High-Performing and Fire-Resistant Biobased Epoxy Resin from Renewable Sources

Epoxy resins with high thermal and mechanical performance as well as good resistance to fire are difficult to synthesize. In this work, a high-performance intrinsically flame-retardant epoxy resin (diglycidyl ether of daidzein (DGED)) was synthesized from renewable daidzein using an efficient one-step process, without the addition of additional flame retardants. The structure of DGED was confirmed by Fourier transform infrared (FTIR), H-1 NMR, and C-13 NMR before it was cured with 4,4'-diaminodiphenylmethane (DDM). A commercial diglycidyl ether of bisphenol A (DGEBA) was cured with the same curing agent. Results indicated that the cured DGED/DDM system possessed glass transition temperature (T-g) of up to 205 degrees C (172 degrees C for DGEBA/DDM), and tensile strength, tensile modulus, flexural strength, and flexural modulus of 83, 2972, 131, and 2980 MPa, respectively, all much higher than those of cured DGEBA/DDM. The cured DGED/DDM system demonstrated excellent flame-retardant properties, showing a residual char of 42.9% at 800 degrees C, limiting oxygen index (LOI) of 31.6%, and flammability rating of V-0 in UL94 test. This work provides us an efficient method to prepare high-performance epoxy resin from renewable resource.