**3.4.1 The influence of temperature in dyeing processes**

The figure 13 shows the influence of the temperature in polyamide dyeing process with the following dyes: Levafix Brilliant Red E-BA (reactive dye for cotton), Sirius Orange 3GDL (direct dye,) Realan Blue EHF (reactive dye for wool) and Telon Blue M-GLW (acid dye). Comparisons were made between the samples with and without plasmatic treatment.

The increase in temperature of all dyeing processes (Figure 13) leads to an increase of the color yield (K/S values) of the polyamide dyed samples. Nevertheless, it is evident that dye absorption mechanism is quite influenced by plasmatic treatment.

In fact, a linear behavior of K/S with temperature is much more present when the fiber is plasma discharged, demonstrating that structural transitions are not the main driving force for dye penetration in polyamide.

Meanwhile it is quite clear that the untreated fiber is highly dependent on temperature to achieve high K/S values, being noticeable that structural changes may occur at temperature around 90ºC.

Therefore, the reduction in energy demand can be considerable in the dyeing process when plasmatic pre treatment is made compromising the same color yield (K/S) at much lower temperatures.

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

> **Without Treatment (K/S)**

Yellow RNL 84.4 88.9 5.4

Levafix Yellow CA 43.1 102.6 137.8

Realan Red EHF 36.1 48.6 34.7 Realan Yellow EHF 54.8 60.9 11.1 Realan Blue EHF 49.9 86.8 73.9

Sirius Scarlet KCF 111.6 185.5 137.8 Sirius Violet RL 100.8 138.7 16.8 Sirius Orange 3GDL 68.4 199.3 45.8

Telon Blue MGWL 51.5 66.1 28.3 Telon Red A2FR 80.7 95.9 18.9 Telon Rot M-6BW 131.2 149.3 13.8

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

results are quite variable for the different colors of each commercial dye.

**3.4.1 The influence of temperature in dyeing processes** 

absorption mechanism is quite influenced by plasmatic treatment.

The gain in color yield obtained with DBD treatment is effective for all the dyes, although

The figure 13 shows the influence of the temperature in polyamide dyeing process with the following dyes: Levafix Brilliant Red E-BA (reactive dye for cotton), Sirius Orange 3GDL (direct dye,) Realan Blue EHF (reactive dye for wool) and Telon Blue M-GLW (acid dye). Comparisons were made between the samples with and without plasmatic

The increase in temperature of all dyeing processes (Figure 13) leads to an increase of the color yield (K/S values) of the polyamide dyed samples. Nevertheless, it is evident that dye

In fact, a linear behavior of K/S with temperature is much more present when the fiber is plasma discharged, demonstrating that structural transitions are not the main driving force

Meanwhile it is quite clear that the untreated fiber is highly dependent on temperature to achieve high K/S values, being noticeable that structural changes may occur at temperature

Therefore, the reduction in energy demand can be considerable in the dyeing process when plasmatic pre treatment is made compromising the same color yield (K/S) at much lower

EXL 15.6 24.9 60.0

**With Treatment (K/S)** 

**DBD gain (%)** 

treated sample when compared to the non treated one.

Remazol Golden

Procion Crimson H-

**Dye Class Commercial Name** 

Reactive for Cotton

Reactive for Wool

Direct

Acid

treatment.

around 90ºC.

temperatures.

for dye penetration in polyamide.

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 weight/fiber weight ).

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

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

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).

Polyamide 6.6 Modified by DBD Plasma Treatment for Anionic Dyeing Process 255

When pH of the dye bath is increased, the color yield reduces considerably in the samples without DBD treatment. On the other hand, if samples are treated with plasma and dyed, a type of "buffer systems" can be observed for all the dyeings, propitiating a very important

Dyeing results are pH independent in the interval 3 to 7, which gives strong indications about the huge influence of plasmatic discharge in chemical composition of fiber surface.

