Enhancing fire safety and mechanical properties of polyurea elastomer via Nitrogen-Boron supramolecularly modified black phosphorus

Polyurea (PUA) coatings are widely used in protective applications but are limited by inherent flammability and reduced mechanical integrity from traditional flame retardants. Herein, we report a facile supramolecular modification of black phosphorus (BP) nanosheets, combining chitosan-assisted ball milling with melamine borate co-assembly to yield the CNB@BP nanohybrid. This nanohybrid showed excellent compatibility and dispersibility in the PUA matrix, providing nanocomposites with synergistic improvements in mechanical, anti-impact, thermal stability, and flame-retardant properties. Notably, 1 wt% loading increased tensile strength by 82.35% and impact resistance for aluminum alloy by 51.42%. At 3 wt% loading, peak heat release rate and total heat release dropped by 26.40% and 21.88%, respectively, with effective suppression of smoke and toxic gas emissions. These fire safety improvements arose from a P-N-B synergistic mechanism across two phases: catalytic charring and physical barriers in the condensed phase, plus radical scavenging and gas dilution in the gas phase. This supramolecular engineering approach thus offers a new paradigm for low-dose nanohybrids, enabling advanced PUA elastomers with balanced mechanical strength and fire safety.