Facile flame-retardant finishing for cotton in supercritical CO ₂

Traditional water-based flame-retardant finishing causes serious pollution due to the use of a large number of chemicals, and color change is easily generated since the flame-retardant finishing takes place after the cotton dyeing. An eco-friendly flame-retardant finishing of dyed cotton was explored using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 2,2′-oxybis-(5,5-dimethyl-1,3,2,-dioxaphosphorinane-2,2′-disulfide) (5060), SiO ₂ , DOPO/SiO ₂ (1:1), 5060/SiO ₂ (1:1) and DOPO/5060 (1:1) in supercritical CO ₂ . The effects of finishing time and pressure as well as temperature on the flame-retarding properties of the cotton were discussed. As expected, samples with the higher weight gain rates exhibit a lower after-flame time as well as after-glow time. In different flame-retardant systems, cotton fabric finished with DOPO presents the lowest after-flame time of 20.6 s and after-glow time of 0 s at 130°C, 22 MPa and 120 min due to its biphenyl ring and O=P-O bond. Moreover, tiny fluctuations of L*, a*, b* and K/ S values occurred from 32.10 to 34.24, 5.78 to 6.05, –37.89 to –37.64 and 10.59 to 10.81 when the cotton samples were treated with DOPO, 5060, SiO ₂ , DOPO/SiO ₂ (1:1), 5060/SiO ₂ (1:1) and DOPO/5060 (1:1), proving that no significant negative role in the color property of the samples occurs after supercritical CO ₂ finishing.