Understanding flame retardancy of phytic acid-based deep eutectic solvents by thermogravimetry, cone calorimetry, and vertical flame testing

Phytic acid has emerged as a safe flame-retardant alternative to traditional halogenated compounds, showing strong flame-retardant potential for natural fibers like wool, silk and cotton. This study explores the application of deep eutectic solvents (DES) based on phytic acid for the flame-retardant treatment of cotton fabrics. DES were synthesized using phytic acid as a hydrogen bond donor (HBD) in combination with choline chloride or ethylene glycol as hydrogen bond acceptors (HBAs). The DES coating were applied via a dip-coating method, and their structure, surface morphology, thermal degradation characteristics and flame retardancy were thoroughly examined. Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) analysis confirmed the successful deposition of DES on the surface, with the presence of several functional groups and the identification of phosphorus, carbon, and nitrogen elements on the treated surfaces. Cone calorimeter test confirmed significant enhancement in flame retardancy for the DES-coated fabrics, with a major drop in the peak heat release rate (pHRR) from 213.4 ± 1.83 kW/m² to as low as 50.3 ± 2.58 kW/m². Thermogravimetric analysis (TGA) showed that DES-coated samples had increased thermal stability, with char residue levels rising from 11.8 % in the blank cotton to 33.5 % in the ChCl 1:1-treated fabrics at 800°C. Vertical flame testing demonstrated that the DES coatings imparted self-extinguishing properties to cotton fabrics, with the ChCl 1:5 coating achieving optimal results, including no after-flame, minimal smoke, and a reduced char length of 3.275 ± 0.19 cm. These findings highlight the novel use of phytic-acid based DES as an effective and sustainable flame-retardant for cotton fabrics marking the first comprehensive study to demonstrate their significant fire-suppressing ability while mitigating the acidity-related degradation of cellulose fibers.