Biobased epoxy resins from itaconic anhydride functionalized lignin: insights and comparison with succinic analogues

Abstract

Lignin, the most abundant renewable aromatic polymer, remains underutilized despite its potential as a sustainable feedstock for polymeric materials. In this work, lignin was functionalized with itaconic and succinic anhydrides to introduce carboxylic acid groups, enabling its use as a polyfunctional macromonomer. The influence of temperature, reaction time, reagent stoichiometry, and catalysts on the functionalization efficiency was systematically investigated. The resulting lignin derivatives were incorporated as crosslinkers into fully biobased epoxy resins formulated with epoxidized soybean oil and Pripol™ 1009, and their mechanical and thermal properties, as well as insights into the curing, were investigated in detail. Elastic moduli ranged from 4.87 to 1.24 MPa. The glass transition temperature (between −36 and −23 °C) was found to be primarily influenced by the aliphatic matrix, while the lignin content and the resulting network architecture strongly affected the mechanical properties of the materials. Comparative studies with succinic anhydride modified lignin highlighted the role of unsaturation due to itaconic acid in the network, especially for mechanical properties. Finally, degradation studies demonstrated depolymerization under alkaline hydrolysis, suggesting potential for designing easily cleavable thermoset systems. This work contributes to the development of greener epoxy networks and highlights lignin's versatility as a reactive renewable building block for sustainable polymer chemistry.