Eugenol‐Derived Siloxane Epoxy Toughener for High‐Performance Diglycidyl Ether of Bisphenol A and Basalt Fiber Composites

Epoxy resins combine high stiffness, thermal resistance, and processability but remain constrained by intrinsic brittleness. Here, a siloxane‐containing bio‐based epoxy toughener, EPMOPTSi, was synthesized from eugenol through hydrosilylation followed by epoxidation and employed to modify commercial diglycidyl ether of bisphenol A (DGEBA). Physicochemical characterizations confirmed the designed molecular structure, with a measured molecular weight of 574.86, consistent with the theoretical value. The optimized EPMOPTSi/DGEBA ratio was 1:10 (DGTSi‐2), yielding a tensile strength of 78.14 MPa, elongation at break of 14.66%, and toughness of 56.72 MJ m −3 , compared with 72.11 MPa, 11.55%, and 36.41 MJ m −3 for unmodified DGEBA. The optimized resin also exhibited a glass‐transition temperature of 87.2°C and an initial degradation temperature of 348.2°C, compared with 65.6°C and 341.0°C, respectively, for the control. Incorporation into basalt‐fiber composites further produced a tensile strength of 345.4 ± 9.6 MPa and an impact strength of 95.9 kJ m −2 . These results demonstrate an effective bio‐based strategy for simultaneously improving epoxy toughness, strength, thermal stability, and composite performance.