**4.3 Wettability study**

46 Textile Dyeing

Polar functional groups are incorporated onto the polymer film during the plasma treatment. These polar groups are readily detected by ESCA (XPS), but are often missed by ATR-FTIR spectroscopy (Wu S, 1982). XPS is the best technique to study such modified surfaces. Several studies showed that air, N2, O2, NH3, etc. plasma incorporates hydrophilic functional groups onto the polymer surfaces thereby increasing wettability and surface energy (Bhat et al., 2011; Navaneetha et al., 2010; P´chal and Klenko, 2009). It has been reported that the treatment carried out in inert gases like Ar introduces oxygen moieties onto the polymer surface because of post plasma exposure of samples to atmosphere (Deshmukh and Bhat, 2003(b); Gupta et al., 2000). Therefore, IR spectra of N2 and O2 plasma treated nylon samples is not given here. The IR spectra of plasma polymerized acrylic acid

**4000 3500 3000 2500 2000 1500 1000 500**

**Wavenumber (cm-1)**

The FTIR spectrum of a PPAA film prepared using the technique of plasma polymerization was very similar to the spectrum of Poly (acrylic acid) prepared by conventional polymerization techniques and it shows all the characteristic bands. In particular, the FTIR spectrum shows that the film contains a high density of C(O)OH groups. The absorption peaks assignment is given in table below (Alaa et al., 2011; Cho et al., 1990; Chilcoti and Ratner, 1993; Eun-Young Choi and Seung-Hyeon Moon, 2007; Jafari et al., 2006; Mirzadeh et

Fig. 3. FTIR spectra of PPAA (A) 2min. deposition, (B) 4min. deposition.

**(B)**

**(A)**

**4.2 FTIR study** 

(PPAA) is given in Fig. 3 below.

**% T**

al., 2002).

The contact angle of untreated nylon fabric was observed to be 830 (±2). Its surface energy comes to be 33.6 mJ/m2. Fig. 4 shows the photograph of water droplet taken on untreated and 4 minute oxygen plasma treated nylon fabric.

However, we could not measure contact angle for any plasma processed samples. It shows that the surface energy of all the samples increases rapidly after the plasma processing. Therefore we have measured wetting time of the samples as given in Table 2.

Pretreatments of Textiles Prior to Dyeing: Plasma Processing 49

Fig. 6. K/S values of nylon fabric subjected to RF plasma treatment.

Control Nylon

oxygen plasma is also more as shown in Fig. 2 (e and f).

The increase in the dyeing in the initial stage could be due to the fact that gaseous plasma etches out the surface of the nylon fibers, creating a rougher surface with irregularities as discussed earlier. The effective surface area increases after the plasma treatment. Thus the interaction and diffusion of the dye molecules is facilitated. The etching of the surface has been confirmed by other researchers (Karahan et al., 2009; Ozdogan et al., 2009). The chemical changes in the nylon fiber surface can lead to the possibility of the formation of free radicals on the nylon chains and the subsequent formation of hydroxyl, carbonyl and carboxyl groups. It is also important to mention that the dyeing process mainly occurs through the amorphous regions. The etching away of the amorphous regions during the plasma treatment (particularly for longer treatment time) can lead to lowering of the dye uptake. Therefore the optimum treatment time needs to be found. Yoon et al. and Thomas et al., have found that longer plasma treatment decreases dye uptake (Thomas et al., 1998; Yoon et al., 1996). It may be noted that the oxygen is more reactive than nitrogen and hence the dye uptake is slightly more for oxygen treated samples. The etching caused due to

N2 4 min Plasma treated

O2 4 min Plasma treated

PPAA 4 min deposited

Plasma polymerization of acrylic acid (PPAA) onto the nylon fabric incorporates good amount of hydroxyl, carbonyl and carboxylic acid groups onto the surface as evident from FTIR studies. These functional groups are responsible for wettability and hence dye uptake. The dyebath exhaustion is slightly more in case of PPAA deposited nylon fabric as compared to that of gaseous plasma treated samples, because of the functional groups which are incorporated during the deposition of PPAA. Deposition causes reduction in the capillary action therefore; we have observed slightly more wetting time for PPAA samples as shown in Table 2. However, when dyeing is carried out for 15 minutes, which is sufficient time for the penetration of dye into the fabric, a major role of functional groups is observed


Table 2. Wetting time of untreated and plasma processed nylon samples.

