Synthesis of a P/N/S-based flame retardant and its flame retardant effect on epoxy resin

In order to meet the requirement in the fields with high flame resistance, the flame retardancy of epoxy resin (EP) must be ameliorated. Herein, a P/N/S-based flame retardant (PAD) was synthesized and used to prepare flame retardant EP. The combustion behavior, thermal property and flame retardant mechanism of the prepared EP thermosets were investigated. PAD induced the decomposition of EP thermoset in advance. Meanwhile, PAD enhanced the flame retardance of EP thermosets and reduced the fire risk of EP matrix. For example, with only 0.5 wt% phosphorus, EP/DDS/PAD-0.5 easily passed UL-94 V-0 rating and achieved a LOI value of 33.6%, together with the declined heat release rate (HRR). Impressively, the glass transition temperature (T-g) of EP/DDS/PAD thermosets dropped by only 3-13 degrees C, compared with that of EP/DDS. During combustion, PAD prompted the formation of an intumescent char layer in condensed phase, and exerted blowing-out effect in gaseous phase.