Study on flame retardancy of TGDDM epoxy resins loaded with DOPO-POSS compound and OPS/DOPO mixture

The DOPO-POSS (polyhedral oligomeric silsesquioxane containing DOPO) and OPS/DOPO (octaphenyl polyhedral oligomeric silsesquioxane/DOPO) are used to flame retard the TGDDM/DDS (tetraglycidyl diamino diphenyl methane/4,4′-diaminodiphenylsulphone) resins. The blowing-out effect can be detected during the UL-94 tests of them. The LOI and UL-94 results indicate that DOPO-POSS or OPS/DOPO could make the LOI values of TGDDM/DDS resins greater than 34% and the UL-94 test reach V-0 rating. When keeping the same content of Si and P elements in the epoxy resins, the OPS/DOPO shows better flame retardancy and make the epoxy resins have better blowing-out intensity. The condensed phase and the gas products of TGDDM/DDS resins with DOPO-POSS and OPS/DOPO are investigated by the TGA, TGA–FTIR, SEM, FTIR and XPS. In the gas phase, DOPO-POSS and OPS/DOPO have negligible action on the gaseous product species of TGDDM/DDS resins. However, in the condensed phase, quite different performance of DOPO-POSS and OPS/DOPO can be observed. The good flame retardancy of the OPS/DOPO on the TGDDM/DDS resins is attributed to the matching between the melt viscosity and fast swelling, accumulation of the pyrolytic gases in the condensed phase, and fast and firm charring. Furthermore, the superabundant C–O-R structure in the condensed phase may be origin of the melt viscosity matching with melt swelling, and firm char during combustion.