A novel durable and high-phosphorous-containing flame retardant for cotton fabrics

A novel high-phosphorous-containing flame-retardant ammonium salt of ethylenediamine tetramethylenephosphonic acid (AEDTMPA) with reactive –P=O(O⁻NH₄ ⁺)₂ groups was synthesized and characterized using Fourier transform infrared spectroscopy and nuclear magnetic resonance. The results showed that AEDTMPA could react with the –OH groups of cellulose molecules to form P–O–C covalent bonds. The finished cotton fabrics had high flame retardancy and excellent durability. The limiting oxygen index value of 100 g/L AEDTMPA-treated cotton fabric was 48.0 % and decreased to 31.2 % after 50 laundering cycles. In the vertical flammability test, the treated cotton fabrics exhibited no afterflame and afterglow, and the char length was only 30 mm. Thermogravimetry and cone calorimetry tests showed that the treated cotton fabric had higher char yield, lower decomposition temperature, and much lower peaks of heat release rate and total heat release than those of untreated cotton fabric. The morphologies of the cotton and residues of the fabrics were investigated using scanning electron microscopy, and the crystal structure of the sample fibers was analyzed using X-ray diffraction. The finished cotton fabrics were soft.