Multifunctional DOPO-based Polydopamine Nanospheres for Simultaneous Flame Retardancy and Antibacterial Enhancement in Epoxy Composites

To develop multifunctional epoxy (EP) composites integrating good flame retardancy, suitable mechanical performance, and superior antibacterial properties, a nanosphere-shaped flame retardant (PDA@KH560-DOPO) was fabricated by grafting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) onto polydopamine (PDA) nanospheres via the bridging of silane coupling agent KH560. This additive exhibited two distinct degradation stages with low maximum degradation rates (1.79 and 1.52 %/min) and high charring ability (58.6 % at 700°C) under N 2 atmosphere. The EP composite containing 8 % PDA@KH560-DOPO achieved a limited oxygen index (LOI) of 31.8 % and a UL-94 V-0 rating, while maintaining good tensile and impact properties comparable to neat EP. The cone calorimeter test showed reductions in peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) by 48.1, 32.1, and 19.0 % respectively. This is attributed to the cooperative flame-retarding mechanisms combining staged free-radical scavenging (phenoxy and P-containing radicals), inert gas dilution, and a reinforced char barrier (18.1 wt% in cone calorimeter test). Crucially, the composite also exhibited potent antibacterial activity, with over 94 % inhibition rate against Gram-positive bacteria (S. aureus). This work provides a practical pathway for expanding the applications of EP composites into domains that require fire-safe and hygienic standards.