Binding Equilibria of Multiazo Dyes with Polymeric Dye Transfer Inhibitors

Dye binding equilibria have been investigated for several anionic multiazo dyes and the polar polymers poly(N‐vinylpyrrolidone), poly(N‐vinylpiperidone), poly(N‐vinylcaprolactam), poly(N‐vinylimidazole) and poly(N‐vinylpyrrolidone)‐co‐(N‐vinylimidazole) in water at 25°C. Spectrophotometric analyses revealed a disparate behavior of four different dyes in the presence of increasing amounts of polymers. Equilibrium constants Kp for the interaction of C.I. Direct Red 80 with the polymers were determined by sorption studies. With an increasing dye/polymer ratio, Kp increases by 1–2 orders of magnitude, attains a maximum value and declines subsequently. These observations are explained by the well known polyelectrolyte character of dye/polymer adducts. The enthalpy ΔrH of the dye/polymer association reaction was determined by microcalorimetric measurements for several polymers and dyes. Inhibition of dye transfer to cotton fabric by the polymers was investigated in a detergent slurry under washing conditions. Qualitatively, spectrophotometric, sorption and microcalorimetric studies agree with the result of the laundering experiments, suggesting that dye/polymer adduct formation operates as an underlying mechanism in modern “color”‐brand detergents.