Development and characterization of nanoparticle-based composites for fire-retardant cotton fabrics

Abstract

Cotton the most widely used natural textile fiber worldwide, but its high flammability posed a great safety concern, especially in occupational environments where workers remain vulnerable to fire-related injuries. There is a growing need for accessible, low-toxicity and effective flame-retardant solutions that can be applied to cotton. In this context, this study evaluates two environmentally conscious treatment routes: one based on chitosan and another based on citric acid combined with sodium hypophosphite (CA + SHP), and examines the effect of the incorporation of zinc oxide nanoparticles (ZnO NPs) into each system. ZnO NPs were synthesized by a typical reproducible precipitation method, producing high-purity, crystalline nanomaterials, confirmed by FTIR, Raman spectroscopy, and SEM. Both treatment systems were applied to cotton fabric without altering its color or dimensions. Chitosan introduced a slight increase in stiffness, while CA + SHP preserved the original softness. SEM confirmed that both coatings were deposited on the fiber surface but formed distinct morphologies, with chitosan generating films and CA + SHP producing localized deposits. Energy dispersive X-ray spectroscopy (EDS) revealed that ZnO NPs were deposited evenly throughout the fabric, without forming agglomerations. FTIR results indicated that the cellulose structure was unchanged after treatment, and XRD confirmed the predominantly amorphous nature of the chitosan films. Thermal analyses revealed that the treatments modified the decomposition behavior of cotton through different mechanisms. The chitosan–ZnO system shifted the main pyrolysis stage by 30 °C, indicating improved thermal stability, whereas the CA + SHP system reduced moisture sensitivity and generated a more thermally stable char residue. DSC supported these observations by showing reduced degradation peak intensities in all treated samples. The vertical flame test highlighted complementary fire-retardant behaviors. Chitosan-based formulations substantially reduced flame duration but produced weak char and long afterglow, whereas the CA + SHP system did not suppress flaming but strongly inhibited glowing combustion and produced short, cohesive char lengths. These differences demonstrate that the two formulations act at different stages of combustion: chitosan primarily affects flaming behavior, while CA + SHP reduces afterflame times. Overall, this work provides a comparative evaluation of two flame-retardant systems for cotton and identifies their respective strengths and limitations. The results suggest that combining their complementary mechanisms may enable more balanced, accessible, and effective fire-retardant treatments for protective clothing, with potential relevance for industries in regions where burn-related injuries remain a critical concern.