Reversible Lignin-Containing Networks Using Diels–Alder Chemistry

The development of bio-based polymers displaying promising end-of-life opportunities would have an immense impact on the polymer industry but has remained largely unexplored. Therefore, in this work, self-healing bio-aromatic networks with lignin contents up to 29 wt % were designed based on the thermoreversible Diels–Alder reaction. The networks were developed by reacting a furan-functionalized solvent-extracted lignin and a furan-bearing polyether (F5000) with a bismaleimide (DPBM). The obtained networks were nanophase-separated between a flexible F5000-rich phase and a rigid lignin-rich phase, which was evidenced by (modulated temperature) differential scanning calorimetry and small angle X-ray scattering. Partially due to the phase-separation, improved mechanical properties were obtained, including a higher Young's modulus and improved toughness. In addition, the thermal stability of the networks significantly increased due to the addition of lignin. Besides the thermomechanical improvement, the networks showed promising stress-relaxation, creep resistance, healing, and reprocessability. A macroscopic healing efficiency of 62% of the toughness was obtained. Moreover, the networks were completely resoluble, which allows for promising recycling possibilities.