Introducing a novel epoxy adhesive with BCP and calixarene for aluminum- aluminum bonded joints: a complete picture applying thermomechanical analyses and ANN modeling

This study proposes a novel hybrid modification strategy to enhance the mechanical performance, thermal stability, and lap shear strength of epoxy-based structural adhesives by incorporating p-tert-butyl calix[4]arene (C4A) as a reinforcing agent and poly(butyl acrylate-block-vinyl acetate) block copolymer as a toughening agent. C4A particles were successfully synthesized and characterized. Tensile and single-lap shear tests were conducted to evaluate bulk mechanical properties and adhesion performance. The curing behavior and thermal stability were investigated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The fracture morphology of optimized samples was examined by field-emission scanning electron microscopy (FESEM), and an artificial neural network (ANN) model was developed to predict mechanical responses. The results show that the simultaneous incorporation of 3 phr copolymer and 3 phr C4A increased tensile strength, tensile modulus, and toughness by 34%, 48%, and 270%, respectively, compared with neat epoxy. The optimized formulation exhibited a lap shear strength of 11.6 MPa, representing a 68% improvement and demonstrating a pronounced synergistic effect between the two modifiers. Contact angle measurements revealed a 39° decrease, indicating enhanced wettability on aluminum substrates. DSC results showed a 5 °C reduction in the onset curing temperature, suggesting improved curing behavior. TGA confirmed enhanced thermal stability, with the onset degradation temperature (Ti) and maximum degradation temperature (Tmax) increasing by 55 °C and 50 °C, respectively. The ANN model achieved high prediction accuracy, with a mean relative error (MRE) below 1.4%.