A bio-based intrinsically flame-retardant epoxy vitrimer from furan derivatives and its application in recyclable carbon fiber composites

The recycling of carbon fiber reinforced polymer composites (CFRPCs) is difficult because the thermosetting matrix is insoluble and does not melt. To overcome this problem, a furan-derived epoxy resin (HMF-GAN-EP) was synthesized from 5-hydroxymethylfurfural and cured with a furan-based curing agent (DIFFA). The cured HMF-GAN-EP/DIFFA system showed excellent flame retardancy (UL-94 V-0 and LOI of 40%). The glass transition temperature, tensile strength, and tensile modulus of the cured HMF-GAN-EP/DIFFA system were approximately 234 °C, 67 MPa and 2273 MPa, respectively, all of which were higher than those of the diglycidyl ether of bisphenol A (DGEBA)-type epoxy thermosets cured by 4,4′-diaminodiphenylmethane (DDM) (151 °C, 56 MPa and 1744 MPa). The cured HMF-GAN-EP/DIFFA system could dissolve in a mixed solution of THF:HCl (8:2, v/v), making it possible for the recycling of carbon fibers from CFRPCs.