Saminathan Ratnapandian

CuSO4.5H20 (g/l)	Thar	Caspian	FeSO4.5H20 (g/l)	Thar
Caspian
5	2.27	2.07	5	2.48	2.57
10	2.18	2.30	10	2.61	2.61
15	2.38	2.64	15	2.73	2.58
20	2.46	2.14	20	2.88	2.60
40	2.46	2.19	40	3.33	3.63
60	2.30	2.39	60	3.22	3.59

In the absence of a definite peak in the reflectance curves, the sum of the K/S values was chosen as the criterion on which to compare the depth of shade obtained by using different mordant concentrations. Based on the above observations, the sum of the K/S values at 15 g/l for copper (II) sulfate or 5 g/l for iron (II) sulfate was taken as the reference benchmark or 100% strength. Relative colour strength was calculated for the other mordant concentrations accordingly and the results are shown in Figure 3.15 and Figure 3.16. In the case of Thar (A. catechu), the use of 40 g/l iron (II) sulfate as mordant resulted in a 45% increase in the sum of the K/S values as compared to the benchmark. However, mordanting with different concentrations of copper (II) sulfate produced only marginal changes. The trend was reversed in the case of Caspian (A. nilotica), with copper (II) sulfate causing a similar 45% increase. These results reiterate the earlier observation that the final shade is dependent on the mordant employed.
160

Relative colour strength (%)
120
80
40

0
5 10


15 20 40 60

Mordant concentration (g/l)
Figure 3.15 Comparison of colour strength (A. catechu) padded on cotton

160

Relative colour strength (%)
120
80
40

0
5 10 15


20 40 60

Mordant concentration (g/l)
Figure 3.16 Comparison of colour strength (A. nilotica) padded on cotton

1. AAS results

The calibration graphs and trend-line equations for copper and iron are shown in Figure
3.17. The high degree of correlation for the trend-line is consistent with the working principles of AAS. The amount of metal in the fabric was calculated based on the trend-line equations.


0.6



Absorption reading
0.5


0.4


0.3


0.2


0.1

0
0 1 2 3 4 5 6

PPM
Figure 3.17 Calibration curve for AAS
The mass of metal padded on and retained by fabric samples weighing 10 g each are presented in Table 3.7. In considering these results, the following facts should be kept in mind: 1) a 10 g fabric sample padded with 5 g/l iron (II) sulfate picks up only 0.04

grams of the salt, which in turn contains a meagre 0.008 g of iron; and 2) a 10 g fabric sample padded with 15 g/l copper (II) sulfate picks up 0.12 g of salt, translated as 0.03 g of metal. It can be observed that both cotton and wool retained increasing quantities of copper or iron as the concentration of the corresponding salt was raised in the pad liquor. However, such increases were not in direct proportion. In the presence of dye, a significant increase in the mass of metal retained was observed for both mordants confirming the formation of a dye-metal-fibre complex as described earlier.

Table 3.7 Metal retained (mg) measured using AAS