A novel P/Fe/Si-doped porphyrin with excellent flame retardancy and ultrastrong toughening effect on epoxy resin

Epoxy resin (EP) is one of the most versatile polymers. Nonetheless, its inherent flammability and brittleness severely limit its broad development. Moreover, existing additives make it difficult to meet the dual requirements of flame retardancy and toughening. Herein, a novel P/Fe/Si-doped porphyrin derivative (MTPD-Fe@SiO2) with nano-cauliflower structure was synthesized to develop advanced EP composites. MTPD-Fe@SiO2 exhibited good dispersion in EP matrix, which is attributed to the π-π interactions between the porphyrin and EP chains, as well as the mechanical interlocking of nano-cauliflower rough structure. Moreover, when 5 % of MTPD-Fe@SiO2 was incorporated, the tensile and flexural strengths of EP composites were increased by 48.1 % and 63.5 %, respectively, showing excellent toughening properties. Additionally, the maximum thermal degradation rate of EP/5 % MTPD-Fe@SiO2 was significantly reduced, indicating its superior thermal stability. Notably, compared with pure EP, the peak heat release rate and the peak smoke production rate of EP/5 % MTPD-Fe@SiO2 were decreased by 36.4 % and 43.6 %, while the residual char and limiting oxygen index increased to 30.9 % and 32.1 %, respectively. This was ascribed to the catalytic charring of transition metals and phosphates, the barrier effect of the solid carbon layer (Fe4(PO4)2O, SiO2), the trapping effect of phosphorus radicals and the dilution effect of incombustibles. This work provides a viable approach to solving the trade-off between refractoriness and mechanical performance.