Cleaner Production of Core–Shell Fe₃O₄ for Enhancing the Fire Safety, Electromagnetic Wave Absorption, and Radar Stealth Performance of Polyurea

Polyurea (PUA) coatings have garnered significant interest as an energy-efficient construction material. However, the facile fabrication of multifunctional PUA, integrating excellent fire resistance, flame retardancy, electromagnetic wave (EMW) absorption, and radar stealth capabilities, remains a formidable challenge. In this study, multifunctional biobased core–shell Fe3O4 (Fe3O4@PM and Fe3O4@PM-Fe) were fabricated using self-assembly technology. The fire safety and EMW absorption of the Fe3O4-reinforced PUA composites were investigated. Benefiting from the powerful surface tension of the modifiers, core–shell Fe3O4 can be well-dispersed in the PUA matrix. Incorporating 20.0 wt % Fe3O4@PM-Fe into PUA led to a marked decrease in peak heat release rate (67.0%), total heat release (39.5%), and total smoke production (65.9%) values. The excellent EMW absorbing performance of loading Fe3O4@PM in the PUA matrix is desirable. Unfortunately, there was slight enhancing in the reflection loss (RL) when Fe3O4 was replaced by Fe3O4@PM. Notably, Fe3O4@PM-Fe, which is formed by building a conductive network on the shell of Fe3O4@PM, was designed to further reduce the RL value. Additionally, the reduction in the radar cross-section performance was validated through Computer Simulation Technology. The radar stealth performance of the PUA composites was also explored. The PUA composite obtained excellent EMW absorption and fire resistance properties, making it a promising material for future applications.