Upcycling birch bark suberin into versatile and recyclable thermosets

There is an urgent need for recyclable thermosets from renewable feedstocks that can be precisely tailored for diverse applications. Here we show that birch outer bark, an abundant forestry by-product, can be converted into fully biobased thermosets with tunable mechanical properties and closed-loop recyclability. Catalyst-free crosslinking of suberin-derived precursors yields materials spanning from elastic adhesives to stiff anticorrosion coatings and carbon fiber composites. These thermosets undergo facile chemical recycling via alkaline hydrolysis and can be thermally repolymerized, exhibiting progressively enhanced strength across multiple cycles. After five recycling rounds, tensile strength increases from 0.5 MPa at 200% strain to 26 MPa at 98% strain, with material recovery yields above 90% at each cycle. This unusual feature was ascribed to ester/ether exchange and enables the preparation of recyclable suberinic acids (SAs)/carbon fiber reinforced polymer (CFRP), where the fiber and polymer properties are not compromised after the recycling process. Overall, the fully biobased thermosets developed in this study can match or even exceed the performance of fossil-based counterparts while providing true circular-economy benefits.