**3. Results and discussion**

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 cotton is rich in C atoms (C-C/C-H bonds), what could indicate the presence of C-C/ C-H bond rich substances, such as waxes, pectin and proteins. The surfaces of bleached and bleached/mercerized cotton fabrics are alike but very different from raw cotton. Bleached and bleached/mercerized cotton samples are pre-oxidized due to the scouring, bleaching and mercerizing process, and therefore more similar to native cellulose. After modifica‐ tions with atmospheric air corona plasma and water vapor low-pressure plasma cotton samples contain a higher O/C ratio (the samples contain more of the oxygen and less of the carbon atoms) (Figure 4).

The increase of O/C ratio is expected since plasma interaction with cotton causes the surface oxidation. Changes of C-atom bonds on raw cotton samples after corona and low-pressure plasma treatment are visible in Figure 3 as the ratio of C-O and C=O bonds increased. The re‐ sults show that increase of relative concentration of C-O bonds is distinctive after corona plas‐ ma treatment (41 %) than after low-pressure plasma treatment (23.9 %). It is similar for C=O bonds. The relative concentration of C=O bonds on the surface of raw cotton increases to 16.6 % after corona plasma treatment and to 8.2 % after low-pressure plasma treatment. Both plas‐ ma treatments result in a formation of O-C=O bonds. C 1s spectrum of plasma-treated sam‐ ples resembles to the spectra of native cellulose, which could indicate that plasma selectively removed the noncellulosic parts present on a surface of a raw untreated cotton fabric. After plasma treatment the oxygen content on surface of bleached and bleached/mercerized cotton samples increases. After a treatment with corona plasma the content of oxygen on bleached cotton sample increases from 34.3 at% to 44.5 at%, while the treatment with low-pressure plas‐ ma increases oxygen to 36.8 at%. After both plasma treatments the content of C-O remains the same (~55 %), the content of C=O bonds increases and appearance of O-C=O bonds is noticea‐ ble. Increase of bonds is distinctive after corona plasma treatment than after low-pressure plasma treatment. Content of C-C/C-H bonds decreases after both plasma treatments. In‐ crease of O/C ratio on plasma-treated bleached/mercerized cotton samples is distinctive after corona plasma treatment, where the oxygen concentration increases to 45.3 at%, while in‐ creases to 37.5 at% after low-pressure plasma treatment. Due to oxidation process in plasma, the content of C-C/C-H bonds deceases and the change is more noticeable for bleached/merc‐ erized cotton than for a bleached cotton fabric. For bleached/mercerized cotton sample con‐ centration of C-O bonds is increased in the case of corona plasma treatment, from 47.6 % to 69.3 %, while it remains almost equal after low-pressure plasma treatment (47.8 %). After both plasma treatments the content of C=O bonds increases and appearance of O-C=O bonds is no‐ ticeable. These changes are more distinct after low-pressure plasma treatment (20.7 % and 6.8 %) than after corona plasma treatment (15.5 % and 3.9 %). The results summarized in Figure 4 show higher concentration of oxygen on atmospheric air corona and water vapor low-pres‐ sure plasma-treated raw cotton than on untreated bleached or bleached/mercerized cotton. From these results it can be concluded that by using plasma technology some of the techno‐ logical processes of pretreatment of cotton fabrics before dyeing can be avoided. Plasma-treat‐ ed raw cotton fabric absorbs the same or more of dyestuff as untreated bleached or bleached/ mercerized cotton fabric [3, 65, 65, 76]. Reactive dyes are typical anionic dyes containing reac‐ tive systems which in alkaline media make bonds with –OH groups of cotton fibers. Increase of dyeability of cotton treated with atmospheric air corona plasma or water vapor low-pres‐ sure plasma is correlated to an increase of the number of hydrophilic groups on the surface of the fibers. In Figure 5 the correlation between color differences (expressed as ΔE\*) of reactive dyed cotton and differences in O/C ratio (expressed as ΔO/C) of untreated and plasma-treat‐ ed cotton is presented. The most perceptible changes in color differences (ΔE\*) are noticeable when differences in O/C ratio (ΔO/C) are higher. Visible color differences between untreated and water vapor plasma-treated cotton were noticeable for raw (ΔE\* = 2.20) and bleached/

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mercerized cotton (ΔE\* = 1.07).

**Figure 3.** Relative concentration of carbon bonds on the surface of cotton samples: R – raw cotton, B – bleached cot‐ ton, BM – bleached/mercerized cotton, AP – atmospheric plasma treatment, LP – low-pressure plasma treatment

**Figure 4.** The concentration ratio between oxygen and carbon on the surface of cotton samples: : R – raw cotton, B – bleached cotton, BM – bleached/mercerized cotton, AP – atmospheric plasma treatment, LP – low-pressure plasma treatment

