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Ecofriendly dyeing of silk with extract of yerba mate (Ilex paraguariensis)

Silk fabric was dyed with extract of roasted yerba mate (Ilex paraguariensis). Dyeing experiments were carried out at varying dyestuff concentration, temperature and pH. The influence of mordants, such as potassium alum and tannin, was investigated. The best results in dyeing were produced with 20 g L–1 of dyestuff concentration, pH 3 and temperature of 90℃. Mordants showed negligible influence. The kinetic study showed that the pseudo-second-order equation better represented experimental data, which is related to the chemisorption process as the rate-controlling step. The equilibrium data were easily adjusted by the Langmuir–Freundlich model, indicating the significant contribution of the chemisorption process in a monolayer followed by a multilayer physisorption. The thermodynamic study indicated that dye adsorption was spontaneous and endothermic.