH/Austria is using LPP plasma reactor (vol. 11 m3) in obtaining permanent hydrophilic and hydrophobic surface modification on textiles. The roll-to-roll system has a 15 m long plasma passage and is able to treat substrates up to 1.60 m in width (Fig. 14). Sefar AG/Switzerland is one of the pioneering companies in high-performance filtration solutions and uses the world largest APP systems, consisted of a high voltage power supply, for industrial applications (Fig. 15). The machine is installed inline textile processing and is capable of treating textiles, nonwovens, polymer webs etc. up to 4.0 m wide and materials speed up to 25 m/min (depending on the hydrophilization effect). The developed processes offer a range of cost-effective, and environmentally sound solutions to problems faced in screen printing. As a process gas He/Ar, and CO2 etc. have been successfully used in their system at modifying textiles.

Fig. 14. Industrial plasma reactor at Textilveredelung Grabher GmbH/Austria

Substrate Independent Dyeing of Synthetic Textiles Treated with Low-Pressure Plasmas 189

Fig. 16. XPS analysis of plasma-activated polypropylene (top: control, and bottom: Ar/O2

While plasma processing represents a dry, eco-friendly technology requiring a small amount of resources, it also has to prove its economic feasibility. Plasma activation processes without deposition of a film are state of the art in order to improve e.g. adhesion and can also be conducted using APP plasmas. Textile industry is thus using corona discharges operated in air for decades. However, the treatments are prone to aging effects (hydrophobic recovery) and show a limited uniformity. For more sophisticated applications such as the discussed (substrate independent) dyeing process, but also for the formation of permanent hydrophilic or hydrophobic surfaces, plasma polymerization processes are required. Thus, a large amount of research and development has been

and CO2 plasmas)

**4.1 Cost analysis** 

Fig. 15. The continuous plasma system at Sefar AG/ Switzerland

They reported that an oxygen containing gaseous mixture (Ar/He with O2 and ratio 20:1) was found to be more efficient compared to pure inert gases (Ar, He etc.) to remove organic contaminants by oxidizing polymer surfaces and to implant polar functional groups on the textile surfaces (Oyama et al., 1998). The use of gaseous mixtures facilitates cross-linking und better hydrophilicity. In this process, oxygen plasma causes reactions with surface contaminants resulting in their volatilization and removal of the degradation products as water vapor, CO, CO2, H2, etc. (Hossain et al., 2006b). Moreover, oxygenated functions such as –OH, -C=O, -COO, -COOR etc. are grafted onto the surface as can be seen in XPS analysis (Fig. 16). Thus, functionalized and activated surfaces can be obtained, which can be used for the subsequent wet processing such as lamination, coating, dyeability, printability etc. The grafted surfaces can also lead to covalent bonds suitable for further attachment of coatings, matrices etc. These new reactive sites can be used to improve adhesion and prevent delamination of the subsequent coatings, thus supporting the formation of abrasion resistant coatings.

Fig. 16. XPS analysis of plasma-activated polypropylene (top: control, and bottom: Ar/O2 and CO2 plasmas)

#### **4.1 Cost analysis**

188 Textile Dyeing

Fig. 15. The continuous plasma system at Sefar AG/ Switzerland

coatings.

They reported that an oxygen containing gaseous mixture (Ar/He with O2 and ratio 20:1) was found to be more efficient compared to pure inert gases (Ar, He etc.) to remove organic contaminants by oxidizing polymer surfaces and to implant polar functional groups on the textile surfaces (Oyama et al., 1998). The use of gaseous mixtures facilitates cross-linking und better hydrophilicity. In this process, oxygen plasma causes reactions with surface contaminants resulting in their volatilization and removal of the degradation products as water vapor, CO, CO2, H2, etc. (Hossain et al., 2006b). Moreover, oxygenated functions such as –OH, -C=O, -COO, -COOR etc. are grafted onto the surface as can be seen in XPS analysis (Fig. 16). Thus, functionalized and activated surfaces can be obtained, which can be used for the subsequent wet processing such as lamination, coating, dyeability, printability etc. The grafted surfaces can also lead to covalent bonds suitable for further attachment of coatings, matrices etc. These new reactive sites can be used to improve adhesion and prevent delamination of the subsequent coatings, thus supporting the formation of abrasion resistant

