Several anthaquinone and azo disperse dyes adsorbed on films of polyester and nylon 6. 6 and dissolved in a mixture of acetone and water have been faded by various lines in the visible spectrum, and the quantum yields (φ) determined by means of the Parker‐Hatchard potassium ferrioxalate actinometer. φ for adsorbed dye lies between ca 10‐4 and 10‐6, decreasing with increase in exposure time, probably owing to the presence of associated dye, and with increase in wavelength of illumination. Values for dye in solution are 20–60 times as high as those for adsorbed dye. The low values for adsorbed dye are the result of a combination of several factors, including association of dye, retardation of gaseous diffusion by the substrate, and the shield or cage effect of the surrounding polymer substrate.

Eight non–ionic (disperse) dyes adsorbed in films of cellulose acetates, nylon and poly(ethylene terephthalate) (PET) have been faded by visible and near–ultraviolet radiation at temperatures in the range 15 to 100°C, and in atmospheres of relative humidities (r. h.) from zero to saturation. Fading is accelerated by rise in temperature, and, at r. h. above 5%, by rise in r. h. Activation energies of fading (Ef) (r. h. > 5%) range between about 3 and 18 kcal/mole, and depend on the nature of the substrate rather than on the structure of the dye. Values rise with increasing crystallinity of the polymer structure, except for PET which gives anomalously low values. The extent of dye–fibre interaction is at a minimum with PET and the rate–controlling step is a purely photochemical one. With the other substrates, the rate of fading is controlled by the dye–substrate interaction. The accelerating action of atmospheric humidity over normal ranges is partly due to its influence on the dye–substrate bonding and partly to its effect in swelling the substrate and thus increasing the diffusion coefficient of oxygen.

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