Enhancing the flame resistance of cotton via N-acryloylglycine-based chemical functionalization

Abstract

Cotton was chemically modified with N-acryloylglycine (NAG) via oxo-Michael addition under basic conditions at 50 °C, producing COT-g-NAG₃ and COT-g-NAG₆ with 3 % and 6 % add-ons, respectively. The goal was to graft onto cotton an analogue of the glycine-based M-GLY polyamidoamine flame retardant repeat unit. Solid-state NMR confirmed the presence and quantity of grafted NAG. SEM and X-ray diffraction analyses showed that the grafting process preserved the fiber morphology and crystalline structure. Thermogravimetric analysis revealed enhanced thermo-oxidative stability between 350 and 450 °C, compared to virgin cotton. Flame retardant performance was evaluated through horizontal (HFST) and vertical flame spread tests (VFST). In VFST, neither sample self-extinguished, but both retained substantial char. In HFST, COT-g-NAG₃ showed a reduced burning rate (0.18 vs. 0.98 mm/s), while COT-g-NAG₆ self-extinguished, leaving 79 wt.% residue, compared to 1 % for untreated cotton. Combustion residues exhibited a porous char typical of intumescent materials, like that observed in M-GLY coatings. These results confirm that NAG grafting imparts effective flame retardancy by inducing intumescence, without compromising cellulose integrity. The covalent nature of the grafting also enhances wash durability, minimizing leaching and environmental release. This strategy highlights the promise of amino acid-based acrylamides for the tailored-design of flame retardant cotton fabrics.