Preparation and characterization of lignin-based epoxy resin via one-step grafting of lignin with E-44 epoxy resin

Aiming for high-value utilization of lignin in pulping black liquor, lignin-based epoxy resin (RLEP) was synthesized by one-step grafting of refined lignin (RL) with E-44 epoxy resin, and then the lignin-based epoxy resin film (RLEPF) was prepared by using phenolic amine as the curing agent. The results showed that the lignin ethers were synthesized by copolymerizing the hydroxyl groups of lignin and the epoxy groups of E-44. Upon increasing the lignin dosage, the epoxy value of RLEP decreased, and the fracture surface of RLEPF changed from a clear-layered structure to an uneven rough surface. Furthermore, the increased lignin dosage resulted in enhancing the elongation at break of RLEPF while the tensile strength and thermal stability were decreased. Compared with the pure E-44 epoxy resin film, the elongation at break of the RLEPF-25 sample significantly improved from 10.61% to 136.51%. Therefore, the lignin-based epoxy resin film prepared by grafting refined lignin with E-44 exhibited excellent toughness. This novel study thus highlights pathways for the resource utilization of the pulping black liquor lignin.