Effect of Dye-Bath pH on Photostability of Dyed Nylon 66

Abstract

Nylon 66 films were dyed in aqueous dye-bath with C. I. Acid Blue 25 (1-amino-4-(aminophenyl)-2-anthraquinone sodium sulfonate) at various pH values ranging from 2.0 to 7.0. Films were exposed to polychromatic irradiation (λ ⪈ 290 nm) at 60°C in air. The extent of photo-oxidation was monitored by FT-IR spectroscopy. Fading of dye with polychromatic irradiation was monitored by UV spectroscopy. We observed a peculiar effect of dye-bath pH on the photostability of dyed nylon 66. Samples were more stable when dyed at pH 3 and above that (up to pH 7), whereas the samples dyed at pH < 3.0 showed sensitized photo-oxidative degradation in nylon 66. Formation of quaternary ammonium salt on dye-chromophore was considered responsible for the pH-controlled behavior of anthraquinone acid dyes. The dyeing pH significantly effects the photofading behavior of dyed samples. The effect of dye-bath pH on photofading of the dyed samples was more pronounced at lower dyeing pH and prevailed up to pH 4. The hydronium ion concentration was considered to be responsible for the enhanced fading of dye for the samples dyed at the lower pH.