Synthesis and application of a novel high durable cotton flame retardant rich in P N covalent bonds and ammonium phosphate groups

In this paper, a novel high molecule and formaldehyde-free reactive flame retardant, ammonium salt of polyethyleneimine phosphamide phosphoric acid (APEIAPAP), was synthesized for cotton fabrics, and its structure was characterized by nuclear magnetism and Fourier transform infrared spectroscopy test (FTIR). In its molecule, there was a p-π conjugation in NP(O) group, resulting in the increase of the stability of NP(O) covalent bond and P(O)OC between the flame retardant and cotton fibers. The FTIR and X-ray photoelectric spectrometer results demonstrated that the APEIAPAP reagent was grafted on cellulose through P(O)OC covalent bond. The results obtained by the vertical flame test, limiting oxygen index (LOI) test, thermogravimetric analysis, thermogravimetric-Fourier infrared spectrometer measurement, and conical calorimetric test showed that the treated samples had outstanding flame retardancy and APEIAPAP performed condensed phase flame retardant mechanism. In addition, the LOI of 25 % APEIAPAP treated cotton fabric could reach 50.6 %, and remain at 37.9 %, even after 50 LCs according to the AATCC 61-2013 3A standard. The microscopic surface morphology showed that the APEIAPAP was mainly grafted on the surface layer of cotton fibers. The tensile strength and bending performance of the treated cotton samples were well sustained. These results demonstrated that introducing the P element into the flame retardant through P(O)N covalent bond, and increasing the flame-retardant molecule weight, were efficient to significantly increase the durability of the treated cotton fabric.