Biomass-Based Diketoenamine Vitrimers: Synthesis, Properties, Reprocessing, and Closed-Loop Chemical Recycling

Diketoenamine bonds have been utilized in building up associate covalent adaptable networks for the preparation of vitrimers with closed-loop chemical recycling features. For further enhancement of their sustainability and properties, a biomass-based diacid, 2,5-furandicarboxylic acid (FDCA), is employed as a raw material for the preparation of the diketoenamine vitrimers in this work. Based on the rigid ring structure of the furan group, the FDCA-based diketoenamine resin shows a high glass transition temperature of 144 °C and good mechanical properties (storage modulus at 50 °C: 2.7 GP, Young's modulus: 1040 MPa, tensile strength: 54.4 MPa, and elongation at break: 7.1%). The resin exhibits a relaxation time of about 420 s at 170 °C and activation energy for stress relaxation of about 69 kJ mol–1, both are higher than the values reported to the aliphatic diacid–based analogues and could be attributed to the rigidity of the furan groups. The resin shows physical recycling and reprocessing features at 190 °C as well as a closed-loop chemical recycling properties through acid-catalyzed hydrolysis reaction of diketoenamine bonds. The monomer (FDCA-based triketone) recycling ratio is of about 68%. Moreover, the chemical recycling feature of the FDCA-based diketoenamine vitrimer also contributes to the full recovery of the carbon fibers (CF) from the diketoenamine vitrimer/CF composites. The biomass-based and sustainable vitrimers have potential applications for replacements of conventional cross-linked resins.