Epoxidized Lignin Derivatives as Bio-based Cross-linkers Used in the Preparation of Epoxy Resins

Lignin, which is the most abundant aromatic polymer in nature, was used as a green substitute for the toxic bisphenol A. In particular, the ability of epoxidized lignin to simultaneously serve as a cross-linker and rigid segment was investigated. The epoxidized lignin was preferably reacted with a monofunctional amine, which acted as a chain extender, to evaluate its performance as a cross-linker, and in the presence of poly(ethylene glycol) diglycidyl ether as a soft segment to adjust the resin properties. Different poly(ethylene glycol) diglycidyl ether/lignin stoichiometric ratios were tested, whereas the amine/epoxy equivalent ratio was fixed at 1:2. Some of the remarkable resin samples were subjected to differential scanning calorimetry analysis and compared with blank samples that did not include lignin in the composition. Moreover, the evolution over time of the molecular weight distribution of the selected compositions was analyzed by gel permeation chromatography until the solubility in tetrahydrofuran was appreciable.