Novel High-Efficiency Casein-Based P–N-Containing Flame Retardants with Multiple Reactive Groups for Cotton Fabrics

Novel, high-efficiency, and halogen-free flame retardants with reactive groups, casein-based FRs, were synthesized based on a casein hydrolysis solution for cotton fabrics. After treated by the casein-based FRs, cotton fabrics exhibited high-efficiency flame retardancy; the limiting oxygen index (LOI) of treated cotton fabric increased to 39.5%. Compared with other nature flame retardants, the novel flame retardants could impart durable flame retardancy to cotton fabrics. The LOI value could sustain at 26.7% after 40 laundering cycles (LCs). Cone calorimetry and vertical burning test confirmed that the cotton fabrics treated by the casein-based FRs achieved markedly enhanced flame retardancy. X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) indicated that the casein-based FRs were grafted on cellulose by P(═O)–O–C and C(═O)–O–C bonds. Scanning electron microscopy (SEM) revealed that the modification was facile. Thermogravimetry (TG), energy-dispersive X-ray (EDX), TG-FTIR and SEM revealed that the casein-based FRs played an important role in condensed phase, together with the flame retardant behavior in gaseous phase. The casein-based FRs mainly prevented the formation of levoglucosan by phosphorylation of cellulose and catalyzed the dehydration of cellulose. The tensile strength and whiteness of cotton fabrics treated by the casein-based FRs were substantially retained.