Effect of multiple reactions induced by a flame retardant containing P/N/S and chain extender on fire safety and mechanical performance of polyamide 6

It is a great challenge to prepare polyamide 6 (PA6) compounds with outstanding fire safety and mechanical properties. In this research, a flame retardant containing P/N/S elements (SNDP) was synthesized using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), 2-thiophene-carboxaldehyde and 4-aminobenzonitrile. The PA6/SNDP compounds were prepared using a melt blending method. Two chain extenders were incorporated into PA6/SNDP compounds to adjust their mechanical properties. The results suggest that PA6 compound with 10 wt% SNDP obtains a UL-94 V-0 rating (1.6 mm) and a limiting oxygen index (LOI) value of 27.4 vol%. SNDP induces the degradation of PA6 and decreases its mechanical properties. While the two chain extenders have reinforced effects on PA6/SNDP and this effect of 1,3-phenylene-bis-oxazoline is superior to another one. Moreover, the main flame-retardant mode of actions for SNDP in PA6 is gas-phase effect, including scavenging free radicals and diluting flammable gases.