Aluminum dihydrogen phosphate-melamine modified hollow spheres/epoxy composites: Enhanced flame retardancy, thermal insulation and wave-absorbing properties

Developing high-performance materials with wave-absorbing, flame-retardant, and heat-insulating properties is strategically crucial for safety protection and functional optimization in aerospace, electronic information, and construction. In this study, carbonaceous microspheres served as templates for preparing inorganic multi-shell hollow spheres (MHS) via simple hydrothermal and calcination processes. AHP-MA@MHS was then synthesized by incorporating aluminum dihydrogen phosphate (AHP) and melamine (MA) into MHS at a controlled ratio of 4:1. When introduced into epoxy resin, results indicate that the resulting composite (AHP-MA@MHS-EP) exhibits excellent thermal insulation performance, with its thermal conductivity reduced to 0.0238 W m −1  K −1 . Flame retardancy was evaluated via the Limiting Oxygen Index (LOI) test, Vertical Flame Test (UL-94), and Cone Calorimeter (CC) test. Test results indicate that AHP-MA@MHS-EP exhibits excellent flame retardancy, with an enhanced LOI value of 27.7 and a V-0 classification in the UL-94 test. Additionally, its peak heat release rate (PHRR) is 524.12 kW m −2 , representing a 38.86 % reduction compared to that of pure EP. Meanwhile, the vector network analyzer indicates that the inclusion of AHP-MA@MHS endows the material with good wave-absorbing performance in the low-frequency band (−35.1 dB). Consequently, the prepared AHP-MA@MHS-EP holds great potential for applications requiring both wave absorption and heat-insulating flame retardancy.