It may be noted from Table 2 that the wetting time of the untreated nylon fabrics was 112 seconds, which dramatically decreases after N2, O2 and acrylic acid plasma treatment. The decrease is more significant in case of O2 plasma treated samples as etching action and oxidation reaction is predominant. On the other hand, the decrease in the wetting time of PPAA treated sample is rather slow. It may be also be noted from the SEM micrographs that the formation of etch-pits and voids is very predominant for O2 plasma treated nylon fabrics, whereas PPAA treated samples reveal coating on the surface due to formation of PPAA. Due to such thin film formation on the surface the water drop may not easily reach the fabric and as a result the capillary action is reduced.

#### **4.4 Dyeing studies**

Plasma processed samples were dyed using acid dye-blue. The dye absorption was determined spectroscopically by measuring the absorption band maximum of the dye-bath solution before starting and after exhaustion. In addition, the amount of dye uptake was also determined from the color matching instrument. The color values are expressed in terms of K/S as the ratio of reflectivity to absorptivity. For each kind of plasma processing, the dye uptake of plasma-treated sample was compared with the untreated sample of the same variety.

Fig. 5. Relation between the dye bath exhaustion and plasma processing time.

0 112 112 112 0.5 18 12 20 1 15 9 16 2 8 6 14 4 4 3 19

It may be noted from Table 2 that the wetting time of the untreated nylon fabrics was 112 seconds, which dramatically decreases after N2, O2 and acrylic acid plasma treatment. The decrease is more significant in case of O2 plasma treated samples as etching action and oxidation reaction is predominant. On the other hand, the decrease in the wetting time of PPAA treated sample is rather slow. It may be also be noted from the SEM micrographs that the formation of etch-pits and voids is very predominant for O2 plasma treated nylon fabrics, whereas PPAA treated samples reveal coating on the surface due to formation of PPAA. Due to such thin film formation on the surface the water drop may not easily reach

Plasma processed samples were dyed using acid dye-blue. The dye absorption was determined spectroscopically by measuring the absorption band maximum of the dye-bath solution before starting and after exhaustion. In addition, the amount of dye uptake was also determined from the color matching instrument. The color values are expressed in terms of K/S as the ratio of reflectivity to absorptivity. For each kind of plasma processing, the dye uptake of plasma-treated sample was compared with the untreated sample of the

Fig. 5. Relation between the dye bath exhaustion and plasma processing time.

Table 2. Wetting time of untreated and plasma processed nylon samples.

the fabric and as a result the capillary action is reduced.

Time to absorb water droplet on the Plasma Processed Nylon Fabrics (in Sec.) N2 Plasma O2 Plasma PPAA

Treatment Time (min.)

**4.4 Dyeing studies** 

same variety.

Fig. 6. K/S values of nylon fabric subjected to RF plasma treatment.

The increase in the dyeing in the initial stage could be due to the fact that gaseous plasma etches out the surface of the nylon fibers, creating a rougher surface with irregularities as discussed earlier. The effective surface area increases after the plasma treatment. Thus the interaction and diffusion of the dye molecules is facilitated. The etching of the surface has been confirmed by other researchers (Karahan et al., 2009; Ozdogan et al., 2009). The chemical changes in the nylon fiber surface can lead to the possibility of the formation of free radicals on the nylon chains and the subsequent formation of hydroxyl, carbonyl and carboxyl groups. It is also important to mention that the dyeing process mainly occurs through the amorphous regions. The etching away of the amorphous regions during the plasma treatment (particularly for longer treatment time) can lead to lowering of the dye uptake. Therefore the optimum treatment time needs to be found. Yoon et al. and Thomas et al., have found that longer plasma treatment decreases dye uptake (Thomas et al., 1998; Yoon et al., 1996). It may be noted that the oxygen is more reactive than nitrogen and hence the dye uptake is slightly more for oxygen treated samples. The etching caused due to oxygen plasma is also more as shown in Fig. 2 (e and f).

