A study of photo-stability of materials and fabrics

Photo- and thermo-oxidative degradation of several dyes, additives and pure cellulose paper, were examined mainly by photo-induced chemiluminescence (PICL) technique. The degradation levels were assessed based on free radical populations of irradiated samples. The chromatic alteration of the samples as a result of accelerated ageing treatments conducted in the study were carried out by measuring CIELAB parameters (L*, a*, b* and ΔE*) using spectrophotometry method. The chemical and physical changes of pure cellulose paper during accelerated ageing was characterised by ATR-FTIR and UV–visible spectroscopic methods. The spectra were focused between 1500–1900 cm–1, where the products of paper ageing appear in the form of various carbonyl groups.<br><br>Dyes and additives may accelerate or inhibit photodegradation of materials by increasing or reducing free radicals. PICL intensity emissions of dyes were found to be dependent on the dye class and chromophore and do not relate to the lightfastness rating of dyes. Higher PICL intensity emissions than a control is associated with lower photostability of samples. The application of UV absorbers, Rayosan C on cotton and Cibafast W on silk, provided efficient photo-protection against the damaging effects of light. The application of the antioxidants, ascorbic acid on cotton and a combination of N-acetyl/oxalic acid on silk provided effective photo-protection by reducing free radicals and inhibiting oxidation reactions. Doping fluorescein dye, eosin Y dye and a photoinitiator into methyl cellulose or ethyl cellulose polymer films successfully accelerated the photooxidation of these polymer films under visible light irradiation. Incorporation of these additives into polymer films, promote free radical oxidation, to enable rapid photo-oxidation of waste polymers in the environment. Study of photo- and thermal ageing of pure cellulose paper showed that colour and chemical changes depend on the type of ageing treatment carried out. Under the current experimental conditions, UVB ageing had the most contributors to colour and chemical change. However, free radical population of these samples was similar to unaged sample as detected by PICL technique. The ATR-FTIR transmission spectra showed a higher absorbance in the carbonyl range (1900–1500 cm–1) and at extended exposure stages, a shift of frequency vibrations from 1650 cm–1 to 1730 cm–1 was observed, indicating the formation of carboxylic groups. Results from PICL experiments showed that free radical oxidation may not be the dominant factor contributing to the photodegradation and photoyellowing of cellulose paper.<br>