Saminathan Ratnapandian

Materials

Cotton and wool fabric described under Section 2.2.1.1 and the mordant dyes mentioned in Section 2.2.1.2 were used in this investigation.

4. Methods

This section describes the exhaust dyeing process obtained from the supplier. The padding sequence and the variables were then investigated. Evaluation of desirable properties of the pad-dyed material is explained. The application of AAS and FTIR in understanding the dyeing mechanism is discussed.

1. Exhaust dyeing

Two commercially available mordant dyes derived from the Acacia family, Thar and Caspian, described in Section 2.2.1.2, were applied on cotton fabric by exhaust dyeing. A 1% shade on the weight of material (OWM) was used as the benchmark for both the dyes. The suggested material to liquor ratio of 1:30 was employed for dyeing, soaping off and rinsing steps.

In the case of Thar, a dye bath was prepared with the required amount of dye (1% OWM) and 5% OWM of mordant (either copper (II) sulfate or iron (II) sulfate) and stirred thoroughly. The fabric sample was introduced into the dye bath and the temperature raised to 80^○C. Dyeing was continued for 45 minutes at this temperature. This was followed by soaping off with 0.5 grams per litre (g/l) solution of non-ionic detergent at 60^○C for 20 minutes. Following soaping off, the dyed fabric was washed in hot water and then in cold water and finally dried.

Dyeing with Caspian required pretreatment of fabric with 3.5% OWM of Alpsfix, a cationic fixing agent, at 80^○C for 30 minutes followed by drying. A dyebath containing the required amount of dye (1% OWM) and 5% OWM of either mordant was prepared and stirred thoroughly. The fabric sample was added to the dye bath and the temperature was raised to 80^○C. Dyeing was continued for 45 minutes at this temperature. The sample was then soaped off with 0.5 g/l solution of non-ionic detergent at 80^○C for 20 minutes. The dyed fabric was sequentially washed in hot water and cold water and then dried.

2. Padding

Thar and Caspian were padded individually on cotton fabric. The squeeze roll pressure was set to achieve 80% wet pick-up. In order to obtain a nominal 1% depth of shade,
the dye liquor for padding was prepared according to the recipe shown in Table 3.1. Sodium alginate served as an anti-migrant to prevent the two-sided effect, while potassium sulfate acted as a cationising agent and promoted dye fixation. Freshly prepared liquor was allowed to stand for 2–3 hours for the sodium alginate to swell and become completely effective.

Table 3.1 Pad liquor (dye) recipe