Plasma polymerization of acrylic acid (PPAA) onto the nylon fabric incorporates good amount of hydroxyl, carbonyl and carboxylic acid groups onto the surface as evident from FTIR studies. These functional groups are responsible for wettability and hence dye uptake. The dyebath exhaustion is slightly more in case of PPAA deposited nylon fabric as compared to that of gaseous plasma treated samples, because of the functional groups which are incorporated during the deposition of PPAA. Deposition causes reduction in the capillary action therefore; we have observed slightly more wetting time for PPAA samples as shown in Table 2. However, when dyeing is carried out for 15 minutes, which is sufficient time for the penetration of dye into the fabric, a major role of functional groups is observed

Pretreatments of Textiles Prior to Dyeing: Plasma Processing 51

dye used was Red-M and natural dye was Thar. When dyeing was carried out and measurements were done for the dyed samples, it was noticed that, in the case of direct dye, the colour strength after plasma treatment were found to have decreased by 2.1 %. However, in the case of reactive dye, there was an increase in colour strength by 3.2%. The natural dye Thar showed a marginal decrease by 1%. It was surprising that, when the plasma treatment, enhances the wettability of cotton fabrics to a great extent, the increase in the dye uptake was not similar. This makes us believe that, the interaction of dye with the polymer (fibre) is important for improved dye uptake. The tremendous work carried out for wool fibres has revealed that while the plasma treatment, invariably leads to increase in the dye uptake, it is not so for other types of fibres (polyester, cotton, nylon etc.). There are several conflicting results of increase at times and decrease for other cases. Our analysis shows that, in addition to the type of gaseous plasma, the structure and morphology of the fibre is important. If a proper group of dye is used, the interaction of the dye with the fibre becomes compatible leading to increase in the dye uptake. Our conflicting results in case of

In case of direct dye, the dyeing phenomena is supposed to be due to diffusion of the dye molecule into the fibre, whereas reactive dye reacts with the OH group of the cellulose chain. The natural dye Thar has a very long chain with many CH groups and possibly cannot diffuse into the fibre. The very short (few seconds) plasma treatment of cotton fabrics leads to removal of wax and other impurities from the surface of the fibre. Further treatment with plasma (up to 5 min) leads to removal of the amorphous portions of the material, thereby decreasing the possibility of interaction with the OH groups of the cellulose chain. There also occurs cross linking on the surface, which would hinder the diffusion of the dye molecules. The plasma interaction etches the surface and the effective area is enhanced and also oxygen moieties are incorporated and will contribute to synergistic effect leading to enhanced dye uptake. However, there is a competitive process of cross-linking and as a

Similarly in another experiment, we thought interesting to see the effect of DC plasma on polyester fabric. Oxygen was used as precursor gas. Plasma treatment of polyester fabrics was carried for different durations of time. The morphological changes in the fiber structure were assessed by SEM which revealed the formation of rough surface together with voids and cracks. The loss of weight increased with the treatment time while the tenacity was affected to a small extent. Moisture regain and wettability was found to be improved with increasing treatment time. The fabrics developed yellowness after the plasma treatment that increased with time. Such plasma treated fabrics were dyed with disperse dye in HTHP machine. The dye uptake was found to have increased initially up to 10 minutes and slightly decreases at higher time of treatment. The increase in the dye uptake was due to combined effect of the production of polar group on the surface, etching of the surface creating higher effective area and the creation of voids and cracks, which can facilitate entry of dye molecules into the interior of the fibre. The maximum increase was found to be 2% . Such minor rise in the dye uptake is probably due to other competitive process of cross linking reaction on the surface which do not allow penetration of the dye into the interior. Therefore when the time of treatment was increased beyond 10 min there appears to be slight reduction in the dye uptake. This

cotton fabric just described above may be explained as follows:

result the net dyeing may not always show increase.

**4.5.3 DC plasma effect on polyester fabric** 

behavior is shown in Fig. 8 below.

on the dyeing behavior rather than wetting time. The deposition is evident from SEM micrographs as shown in Fig. 2 (g and h).

The increase in the dye uptake due to plasma treatment is also evident from the measurement of K/S values shown in the Fig. 6. The bar-graph shows K/S values for control and plasma treated samples for four minutes in different gases. The highest gain is seen to be for PPAA deposited nylon fabrics followed by oxygen treated sample. This trend is similar to that observed for the data of dye bath exhaustion.

#### **4.5 Few results of case studies**

#### **4.5.1 Dyeing behavior of nylon fabric treated in APGD**

Similarly, nylon fabric was treated in atmospheric pressure glow discharge, for various durations of time, it was found that there is increase in the dye uptake with time as shown in Fig. 7. The dye used in these studies was acid dye-red. It may be seen that when the dyeing time was 15 minutes, the differences in the K/S values of the control and the atmospheric pressure plasma (He +air) treated is quite noticeable. The increase in dye is significant. However, as the dyeing time is increased to 60 minutes the equilibrium dye uptake is reached for control as well as plasma treated samples and the difference reduces. This proves that the plasma pretreatment can reduce the time of dyeing and as a result power can be saved.