While plasma processing represents a dry, eco-friendly technology requiring a small amount of resources, it also has to prove its economic feasibility. Plasma activation processes without deposition of a film are state of the art in order to improve e.g. adhesion and can also be conducted using APP plasmas. Textile industry is thus using corona discharges operated in air for decades. However, the treatments are prone to aging effects (hydrophobic recovery) and show a limited uniformity. For more sophisticated applications such as the discussed (substrate independent) dyeing process, but also for the formation of permanent hydrophilic or hydrophobic surfaces, plasma polymerization processes are required. Thus, a large amount of research and development has been

Substrate Independent Dyeing of Synthetic Textiles Treated with Low-Pressure Plasmas 191

Fig. 17. Cost analysis for the comparison of LPP and APP processes for the permanent hydrophilization of textiles for 1.5 m in width and 5 km output per day showing the investment (at time zero) and the (constant) running costs. After 14 months both processes were producing 1500 km of functionalized textiles at a total cost of 0.78 \$/m2, which is

This study investigated an alternative procedure to dye synthetic textiles, namely polyester, polypropylene etc., at low temperature using two different plasma polymerization methods, based on an original process of plasma deposition of nanoporous coatings. LPP discharge was performed for the modifications which avoid heat generation to the surface and additionally, it delivers high activation energy. The plasma modification alters the surface properties of textiles from hydrophobic to hydrophilic and to enable the dyeing of synthetics at low temperatures. Ammonia/hydrocarbon mixtures were investigated within a RF plasma using a web coater in order to deposit a-C:H:N coatings on PET textiles. Pure hydrocarbon discharges at low pressures can be used to deposit crosslinked a-C:H coatings. In particular, high deposition rates can be obtained with unsaturated hydrocarbon monomers such as acetylene and ethylene by producing the divalent radicals. Admixture of ammonia to the hydrocarbon discharge influenced the plasma polymerization mechanism depending mainly on gas ratio and energy input. Amine terminating groups, NH2 and eventually NH, were embedded in hydrogenated carbon films (a-C:H films) using ammonia/hydrocarbon plasma. In addition, nitrogen incorporation in a-C:H films facilitated in forming crosslinked and branched plasma polymers. Thus, a nanoporous structure with a large specific surface area was achieved that contained functional groups inside the coating volume, which were accessible to e.g. acid dye molecules, thus facilitating substrate independent dyeing. It was found that dyeability is strongly influenced by both

further reducing with time.

plasma parameters and fabric structure.

**5. Conclusion** 

done to explore both LPP and APP technologies. Nowadays, both systems are industrially available as mentioned above, which enable a comparison of special processes also regarding the costs.

Certainly, LPP offers more and different possibilities such as physical and chemical vapor deposition utilizing energetic particle interactions (sputtering, ion-induced etching, ion implantation, subplantation and densification). Moreover, LPP are able to penetrate deeper into complex material structures such as textiles. Finally, LPP processes are well established, reliable and robust. For plasma processes based on plasma-chemical reactions, however, it could be shown that both LPP and APP processes can be compared (Sawada et al., 1995). For instance, the incorporation of polar groups in ultrathin plasma polymer films might be examined yielding a permanent hydrophilic surface (Herbert et al., 2009). The deposition rate is mainly determined by the monomer flow rate due to a comparable energy input into the plasma phase. As reactive gases N2, NH3, H2, O2, CO2, H2O etc. might be added, again at a comparable flow rate. APP in addition requires a "filling gas" to reach atmospheric pressure, where helium (He) shows the best characteristics regarding plasma stability and energetic UV radiation (used for crosslinking). LPP on the other hand, requires (expensive) vacuum technology and the corresponding pumping system leading to the common assumption that APP may be advantageous. APP might be operated with a simple housing, but requires high flow rates of the filling gas in order to provide a sufficiently defined plasma atmosphere and to obtain a drift of the reactants to the surface, since convection processes have to be overcome.

Assuming that additional costs might be comparable in both technologies, i.e. personal costs, infrastructure, maintenance and (low) energy costs, a cost analysis can be performed on the basis of the investment and the running costs. While the investment is certainly higher for a LPP system, the running costs are actually higher for the APP system due to the high amount of required filling gas. Beside the already mentioned technological arguments, now also the costs can be estimated and compared for both plasma processes, which supports industry in selecting the best technology for their requirements.

