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.

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A casein derivative (CADP) was synthesized using casein, which is bifunctional containing both -P=O(O -NH 4 + ) 2 reactive groups and -P(=O)-O-C-groups, and the durable ame-retardant cotton fabrics were successfully prepared by CADP. The -P=O(O -NH 4 + ) 2 reactive groups allowed CADP to be rmly grafted onto cellulose. The -P(=O)-O-C-groups made ame-retardant cotton fabrics more resistant to soaping and improved its durability. The modi cation by 40% CADP increased the limited oxygen index value (LOI) of cotton fabric from 17.4% to 41.6%, which maintained at 26.4% after 50 cycles of home machine washes. The results of TG, TG-FTIR and SEM indicated that CADP increased the condensed components and decreased the ammable gaseous compounds, resulting the positive effect on char formation of cellulose. The whiteness and tensile strength of cotton fabrics were retained well after modi cation, and the treated cotton fabrics didn't have skin irritation.