Modified lignin: Preparation and use in reversible gel via Diels-Alder reaction

In this study, popular soda lignin was modified with either furan or maleimide ring, and the modified lignins were subjected to reversible Diels−Alder reaction. A new process was proposed to prepare the functionalized lignin. A long chain was introduced to the hydroxyl groups of lignin, and then either the furan or maleimide ring was added to the other end of the chain. The test results confirmed that either the furan ring or the maleimide ring was bound to lignin. Furan- and maleimide-functionalized lignins were also combined to generate crosslinking via Diels-Alder [4 + 2] cycloaddition reaction. Under appropriate conditions, the formation of a gel was identified, which reverted to liquid state after retro Diels-Alder reaction upon heating at 120 °C. This study reveals the significant versatility and potential of the developed strategy for the utilization of lignin-based recyclable networks.