The combination of eco-respectful epoxy compounds with the humins, a by-product of biomass chemical conversion technologies, allow the obtention of materials with high added value. In this work, we propose the chemical connection study of humins with two aliphatic diepoxides through the copolymerization reactions to synthesize sustainable bio-based thermosets. The mechanism insights for the crosslinking between the epoxides and humins was proposed considering the different functionalities of the humins structure. FT-IR spectroscopy, 1 D and 2 D NMR spectroscopy techniques were used to build the proposed mechanism. By these techniques, the principal chain connections and the reactivity of all the components were highlighted in the synthesized networks.

This study presents the development of a diglycidyl monomer containing two imine groups that can act as dynamic and reversible bonds. During the curing of the monomer with two different amine hardeners, we confirmed the formation of new imine groups due to the transamination reaction, not reported before, between the imine groups of the diepoxy monomer with the amine groups of the hardener. The effect of this structural change is observed for the first time in the stress relaxation behavior, resulting in the overlapping of two different relaxation modes. The analytical modelling could extract two distinct characteristic relaxation times using a double-element Maxwell model. A second characterization of the stress relaxation process by frequency sweep experiments was performed to corroborate the results obtained, confirming speedy stress relaxation. Acid-catalyzed hydrolysis was performed on the studied materials, demonstrating the complete degradation of the network. We finally confirmed that the synthesized diepoxy compound is suitable for preparing carbon fiber-reinforced composite materials, demonstrating easy fiber impregnation, fast reshaping and especially a total degradation of the polymer matrix that allows the recovery of the carbon fibers in mild conditions. This epoxy-amine system is an excellent candidate for overcoming the traditional limits of thermosets in preparing fiber-reinforced composites.