UV Grafting of a DOPO-Based Phosphoramidate Monomer onto Polyamide 66 Fabrics for Flame Retardant Treatment

A novel DOPO-based phosphorus- and nitrogen-containing monomer named DOPO-DAAM was synthesized and grafted onto the surface of polyamide 66 (PA 66) fabrics via UV grafting in order to improve the flame retardancy. To facilitate the grafting efficiency, the PA66 fabric surface was first modified through the HCl treatment. In the UL-94 vertical burning test, the PA66 fabrics treated with DOPO-DAAM could stop the melt-dripping. Cone calorimetry results showed that a 22% reduction in peak heat release rate was achieved for PA66 fabrics grafted with 20 wt % DOPO-DAAM. Thermogravimetric analysis indicated that the presence of grafted monomer catalyzed the degradation pathway of virgin PA66 fabrics where the initial decomposition temperature was reduced and the char yield was enhanced for all treated fabric samples. Moreover, real time FTIR analysis confirmed that the DOPO-DAAM decomposed ahead of virgin PA66 and catalyzed the formation of char residue.