**3.2.2 Contact angle measurement**

The hydrophilicity of the polyamide fabric is highly improved by the plasmatic treatment in accordance with the results published by several authors for different synthetic and natural fibers, mentioning modifications in accessible polar groups at the surface and creation of microporosity (Pappas et al., 2006, Oliveira et al., 2009, Yip et al., 2002).

This surface modification might transform the synthetic fiber from hydrophobic to hydrophilic which is key point for the absorption of aqueous dye solutions.

The static and dynamic contact angle evaluation of a water droplet in the textile polyamide fabric is shown in figures 5, 6 and 7, corresponding to a mean value of five measurements.

Fig. 5. Contact of water drop in the sample without (a) and with DBD plasma treatment (b) (time =0 s and after 30 s).

Polyamide 6.6 Modified by DBD Plasma Treatment for Anionic Dyeing Process 249

**Sample Atomic composition (%) Atomic ratio** 

Untreated 74.67 17.75 7.58 9.85 4.21 DBD Treated 70.25 19.83 9.92 7.08 3.54

The figure 8 shows the increase of O1s and N1s atoms and consequently decrease of C1s when DBD treatment is applied, which corresponds to an enhancement of hydrophilicity of fabrics

N1s N1s

Fig. 8. XPS analysis of polyamide fabric a) without treatment and b) with DBD treatment.

The surface modification by DBD plasma on polyamide fabrics was detected by the scanning electron micrographs (Figure 9). Compared to untreated polyamide 6.6, the DBD plasma treated polyamide 6.6 presents small patches on the surface responsible for an

The comparison of the images obtained with and without DBD plasma treatment, shows a

Fig. 9. Increase of roughness after DBD treatment (right) in SEM micrographic

Table 4. XPS results in samples with and without DBD treatment

a) b)

**3.2.4 Scanning electron microscopy** 

somewhat different surface morphology.

increase of surface area.

due to an increase of polar groups in the surface of polyamide fabrics.

O1s C1s O1s

C O N C/N C/O

C1s

After DBD treatment, the wettability of the polyamide fabric considerably increases. This result may be attributed to the incorporation of polar groups onto the fabric surface.

Fig. 6. Static contact angle measurement of a water drop for the samples: untreated and with different plasma dosages.

Fig. 7. Dynamic contact angle measurement of a water drop in the sample without treatment (a) and treated with dosage 2400 W.min.m-2 (b).

#### **3.2.3 X-ray photoelectron spectroscopy**

The XPS analysis shows that the oxygen and nitrogen content level was increased after DBD treatment. This indicates a substantial incorporation of these atoms onto the fabric surface. Chemical states of atoms, represented by relative peak areas, can be obtained by wave separation method. The carbon component can be divided into peaks (280.5 to 294.0 eV), assigned as CH2, CH2CO, CH2NH and NHCO (Pappas et al., 2002). It can be observed that the relative peak areas of sub-components change significantly after DBD treatment.

Results reveal that the element C1s decreases while both N1s and O1s increase. DBD treatment can be responsible for the breaking of the long chain molecules of polyamide 6.6, causing an increase of carboxyl and amine end groups. The table 4 shows the elementary composition and the atomic ratio before and after plasma treatment.


Table 4. XPS results in samples with and without DBD treatment

The figure 8 shows the increase of O1s and N1s atoms and consequently decrease of C1s when DBD treatment is applied, which corresponds to an enhancement of hydrophilicity of fabrics due to an increase of polar groups in the surface of polyamide fabrics.

Fig. 8. XPS analysis of polyamide fabric a) without treatment and b) with DBD treatment.

