Synthesis of a reactive boron-based flame retardant to enhance the flame retardancy of silk

In this study, a reactive boron-containing flame retardant (FR) namely glycerol borate citric acid ester (GBCAE) was synthesized using boric acid, glycerol and citric acid, and was applied to improve the flame retardancy of silk fabric. The chemical structure of GBCAE and its potential cross-linking reactions with silk fiber were characterized. The thermal stability, smoke and heat suppression capacity and FR ability of the treated silk were evaluated. The treated silk fabrics with a weight gain of higher than 7.3% had self-extinguishing ability. The FR treatment endowed high thermal stability and excellent flame retardancy to silk, and suppressed the smoke and heat release of silk by nearly 50%. The treated silk could still self-extinguish after 5 washing cycles and showed good washing durability, which is attributed to the covalent cross-linking action between GBCAE and silk fiber. The char residue analyses on morphology and functional groups indicated the intumescent FR mechanism for the treated silk. The prepared GBCAE has great potential to serve as suitable alternative to toxic halogen-based agents for improving the flame retardancy of silk textiles