The increase of O/C ratio is expected since plasma interaction with cotton causes the surface oxidation. Changes of C-atom bonds on raw cotton samples after corona and low-pressure plasma treatment are visible in Figure 3 as the ratio of C-O and C=O bonds increased. The re‐ sults show that increase of relative concentration of C-O bonds is distinctive after corona plas‐ ma treatment (41 %) than after low-pressure plasma treatment (23.9 %). It is similar for C=O bonds. The relative concentration of C=O bonds on the surface of raw cotton increases to 16.6 % after corona plasma treatment and to 8.2 % after low-pressure plasma treatment. Both plas‐ ma treatments result in a formation of O-C=O bonds. C 1s spectrum of plasma-treated sam‐ ples resembles to the spectra of native cellulose, which could indicate that plasma selectively removed the noncellulosic parts present on a surface of a raw untreated cotton fabric. After plasma treatment the oxygen content on surface of bleached and bleached/mercerized cotton samples increases. After a treatment with corona plasma the content of oxygen on bleached cotton sample increases from 34.3 at% to 44.5 at%, while the treatment with low-pressure plas‐ ma increases oxygen to 36.8 at%. After both plasma treatments the content of C-O remains the same (~55 %), the content of C=O bonds increases and appearance of O-C=O bonds is noticea‐ ble. Increase of bonds is distinctive after corona plasma treatment than after low-pressure plasma treatment. Content of C-C/C-H bonds decreases after both plasma treatments. In‐ crease of O/C ratio on plasma-treated bleached/mercerized cotton samples is distinctive after corona plasma treatment, where the oxygen concentration increases to 45.3 at%, while in‐ creases to 37.5 at% after low-pressure plasma treatment. Due to oxidation process in plasma, the content of C-C/C-H bonds deceases and the change is more noticeable for bleached/merc‐ erized cotton than for a bleached cotton fabric. For bleached/mercerized cotton sample con‐ centration of C-O bonds is increased in the case of corona plasma treatment, from 47.6 % to 69.3 %, while it remains almost equal after low-pressure plasma treatment (47.8 %). After both plasma treatments the content of C=O bonds increases and appearance of O-C=O bonds is no‐ ticeable. These changes are more distinct after low-pressure plasma treatment (20.7 % and 6.8 %) than after corona plasma treatment (15.5 % and 3.9 %). The results summarized in Figure 4 show higher concentration of oxygen on atmospheric air corona and water vapor low-pres‐ sure plasma-treated raw cotton than on untreated bleached or bleached/mercerized cotton. From these results it can be concluded that by using plasma technology some of the techno‐ logical processes of pretreatment of cotton fabrics before dyeing can be avoided. Plasma-treat‐ ed raw cotton fabric absorbs the same or more of dyestuff as untreated bleached or bleached/ mercerized cotton fabric [3, 65, 65, 76]. Reactive dyes are typical anionic dyes containing reac‐ tive systems which in alkaline media make bonds with –OH groups of cotton fibers. Increase of dyeability of cotton treated with atmospheric air corona plasma or water vapor low-pres‐ sure plasma is correlated to an increase of the number of hydrophilic groups on the surface of the fibers. In Figure 5 the correlation between color differences (expressed as ΔE\*) of reactive dyed cotton and differences in O/C ratio (expressed as ΔO/C) of untreated and plasma-treat‐ ed cotton is presented. The most perceptible changes in color differences (ΔE\*) are noticeable when differences in O/C ratio (ΔO/C) are higher. Visible color differences between untreated and water vapor plasma-treated cotton were noticeable for raw (ΔE\* = 2.20) and bleached/ mercerized cotton (ΔE\* = 1.07).

cotton is rich in C atoms (C-C/C-H bonds), what could indicate the presence of C-C/ C-H bond rich substances, such as waxes, pectin and proteins. The surfaces of bleached and bleached/mercerized cotton fabrics are alike but very different from raw cotton. Bleached and bleached/mercerized cotton samples are pre-oxidized due to the scouring, bleaching and mercerizing process, and therefore more similar to native cellulose. After modifica‐ tions with atmospheric air corona plasma and water vapor low-pressure plasma cotton samples contain a higher O/C ratio (the samples contain more of the oxygen and less of

**Figure 3.** Relative concentration of carbon bonds on the surface of cotton samples: R – raw cotton, B – bleached cot‐ ton, BM – bleached/mercerized cotton, AP – atmospheric plasma treatment, LP – low-pressure plasma treatment

**Figure 4.** The concentration ratio between oxygen and carbon on the surface of cotton samples: : R – raw cotton, B – bleached cotton, BM – bleached/mercerized cotton, AP – atmospheric plasma treatment, LP – low-pressure plasma

the carbon atoms) (Figure 4).

12 Eco-Friendly Textile Dyeing and Finishing

treatment

The samples modified in tetrafluoromethane low-pressure plasma (CF4 plasma) gave differ‐ ent results. There was no visible color difference between untreated and CF4 plasma-treated bleached/mercerized cotton samples (ΔE\* = 0.62). Both samples were practically equally col‐ ored. Treating cotton fabrics for 10 sec with CF4 plasma does not influence their dyeing properties. The results of XPS study show a small increase in the concentration of oxygen

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after CF4 plasma treatment, but the result is hardly remarkable (Figure 6 and 7).

**Figure 8.** SEM images of untreated and plasma-treated cotton samples

It is interesting, however, that no fluorine was observed in the XPS spectra, but that the addi‐ tional ISE analysis indicated the presence of <5 ppm of total fluoride on CF4 plasma-treated

**Figure 5.** The correlation between color differences (expressed as ΔE\*) of reactive dyed cotton and differences in O/C ratio (expressed as ΔO/C) of untreated and plasma-treated cotton (R – raw cotton, B – bleached cotton, BM – bleach‐ ed/mercerized cotton)

**Figure 6.** The concentration ratio between oxygen and carbon on the surface of untreated (BM) and CF4 plasma-treat‐ ed (BM\_CF4) cotton samples

**Figure 7.** Relative concentration of carbon bonds on the surface of untreated (BM) and CF4 plasma-treated (BM\_CF4) cotton samples

The samples modified in tetrafluoromethane low-pressure plasma (CF4 plasma) gave differ‐ ent results. There was no visible color difference between untreated and CF4 plasma-treated bleached/mercerized cotton samples (ΔE\* = 0.62). Both samples were practically equally col‐ ored. Treating cotton fabrics for 10 sec with CF4 plasma does not influence their dyeing properties. The results of XPS study show a small increase in the concentration of oxygen after CF4 plasma treatment, but the result is hardly remarkable (Figure 6 and 7).

