Biobased Hyperbranched\nFlame Retardant for Epoxy Resin\nModification: Simultaneously Improved Flame Retardancy, Toughness,\nand Smoke Toxicity Suppression

Reducing both the flammability and the frangibility of\nepoxy resins\n(EPs) while inhibiting the smoke toxicity of combustion presents a\nsignificant challenge. In this study, a hyperbranched low-phosphorus\n(P)-containing flame-retardant polymer (HBFR) was synthesized to chemically\nmodify epoxy resin. Results demonstrated that the modified epoxy achieved\na V-0 rating in the UL-94 test and exhibited a limiting oxygen index\n(LOI) of 31.5%, with a P content of only 0.42 wt %. The peak heat\nrelease rate (PHRR) and total smoke production (TSP) of C-EP<sub>92.5</sub>HBFR<sub>7.5</sub> decreased by 31.4% and 19.1%, respectively, compared\nto cured pristine EP (C-EP). The maximum carbon monoxide emission\nof C-EP<sub>92.5</sub>HBFR<sub>7.5</sub> decreased by 39.4% and 16.2%\nduring combustion compared with C-EP and commercial flame retardants,\nrespectively. Furthermore, the impact and flexural strength of C-EP<sub>92.5</sub>HBFR<sub>7.5</sub> increased remarkably by 257.5% and 20.3%,\nrespectively, due to the enhanced free volumes and toughening effects\ncaused by HBFR. Meanwhile, the modified epoxy thermosets still maintained\nhigh <i>T</i><sub>g</sub> (>168 °C) and thermostability\n(<i>T</i><sub>d5%</sub> > 361 °C). In sum, this\nwork\nprovides an efficient and eco-friendly strategy for concurrently enhancing\nthe flame retardancy (FR) and toughness of epoxy thermosets.