Enhancement of flame retardancy of cotton fabrics by grafting a novel organic phosphorous-based flame retardant

In this study, a novel, halogen-free, formaldehyde-free, organic phosphorus-based flame retardant, ammonium salt of hexamethylenediamine-N,N,N′,N′-tetra(methylphosphonic acid) (AHDTMPA), was synthesized using urea and hexamethylenediamine-N,N,N′,N′-tetra(methylphosphonic acid) (HDTMPA). AHDTMPA reacted with the O-6 hydroxyls of glucose residues in the cellulose of cotton fabric to form P–O–C covalent bonds. This ability was confirmed by Fourier-transform infrared (FTIR) spectroscopy, attenuated total reflection FTIR spectroscopy, and X-ray diffraction. Cotton fabric treated with 70 g/L AHDTMPA had a limiting oxygen index (LOI) value of 36.0 %, which remained relatively stable after 50 laundering cycles with a 28.0 % LOI value. The surface morphology and thermal stability of treated cotton fabrics were investigated using scanning electron microscopy and thermogravimetric analysis (TGA), respectively. TGA showed that AHDTMPA could exhibit flame retardancy at temperatures lower than the pyrolysis temperature of cotton fabrics. Additionally, the cotton fabric was treated with AHDTMPA through a pad-cure process, as its ease of operation, high efficiency, and excellent application made it an attractive treatment.