**Figure 8.** SEM images of untreated and plasma-treated cotton samples

**Figure 5.** The correlation between color differences (expressed as ΔE\*) of reactive dyed cotton and differences in O/C ratio (expressed as ΔO/C) of untreated and plasma-treated cotton (R – raw cotton, B – bleached cotton, BM – bleach‐

**Figure 6.** The concentration ratio between oxygen and carbon on the surface of untreated (BM) and CF4 plasma-treat‐

**Figure 7.** Relative concentration of carbon bonds on the surface of untreated (BM) and CF4 plasma-treated (BM\_CF4)

ed/mercerized cotton)

14 Eco-Friendly Textile Dyeing and Finishing

ed (BM\_CF4) cotton samples

cotton samples

It is interesting, however, that no fluorine was observed in the XPS spectra, but that the addi‐ tional ISE analysis indicated the presence of <5 ppm of total fluoride on CF4 plasma-treated samples. Here, it is worth mentioning that we are not the first group to observe little or no flu‐ orine on organic materials treated with CF4 plasma [76, 77]. Although XPS analysis did not show specific chemical surface differences between untreated and CF4 plasma-treated cotton samples, the SEM analysis showed strongly modified surface morphology of plasma-treated cotton (Figure 8), while smaller changes of the surface morphology of cotton samples treated with atmospheric air corona plasma and water vapor low-pressure plasma are noticed.

**Figure 9.** Tensile stress (cN/dtex) of cotton after plasma treatment: U – untreated, H2O - ICRF water vapor plasma-

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**Figure 10.** Elongation (%) of cotton after plasma treatment: U – untreated, H2O - ICRF water vapor plasma-treated,

A textile surface with such extremely rich surface morphology (as seen from SEM) is likely to influence higher adsorption of silver nanoparticles, which is in accordance with our ICP-MS results in Table 1, where the quantity of adsorbed silver onto cotton samples is presented.

From the results summarized in Table 1, it is clear that 30 nm silver nanoparticles are more adhesive to the cotton fabric than 80 nm silver nanoparticles. Regarding their volume, nano‐ particles have a high specific surface area. By decreasing the size of a particle, its surface dis‐ tribution rate increases [87]. The quantity of adsorbed silver on untreated bleached/ mercerized cotton was 32 ppm when 30 nm silver nanoparticles were used and 13 ppm when 80 nm silver nanoparticles were used. Similar trend can be observed when cotton was modified with plasma. When cotton was treated with water vapor low-pressure plasma the quantity of adsorbed 30 nm silver nanoparticles was 50 ppm and the quantity of adsorbed 80 nm silver nanoparticles was 17 ppm, which means that adsorption of 80 nm silver nano‐ particles was three times lower than the adsorption of 30 nm silver nanoparticles. The re‐ sults show that plasma heavily modifies the morphology and surface chemical properties of

treated, CF4 - ICRF tetrafluoromethane plasma-treated

CF4 - ICRF tetrafluoromethane plasma-treated

SEM image of untreated cotton (Figure 8 a) shows a typical grooved surface morphology with macrofibrils oriented predominantly in the direction of the fiber axis. The outlines of the macrofibrils are still visible, and they are smooth and distinct due to the presence of an amorphous layer covering the fiber. The surface of corona plasma-treated cotton has striped, cleaned and more distinct macrofibrilar structure (Figure 8 b). The same effect can be notice‐ able on the surface of cotton fibers treated with water vapor low-pressure plasma (Figure 8 c). The plasma-treated fiber surface remains grooved and the macrofibrile structure has gained a much sharper outline. The individual macrofibrils (0.2–1 nm) and their transversal connections are visible in the primary cell wall. Between them, narrow voids thinner than 10 nm are noticeable. The surface morphology of CF4 plasma-treated cotton (Figure 8 d) is very different comparing to those treated with water vapor low-pressure or corona plasma. CF4 plasma-treated cotton has an extremely rough and nanostructured surface with dimensions of the grains roughly between 150 and 500 nm. Dissociation energies of plasma molecules are the reason for such rich etched surface. Both CF4 and H2O molecules get dissociated in our plasma [78]. The dissociation energy of CF4 is 12.6 eV [79] while the ionization energy of CF4 is about 16 eV, which is much higher than the dissociation energy of water vapor or OH molecules, which is at about 5 and 4 eV, respectively. The electrons with energy of few eV are therefore likely to dissociate water and OH molecules rather than dissociate the CF4 mol‐ ecules. The result is an extremely high dissociation fraction of water molecules and a moder‐ ate dissociation fraction of CF4 molecules. Since the partial pressures of water and CF4 are comparable, it can be concluded that the density of O and OH radicals in our plasma is at least as high as the density of CFx radicals if not more so. The textile sample exposed to plas‐ ma is therefore subjected to interact with CFx, O, OH, F and H radicals. The density of H is probably as high as that of F so extensive recombination to HF is expected. CFx radicals tend to graft onto the textile, but the grafting probability on cellulose is low compared to the in‐ teraction probability with O and OH radicals. O and OH radicals are extremely reactive and cause etching of cellulose. Fluorine atoms are efficient at abstracting hydrogen in the first step of the oxidation reaction. In addition, the presence of fluorine atoms in the plasma en‐ hances the dissociation of the oxygen, further increasing the ashing rates [80]. CF4 is the gas most commonly added to oxygen to enhance the generation of atomic oxygen in plasma and to increase polymer etch rates [81].

While the surface of plasma-treated cotton was changed, the mechanical properties of cotton fabrics did not alter after plasma modification. The breaking strength and elongation of tex‐ tiles practically do not change (Figure 9 and 10) [3, 27]. These results are in accordance with the results obtained by other authors [82-85]. Plasma modification of textiles does not impair their mechanical properties.

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samples. Here, it is worth mentioning that we are not the first group to observe little or no flu‐ orine on organic materials treated with CF4 plasma [76, 77]. Although XPS analysis did not show specific chemical surface differences between untreated and CF4 plasma-treated cotton samples, the SEM analysis showed strongly modified surface morphology of plasma-treated cotton (Figure 8), while smaller changes of the surface morphology of cotton samples treated with atmospheric air corona plasma and water vapor low-pressure plasma are noticed.

