In situ construction of iron-rich metal-organic frameworks on wool surface for enhanced flame retardancy and low smoke generation

The incorporation of metal-organic frameworks (MOFs) on textile materials to enhance flame retardancy is of interest and challenge. In this study, an iron-rich MOF (Fe-MOF) was constructed in situ on wool fabric surface through the alternating assembly of ferric metal salt and the carboxylic acid ligand 1,3,5-benzenetricarboxylic acid. The surface morphology, flame retardancy, smoke and heat release performance, thermal stability, and flame-retardant mechanism of the Fe-MOF coated wool fabric were investigated. Square-shaped crystals were observed on the coated wool fabric, indicating successful construction of Fe-MOF on the wool surface. The coated wool fabric with an add-on of 6.8% exhibited excellent flame retardancy, as evidenced by its self-extinguishing ability during the vertical burning test and a significantly enhanced limiting oxygen index of 32.6%. Moreover, the coated wool fabric demonstrated a remarkable reduction in heat and smoke production of 23.8% and 68.4%, respectively, indicating enhanced fire safety. The analysis of char residue, including thermal stability, surface morphology, iron content, and graphitization degree, supported the formation of ferric oxides as a protective layer, contributing to the improved flame retardancy of the Fe-MOF coated wool in the condensed phase. The in situ construction of Fe-MOF on wool macromolecules offers a promising and innovative approach for developing nonhalogen and nonphosphorus flame-retardant systems.