High performance fire-retarded epoxy imparted by a novel phenophosphazine-containing antiflaming compound at ultra-low loading

A novel phenophosphazine-containing compound, HD-DPPA, was successfully synthesized via the addition reaction between 5,10-dihydro-phenophosphazinine-10-oxide and Schiff base obtained in advance by condensation of 4,4′-dimninodiphenylmethane (DDM) and 4-hydroxybenzaldhehyde, and used as a co-curing agent of DDM and a flame retardant for DGEBA epoxy resin. The cured epoxy resin passed UL-94 V-0 rating with limiting oxygen index (LOI) of 31.3% at only 2.5 wt% HD-DPPA, where phosphorus content was as low as 0.19 wt%. The formation of intumescent char layer and blowing-out effect during combustion are responsible for high flame retardancy of epoxy resin. The flame-retarded epoxy resin exhibited the improved tensile and impact strength compared with the pristine epoxy resin.