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A novel phosphorus- and nitrogen-containing flame retardant (APNTHE) was synthesized through the reaction of N, N, N′, N′-tetrakis (2-hydroxypropyl) ethylenediamine, phosphoric acid and urea. Then, the APNTHE solution with a concentration of 120 g/L was used for the preparation of flame retardant cotton (FR-cotton). The elemental compositions, surface morphology, thermal stability and combustion behavior of the cotton before and after modification were investigated. Thermogravimetric (TG) analysis showed that the char residue of the treated fabric at 800°C was as high as 35.09% under a nitrogen atmosphere. Flammability tests after different LCs indicated that FR-cotton had durable flame retardancy. Compared to the blank sample, the peak of heat release rate and total heat release of the FR-cotton decreased by 91.89% and 90.53%, respectively. The char residual and TG-Fourier transform infrared spectroscopy analysis illustrated that APNTHE played a flame retardant role both in the gas phase and the condensed phase. All the results demonstrated that APNTHE can be regarded as a prospective flame retardant for cotton.

The recycling and reutilization of cotton waste are in line with the sustainable development of society. Therefore, in this work, an environmentally friendly cellulose phosphate ammonium salt was synthesized by phosphorylation of cotton waste. Then the cotton fabrics were modified with cellulose phosphate ammonium salt by using the dip–dry–cure technique to obtain flame-retardant cotton fabric. The surface morphology, characteristic functional groups, and elemental components were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The results indicated that the cellulose phosphate ammonium salt was immobilized onto the cotton fabric through a P–O–C chemical bond. Vertical combustion tests before and after washing showed that the treated cotton fabric had durable flame-retardant properties. Thermogravimetry demonstrated that the treated cotton fabric retained a large amount of residual char and the pyrolysis temperature was significantly earlier than that of the control sample. Compared with the blank sample, the peak of heat release rate and total heat release of the modified fabric was reduced by 90.8% and 84.1%, respectively. Thermogravimetric infrared of flame-retardant cotton fabric proved that cellulose phosphate ammonium salt acted both in the gas and condensed phase during the decomposition of the treated fabric.