Choosing the Right Lignin to Fully Replace Bisphenol A in Epoxy Resin Formulation

Thirteen unmodified lignin samples from different biomass sources and isolation processes were characterized and used to entirely replace bisphenol A (BPA) in the formulation of solubilized epoxy resins using a developed novel method. The objective was to measure the reactivity of different lignins toward bio‐based epichlorohydrin (ECH). The epoxy contents of various bio‐based epoxidized lignins were measured by titration and (1)H NMR spectroscopy methods. A partial least square regression (PLS‐R) model with 92 % fitting accuracy and 90 % prediction ability was developed to find correlations between lignin properties and their epoxy contents. The results showed that lignins with higher phenolic hydroxy content and lower molecular weights were more suitable for replacing 100 % of toxic BPA in the formulation of epoxy resins. Additionally, two epoxidized lignin samples (highest epoxy contents) cured by using a bio‐based hardener (Cardolite GX‐3090) were found to show comparable thermomechanical performances and thermal stabilities to a petroleum‐based (DGEBA) epoxy system.