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°C, 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., π–π 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.