A sustainable, alkali-free cotton pretreatment based on sequential sonochemical and VUV processes

Conventional three-stage pretreatment of Grey cotton fabric (desizing, scouring, and bleaching) is resource-intensive and generates highly alkaline, chemically loaded effluents (pH 10–13; COD up to 20,000 mg/L), posing significant environmental and operational challenges. This study presents a single-liquor, alkali-free pretreatment strategy based on the sequential integration of probe sonication (PS) and 185 nm vacuum ultraviolet (VUV) irradiation, applied in a segmented sequence (PS-UV-PS-UV), followed by laundro washing using the same recovered process liquor without replenishment. The process leverages dual hydroxyl radical (•OH) generation pathways via H 2 O 2 photolysis and water photodissociation under VUV irradiation, complemented by cavitation-induced radical formation from H 2 O 2 during sonication, enabling effective impurity removal under mild conditions. The protocol achieved a whiteness index (WI) of 75.6 ± 0.72 and Tegewa rating of 9, comparable to conventionally processed fabric (WI = 76.8 ± 0.46), meeting industrial requirements for subsequent dyeing and finishing. Surface characterization confirmed near-equivalent chemistry (XPS O/C: 0.57 vs. 0.52), while FTIR, SEM, and reactive dyeing performance confirmed retention of cellulose structure and functional equivalence, with mechanical testing showing tear strength and elongation comparable to conventional processing and a moderate reduction in tensile strength and elongation. Effluent analysis of the spent liquor indicated substantially lower pH and COD than in conventional pretreatment, indicating a lower effluent load. The developed process achieves a 38.5% reduction in water consumption, a 38.9% reduction in total chemical usage, and a 52.4% reduction in H 2 O 2 demand, while eliminating all auxiliary chemicals and consolidating three processing stages into one. The use of H 2 O 2 , which decomposes into water and oxygen, combined with the reuse of process liquor, significantly reduces the chemical waste.