Fading characteristics of some monoazo dyes on cellulose diacetate and polyamide films: Part I

The absorption spectra of seven different monoazo dyes at different concentrations in water and in methanol as well as their absorption on cellulose diacetate (CDA) and polyamide (PA) films were examined. It was found that the extent of dye aggregation in methanol is greater than in water despite the higher dielectric constant of the latter, reflecting the anomalous behaviour of water. However, structural characteristics and concentration of the dye determine the state of dye molecules in water and methanol. Some of the dyes examined had greater tendency to aggregate while the others were probably present in monodispersed form. On the contrary, all the dyes used seem to have a strong tendency to aggregate on the CDA and PA films, indicating that involvement of the dye in an interaction with the substrate alters the structural characteristics of the dye and, therefore, its ability to aggregate. In accordance with this were the results of studies dealing with evaluation of the lightfastness of the same dyes on both films using daylight as well as a lightfastness tester for different exposure periods.