In-situ Polymerized B4C-MUF@Perfluoro(2-methyl-3-pentanone) Microcapsules for Enhanced Thermal Stability and Synergistic Flame Retardancy

Microencapsulated flame retardants with high thermal stability and efficacy are critical for polymer safety. Conventional systems often face issues like poor shell stability and low char residue, leading to early core release and reduced flame-retardant performance. This study presents a novel approach using a silane coupling agent (KH-550) to integrate surface-hydroxylated nano boron carbide (B 4 C) into a melamine-urea-formaldehyde (MUF) shell. Using perfluoro(2-methyl-3-pentanone) (PMP, C 6 F 12 O) as the core material, we developed BMP (B 4 C&MUF@PMP) composite microcapsules through in situ polymerization. These microcapsules, with 6 wt% B 4 C, showed a smooth spherical morphology, sealed micropores, and enhanced thermal stability, with a 5% weight loss temperature rising from 78.3°C to 123°C and char residue increasing from 0.88% to 6.91%. When incorporated into epoxy resin, the EP/BMP composite achieved a limiting oxygen index of 31.2%, passed the UL-94 V-0 rating, and reduced peak heat release rate and total heat release by 48.7% and 48.8%, respectively, while suppressing CO generation. This approach strengthens the MUF shell via B 4 C integration, enabling controlled PMP release and synergistic flame retardancy through a dense char layer, offering a new pathway for high-performance flame-retardant microcapsules.