New Reactive Isoeugenol Based Phosphate Flame Retardant: Toward Green Epoxy Resins

A biobased reactive phosphate flame retardant derived from isoeugenol was synthesized and fully characterized ( 1 H, 13 C, 31 P NMR, FTIR, MS) with the aim of improving flame retardancy behavior of biobased epoxy thermosets. This new green flame retardant, diepoxy-isoeugenol phenylphosphate (DEpiEPP), was then copolymerized either with conventional diglycidyl ether of bisphenol A resin (DGEBA) or with a totally biobased glycidyl ether epoxy isoeugenol (GEEpiE) resin using a biobased camphoric anhydride (CA) as hardener. Resulting thermosets with varying rates of flame retardant (1.0 to 4.3 wt % phosphorus) were then characterized (FTIR, DSC, nanoindentation, three-point bending test, TGA, PCFC, cone calorimeter). In this way, a new solution was proposed allowing (i) to increase the biobased content of thermosets, (ii) to improve the flame retardancy properties by a reactive way, and (iii) to provide epoxy thermosets with high T g, excellent mechanical properties, and a curing temperature compatible with the use of vegetable fibers. For instance, with a weight content of 2.0 wt % P, both GEEpiE-CA-DEpiEPP (95% biobased content) and partially biobased DGEBA-CA-DEpiEPP (57% biobased content) epoxy thermosets possess high T g (respectively 129 and 105 °C) and bending elastic modulus and strength of respectively 4.08 GPa and 90 MPa and demonstrate good flame-retardant properties due to char promotion showing high promise for application.