The light stability of azo dyes and azo dyeings - I. Light stability of dyeings with reactive and non-reactive derivatives, respectively, of two, selected azochromophores

The light stability of RC-dyed (conventional reactive dyeing) and N-dyed (substantive dyed without subsequent rinsing) cotton fabric dyeings produced with the members of two groups of dyes, viz., 'A'-dye and 'B'-dye groups, respectively, have been studied. The best light stability was achieved in the 'A'-dye group on the sample RC-dyed with A(MCT-VS). N-ethyl substitution on the NH-bridge between the two reactive groups (A(MCT-VS)(Et,RC)) did not improve the fastness, whereas methoxy substitution on the diazo component (A(MCT-VS)(Met,RC)) deteriorated the light stability, No detectable difference could be observed in the light stability of RC-dyeings with A(MHT-VS) and A(MCT-VH), but the values achieved were not as good as that obtained with the original bifunctional variety (A(MCT-VS)(RC)). The light stability of all the RC- or N-dyeings produced with reactive group containing members of the 'A'-group were better than those of N-dyeings produced with A(Chr) and A(MHT-VH), respectively. All the RC- and N-dyeings (except B(Chr)(N)) of the 'B'-group had identical light stability. No explanation could be found for the good light stability of the B(MHT-VH)(N) dyeing. RC-dyeings within the 'A'-group are more stable to light than those within the 'B'-group, equatable to the difference in the light stability of the respective chromophores. (C) 1998 Elsevier Science Ltd.