Clustered Phosphaphenanthrene Micro-Aggregates: Synergistic Dual-Phase Flame Retardancy and Toughness Retention in Epoxy Resins

A “microaggregation of flame-retardant groups” strategy was utilized to address the inherent flammability of epoxy resin (EP) and the persistent challenge of balancing flame retardant efficiency with mechanical properties in conventional modifications. This approach involved the structural integration of a phosphaphenanthrene derivative ABD with triglycidyl isocyanurate (TGIC) to construct clustered micro-aggregates featuring controllable phosphaphenanthrene density (DE-GAM). The design synergized the regulation of phosphaphenanthrene micro-aggregation with group cooperation. Flame retardancy tests revealed that EP containing only 3 wt % DE-GAM achieved a limiting oxygen index (LOI) of 32.4%, significantly higher than pure EP at 23.7%, and passed the UL-94 V-0 rating with a reduced total burning time of 1.9 s. Furthermore, the EP composite incorporating 3 wt % DE-GAM exhibited a total heat release (THR) of 91.26 kJ/m2, which is 19.3% lower than that of the 3 wt % ABD-containing composite. Mechanism studies indicated that the phosphaphenanthrene micro-aggregated structure acted as catalytic centers in the condensed phase, promoting the formation of a dense protective char layer. Simultaneously, it facilitated the targeted release of high-concentration radical scavengers into the gas phase to quench combustion chain reactions. The impact strength of DE-GAM/EP/DDM with 3 wt % loading maintained 81.3% of that of pure EP, implying DE-GAM enhanced interfacial compatibility through the formation of a cross-linked network, effectively alleviating stress concentration and absorbing impact energy.