Saminathan Ratnapandian

Wickingheight(cm)

Fabric	Wool					Cotton
Plasma gas	Nil^a	He^b		Mix^c		Nil^a	He^b		Mix^c
Time		7 sec	14 sec	7 sec	14 sec		7 sec	14 sec	7 sec	14 sec
0.5 min	0.0	1.0	1.2	1.0	1.2	0.5	0.75	0.75	0.75	0.7
1 min	0.25	2.0	2.4	2.1	2.5	1.2	1.3	1.3	1.3	1.3
5 min	0.50	4.0	4.0	3.8	4.1	4.6	4.5	4.6	4.5	4.7
15 min	1.0	5.2	5.5	5.3	5.5	8.5	8.5	8.5	8.5	8.5

a – untreated, b – Helium (100%), c – Helium (95%) + Nitrogen (5%)

2. Effect of plasma treatment on shade obtained

Plasma-treated and untreated cotton and wool fabric samples were dyed with natural dyes derived from the Acacia family using the padding method and post-mordanting technique. Similar to the results reported in Chapter 3, mordanting with copper (II) sulfate resulted in a copper-beige shade while iron (II) sulfate yielded a yellowish-grey shade. A definite increase in the depth of shade was observed only on wool fabric for both plasma gases used, irrespective of the dye and mordant applied. The darkest shade was obtained when pure helium was used as the plasma gas and at 14 second exposure duration. Reflectance curves shown from Figure 4.5 through Figure 4.8 are evidence of the above.

Similar to the wicking behaviour, plasma pretreatment did not significantly improve the dyeing of cotton. In general, a more uniform dye distribution was visually observed on the surface of plasma-treated fabric (both wool and cotton) as compared to untreated

fabric. This was confirmed by a less than 2% variation in the sum of the K/S values measured at 10 points across the sample.
₄₀ Thar dye mordanted with copper (II) sulfate
35
30

Reflectance (%)
25
20
15
10
5
0
400 450 500 550 600 650 700
Wavelength (nm)
Figure 4.5 Effect of plasma gas on depth of shade
(fabric wool, exposure time 14 s, dye Thar, mordant copper (II) sulfate)

Thar dye mordanted with iron (II) sulfate

35


30


25



Reflectance (%)
20


15


10


5


0
400 450 500 550 600 650 700
Wavelength (nm)
Figure 4.6 Effect of plasma gas on depth of shade
(fabric wool, exposure time 14 s, dye Thar, mordant iron (II) sulfate)

Caspian dye mordanted with copper (II) sulfate

45
40
35

Reflectance (%)
30
25
20
15
10
5
0
400 450 500 550 600 650 700
Wavelength (nm)
Figure 4.7 Effect of plasma gas on depth of shade
(fabric wool, exposure time 14 s, dye Caspian, mordant copper (II) sulfate)


Caspian dye mordanted with iron (II) sulfate
40
35

Reflectance (%)
30
25
20
15
10
5
0
400 450 500 550 600 650 700
Wavelength (nm)
Figure 4.8 Effect of plasma gas on depth of shade
(fabric wool, exposure time 14 s, dye Caspian, mordant iron (II) sulfate)
Figure 4.9 and Figure 4.10 are graphical representations of the sum of the K/S values for wool fabrics dyed using the two natural dyes in individual combinations with the two mordants. The graphs bring out the effect of the composition of gas and duration of plasma treatment on the final shade obtained. They also include results regarding the
outcomes of blocking the plasma using a paper mask. The value for samples dyed without plasma treatment was used as the benchmark (100%).

a) Untreated; b) 7 s mix masked; c) 7 s mix; d) 14 s mix masked;

e) 14 s mix; f) 7 s He masked; g) 7 s He; h) 14 s He masked; i) 14 s He
Figure 4.9 Effect of varying the plasma parameters on padding Caspian dye on wool fabric

a) Untreated; b) 7 s mix masked; c) 7 s mix; d) 14 s mix masked;

e) 14 s mix; f) 7 s He masked; g) 7 s He; h) 14 s He masked; i) 14 s He
Figure 4.10 Effect of varying the plasma parameters on padding Thar dye on wool fabric
An overall increase in depth of shade was observed as the exposure period increased irrespective of the gas used or dye-mordant combination. A treatment time of 14 seconds in plasma produced from pure helium resulted in an average increase of 60% in the depth of shade (Figure 4.9 and Figure 4.10 (i)). This could be attributed to sustained surface modification (etching) due to increased duration of plasma treatment. However, when treatment duration was increased to 14 seconds in plasma produced from the gas mixture, the increase in depth of shade was either marginal or reversed (Figure 4.9 and Figure 4.10 (c and e)). Apparently, as treatment time increased, the addition of nitrogen reduced the effect of the pretreatment. Similar trends, albeit of a lower proportion, are seen in the masked area as well. This indicates that the paper mask is only partially effective in blocking the plasma.

Generally, a higher increase in relative colour strength is seen when copper (II) sulfate is used as a mordant instead of iron (II) sulfate irrespective of plasma gas or dye. This could be due to the higher reactivity of the copper chelate with the plasma activated surface.

The multi-dentate structure of the polyphenolic dyes used possesses several hydroxyl groups that make them have properties similar to those of hydrophilic acid dyes.

Consistent with an earlier publication [160], the observed enhancement in depth of shade on plasma treated fabrics confirms the hydrophilic nature of the dyes.

As mentioned earlier, the paper mask employed was able to partially block the plasma. When the fabric was padded, a tone-on-tone pattern (Figure 4.11) due to differential dyeing was obtained in a single step. This may be employed to simplify current printing processes. The novel patterning effects could be exploited by designers to cater to niche markets. A limitation was that the composite (mask and fabric) should pass unhindered between the electrodes during plasma treatment which restricts thick fabrics from being treated in this manner.

Copper (II) sulfate

Figure 4.11 One-step patterning

3. Fastness properties

Plasma treatment improved the depth of shade but did not affect the fastness properties of the natural dyes under consideration. As can be seen from Table 4.4, the fastness properties of wool fabric dyed after plasma treatment are identical to those of cotton fabric without plasma treatment reported in Chapter 3 (Table 3.9). Depth of shade as well as fastness properties of cotton fabrics are not affected by plasma pretreatment.
Hence the results are not presented here.
Table 4.4 Fastness properties of wool dyed after plasma treatment (Plasma gas – Helium, treatment duration – 14 s)