Novel P/N/Si/S-containing Mononickel Complex as a Metal-based Intumescent Flame Retardant for Cotton Fabrics

A new P/N/Si/S-containing mononickel complex NiS, which can be regarded as a rare type of the metal-based intumescent flame retardant, has been prepared through the condensation reaction of precursor NiCl with 1, 2-ethanedithiol in the presence of triethylamine as acid-binding agent. Its molecular structure is well characterized by elemental analysis, infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies. The target flame retardant NiS has been successfully applied to cotton fabrics through a pad-dry-cure method. Thermal degradation properties of neat and treated cotton fabrics with 10.7 wt% NiS are studied by thermogravimetric analysis (TGA). Flammability behaviors of neat and treated cotton with 10.7 wt% NiS are evaluated using vertical burning test, limiting oxygen index (LOI) and microscale combustion calorimeter (MCC). Meanwhile, to further investigate the flame retardancy of NiS for cotton fabrics, the char layers of neat and treated samples after combustion are analyzed by SEM image and Raman spectroscopy. As a result, the improved thermal and flammability performance for cotton fabrics by introduction of NiS might be due to the metal-assisted catalytic charring effect of NiS on the formation of the compact char layer and the release of the flammable gas.