Interface engineering using MOFs to bionically construct ultra-rough nanostructures to enhance the flame retardancy and mechanical properties of polyurea

Polyurea, an environmentally friendly coating with no volatile solvents, is widely applied in construction waterproofing, marine anti-corrosion, and automotive coatings due to its excellent properties. However, its inherent flammability and release of substantial heat and toxic smoke limit its use in high-safety fields. To overcome the limitations of traditional ammonium polyphosphate (APP) flame retardants, this study introduces a biomimetic interface engineering strategy inspired by the rough structures of natural pollen. A multilayered core-shell APP@MOF@MoS₂ composite was constructed by sequential deposition of CoZn-MOF and hydrothermal growth of MoS₂ on APP particles. Incorporating only 4 wt% APP@MOF@MoS₂ into polyurea significantly reduced the peak heat release rate, peak smoke production rate, total heat release, total smoke production, and peak CO₂ production by 48.05 %, 51.41 %, 41.58 %, 64.91 %, and 63.04 %, respectively. The composite achieved UL-94 V-0 rating and a limiting oxygen index of 23.5 %. The enhanced flame retardancy is attributed to the combined effects of MoS₂ barrier formation, phosphate radical trapping, and catalytic carbonization by Co, Zn, and Mo. Moreover, the core-shell structure and size mismatch improved compatibility and mechanical properties compared to APP alone. This work provides a new biomimetic strategy for developing polyurea composites with superior flame retardancy, smoke suppression, and mechanical performance.