Bio-Based Fluorescent Epoxies: Emission Control through Molecular Packing and Phase Separation

This study demonstrates the sustainable conversion of agricultural waste into high-performance fluorescent epoxy resins through direct blending of coumaric acid epoxy (CE) and ferulic acid epoxy (FE) derived from corn stover. These bio-based resins exhibit tunable photoluminescence, with emission maxima shifting from 299 nm to 841 nm as FE content increases from 0 to 33 wt%. In contrast, blends based on commercial bisphenol A diglycidyl ether (BADGE) reach emission saturation around 550 nm and exhibit phase separation at higher FE concentrations, as confirmed by light microscopy. The synthesized CE-FE blends achieve superior or comparable thermomechanical properties, including flexural moduli (3.2-3.4 GPa), glass transition temperatures, and storage moduli, relative to commercial BADGE-based resins. Impact toughness is consistent across all blends except for BADGE containing 33 wt% FE, which decreases significantly from 63 J m^-1 (neat BADGE) to 12 J m^-1 due to phase separation. Enhanced fluorescence intensity in CE-rich blends is attributed to their compact aromatic structures, limiting free volume and nonradiative decay. Unlike existing fluorescent epoxy systems requiring complex synthesis or additives, this straightforward blending approach provides a sustainable, high-performance alternative ideal for practical integration into biorefineries, with promising applications in optical sensors, bioimaging materials, and smart coatings.