Synthesis of fully bio-based diepoxy monomer with dicyclo diacetal for high-performance, readily degradable thermosets

Thermosets are very versatile owing to their high dimensional stability, chemical resistance and thermal and mechanical properties; however, they are difficult to be recycled or reworked because of their permanent cross-linked structure. In this paper, we synthesized a novel fully bio-based diepoxy monomer via acetalization of lignin derivative vanillin with bio-based polyol erythritol followed by reacting with bio-derived epichlorohydrin. Due to the degradability of dicyclo diacetal structure in the diepoxy monomer, the cross-linked epoxy network could be readily decomposed (completely dissolved in 1 M HCl solution at 50 °C within 40 min). While it was stable under neutral and basic conditions even during hot-humid aging test. Meanwhile, due to the rigidity of the dicyclo diacetal structure, it showed high glass transition temperature of 184 °C, and its modulus (4.7 GPa) and hardness (0.30 GPa) are even higher than those of conventional bisphenol A epoxy resin.