Vat dye sensitised fibre damage and dye fading by catalytic and activated peroxide bleaching

Abstract

At equal levels of performance, activated (TAED) and catalytic (Mn-TMTACN) laundry bleaching can differ considerably in terms of the concomitant damage to fibres and dyes. To quantify this damage, differently dyed cotton fabrics, and a representative set of eight vat dyes and CI Reactive Brown 7 were used. It is shown that dye fading and fibre degradation are dye-specific and are both highly coupled phenomena. The interpretation of the damage data is based on dye chemistry, reflectance spectroscopy (UV/VIS and NIR) and EPR measurements. Whereas compelling evidence for a genuine catalytic cycle with the quoted manganese complex is lacking, a possible catalytic role of the dyes is proposed. The dramatic green shift resulting from the catalytic bleaching of Cl Vat Blue 4 is explained in detail. The corresponding oxidation is reversible and possibly useful as a fibre damage indicator.