Innovative development of green nitrogen-phosphorus-based flame retardant for enhancing fire safety of cotton fabrics

This study presents the synthesis and application of a novel green nitrogen-phosphorus flame retardant, ammonium salt of neopentyl glycol phosphate acid (ASNGPA), for cotton fabrics to enhance their fire resistance. ASNGPA was developed utilizing neopentyl glycol, phosphoric acid, and urea as the primary raw materials, which resulted in the formation of target product containing the active group -O-P(=O) -(ONH₄⁺)₂. Subsequently, fire-retardant fabric could be achieved by grafting ASNGPA onto the fabrics through forming -O-P(=O)-O-C- bonds in dipping and high-temperature process. Structural characterization by nuclear magnetism resonance (NMR), Fourier transform infrared spectroscopy test (FT-IR), and X-ray diffraction (XRD), as well as scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), confirmed the chemical structure and elemental composition of ASNGPA and ASNGPA-treated fabrics. Thermal stability tests indicated the improved thermal behavior, delayed onset of decomposition and reduced weight loss rates of samples during heating. The comprehensive assessment of fabric's flame retardancy through vertical flame vest, limiting oxygen index (LOI) measurements, and cone calorimetry has significantly demonstrated the enhanced fire resistance properties. The LOI values of the samples with 10 %, 20 % and 30 % concentration are all above 40 % while ASNGPA-treated fabrics exhibited reduced heat and smoke release velocities when compared to their untreated cotton counterparts. Furthermore, ASNGPA-treated fabrics preserved their satisfactory durability even after numerous washing cycles. The eco-friendliness of ASNGPA lies in its formaldehyde-free synthesis process and the absence of harmful halogenated gases produced during combustion, despite slight modifications in its mechanical properties. The research on this new nitrogen-phosphorus flame retardants would enhance the flame retardancy of materials. By integrating the advantages of nitrogen and phosphorus, it could reduce fire risks while mitigating environmental pollution, aligning with the trend of green development.