Fading on exposure in light is undoubtedly the '~ost complex of the reactions which dyes undergo on a fibre. Energy in the form of light is absorbed by the dye and causes some of its molecules to become unstable and under these conditions, the dye may react with surrounding materials. The decomposition of the dye subsequent to its photochemical activation occurs usually by reduction and in azo dyes the azo likage seems to be attacked. Dyes containing strongly electron donating substituents tend to fade oxidatively, whereas those with strongly electron withdrawing groups prefer a reductive degradation pathways. In dry state a reductive fading mechanism becomes oxidative. Fastness to washing, wet rubbing and perspiration also showed changes in colour coordinates of the dyes studied.
C M ASHRAF ,S WAHEED ,
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