Blowing-out effect in flame retarding epoxy resins: Insight by temperature measurements during forced combustion

The temperature measurements within burning epoxy resins (EPs) were used to study the thermo physical evolution up and inside of samples during different applied heat fluxes cone calorimeter tests. A series of flame retarded epoxy resins (EP) were prepared with polyhedral oligomeric silsesquioxane containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-POSS). The flame retardancy of these EPs was tested by both flammability tests (LOI, UL-94) and forced combustion in cone calorimeter, to assess DOPO-POSS effects on the flame retardancy of EP composites. 2.5 wt% DOPO-POSS incorporation into epoxy resin perform interesting blowing-out effect, which results in a LOI value 27.1 and UL-94 V-1 (t₁=8 s and t₂=5 s) rating. The details of fire behavior, such as the values of TTI, HRR, p-HRR, and THR have been tested using a cone calorimeter. The temperature measurements during cone calorimeter tests indicate that the char layer of EP/2.5 DOPO-POSS has the best performance on heat insulation and play an effective role (heat insulation) quicker than that of EP/5 DOPO-POSS or EP/10 DOPO-POSS. This heat insulation performance of char layer produced by EP/2.5 DOPO-POSS explains its good performance on LOI and UL-94 test.