**3.5 Washing and rubbing fastnesses**

254 Textile Dyeing

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,

Figure 14 shows a considerable increase of color yield with the increase of dye concentration

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

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

The figure 15 a, b, c and d shows the influence of the pH in the polyamide dyeing process,

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

b)

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%

comparing results between the samples with and without plasmatic treatment.

being that the total amount of dye in the fiber is always higher after DBD treatment.

materials in darker colors by adopting a much more economic process.

level of linkage groups in the plasmatically treated polyamide.

c) d)

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

dyed materials (Burkinshaw, 1995).

a)

dye concentration).

1996).

Table 7 shows the results of washing fastness for reactive (wool, cotton) and acid dyes in dyeing of polyamide 6.6.

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 fastness.

The results of rubbing fastness in dyed fabrics with and without treatment are very good. The value 5 in the gray scale was obtained for all the samples.


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

Table 7. Washing fastness of reactive and acid dyeing with previous DBD treatment by Norm ISO 105C06/A1S
