Cleaner Production of Core–Shell Fe<sub>3</sub>O<sub>4</sub> for Enhancing the Fire Safety, Electromagnetic Wave\nAbsorption, and Radar Stealth Performance of Polyurea

Polyurea\n(PUA) coatings have garnered significant interest as an\nenergy-efficient construction material. However, the facile fabrication\nof multifunctional PUA, integrating excellent fire resistance, flame\nretardancy, electromagnetic wave (EMW) absorption, and radar stealth\ncapabilities, remains a formidable challenge. In this study, multifunctional\nbiobased core–shell Fe<sub>3</sub>O<sub>4</sub> (Fe<sub>3</sub>O<sub>4</sub>@PM and Fe<sub>3</sub>O<sub>4</sub>@PM-Fe) were fabricated\nusing self-assembly technology. The fire safety and EMW absorption\nof the Fe<sub>3</sub>O<sub>4</sub>-reinforced PUA composites were\ninvestigated. Benefiting from the powerful surface tension of the\nmodifiers, core–shell Fe<sub>3</sub>O<sub>4</sub> can be well-dispersed\nin the PUA matrix. Incorporating 20.0 wt % Fe<sub>3</sub>O<sub>4</sub>@PM-Fe into PUA led to a marked decrease in peak heat release rate\n(67.0%), total heat release (39.5%), and total smoke production (65.9%)\nvalues. The excellent EMW absorbing performance of loading Fe<sub>3</sub>O<sub>4</sub>@PM in the PUA matrix is desirable. Unfortunately,\nthere was slight enhancing in the reflection loss (<i>RL</i>) when Fe<sub>3</sub>O<sub>4</sub> was replaced by Fe<sub>3</sub>O<sub>4</sub>@PM. Notably, Fe<sub>3</sub>O<sub>4</sub>@PM-Fe, which\nis formed by building a conductive network on the shell of Fe<sub>3</sub>O<sub>4</sub>@PM, was designed to further reduce the <i>RL</i> value. Additionally, the reduction in the radar cross-section\nperformance was validated through Computer Simulation Technology.\nThe radar stealth performance of the PUA composites was also explored.\nThe PUA composite obtained excellent EMW absorption and fire resistance\nproperties, making it a promising material for future applications.