One-step green synthesis of eco-friendly novel N–P synergistic flame retardant for cotton fabric

A novel N–P ammonium salt 1,3-propylene glycol diphosphate ester (APGDPE) flame retardant was tersely synthesized under solvent-free condition to lower cotton fabric fire hazard. The APGDPE structure was characterized by 1 H NMR, 13 C NMR, 31 P NMR and IR spectroscopy. The reactive P = O(NH 4 + ) 2 and PO(OH) 2 groups of APGDPE were successfully grafted into cotton fabric to form P–O–C covalent bond. The limiting oxygen indexes (LOI) of treatment cotton with weight gain rate of 14.7%, 17.2% and 20.8% reach 40–44.5%. After 50 laundering cycles (LCs), the LOI value of treatment cotton with weight gain rate of 20.8% still maintains 27.3%. These results verified that the treated cotton has obtained outstanding flame retardancy and prominent durability. TG test indicates that the thermal stability and thermal oxidative stability of treated cotton are much higher than those of control cotton. TG-IR test displayed that treated cotton released less flammable volatile gases than those of control cotton. Cone calorimetry revealed that the PHRR and THR values of treated cotton decreased by 5.57% and 26.8%, respectively. XRD results suggest that the crystallization zone of cotton fabric before and after treatment hardly change. TG-IR and cone calorimetry tests verified the APGDPE condensation phase mechanism for treated cotton.