SEM image of untreated cotton (Figure 8 a) shows a typical grooved surface morphology with macrofibrils oriented predominantly in the direction of the fiber axis. The outlines of the macrofibrils are still visible, and they are smooth and distinct due to the presence of an amorphous layer covering the fiber. The surface of corona plasma-treated cotton has striped, cleaned and more distinct macrofibrilar structure (Figure 8 b). The same effect can be notice‐ able on the surface of cotton fibers treated with water vapor low-pressure plasma (Figure 8 c). The plasma-treated fiber surface remains grooved and the macrofibrile structure has gained a much sharper outline. The individual macrofibrils (0.2–1 nm) and their transversal connections are visible in the primary cell wall. Between them, narrow voids thinner than 10 nm are noticeable. The surface morphology of CF4 plasma-treated cotton (Figure 8 d) is very different comparing to those treated with water vapor low-pressure or corona plasma. CF4 plasma-treated cotton has an extremely rough and nanostructured surface with dimensions of the grains roughly between 150 and 500 nm. Dissociation energies of plasma molecules are the reason for such rich etched surface. Both CF4 and H2O molecules get dissociated in our plasma [78]. The dissociation energy of CF4 is 12.6 eV [79] while the ionization energy of CF4 is about 16 eV, which is much higher than the dissociation energy of water vapor or OH molecules, which is at about 5 and 4 eV, respectively. The electrons with energy of few eV are therefore likely to dissociate water and OH molecules rather than dissociate the CF4 mol‐ ecules. The result is an extremely high dissociation fraction of water molecules and a moder‐ ate dissociation fraction of CF4 molecules. Since the partial pressures of water and CF4 are comparable, it can be concluded that the density of O and OH radicals in our plasma is at least as high as the density of CFx radicals if not more so. The textile sample exposed to plas‐ ma is therefore subjected to interact with CFx, O, OH, F and H radicals. The density of H is probably as high as that of F so extensive recombination to HF is expected. CFx radicals tend to graft onto the textile, but the grafting probability on cellulose is low compared to the in‐ teraction probability with O and OH radicals. O and OH radicals are extremely reactive and cause etching of cellulose. Fluorine atoms are efficient at abstracting hydrogen in the first step of the oxidation reaction. In addition, the presence of fluorine atoms in the plasma en‐ hances the dissociation of the oxygen, further increasing the ashing rates [80]. CF4 is the gas most commonly added to oxygen to enhance the generation of atomic oxygen in plasma and

While the surface of plasma-treated cotton was changed, the mechanical properties of cotton fabrics did not alter after plasma modification. The breaking strength and elongation of tex‐ tiles practically do not change (Figure 9 and 10) [3, 27]. These results are in accordance with the results obtained by other authors [82-85]. Plasma modification of textiles does not impair

to increase polymer etch rates [81].

16 Eco-Friendly Textile Dyeing and Finishing

their mechanical properties.

**Figure 9.** Tensile stress (cN/dtex) of cotton after plasma treatment: U – untreated, H2O - ICRF water vapor plasmatreated, CF4 - ICRF tetrafluoromethane plasma-treated

**Figure 10.** Elongation (%) of cotton after plasma treatment: U – untreated, H2O - ICRF water vapor plasma-treated, CF4 - ICRF tetrafluoromethane plasma-treated

A textile surface with such extremely rich surface morphology (as seen from SEM) is likely to influence higher adsorption of silver nanoparticles, which is in accordance with our ICP-MS results in Table 1, where the quantity of adsorbed silver onto cotton samples is presented.

From the results summarized in Table 1, it is clear that 30 nm silver nanoparticles are more adhesive to the cotton fabric than 80 nm silver nanoparticles. Regarding their volume, nano‐ particles have a high specific surface area. By decreasing the size of a particle, its surface dis‐ tribution rate increases [87]. The quantity of adsorbed silver on untreated bleached/ mercerized cotton was 32 ppm when 30 nm silver nanoparticles were used and 13 ppm when 80 nm silver nanoparticles were used. Similar trend can be observed when cotton was modified with plasma. When cotton was treated with water vapor low-pressure plasma the quantity of adsorbed 30 nm silver nanoparticles was 50 ppm and the quantity of adsorbed 80 nm silver nanoparticles was 17 ppm, which means that adsorption of 80 nm silver nano‐ particles was three times lower than the adsorption of 30 nm silver nanoparticles. The re‐ sults show that plasma heavily modifies the morphology and surface chemical properties of cotton and by that has a great impact on the adsorption of silver nanoparticles onto fabrics. Atmospheric air corona treatment of cotton fabrics enhanced the quantity of silver onto raw cotton up to 4 times and onto bleached/mercerized cotton up to 2 times [64]. The adsorption of 80 nm silver nanoparticles onto CF4 plasma-treated cotton was 2 times higher and onto water vapor plasma-treated cotton was 1.3 times higher than on untreated cotton. These fab‐ rics had a sufficient antimicrobial effectiveness against *Escherichia coli* and *Pseudomonas aeru‐ ginosa* (Table 1) [3]. The adsorption of 30 nm silver nanoparticles onto CF4 plasma-treated cotton is 1.7 times higher and onto water vapor plasma-treated cotton was 1.6 times higher than on untreated cotton. This gave a good antimicrobial effectiveness against *Enterococus faecalis* and *Pseudomonas aeruginosa* (Table 1) [27].

**Plasma modification of**

**Functionalization with silver nanoparticles**

ICRF water vapor 30 nm 50 26

ICRF CF4 30 nm 54 36

**Table 2.** The quantity of silver (ppm) before and after washing

by plasma and washed 10 times at 95°C.

plasma and water vapor low-pressure plasma.

bial analysis of samples are presented in Table 3.

