Combination of gallic acid, polyethyleneimine and metal ions: A durable flame retardant for silk fabric

Developing efficient and durable functional fabrics using natural plant-derived polyphenols is environmentally friendly. Gallic acid (GA), a widely available natural polyphenol, has been extensively used for functional materials modification due to its cost-effectiveness and high reactivity. In this work, a combination of gallic acid, polyethyleneimine (PEI) and metal ions was employed to prepare flame-retardant silk fabrics through a simple impregnation-drying method. The silk fabrics modified with different metal ions (Fe 2+ , Fe 3+ , Al 3+ and Ti 4+ ) achieved self-extinguishing properties in vertical combustion tests with damaged char lengths of 9.2, 8.3, 9.3, and 8.2 cm and limiting oxygen index values of 29.8%, 30.2%, 27.4%, and 33.0%, respectively. The damaged char length of Fe 3+ -treated silk remained below 15 cm even after 50 washing cycles. The total heat release rate (THR) and peak heat release rate (pHRR) of all four silk fabrics modified with metal ions were significantly reduced in cone calorimetry tests. Concurrently, the potential flame retardant mechanisms were postulated based on the analysis of combustion products from the samples in both gaseous and condensed phases. Furthermore, the Fe 3+ -treated silk demonstrated excellent antibacterial properties. This simple approach to preparing functionalized silk fabrics provides a novel pathway for developing advanced and durable silk textiles.