**2. Experimental setup and methodology**

Low-pressure plasma of different working gases and air atmospheric corona plasma were used for a modification of textiles. Untreated and plasma-treated textile substrates were ad‐ ditionally modified by loading of silver nanoparticles during dyeing process. Morphologi‐ cal, chemical and physical properties of plasma-treated textile substrates were studied using microscopy (SEM), spectroscopy (XPS) and measuring of the breaking strength and elonga‐ tion of textiles. The quantity of adsorbed silver was determined using mass spectrometry (ICP-MS), while the antibacterial efficiency of functionalized textiles was determined using microbiological tests.

#### **2.1. Plasma modification of textiles**

for *in situ* synthesis of nanoparticles and plasma sputtering process [3, 27, 48-54]. The possi‐ bility of loading nanoparticles using exhaustion method started recently [55]. The exhaus‐ tion method is the best process for uniform distribution of nanoparticles and is especially appropriate to be used when the simultaneous application of nanoparicles and dye onto fab‐ ric is performed, and dyed and antimicrobial effective fabric is achieved at the same time [3, 24, 25, 27]. Depending on the desirable functionality of a functionalized fabric, a treating bath may contain only dye, dye and silver nanoparticles or silver nanoparticles alone. An exhaustion method for loading of silver nanoparticles onto textile substrate was also used on silk fibers [54]. In that research, different concentrations of colloidal silver were used (10, 25, 50 and 100 ppm) and the effect of medium pH on the silver nanoparticles uptake on the fibers was studied. The antimicrobial effectiveness of functionalized fibers was better for samples with higher silver concentration and for samples treated in a medium with a lower pH. Also the use of salt (NaCl) improved a uniform distribution of silver particles on the fibers' surface which consequently improved antimicrobial effectiveness of fabrics. A differ‐ ence between pad-dry-cure and exhaustion method on adhesion and antimicrobial activity of fabrics was performed with commercial silver nanoparticles and a reactive organic-inor‐ ganic binder [45]. Results revealed that using the same initial concentration of silver, the pad-dry-cure method resulted in a much lower quantity of adsorbed silver nanoparticles in comparison to the exhaust method. Another possible method for applying silver onto tex‐ tiles is plasma polymerization method where surface of textile is functionalized with nano‐

When dealing with modification of textiles by silver it is important to know how the func‐ tionalization will affect the color change of fabric. A reflectance (UV/VIS) spectrophotometry is one of the methods to be used when detecting or controlling the presence of silver nano‐ particles in a solution or on a textile substrate. It is a direct measure that the abundance of silver is in the topmost layer of the textile fabric [30]. The instrument analyzes the light be‐ ing reflected from the sample and produces an absorption spectrum. Some of the electrons in the nanoparticles are not bound to the selected atom of silver, but are forming an elec‐ tronic cloud. Light falling on these electrons excite the collective oscillations, called surface plasmons. The resonance condition is established when the frequency of light photons matches the natural frequency of surface electrons oscillating against the restoring force of positive nuclei. Surface plasmon resonance is the basis of many standard tools for measur‐ ing adsorption of material onto planar metal (typically gold and silver) surfaces or onto the surface of metal nanoparticles. It is the fundamental principle behind many color-based bio‐ sensor applications. As a result of the particles growth, an intense absorption band at 400 nm to 415 nm caused by collective excitation of all free electrons in the particles was ob‐ served [57]. Increase in diameters of the nanoparticles from 1 to 100 nm induces a shift of the surface plasmon absorption band to higher wavelength [50, 57-59]. That means that the size of nanoparticles is defined by their optical response, therefore by that the color that can be seen [50, 60]. Loading of colloidal silver nanoparticles onto bleached cotton fabric caused yellowish coloring of fabric with absorption maximum at 370 nm [24, 30]. The evaluation of color changes of textiles modified by silver nanoparticles was also determined in CIELAB color space [60]. Loading of colloidal silver nanoparticles in concentration of 10 ppm in‐

structured silver film by magnetron sputtering [56].

6 Eco-Friendly Textile Dyeing and Finishing

Cotton substrates were modified using different plasma systems, i.e. atmospheric air corona plasma [63-65] and low-pressure inductively coupled radiofrequency (ICRF) discharge plas‐ ma of different working gases, water vapor [3, 26, 66, 67] and tetrafluoromethane [27], respec‐ tively. ICRF plasma is particularly suitable for treatment of delicate materials with a large surface for the following reasons: the neutral gas kinetic temperature remains close to the room temperature; the plasma-to-floating potential difference is small; the density of neutral reac‐ tive particles is large; and extremely high treatment uniformity is achieved. The use of lowpressure plasma is a contemporary technological process, not yet fully applied in textile industry due to its discontinuous process. For a continuous, on-line processing interfaced to a conventional production line the use of corona atmospheric pressure plasma is recommend‐ ed. Furthermore, the corona plasma treatment also introduces new functional groups onto fi‐ bers surfaces, produces surface cleaning and etching effect of treated textiles. The comparative research of corona plasma treatment of polyester was presented as well [24].

tween electrodes was adjusted with air gap adjusters at both sides of the electrode to 2 mm. Corona discharge was generated within the air gap between the electrode and backing roll‐

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**Figure 2.** Picture of atmospheric corona plasma reactor and a detail of treating area shown in a red circle

**textiles**

*2.2.1. X-ray photoelectron (XPS) analysis*

*2.2.2. Scanning Electron Microscopy (SEM)*

ples were coated with carbon and a 90% Au/10% Pd alloy layer.

data from the literature.

