Epoxy‐based composite adhesives with improved lap shear strengths at high temperatures for steel‐steel bonded joints

High‐performance room temperature‐cure epoxy structural adhesives utilizing simplified formulation are developed. The developed structural adhesive consists of diglycidyl ether of bisphenol A (DGEBA) and novolac epoxy blend as a base resin, micrometer‐sized silica particles as a reinforcing filler, and triethylenetetramine as a curing agent. The developed ambient temperature‐cure epoxy structural adhesive with optimized formulation exhibits outstanding properties including high glass transition temperature of 95°C, high thermal stability with degradation temperature at 5% weight loss of 364°C, exceptionally high rubbery plateau modulus of 320 MPa, good flame‐retardant characteristics with limiting oxygen index of 40, and high single lap shear strength for single lap steel‐steel bonded joint of 548 MPa at the temperature of 80°C. The silica‐filled DGEBA/novolac epoxy composite adhesive is a potential candidate for applying as a structural adhesive for construction with long‐term durability.