A sustainable lignin-based epoxy resin: Its preparation and combustion behaviors

Lignin, commonly treated as a waste from industrial or agricultural/forestry activities, can be used as a sustainable alternative of fossil phenol to fabricate lignin-based epoxy resins. In this study, the cured samples of lignin-based epoxy resins were prepared after curing process, and their combustion behaviors were investigated by thermogravimetric analysis coupled with Fourier transform infrared spectrometer (TG-FTIR) and cone calorimeter test. Results showed that these as-prepared epoxy thermosets (containing 0%, 5%, and 10% lignin) contained a higher LOI (limited oxygen index) value compared to others commercial resins reported in previous literature. Furthermore, they were all self-extinguishing materials during the first burning process, which was primarily contributed to their high-compactness crosslinking structure. Lignin addition would cause a negative effect on the thermomechanical properties of cured samples due to the decrease of crosslinking density, while better excellent gaseous inhibition and charring capacity can be obtained after lignin addition. This study presented an effective strategy to incorporate lignin into epoxy resin system via chemical crosslinking using glyoxal in place of formaldehyde as a green crosslinking agent to improve the combustion behaviors via reducing smoke releasing and increasing char formation, which was also beneficial for lignin valorization.