Adhesion and Stiffness Matching in Epoxy-Vitrimers/Strain Sensor Fiber Laminates

Hybrid networks, including physical and chemical cross-links, were synthesized from biosourced fatty acid fragments, linked to each other by a controlled number of nonexchangeable ether bonds, exchangeable ester bonds, and noncovalent hydrogen bonds. The mechanical properties of these networks are tuned by the ratio of di- versus tetraepoxide and the stoichiometry acid/epoxy. Creep tests and insolubility demonstrated the vitrimer or vitrimer-like nature of the resulting materials. The thermostimulated welding ability of the materials was exploited to incorporate strain sensors by embedding electrically conductive fibers into the rubbery vitrimer matrix. Both the efficiency of the welding procedure at moderate temperatures (80 °C) and the tunability of mechanical properties are attractive assets for the effective incorporation of thermodegradable conductive fibers while preserving their mechanical and electrical integrity. The mechanical and electrical behaviors of the sensor composites were simultaneously tested, either in quasi-static or in cyclic tensile experiments, at room temperature and at a larger distance from Tg of the matrices. The study emphasizes the importance of matching Young’s moduli of components in composite samples, which is strongly temperature-dependent.