Photofading of vinylsulfonyl reactive dyes on cellulose under wet conditions

Abstract

The fading on cellulose of six vinylsulfonyl ( VS) reactive dyes, an aminopyrazolinyl azo dye ( 1). C.I. Reactive Red 22 ( 2), a copper-complex azo dye ( 3), a copper phthalocyanine dye ( 4), C.I. Reactive Blue 19 ( 5) and Black 5( 6) was investigated under wet conditions. The rate of fading for VS dyes on cellulose, except for dye 2, decreased with increase in the concentration; that for dye 2 increased. The rate of fading for the VS dyes examined was in the following order: 2 > 1 > 3 > 6 > 4 > 5. This order was similar to that for the rate of fading for VS dyes on cellulose on which Rose Bengal was adsorbed, except for the reversal between dyes 1 and 2. The photosensitivity of VS dyes was confirmed by exposing films dyed with a mixture ofl with the other dyes and by shielding dye 1 by the use of a filter (5̆10nm). No fading of these dyes on cellulose in deaerated water occurs under a nitrogen atmosphere. These results suggest a singlet oxygen mechanism for the fading of VS dyes on cellulose under wet conditions. The rate of fading for a VS dye was dependent mainly on the ease with which it was oxidized and secondly on its efficiency and that of the partner dye to generate singlet oxygen.