A New Nitrogen–Phosphorus Bio-Based Flame Retardant for Cotton Fabric: Investigation of Combustion Behavior and Fire Safety Parameters

A bio-based flame retardant, melamine salt of folic phosphate (MFP), was synthesized through a two-step reaction involving phosphoric acid, folic acid, and melamine. The chemical structure of MFP was confirmed using FTIR, 1H NMR, 31P NMR, and XRD analyses. MFP was applied to cotton fabric (CF), resulting in treated samples with weight gains of 10% (CF10) and 20% (CF20). Thermogravimetric analysis (TGA) results revealed that MFP improved the char yield of CF at 750°C, indicating its effectiveness as a char-forming agent. The CF20 sample exhibited self-extinguishing properties, in a vertical flame test (VFT), with a char length of 10.4 cm. Additionally, the limiting oxygen index (LOI) increased from 18.2% in CF to 31.5% in CF20, confirming its transition from a flammable to a flame-resistant material. Cone calorimetry results indicated that the MFP treatment significantly improved the fire safety parameters of the CF. Specifically, the peak of heat release rate (pHRR) and total heat release (THR) were reduced by 48.9% and 34.3%, respectively, for the CF20 sample compared to the untreated CF. Furthermore, the fire growth index (FGI) decreased from 17 kW/m2 s in the untreated CF to 8.2 kW/m2 s in CF20. Conversely, the fire performance index (FPI) increased from 0.008 m2 s/kW to 0.034 m2 s/kW. The mechanical properties analysis indicated that the tensile strength of the treated samples increased by 2.5% for CF20, while the extension at break exhibited a slight decrease of 15.6%. This work offers a new methodology to engineer fire-safe CF without compromising its inherent material properties.