**2.2. Morphological, chemical and physical properties of untreated and plasma-treated**

Information on the chemical composition and chemical bonds of surface atoms of untreated and plasma-treated textile samples was obtained with XPS analysis. During the XPS analy‐ sis, a sample is illuminated with monochromatic X-ray light in an XPS spectrometer and the energy of emitted photoelectrons from the sample surface is analyzed. In the photoelectron spectrum, which represents the distribution of emitted photoelectrons as a function of their binding energy, peaks can be observed that may correspond to the elements present on the sample surface up to about 6 nm in depth. From the shape and binding energy of the peaks within XPS spectra, the chemical bonding of surface elements was inferred with the help of

The morphological surface properties of fibers and their changes after plasma treatment were studied using scanning electron microscopy (JEOL SEM type JSM-6060LV). All sam‐

er. The power was 900 W and the number of passages was set to 30.

#### *2.1.1. Low-pressure plasma treatment*

A RF generator with a nominal power of 5 kW and a frequency of 27.12 MHz was applied. The power absorbed by plasma, however, was much smaller due to poor matching and was estimated to about 500 W. The discharge chamber was a cylindrical Pyrex tube with a diam‐ eter of 27 cm and a length of 30 cm. Cotton fabric was put onto a glass holder mounted in the center of the discharge chamber. After closing the chamber the desired pressure of 0.4 mbar was achieved by a two-stage rotary pump with a nominal pumping speed of 65 m3 /h. The pressure was fairly stable during the experiment. Although the ultimate pressure of the rotary pump was below 1 Pa, the pressure remained much higher at 40 Pa. The source of water vapor was the cotton fabric itself. When tetrafluoromethane was used as a working gas, it was leaked into the chamber in order to obtain a pressure of about 100 Pa, the pres‐ sure where plasma is most reactive. By switching on the RF generator, the gas in the dis‐ charge chamber was partially ionized and dissociated, starting the plasma treatment of the fabric. The plasma treatment time was 10 s in both cases. The schematic diagram of lowpressure RF plasma reactor is presented in Fig. 1.

**Figure 1.** Schematic diagram of low-pressure RF plasma reactor

#### *2.1.2. Atmospheric plasma treatment*

Textile samples were treated in a commercial device, Corona-Plus CP-Lab MKII (Vetaphone, Denmark) (Fig. 2). Samples (270 × 500 mm2 ) were placed on a backing roller (the electrode roll covered with silicon coating), rotating at a working speed of 4 m/min. The distance be‐ tween electrodes was adjusted with air gap adjusters at both sides of the electrode to 2 mm. Corona discharge was generated within the air gap between the electrode and backing roll‐ er. The power was 900 W and the number of passages was set to 30.

**Figure 2.** Picture of atmospheric corona plasma reactor and a detail of treating area shown in a red circle

#### **2.2. Morphological, chemical and physical properties of untreated and plasma-treated textiles**

#### *2.2.1. X-ray photoelectron (XPS) analysis*

bers surfaces, produces surface cleaning and etching effect of treated textiles. The comparative

A RF generator with a nominal power of 5 kW and a frequency of 27.12 MHz was applied. The power absorbed by plasma, however, was much smaller due to poor matching and was estimated to about 500 W. The discharge chamber was a cylindrical Pyrex tube with a diam‐ eter of 27 cm and a length of 30 cm. Cotton fabric was put onto a glass holder mounted in the center of the discharge chamber. After closing the chamber the desired pressure of 0.4 mbar was achieved by a two-stage rotary pump with a nominal pumping speed of 65 m3

The pressure was fairly stable during the experiment. Although the ultimate pressure of the rotary pump was below 1 Pa, the pressure remained much higher at 40 Pa. The source of water vapor was the cotton fabric itself. When tetrafluoromethane was used as a working gas, it was leaked into the chamber in order to obtain a pressure of about 100 Pa, the pres‐ sure where plasma is most reactive. By switching on the RF generator, the gas in the dis‐ charge chamber was partially ionized and dissociated, starting the plasma treatment of the fabric. The plasma treatment time was 10 s in both cases. The schematic diagram of low-

Textile samples were treated in a commercial device, Corona-Plus CP-Lab MKII (Vetaphone,

roll covered with silicon coating), rotating at a working speed of 4 m/min. The distance be‐

) were placed on a backing roller (the electrode

/h.

research of corona plasma treatment of polyester was presented as well [24].

