Estimation of potential photochemical properties for monochlorotriazinyl reactive dyes and their manifestations in the fading of dyed cellulose

Cellulose films dyed with 10 monochlorotriazinyl reactive dyes were exposed to light in various aqueous solutions and the following potential photochemical reactivities of dyes estimated: (i) ease with which the dyes are photo-oxidized, (ii) ease with which dyes are photo-reduced, (iii) apparent photosensitivity, and (iv) the rates of fading in aerated water. On irradiating the dry reactive cotton dyeings, fading proceeded in two steps, viz. many dyes exhibited a considerable initial fading, accompanied by slow subsequent fading. On exposing the dry dyed cellulose films, little initial fading was observed. The fading behavior of some dyes could be explained by their potential properties, while other dyes underwent slow fading, probably due to a compensation between oxidative and reductive photofading processes even though the dyes had high photoreactivity. The concentration dependence on the fading behavior of dyed films could be explained by the filter effect with some exceptions, where dyes with high photosensitivity showed larger or similar fading in deep dyeings than that in the paler dyeings. (C) 1997 Elsevier Science Ltd.