Synergistic barrier flame-retardant effect of aluminium poly-hexamethylenephosphinate and bisphenol-A bis(diphenyl phosphate) in epoxy resin

Two flame retardants, aluminium poly-hexamethylenephosphinate (APHP) and bisphenol-A bis(diphenyl phosphate) (BDP), were incorporated into diglycidyl ether of bisphenol A (DGEBA) thermoset with 4,4-diaminodiphenyl sulfone (DDS) as curing agent, and then the synergistic flame-retardant behaviors of the cured thermosets were investigated. Compared with thermosets containing 10 wt% APHP and 10 wt% BDP alone, the sample with 3.3 wt% APHP and 6.7 wt% BDP (3.3%APHP/6.7%BDP/EP; EP is DGEBA/DDS) possessed a better flame-retardant effect since its limited oxygen index reached 35.0% and in the UL94 test it passed the V-0 rating. The cone calorimeter test revealed that the 3.3%APHP/6.7%BDP/EP sample generated less gaseous fragments and more smoke particles instead of fuels and verified that APHP and BDP exhibited an outstanding synergistic effect on the barrier effect. Macroscopic digital photos and micrographs from scanning electron microscopy further disclose that BDP facilitated the formation of a flexible film covering holes in the residue. The flexible film was combined with aluminium phosphate particles which were produced by decomposed APHP, thereby forming a char layer with increased barrier effect. The synergistic barrier effect from APHP and BDP imposed a better flame-retardant performance for epoxy thermosets. (c) 2017 Society of Chemical Industry