A nitrogen-oxygen triazine flame retardant for simultaneously improving flame retardancy and mechanical performance of nylon 6

• TPT exhibits high flame-retardant efficiency towards polyamide 6. • TPT effectively retards the initial degradation of polyamide 6. • TPT significantly improves the mechanical properties of polyamide 6. • TPT exerts radical capturing effect during combustion of polyamide 6. The rapid advancement of modern industries has placed higher demands on the comprehensive performance of nylon 6 (PA6) and addressing its flammability issue has also received significant attention. Therefore, developing flame-retardant PA6 with superior overall performance has become a key research objective. In this work, a novel and highly efficient triazine-based flame retardant, phthalimidoxy-1,3,5-triazine (TPT), was successfully synthesized, and it was found to have a radical quenching mechanism analogous to that of hindered amine light stabilizers (HALS). Incorporating only 1.5 wt% TPT significantly improved the limiting oxygen index (LOI) of PA6/1.5TPT to 28% and increased both tensile strength and flexural strength to 80.49 and 93.25 MPa, respectively. Compared to pure PA6, the time to ignition (TTI) of PA6/1.5TPT was extended by 46.7%, and the total smoke production (TSP) was reduced by 42%. The hygrothermal aging results demonstrated that the PA6 composites maintained outstanding flame-retardant performance and mechanical integrity even after aging. Moreover, density functional theory (DFT) calculations and gas-phase mechanism analysis indicated that TPT generated stable radicals during thermal decomposition, which effectively captured hydrogen (H·) and carbon (C·) radicals produced in the initial degradation stage of PA6, thereby suppressing the combustion. This work presents a promising strategy for creating high-efficiency, multifunctional flame retardants for PA6, thus broadening its application potential.