Table 7 shows the results of washing fastness for reactive (wool, cotton) and acid dyes in

The results of washing fastness at 40 ºC are very good confirming the level of dye diffusion and fixation into the fiber. The surface modification of the polyamide fiber after DBD plasma treatment permits to obtain very fast colors, with the best result for washing

The results of rubbing fastness in dyed fabrics with and without treatment are very good.

Procion Yellow H-EXL UT\* 4/5 4 5 5 5 4/5 4

Levafix Red EBA UT\* 4/5 3 4/5 5 5 5 4

Sirius Orange 3GDL UT\* 5 4/5 5 5 5 5 4

Sirius Blue KCFN UT\* 5 4/5 5 5 5 5 5

Telon Blue M-GLW UT\* 5 5 5 5 5 5 4/5

Realan Blue EHF UT\* 5 4/5 5 5 5 5 4

Table 7. Washing fastness of reactive and acid dyeing with previous DBD treatment by

Figure 16 shows the results obtained from fluorescence microscopy analysis in the case of polyamide dyed with reactive dyes for cotton (Levafix Red – EBA). The dye shows a perypherical distribution in the sample without treatment (c), while in the case of the plasma treated sample the dye presents a deeper diffusion into the core of the fiber (d).

Dyes **Sample AC CO PA PES PAC WO Color** 

T\*\* 5 4/5 5 5 5 5 4/5

UT\* 5 5 5 5 5 5 5 T\*\* 5 5 5 5 5 5 4/5

T\*\* 4/5 3/4 4/5 5 5 5 4

T\*\* 5 4 5 5 5 5 3

T\*\* 5 4/5 5 5 5 5 4/5

T\*\* 5 5 5 5 5 5 4/5

T\*\* 5 5 5 5 5 5 4

**Change** 

stabilization during the dyeing process in case of pH variations.

The value 5 in the gray scale was obtained for all the samples.

**3.5 Washing and rubbing fastnesses** 

dyeing of polyamide 6.6.

Remazol Blue Navy RGB

Norm ISO 105C06/A1S

**3.6 Fluorescence microscopy** 

\*UT – Sample Untreated \*\* T - Sample with treatment

fastness.

Since polyamide has only a small number of amine end-groups, saturation is easily got and it is difficult to achieve darker colors by dyeing with anionic dyes (Yip et al., 2002; Perkins, 1996).

Figure 14 shows a considerable increase of color yield with the increase of dye concentration being that the total amount of dye in the fiber is always higher after DBD treatment.

Darker colors in the fabric of polyamide 6.6 can be achieved when the plasmatic treatment is applied, with less dye concentration, meaning that is now possible to dye polyamide materials in darker colors by adopting a much more economic process.

The form of the curves concerning polyamide dyeing with the reactive dye for cotton, direct dye and acid dye shows a much higher but limited saturation in plasma treated fabric, whenever the behavior of the reactive dye for wool demonstrates the formation of higher level of linkage groups in the plasmatically treated polyamide.

#### **3.4.3 The influence of pH in dyeing processes**

The figure 15 a, b, c and d shows the influence of the pH in the polyamide dyeing process, comparing results between the samples with and without plasmatic treatment.

When acid is added to dye bath, the polyamide fiber develops an overall positive charge (-NH3+). Thus, in acidic conditions the polyamide fiber becomes positively charged and strongly attracts the negative groups of the anionic dyes. At pH 3 all the studied dyes give similar dyeing yield, either plasma treated or not treated polyamide. However, at pH 3 the polyamide 6.6 fabrics can be degraded, which is very inconvenient for the final quality of dyed materials (Burkinshaw, 1995).

Fig. 15. 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 dyebath pH (dyeing conditions: 100ºC and 1% dye concentration).

When pH of the dye bath is increased, the color yield reduces considerably in the samples without DBD treatment. On the other hand, if samples are treated with plasma and dyed, a type of "buffer systems" can be observed for all the dyeings, propitiating a very important stabilization during the dyeing process in case of pH variations.

Dyeing results are pH independent in the interval 3 to 7, which gives strong indications about the huge influence of plasmatic discharge in chemical composition of fiber surface.
