Conferring flame retardancy on cotton using novel halogen-free flame retardant bifunctional monomers: synthesis, characterizations and applications

Two novel halogen-free phosphorous–nitrogen flame retardant bifunctional monomers were synthesized and characterized using attenuated total reflectance/Fourier transform-infrared (ATR/FT-IR) and electrospray ionization mass spectrometry (+ESI-MS). The monomers were applied separately and graft polymerized on cotton in the presence of the thermal initiator K2S2O8. The performance of each monomer was evaluated using thermal gravimetric analysis (TGA), grafting efficiency, and vertical flame test. It was shown that the performance of N,N-dimethyl di(acryloyloxyethyl)phosphoramide (DMDAEP) (monomer 2) as flame retardant outperformed that of ethyl di(acryloyloxyethyl)phosphorodiamidate (EDAEP) (monomer 1). The superior performance of DMDAEP was attributed to the presence of more nitrogen atoms compared to EDAEP. The increased nitrogen content in DMDAEP increased the synergistic effect of the P–N system. Cotton treated using padding methods showed more promising results than cotton treated by exhaust methods.