Novel and Integrated Process for the Valorization of Kraft Lignin to Produce Lignin-Containing Vitrimers

The valorization of lignin into value-added products by oxidative conversion is a widely studied strategy. However, in many cases, this approach has limited scope for integration into industrial processes. The objective of our work is to maximize overall lignin utilization to produce diverse value-added products with a focus on integration in the existing industrial pulp and paper processes. The utilization of the sequential oxidation strategy using oxygen and ozone resulted in kraft lignin with a marked improvement in carboxyl content and also allowed the formation of vanillin and vanillic acid in the oxygen stage. The sequentially oxidized lignin (OxL-COOH) was then cured with poly(ethylene glycol) diglycidyl ether (PEG-epoxy) to form high-lignin-content (>48 wt %) vitrimers with high thermal stability, fast relaxation, swelling, and self-healing due to the presence of bond-exchangeable cross-linked networks. Overall, this study provides a novel approach for the multidimensional valorization of lignin and demonstrates an integrated approach for kraft lignin valorization in the pulp and paper industry.

Automated summary

The valorization of lignin into value-added products through oxidative conversion is a popular research strategy, but its integration into industrial processes is often limited. This study aims to maximize lignin utilization to produce diverse value-added products, with a specific focus on integration in the existing pulp and paper industry. Sequential oxidation using oxygen and ozone improved the carboxyl content of kraft lignin and allowed the formation of vanillin and vanillic acid. The resulting oxidized lignin was then cured with PEG-epoxy to form high-lignin-content vitrimers with excellent thermal stability and self-healing properties. This study presents a novel approach for lignin valorization and demonstrates its integration in the pulp and paper industry.