**Ag quantity (ppm) on cotton before washing**

Multifunctional Textiles – Modification by Plasma, Dyeing and Nanoparticles

80 nm 17 10

80 nm 26 22

When cotton was modified by water vapor plasma the quantity of 30 nm silver nanoparti‐ cles decreased by 48%, and when modified by CF4 plasma the quantity of silver nanoparti‐ cles decreased by 34%. The drop in the concentration of silver on the cotton after ten wash cycles is also observed with the 80 nm silver nanoparticles. Cotton that is treated with water vapor plasma loses 41%; however, cotton treated with CF4 plasma loses 15% of the silver nanoparticles. After a 10-second treatment with CF4 plasma, the surface of the bleached/ mercerized cotton is more liable to the adsorption of silver nanoparticles than the surface that was modified by the water vapor plasma. The particle adhesion is a complex phenom‐ enon depending on the interaction mechanism between particles and the surface of a materi‐ al. Adsorption of silver nanoparticles onto cotton from a dyeing bath is much higher for smaller particles than for larger ones. When particles are already on the surface of cotton fi‐ bers the attractive interactions and forces are stronger for 80 nm silver nanoparticles than for 30 nm silver nanoparticles. That is the reason for a better wash durability of 80 nm silver particles. From the results presented in Table 1 and 2, it is evident that the quantity of silver on untreated and unwashed cotton is almost the same as on the samples that were modified

The further experiments in functionalization of cotton with other forms of silver nanoparti‐ cles (i.e. commercial form RucoBac AGP and laboratory synthesized colloidal silver nano‐ particles) were based on the obtained adhesion results of silver nanoparticles of known dimensions. The application of RucoBac AGP and synthesized colloidal silver nanoparticles was carried on a bleached/mercerized cotton fabric modified by atmospheric air corona

The exhaustion method was used for the deposition of RucoBac AGP onto blank dyed, dyed, plasma-treated blank dyed and plasma-treated dyed cotton samples. 0.1 % of RucoBac AGP was used, which represents a half of the lowest concentration recommended by the agent producer. The reason for such a decision was to verify the possibility in achieving good antibacterial efficiency of a cotton fabric with the use of a very low concentration of silver composite. The liquor ratio was 10 : 1, and the treatment time 30 min at 50 ºC. After‐ wards, the samples were dried at 130 ºC for 4 min. The results of the ICP-MS and antimicro‐

**Ag quantity (ppm) on cotton after washing**

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**cotton**


**Table 1.** The quantity of silver (ppm) and antimicrobial efficiency expressed as a bacterial reduction (%) of untreated and plasma-treated cotton samples functionalized with powdered silver nanoparticles

Although the purpose of our research was to study the efficiency and appropriateness of plasma modification of textiles in order to achieve a higher adsorption of nanoparticles onto their surfaces, the wash fastness of functionalized textiles was examined as well. Wash fast‐ ness test was carried out in a laboratory apparatus Launder-O-Meter [3, 27]. The samples were washed repetitively ten times at 95°C in a solution of 5 g/l of SDC standard detergent and 2 g/l of Na2CO3 (where 10 globules were added). The duration of the washing cycles was 30 min. After every wash cycle, the samples were rinsed twice in distilled water and then for 10 minutes under a tap water, which was followed by squeezing and air drying. In Table 2 the results of silver quantity on washed cotton samples are presented. From the re‐ sults it can be seen that after ten times washing at 95°C the quantity of silver on the cotton samples decreased (Table 2).


**Table 2.** The quantity of silver (ppm) before and after washing

cotton and by that has a great impact on the adsorption of silver nanoparticles onto fabrics. Atmospheric air corona treatment of cotton fabrics enhanced the quantity of silver onto raw cotton up to 4 times and onto bleached/mercerized cotton up to 2 times [64]. The adsorption of 80 nm silver nanoparticles onto CF4 plasma-treated cotton was 2 times higher and onto water vapor plasma-treated cotton was 1.3 times higher than on untreated cotton. These fab‐ rics had a sufficient antimicrobial effectiveness against *Escherichia coli* and *Pseudomonas aeru‐ ginosa* (Table 1) [3]. The adsorption of 30 nm silver nanoparticles onto CF4 plasma-treated cotton is 1.7 times higher and onto water vapor plasma-treated cotton was 1.6 times higher than on untreated cotton. This gave a good antimicrobial effectiveness against *Enterococus*

Ag quantity (ppm) on

Bacterial reduction (%)

64 (*P. aeruginosa*)

77 (*P. aeruginosa)*

cotton

80 nm 13 –a

80 nm 17 –a

*faecalis* and *Pseudomonas aeruginosa* (Table 1) [27].

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Plasma modification of cotton Functionalization with silver

–a

no bacterial reduction

samples decreased (Table 2).

nanoparticles

Untreated 30 nm 32 –a

Corona air 80 nm 39 –a

ICRF water vapor 30 nm 50 52 (*E. coli*)

ICRF CF4 30 nm 54 68 (*E. faecalis)*

80 nm 26

and plasma-treated cotton samples functionalized with powdered silver nanoparticles

**Table 1.** The quantity of silver (ppm) and antimicrobial efficiency expressed as a bacterial reduction (%) of untreated

Although the purpose of our research was to study the efficiency and appropriateness of plasma modification of textiles in order to achieve a higher adsorption of nanoparticles onto their surfaces, the wash fastness of functionalized textiles was examined as well. Wash fast‐ ness test was carried out in a laboratory apparatus Launder-O-Meter [3, 27]. The samples were washed repetitively ten times at 95°C in a solution of 5 g/l of SDC standard detergent and 2 g/l of Na2CO3 (where 10 globules were added). The duration of the washing cycles was 30 min. After every wash cycle, the samples were rinsed twice in distilled water and then for 10 minutes under a tap water, which was followed by squeezing and air drying. In Table 2 the results of silver quantity on washed cotton samples are presented. From the re‐ sults it can be seen that after ten times washing at 95°C the quantity of silver on the cotton When cotton was modified by water vapor plasma the quantity of 30 nm silver nanoparti‐ cles decreased by 48%, and when modified by CF4 plasma the quantity of silver nanoparti‐ cles decreased by 34%. The drop in the concentration of silver on the cotton after ten wash cycles is also observed with the 80 nm silver nanoparticles. Cotton that is treated with water vapor plasma loses 41%; however, cotton treated with CF4 plasma loses 15% of the silver nanoparticles. After a 10-second treatment with CF4 plasma, the surface of the bleached/ mercerized cotton is more liable to the adsorption of silver nanoparticles than the surface that was modified by the water vapor plasma. The particle adhesion is a complex phenom‐ enon depending on the interaction mechanism between particles and the surface of a materi‐ al. Adsorption of silver nanoparticles onto cotton from a dyeing bath is much higher for smaller particles than for larger ones. When particles are already on the surface of cotton fi‐ bers the attractive interactions and forces are stronger for 80 nm silver nanoparticles than for 30 nm silver nanoparticles. That is the reason for a better wash durability of 80 nm silver particles. From the results presented in Table 1 and 2, it is evident that the quantity of silver on untreated and unwashed cotton is almost the same as on the samples that were modified by plasma and washed 10 times at 95°C.

