Optical Brightening Agents and Fluorescent Dyes

Optical brightening agents are colorless organic compounds absorbing invisible UV light (340-380 nm) and re-emitting visible blue-violet light (420-470 nm) creating illusion of enhanced whiteness and brightness by compensating yellowish tint in white textiles. Chemical classes include stilbene derivatives (60-70% market, anionic sulfonated, 0.05-0.5% owf for cellulosics, whiteness increase +10-25 units, wash durable 10-30 cycles), coumarin derivatives (cationic for synthetics, 0.01-0.3% owf, brilliant white on polyester), benzoxazole and benzimidazole derivatives (nonionic or cationic for wool and silk, 0.05-0.5% owf, good light fastness 4-6), and pyrazoline derivatives (nonionic, moderate performance, cost-effective). Application via exhaust (0.05-0.5% owf, 40-95°C, pH 7-10, 20-60 min), padding (1-5 g/L continuous pad-dry-cure for sheets and towels), or detergent incorporation (0.1-0.5% maintaining whiteness during washing). Performance measured via CIE whiteness index (unbleached cotton 40-60, bleached 70-80, OBA-treated 85-95), fluorescent emission under UV, and tint measurement. Applications include white cotton textiles, polyester white fabrics, wool and silk garments, paper industry, and laundry detergents achieving brilliant white appearance and competitive differentiation. Trade-offs include masking not removing yellowing, environmental persistence (biodegradability 20-80%), aquatic toxicity, and rare allergenic potential with regulations like EU Ecolabel, GOTS, and Oeko-Tex restricting certain types.