Hardener-Dependent Properties of Twice Renewable Epoxy Resins Combining Tailored Lignin Fractions and Recycled BPA

The use of biosourced and/or recycled raw materials represents a promising strategy for making the polymer industry more renewable. In this context, both biobased lignin fractions and chemically recycled bisphenol A (r-BPA) have been independently considered as promising renewable alternatives to aromatic fossil monomers. Here, renewable thermosetting epoxies were designed by combining tailored lignin fractions and r-BPA, while the influence of several hardeners on the physical structure and properties of the obtained resins was systematically investigated. To do so, the phenolic groups of r-BPA derived from polycarbonate waste and solvent-extracted Kraft lignin (EKL) were both glycidylated with epichlorohydrin. This led to the renewable epoxy precursors r-BPA diglycidyl ether (r-DGEBA) and glycidylated extracted Kraft lignin, respectively. Twenty different formulations were then designed by tailoring the structural parameters of the resins, such as the hardener length and functionality, the epoxide/hardener (E/H) ratio, and the lignin content. The thermomechanical properties were investigated and the structure−property relationships established, highlighting the excellent and tunable performance of these renewable epoxies. Finally, flexible coatings were produced with lower cross-link density formulations that demonstrated excellent performance, even with 30% of lignin content. Overall, our results show how biobased and recycled aromatic building blocks could be combined for the design of epoxy resins with superior properties in both sustainable and technical terms.