Efficient self-welding of highly cross-linked thermoset composites assisted by universally multiple solvents

Abstract

Welding through bond exchange reactions (BERs) has attracted widespread attention in highly cross-linked thermoset composites. However, thermosets with permanently cross-linked networks cannot undergo BERs, and therefore cannot be self-welded intrinsically. In this work, multiple solvents are proposed to efficiently assist in self-welding for thermoset composites. This innovative approach involves immersing the epoxy composites in a catalyst solution, where the solvent delivers the catalyst into the epoxy matrices. Upon contact, BERs occurs between the separated polymer networks, leading to the formation of dynamic covalent bonds across the contacted interface. To examine the universality and feasibility of such a welding method, we arbitrarily choose eight of the most commonly used solvents. A high shear strength of 31.5 MPa is obtained in the single lap-shear test, which is 5 times larger than direct joining. Moreover, the maximum shear strength of self-welding is 1.4 times larger than extrinsic welding. This is because BERs in extrinsic welding extend the polymer chains and thus make them more flexible, while it does not occur in the self-welding method. Solvent with lower polarity, higher molecular weight and lower boiling point is beneficial to the self-welding. This work broadens the applicable solvent for welding of highly cross-linked thermoset composites.