Closed-loop recycling of sustainable lignin-based vinylogous urethane vitrimers

Abstract

• One-step chemical modification of organosolv lignin into highly functionalized acetoacetate macromonomer. • Detailed study of the reaction of phenylacetoacetates with amines. • Synthesis of sustainable vinylogous urethane vitrimers with high lignin content (from 20 to 50 wt%). • Analysis of the structure – properties relationships of lignin-based vitrimers. • Fully recyclable lignin-based materials over three consecutive thermomechanical recycling cycles. Lignins are abundant biomacromolecules, the first source of renewable aromatics structures. Thanks to their high functionality, they are interesting precursors for aromatic thermoset materials. However, thermosets usually lack efficient recyclability. To achieve a controlled end-of-life, the design of sustainable lignin-based vitrimers is an elegant strategy to overcome the recycling limits of thermosets without compromising properties. In this work, we report the synthesis and evaluation of lignin-based vinylogous urethane vitrimers. A novel route for the grafting of acetoacetate groups onto organosolv lignin was developed, and a series of biobased vitrimers was prepared by condensation with polyetheramines of different chemical structures. The materials were deeply characterized to establish structure–property relationships. The structure of the diamine was found to strongly influence the morphological and mechanical properties of the vitrimers. Besides, different closed-loop recycling approaches were studied. Three cycles of physical recycling were performed, showing a good preservation of chemical structure and physical properties. Chemical recycling by acid-catalyzed depolymerization was also investigated, offering an additional option for efficient closed-loop recycling.

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