Colour Fastness to Chlorinated Swimming Pool Water
topic
ISO 105-E03 chlorinated water fastness tests swimming pool conditions (50 mg/L active chlorine, pH 7.5, 20°C) by impregnating specimen in artificial chlorinated water bath for 1 hour with occasional agitation, then loading specimen against multifibre adjacent fabric at 4.5 kPa pressure for 4 hours at 37°C — assessing colour change and staining after drying. Active chlorine preparation: commercial sodium hypochlorite (NaOCl, available chlorine 5–14%) diluted to exactly 50 mg/L active chlorine, verified by iodometric titration (ISO 7393-1 DPD method) before each test. Chlorine concentration verification critical: degraded hypochlorite solution (decomposition rate doubles per 5°C temperature increase — stored NaOCl solution loses 50% active chlorine in 3–6 months at room temperature) gives false-high fastness results — preparation from fresh hypochlorite concentrate on test day essential. Dye class response to ISO 105-E03: reactive dyes on cotton (colour change grade 2–3, severe — hypochlorite oxidatively cleaves azo bonds –N=N– in azo reactive dyes at Cl₂ + H₂O ↔ HOCl + HCl mechanism, HOCl oxidises aromatic amine to quinone, bleaching chromophore); vat dyes (grade 4–5, excellent — leuco-anthraquinone vat dye structure resistant to HOCl oxidation); disperse dyes on polyester (grade 4–5 — non-ionic dye isolated within polymer matrix, impervious to aqueous chlorine); acid dyes on nylon (grade 2–3 for azo-based, grade 3–4 for anthraquinone-based). Extended chlorine exposure (ASTM D5427, 8-hour immersion at 100 mg/L active chlorine at pH 7.5): simulates heavy recreational swimmer exposure (8 hours pool use per week, 2-year swimsuit life = 800+ hours equivalent) — specification: vat-dyed nylon swimwear colour change ≥ 3 at 8-hour ASTM D5427 exposure.
Role
Chlorinated water fastness testing is the critical performance qualification for swimwear colour durability — with reactive-dyed swimwear failing ISO 105-E03 at grade 2–3 within single pool exposures versus vat-dyed swimwear grade 4–5 over multiple seasons, fastness data directly drives dye class selection decisions for competitive swimwear brands, justifying the 2–4× cost premium of vat dyes over reactive dyes in performance swimwear production.