Route‐dependent ozone bleaching of cotton/elastane denim: Colour removal, mechanical retention and surface morphology compared with hypochlorite treatment

Abstract This study evaluated ozone‐assisted bleaching as a chlorine‐free alternative to conventional hypochlorite bleaching for 100% cotton, 99% cotton/1% elastane and 98% cotton/2% elastane denim fabrics. Seven ozone‐based treatments, including dry, wet, booster‐assisted and towel‐assisted humid ozone, were compared with hypochlorite bleaching. Treated fabrics were assessed for colour characteristics, colour strength, fastness, mechanical properties, surface morphology and environmental impact. Ozone‐treated fabrics showed whiteness index values of 171.86–197.72 compared with 190.30–203.73 for hypochlorite‐treated fabrics, while Kubelka–Munk colour strength ( K / S ) ranged from 8.58–22.05 and 12.60–18.20, respectively. CIELAB analysis confirmed increased lightness after ozone treatment, with chromatic changes dependent on treatment route and fabric composition. Wet ozone and selected booster‐assisted treatments produced colour characteristics comparable to hypochlorite bleaching while maintaining satisfactory fastness. Mechanical properties, including fabric weight, tensile strength and tear resistance, showed no statistically significant differences among treatments (ANOVA, p = 0.068–0.919). Scanning electron microscopy revealed greater fibrillation and micro‐cracking in hypochlorite‐treated fabrics, whereas ozone‐treated samples exhibited less fibre damage. Environmental impact measurement analysis demonstrated lower water and chemical impacts for ozone treatments. Weighted performance index analysis identified towel‐assisted ozone as optimal for 100% cotton denim and wet ozone as the best‐performing treatment for elastane‐containing fabrics. Overall, ozone‐assisted bleaching provided comparable bleaching performance with reduced environmental impact and better preservation of fabric quality.