Preparation of eco-friendly flame-retardant cotton fabrics based on chemical grafting and calcium chelation

In this study, a novel strategy is proposed to prepare eco-friendly flame-retardant cotton fabrics, where chloroacetic acid (MCA) and L-glutamic acid (L-Glu) are used as raw materials to enhance the chelation ability between carboxyl groups (-COO-) and calcium ions (Ca2+). The morphological and structural characterizations of the prepared cotton fabrics indicate that the three free hydroxy groups (2, 3, 6) in the cellulose macromolecule are chemically modified to graft a large number of carboxyl groups, and Ca2+ ions are successfully chelated on the surface of cotton fabric. The thermal stability of cotton fabrics is greatly improved in both air and nitrogen atmosphere. The residual mass of flame-retardant cotton fabric (COT-Glu-Ca) is much higher than that of original cotton fabric, increasing from 0.03% to 5.6% in air and from 8.1% to 28.2% in N2, respectively. At the same time, the limiting oxygen index (LOI) of COT-Glu-Ca fabric is as high as 33.6%. The prepared flame-retardant cotton fabric can undergo vertical combustion tests with a char length of only 53 mm, and afterflame and afterglow are not observed, which proves that the grafted cotton fabric had a good flame retardancy due to a series of modifications and adsorption of Ca2+ ions. The properties of the cotton fabric, including tensile strength, whiteness, and moisture absorption, are all retained at a satisfactory level. Overall, this study provides a promising strategy for manufacturing eco-friendly, phosphorus-free, halogen-free, and fire-resistant cotton fabrics with enhanced metal ion chelation ability.