Epoxy resin-hollow glass microsphere composites (EHC) exhibit low density and excellent mechanical properties, making them promising candidates for marine/aerospace applications. However, their high flammability severely restricts broader use. To improve flame retardancy while maintaining low density, ammonium polyphosphate-coated hollow glass microspheres (APP-HGM) were utilized to fabricate flame-retardant epoxy composites (EAHC). EAHC achieved improved flame retardancy and maintained low density, but it suffered from insufficient flame-retardant efficiency and notable mechanical degradation. To address these drawbacks, SmMn 2 O 5 mullite nanoparticles (SMO) were further incorporated to fabricate the multi-component flame-retardant epoxy composite (SMO-EAHC). Systematic characterizations including thermogravimetric analysis (TG), limiting oxygen index (LOI), vertical burning (UL-94) and cone calorimeter test confirmed that APP-HGM serves as both a flame-retardant filler and a lightweight matrix component, while SMO catalyzes the decomposition of APP and promotes the formation of compact char layers. SMO-EAHC achieved a LOI of 27.6% and a UL-94 V-1 rating, and presented remarkable reductions of 58.81%, 38.67%, 73.65% and 62.96% in peak heat release rate (pHRR), total heat release (THR), peak smoke production rate (pSPR) and total smoke production (TSP) compared with unmodified EHC. Meanwhile, SMO-EAHC exhibited a compressive strength of 23.84 MPa, representing a 32.08% improvement relative to EAHC, while maintaining a low density of 0.66 g/cm³. In summary, this work proposes a targeted two-step modification strategy, involving APP-HGM functionalization followed by SMO complementation, to address the flammability of EHC. This strategy realizes the balanced integration of flame retardancy, lightweight characteristic and pressure resistance, providing technical support for the application of polymer composites in extreme environments. • Prepare SMO-EAHC by integrating APP-HGM and SmMn₂O₅ into modified epoxy. • SMO catalyzes APP decomposition, consolidates char layer. • SMO-EAHC attains LOI 27.6% (UL-94 V-1), 58.81% pHRR & 73.65% pSPR cuts vs EHC. • Retains low density (0.66 g/cm³) and high pressure resistance (23.84 MPa). • Offers technical support for flame-retardant composites in marine/aerospace.
Lu et al. (Sun,) studied this question.
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