*2.1.1. Low-pressure plasma treatment*

8 Eco-Friendly Textile Dyeing and Finishing

pressure RF plasma reactor is presented in Fig. 1.

**Figure 1.** Schematic diagram of low-pressure RF plasma reactor

Denmark) (Fig. 2). Samples (270 × 500 mm2

*2.1.2. Atmospheric plasma treatment*

Information on the chemical composition and chemical bonds of surface atoms of untreated and plasma-treated textile samples was obtained with XPS analysis. During the XPS analy‐ sis, a sample is illuminated with monochromatic X-ray light in an XPS spectrometer and the energy of emitted photoelectrons from the sample surface is analyzed. In the photoelectron spectrum, which represents the distribution of emitted photoelectrons as a function of their binding energy, peaks can be observed that may correspond to the elements present on the sample surface up to about 6 nm in depth. From the shape and binding energy of the peaks within XPS spectra, the chemical bonding of surface elements was inferred with the help of data from the literature.

#### *2.2.2. Scanning Electron Microscopy (SEM)*

The morphological surface properties of fibers and their changes after plasma treatment were studied using scanning electron microscopy (JEOL SEM type JSM-6060LV). All sam‐ ples were coated with carbon and a 90% Au/10% Pd alloy layer.

#### *2.2.3. Dynamometer tensile testing*

Breaking strength and elongation of untreated and plasma-treated fabrics were analyzed ac‐ cording to the ISO 2062:1997 standard. Instron 6022 was used for this purpose. 100 mm sam‐ ples of cotton yarn were analyzed using a pre-loading of 0.5 cN/tex and a speed of 250 mm/ min. Samples were conditioned according to the ISO 139 standard. Tensile stress (cN/dtex) and elongation ε (%) are the mean values of the measured tensile strength and the elonga‐ tion of 10 specimens, respectively, in the warp and in the weft directions.

*2.3.2.2. Vat dyeing procedure*

**2.4. Color measurements**

*aeruginosa* (ATCC 27853).

**3. Results and discussion**

5 min and rinsed in deionised water for 5 min.

measuring port of the spectrophotometer was 9 mm.

**2.5. Elemental and antimicrobial analysis**

Vat dyeing was performed on untreated and plasma-treated cotton samples. The dyed cot‐ ton fabrics were post-treated in a colloidal silver solution [71]. A dyeing bath was prepared with 4% owf Bezathren Blau BCE, 15 ml/l NaOH 38°Bé and 3.5 g/l Na2S2O4. The liquor ratio was 83.3 : 1. The dyeing of cotton fabrics was performed at 60°C for 60 min. The dyed sam‐ ples were rinsed twice in deionised water for 5 min, post-treated in 2 ml/l HCOOH 85% for

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Color measurements of differently modified samples were performed after conditioning them according to the ISO 139 standard. CIE standard illuminant D65/10 was used on a Da‐ tacolor Spectraflash SF 600-CT reflection spectrophotometer. The aperture diameter of the

The quantity of adsorbed silver was determined using ICP-MS. This technique combines a high-temperature inductively coupled plasma (ICP) source with a mass spectrometer (MS). The antibacterial efficiency of functionalized textiles was determined using microbiological tests according to the ASTM Designation: E 2149–01 method. Antibacterial activity of the cotton fabrics was tested by a certified laboratory against *Staphylococcus aureus* (ATCC 25923), *Escherichia coli* (ATCC 25922), *Streptococcus faecalis* (ATCC 27853) and *Pseudomonas*

The influence of different plasma systems on the adhesion of nanoparticles is discussed. The emphasis of the study is to use minimal concentrations, initially, of nanoparticles for loading onto textiles and to achieve maximum quantity on the material. Exhaust dyeing process was used for loading of silver nanoparticles onto textiles. Before applying nanoparticles to any material, its surface needs to be adequately prepared and chemically and morphologically well analyzed. Only good conditions on the substrate surface can provide a qualitative dep‐ osition of particles [73]. In literature one can find quotations of XPS analysis of plasma modi‐ fied cotton substrates which were pre-prepared with various procedures prior to plasma modification (i.e. alkaline boiling, scouring, laundering). But to study plasma modification of cotton it is important to know about the surface changes of substrates that were not cleaned or otherwise pre-prepared. Therefore, the chemical surface changes were evaluated

for raw, bleached and bleached/mercerized cotton before and after plasma treatment.

The surface of raw untreated cotton fabric contains a high concentration of carbon and a low concentration of oxygen. This is not characteristic for native cellulose [74]. XPS spec‐ trum C 1s of cellulose also does not include C-C/C-H bonds (Figure 3). The surface of raw

### **2.3. Modification by dyeing and nanoparticles**
