Bio-Based Flame Retardant for Cotton Fabric Prepared from Eggshell Microparticles, Phytic Acid, and Chitosan: An Eco-Friendly Approach for Dry Use

This study investigates the development of a sustainable flame-retardant treatment for cotton fabrics using a hybrid coating composed of chitosan, phytic acid, APTES, and eggshell powder at concentrations of 2% and 4%, applied in one and two cycles. FTIR confirmed the deposition of the organic–inorganic layer through the appearance of characteristic bands. Thermogravimetric analysis (TGA/dTGA) revealed enhanced thermal stability for all treated samples, with increased char yield and a shift in the main cellulose degradation peak. Vertical flammability tests demonstrated that all coated fabrics achieved self-extinguishing behavior within 12 s, meeting NFPA 701 criteria. The 2% eggshell formulation with two applications (S2%-II) exhibited the best balance between flame retardancy and mechanical performance. Tensile tests indicated improved fiber cohesion for treated samples, while SEM micrographs confirmed uniform coating deposition and particle integration. Colorimetric analysis showed that the treatment did not cause a significant change in the natural color of the cotton. Although washing resistance remains a limitation due to the natural origin of the components, the samples remained stable over time without microbial growth or staining, suggesting potential for upholstery and covering fabrics not subjected to domestic washing. The results highlight the feasibility of using agro-industrial waste to create eco-friendly flame-retardant finishes for cotton textiles.