The further experiments in functionalization of cotton with other forms of silver nanoparti‐ cles (i.e. commercial form RucoBac AGP and laboratory synthesized colloidal silver nano‐ particles) were based on the obtained adhesion results of silver nanoparticles of known dimensions. The application of RucoBac AGP and synthesized colloidal silver nanoparticles was carried on a bleached/mercerized cotton fabric modified by atmospheric air corona plasma and water vapor low-pressure plasma.

The exhaustion method was used for the deposition of RucoBac AGP onto blank dyed, dyed, plasma-treated blank dyed and plasma-treated dyed cotton samples. 0.1 % of RucoBac AGP was used, which represents a half of the lowest concentration recommended by the agent producer. The reason for such a decision was to verify the possibility in achieving good antibacterial efficiency of a cotton fabric with the use of a very low concentration of silver composite. The liquor ratio was 10 : 1, and the treatment time 30 min at 50 ºC. After‐ wards, the samples were dried at 130 ºC for 4 min. The results of the ICP-MS and antimicro‐ bial analysis of samples are presented in Table 3.


treatment. The difference in both plasma treatments is noticeable from the ICP-MS results also (Table 3), since the adsorption of RucoBac AGP onto cotton was greater after modifica‐ tion by water vapor low-pressure plasma. Nevertheless, all modified cotton fabrics had an excellent antimicrobial effectiveness against *Staphylococcus aureus*, *Escherichia coli*, *Streptococ‐*

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The objectives for textile industry have been continuous on-line treatments of fabrics. Lowpressure plasma reactors, such as radio frequency powered plasma, provide greater stability and uniformity but generally require more handling of textile materials through the vacuum system than corona discharges at atmospheric pressures. In this respect, the use of corona plasma is more appropriate for the industry. In our following research when laboratory col‐ loidal silver was used, we focused on treating cotton fabric with atmospheric corona plasma. The synthesis of colloidal silver was performed by reducing silver salt in an aqueous solu‐ tion at room temperature under argon atmosphere. The procedure was described previous‐ ly, in section 3.2.1. A synthesis of colloidal silver and loading of silver onto cotton fabric was performed as the second phase after dyeing cotton fabrics with a blue vat dye. To verify whether vat-dyeing influences the adsorption of colloidal silver onto cotton fabric, a blank vat-dyeing procedure (dyeing with all chemicals and no dye) was also performed [71]. Apart from indigo, the vat dyes used in dyeing applications are mainly derivatives of an‐ thraquinone and of higher condensed aromatic ring systems with a closed system of conju‐ gated double bonds. They generally contain two, four or six reducible carbonyl groups [88].

(a) (b) (c)

The vat dyes are insoluble in the keto form (Figure 11a). For dyeing they must be trans‐ formed to a water soluble enolate (leuko) form (Figure 11c) by a reduction. This form of the dye is appropriate for cellulose dyeing, but the addition of electrolyte is also required. After the dyeing, the dye in amorphous regions is transformed through leuko acid (Figure 11b) into its original water insoluble form by rinsing and oxidation [89]. The vat dyeing of bleached/mercerized cotton fabric before colloidal silver treatment significantly influences the adsorption of silver onto cotton fabrics [71]. Also the adsorption of silver is influenced by an immersion time of cotton into colloidal silver solution. Although it was proven that modification of cotton by corona plasma strongly influences the adsorption of powdered sil‐ ver nanoparticles by increasing their quantity on the modified cotton, the experiment using synthetized colloidal silver on corona treated cotton had to be conducted. The Table 4 presents the results of ICP-MS and antimicrobial analysis of untreated, corona and vat dyed

**Figure 11.** Scheme of reduction and oxidation process of carbonyl group of vat dye

colloidal silver loaded cotton.

*cus faecalis* and *Pseudomonas aeruginosa*.

**Table 3.** The quantity of silver (ppm) and antimicrobial efficiency, expressed as a bacterial reduction (%), of untreated and plasma-treated cotton samples functionalized with RucoBac AGP

The results summarized in Table 3 show low adsorption of silver onto untreated blank dyed cotton. The adsorption of silver onto corona modified cotton did not significantly increase. Both samples do not exhibit the antimicrobial effectiveness. However, treating cotton with water vapor low-pressure plasma increased the adsorption of silver onto cotton up to 7 times, which resulted in an excellent antimicrobial effectiveness against *Streptococcus faecalis* and a sufficient antimicrobial effectiveness against *Escherichia coli*. The adsorption of silver significantly increased when RucoBac AGP was applied onto dyed cotton fabric, regardless of plasma treatment. RucoBac AGP is a nano-dispersion of TiO2 as the carrier of the active component AgCl. In the presence of moisture, silver cations react with hydroxyl functional cellulosic groups and are attached to each other electrostatically. The presence of a reactive dye on cotton and the introduction of additional covalently bound sulfonic acid groups will facilitate the uptake of a cationic antimicrobial agent [87]. Therefore, it is possible to con‐ clude that RucoBac AGP is bound to the cotton surface through sulfonic groups of a cova‐ lently bound dye and through partially ionized hydroxyl and carboxyl groups present on the fiber [72]. The significant increased adsorption of silver can be also noticed with samples modified by water vapor low-pressure plasma and dyeing, while there was no noticeable change when samples were modified by corona plasma. Results obtained from XPS analysis showed that plasma modification of bleached/mercerized cotton increased the content of oxygen on the surface. In addition, after both plasma treatments the appearance of new bonds was noticeable (O-C=O) and the content of C=O bonds increased. That means that oxygen rich functional groups incurred on the surface of plasma modified cotton. These changes were more distinct after low-pressure plasma treatment than after corona plasma treatment. The difference in both plasma treatments is noticeable from the ICP-MS results also (Table 3), since the adsorption of RucoBac AGP onto cotton was greater after modifica‐ tion by water vapor low-pressure plasma. Nevertheless, all modified cotton fabrics had an excellent antimicrobial effectiveness against *Staphylococcus aureus*, *Escherichia coli*, *Streptococ‐ cus faecalis* and *Pseudomonas aeruginosa*.

