Bio-Based Vi-nylogous Ure-thane Vitrimers from Waste-Wood Lignosul-fonate and En-zymatic Lignin: Explorations in Stress Relaxa-tion Behavior and Mechanical Strength

Abstract

Lignin is one of the most promising materials for a biocircular economy. It is not only the most abundant biomaterial, but it has also gathered significant interest in both academia and industry as a new feedstock for plastics. Lignin is primarily produced as a byproduct in the pulping industry, but it can also be extracted from lignocellulosic biomass contributing to waste-wood valorization. The combination with thermomechanical reprocessable polymers, such as vitrimers, enables the synthesis of thermosetting materials with high mechanical strength that can be reused. Herein, we present catalyst-free vinylogous urethane vitrimers based on lignosulfonate and enzymatic lignin, using a commercial bio-based diamine and a bio-based diol linker. Materials are synthesized following green chemistry principles using a direct acetoacetylation process of lignin in non-toxic solvents, which can subsequently be used to produce homogeneous films and materials. The thermomechanical properties and recyclability over five cycles demonstrate that the materials represent a promising class of tougher, greener, and sustainable vitrimers. The stress-relaxation properties of the materials are characterized through a detailed study focusing on the influence of the glass transition temperatures of the materials. Mechanical testing yielded elastic moduli of up to 0.83 GPa and tensile strengths of up to 30 MPa. Additionally, processing through injection molding was demonstrated, producing homogeneous samples for tensile testing.