Fig. 7. K/S values of Nylon fabrics dyed with reactive dye after subjecting the fabrics to atmospheric pressure plasma for different duration of time.

#### **4.5.2 Dyeing behavior of cotton fabric treated in air plasma**

In another recent study (just results are summarized), cotton fabrics (desized, scoured and bleached) were treated with air plasma (RF), for 4 minutes. In order to understand the effect of such treatment on dyeing behavior, it was decided to use three different dyes namely, direct dye, reactive dye and natural dye. The direct dye used was Congo red, the reactive

on the dyeing behavior rather than wetting time. The deposition is evident from SEM

The increase in the dye uptake due to plasma treatment is also evident from the measurement of K/S values shown in the Fig. 6. The bar-graph shows K/S values for control and plasma treated samples for four minutes in different gases. The highest gain is seen to be for PPAA deposited nylon fabrics followed by oxygen treated sample. This trend

Similarly, nylon fabric was treated in atmospheric pressure glow discharge, for various durations of time, it was found that there is increase in the dye uptake with time as shown in Fig. 7. The dye used in these studies was acid dye-red. It may be seen that when the dyeing time was 15 minutes, the differences in the K/S values of the control and the atmospheric pressure plasma (He +air) treated is quite noticeable. The increase in dye is significant. However, as the dyeing time is increased to 60 minutes the equilibrium dye uptake is reached for control as well as plasma treated samples and the difference reduces. This proves that the plasma pretreatment can reduce the time of dyeing and as a result

Fig. 7. K/S values of Nylon fabrics dyed with reactive dye after subjecting the fabrics to

In another recent study (just results are summarized), cotton fabrics (desized, scoured and bleached) were treated with air plasma (RF), for 4 minutes. In order to understand the effect of such treatment on dyeing behavior, it was decided to use three different dyes namely, direct dye, reactive dye and natural dye. The direct dye used was Congo red, the reactive

atmospheric pressure plasma for different duration of time.

**4.5.2 Dyeing behavior of cotton fabric treated in air plasma** 

micrographs as shown in Fig. 2 (g and h).

**4.5 Few results of case studies** 

power can be saved.

is similar to that observed for the data of dye bath exhaustion.

**4.5.1 Dyeing behavior of nylon fabric treated in APGD** 

dye used was Red-M and natural dye was Thar. When dyeing was carried out and measurements were done for the dyed samples, it was noticed that, in the case of direct dye, the colour strength after plasma treatment were found to have decreased by 2.1 %. However, in the case of reactive dye, there was an increase in colour strength by 3.2%. The natural dye Thar showed a marginal decrease by 1%. It was surprising that, when the plasma treatment, enhances the wettability of cotton fabrics to a great extent, the increase in the dye uptake was not similar. This makes us believe that, the interaction of dye with the polymer (fibre) is important for improved dye uptake. The tremendous work carried out for wool fibres has revealed that while the plasma treatment, invariably leads to increase in the dye uptake, it is not so for other types of fibres (polyester, cotton, nylon etc.). There are several conflicting results of increase at times and decrease for other cases. Our analysis shows that, in addition to the type of gaseous plasma, the structure and morphology of the fibre is important. If a proper group of dye is used, the interaction of the dye with the fibre becomes compatible leading to increase in the dye uptake. Our conflicting results in case of cotton fabric just described above may be explained as follows:

In case of direct dye, the dyeing phenomena is supposed to be due to diffusion of the dye molecule into the fibre, whereas reactive dye reacts with the OH group of the cellulose chain. The natural dye Thar has a very long chain with many CH groups and possibly cannot diffuse into the fibre. The very short (few seconds) plasma treatment of cotton fabrics leads to removal of wax and other impurities from the surface of the fibre. Further treatment with plasma (up to 5 min) leads to removal of the amorphous portions of the material, thereby decreasing the possibility of interaction with the OH groups of the cellulose chain. There also occurs cross linking on the surface, which would hinder the diffusion of the dye molecules. The plasma interaction etches the surface and the effective area is enhanced and also oxygen moieties are incorporated and will contribute to synergistic effect leading to enhanced dye uptake. However, there is a competitive process of cross-linking and as a result the net dyeing may not always show increase.

