Dye Exhaustion, Adsorption Isotherms and Fixation
topic
Disperse dye adsorption on PET follows Nernst (partition) isotherm for small dyes (C_fibre = K·C_solution) and Freundlich isotherm for large dyes. Saturation value (Cs) at 130°C: 10–80 mg dye/g fibre depending on dye structure and fibre crystallinity. Exhaustion E% = (C₀ − Cf)/C₀ × 100. Fixation = dye permanently retained after reduction clearing. Unfixed dye contributes to poor wash fastness and effluent load.
Role
Adsorption isotherm analysis is fundamental to understanding dye–fibre affinity, predicting exhaustion levels, and designing efficient dyeing recipes with minimum dye waste and effluent load — essential for both academic dyeing science and industrial sustainability.