Facile synthesis of intrinsically flame-retardant epoxy thermosets with high mechanical properties from lignin derivatives

Preparing bio-based epoxy resins with high performance is crucial to sustainable development. However, seeking renewable and flame-retardant epoxy resins with high mechanical properties are still challenging. Here, we reported a facile way to transform lignin derivatives to intrinsic flame-retardant epoxy resins with satisfactory mechanical properties. Two guaiacol-based novolac epoxy resins (i.e., GTEP/DDM and GPEP/DDM) were prepared as alternatives for petroleum-based DGEBA/DDM. The cured GTEP/DDM product showed a high T-g of 209.5?, a high tensile modulus of 3.13 GPa, and a high LOI of 28.6% with UL-94 V-1 rating, which outperformed DGEBA/DDM system. Specially, GPEP/DDM resin possessed more superior mechanical properties (e.g., tensile strength of 73.9 MPa, and tensile modulus of 5.85 GPa) owing to additional interactions (i.e., pi-pi interactions and hydrogen bonds), and outstanding anti-flammability (e.g., LOI of 31.2% with UL-94 V-0 rating) due to the endow of phosphorus-containing groups. The mechanical reinforcement and flame-retardant mechanisms were clarified based on structural evolution and performance variation. This work provides an efficient synthesis route to achieve a high-performance thermoset, which is a promising alternative for substituting conventional bisphenol-A epoxy resin for use as fireproof materials.