Programming interfacial hybrid networks via green geopolymers for high-performance adhesives with multi-scale environmental barriers

Traditional epoxy resin (EP) adhesives are indispensable in modern engineering, yet their inherent trade-off between cross-linking density and fracture toughness, coupled with catastrophic interfacial degradation under extreme hygrothermal and high-temperature environments, severely limits their advanced applications. Herein, we propose a tailored "organic-inorganic topological bridging" strategy to construct a robust, highly cross-linked interpenetrating polymer network using core-shell functionalized green geopolymers (GP). By covalently grafting bi-functional silanes (KH550 and KH560) onto the SiO₄/AlO₄ inorganic frameworks, the incompatibility between polar GP and the epoxy matrix was effectively mitigated. At an optimized loading of 0.75 wt%, the KH560-GP/EP composite exhibited a 158% increase in fracture toughness (K IC = 3.1 MPa·m 1/2) and a 176% enhancement in tensile toughness. Furthermore, the hierarchical hybrid architecture improved the resistance of the adhesive to water, salt solution, acid, alkali, salt spray, and aviation kerosene. After thermal aging at 250 °C for 200 h, the optimized KH560-GP/EP adhesive retained a residual lap shear strength of 10.2 MPa when tested at room temperature, indicating improved resistance to irreversible thermal-aging-induced interfacial degradation.