Synthesis of three novel amino acids-based flame retardants with multiple reactive groups for cotton fabrics

Abstract

Three novel high efficient, halogen-free and formaldehyde-free flame retardants containing –P=O(O−NH4+)2 and –COO−NH4+ multiple reactive groups, ammonium salt of N,N-bis(phosphonomethyl) glycine (FR-G), ammonium salt of N,N-bis(phosphonomethyl) aspartic acid (FR-A) and ammonium salt of N,N,N,N-tetra(phosphonomethyl) lysine (FR-L), were synthesized for cotton fabric based on glycine, aspartic acid and lysine. The flame retardant properties and thermal stabilities of treated cotton fabrics were evaluated by limiting oxygen index (LOI), vertical flammability test, cone calorimetry test and thermogravimetric analysis (TG). The modifications and flame retardant mechanisms were investigated by TG-IR, FTIR, SEM, EDX. The comparison of three flame retardants was also investigated. The results reveal that flame retardants could graft on cotton fabric by the formation of P–O–C and C–O–C covalent bonds, the LOI value of cotton fabric treated by 30% FR-L could achieve 42.1%, which remained well after 40 laundering cycles with a LOI value of 27.1%. Vertical flammability test and cone calorimetry test also show that the flame retardancy of modified cotton fabrics was greatly improved. The results indicate that cellulose was phosphorylated by these flame retardants to prevent the formation of levoglucosan and promote the dehydration and charring. Moreover, the physical properties of treated cotton fabrics were maintained well.