**3.1 Optimal plasma dosage**

The color depth of dyed polyamide 6.6 was increased by using a reactive dye for wool dyeing (Lanasol Blue 3G), a reactive dye for cotton dyeing (Remazol Yellow Golden RNL) and a direct dye (Sirius Scarlet KCF), when different dosages of plasmatic discharge are used varying power of discharge and number of passages (Figure 3). The K/S values in polyamide samples depend on plasma conditions, being more intense for higher dosages. This criterion was used to choose optimal plasma dosage.

A significant difference in the quantity of residual dye is noticed (Figure 4) by comparing colors of the baths obtained after dyeing process of the samples submitted to different dosages.

Fig. 4. Final dyeing baths corresponding to samples with increasing dosages of plasmatic discharge – a) Reactive Lanasol Blue and b) Reactive Remazol Yellow Golden.

According to the results obtained, the dosage of 2400 W.min.m-2 is enough to obtain maximum values of K/S and minimum quantity of dye in residual bath for the three dyes, with the following working parameters in DBD machine: power of discharge -1500 W; speed - 2,5 m.min-1; nº of passages – 2. This dosage was further applied to all polyamide samples submitted to dyeing.