For comparison, we selected a hydrophilic plasma treatment based on the deposition of an ultrathin (25 nm) plasma polymer film containing functional polar groups such as the one described in this chapter (LPP). For the comparable APP process, He at a flow rate of 100 slm is considered as filling gas. Both processes enable coating of 150 cm in width at a comparable process velocity in order to obtain the same amount of produced functional textiles per day. Fig. 17 displays the evolution of the costs with time. As it can be noticed, the break-even of the LPP system with the APP process is already reached after 14 months of operation due to the high running costs by He use. Even when recycling of He (recovery around 80%) can be considered causing increased investment costs, the break-even is reached after around 3 years. A similar analysis holds for the use of Ar or N2 as filling gas as well as for hydrophobic treatments, again showing that LPP is beside many further advantages the more cost-efficient technology.

For the presented dyeing process thicker coatings might be required (see Fig. 9) which reduces the amount of functionalized textile per day and should be regarded for the cost analysis. Process optimization can still be expected. Also note that a 4 m wide plasma system as used by Sefar with APP might not be feasible using LPP. A well-based cost analysis, however, should be done by potential applicants giving good reasons for LPP systems as used by Textilveredelung Grabher.

Fig. 17. Cost analysis for the comparison of LPP and APP processes for the permanent hydrophilization of textiles for 1.5 m in width and 5 km output per day showing the investment (at time zero) and the (constant) running costs. After 14 months both processes were producing 1500 km of functionalized textiles at a total cost of 0.78 \$/m2, which is further reducing with time.

#### **5. Conclusion**

190 Textile Dyeing

done to explore both LPP and APP technologies. Nowadays, both systems are industrially available as mentioned above, which enable a comparison of special processes also

Certainly, LPP offers more and different possibilities such as physical and chemical vapor deposition utilizing energetic particle interactions (sputtering, ion-induced etching, ion implantation, subplantation and densification). Moreover, LPP are able to penetrate deeper into complex material structures such as textiles. Finally, LPP processes are well established, reliable and robust. For plasma processes based on plasma-chemical reactions, however, it could be shown that both LPP and APP processes can be compared (Sawada et al., 1995). For instance, the incorporation of polar groups in ultrathin plasma polymer films might be examined yielding a permanent hydrophilic surface (Herbert et al., 2009). The deposition rate is mainly determined by the monomer flow rate due to a comparable energy input into the plasma phase. As reactive gases N2, NH3, H2, O2, CO2, H2O etc. might be added, again at a comparable flow rate. APP in addition requires a "filling gas" to reach atmospheric pressure, where helium (He) shows the best characteristics regarding plasma stability and energetic UV radiation (used for crosslinking). LPP on the other hand, requires (expensive) vacuum technology and the corresponding pumping system leading to the common assumption that APP may be advantageous. APP might be operated with a simple housing, but requires high flow rates of the filling gas in order to provide a sufficiently defined plasma atmosphere and to obtain a drift of the reactants to the surface, since convection

Assuming that additional costs might be comparable in both technologies, i.e. personal costs, infrastructure, maintenance and (low) energy costs, a cost analysis can be performed on the basis of the investment and the running costs. While the investment is certainly higher for a LPP system, the running costs are actually higher for the APP system due to the high amount of required filling gas. Beside the already mentioned technological arguments, now also the costs can be estimated and compared for both plasma processes, which supports industry in selecting the best technology for their

For comparison, we selected a hydrophilic plasma treatment based on the deposition of an ultrathin (25 nm) plasma polymer film containing functional polar groups such as the one described in this chapter (LPP). For the comparable APP process, He at a flow rate of 100 slm is considered as filling gas. Both processes enable coating of 150 cm in width at a comparable process velocity in order to obtain the same amount of produced functional textiles per day. Fig. 17 displays the evolution of the costs with time. As it can be noticed, the break-even of the LPP system with the APP process is already reached after 14 months of operation due to the high running costs by He use. Even when recycling of He (recovery around 80%) can be considered causing increased investment costs, the break-even is reached after around 3 years. A similar analysis holds for the use of Ar or N2 as filling gas as well as for hydrophobic treatments, again showing that LPP is beside many further

For the presented dyeing process thicker coatings might be required (see Fig. 9) which reduces the amount of functionalized textile per day and should be regarded for the cost analysis. Process optimization can still be expected. Also note that a 4 m wide plasma system as used by Sefar with APP might not be feasible using LPP. A well-based cost analysis, however, should be done by potential applicants giving good reasons for LPP

regarding the costs.

processes have to be overcome.

advantages the more cost-efficient technology.

systems as used by Textilveredelung Grabher.

requirements.

