Development of Renewable and Recyclable Epoxy Thermosets Based on Lignin Derived Phenols

Epoxy thermoset represents one of the most versatile thermosetting materials that has been used as coatings, adhesives, electronic materials and structural composites. However, by far more than 90% of the epoxy cross−linked polymers involve the use of petroleum−based bisphenol A (BPA). Lignin is an abundant, low−cost and renewable source that can provide building blocks for epoxy thermosets. Lignin−derived monomers, oligomers and bulk lignin were modified through methods including demethylation, phenolation and condensation to make renewable BPA analogs. Glycidylation of these analogs followed by cross−linking process yielded renewable thermosets with marked thermomechanical properties that could replace or supplement the BPA−based counterparts. While most of the traditional epoxy thermosets cannot be reprocessed after cross−linking, incorporating reversible bonds into the backbone of thermosets can achieve stress relaxation and reversible depolymerization through cross−link exchange and bonds cleavage−reformation. This affords malleability, weldability and recyclability to the renewable thermosets