Synthesis of a novel P-N flame retardant for preparing flame retardant and durable cotton fabric

A novel triethylenetetramine-phosphorous acid-based flame retardant (FR) containing high amounts of P and N elements was designed and characterized by Fourier transform infrared (FT-IR) and nuclear magnetic resonance spectroscopy (1H NMR, 13C NMR, and 31P NMR). The FR can be grafted onto cotton fabric via P-O-C covalent bonds. The limiting oxygen index (LOI) value of 26.5% weight gain (WG) treated cotton was improved to 39.5 from 17.0%, and the LOI could still reach 30.9% after 50 laundering cycles (LCs), indicating that the treated cotton was endowed with outstanding flame retardancy and durability. Cone calorimetry (CONE) suggested that the peak heat release rate (PHRR) of the control cotton decreased from 171.1 to 17.8 kW/m2 of treated cotton, and the total heat release (THR) decreased from 6.3 to 1.1 MJ/m2 after finishing. Thermogravimetry (TG) verified that the initial decomposition temperatures of the treated cotton in N2 and air were 157.9 and 157.7 ℃, respectively, which were lower than that of control cotton. The addition of FR inhibited the initial thermal degradation temperature of cotton fabric under heating conditions and formed more carbon residue in the combustion zone, which was beneficial to the formation of an expanded char layer during combustion. Finally, the flame retardant mechanism was evaluated by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Raman spectroscopy, XPS (X-ray photoelectron spectrometry), and TG-IR. Moreover, the mechanical properties of the treated cotton decreased slightly but did not affect use in the subsequent stage. Together, the results demonstrated that FR achieved excellent flame retardancy and durability when used in cotton fabric.