# Upcycling birch bark suberin into versatile and recyclable thermosets

## TL;DR

Scientists turned birch bark into recyclable, high-performance materials that can be reused multiple times without losing strength.

## Contribution

A novel method to create fully biobased, recyclable thermosets from birch bark suberin with tunable properties and closed-loop recyclability.

## Key findings

- Thermosets made from birch bark suberin show improved tensile strength after multiple recycling cycles.
- Materials retain over 90% recovery yield and maintain structural integrity after five recycling rounds.
- The process enables scalable circular-economy materials that match or exceed fossil-based thermosets in performance.

## Abstract

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.

Suberinic acids from birch bark are converted into robust, fully recyclable thermosets with control over crosslink density via reversible ester chemistry, enabling a scalable route to circular high-performance materials from forestry residues.