**Sample Treatment Plasma treatment of cotton Ag quantity**

and plasma-treated cotton samples functionalized with RucoBac AGP

Functionalization with 0.1 % RucoBac AGP

20 Eco-Friendly Textile Dyeing and Finishing

Dyeing with reactive dye and functionalization with 0.1 % RucoBac AGP

no bacterial reduction

—a

**(ppm) on cotton**

Untreated 8,9 100 (*E.coli, S.aureus, S.faecalis*

Corona air 8,4 100 (*E.coli, S.aureus, S.faecalis*

ICRF water vapor 13 80 (*S.aureus* and *E.coli*)

Untreated 1,5 —a Corona air 1,8 —a

**Table 3.** The quantity of silver (ppm) and antimicrobial efficiency, expressed as a bacterial reduction (%), of untreated

The results summarized in Table 3 show low adsorption of silver onto untreated blank dyed cotton. The adsorption of silver onto corona modified cotton did not significantly increase. Both samples do not exhibit the antimicrobial effectiveness. However, treating cotton with water vapor low-pressure plasma increased the adsorption of silver onto cotton up to 7 times, which resulted in an excellent antimicrobial effectiveness against *Streptococcus faecalis* and a sufficient antimicrobial effectiveness against *Escherichia coli*. The adsorption of silver significantly increased when RucoBac AGP was applied onto dyed cotton fabric, regardless of plasma treatment. RucoBac AGP is a nano-dispersion of TiO2 as the carrier of the active component AgCl. In the presence of moisture, silver cations react with hydroxyl functional cellulosic groups and are attached to each other electrostatically. The presence of a reactive dye on cotton and the introduction of additional covalently bound sulfonic acid groups will facilitate the uptake of a cationic antimicrobial agent [87]. Therefore, it is possible to con‐ clude that RucoBac AGP is bound to the cotton surface through sulfonic groups of a cova‐ lently bound dye and through partially ionized hydroxyl and carboxyl groups present on the fiber [72]. The significant increased adsorption of silver can be also noticed with samples modified by water vapor low-pressure plasma and dyeing, while there was no noticeable change when samples were modified by corona plasma. Results obtained from XPS analysis showed that plasma modification of bleached/mercerized cotton increased the content of oxygen on the surface. In addition, after both plasma treatments the appearance of new bonds was noticeable (O-C=O) and the content of C=O bonds increased. That means that oxygen rich functional groups incurred on the surface of plasma modified cotton. These changes were more distinct after low-pressure plasma treatment than after corona plasma

ICRF water vapor 11 58 (*E.coli*)

**Bacterial reduction (%)**

98 (*S.faecalis*)

and *P.aeruginosa*)

and *P.aeruginosa*)

100 (*S.faecalis*)

The objectives for textile industry have been continuous on-line treatments of fabrics. Lowpressure plasma reactors, such as radio frequency powered plasma, provide greater stability and uniformity but generally require more handling of textile materials through the vacuum system than corona discharges at atmospheric pressures. In this respect, the use of corona plasma is more appropriate for the industry. In our following research when laboratory col‐ loidal silver was used, we focused on treating cotton fabric with atmospheric corona plasma. The synthesis of colloidal silver was performed by reducing silver salt in an aqueous solu‐ tion at room temperature under argon atmosphere. The procedure was described previous‐ ly, in section 3.2.1. A synthesis of colloidal silver and loading of silver onto cotton fabric was performed as the second phase after dyeing cotton fabrics with a blue vat dye. To verify whether vat-dyeing influences the adsorption of colloidal silver onto cotton fabric, a blank vat-dyeing procedure (dyeing with all chemicals and no dye) was also performed [71]. Apart from indigo, the vat dyes used in dyeing applications are mainly derivatives of an‐ thraquinone and of higher condensed aromatic ring systems with a closed system of conju‐ gated double bonds. They generally contain two, four or six reducible carbonyl groups [88].

$$\mathbf{C} = \underbrace{\overbrace{\underset{\mathbf{w}\mathbf{a}\mathbf{s}\mathbf{a}\mathbf{s}\mathbf{u}}}\_{\mathbf{w}\mathbf{a}\mathbf{s}\mathbf{u}\mathbf{a}\mathbf{s}\mathbf{u}}}\_{\mathbf{w}\mathbf{a}\mathbf{s}\mathbf{u}\mathbf{a}\mathbf{s}\mathbf{u}}\qquad\mathbf{C} = \underbrace{\overbrace{\underset{\mathbf{w}\mathbf{a}\mathbf{s}\mathbf{a}\mathbf{s}\mathbf{u}\mathbf{a}\mathbf{s}}}\_{\mathbf{w}\mathbf{a}\mathbf{s}\mathbf{u}\mathbf{a}\mathbf{s}}}\_{\mathbf{w}\mathbf{a}\mathbf{s}\mathbf{u}}\qquad\mathbf{0}$$