This study investigated an alternative procedure to dye synthetic textiles, namely polyester, polypropylene etc., at low temperature using two different plasma polymerization methods, based on an original process of plasma deposition of nanoporous coatings. LPP discharge was performed for the modifications which avoid heat generation to the surface and additionally, it delivers high activation energy. The plasma modification alters the surface properties of textiles from hydrophobic to hydrophilic and to enable the dyeing of synthetics at low temperatures. Ammonia/hydrocarbon mixtures were investigated within a RF plasma using a web coater in order to deposit a-C:H:N coatings on PET textiles. Pure hydrocarbon discharges at low pressures can be used to deposit crosslinked a-C:H coatings. In particular, high deposition rates can be obtained with unsaturated hydrocarbon monomers such as acetylene and ethylene by producing the divalent radicals. Admixture of ammonia to the hydrocarbon discharge influenced the plasma polymerization mechanism depending mainly on gas ratio and energy input. Amine terminating groups, NH2 and eventually NH, were embedded in hydrogenated carbon films (a-C:H films) using ammonia/hydrocarbon plasma. In addition, nitrogen incorporation in a-C:H films facilitated in forming crosslinked and branched plasma polymers. Thus, a nanoporous structure with a large specific surface area was achieved that contained functional groups inside the coating volume, which were accessible to e.g. acid dye molecules, thus facilitating substrate independent dyeing. It was found that dyeability is strongly influenced by both plasma parameters and fabric structure.

Substrate Independent Dyeing of Synthetic Textiles Treated with Low-Pressure Plasmas 193

Zhongfu, R.; Gao, Q.; Xiandong, R. & Zhonghua, W. (2007). Continuous modification

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based carbon fibers tuned by anodic oxidation in different alkaline electrolyte

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Besides plasma parameters the gas ratio plays a very important role in determining high color yields. Higher gas ratios were found to be less colored due to fewer amino functional groups, while they show higher hydrophilicity owing to the addition of polar functions on the surfaces during post plasma reactions. At gas ratios of around 1.25 for NH3/C2H2 and 1.0 for NH3/C2H4 crosslinked and branched a-C:H:N coatings were produced, which posed high number of accessible nitrogen functional groups, i.e. amino groups, resulting in high color intensity. Although their wetting properties were less pronounced as for higher ammonia content, dye molecules could easily enter the nanoporous film structure and chemically bound with the nitrogen functionalities. Thus, high K/S values per film thickness have been obtained. The uniformity of plasma polymers provides information about the even dyeing. Moreover, the plasma-deposited and dyed PET fabrics showed a good rubbing and washing fastness demonstrating the coating-functional permanency. The excellent abrasion resistance confirmed that the coating was permanently adhered to the substrate. Hence, the same dyeing principle can also be applied to all hydrophobic synthetic textiles and their blends with natural textiles which are difficult to dye.

A thorough cost analysis based on existing plasma processes were performed showing the ecological potential of plasma processes, in particular of low pressure plasma systems due to low running costs.

These findings demonstrate that plasma polymerization provides an eco-friendly multifunctionalized surface modification, since the use of chemicals; waste water etc. can be eliminated. Furthermore, since the coating thickness is in the nanometer range (<300 nm), the materials, architectural porosity, touch, and comfort etc. are not affected. The nanoporous plasma polymers can be effectively used as a foundation for multifunctional applications such as fiber-reinforced composites, superhydrophobicity, cell-adhesion etc. Thus, the developed nanoporous coatings that incorporate accessible functional groups are most promising candidates for technical textiles.

