SIMULTANEOUS OXIDATIVE AND REDUCTIVE PHOTOFADING OF CI REACTIVE RED 22 AND BLACK 5 ON CELLULOSE IN THE PRESENCE OF OXYGEN AND SUBSTRATE UNDER WET CONDITIONS

The reductive and oxidative photofading of Red 22 and Black 5 on cellulose on exposure in substrate solutions was kinetically examined by spectral analysis. In the presence of DL-mandelate and oxygen, the oxidative and reductive fading of both the dyes occurred simultaneously from the beginning, and later the oxidative fading was suppressed depending upon the concentration of oxygen. On exposure of Red 22 in the presence of lactate of high concentration and oxygen, oxidation initially occurred and was followed by reduction with complete inhibition of oxidation. An increase in the concentration of oxygen promoted the initial oxidation and an increase in the concentration of substrate promoted subsequent reduction. On exposure of Black 5 in the presence of lactate of high concentration and oxygen, similar fading behavior to that in DL-mandelate solutions was observed, but the oxidation products formed were immediately further photo-reduced.