Sustainable High‐Performance Structural Adhesives With Intrinsic Thermo‐ and Piezoresistive Sensing Capabilities

ABSTRACT

Epoxy adhesives are key enablers of lightweight, high‐performance structures, providing efficient bonding of dissimilar materials for demanding engineering applications. Meanwhile, sustainable bio‐based formulations with performances comparable to petroleum‐derived systems are emerging as environmentally friendly alternatives. By incorporating carbon nanotubes (CNTs), these adhesives become multifunctional materials capable of simultaneously carrying loads and monitoring their structural state. Herein, a commercial Araldite epoxy and a bio‐based resin, together with their composites containing 1, 3, and 5 wt% CNTs, were processed using a three‐roll mill and systematically characterized. The bioresin exhibited higher tensile strength but lower strain‐at‐break than Araldite, while CNT incorporation caused only a slight reduction in the mechanical performance of both matrices. Although lap shear strength decreased after functionalization, all formulations remained suitable for semi‐structural bonding applications. Thermoresistive sensitivity was maximized near the electrical percolation threshold, reaching ST ≈ −0.29 and −0.23% °C ⁻¹ between 30°C and 100°C for Araldite and the bioresin, respectively. Load sensing was successfully demonstrated under shear loading in single‐lap joints up to 50 N, with piezoresistive sensitivities approaching 300 Ω/N for Araldite containing 3 wt% CNTs and 25 Ω/N for the bioresin with 5 wt% CNTs. These findings demonstrate that both petroleum‐based and bio‐based epoxy adhesives can be transformed into sustainable multifunctional bonding materials with integrated thermo‐ and piezoresistive sensing capabilities for next‐generation structural applications.