Furan-derived phosphine flame-retardant furan-derived epoxy thermosets with combined mechanical properties, thermal stability and flame retardancy

Currently, most commercial epoxy thermosets are derived from the thermal curing of diglycidyl ether of bisphenol A (DGEBA)-type epoxy prepolymers, whose manufacture is highly dependent upon fossil resources. Over the past decade, increasing efforts have been devoted to developing bio-based epoxy monomers to replace DGEBA-type epoxy prepolymers for sustainable development. Another shortcoming of DGEBA-type epoxy thermosets is their high fire risk. To overcome the above issues, a bio-based epoxy monomer, N, N-diglycidyl furfurylamine (DGFA), was synthesized from furfurylamine, and a bio-based flame retardant (DFDA-DPPO) was also synthesized from furfurylamine, furfural, and diphenylphosphine oxide (DPPO). DFDA-DPPO was incorporated into DGFA at different loadings to prepare a series of flame-retardant bio-based epoxy thermosets, with 4, 4’-diaminodiphenylmethane (DDM) as a hardener. The influence of DFDA-DPPO on the curing kinetics, thermal stability, mechanical strength and flame-retardant properties of DGFA/DDM thermosets was investigated. Specifically, the DGFA/DDM thermoset with a 1.5 % phosphorus content achieved a tensile strength of 81.9 MPa, an impact strength of 16.7 kJ/m 2 , an LOI of 33.5 %, a UL94 V-0 rating, and a glass transition temperature of 98.5 °C. Furthermore, the flame-retardant mechanisms of DFDA-DPPO were also studied in both the condensed and gaseous phases. This work provides a good substitute for DGEBA in the fabrication of bio-based epoxy thermosets with combined mechanical properties, thermal stability and flame retardancy.