Study of the synergistic effect of silicon and phosphorus on the blowing-out effect of epoxy resin composites

A series of flame retarded epoxy resins (EP) was prepared loaded with OPS (octaphenyl polyhedral oligomeric silsesquioxane) and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide). The flame retarding properties of these EP composites were tested using the LOI and UL-94 procedures. The results indicate that the mixture of OPS and DOPO has a remarkable influence on the blowing-out effect of these flame retarded EP composites. The pyrolytic gases produced and the thermal stability of the EP composites with different flame retardant were detected by TGA-FTIR in an air atmosphere. The gaseous species produced by the flame retarded EP composites are the same as those from pure EP. The synergistic effect of the OPS and DOPO was detected from the HRR, p-HRR, TSR, and SEA results after the cone calorimeter test. The char produced by the EP composites after the cone calorimeter test were investigated by FTIR and XPS. It is proposed that the interaction between OPS and DOPO takes place through a chemical reaction in the condensed phase. Further investigation is required to fully reveal the reason behind the remarkable blowing-out effect.