#### **6. References**


Besides plasma parameters the gas ratio plays a very important role in determining high color yields. Higher gas ratios were found to be less colored due to fewer amino functional groups, while they show higher hydrophilicity owing to the addition of polar functions on the surfaces during post plasma reactions. At gas ratios of around 1.25 for NH3/C2H2 and 1.0 for NH3/C2H4 crosslinked and branched a-C:H:N coatings were produced, which posed high number of accessible nitrogen functional groups, i.e. amino groups, resulting in high color intensity. Although their wetting properties were less pronounced as for higher ammonia content, dye molecules could easily enter the nanoporous film structure and chemically bound with the nitrogen functionalities. Thus, high K/S values per film thickness have been obtained. The uniformity of plasma polymers provides information about the even dyeing. Moreover, the plasma-deposited and dyed PET fabrics showed a good rubbing and washing fastness demonstrating the coating-functional permanency. The excellent abrasion resistance confirmed that the coating was permanently adhered to the substrate. Hence, the same dyeing principle can also be applied to all hydrophobic synthetic

A thorough cost analysis based on existing plasma processes were performed showing the ecological potential of plasma processes, in particular of low pressure plasma systems due

These findings demonstrate that plasma polymerization provides an eco-friendly multifunctionalized surface modification, since the use of chemicals; waste water etc. can be eliminated. Furthermore, since the coating thickness is in the nanometer range (<300 nm), the materials, architectural porosity, touch, and comfort etc. are not affected. The nanoporous plasma polymers can be effectively used as a foundation for multifunctional applications such as fiber-reinforced composites, superhydrophobicity, cell-adhesion etc. Thus, the developed nanoporous coatings that incorporate accessible functional groups are

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Aubrecht, L; Pichal, J.; Spatenka, P.; Vatuna, T. & Martinkova, L. (2006). Etching of PES fabric by O2/CH4 plasma, *Czechoslovak Journal of Physics*, 56 (S2): B1126-1131. Öktem, T; Seventekin, N.; Ayhan, H. & Piskin, E. (2002). Improvement in surface-related

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properties of poly(ethylene terephthalate)/cotton fabrics by glow-discharge

textiles and their blends with natural textiles which are difficult to dye.

irradiation, *European Polymer Journal,* 39: 199-202.

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disperse dyes in supercritical CO2, *Dyes Pigments,* 45: 75-79.

most promising candidates for technical textiles.

to low running costs.

**6. References** 


**1. Introduction** 

Fig. 1. An Ionamine dye.

**10** 

Joonseok Koh *Konkuk University South Korea* 

**Dyeing with Disperse Dyes** 

Before the First World War, almost all dyes were applied from solution in an aqueous dyebath to substrates such as cotton, wool, silk and other natural fibres. However, the introduction of a man-made fibre, cellulose acetate, with its inherent hydrophobic nature, created a situation where very few of the available dyes had affinity for the new fibre. Water-soluble anionic dyes had little substantivity for the fibre and the alkaline conditions required for the application of vat dyes brought about a loss in tensile strength and

The development of disperse dyes for dyeing secondary cellulose acetate fibres in the early 1920s was a major technological breakthrough although their major use today is for the coloration of polyesters, the most important group of synthetic fibres (Broadbent, 2001). The first systematic study of dyes that was suitable for application to cellulose acetate by a direct dyeing process was carried out by Green. The presence of hydroxyl and amino groups, a low relative molecular mass and an almost neutral or basic character were found to be advantageous. As a result of these investigations, in 1922, Green and Saunders developed the Ionamine Dyes (British Dystuffs Corporation) for application to acetate fibres (Green & Saunders, 1923; Green, 1924) (Fig. 1). These water-soluble dyes were hydrolyzed in the aqueous dyebath to produce the sparingly soluble free base in a very fine suspension that was then absorbed by the fibre. This discovery, that aqueous dispersions of almost waterinsoluble dyes were highly suitable for the dyeing of secondary acetate, lead to the rapid

In 1923, aqueous dispersions of dyes were examined independently by the British Celanese Corporation and the British Dyestuffs Corporation and Ionamine dyes were superseded by ranges of disperse dyes, such as SRA (British Celanese Corporation) and Duranol (ICI), that were devoid of ionic solubilising groups (Fig. 2). These sparingly water-soluble acetate dyes were applied to cellulose acetate in the form a fine aqueous dispersion (Burkinshaw, 1995). The advent of other man-made fibres, such as nylon in 1938 and acrylic in the early 1940s, both of which possess a significant hydrophobic nature, further increased the use of disperse dyes. However, it was the discovery in 1941 and subsequent commercial introduction in

deterioration in fibre appearance due to the rapid hydrolysis of acetyl groups.

development of other such dyes for dyeing cellulose acetate.

