Establishing an energy-saving scouring/bleaching one-step process for cotton/spandex fabric using UVA-assisted irradiation

Abstract

To reduce the energy and water consumption from a conventional textile industry, a facile and efficient UVA-assisted scouring/bleaching strategy has been customized for cotton/spandex in this research. The bleaching efficacy under UVA irradiation is explored by comparing diverse processes, i.e., Scouring only (Sc.); Conventional scouring and pad-steam bleaching (Sc/Bl_Conv-PS); Conventional scouring and cold pad-batch bleaching (Sc/Bl_Conv-CPB); and one or two-step scouring and UVA-assisted bleaching (Sc/Bl_UVA-I, Sc/Bl_UVA-II). The significance, interactive effect and optimisation of parameters on the whiteness index (WI) of fabric are investigated through mathematical modelling. The bleaching mechanism is analysed by a fluorescence labelling method. The dyeing and tensile properties of fabrics and the energy conservation during processing are also demonstrated. Results show that Sc/Bl_UVA-I achieves an equivalent scouring and bleaching effect as Sc/Bl_UVA-II. A superior bleaching effect of Sc/Bl_UVA-II over that of Sc/Bl_Conv-PS reveals the better function of catalytic UVA than conventional steam. Under the theoretical optimal bleaching conditions (H₂O₂ conc. 42.96 g L⁻¹, pH 10.24 and irradiation time 3.68 h), a calculated highest WI of 77.19 (1.48 times higher than that of untreated fabric) can be achieved based on the mathematical modelling. Through mechanism studies, hydroxyl radicals are confirmed as the main oxidative species taking part in UVA-assisted bleaching and their concentration in simulated bleaching solution dramatically increases upon the introduction of UVA. The fabric treated by Sc/Bl_UVA-I exhibits an acceptable strength decrease (<10%) and excellent dyeing performance with reactive dyes. The Sc/Bl_UVA-I strategy enables more than ca. 70% of energy conservation than the Sc/Bl_Conv-PS process. The encouraging results manifest the practicability and promising prospects of UVA-assisted pre-treatment which contributes to enhancing the sustainability of the textile industry.