Fabrication of highly efficient flame-retardant and biocompatible ramie fabrics through covalent bonding and layer-by-layer assembly methods

Ramie fibers have poor flame-retardant properties, which limits their application. To improve the flame-retardant properties of ramie fabric (RF), a durable flame-retardant coating was successfully realized on RF by combining covalent bonding and electrostatic adsorption. Si/P/N flame-retardant coatings were constructed on RF using cationic polyethyleneimine (PEI) and anionic sodium hexametaphosphate (PSP) via the layer-by-layer (LBL) assembly approach with the introduction of 3-glycidoxypropyltrimethoxysilane (GPTMS) as an organic cross-linker. Compared with the untreated RF samples, the fabrics treated with the flame-retardant coating PEI/PSP via the LBL method presented reductions of 51.06%, 48.30%, and 40.05% in the fire growth rate, peak heat release rate, and total heat release, respectively, in the cone calorimeter test. In addition, at a weight gain of 31.57%, the fabric self-extinguished in the UL-94 test within 10 s after leaving the ignition source, resulting in a damaged length of 6.13 cm. G-3 retained the limiting oxygen index (LOI) of 26.40% after 6 laundering cycles (LCs). The TG results revealed that the char residue of G-3 at 800 °C reached 30.34 wt%. The surface of the flame-retardant coating of GPTMS-PEI/PSP had good char formation. This study provides a feasible method for realizing durable flame-retardant RFs.