There is an urgent need to develop bio-based circular materials to overcome the ongoing environmental pollution by single-use fossil materials. Lignin is regarded as one of the most promising natural polymers owing to its rigid aromatic structure and versatile reactivity. However, it has been challenging to develop lignin-based materials that are designed for reuse. Here we show synthesis of a series of lignin-based vitrimers that can be recovered and thermally reprocessed. A one-pot reaction of softwood kraft lignin with poly(ethylene glycol) divinyl ether yielded vitrimers with a gel content exceeding 95%. Their mechanical properties could be widely tuned in a facile way by varying the lignin content. The vitrimer with a lignin content of 28% showed a tensile strength of 3.3 MPa with 35% elongation at break, while at 50% lignin content the values were 50.9 MPa and 1.0 %, respectively. We demonstrated these lignin-based vitrimers as recoverable adhesives for aluminum and pine wood, with lap shear test strengths of 6.0 MPa and 2.6 MPa, respectively. The vitrimer adhesives preserved more than 90% of the adhesion performance after re-gluing, which encourages further development of these sustainable circular materials.

Lignin vitrimers with tunable mechanical properties: Circular polymers and recoverable adhesives

ACS Spring 2022

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