#### **4.5.3 DC plasma effect on polyester fabric**

Similarly in another experiment, we thought interesting to see the effect of DC plasma on polyester fabric. Oxygen was used as precursor gas. Plasma treatment of polyester fabrics was carried for different durations of time. The morphological changes in the fiber structure were assessed by SEM which revealed the formation of rough surface together with voids and cracks. The loss of weight increased with the treatment time while the tenacity was affected to a small extent. Moisture regain and wettability was found to be improved with increasing treatment time. The fabrics developed yellowness after the plasma treatment that increased with time. Such plasma treated fabrics were dyed with disperse dye in HTHP machine. The dye uptake was found to have increased initially up to 10 minutes and slightly decreases at higher time of treatment. The increase in the dye uptake was due to combined effect of the production of polar group on the surface, etching of the surface creating higher effective area and the creation of voids and cracks, which can facilitate entry of dye molecules into the interior of the fibre. The maximum increase was found to be 2% . Such minor rise in the dye uptake is probably due to other competitive process of cross linking reaction on the surface which do not allow penetration of the dye into the interior. Therefore when the time of treatment was increased beyond 10 min there appears to be slight reduction in the dye uptake. This behavior is shown in Fig. 8 below.

Pretreatments of Textiles Prior to Dyeing: Plasma Processing 53

Even if the increase is small, if the process can lead to sufficient dye uptake at a reduced temperature or time, it would serve a good purpose. Advantages of the process in terms of eco-friendliness, water saving and energy saving be explored and emphasized so that the

Further work needs to be carried out by using pulsed plasma as it may avoid the degradation of fabrics when subjected to longer durations of treatments. In-situ cooling of the samples is also desirable to maintain the temperature of substrate constant. It is also necessary to find the electron and ion densities or rather the number of ions hitting the

We thank Miss. G. A. Arolkar and Mr. Kiran Kale for helping us to treat samples in low

Abidi N. and Hequet E., Cotton Graft Copolymerization Using Microwave Plasma. I.

Abidi N. and Hequet E., Cotton Graft Copolymerization Using Microwave Plasma. II.

Abidi N, in Surface modification of textiles, Q. Wei (Ed), Woodhead publishing in Textiles,

Alaa Fahmy, Renate Mix, Andreas Scho¨nhals, Jo¨rg F. Friedrich., Structure of Plasma-Deposited Poly(acrylic acid) Films, Plasma Process. Polym., 8, 147–159, (2011). Araujo R., Casal M., and Cavaco-Paulo A., Applications of Enzymes for textile fibre

Bhat N.V. and Nadiger G.S., Effect of nitrogen plasma on the morphology and allied textile properties of tassar silk fibres and fabrics. Textile Res J; 48: 685–691, (1978) Bhat N.V. and Benjamin Y.N., Surface Resistivity Behaviour of Plasma Treated and Plasma Grafted Cotton and Polyester Fabrics, Textile Res J., 69(1), 38-42, (1999). Bhat N.V. and Deshmukh R.R., X-ray crystallographic studies of polymeric materials

Bhat N. V., Upadhyay D. J., Deshmukh R. R., and Gupta S. K., Investigation of Plasma-

Bhat N.V., Netravali A.N., Gore A.V., Sathianarayanan M.P., Arolkar G.A. and Deshmukh

Bhattacharyya D., Xu H., Deshmukh R.R., Timmons R.B. and Kytai T.N., Surface chemistry and

Cao G., Nanostructures and Nanomaterials-Synthesis, Properties and Applications, Imperial

Induced Photochemical Reaction on a Polypropylene Surface, J. Phys. Chem. B, 107*,* 

R.R., Surface modification of cotton fabrics using plasma technology, Textile Res J.,

polymer film thickness effects on endothelial cell adhesion and proliferation, Journal of Biomedical Materials Research Part A, Volume 94A, Issue 2, pages 640–648, (2010). Bozzi A., Yuranova T. and Kiwi J., Self Cleaning of Wool, Polyamide and Polyester Textile

by TiO2 Rutile Modification Under Daylight Irradiation at Ambient Temperature, J.

Indian Journal of Pure & Applied Physics, 40 (5) 361-366, (2002).

Universal ATR-FTIR Study, J. Appl Polym Sci., 93, 145-154, (2004).

Physical Properties, J. Appl Polym Sci., 98, 896-902, (2005).

processing. Biocat.Biotrans. 26(5), 332-349, (2008).

Photochem Photobiol A: Chem 172, 27-34, (2005).

technology is acceptable to all.

**7. Acknowledgement** 

UK (2009).

4550-4559, (2003).

81, 1014-1026, (2011).

College Press, London. (2004).

**8. References** 

sample to calculate the energy deposited during processing.

pressure and in atmospheric pressure plasma respectively.

Fig. 8. Dye uptake of DC plasma treated polyester fabric
