Saminathan Ratnapandian

Constituent
Concentration (g/l)
Caspian (A. nilotica) or Thar (A. catechu)	10
Sodium alginate	1
Potassium sulfate	1

All three mordanting techniques, pre-mordanting, meta-mordanting and post- mordanting as described in Section 1.2.1.2, were evaluated individually for each of the selected mordants, copper (II) sulfate and iron (II) sulfate. A mordant concentration of 60 g/l was utilised based on the results published by Patel et al. [94]. Sodium alginate at 1 g/l was also incorporated into the mordant liquor. Similar to the dye liquor, the mordant liquor was prepared and left undisturbed for 2–3 hours.

1. Optimising process sequence

Padding can be differentiated into three distinct steps of pad (P), dry (D) and steam (S). The drying and steaming steps can be interchanged. Thus for every padding step two process sequences of PDS and PSD exist. Hence in the pad-dyeing of mordant dyes all possible process-sequence combinations need to be evaluated to identify the ideal sequence. This set of combinations is depicted in Figure 3.5. Each dye-mordant pair was individually pad-dyed in all the process-sequence combinations. After every PDS or PSD step, the samples were dried at 65°C to facilitate handling.
^Mordant Dye

1. Pre-mordanting

Mordant + Dye

Pad  Dry  Steam

Pad  Steam  Dry
OR

Dye

2. Meta-mordanting

Mordant

3. Post-mordanting

Figure 3.5 Mordanting and dyeing combinations

2. Optimising dye-mordant ratio

The next stage was to determine the optimum dye-mordant concentration. Mordanting liquors containing 5, 10, 15, 20 and 40 g/l of mordant were prepared. Cotton fabric samples padded with 10 g/l of dye were mordanted individually with each of these liquors. The evaluation was conducted for all four possible dye-mordant combinations namely: a) Thar-copper (II) sulfate; b) Thar-iron (II) sulfate; c) Caspian-copper (II) sulfate; and d) Caspian-iron (II) sulfate.

Wool fabric was padded with individual combinations of the two dyes and two mordants using the optimised process sequence and the ideal dye-mordant ratio determined from the above experiments.

3. Steaming and washing off

Steaming, in all scenarios, was conducted at 100˚C and 100% RH for 10 minutes, and followed by drying at 65˚C. The dried samples after padding and mordanting were

washed off (soaped) with 1 g/l anionic detergent solution at the boil for 20 minutes to simulate extreme washing conditions. This was followed by consecutive rinses in hot and cold water respectively.

4. Dyeing evaluation

Dyed samples were conditioned for at least 24 hours under standard conditions of 65% RH and 20 ± 2^○C and evaluated for colour strength and fastness properties as described in Section 2.2.3.

5. Atomic Absorption Spectrometry (AAS)

Sample solutions were prepared as detailed in Section 2.2.3.3 using concentrated nitric acid (70% w/w). Undyed and unmordanted pristine fabric was used as the reference (control). In order to establish the capacity of the fabric to retain metal ions by itself, AAS studies were conducted on cotton and wool fabrics mordanted by the PSD process and washed at the boil similar to final washing off (Section 3.3.1). Individual concentrations of 5, 10, 15 and 20 g/l of copper (II) sulfate and 3, 5, 10 and 15 g/l of iron (II) sulfate were evaluated. Fabrics dyed by post-mordanting with 5 g/l iron (II) sulfate or 15 g/l copper (II) sulfate were subjected to AAS to bring out the effect of dye in altering the ability of fabric to retain metal.

Table 3.2 and Table 3.3 present the calculations that were used to determine the maximum mass of metal that may be applied on a 0.2 gram fabric sample at the abovementioned mordant concentration, assuming a wet pick-up of 80%. This was the basis for preparing calibration solutions containing 0, 1, 2, 3, 4 and 5 PPM of metal ion (copper or iron). These solutions were analysed using AAS with the detector set at the wavelength specified for the metal under consideration as mentioned in Section 3.2.4. The average of three readings of absorbance was recorded for each of the samples. The data from the calibration samples was plotted as a scatter graph. A trend-line was fitted to this graph and its equation derived. This equation was used to calculate the amount of metal present in an unknown sample that is the sample solutions prepared by the digestion of fabric. The results were extrapolated to determine the mass of metal retained by a unit mass of fabric.

Table 3.2 Atomic mass of elements present in mordants