Phenylenediamine‐phenyl phosphonic acid salts toward good flame retardancy and smoke suppression epoxy resin

An environmentally friendly flame retardant named PO‐PA was designed to enhance the flame retardancy of epoxy resin (EP). Following the principles of efficiency and simplicity, PO‐PA was synthesized through a one‐pot reaction between phenyl phosphonic acid and p‐phenylenediamine. The chemical structure of PO‐PA was characterized by Fourier‐transform infrared (FTIR) spectroscopy, X‐ray photoelectron spectroscopy (XPS), elemental analysis (EA) and thermogravimetric analysis (TGA). EP containing 10 wt% PO‐PA (EP/10%PO‐PA) passed the UL94 V‐0 rating without dripping. In the cone calorimeter test, the total heat release and total smoke production of EP/10%PO‐PA decreased by 44% and 65%, respectively. TG‐FTIR and Py‐GC/MS were used to investigate the pyrolysis gases of the EP composites and PO‐PA, respectively. Scanning electron microscopy (SEM), FTIR, EA and XPS were utilized to study the char residues. It was proved that PO‐PA notably promoted the formation of smooth protective char layer in the condensed phase and effectively inhibited the oxidation chain reactions through releasing the phosphorus‐containing radicals in gas phase, which was not mentioned in the similar research based on phenyl phosphonic acid.