P/N/Si-containing synergistic flame retardants endowing lignin-based epoxy resin with good flame retardancy, mechanical properties and heat resistance

Biobased epoxy resins are gaining attention as a renewable alternative to petroleum-based resins. However, their inherent flammability requires flame-retardant treatment. In this study, hexaphenoxycyclotriphosphazene (HPCP) and various synergists were utilized to improve the flame retardancy of lignin-based epoxy resin (EP-L). Results showed that (3-aminopropyl)triethoxysilane (APTES) had the most effective synergistic effect for HPCP to form a P/N/Si-containing system, resulting in a compact crosslinked char layer. Upon the incorporation of HPCP and APTES (6∶1, 12 wt% of EP mass) into EP, a V-0 classification was achieved in the UL-94 vertical burning assessment, with a limiting oxygen index of 33.6% and a 47.77% decrease in the peak of heat release rate. This system minimally influenced the tensile strength of the composite (a 16.51% reduction), and maximumly increased its initial degradation temperature by 83 °C, compared with EP-L. © 2023 Society of Industrial Chemistry.