Abstract
Pineapple (Ananas comosus) peel, an abundant agro-industrial by-product, offers significant potential as a sustainable natural dye for textile applications. This study optimized colourant extraction using an alkaline-water system and evaluated dyeing performance on cotton fabrics. Statistical optimization through four-factor linear regression identified optimal conditions: mass-to-liquid ratio of 1 : 10, 12% NaOH, 80°C and 2 h extraction time, yielding 35-40% colourant, significantly outperforming organic solvents (<1%). High-performance liquid chromatography analysis revealed distinctive polyphenolic profiles between alkaline and water extraction methods, demonstrating altered compound distribution and enhanced extraction efficiency under alkaline conditions. Thermogravimetric analysis revealed dye stability up to 160°C, while particle size analysis showed a mean size of 266 nm, enabling effective fibre penetration. Quantitative dyeing evaluation demonstrated 43.05% exhaustion, 27.76% total fixation efficiency and 0.64 fixation ratio. Colorimetric analysis revealed significant mordant-dependent variations, with tannic acid achieving superior colour strength (K/S = 21.4) compared to metallic mordants: zinc sulfate, alum and ammonium ferrous sulfate. CIELab coordinates confirmed successful dye uptake (L* = -6.92 to -12.83). Post-mordanting with zinc sulfate achieved excellent fastness properties: wash (4-5), light (4) and rubbing (4) fastness. Cationization minimized electrostatic repulsion between cotton and anionic dye molecules, enhancing dye absorption. The findings demonstrate pineapple peel waste viability as a cost-effective natural dye with quantified performance metrics supporting commercial feasibility and circular economy principles in sustainable textile manufacturing.