Mechanism of Light Fading of Azo Dyes on Polyvinyl Chloride and Poly(ethylene Terephthalate)

A series of monoazo compounds based on phenyl azo-β-naphthol and phenyl azo-8-hydroxyquinoline were applied to polyvinyl chloride and poly(ethylene terephthalate), respectively. From the relation between the electron attracting or withdrawing properties of the substituents in the benzene nucleus and relative fading rates, the conclusion was that the fading reaction in both the dye-fiber systems is probably oxidative. This conclusion agrees with that from an earlier analysis of fading products of anthraquinone disperse dyes on polyester. It is therefore clear that both polyvinyl chloride and poly(ethylene terephthalate) conform with the general observation that fading on any nonprotein is oxidative, provided the oxygen has access to the dye. Lightfastness of phenyl azo-β-naphthol dyes on polyvinyl chloride and that of phenyl azo-8-hydroxyquinoline dyes on poly(ethylene terephthalate) was very low. Also, in both the systems, the dyes in the substrate were in the form of a collection of particles of many different sizes.