#### **3.2.4 Scanning electron microscopy**

248 Textile Dyeing

After DBD treatment, the wettability of the polyamide fabric considerably increases. This

Fig. 6. Static contact angle measurement of a water drop for the samples: untreated and with

Fig. 7. Dynamic contact angle measurement of a water drop in the sample without treatment

The XPS analysis shows that the oxygen and nitrogen content level was increased after DBD treatment. This indicates a substantial incorporation of these atoms onto the fabric surface. Chemical states of atoms, represented by relative peak areas, can be obtained by wave separation method. The carbon component can be divided into peaks (280.5 to 294.0 eV), assigned as CH2, CH2CO, CH2NH and NHCO (Pappas et al., 2002). It can be observed that

Results reveal that the element C1s decreases while both N1s and O1s increase. DBD treatment can be responsible for the breaking of the long chain molecules of polyamide 6.6, causing an increase of carboxyl and amine end groups. The table 4 shows the elementary

the relative peak areas of sub-components change significantly after DBD treatment.

composition and the atomic ratio before and after plasma treatment.

different plasma dosages.

(a) and treated with dosage 2400 W.min.m-2 (b).

**3.2.3 X-ray photoelectron spectroscopy** 

result may be attributed to the incorporation of polar groups onto the fabric surface.

The surface modification by DBD plasma on polyamide fabrics was detected by the scanning electron micrographs (Figure 9). Compared to untreated polyamide 6.6, the DBD plasma treated polyamide 6.6 presents small patches on the surface responsible for an increase of surface area.

The comparison of the images obtained with and without DBD plasma treatment, shows a somewhat different surface morphology.

Fig. 9. Increase of roughness after DBD treatment (right) in SEM micrographic

Polyamide 6.6 Modified by DBD Plasma Treatment for Anionic Dyeing Process 251

Whiteness of polyamide fabric slightly decreases (2.8 degrees for a dosage of 3600 W.min.m-2)

Results show the effect of the plasma discharge on dyeing behavior of polyamide 6.6 with

The surface modification of the polyamide fiber after DBD plasma treatment permits very

Fig. 12. Exhaustion results for a) direct dye, b) reactive dye for cotton, c) reactive dye for wool and d) acid dye in polyamide 6.6 samples with and without DBD treatment (dyeing

The complete bath exhaustion was obtained in very short time during dyeing processes with remarkable positive difference when a plasmatic treatment is made on polyamide fabrics (Figure 12). Forty minutes are enough to exhaust dye from dyebath which is a very

The direct and acid dyes are anionic and water soluble and the increase of fiber hydrophilicity with plasmatic treatment is favorable to dye adsorption, essential to promote

Reactive dyes are also water soluble and anionic, apart being able to form covalent bonding with reactive groups in the fiber, namely the amine groups of polyamide. The same factors promoting adsorption and diffusion of dye in the fiber for the acid dyes are present for reactive dyes, explaining complete exhaustion of dye in the fiber after forty minutes of

The table 6 shows the comparative results of K/S with reactive dyes, direct dyes and acid dyes in polyamide 6.6 with and without plasma (DBD) treatment. The results demonstrate

for higher dosages, although without noticeable effect in product characteristics.

intense and fast colors with dye exhaustion almost reaching 100% in every case.

direct dyes, reactive dyes for cotton and wool and acid dyes.

a) b)

c) d)

conditions: 100ºC and 1% dye concentration).

dyeing.

attractive behavior regarding industrial application.

coulombic dye fixation to protonated amine groups of the polyamide.

**3.4 Dyeing properties** 

#### **3.2.5 Atomic force microscopy**

The increase in roughness can be better understood when AFM images are compared (Figure 10). The following results were obtained for Ra (arithmetic average roughness ), Rq (root mean squared roughness) and Rmax (Table 5), regarding untreated and plasma treated samples.

Fig. 10. AFM increase of roughness after DBD treatment (b)


Table 5. AFM results for samples with and without treatment

The surface of the sample without treatment is relatively smooth while the treated polyamide has rougher surfaces.

The AFM analysis shows that the Ra, Rq and Rmax roughness increases with the DBD plasma treatment and the modification of the shape of surface features is quite evident. The applications of these results illustrate, for example, the increasing of wettability (as showed by contact angle measurements) and consequently polyamide dyeability properties.

#### **3.3 Berger whiteness**

The figure 11 shows the results obtained for Berger whiteness when different plasma dosages were applied to the polyamide fabric.

