A Biobased Epoxy Vitrimer with Dual Relaxation Mechanism: A Promising Material for Renewable, Reusable, and Recyclable Adhesives and Composites

Abstract

This study presents the synthesis of a novel biobased epoxy monomer derived from vanillin and cystamine, incorporating imine and disulfide exchangeable groups within its structure. A series of epoxy-based vitrimers with two simultaneous exchange relaxation processes have been produced using this monomer. These exchange mechanisms operate without the need for any catalyst. Four different amine curing agents have been employed to achieve vitrimers with glass transition temperatures around 100 °C and excellent thermal stability. Through dynamic-mechanical analyses, thermomechanical properties and vitrimeric characteristics have been investigated, revealing remarkably fast stress relaxation at relatively low temperatures without significant creep below the glass transition temperature. Leveraging the dual exchange mechanism, the chemical degradability of these vitrimers has been explored through two accessible methodologies, and the material's reformation after degradation has been demonstrated in both cases. Furthermore, the material has been mechanically recycled, maintaining almost the same properties. Finally, these materials have been used to fabricate and recycle carbon-fiber-reinforced composite material and reversible adhesives, showcasing their promising potential applications.

Hardener-Dependent Properties of Twice Renewable Epoxy Resins Combining Tailored Lignin Fractions and Recycled BPA

“…A complementary strategy to prevent BPA-derived waste could involve using biobased alternatives to produce more sustainable epoxy resin, which is vital for a material industry in continuous expansion . From the perspective of chemical structure similarity with BPA, biobased small molecules such as eugenol and vanillin have been proposed as suitable candidates, − but their high obtention price, availability and modification process limit the upscaling production . In recent years, the lignin biopolymer has attracted significant interest as a biobased candidate due to its three-dimensional structure rich in aromatics and active phenolic groups, which provides rigidity, strength, and reactive points. , Additionally, lignin is the most abundant natural aromatic biopolymer and around 85% of the total global production is originated as a byproduct from the Kraft pulp process for paper production. , For the time being, the Kraft lignin is regarded as waste and incinerated to partially recuperate the operational energy from the pulp process, which makes the valorization of Kraft lignin into high-value products a suitable biobased alternative to BPA for the production of more sustainable epoxy resins .…”