Fe3 +-doped PDA and phytic acid modified BN anchored with Co-Ni/B nanosheets for improved flame protection of waterborne epoxy coatings

PDA@Fe was loaded onto BN surface, imparting abundant functional groups and enhancing carbonization performance. • High-phosphorus-content PA was grafted onto the BN/PDA@Fe surface to promote the cross-linking of the polymer into a char. • Co-Ni/B were uniformly loaded onto the BN/PDA@Fe surface to construct a hierarchical BN/PFPA@Co-Ni/B flame retardant. • The nano-reinforcing agent combines high P-N-B content with Fe, Co, Ni to achieve synergistic flame retardancy. Boron nitride (BN) is regarded as an effective nano-flame retardant due to its high thermal stability and thermal shielding effect. Here, Fe 3+ -doped polydopamine (PDA@Fe) was first immobilized on the BN surface to provide abundant functional groups and enhance its catalytic carbonization capability. Subsequently, high-phosphorus phytic acid (PA) and cobalt-nickel borate nanosheets (Co-Ni/B) were loaded onto the BN/PDA@Fe surface to prepare the BN/PFPA@Co-Ni/B composite flame-retardant material. Notably, this multi-level structured nano-reinforcer combines the synergistic flame-retardant effect of high P-N-B content with the highly efficient catalytic charring ability of multiple metal ions (Fe, Co, Ni). Notably, the BN/PFPA@Co-Ni/B/EP composite coating achieved the lowest back surface temperature (167.9 °C) and exhibited the highest expansion height (25.2 mm) and expansion ratio (19.69), demonstrating its excellent thermal insulation performance. Furthermore, the BN/PFPA@Co-Ni/B/EP composite coating exhibited the highest residual carbon content (29.9%) and the lowest smoke density (39.2%). This can be attributed to the strong catalytic pyrolysis effect of the multi-metal ions, which converts more pyrolysis intermediates into stable carbon, thereby increasing carbon residue while reducing smoke emissions. Microstructural analysis revealed a dense and intact carbon layer, providing strong support for its exceptional thermal protection performance. The successful preparation of this novel flame retardant, which combines high barrier properties, high phosphorus and nitrogen content, and multi-metal-catalyzed carbonization, offers a new approach for developing high-performance refractory coatings. Download: Download high-res image (430KB) Download: Download full-size image