Dyeing studies with hydroxyanthraquinones extracted from Indian madder. Part 1: Dyeing of nylon with purpurin†

Purpurin (1,2,4‐trihydroxyanthraquinone) is the major colorant present in the roots of Indian madder (Rubia cordifolia). Its structure is similar to that of disperse dyes. To gain an understanding of the dyefibre interactions involved, kinetic and thermodynamic studies have been conducted with purpurin on nylon fibre. Dyeing corresponds to the Nernst isotherm as linear isotherms were obtained. The dye is found to be sensitive to pH and high temperature. The rate of dye uptake, diffusion coefficient, standard affinity, heat of dyeing and entropy have been calculated and discussed.