Recyclable and bio-based waterborne acetal thermosets and composites.

Fully recyclable waterborne acetal thermosets were synthesized via the condensation of sorbitol and glutaraldehyde, utilizing oxalic acid as a green and in situ decomposable catalyst. Via a simple one-pot polycondensation in water the catalyst-free densely crosslinked networks are formed, combining high mechanical performance (tensile strength >90 MPa), stiffness (Young's modulus 3.3 GPa), and excellent thermal and solvent stability. While the materials remain fully stable under neutral conditions, the acetal linkages enable complete depolymerization under acidic environments, producing a homogeneous solution that can be recondensed into new thermosets with properties indistinguishable from the original, thus achieving true closed-loop recycling. The resins also exhibit outstanding compatibility with glass and carbon fibers, enabling the fabrication of high-performance, recyclable composites from which pristine fibers can be recovered. Together, these results establish waterborne, bio-based acetal chemistry as a scalable and sustainable platform for high-performance thermosets and fiber composites, offering a practical and circular route toward next-generation materials design.