Ultrastrong intrinsic bonding for thermoset composites via bond exchange reactions

Developing high-efficient and high-quality joining method for thermoset composites has long been an important goal in industry. However, conventional bonding methods are limited by the challenge of establishing covalent bonds at the interface between the thermosets. Hot-pressing welding approaches using dynamic covalent chemistry have shown good potential but the reported methods could not obtain high strength that can meet industrial needs. In this paper, we developed a new intrinsic bonding method by using highly permeable prepolymerized vitrimer adhesive to trigger bond exchange reactions at the interface between the adhesive and the commercial composite. Our experiments showed that this new method offered excellent bonding performance. Specifically, the shear strength could reach 25 MPa by using the vitrimer adhesive after heating at 130 °C for 25 min. This strength was close to or higher than the interlaminar strength of the composites used in this study, as evidenced by the severe fiber-tear failure accompanied by the delamination of woven fiber layers in the lap shear tests. These results indicate that the new method can be used to build strong bonding joints in commercial thermoset composites for practical applications.