Mechanical and thermal properties of epoxy hybrid foams with inorganic and organic microspheres

This study reports the preparations and properties of hybrid composite foams composed of epoxy (E−51) resin, organic expandable microspheres (EMP), and inorganic hollow glass microspheres (HGM). The EMP content was fixed 4 wt% and the effect of HGM loading on the microstructure, mechanical and thermal properties of E−51/EMP/HGM foams were systematically evaluated. E−51/EMP/HGM foam achieved a low density of 0.5 g/cm 3 and a high porosity of 60 %, with no visible superficial defects. A microstructure transition from organic-dominant to inorganic-dominant was observed at 4 wt% HGM content. This transition profoundly influenced its compressive failure mechanism, with the organic-dominant structure exhibiting superior load-bearing capacity. The char residue of E−51/EMP/HGM foam is 12.67 % higher than E−51/EMP foam. At equivalent thermal-insulation levels, E−51/EMP/HGM foam surpasses E−51/EMP foam in mechanical properties and thermal stability, while simultaneously lowering raw-material costs and reducing processing complexity. This work provides valuable insights into the industrial development of epoxy foams through the combination of inorganic and organic microspheres. • Epoxy foams co-reinforced with organic EMP & inorganic HGM via synergy • HGM content steers microstructure from organic- to inorganic-dominant. • Mechanism linking microstructure to mechanical & thermal gains unveiled. • Lightweight, high-strength, insulating foam with superior thermal stability.