Core-satellite PAPP@MxOy hybrids enable simultaneous enhancement of fire safety and mechanical properties in epoxy composites

Overcoming the inherent flammability of epoxy resins while achieving a well-balanced combination of properties is an urgent requirement for the development of multifunctional epoxy materials. In this study, metal oxide nanoparticles (M x O y ), including Fe 3 O 4 , CoO, and MnO, were assembled onto piperazine pyrophosphate (PAPP) via ultrasound-assisted interfacial self-assembly to construct core-satellite-structured hybrid fillers, denoted as PAPP@M x O y . The integrated suprastructure and nanoparticle-decorated surface improved the dispersion of PAPP in the EP matrix while promoting catalytic char formation, thereby endowing the resulting EP composites with enhanced comprehensive performance. With only 9 wt% PAPP@M x O y , the EP composites achieved a UL-94 V-0 rating and a limiting oxygen index (LOI) of up to 35.8 vol%. Compared with neat EP, the peak heat release rate (pHRR), total heat release (THR), and total smoke release (TSR) were reduced by 61.5%, 29.7%, and 49.6%, respectively. A systematic comparison further revealed that Fe 3 O 4 -decorated PAPP exhibited a relatively balanced overall fire-safety performance among the single- and dual-metal-oxide-decorated counterparts, with simultaneous improvements in heat-release suppression and smoke reduction. In addition, compared with EP composites containing pristine PAPP, the PAPP@M x O y -filled systems exhibited improved tensile, flexural, and impact strengths, indicating that surface-assembly modification effectively mitigated the mechanical deterioration commonly caused by flame-retardant fillers. This work presents an efficient and versatile surface-assembly strategy for constructing high-performance flame-retardant fillers and offers a practical route toward simultaneously improving the fire safety and mechanical properties of EP composites.