**Figure 11.** Scheme of reduction and oxidation process of carbonyl group of vat dye

The vat dyes are insoluble in the keto form (Figure 11a). For dyeing they must be trans‐ formed to a water soluble enolate (leuko) form (Figure 11c) by a reduction. This form of the dye is appropriate for cellulose dyeing, but the addition of electrolyte is also required. After the dyeing, the dye in amorphous regions is transformed through leuko acid (Figure 11b) into its original water insoluble form by rinsing and oxidation [89]. The vat dyeing of bleached/mercerized cotton fabric before colloidal silver treatment significantly influences the adsorption of silver onto cotton fabrics [71]. Also the adsorption of silver is influenced by an immersion time of cotton into colloidal silver solution. Although it was proven that modification of cotton by corona plasma strongly influences the adsorption of powdered sil‐ ver nanoparticles by increasing their quantity on the modified cotton, the experiment using synthetized colloidal silver on corona treated cotton had to be conducted. The Table 4 presents the results of ICP-MS and antimicrobial analysis of untreated, corona and vat dyed colloidal silver loaded cotton.


concentration of AgNO3 and NaBH4. In this case, the corona plasma modified and undyed cotton contained 1.6 ppm of silver. The quantity of silver was so low that the fabric did not have an antimicrobial efficiency. However, when cotton fabric was modified by corona plas‐ ma and then vat dyed the quantity of silver was 4.6 ppm, which gave the fabric an excellent antimicrobial efficiency against *Staphylococcus aureus*, *Escherichia coli*, *Streptococcus faecalis* and *Pseudomonas aeruginosa*. The antimicrobial analysis showed the antimicrobial ineffective‐ ness of dyed cotton sample, therefore the dye itself did not contribute to the antibacterial ef‐

Multifunctional Textiles – Modification by Plasma, Dyeing and Nanoparticles

http://dx.doi.org/10.5772/53376

23

Our research shows that plasma treatment is an effective method to be used in achieving surface changes on the textile material by changing the functional groups on the textile sur‐ face and by changing the morphology of the fibers. The results of adsorption of different forms of silver nanoparticles on untreated and plasma-treated surfaces of fabrics confirm the fact that, for nanotechnological processes, the surface of the material has to be properly pre‐ pared. The adsorption of metal nanoparticles on textile materials depends on specific chemi‐ cal and morphological properties of fibers. Plasma modification of cotton had a positive influence on the increased adsorption of silver nanoparticles loaded during exhaust dyeing process. From the bath, which contained a low concentration of silver nanoparticles, we have successfully applied a greater quantity of silver onto plasma modified cotton (up to four times). In some cases using plasma the dyeability of cotton was also improved. We suc‐ ceeded to create a cotton fabric containing minimal quantity of silver with an excellent anti‐ microbial efficiency. This is very interesting from the technological point of view since by this method the quantity of silver in wastewater can be dramatically reduced. Another im‐ portant result of the research was that plasma modification did not impair the mechanical properties of textiles. By using plasma technology new and improved properties of materi‐ als can be created that cannot be achieved by standard procedures, where nanostructuring of natural and synthetic fibers is emphasized. The use of plasma for modification of textiles brings to the textile industry many novelties, since plasma technology can be used as a sub‐ stitute or as a support to the existing technologies, and by that positively influences the economy and ecology of the industrial processes. The knowledge of using plasma technolo‐ gy enables an introduction of contemporary (state-of-the-art) and ecological process of a tex‐ tile modification into the textile industry and a development of highly technological

This work was financially supported by Slovenian Research Agency (Programme P2-0213

ficiency of the functionalized cotton sample.

products with improved or new properties.

Textile and Ecology), and Eureka Nanovision project.

**Acknowledgements**

**4. Conclusion**

**Table 4.** The quantity of silver (ppm) and antimicrobial efficiency, expressed as a bacterial reduction (%), of untreated and plasma-treated cotton samples functionalized with synthetized colloidal silver

The results summarized in Table 4 show that atmospheric air corona treatment enhanced the quantity of silver onto dyed cotton up to 1.8 times comparing to the untreated dyed cot‐ ton. In addition to the morphological changes induced by plasma (seen by SEM), XPS analy‐ sis showed the increase of C-O and C=O bonds and formation of O-C=O bonds on the surface of treated cotton. The increased concentration of oxygen and newly formed bonds contributed to a better adhesion of Ag+ ions from the colloidal solution onto cellulosic fibers. In addition to the increased number of functional groups containing oxygen, the dyed cot‐ ton fabric contains additional anionic sites due to the partial ionization of the molecules of insoluble vat dye. Colloidal silver is produced in a water solution using AgNO3 reduced by NaBH4. NaBH4 also slightly reduces the water insoluble vat dye on the dyed fabric into a slightly soluble form. Although NaBH4 is not a sufficiently strong reducing agent for dyeing cotton with a vat dye [90], it is nevertheless strong enough to enhance the negative charge of the dye on the fabric [91] such that silver ions (Ag+ ) from a silver colloidal solution can be electrostatically attracted to the dyed cotton surface. It was reported that while Ag+ ions from a colloidal silver solution are exhausted to the anionic cotton fibers to a high degree because of the attractive electrostatic interactions, the high increase of the adsorption ability of silver nanoparticles caused by the van der Walls forces resulted from the high surface area to volume ratio of these particles [43].

The important goal of our research was to use minimal concentrations, initially, of silver nanoparticles for loading onto textiles and to achieve a maximum quantity on the material, and thus to achieve functionalized cotton textile with an excellent antimicrobial efficiency. Since the cotton fabrics already had an excellent antimicrobial efficiency when functional‐ ized with rather low concentration of silver, the decision was made to verify the possibility in achieving good antibacterial efficiency of a cotton fabric with the use of half of the initial concentration of AgNO3 and NaBH4. In this case, the corona plasma modified and undyed cotton contained 1.6 ppm of silver. The quantity of silver was so low that the fabric did not have an antimicrobial efficiency. However, when cotton fabric was modified by corona plas‐ ma and then vat dyed the quantity of silver was 4.6 ppm, which gave the fabric an excellent antimicrobial efficiency against *Staphylococcus aureus*, *Escherichia coli*, *Streptococcus faecalis* and *Pseudomonas aeruginosa*. The antimicrobial analysis showed the antimicrobial ineffective‐ ness of dyed cotton sample, therefore the dye itself did not contribute to the antibacterial ef‐ ficiency of the functionalized cotton sample.
