Adsorption Isotherms and Mordant Dyeing Properties of Tea Polyphenols on Wool, Silk, and Nylon

The adsorption behaviors of tea polyphenols (TP) on wool, silk, and nylon at 4.0 were investigated. The Langmuir-Nernst model had the best fitting to the adsorption isotherms. The analysis of adsorption mechanism suggested that the hydrogen bonding and electrostatic interactions operating between TP and fibers contribute to Langmuir adsorption, whereas other interactions (hydrophobic interaction and van der Waals forces) contribute to Nernst partition adsorption. Langmuir adsorption had greater contribution to total adsorption of TP on nylon, whereas partition adsorption imparted greater influence to TP adsorption on silk. In terms of the mordant dyeing of TP, silk and wool displayed much deeper color than nylon due to their higher content of the functional groups having the complex-forming ability, although they had lower adsorption capability for TP than nylon. The colors of the dyed fabrics mordanted with different metallic salts as well as their depth, were greatly dependent on the chemical nature of mordants and fibers, the metal ion TP fiber complex-forming ability, and the related complex structure.