The influence of the phosphorus-based flame retardant on the flame retardancy of the epoxy resins

A series of flame-retarded epoxy resins (EPs) have been prepared loaded with PEPA (1-oxo-4-hydroxymethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2] octane), APP (Ammonium polyphosphate), and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide), respectively with or without OPS (Octaphenyl polyhedral oligomeric silsesquioxane). The different influences of PEPA, APP, and DOPO due to their different chemical structures are detected by the HRR, p-HRR, TSR, and SEA results after cone calorimeter test. Coupled with TGA analysis, the PEPA shows more condensed phase flame retardancy and the DOPO shows a more gas phase flame retardancy action are detected. The gas phase and condensed phase of EP or EP/OPS composites with PEPA, APP, and DOPO are investigated by the TGA-FTIR, visual observation, and FTIR. It is considered that the kind of phosphorus-containing flame retardants decide the structure of char layer of epoxy resins, which could seriously affect their flame retardant performance. Furthermore, The flame retardancy of these EPs are tested by the LOI, UL-94, which indicates that the model of flame retardancy of samples are decided by the chemical structure of phosphorus flame retardants, the synergy of OPS could reinforce this kind of action.