Natural indigo dye, Indigofera tinctoria, was applied on poly (lactic acid) (PLA) fabrics by exhaust dyeing in the presence of 5 g/L sodium dithionite and 0.2 g/L NaOH. Three dyeing parameters e.g. dyeing temperature, dyeing time and dye concentration were studied. When 5%owf indigo dye was applied on PLA, the maximum color strength was obtained at 80°C and 60 minutes. The color strength also increased as the dye concentration increased in the range of 4–20%owf. Applying natural indigo dye to PLA fabrics is more attractive than the commercial one due to better energy savings and the process being environmentally friendly.
The blocking effect of reactive dye combinations during the exhaust dyeing of cotton was studied using C.I. Reactive Yellow 176, C.I. Reactive Red 239 and C.I. Reactive Black 5. In the exhaust dyeing of binary reactive dye combinations, reverse order of dyeing was carried out at the dye concentration of 1%owf. After the shade of dyed cottons were evaluated, we found that the combination of C.I. Reactive Yellow 176 and C.I. Reactive Black 5 exhibited a blocking effect. The blocking took place readily in the dyebath. Therefore, C.I. Reactive Blue 250 was used to replace C.I. Reactive Black 5 because of the similarity of their chromophores and reactive groups. The results showed less blocking effect, indicating low interaction between the dyes in the combination.
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