Reversible adhesives and debondable joints for fibre-reinforced plastics: Characteristics, capabilities, and opportunities

Fibre reinforced polymer (FRP) materials are well established in both the wind energy and aerospace industries, with the adoption of FRPs beginning to grow significantly in the automotive sector due to their favourable mechanical and physical properties. Their increased usage, coupled with the inherent complexity of forming FRP–FRP joints, has led to an increase in adhesives as a typical joining method. However, such adhesive joints pose a challenge when undertaking repair or at end-of-life (EoL). Separating the joint to facilitate recycling of the high-value FRP can be extremely labour- and time-intensive. Therefore, the introduction of debondable and reversible technologies into conventional structural adhesives such as acrylics, epoxies and polyurethanes has begun to attract interest within academia and industry which can overcome this challenge by demonstrating reversibility. Nevertheless, such adhesives are at various stages of technology readiness. The next step in adhesive materials development aims to meet current requirements and deliver an evolutionary advantage by enabling repair (when necessary), recycling, and transition towards a circular economy for FRP materials. For example, the use of reversible chemistries such as Diels-Alder or Covalent Adaptable Networks. This comprehensive review considers the latest literature for current debonding technologies including mechanical and thermal debonding, thermally expanding microspheres, induction heating, foaming agents and chemical degradation as well as a variety of reversible chemistries that could be introduced into adhesives for potential use in FRP-FRP joints, including how such reversibility might be activated and any consequences for practical application. The aim is to give readers a deeper understanding of their properties and potential application.