BINDING EQUILIBRIA OF MULTIAZO DYES WITH POLYMERIC DYE TRANSFER INHIBITORS

Dye binding equilibria have been investigated for several anionic mult iazo dyes and the polar polymers poly(N-vinylpyrrolidone), poly(N-viny lpiperidone), poly(N-vinylcaprolactam), poly(N-vinylimidazole) and pol y(N-vinylpyrrolidone)-co-(N-vinylimidazole) in water at 25 degrees C. Spectrophotometric analyses revealed a disparate behavior of four diff erent dyes in the presence of increasing amounts of polymers. Equilibr ium constants Kp for the interaction of C.I. Direct Red 80 with the po lymers were determined by sorption studies. With an increasing dye/ po lymer ratio, K-p increases by 1-2 orders of magnitude, attains a maxim um value and declines subsequently. These observations are explained b y the well known polyelectrolyte character of dye/polymer adducts. The enthalpy Delta(r)H of the dye/polymer association reaction was determ ined by microcalorimetric measurements for several polymers and dyes. Inhibition of dye transfer to cotton fabric by the polymers was invest igated 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.