**3.7 Dyeing process optimization**

The dyeing process of polyamide 6.6 is usually performed at boiling temperature and the time required for this process is around 120 minutes (Figure 2a). However, after DBD plasma treatment (2400 W.min.m-2) a new process will be checked with lower temperature and time than those generally used in the polyamide dyeing. This process will start at 40ºC, the temperature is raised until 70°C with a gradient of 1ºC/min and remains in this temperature during 60 minutes.

The maximum values of exhaustion for samples with and without treatment (traditional process 100ºC) and for the samples dyed by optimized dyeing process at 70ºC are shown in table 8.

In this optimized dyeing process, the temperature and dyeing time were reduced of 30°C and 25% respectively. The best results are obtained when DBD treatment was applied. The reduction of bath exhaustion, when compared the process (b) at 100ºC with process (c) at 70ºC were: 0.5% for the direct dye Sirius 3GDL, 2.6% for the acid dye Telon MGLW, 3.8% for Levafix Red EBA and 4.1% for Red dye Levafix EBA. This way, it is possible to dye polyamide 6.6, treated with DBD, at 70ºC with an excellent bath exhaustion.

**b)** 

**d)** 

Fig. 16. Fluorescence microscopy (Levafix Red EBA dye): a) polyamide control in bright field b) polyamide control in fluorescence field c) untreated polyamide after dyeing and d)

These results are very promising, because after the plasma treatment the dye is able to

The dyeing process of polyamide 6.6 is usually performed at boiling temperature and the time required for this process is around 120 minutes (Figure 2a). However, after DBD plasma treatment (2400 W.min.m-2) a new process will be checked with lower temperature and time than those generally used in the polyamide dyeing. This process will start at 40ºC, the temperature is raised until 70°C with a gradient of 1ºC/min and remains in this

The maximum values of exhaustion for samples with and without treatment (traditional process 100ºC) and for the samples dyed by optimized dyeing process at 70ºC are shown in

In this optimized dyeing process, the temperature and dyeing time were reduced of 30°C and 25% respectively. The best results are obtained when DBD treatment was applied. The reduction of bath exhaustion, when compared the process (b) at 100ºC with process (c) at 70ºC were: 0.5% for the direct dye Sirius 3GDL, 2.6% for the acid dye Telon MGLW, 3.8% for Levafix Red EBA and 4.1% for Red dye Levafix EBA. This way, it is possible to dye

polyamide 6.6, treated with DBD, at 70ºC with an excellent bath exhaustion.

penetrate into the fiber so giving high guaranty of good fastness results.

polyamide treated after dyeing.

**3.7 Dyeing process optimization** 

temperature during 60 minutes.

table 8.

**a)** 

**c)** 


Table 8. Comparison of the maximum exhaustion for different dyeing processes.

The figure 17 shows the bath exhaustion behavior of the reactive dye Levafix Red, for the samples prepared with DBD discharge (b, c) and dyed at 100ºC and 70ºC respectively, compared with the untreated sample conventionally dyed at 100ºC (a). A smoothest curve and excellent bath exhaustion of 93% are observed for the optimized process performed at 70ºC.

Fig. 17. Exhaustion curves of polyamide dyeing with Levafix Red EBA dye for samples with and without treatment dyed at 100ºC (b, a) and with treatment dyed at 70ºC (c).

#### **3.7.1 Washing and rubbing fastnesses**

Table 9 shows the results of washing fastness for direct, acid and reactive dyes for the optimized dyeing of polyamide 6.6. The results of washing fastness are very good, confirming the level of dye fixation and diffusion into the fiber, despite of this process had been performed at 70ºC.


Table 9. Washing fastness of reactive and acid dyeing with previous DBD treatment (norm ISO 105C06/A1S)

Polyamide 6.6 Modified by DBD Plasma Treatment for Anionic Dyeing Process 259

Another important possibility is to achieve different and wider gamut of colors in polyamide fibers provided by direct and reactive dyes, with lower energetic and processing time costs and very important environmental gains, meaning excellent opportunities to add

We gratefully acknowledge the financial support from FCT (Fundacão do Ministério de Ciência e Tecnologia i.e., The Science and Technology Foundation of Portugal), for the

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**5. Acknowledgments** 

**6. References** 

The optimized process performed at lower temperature and time than conventional dyeing of untreated polyamide did not change the washing fastness results.

The results of rubbing fastness in dyed fabrics with and without treatment are very good. The value of 4/5 or 5 in the gray scale was obtained for all the samples.

#### **3.8 Cost of DBD plasma treatment**

The DBD treatment used the following parameters: power - 1500 W, number of passage - 2, velocity - 2.5 m.min-1.

The cost to treat one kilogram of polyamide 6.6 fabric (weight : 105 g.m-2) is calculated according to table 10.


Table 10. Cost of DBD plasma treatment (\* mean value of kW.h - Portugal 2010).

Despite the cost of the treatment DBD is around 0.036 €.kg-1, several benefits are achieved such as: reduction of 30ºC in the temperature of dyeing with an excellent bath exhaustion; reduction of dyeing time of around 25%; reduction of the quantities of dyeing auxiliaries and the possibility to get more intense colors.
