A multi-element flame retardant on the basis of silicon-phosphorus-nitrogen for combustibility suppressing of epoxy

Expanding the application field of epoxy resins is absolutely required to improve their flame retardant performance. Reactive-type silicon-phosphorus-nitrogen contained flame retardants can improve the flame retardancy of epoxy resins, while suppress the migration of retardants from the interior to the surface of the matrix. Therefore, a novel reactive multi-element flame retardant, N-((4-hydroxyphenyl)- (9,10-dihydro-9-oxa-10-phosphaphenanthene-10–yl) methyl) amino propyl heptaisobutyl silsesquioxane (PmDOH) was designed and synthesized. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results show that the maximum mass loss rate of the PmDOH modified epoxy resin (EP) decreases, while the char residue increases gradually with the increase of PmDOH. Moreover, the limiting oxygen index (LOI) value of PmDOH/EP thermosets with 10 wt% of PmDOH (EP-10%) increases to 30.4%, and vertical burning test (UL-94) arrives to V-0 grade. Micro combustion calorimeter (MCC) results show that the PHRR and the THR of PmDOH/EP reduce gradually with the increase of PmDOH. FT-IR and SEM results demonstrate that the PmDOH modified EP is more easily carbonized and a more compact and continuous structure char layer is generated during the combustion process in comparison with the pure EP.