Fig. 11. Whiteness degree – Illuminant D65/observer 10º

Whiteness of polyamide fabric slightly decreases (2.8 degrees for a dosage of 3600 W.min.m-2) for higher dosages, although without noticeable effect in product characteristics.

#### **3.4 Dyeing properties**

250 Textile Dyeing

The increase in roughness can be better understood when AFM images are compared (Figure 10). The following results were obtained for Ra (arithmetic average roughness ), Rq (root mean squared roughness) and Rmax (Table 5), regarding untreated and plasma treated samples.

> **Samples Ra (nm) Rq (nm) Rmax (nm)**  Untreated 2.36 3.21 29.2 Treated 6.50 7.99 48.0

The surface of the sample without treatment is relatively smooth while the treated

The AFM analysis shows that the Ra, Rq and Rmax roughness increases with the DBD plasma treatment and the modification of the shape of surface features is quite evident. The applications of these results illustrate, for example, the increasing of wettability (as showed

The figure 11 shows the results obtained for Berger whiteness when different plasma

by contact angle measurements) and consequently polyamide dyeability properties.

**3.2.5 Atomic force microscopy** 

polyamide has rougher surfaces.

dosages were applied to the polyamide fabric.

Fig. 11. Whiteness degree – Illuminant D65/observer 10º

**3.3 Berger whiteness** 

Fig. 10. AFM increase of roughness after DBD treatment (b)

a) b)

Table 5. AFM results for samples with and without treatment

Results show the effect of the plasma discharge on dyeing behavior of polyamide 6.6 with direct dyes, reactive dyes for cotton and wool and acid dyes.

The surface modification of the polyamide fiber after DBD plasma treatment permits very intense and fast colors with dye exhaustion almost reaching 100% in every case.

Fig. 12. Exhaustion results for a) direct dye, b) reactive dye for cotton, c) reactive dye for wool and d) acid dye in polyamide 6.6 samples with and without DBD treatment (dyeing conditions: 100ºC and 1% dye concentration).

The complete bath exhaustion was obtained in very short time during dyeing processes with remarkable positive difference when a plasmatic treatment is made on polyamide fabrics (Figure 12). Forty minutes are enough to exhaust dye from dyebath which is a very attractive behavior regarding industrial application.

The direct and acid dyes are anionic and water soluble and the increase of fiber hydrophilicity with plasmatic treatment is favorable to dye adsorption, essential to promote coulombic dye fixation to protonated amine groups of the polyamide.

Reactive dyes are also water soluble and anionic, apart being able to form covalent bonding with reactive groups in the fiber, namely the amine groups of polyamide. The same factors promoting adsorption and diffusion of dye in the fiber for the acid dyes are present for reactive dyes, explaining complete exhaustion of dye in the fiber after forty minutes of dyeing.

The table 6 shows the comparative results of K/S with reactive dyes, direct dyes and acid dyes in polyamide 6.6 with and without plasma (DBD) treatment. The results demonstrate

Polyamide 6.6 Modified by DBD Plasma Treatment for Anionic Dyeing Process 253

b)

Fig. 13. K/S values of reactive dye for cotton (a), direct dye (b), reactive dye for wool (c) and acid dye (d) in polyamide 6.6 with different temperatures (dye concentration: 1% dye

The figure 14 a, b, c and d shows the influence of the dye concentration in the polyamide

b)

Fig. 14. K/S values of reactive dye for cotton (a), direct dye (b), reactive dye for wool (c) and acid dye (d) in polyamide 6.6 with different dye concentrations (dyeing temperature: 100ºC).

**3.4.2 The influence of dye concentration in dyeing processes** 

c) d)

c) d)

a) a) b)

c) d)

weight/fiber weight ).

a)

dyeing.


that in dyeings carried with these anionic dyes, the color strength (K/S) is considerably higher for the fabric with DBD treatment, quantified by means of the percentage gain of the treated sample when compared to the non treated one.

Table 6. K/S values for dyeings of polyamide 6.6 fabric with and without DBD treatment

The gain in color yield obtained with DBD treatment is effective for all the dyes, although results are quite variable for the different colors of each commercial dye.
