Polyamidoamine-based photostabilizers for cotton fabrics

Four water-soluble α-amino acid-derived polyamidoamines (PAAs) obtained by reacting N,N’-methylenebisacrylamide with glycine, leucine, arginine and glutamic acid were studied as photostabilizers of cotton. Untreated and PAA-treated cotton strips with 10 % PAA add-on underwent accelerated photoaging by UV irradiation in air at temperature from 25 to 50◦C and 30 % relative humidity. Irradiation was applied in consecutive 4 h cycles, after each of which samples were analyzed by different techniques. After 30 h irradiation, the whiteness index and colorimetric parameters indicated significant yellowing of cotton, which became slightly more intense after 100 h irradiation. On irradiation, PAA-treated samples showed only slow decrease in whiteness and increase in yellowing. After 100 h, yellowing achieved significantly lower levels than in untreated cotton. In no case did the infrared spectroscopy and electron microscopy reveal detectable structural and morphological alterations, even after 100 h of UV exposure. Thermogravimetric analysis showed only little changes of thermograms following photoaging. X-ray diffraction analysis revealed slight deformation of the cellulose crystalline structure following both PAA treatment and UV irradiation. Finally, the PAA coatings were extracted from the cotton strips and analyzed by 1H-NMR analysis. Only the glutamic acid-derived PAA showed detectable structural changes that did not involve the main chain. The FT-IR spectra and white indexes of the washed cotton strips did not differ from those of untreated cotton. Overall, it was proven that α-amino acid-derived PAAs protect cotton from photo-oxidation. Their performance was attributed to the radical scavenging ability of tert-amine groups present in their repeat units.