Synergistic effect between melamine cyanurate and a novel flame retardant curing agent containing a caged bicyclic phosphate on flame retardancy and thermal behavior of epoxy resins

•A novel curing and flame retardant agent (PEPA-TMA) were synthesized and demonstrated better flame retardancy in Epoxy resin (EP).•Thermal stability of phosphorous-containing EP composites were investigated using TGA-FTIR.•The possible thermal degradation mechanism of EP composites is speculated according to the results of TG-FTIR and EDS.•Detailed compositions in the volatiles of EP composites pyrolysis were determinated.

A novel curing and flame retardant agent (PEPA-TMA), has been synthesized via 2,6,7- trioxa-l-phosphabicyclo-[2.2.2]-octane-4-methanol (PEPA) to react with trimellitic anhydride (TMA). PEPA-TMA and melamine cyanurate (MCA) were combined into epoxy resin (EP) to obtain halogen-free flame retardant epoxy resin composites. The flame retardancy was characterized by limited oxygen index (LOI) and UL-94 testing. The results showed that the incorporation of PEPA-TMA/MCA into EP can improve the flame retardancy relatively. The thermal degradation process was characterized using thermogravimetric analysis/infrared spectrometry (TGA-FTIR). The formed volatilized products on thermal degradation of flame retarded epoxy resin (EP) systems indicated that the volatilized products are mainly phosphine (PH3), carbon dioxide (CO2), water (H2O) and aromatic compounds. The char yield was 33.7% at 800 °C. The morphologies of formed residue chars were observed by scanning electron microscopy (SEM) demonstrating that the most effective amount of phosphorus is 2.5 wt%. The flame retarded mechanism was studied by TGA-FTIR and Energy-dispersive X-ray spectroscopy (EDS) coupled with the analysis of the char residues.