Facile synthesis of a high efficiency and durability L-citrulline flame retardant for cotton

A novel flame retardant (FR), the ammonium salt of dtrulline-penta (methylphosphonic add) (ACPMPA) based on L-citrulline was synthesized, and its structure was characterized by C-13, H-1, and P-31 nuclear magnetic resonance (NMR) spectroscopy. The ACPMPA flame retardant molecule contains five ammonium salts of phosphorus add and one ammonium salt of carboxylic add, which allowed the covalent attachment of ACPMPA onto cellulose via -P=O(-O-C) and -COOC bonds. The results showed that the treated cotton fabrics had very high flame retardance and excellent durability. The limiting oxygen index (LOI) of cotton fabric treated with 35%-ACPMPA reached 492% and only decreased to 342% after 50 laundry cycles. Vertical flame tests also demonstrated that the treated cotton fabric acquired good flame retardance. The thermogravimetry (TG) and TG-lR results showed that the treated cotton left more residues and released almost no flammable volatiles at high temperatures. The cone calorimetry results showed that the treated cotton released less heat than pure cotton. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results demonstrated that the structure of the treated cotton fabric was almost unchanged, and no free formaldehyde was detected, indicating that the treated cotton was safe. The treated cotton fabric also retained good tensile strength and whiteness. (C) 2020 Published by Elsevier B.V.