Bio-Based Epoxy Binders from Lignin Derivatized with Epoxidized Rapeseed Fatty Acids in Bimodal Coating Systems

In the recent decade, a strong push toward development of more biobased binders for coating applications as part of the transition toward independence from nonrenewable fossil-based raw materials has been seen. Here we present a biobased epoxy lignin/rapeseed fatty acid derivative (eFA-L), which has been applied in coating systems, leading to coatings with >97% biobased content and Y = 130 MPa. To approach the strength of classical epoxy systems, a series of bimodal systems, containing low molecular weight adducts of biobased diglycidyl furan-2,5-dicarboxylate (DGFDC) and fossil-based diglycidylether bisphenol A (DGEBA) were prepared. In these bimodal systems, it was shown that DGEBA contributes to higher mechanical strength compared to DGFDC at equivalent cross-linking density, which was attributed to increased π–π stacking interactions. The biobased bimodal binder system composed of eFA-L and DGFDC (30 wt %) resulted in a coating with a biobased content of 93 wt %, Y = 440 MPa, and Tg > 50 °C. Better mechanical properties (Y = 700 MPa) were achieved by use of DGEBA (30 wt %), but it results in a significant reduction in biobased content to 62 wt %.